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Revealing climatic variability of the last three millennia in Northwestern Iberia using pollen influx data
Abstract
Climatic variability of the last 3 millennia in NW Iberia has been documented using high-resolution pollen analysis of Vir-18 core, retrieved from the Rı́a de Vigo (42°14.07′N, 8°47.37′W). The depth–age model is based on two accelerator mass spectrometry 14C dates and three historically dated botanical events in Galicia: the expansion of Juglans and Pinus, as well as the introduction of Eucalyptus. During the last 3000 years, the relative pollen record demonstrates the occurrence of an open deciduous oak forest, indicating a humid and temperate climate in northwestern Iberia. Two-step forest reduction since 975 cal BC suggests climate as the main cause rather than major socio-economic changes documented in historical archives. Absolute pollen influx has been compared with instrumental summer and winter temperatures and tentatively used as a proxy of short (decadal-scale) and low-amplitude (∼1°C) temperature variations. This new approach allows us to detect for the first time in NW Iberia the millennial-scale climatic cyclicity suggested by North Atlantic records, challenging the apparent climatic stability reflected by the relative pollen record. The Little Ice Age is recorded as low pollen influx values between 1400 and 1860 cal AD, with a cold maximum at 1700 cal AD (Maunder Minimum). The Roman and Medieval Warm Periods are detected through high pollen influx values at 250 cal BC–450 cal AD and 950–1400 cal AD, respectively.
... The evidence of a warming climate between the 3 rd century BCE and the 2 nd century CE based on various continental and oceanic paleoclimate proxies [1][2][3] has led to questions about its on the territory of the Phocean colony [6]. During the Iron Age, Marseille wine was sold in Southern Gaul, as indicated by the discoveries of Massaliot amphorae that contained this wine [7]. ...
... Around the 2 nd century BCE, both Latin agronomists Saserna evoked a climate change that would have made it possible to gain for the cultivation of the vine and the olive tree areas of altitude previously too cold (probably in the Apennines) to be able to practice these crops (passage quoted in Columella, De Re Rustica, I, 1). The reality of this significant global warming, now called the Roman Climate Optimum (RCO) or Roman Warm Period (RWP) has been highlighted by several paleoclimatic studies [2,3]. This would have occurred as early as the middle of the 3 rd century BCE and may have been particularly important. ...
... According to the results of isotopic studies carried out on sedimentary cores, the temperatures of the surface waters of the Mediterranean would have been even during the Roman period 2˚C higher than the current one [1]. The precise end of this period of climatic optimum is variably estimated between the 2 nd century CE and the 4 th century CE according to studies [1][2][3], before the beginning of the cooling of the Late Antique Little Ice Age (LALIA), paroxysmal in the 6 th and 7 th centuries CE [43]. ...
What impact did the Roman Climate Optimum (RCO) and the Late Antique Little Ice Age (LALIA) have on the rise and fall of the Roman Empire? Our article presents an agent-based modelling (ABM) approach developed to evaluate the impact of climate change on the profitability of vineyards, olive groves, and grain farms in Southern Gaul, which were the main source of wealth in the roman period. This ABM simulates an agroecosystem model which processes potential agricultural yield values from paleoclimatic data. The model calculates the revenues made by agricultural exploitations from the sale of crops whose annual volumes vary according to climate and market prices. The potential profits made by the different agricultural exploitations are calculated by deducting from the income the operating and transportation costs. We conclude that the warm and wet climate of the Roman period may have had an extremely beneficial effect on the profitability of wine and olive farms between the 2 nd century BCE and the 3 rd century CE, but a more modest effect on grain production. Subsequently, there is a significant decrease in the potential profitability of farms during the Late Antique Little Ice Age (4 th -7 th century CE). Comparing the results of our model with archaeological data enables us to discuss the impact of these climatic fluctuations on the agricultural and economic growth, and then their subsequent recession in Southern Gaul from the beginning to the end of antiquity.
... Apart from these broad global events of MWP and LIA, our climate reconstruction is also comparable with other climatic events that occurred elsewhere in the globe [164] but were not widely explained compared to MWP and LIA. These events were recorded in the reconstruction before the MWP period. ...
... These events were recorded in the reconstruction before the MWP period. The cooling of temperature at the beginning of the reconstructed MTWA (2992-2870 years BP, BC 1042-920) might be linked with the Sub-Atlantic Cold Period (SACP) that occurred during BC 975-250 [164]. The rise in temperature in the present MTWA reconstruction during 2188-1551 cal years BP (BC 238-399) is similar to the Roman Warm Period (RWP) observed during BC 250-AD 450 [164]. ...
... The cooling of temperature at the beginning of the reconstructed MTWA (2992-2870 years BP, BC 1042-920) might be linked with the Sub-Atlantic Cold Period (SACP) that occurred during BC 975-250 [164]. The rise in temperature in the present MTWA reconstruction during 2188-1551 cal years BP (BC 238-399) is similar to the Roman Warm Period (RWP) observed during BC 250-AD 450 [164]. Another event known as the Dark Age Cold Period (DACP), which took place during AD 450-950 [164], is also comparable with the cooling events observed in our temperature reconstruction during the later part of 1157-1021 cal years BP (AD 793-929). ...
The Late Holocene fossil pollen records from the Zemu glacier, located in Yabuk, North Sikkim, in the eastern Himalayas, effectively generated quantitative climate reconstructions based on the transfer function model. The transfer function model was developed by establishing a modern pollen-climate calibration set from the temperate alpine belt of North Sikkim. A redundancy analysis was carried out to detect the pattern of variation of climatic variables in the modern pollen datasets. The mean annual precipitation (MAP) and mean temperature of the warming month (MTWA) had the strongest influence on the composition of the modern pollen samples among the climatic variables considered in the analysis. Proxy data in the form of fossil pollen records were analyzed for reconstructing past climate based upon the relationships between modern pollen vegetation assemblages and climatic patterns. Transfer functions for MAP and MTWA were developed with the partial least squares (PLS) approach, and model performance was assessed using leave-one-out cross-validation. The validated model was used to reconstruct MAP and MTWA for the last 2992 cal years BP (1042 BC) in North Sikkim. The variability observed in the reconstructions was analyzed for past global climatic events. It was further compared with the available regional and hemispheric proxy-based climate reconstructions. The reconstructions captured comparable Medieval Warm Period (MWP) and Little Ice Age (LIA)-like events from the Zemu glacier region. The fossil pollen data and climate reconstructions were further compared with the mineral magnetism data of the subsurface sediment profile.
... Palynological studies in Ría de Vigo's marine sediment cores have shown that the Late Holocene is characterised by strong human interference on the landscape, as low arboreal percentages point to an established open landscape (Figures 4 and 5; Desprat, Sáchez Goñi, & Loutre, 2003;Muñoz Sobrino et al., 2007. However, environmental changes were not restricted to landscape-scale vegetation changes but also to local coastal ones. ...
... Therefore, both the Early and Late Roman Empire landscapes are characterised by mesophilous trees in an open landscape. The larger importance of mesophilous trees compared with Zone-IA-3, which has a post-Roman chronology, agrees with the increased pollen influx of mesophiles detected by Desprat et al. (2003) in the Ría de Vigo during the RWP. ...
... Palynological data points to a stronger terrestrial influence, as PC1 explains most of the variance, reconstructing the dominance of herbs versus trees in an open landscape. This result agrees with the decreased pollen influx of mesophiles by Desprat et al. (2003) in the Ría de Vigo during the DACP. ...
The NW Iberian city of Vigo contains buried structures of a Roman salinae that follow the ancient coastline. To investigate its environmental legacy, we studied two pedo-sedimentary profiles at the O Areal saltworks to reconstruct human activities during and after the salinae use, as well as framing them within the last two millennia of climate variability. The bottom layer consists of organic-rich sands, with marine palynomorphs, confined within the saltworks’ structures that operated during the Early Roman Empire, when the demand in fish-salted products increased and the salting industry fluorished on the Atlantic coast of Iberia. During the Late Roman Empire, salt production at the O Areal may have ended, coeval with the development of a marsh with hydro-hygrophyte vegetation and the salting industry demise. The Roman environment also experienced intense agropastoralism that triggered water eutrophication. After Roman times, a dune phase sealed the archaeologicl structures. The overall trend points to a shift from a marine to a terrestrial setting coeval to known periods of climate variability. Therefore, humans and climate impacted the coast during the last two millennia, including the very intense Roman-period saltworks, agriculture and livestock. Roman times climate would have also influenced the saltworks’ establishment and abandonment.
... The beginning of this process has been set, through archaeological research, in the Late Antiquity-Early Middle Ages [23,[87][88][89]. Reasons for these transformations have probably to be traced back to climate and productive factors [23,24], including enhanced soil erosion and a lower agricultural productivity that resulted from the Cold Medieval Period climate conditions [90][91][92]. Furthermore, some authors hypothesize about the use of these agricultural infrastructure interventions, in particular terraces construction or refurbishment, for intentionally "attaching the rural population to the land, to facilitate the development of feudalism, and the productive apparatus which later enables the Romanesque" [93]. Indeed, the specific geographical implementation of these interventions followed the requirements of the Christian expansion in the region [94]. ...
... The sediment input to the site could have been enhanced by the climate deterioration corresponding to the end of the Medieval Climate Anomaly and the onset of the Little Ice Age (LIA, Figure 4) from 1400 AD [90]. The LIA brought low temperatures -1 to 2 • C lower than the average for the period 1960-1990 [95] at a hemispheric scale, accompanied by a larger climate variability [120]-which undermined agricultural production and produced "a long-term, continent-wide agricultural crisis" [121]. ...
... The climate at the beginning of this period is marked by the cold conditions of the Maunder Minimum (1645-1715 cal AD) [90]. Historical documents reveal that a critical period occurred in this region between 1680 and 1700, when severe cold and prolonged droughts caused serious famines in farming communities [123,124]. ...
Landscape multifunctionality is increasingly recognized as an important aspect in sustainability and developmental debates. Yet, how and why a multifunctional landscape configuration develops over time has not been sufficiently studied. Here we present the geoarchaeological investigation of the Santa Mariña de Augas Santas site, in northwestern Spain. We focus on the role of religious practice, and of its interplay with productive strategies, in landscape transformation. A geochemical, mineralogical, and geochronological characterization of the pedo-sedimentary record (including XRF, EA-IRMS, XRD, OSL and 14C measurements) allowed to characterize catchment scale sedimentation processes in relation to agricultural activities. The geographical and chronological coincidence of production functions with documented religious activities demonstrate that both aspects shared geographical spaces during the last millennium. Current landscape multifunctionality at Santa Mariña is thus not the final outcome of a specific evolution, but an essential aspect of traditional land use strategies through history and a driver of change. This work highlights the need of a long-term study of the processes of landscape configuration when assessing the sustainability of traditional productive systems.
... According to Vacchi et al. (2016Vacchi et al. ( , 2017, the MSL has increased from ~7.3 m (4750 cal yr BP) to ~8.5 m (3930 cal yr BP) between the C. caespitosa settlement and the P. oceanica meadow colonization. Thus, the progression of the upper limit of the P. oceanica meadow towards the coast could be related to the MSL rise and coincides with the 4.2 kyr event (Fig. 2) characterized by a global climatic shift and major drought through the Mediterranean region (Desprat et al., 2003;Roberts et al., 2011b;Magny et al., 2013). Furthermore, the occurrence of C. caespitosa may have also influenced the settlement of the P. oceanica in this area. ...
... The first oscillation coincides with the Cold Phase of the Subatlantic period (2925-2200 cal yr BP) and the beginning of the Roman Warm Period -RWP (2200-1500 cal yr BP; Desprat et al., 2003;Klimenko and Klimanov, 2003). Over the first oscillation, the annual mean growth rate was 2.2 ± 0.3 mm yr − 1 and was characterized by intermediate and low mean growth rate (Fig. 7). ...
... The second oscillation coincides with the climatic RWP in Corsica (Desprat et al., 2003;Currás et al., 2017) and the Dark Ages Cold Period -DACP (1500-1000 cal yr BP; Ljungqvist, 2010). This oscillation is characterized by a slightly higher mean growth rate of corallites and SAR than during the first oscillation, with 2.4 ± 0.4 mm yr − 1 and 0.4 ± 0.0 mm yr − 1 , respectively. ...
Along most Mediterranean coasts, the endemic seagrass species Posidonia oceanica builds extensive meadows and complex peat-like bioconstruction known as ‘mattes’. These belowground deposits are recognized as a valuable long-term archive allowing the reconstruction and the study of palaeo-climatic and palaeo-ecological changes in the coastal environment over the Holocene period. One of the P. oceanica matte cores sampled during a coring survey along the eastern continental shelf of Corsica Island (France, NW Mediterranean) revealed the unprecedented finding of a dead bank of the scleractinian coral Cladocora caespitosa embedded in the matte. Measurement of the morphological and biometrical features of corallite fragments coupled to biogeosedimentological analysis and radiocarbon dating contributed to provide a basis for the reconstruction of the stratigraphic sequence since the mid-Holocene (last 4750 years). The study of the sediment core enabled identification of three major phases: (i) the settlement of the C. caespitosa colonies (~4750-3930 cal yr BP), (ii) the coexistence of the C. caespitosa bank and the P. oceanica meadow (~3930-1410 cal yr BP), followed by (iii) the death of the coral bank and the development of only the P. oceanica meadow (~1410 cal yr BP-present). The sclerochronological analysis completed on the well-preserved corallite fragments revealed that the mean annual growth rate of the coral ranged between 1.9 and 3.1 mm yr⁻¹ with a mean value estimated at 2.3 ± 0.8 mm yr⁻¹. Trend analysis showed semi-millennial to millennial oscillations in annual growth rates which are probably related to environmental climatic changes since the Cold Phase of the Subatlantic period (2925-2200 cal yr BP). During the Roman Warm Period (2200-1500 cal yr BP), the decline and the death of the bank (~1410 cal yr BP) was probably due to the combined effect of a prolonged increase in summer temperatures and an increase in the competition with the P. oceanica meadow.
... Gran parte de la ocupación del castillo coincide con la Pequeña Edad del Hielo (1300-1850), un período frío en el que se han distinguido diferentes fases y cuyas evidencias han sido documentadas tanto en el registro paleoambiental del noroeste (Martínez--Cortizas et al. 1999, Desprat et al. 2003) como en las fuentes históricas (Fernández-Cortizo 2016). Para el período que nos interesa en relación con la ocupación del Castillo de Pambre, entre el 1300 y el 1480 se documenta un enfriamiento creciente con oscilaciones climáticas moderadas, entre 1480 y 1570 se dan unas condiciones más templadas, seguidas posteriormente de un enfriamiento gradual entre 1570 y 1620, llegando al período más frío conocido como el Mínimo de Maunder entre los años 1620 y 1715, con temperaturas aproximadamente 2ºC por debajo de las actuales (Oliva et al. 2018). ...
... A partir de los análisis dendroclimáticos, los períodos que concentran una mayor cantidad de oscilaciones se producirían en los intervalos comprendidos entre el 1400 y c 1600 y las temperaturas alcanzarían sus valores más bajos en el 1500 (Manrique y Fernández Cancio 2000). En el noroeste de Iberia los registros documentados en las turberas y en los depósitos marinos señalan el año 1700 como el momento en el que se alcanzan los episodios más fríos de la Pequeña Edad del Hielo (Martínez-Cortizas et al. 1999, Desprat et al. 2003. ...
... La legislación proteccionista sobre bosques y árboles (Carlé 1976), así como el retroceso del bosque, que es acusado en este momento tal y como está documentado en diferentes secuencias palinológicas del noroeste peninsular (Martínez-Cortizas et al. 2000, Santos et al. 2000, Desprat et al. 2003, López-Sáez et al. 2003, Martínez-Cortizas et al. 2005, Silva-Sánchez et al. 2014, puede ser el motivo de que haya una gran diversificación en el aprovisionamiento, incluyendo árboles frutales, y una preferencia por leña de mediano a pequeño calibre, obtenido probablemente de ramas de mediano y pequeño tamaño, frente a la preferencia por madera de gran calibre que implicaría abatir árboles. El uso de las ramas, incluyendo en algunos casos la posibilidad de la existencia de prácticas como el desmoche, el trasmoche o el clareo, permitiría asegurar una renovación cíclica de los recursos, o el aprovechamiento de los residuos de la poda en el caso de los frutales. ...
Se presentan los resultados del análisis antracológico, así como los datos dendrológicos y tafonómicos de varias muestras de carbón. Estas fueron recuperadas durante la intervención arqueológica desarrollada en el Castillo de Pambre (Palas de Rei, Lugo) en el año 2014, en relación con las tareas de rehabilitación del conjunto de edificaciones del castillo. Los datos obtenidos nos permiten definir el uso como combustible de los recursos leñosos que realizaron los ocupantes del castillo durante los siglos XV-XVII. Se documenta un predominio de la madera de roble (Quercus sp. caducifolio), seguida del avellano (Corylus avellana) junto con una gran diversidad de taxones, especialmente de árboles fruta-les, mientras que los taxones de matorral son poco significativos en el conjunto. Esto a pesar de coincidir con un período frío, la Pequeña Edad del Hielo, y de la importante deforestación registrada tanto en los datos paleoambientales como en la documentación.
Abstract: This paper presents the results of charcoal analysis as well as dendrological and taphonomical attributes of charcoal samples. These were recovered during the archaeological survey in the Pambre Castle (Palas de Rei, Lugo) during 2014 and in relation to the rehabilitation activities in the group of buildings of the castle. The data obtained let us to define the use as firewood of wood resources performed by the inhabitants of the castle between 15 th to 17 th centuries AD. A predominance of oak (deciduous Quercus), followed by ha-zel wood (Corylus avellana) has been attested, besides a great taxa diversity, predominantly fruit trees whilst scrubland taxa are not significant in the assemblage. This even though it coincided with a cold period, the Little Ice Age, and the major deforestation registered in the paleoenvironmental proxies as well as in the written sources.
... The first oscillation ranged between the minimum growth rates observed at 224-225 Desprat et al., 2003;Klimenko and Klimanov, 2003). Over the first oscillation, the annual mean growth rate was 2.2 ± 0.3 mm yr -1 and was characterized by intermediate and low mean growth rate (Fig. 6.7). ...
... yr BP). This oscillation coincides with the historic and climatic Roman periods in Corsica (Currás et al., 2017;Desprat et al., 2003) and the Dark Ages Cold Period -DACP (1500-1000 cal. yr BP; Ljungqvist, 2010). ...
Dans le contexte du changement climatique, la nécessité de réduire les concentrations atmosphériques de dioxyde de carbone (CO2) pour atteindre les objectifs de l'Accord de Paris a récemment accentué l'intérêt pour la quantification de la capacité des écosystèmes côtiers (i.e. les herbiers marins, les mangroves et les prés-salés) à séquestrer le carbone communément appelé « Carbone Bleu ». Bien que ces écosystèmes à Carbone Bleu représentent moins de 1 % de la surface des océans, ils sont notamment reconnus pour séquestrer et stocker de grandes quantités de carbone dans leurs sédiments constituant des puits de carbone majeurs en zone côtières. En Méditerranée, l’espèce endémique Posidonia oceanica (Linnaeus) Delile constitue de vastes herbiers marins considérés comme (i) des puits de carbone à long terme et (ii) des archives biologiques dû à la formation d’une structure remarquable appelée « matte ». Ces dépôts, composés de débris d’herbiers très réfractaires enfouies dans les sédiments, constituent des puits de carbone à long terme pouvant être préservé pendant des siècles voire des millénaires et atteindre plusieurs mètres d'épaisseur. Afin d'estimer la contribution de ces herbiers à l'atténuation du changement climatique, une estimation des stocks de carbone a été réalisée dans la zone Natura 2000 « Grand Herbier de la Côte Orientale » en Corse (France). Cette approche expérimentale est basée sur l’analyse de plus de 1380 km de données de sismique-réflexion haute résolution et de 49 carottes sédimentaires (40-365 cm de long) collectées entre 10 et 50 m de profondeur lors de trois campagnes océanographique à bord du navire « L'Europe » (Ifremer). La conversion temps-profondeur des données sismiques a été obtenue en déterminant la vitesse de l’onde acoustique dans la matte (1664,4 m.s-1) après un processus d'intercalibration (sondeur multifaisceaux, LiDAR et données terrains). La cartographie prédictive établie par krigeage ordinaire met en évidence une forte hétérogénéité spatiale des épaisseurs de matte dans le site d'étude. La hauteur des mattes (moyenne : 251,9 ± 0,2 cm) augmente dans les eaux peu profondes, près des embouchures des fleuves et lagunes côtières, où une épaisseur de matte atteignant 867 cm a été enregistrée. Les datations au 14C révèle la présence des herbiers depuis l'Holocène (7 000-9 000 ans avant aujourd’hui) ainsi qu’une forte variabilité dans l'accrétion de la matte résultant de l'interaction de multiples facteurs biotiques et abiotiques (e.g. structures des herbiers, profondeur, hydrodynamisme, géomorphologie). En se basant sur la surface occupée par ces herbiers et l'épaisseur moyenne relevée, le volume de matte a été estimé à 403,5 ± 49,4 millions de m3. Les analyses biogéochimiques et sédimentologiques ont montré une forte variation dans l'accumulation et les stocks de carbone organique et inorganique (respectivement Corg et Cinorg). Les stocks de Corg et Cinorg (moyenne : 327 ± 150 t ha-1 et 245 ± 45 t ha-1, respectivement), présentent des tendances contrastées. Ainsi, les herbiers superficiels ou implantés sur une matrice sableuse possèdent des stocks de Corg significativement plus important que les herbiers profonds ou situées dans les zones rocheuses. Inversement, les stocks de Cinorg sont plus élevés sur fonds rocheux, en mer ouverte, mais aussi en zones profondes. La signature isotopique (δ13C) révèle une contribution accentuée des apports allochtones en matière organique (macroalgues et sestons) aux puits de carbone en milieu estuarien et dans les zones superficielles. Les estimations des quantités de carbone stockées sur les premiers 250 cm de matte (épaisseur moyenne au niveau du site) ont été estimées à 13,2 millions de t Corg et 14,4 millions de t Cinorg, soulignant le rôle majeur de P. oceanica comme puits de carbone côtier. De plus, l’une des carottes sédimentaires prélevées a révélée l’existence d'un ancien banc de corail Cladocora caespitosa (Scleractinia) enfouie dans la matte.
... Similar drought conditions along the eastern Adriatic coast were recorded from approximately 800 to 1,350 years BP, during the socalled small medieval climate optimum (Rudzka et al., 2012) when western Mediterranean temperatures were 1.5 °C higher than today (Harding et al., 2009). From 1,300 to 1,850 years BP, and especially between 1,450 to 1,700 years BP, there was a series of very cold winters in Europe called the Little Ice Age (Lamb, 1995;Bond, 1999;Desprat et al., 2003). Subsequently, average winter temperatures in Europe were 1-2 °C lower than today (Mann, 2009) while summers were more humid. ...
... do 1700. godine na području Europe zabilježen je niz vrlo hladnih zima zbog čega je to razdoblje nazvano malo ledeno doba ili Little Ice Age -LIA (Lamb, 1995, Bond, 1999Desprat et al., 2003). Prosječne zimske temperature u Europi bile su 1-2 °C niže nego danas (Mann, 2009), a ljeta vlažnija. ...
The chapter presents the basic natural and social characteristics of the Municipality of Pakoštane and their interdependence in the context of the settlement and the use of space. Also, an overview of the paleoenvironmental changes in the wider area of the Municipality of Pakoštane is given, with special emphasis on the impact of climate change on the relief and hydrological features during the Holocene.
... Furthermore, the increased values of CIA and PIA along with the highest peak of moisture index confirms the onset of warming period during 2046 cal yr BP. This period is well coinciding with RWP when a warm and humid climate was experienced throughout the globe (Desprat et al., 2003;Ji et al., 2005;Wang et al., 2012). ...
Deltas are shaped by the interaction of fluvial and marine forces and the deltaic sediments are partially sub-aerial allochthonous river driven terrestrial debris deposited into or against a constant water body. It lies at the transition zone between the marine and terrestrial environments and retains fingerprints of human civilization development. Hence, the palaeo-environmental reconstruction of deltaic sediments serves a crucial role in assessing the present and future climate fluctuations. Climate change potentially alter the deltaic ecosystem through temperature changes, increase/decrease in tidal amplitude with sea level fluctuations, salinity status, and changing flow volume into and through the delta.
Understanding the impact of climate change on the rainfall/precipitation and vegetation cover in the past is crucial for predicting the future scenario and its consequences. Present study integrates biotic (palynological analysis) and abiotic proxy (sediment chemistry, and grain size analysis) records in chronologically constrained sedimentary sequences from the lower deltaic plain of the Mahanadi River delta to reconstruct the climatic variability since 2600 years. Also, an attempt has been made to forecast the future climatic scenario (for 2050 and 2070 years) by using the current distribution of two selected mangrove taxa i.e. Avicennia officinalis and Rhizophora mucronata.
The study area lies in the lower deltaic part of the Mahanadi river Delta. Geologically the area is covered by Quaternary sediments which is underlained by Baripada beds of Tertiary age. The study area is covered by many geomorphic landforms such as sea mounts, river meanders, flood plains, palaeo-levees, palaeo-distributaries and a large area of mudflats and mangroves. Four trench sites have been selected to understand climatic variability of the past 2600 years in the study area.
The grain size analysis of the trench sites reveals a marked variations according to their locations. BT trench is mainly comprised of silt fraction that is deposited under a calm environmental condition. Whereas, BL trench that is dominated by silt content and it is replaced by the sand content towards the top of the trench (after 80cm).The sediments here are mostly deposited under a calm environments, except some few at the top. In case of SB trench the size fraction is mainly dominated by silt content suggesting a calm depositional environments. Whereas, KJ trench is majorly dominated by fine sand infers the deposition was under a relatively low to high energy conditions.
Dominance of herbaceous taxa like Poaceae and Cyperus, increased aridity index, decrease in concentrations of clastic input and low CIA and PIA value in the BL trench possibly suggest a relatively dry and arid climate in the study region during ~2600-2000cal yr BP which may be attribute to the Iron Age cold period (IACP). Only BL trench reflects the record of past 2600 years.
During the period 2000-1500cal yr BP, a well-developed estuarine condition was observed at the BT trench site due to the presence of mangroves alongside terrestrial taxa, indicating a favourable environment for the coastal ecosystem. The presence of diverse mangrove and a peak in moisture index at the BL trench suggest a warm and humid climate condition associated with a strengthened monsoon, which may be attributed to the Roman Warm Period (RWP).
At the BT trench site, there was a dominance of Sonneratia and a decline in terrestrial taxa around 1420cal yr BP, indicating a less precipitation condition. High moisture index and increased CIA and PIA values at the BL trench site during about 1100cal yr BP may indicate a wet phase with the onset of the Medieval Climatic Anomaly (MCA), which then changed to an arid climate during about 1100-800cal yr BP. The variety of mangrove, tree, and herbaceous taxa near SB trench suggests that the study site received significant rainfall between 1300 and 400cal yr BP.
The development of supra-tidal back mangroves in response to the aridification and forest clearing at BT trench after 700cal yr BP is explained by an expansion of Avicennia sp. Absence of pollen records and a sharp decline in weathering intensity at the BL trench site point to a period of high physical erosion and a dry, arid climate. All trench sites' proxy records collectively indicate a climate that is largely dry and arid with less precipitation, possibly due to the Little Ice Age (LIA).
Through an ensemble modelling approach, the study identified the effects of precipitation and temperature variations on the distribution of two mangrove species, Rhizophora mucronata and Avicennia officinalis.
... Before ca. 400 CE the percentages of Cyperaceae and Poaceae reach high and stable values, suggesting a wetter climate, which could be a reflection of the Roman Warm Period (RWP; Desprat et al., 2003;Wang et al., 2012a;Sun et al., 2020c). After ca. ...
... Such episodes of increased surface runoff in the study area coincide with wetter conditions in Lonar Lake and enhanced precipitation in the NW Himalaya ( Figure 8) suggesting a strengthened monsoon condition across the Indian subcontinent. This period is well coinciding with RWP when a warm and humid climate was experienced throughout the globe (Desprat et al., 2003;Ji et al., 2005;Wang et al., 2012). A high resolution palaeoenvironmental reconstruction based on marsh benthic foraminifera from Minho estuary, NW Iberia suggested a period of rainfall intensification from 2090 to 2140 cal BP (Moreno et al., 2014). ...
Understanding the impact of climate change on the vegetation cover in the past is crucial for predicting the future warming scenario and its consequences. The present study integrates biotic (palynological analysis) and abiotic proxy (sediment chemistry, clay mineral assemblages and grain size end member (EM) analysis) records in a chronologically constrained sedimentary sequence from the southeastern part of the Mahanadi River delta to reconstruct the hydroclimate since 2600 years. The Mahanadi delta sediments are primarily derived from felsic rock source possibly composed of granites or granulites. The dominance of herbaceous taxa, high aridity index and deposition of fine grain (EM1) sediment possibly suggest a relatively cold and dry climate in the study region during ~2600–2100 cal yr BP corresponding to the Iron Age Cold Period (IACP). Presence of diverse mangrove and tree taxa, deposition of coarser sediment (EM3) and relatively high abundance of secondary clay minerals possibly indicate high precipitation associated with the Roman Warm Period (RWP, ~2100–1800 cal yr BP). A decline in mangroves, dominance of herbaceous taxa and high deposition of fine grain (EM2) sediment from ~1800 to 1300 cal yr BP may indicate a relatively drier climate coinciding with the Dark Age Cold Period (DACP). High moisture index and an increased value of Rb/Sr during ~1300 cal yr BP may suggest a wet phase with the onset of the Medieval Climatic Anomaly (MCA) and later shifted to an arid climate during ~1100–800 cal yr BP. After ~800 cal yr BP, a sharp decline in all weathering indices and vegetation cover, dominance of illite indicates a relatively dry climate which could mark the Little Ice Age (LIA, ~800–300 cal yr BP). A small increase in the terrestrial flux, as well as the weathering indices after ~300 cal yr BP, may suggest the onset of recent warming.
... Hence, it is considered that the summer monsoon was intensified within this relatively warm interval causing higher precipitation over the Indian subcontinent, which in turn was responsible for the substantial freshwater influx to the BoB and lowering the salinity of this zone. Desprat et al. (2003) have pursued temperature reconstruction and high-resolution pollen analysis from NW Iberia and suggested the period from 250 BC to 450 AD was relatively warmer and humid and considered the RWP. The RWP is also recorded in and around the Indian subcontinent. ...
The present work is pursued on the benthic foraminiferal groups obtained from NGHP core samples of the western Bay of Bengal to understand the
variations of paleoceanography and Indian Summer Monsoon (ISM), as well as socio-economic changes in ancient India. Benthic foraminiferal AMS 14C
dating reveals that the studied interval spans between 335 BC and 1355 AD, covering the history of the last 1690years. We compared foraminifera group
counts with published isotopes, sunspot number, summer monsoon index, hematite-stained grain, Al/Ca, 14C data sets. Angular Asymmetrical Benthic
Foraminifera, infaunal, and dysoxic groups exhibit declining trends with warm, humid intervals with intensified ISM signature from 335 BC to 406 AD
(Roman Warm Period) and from 787 to 1202 AD (Medieval Warm Period). The Increasing trend of the above foraminiferal groups captures the signature
of weak ISM from 406 to 787 AD (Dark Age Cold Period) and from 1202 to 1355 AD (Medieval Warm Period and Little Ice Age Transition). Whereas
rounded symmetrical benthic foraminifera, epifaunal, and oxic groups show a reverse relation with the abovementioned groups. Spectral analysis of
foraminiferal groups shows significant periodicities of 563/561, 450, 321, 281/250, 22/27, and 17/16/15 years, corresponding to various solar cycles. This
research uncovers the relationship between solar activity and monsoonal changes, which influenced India’s economic growth and played a crucial role in
the establishment and demise of successive dynasties throughout the Indian subcontinent during the late-Holocene.
... It is likely that this event was more arid than previous events, such as the 8. and suggests a period of cooler conditions that can be correlated with the first cold phase of the Subatlantic period, also called the "Iron Age Cold Epoch" (Van Geel et al., 1996). This period has been recognized by Desprat et al. (2003) in sediments from the Ría de Vigo on the northwestern coast of Spain, in a speleothem d 13 C record from northern Spain (Martín-Chivelet et al., 2011), from different areas and proxies in central and western Europe (e.g., Blaauw et al., 2004;Plunkett and Swindles, 2008;Speranza et al., 2003;Van Geel et al., 1996) and Greenland (O'Brien et al., 1995), and was also identified as the ice-rafted debris event 2 (~2700 yr BP) in Atlantic sediment cores (Bond, 1997;Bond et al., 2001) (Fig. 6F). Several hypothesis have considered to explain this cold event, but likely changes in solar activity were one of the dominant forcings, as proposed by Zielhofer et al. (2017). ...
Recent hydroclimate studies on the Iberian Peninsula have shown a complex regional pattern in timing and intensity of climate change spanning the Younger Dryas and the Holocene. These changes are due to multifaceted interactions between climate variability that characterizes the Atlantic Ocean region and hydroclimatic processes associated with the Mediterranean climate, thus making it difficult to reconstruct centennial-and millennial-scale variability in rainfall. In this study we present a composite and continuous isotopic record (d 13 C and d 18 O) consisting of four stalagmites from Mendukilo cave (MEN composite) in the western Pyrenees covering the Younger Dryas and the entire Holocene. This record reveals millennial-scale shifts in carbon isotopes in response to changes in the hydroclimate in the northern part of Iberia. The MEN oxygen isotopes show little variation on millenial time scales but reveal centennial changes that correlate with North Atlantic events (e.g., the 8.2 kyr BP cooling event). We observe a delay in the onset of humid conditions in the early Holocene and a subsequent trend towards drier and colder conditions between 6.0 and 2.5 kyr BP. This new, high-resolution and replicated spe-leothem record denotes the complex connection that exists between the North Atlantic and Western Europe during last millennia and the strong regional heterogeneity of the hydroclimate of Iberia during this time.
... This irreversible decline in forest cover affected large parts of the region as recorded in soil profiles and peat archives between c. 1500 and c. 1200 cal. BP ( [22,24] and references therein). Both the recovery and permanent decline in oak-hazel forest is marked by a series of CPs (Figures 5 and 6). ...
An 8500-year record of high-resolution pollen, non-pollen palynomorph, microscopic charcoal and selected geochemical data (Ti, Zr and Pb) is presented from an ombrotrophic mire from the Xistral Mountains, Galicia, North-West Iberia. The results suggest that vegetation changes over the last eight millennia are primarily the result of human disturbance, fire and climate change. Climate and fire were the main factors influencing vegetation development during the early to mid-Holocene, including a short-lived decline in forest cover c. 8.2 cal. ka BP. Changes associated with the 4.2 and 2.8 cal. Ka BP events are less well defined. Human impact on vegetation became more pronounced by the late Holocene with major periods of forest disturbance from c. 3.1 cal. ka BP onwards: during the end of Metal Ages, Roman period and culminating in the permanent decline of deciduous forests in the post-Roman period, as agriculture and metallurgy intensified, leading to the creation of a cultural landscape. Climate change appears to become less influential as human activity dominates during the Late Holocene.
... Such episodes of increased surface runoff in the study area coincide with wetter conditions in Lonar Lake and enhanced precipitation in the NW Himalaya ( Figure 8) suggesting a strengthened monsoon condition across the Indian subcontinent. This period is well coinciding with RWP when a warm and humid climate was experienced throughout the globe (Desprat et al., 2003;Ji et al., 2005;Wang et al., 2012). A high resolution palaeoenvironmental reconstruction based on marsh benthic foraminifera from Minho estuary, NW Iberia suggested a period of rainfall intensification from 2090 to 2140 cal BP (Moreno et al., 2014). ...
... Integrating well-dated and high-resolution hydroclimate proxy records from Iberia and northwestern Africa will help facilitate the construction of a regional analysis of effective precipitation variability during the last 1200 years. Numerous studies have focused on past climate in the Iberian Peninsula/northwest Africa region through the use of lake and ocean sediment cores (Moreno et al. 2012), riverine discharge (Trigo et al. 2004), pollen spectra (Desprat et al. 2003) and marsh sediment chemistry (Moreno et al. 2015). However, in order to construct a regional depiction of hydroclimate, we selected only time series that were sampled at high-resolution (at least decadal), had strong chronological control, overlapped substantially with our records for the past 1200 years, and were sensitive to precipitation dynamics. ...
The state of the atmospheric circulation and the associated hydroclimate in the North Atlantic during the last millennium remain the subject of considerable debate in both proxy- and model-based studies. Of particular interest in the Iberian region is the Azores High (AH) system, the southern node of the North Atlantic Oscillation (NAO), an atmospheric dipole closely tied to regional hydroclimate. Hydroclimate-sensitive proxy reconstructions from this region offer some insights into atmospheric dynamics, but large spatiotemporal gaps in these data inhibit a robust evaluation of hydroclimate variability. In this study, we present a continuous, sub-decadally-resolved composite stalagmite carbon isotopic record from three partially overlapping stalagmites from Buraca Gloriosa (BG) cave, western Portugal, situated within the center of the AH, that preserves evidence of regional hydroclimate variability from approximately 800 CE to the present. Chronologies are derived from U/Th dating and annual laminae. Stalagmite carbon isotopic values primarily reflect the amount of effective moisture and reveal generally dry conditions during the Medieval Climate Anomaly (MCA; ~ 850–1250 CE) and Modern Climate/Industrial Era (1850 CE-present), and wetter conditions during the Little Ice Age (LIA; ~ 1400–1850 CE). Multidecadal to centennial variability in the BG record and state-of-the-art last millennium climate model simulations show considerable coherence with precipitation-sensitive records from Spain and Morocco that, like BG, are strongly influenced by the intensity, size, and location of the AH. Model-proxy synthesis suggests that western Portugal was persistently dry during much of the MCA consistent with other NAO reconstructions; however, even considering age uncertainties, the apparent timing in the transition from a relatively dry MCA to a wetter LIA is spatially variable and confirms the non-stationary behavior of the AH system indicated by model output.
... The last 2000 yr represent an interval of interest for the study of natural climate variability and its interaction with anthropic activities. Climate changes during this interval are relatively well documented from European historical and climate proxy records as a succession of warm and cold phases associated with the Roman Warm Period, Dark Ages Cold Period, Medieval Warm Period, and Little Ice Age (LIA) (e.g., Desprat et al., 2003;Helama et al., 2017). However, little is known about the magnitude and pacing of climate changes in eastern Canada during this time interval because of limited historical data, the oldest dating from the European colonization in the sixteenth century (e.g., Ramsden, 1978). ...
Climate changes over the past two millennia in the central part of the Gulf of St. Lawrence are documented in this paper with the aim of determining and understanding the natural climate variability and the impact of anthropogenic forcing at a regional scale. The palynological content (dinocysts, pollen, and spores) of the composite marine sediment core MSM46-03 collected in the Laurentian Channel was used to reconstruct oceanographic and climatic changes with a multidecadal temporal resolution. Sea-surface conditions, including summer salinity and temperature, sea-ice cover, and primary productivity, were reconstructed from dinocyst assemblages. Results revealed a remarkable cooling trend of about 4°C after 1230 cal yr BP (720 CE) and a culmination with a cold pulse dated to 170–40 cal yr BP (1780–1910 CE), which likely corresponds to the regional signal of the Little Ice Age. This cold interval was followed by a rapid warming of about 3°C. In the pollen assemblages, the decrease of Pinus abundance over the past 1700 yr suggests changes in wind regimes, likely resulting from increased southerly incursions of cold and dry Arctic air masses into southeastern Canada.
... During the Roman Warm Period, between 2500 and 1600 cal yr BP (Wang et al. 2012), d 18 O values inferred from the Mohos record were more or less stable, and an increasingly dry climate can be inferred from the d 13 C values. Other European and North Atlantic records suggest this period was unusually warm (Desprat et al. 2003;Cristea et al. 2014). ...
We measured stable isotopes (δ ¹⁸ O and δ ¹³ C) in Sphagnum cellulose that was extracted from a long peat core drilled in the ombrotrophic Mohos peat bog, Ciomadul Mountain, Romania. The 10-m-long peat profile spans the period from 11,800 cal yr BP to present. The δ ¹⁸ O and δ ¹³ C data indicate there were several cooling events and warm periods in the area of the Mohos peat bog during the Holocene. The 8.2-ka cold event, however, was not detected using δ ¹⁸ O and δ ¹³ C values. Response of the peat bog to changing environmental conditions was inferred using data on organic matter accumulation, independent of the stable isotope results. All cool periods during the Holocene, whether of short or long duration, were identified as times of reduced organic matter accumulation rate. Similarly, dry periods were also correlated with reduced accumulation rates of organic matter.
... This new sediment export level was probably not only related to the sediment dynamics in the estuaries since it also coincides with a regional climatic shift towards a humid period following a period characterized by drought dominance, as evidenced in the nearby Doñana National Park (Jiménez- and in other regional records along southern Spain, suggesting higher lake levels from 2.6 to 1.6 cal ka BP (Martín-Puertas et al., 2008), more humid vegetation (Carrion et al., 2001), and higher sediment availability in river valleys (Goy et al., 1996). Humidity was found to have increased over northwestern Africa and the Mediterranean in general (Desprat et al., 2003;Hanebuth and Lantzsch, 2008;McCormick et al., 2012;Currás et al., 2012). ...
Mud depocenters (MDCs) are common elements on modern continental shelves and act as a major shallow-marine sink for fluviogenic material. These most proximal depocenters, thus, play a major role in material cycling and carbon availability on global and regional scales, though individual formation history, dependence on external forcing mechanisms, and material composition makes each of them a unique case. This study establishes a chronostratigraphic framework and deciphers the depositional dynamics for the two main MDCs on the continental shelf in the eastern Gulf of Cadiz, as a prime example, with the goal to calculate a regional sediment and carbon budget. Based on the analysis of 2040 km of subbottom profiles and 18 sediment cores, the fine-grained depocenters began to grow during maximum flooding around 6.5 cal ka BP. Sedimentation rates ranged between 2 and 35 cm/ka until 2.7 cal ka BP and increased significantly around the Roman Warm Period (30–200 cm/ka), caused by regional humidification as well as mining and agricultural activities. After 1.0 cal ka BP, sedimentation rates rose further (20–3000 cm/ka), due to land clearing in coincidence with erosion-favoring aridity during the Islamic period and the Medieval Climate Anomaly. Unprecedented sediment accumulation started with the Industrial Era. The total sediment volume of the two MDCs is 5.80 km³ with a dry mass of 12,971 Mt. 85 Mt. of organic matter and 3637 Mt. of carbonate make this depocenter an important shallow-marine sink, with a total of 521 Mt. carbon as a significant player in the regional terrestrial-marine carbon cycle.
... As visible in section GA-VI, colluvial deposits date already back to 5.6 ka (Fig. 7) suggesting that processes of flood loam deposition and colluvial deposition took place simultaneously, which is not surprising since slope erosion is the main sediment supplier to floodplains. Regarding the palaeoenvironmental context, such intense colluviation processes can be interpreted as further evidence for arid conditions promoting thinning of vegetation cover and soil erosion (Eybergen and Imeson, 1989;Desprat et al., 2003;Vicente-Serrano et al., 2006;Ruiz-Sinoga and Romero Diaz, 2010). Alternatively, changes in human land-use practises or intensified agricultural activity may likewise be able to initiate vegetation clearing and soil erosion processes. ...
The concrete relationships between fluvial system behavior and potential influencing factors that are, among others, climate for cing, tectonics, and human activity are a key issue in geomorphological research. In this regard, especially the Iberian Peninsula is an area of great interest because its landscapes are highly sensitive towards climate changes and anthropogenic impact. Nowadays, the Iberian Peninsula reveals a strongly heterogeneous and spatially fragmented climate configuration. This should give rise to disparate behavior of fluvial geomorphic systems considering that climate is generally assumed the most important trigger of fluvial dynamics. In fact, river systems located in more humid and more arid regions in Iberia often reveal deviating patterns of Holocene floodplain evolution. This raises the question of whether these patterns were actually caused by a different climate history or if, alternatively, other factors might have been responsible. In this study, we investigated the Holocene floodplain evolution of the Galera River that is located in the upland of Eastern Andalucía (SE-Spain) named Baza Basin. A combination of detailed stratigraphic profile logging and close-meshed radiocarbon dating revealed that Holocene river dynamics generally followed the regional climatic development, which proves the Galera floodplain record to be a valuable archive of Holocene landscape evolution. However, we demonstrate that fluvial dynamics of the Galera system are hardly comparable to other river systems in Iberia even if the climate evolution was not so different. Our results suggest that in river systems with different basic conditions and catchment-specific configurations, similar climatic influences may lead to deviating fluvial process regimes (divergence phenomenon) because of substantial imprints of other parameters such as geological substratum, relief composition, tectonics, or human interventions.
... Ma, in epoca storica, di questa città si perdette ogni traccia, e il nome di Laurentum rimase solo a indicare il territorio attraversato dalla via omonima, FLORILEGIUM. 195 Plinio, Libro I, 25 197 (Desprat & Goñi, August 2003) 119 zanzare. L'antica Roma potrebbe fornire un caso di approfondimento soffermandosi sulla sua storia epidemica. ...
1. Cambiamenti climatici e cambiamenti sociali. Prima di affrontare la questione climatica e la sua interazione con gli eventi storici e cosa assennata ricordare questa affermazione di Di Cosmo rilasciata in una intervista recente alla giornalista scientifica Joanne Lipman 157 : Gli storici sono interessati al clima da molto tempo, ma l'uso dei dati climatici è controverso da tempo. Negli ultimi anni, grazie al crescente interesse per il cambiamento climatico, la "paleoclimatologia" è diventata molto più precisa. Questa è la scienza che ricostruisce il clima per lunghi periodi di tempo utilizzando archivi naturali, come carote di ghiaccio, anelli di alberi, sedimenti di laghi o formazioni di grotte. In alcuni casi, può fornire ricostruzioni ad alta risoluzione. Mentre in precedenza potevamo avere scale molto grandi-secoli o millenni-ora possiamo scendere a un'analisi anno per anno. Questo tipo di progresso nella scienza consente agli storici di utilizzare i dati climatici per scopi rilevanti per gli eventi umani, e quindi per la ricerca storica." 158 Nel primo capitolo ci si è concentrati nel mettere in evidenza da prima gli eventi storici significativi per il periodo trattato e successivamente si è tentata una comparazione tra il i due imperi, al fine di comprendere se nella loro fase iniziale, di espansione e crollo vi fossero dei punti di contatto significativi. Si è ulteriormente approfondita la relazione con le popolazioni 157 Sulla quale si veda la pagina https://www.ias.edu/scholars/joanne-lipman. 158 (Di Cosmo 2020).
... In regard to the introduction of eucalypts, he claims that it was "prior to 1840" [sic]; previously, he states that introduction "would have taken place around 1830-1840." Desprat et al. (2003) detect the presence of Eucalyptus pollen in marine deposits in the Vigo estuary (Pontevedra) and estimate it was deposited toward 1856, following the sowing of seeds about 10 years earlier, although the inherent variability of the method may lead to slight changes of dates and thus might make them match other more trustworthy data about the presence of the tree in the area (Silva-Pando and Pino Pérez 2016). Similarly, Zacharin (1978) claims 1847 as the probable date, but possibly on the basis of other authors who indicate that date as the year when seeds were sent by Von Müeller from Australia on his arrival in Adelaide in December 1847, prior to being hired by the Government of New South Wales (1853) and also before he was Director of the Melbourne Botanical Gardens (1857). ...
The genus Eucalyptus was probably planted for the first time in Europe between 1771 by James Lee in London or 1774 at the Kew Gardens Greenhouse, and in 1794 in the Gardens of the Royal Palace of Caserta (Naples) outdoors. From then on, numerous plantations were carried out for ornamental and medicinal purposes or to recover swampy land. It was only from the middle of the nineteenth century that plantations started to be established for the purpose of logging, first for mines and railway sleepers and later to produce cellulose fiber for paper or textiles. It took root more consistently in Southwestern Europe (Spain, France, Italy, Portugal), thanks to the favorable climatic and topographic conditions. The 1960s saw the onset of the remarkable increase in eucalypt land cover. Based on bibliographical references and unpublished data, this paper reviews the introduction of these trees into Southwest Europe, focusing mainly on the periods up to 1880 and from 1960 onwards, while also including a number of references to the intermediate period and the creation of arboretums for demonstration and trial purposes. Certain outstanding examples are mentioned, and the way land cover has evolved in the region over recent decades is demonstrated. The novelty of this work lies in the proposed changes to the dates eucalyptus was introduced and the possible origins of the materials used, especially in the early decades of its introduction. Mention is also made of how public opinion has evolved since it began to be used and the success these plants have achieved so far.
... It has been observed that there are important changes in vegetation in the area. Namely, a decrease in autochthonous tree species (Quercus, Alnus) and an increase in both shrubby (Ulex, Erica, Calluna, etc.) and herbaceous plants (Poaceae and Cyperaceae) has been reported in correlation with the increase of farming areas and wildfires in the Medieval period (Pallarés and Portela, 2007), as it has been observed in pollen records and anthracological studies (Mighall et al., 2006;Desprat et al, 2003;Martinez-Cortizas et al., 2005;Carrión et al, 2010;Kaal et al., 2011). ...
Fluvial sediments provide environmental records of the Quaternary. In some cases, fluvial deposits are caused by anthropogenic processes that cause changes in the water regime of some river stretches. This is the case of dams. It has been reported that some dams or partial damming systems existed in the past, at least from some thousands of years ago. Such dams were used for fishing purposes and are referred as fishing weirs. In a recently published work it has been demonstrated that a fluvial thick deposit was caused by a damming system in a river of NW Iberia (River Miño, Pontevedra). Optically stimulated luminescence (OSL) provided the burial age of such fluvial deposit, showing a 1300-year-old fluvial record. The sedimentation rates of the record did not match with known climate fluctuations in the area. In this work, the sedimentation phases of such record are identified, and the detrital and organic matter content is studied to assess any change occurred in the environmental and fluvial conditions during the deposition period of the record that ranges from 814±134 to 1837±11 AD.
... In regard to the introduction of eucalyptus, he claims that it was "prior to 1840" [sic]; previously, he states that introduction "would have taken place around 1830-1840." Desprat et al. (2003) detect the presence of Eucalyptus pollen in marine deposits in the Vigo estuary (Pontevedra) and estimate it was deposited toward 1856, following the sowing of seeds about 10 years earlier, although the inherent variability of the method may lead to slight changes of dates and thus might make them match other more trustworthy data about the presence of the tree in the area (Silva-Pando and Pino Pérez 2016). Similarly, Zacharin (1978) claims 1847 as the probable date, but possibly on the basis of other authors who indicate that date as the year when seeds were sent by Von Mueller from Australia on his arrival in Adelaide in December 1847, prior to being hired by the Government of New South Wales (1853) and also before he was Director of the Melbourne Botanical Gardens (1857). ...
The genus Eucalyptus was probably planted for the first time in Europe between 1771 by James Lee in London or 1774 at the Kew Gardens Greenhouse, and in 1794 in the Gardens of the Royal Palace of Caserta (Naples) outdoors. From then on, numerous plantations were carried out for ornamental and medicinal purposes or to recover swampy land. It was only from the middle of the 19th century that plantations started to be established for the purpose of logging, first for mines and railway sleepers and later to produce cellulose fiber for paper or textiles. It took root more consistently in Southwestern Europe (Spain, France, Italy, Portugal), thanks to the favorable climatic and topographic conditions. The 1960s saw the onset of the remarkable increase in eucalypt land cover. Based on bibliographical references and unpublished data, this paper reviews the introduction of these trees into Southwest Europe, focusing mainly on the periods up to 1880 and from 1960 onwards, while also including a number of references to the intermediate period and the creation of arboretums for demonstration and trial purposes. Certain outstanding examples are mentioned, and the way land cover has evolved in the region over recent decades is demonstrated. The novelty of this work lies is the proposed changes to the dates eucalyptus was introduced and the possible origins of the materials used, especially in the early decades of its introduction. Mention is also made of how public opinion has evolved since it began to be used and the success these plants have achieved so far.
... Most of the studies of continental western Europe (essentially Spain, France and Italy) suggest a warm (e.g. McDermott et al., 2001;Roberts et al., 2001;Desprat et al., 2003;Holzhauser et al., 2005;Frisia et al., 2005;Berger and Bravard, 2012;Esper et al., 2012) and humid (e.g. Nesje et al., 2000;Wick et al., 2003;Ferrio et al., 2006;Magny et al., 2007;Migowski et al., 2006;Zanchetta et al., 2007) climatic episode. ...
The Roman Warm Period (from ≈300 BCE to ≈300 CE) is a climatic optimum, which had a key role in the development of the Roman civilization. This study provides new Mean Air Temperatures (MATs) inferred from the oxygen isotope composition of 80 bones and teeth apatite from 8 humans and 8 animals of the Gallic site of Thézy-Glimont, Picardie, France, dated between the 3rd and 2nd century BCE. Various bones from the cephalic, axial and appendicular skeleton of three human individuals were sampled. All bones have similar phosphate δ¹⁸O values for each individual, showing that the oxygen isotope signal of phosphate groups may be homogeneously recorded in bones. The sampled individuals were assumed to drink water from the nearby Avre river collecting local meteoric waters. The MATs were reconstructed combining (1) oxygen isotope fractionation equations between phosphatic tissues (δ¹⁸Op) and drinking water (δ¹⁸Ow), and (2) relationships between MATs and δ¹⁸Ow. Depending on the used MAT-δ¹⁸Ow relationship, the reconstructed MATs are 10.2 °C ± 1.4 °C and 10.5 °C ± 1.7 °C, which are comparable to present days (10.9 °C). This study shows that the Gallic civilization also experienced relatively high temperatures since the initiation of the Roman Warm Period.
... This is coeval with a slightly higher recovery of pine woods, which may suggest drier conditions occurring at that time. This could be a slight indication of the climatic shift identified in other sites of Atlantic Iberia (Desprat et al., 2003;Santos and Sánchez-Goñi, 2003) and in the Northern Hemisphere (Bond et al., 1997), where a cold and dry period is often described. ...
Pollen and NPP analysis performed on the sedimentary deposits accumulated in the inter-tidal banks of the Tagus Estuary allow for the reconstruction of vegetation history and landscape changes that occurred in Lisbon from the 1st to the 6th century cal AD. The high chronological resolution of this investigation makes it possible to identify changes in human activities that took place during the Roman period and reveals the extent of land use in the 2nd century cal AD. However, the most considerable landscape transformation of this 600-year period dates back to the late 5th century cal AD, when significant deforestation and increasing human activity, particularly pasturing, spread throughout the territory. This feature bears witness to the outcome of a deep socioeconomic transformation following the disintegration of the Roman administration and sheds light on a poorly known period in this part of Iberia.
... In general, the Roman conquest of Hispania led to significant changes in the social, cultural, and economic life of the Iberian Peninsula (Santos Yanguas and Cruz Andreotti, 2012). This coincided with the "Warm Roman Period", from 250 BCE to 450 CE (Desprat et al., 2003), which also increased land productivity. The Roman occupation was associated with increased deforestation due to military activities and the need for fuel and materials for building and transport (Hughes, 1994;Aranbarri et al., 2014) and with intensive cultivation, particularly in the lowlands. ...
A key problem in explaining the mountain landscapes of the Mediterranean region is the relationship between the development of transhumance (seasonal movement of livestock over long distances) and deforestation of the subalpine and upper montane belts at 1350–2200 m above sea level (m a.s.l.). We examined this relationship in the Central Southern Pyrenees using information from multiple proxies—archaeology, pollen analysis, lacustrine sedimentation patterns, historical documents, and geomorphology. Although there is evidence of forest clearing since the Neolithic, and we can infer the presence of shepherds and livestock in mountain areas based on archaeological sites and pollen analysis in some lacustrine records, there is no strong evidence for transhumance between the Ebro Depression and the Pyrenees during the Prehistory. Instead, we found evidence of transterminance (seasonal movement of livestock over short distances) during this time. Growth of human populations and the establishment of large-scale markets favored longer livestock movements during the Roman period, although we only have indirect information on this for other areas of the Iberian Peninsula and the Mediterranean region. A few documents indicate the occurrence of transhumance during the Early Middle Ages, whereas all other proxies indicate a general expansion of livestock and transhumance during the 12th and 13th centuries. This coincides with the Christian conquest of the Central Ebro Depression by the Aragon Kingdom, the organization of large wool markets in Western Europe, and the exemptions conferred by the kings of Aragon to herders in the city of Saragossa. This led to rapid deforestation, in that forests were rapidly logged or burned to expand the summer grasslands. During this period, written documents indicate many conflicts between people in the villages and valleys for control of summer grasslands, pollen analyses show a rapid decline of arboreal pollen, and geomorphology studies indicate greatly increased sedimentation rates following deforestation, suggesting intense erosion. Transhumance has declined since the end of the 18th century, and particularly throughout the 20th century, and this has led to tree re-colonization of less accessible and marginal areas. The hydrological and geomorphological consequences of these recent events are important topics for future studies.
... This decline cannot clearly be associated with the introduction of corn although, considering the chronological uncertainties of the pollen sequences, this could have been a factor. A change in climate could have been significant as the period associated with the Maunder Minimum (AD 1645-1715) is thought to have been one of the coldest phases of the Little Ice Age (Desprat et al., 2003;Moreno et al., 2012). Adverse climate conditions at both Cabreira and UTV are mentioned in documents from AD 1758 (Capela and Borralheiro, 2000;Capela et al., 2006). ...
In Europe, mountain landscapes have evolved in a long‐term relationship with human communities and present‐day landscapes reflect that ancient interaction. The present study aims to reconstruct human activity in two mountain areas in northern Portugal using palynological analysis integrated with the available regional historical, archaeological and palaeoenvironmental archives. Pollen records from two sedimentary sequences span the Medieval and Modern periods and show that mixed agriculture and livestock grazing were consistently present in both regions throughout these times. Variations in cultural indicators show that the extent of farming fluctuated throughout time, with a general increase in cultivation during the Medieval period but with contractions likely coinciding with times of social disturbance. Historical sources suggest that sociopolitical factors and population pressure were fundamental in the utilisation of upland spaces. This study did not find any convincing evidence to suggest that fire was a fundamental factor in heathland spread. We conclude that long‐term occupation of the uplands was sustained by low‐intensity land use throughout the Medieval to post‐Medieval periods, and that the present landscape has assumed a very different character following depopulation of the mountain areas and a shift towards commercial forestry.
... Moreover, almost all of the abrupt dry and wet periods revealed by our record coincide with well-documented climatic events. The dry periods during ~3000-2800 and ~550-210 cal yr BP coincide with the 2.8 ka event (Bond et al., 1997) and the Little Ice Age (LIA) (AD ~1400-1700) (Mann et al., 2009), respectively (Supplementary materials Figure S5, available online), and the wet period during ~2150-1700 cal yr BP falls within the Roman Warm Period (RWP) (250 BC to AD 450) (Desprat et al., 2003) (Supplementary materials Figure S5, available online). It was recently suggested that in the southeastern boundary area of the TP, precipitation during the LIA was higher than during the Medieval Warm Period (MWP) because of a shift in the rainfall belt associated with changes in solar activity (Tan et al., 2018b). ...
The Asian summer monsoon and the mid-latitude Westerlies are major atmospheric circulation systems which influence the climate of the Tibetan Plateau (TP), and hence the water resources, ecology, and socioeconomic well-being of the region. The interplay between the monsoon and the Westerlies has been investigated on glacial–interglacial, millennial, and decadal scales. However, due to the scarcity of high-resolution climate records from the TP, there is a lack of information on the centennial scale, which is more closely related to the development of civilization. Here we present a decadal-resolution precipitation record covering the past ~3600 years from Ngamring Co in the southern TP. The record suggests the gradual weakening of the Indian Summer Monsoon (ISM) with multiple centennial-scale fluctuations, which are synchronous with temperature changes. Precipitation was relatively high during the Medieval Warm Period (MWP) and low during the Little Ice Age (LIA). A wet Roman Warm Period (RWP) and an abrupt dry spell at 2.8 ka are also identified. Comparisons suggest that an intensified Westerlies penetrated the southern TP during dry intervals, such as during the 2.8 ka event, ~1700–1450 cal yr BP, and the LIA; whereas an intensified monsoon prevailed during warm periods such as the MWP. The centennial-scale oscillations of precipitation in the southern TP during the late Holocene suggest the role of the Westerlies in regulating ISM moisture delivery to the region, which likely resulted from variations in the surface temperature of the North Atlantic together with solar activity.
... Ait Brahim et al., 2019;Wassenburg et al., 2016). Over orbital and millennial time scales, hydroclimate in westcentral Portugal has generally tracked North Atlantic SST variability (Sánchez Goñi et al., 2008Goñi et al., , 2013Goñi et al., , 2016, and these changes have been preserved within BG stalagmites (Denniston et al., 2018) with warmer (cooler) Atlantic SSTs corresponding to more humid (drier) conditions at BG. Coherent changes between North Atlantic SSTs and western Iberia climate have also been documented for the Holocene (Boessenkool et al., 2001;Desprat et al., 2003;Pyrina et al., 2019). Martrat et al. (2007) indicate that following an abrupt warming following deglaciation after 20 ka BP, a more gradual warming of Iberian SSTs occurred until 7 ka BP after which they have gradually decreased until present day ( Figure 5). ...
Iberia is predicted under future warming scenarios to be increasingly impacted by drought. While it is known that this region has experienced multiple intervals of enhanced aridity over the Holocene, additional hydroclimate-sensitive records from Iberia are necessary to place current and future drying into a broader perspective. Toward that end, we present a multi-proxy composite record from six well-dated and overlapping speleothems from Buraca Gloriosa (BG) cave, located in western Portugal. The coherence between the six stalagmites in this composite stalagmite record illustrates that climate (not in-cave processes) impacts speleothem isotopic values. This record provides the first high-resolution, precisely dated, terrestrial record of Holocene hydroclimate from west-central Iberia. The BG record reveals that aridity in western Portugal increased secularly from 9.0 ka BP to present, as evidenced by rising values of both carbon (δ13C) and oxygen (δ18O) stable isotope values. This trend tracks the decrease in Northern Hemisphere summer insolation and parallels Iberian margin sea surface temperatures (SST). The increased aridity over the Holocene is consistent with changes in Hadley Circulation and a southward migration of the Intertropical Convergence Zone (ITCZ). Centennial-scale shifts in hydroclimate are coincident with changes in total solar irradiance (TSI) after 4 ka BP. Several major drying events are evident, the most prominent of which was centered around 4.2 ka BP, a feature also noted in other Iberian climate records and coinciding with well-documented regional cultural shifts. Substantially, wetter conditions occurred from 0.8 ka BP to 0.15 ka BP, including much of the ‘Little Ice Age’. This trend was followed by increasing aridity toward present day. This composite stalagmite proxy record complements oceanic records from coastal Iberia, lacustrine records from inland Iberia, and speleothem records from both northern and southern Spain and depicts the spatial and temporal variability in hydroclimate in Iberia.
... The temperature after the C4 event was relatively high compared to that at present, which may have been caused by a relatively high solar activity and the absence of major volcanic eruptions during this period (Wanner et al., 2015). The moderate climate, known as the RWP, occurred during this period in the northern hemisphere (Desprat et al., 2003;Patterson et al., 2010;Wang et al., 2012). ...
The regional paleoenvironmental record of Tokyo, central Japan, is required to enrich our understanding of climate change in East Asia and its impact on Japanese civilizations. Previous studies have generated paleotemperature records based on the analysis of shell mounds along the coast of Tokyo Bay and pollen from terrestrial borehole cores. However, a continuous, high time-resolution, quantitative paleotemperature record does not exist. A piston core was recovered from Tokyo Bay from which 22 mollusk shells were extracted. An age model for the core, determined via accelerator mass spectroscopy (AMS) ¹⁴C dating of the shells and a scoria layer from the Hoei eruption (1707 CE), showed that the core contains continuous record from ca. 2400 BCE. We analyzed the alkenone unsaturation ratios (UK’37) to reconstruct the variations in the paleotemperature. The temperature during the Meghalayan was generally warmer than that at present exhibiting a declining trend, which roughly matches the changes in the orbital-forcing summer insolation and the millennial-scale latitudinal shift of the subarctic front in the northeastern Pacific Ocean. The largest cold period, which occurred ca. 2300 BCE and had a minimum temperature of 19.5 °C, interrupted the warm conditions. This cold period may correspond to the global cooling/drying “4.2 ka BP event,” which marks the boundary between the Northgrippian and Meghalayan. Our results also revealed that several cold periods occurred, which may have been caused by decreases in solar activity or large volcanic eruptions. Particularly, large decadal to centennial-scale cold periods were observed ca. 440 BCE and 100 CE during the Yayoi era (ca. 900 BCE–300 CE). The coldest period after the establishment of a centralized system of government (ca. 300 CE–present) was recorded ca. 1050 CE, which may have been caused by the combination of a strong El-Niño mode and reduced solar activity. These climate change events can all be linked and, therefore, may be the potential causes of significant periods of famine and civil war in Japanese history, which eventually led to major shifts in Japanese social systems.
... Synchronous pine establishment has also been recorded at the Auk stumala (Edvardsson et al., 2016a) and U zpelkių Tyrelis peatlands (Pukien _ e, 1997), which reinforces the hypothesis of regionally warm and dry conditions in the southern Baltic region during the early portion of the discussed period. During the same time, low lake levels have been recorded from southwest Europe (Desprat et al., 2003), south-central Sweden (Harrison and Digerfeldt, 1993) and Poland (Madeja, 2013). The period, sometimes referred to as the Roman Warm Period (RWP), can also be detected in summer temperature reconstruction from Latvia (Heikkil€ a and Sepp€ a, 2010) as well as Central Europe (Büntgen et al., 2011). ...
To increase our understanding of long-term climate dynamics and its effects on different ecosystems, palaeoclimatic and long-term botanical reconstructions need to be improved, in particular in underutilized geographical regions. In this study, vegetation, (hydro)climate, and land-use changes were documented at two southeast Lithuanian peatland complexes – Čepkeliai and Rieznyčia – for the Late-Holocene period. The documentation was based on a combination of pollen, plant macrofossils, peat stratigraphic records, and subfossil trees. Our results cover the last two millennia and reveal the existence of moist conditions in Southern Lithuania between 300 and 500 CE and from 950 to 1850 CE. Conversely, changes towards warmer and/or dryer conditions have been recorded in 100, 600, and 750 CE, and since the 1850s. Significant differences with other Baltic proxies prevent deriving a complete and precise long-term reconstruction of past hydroclimatic variability at the regional scale. Yet, our results provide an important cornerstone for an improved understanding of regional climate change, i.e. in a region for which only (i) few detailed palaeobotanical studies exist and which has, in addition, been considered as (ii) an ecologically sensitive region at the interface between the temperate and boreal bioclimatic zones.
... These events correspond relatively well with advance and retreat phases of glaciers in the Alps (Fig. 7M) with some exceptions that may be linked with precipitation variability (Solomina et al., 2015). Despite slight differences in timing which may have resulted from the regional variability of rapid climate changes (e.g., Desprat et al., 2003;Viau et al., 2006;Jansen et al., 2007;Wanner et al., 2008), the events observed in St Front present a timing, temperature pattern and amplitude similar to other regional and global records based mainly on oceanic (Marcott et al., 2013) or continental data ( Fig. 7BeJ; Vollweiler et al., 2006;Pei et al., 2017;Marsicek et al., 2018;Affolter et al., 2019). ...
The evolution of temperatures during the Holocene is controversial, especially for the early Holocene. The occurrence of the Holocene Thermal Maximum (HTM) during the early Holocene has recently been reconsidered and seasonal biases have been suggested in the paleoclimatic proxies. High regional variability and a low number of reliable and continuous quantitative reconstructions compared with the oceanic realm further complicate study of the Holocene climate in the continental realm. We analyzed branched glycerol dialkyl glycerol tetraethers (brGDGTs), an organic paleothermometer, and palyno-logical signals as part of a multiproxy analysis of the sedimentary record from Lake St Front, in the Massif Central (France). Identification of a shift in brGDGT sources through the Holocene required removing terrigenous influences from the temperature signal. BrGDGT-and pollen-inferred paleotemperature reconstructions (based on the Modern Analog Technique and the Weighted Averaging Partial Least Squares method) were compared. Both showed a thermal maximum during the early Holocene followed by a decrease of temperatures. We evaluated biases which could potentially influence the reconstructed signal. There was no evidence for a summer temperature bias either for brGDGT-derived temperatures or for pollen-derived temperatures. The Lake St Front data, in agreement with other regional records, confirm the occurrence of the HTM as a general warm period during the early Holocene followed by mid-Holocene cooling in Western Europe and suggest that seasonal biases are not the main explanation of the Holocene conundrum d the disagreement between model simulations and proxy-based temperature reconstructions for the northern hemisphere.
... After 500 cal bc, the occurrence of human-related taxa becomes more frequent, a process that is coeval with evidence of erosive dynamics that has been linked to the development of forest clearances resulting from human activities (Fábregas-Valcarce et al. 2003;Muñoz Sobrino et al. 2012). Pollen analysis of marine and intertidal quaternary sedimentary deposits (Gómez-Orellana et al. 1996;Desprat et al. 2003;Muñoz Sobrino et al. 2007Costas et al. 2009) provides an insight into the vegetation history of southwest Galicia during the Holocene, but precise information on vegetation evolution during the first millennium bc and the beginning of the first century ad is not abundant due to chronological uncertainties and lack of data. Regarding wood resource management, the human communities that inhabited the northwest of the Iberian Peninsula during the Iron Age combined the exploitation of woodland, riparian forests and scrubland for firewood and timber procurement in a diversified strategy of wood resource supply (Figueiral 1995;Figueiral and Bettencourt 2004;. ...
The existence of a fire event at the Iron Age hillfort of Nabás, which is located on the southern bank of the Ría de Vigo (Galicia, NW of the Iberian Peninsula), favoured an extraordinary preservation of carbonised plant remains and offered an unusual opportunity to focus our research on the study of the final episode of a house life-cycle. The archaeobotanical approach focused on perishable materials combining charcoal, with carpology and pollen analysis, in tandem with a taphonomic assessment. The charcoal assemblage includes charcoal without signs of working, and wooden manufactures although the former group was probably related to the roof and timber of the round-house. This interpretation is based on the size and concentration of charcoal fragments, as well as the short taxonomic list (deciduous and evergreen Quercus sp., Fabaceae, Corylus avellana, Rosaceae/Maloideae, Salix/Populus, Alnus sp., Frangula alnus, Betula sp., Phragmites/Arundo and Ulmus sp.), and the recurrence of biological alterations such as xylophages’ galleries and hyphae. Aggregated grains and chaff of foxtail millet (Setaria italica) were found in several samples suggesting their storage, probably inside an organic container. Finally, pollen analysis offered clues about the uses of plants such as Ericaceae during the occupation phase of the round-house.
... The solar 11-year Schwabe cycle was identified in site 46 (Chen et al., 2013) and several other case studies from the region (Chen et al., 2011;Cini Castagnoli et al., 2002;Cini Castagnoli et al., 2005;Li et al., 2011). Other Mediterranean palaeotemperature studies have suggested centennial-and millennial-scale sun-climate coupling, partly in combination with the NAO (Desprat et al., 2003;Diodato & Bellocchi, 2012;Morellón et al., 2011;Morellón et al., 2012;Moreno et al., 2019;Nieto-Moreno et al., 2015;Sánchez-López et al., 2016;Versteegh et al., 2007). ...
The Medieval Climate Anomaly (MCA) is a preindustrial phase of pronounced natural climate variability with a core period from 1000 to 1200 CE. The paper presents a synthesis that integrates palaeotemperature records from the Greater Mediterranean Region encompassing the past 1,500 years based on multiproxy data from 79 published land and marine sites. MCA warming dominated the Western Mediterranean (Iberia, NW Africa) as well as the northern land areas of the Central and Eastern Mediterranean region. MCA cooling prevailed in the Canary Current Upwelling System, southern Levant, and some sea areas of the Central and Eastern Mediterranean. Previous palaeoreconstructions suggest persistent positive Atlantic Multidecadal Oscillation (AMO+) and North Atlantic Oscillation (NAO+) conditions during the MCA, while the Little Ice Age was dominated by an AMO− and NAO− regime. During the past 150 years, AMO+ conditions are typically associated with warming episodes in the Mediterranean area. A similar relationship appears to have also been established during the MCA as the majority of all Mediterranean land sites experienced warm climate conditions. In contrast, the NAO typically leads to a characteristic west‐east temperature dipole pattern in the basin, as documented for the last decades. During NAO+ conditions the Western Mediterranean is generally warm (and dry), while large parts of the Central and Eastern Mediterranean are cold. Similar trends seem to have been developed during the MCA when the NAO+ regime led to consistent warming in the Western Mediterranean, while a significant number of sites with MCA cooling existed in the Central and Eastern Mediterranean.
A detailed mid to late Holocene sedimentary infilling history of salt lakes situated on the northern edge of the Jeffara coastal plain (southeastern Tunisia) is presented. This work builds upon the findings of our three previous studies and synthesizes the results found in three short cores taken from the Mhabeul (Mh1: 93 cm and Mh2: 135 cm) and el Melah sabkha (Ml: 146 cm) for a possible lithological and event correlation between these two sabkhas. In fact, nine facies are determined through grain size, geochemical properties, magnetic susceptibility, and quartz grain microtexture proxies. The chronology of sediment records was derived from previous studies and is based on: (1) the predetermined dating of the huntite level in the sabkha el Melah, which dates back to around 5330 ± 170 years BP, and (2) the characterization of the volcano source, as well as the age of the tephra layers deposited in the sabkha Mhabeul sediments from volcanic eruptions in the Mediterranean. The contribution of this study is to reconstruct the Holocene climatic and sedimentological conditions on a regional and Mediterranean scale involved in the filling of the playas in southeastern Tunisia. Indeed, the sabkha deposits comprise regressive hypermagnesian carbonates deposit, a thin saline lake facies (gypsum crust) and the supratidal sabkhas characterized by an alternation of fluvio-aeolian-evaporite deposits. In the three cores, extreme paleo-events (fluvial and aeolian) have occurred during almost all climatic ages; some are well correlated. Since the last 2500 years BP, centennial-scale major hydrological events are evidenced at ~ 2500, 1850, 1300 and 600 years BP with periodicities of about 600 years. Moreover, the climatic conditions in southeast Tunisia are influenced by high- and low-latitude atmospheric patterns (e.g., Nord Atlantic Oscillation (NAO), Intertropical Convergence Zone, Asian monsoons) and the effects of the Mediterranean Sea.
Past global changes are typically registered in both natural (e.g., geologic-geomorphological, atmospheric-climatic, hydrologic-glacial and biological) and cultural records (e.g., archaeological, historical and documentary sources). Nevertheless, there are few sites in the world where sedimentary and archaeological evidence combine to provide information about two or more past millennial climate changes. In this regard, the Roman city of Guadix (Granada, SE Spain) represents a singular location, whose Roman theatre (1st century AD), recently discovered in 2007, contains palaeo-flood evidences that can be related to the two latest global warm periods: the Roman and Medieval epochs. In this research, detailed geological analyses are carried out. These analyses consisted in careful descriptions of vertical stratigraphic sections (lithology, structures...) and lateral correlation panels; as well as fluvial facies models to interpret the sedimentary environments for each sequence. This sedimentological information was combined with the study of archaeological remains, radiocarbon dating and optically stimulated luminescence, and three major flood events have been identified: two of them dating back to the beginning of the 1 st century AD (period of the Pax Romana Empire); and the other occurring at the end of the 12 th century (Islamic Almohad period). Such extreme hydrological events were synchronous with two warm periods: the Roman Climatic Optimum and the Medieval Warm Period. This seems to suggest that the meteorological fluctuations associated to climate changes during warming periods (such as the current one associated with present-day climate change) very likely produce such extraordinary or extreme events, which can mobilise large amounts of solid load (sands, silts and clays) and trigger sudden changes in the configuration of the river system (channel avulsions, meander cutoffs and captures among tributaries) and alluvial fans (at tributary mouths). We believe that the documented observations provide an analogy for the current warming period. In this regard, flood risk management in the current city of Guadix, whose hazard and risk maps were drawn up according to the criteria of the European Flood Directive, should take into account: (i) the millennial recurrent character of catastrophic floods in Guadix, well above the 500-year return period officially considered; (ii) the importance of the mobilisation of solid load in flood hazard and risk, which can obstruct drains and reduce the capacity of channels and bridges; (iii) the geomorphological dynamics, capable of modifying the position of the channels and thus the delimitation of hazard and risk zones; (iv) the role of non-permanent tributaries of the Guadix River during storms and heavy rain, related to quasi-stationary convective cells. Only in this way, will flood hazard and risk maps be useful in territorial and urban planning, civil protection during emergencies and the reduction of damage from future catastrophic floods. The present study highlights how geoarchaeological and palaeo-environmental records can be a highly valuable source of data for the improvement of flood hazard assessments in the 21st Century.
Durant les âges du Fer, la vallée du Rhône se trouve à la jonction entre le monde celtique du nord et du centre de l’Europe et le monde méditerranéen. Elle constitue donc un espace de circulation soumis à différentes influences culturelles. L’étude des faunes archéologiques issues des sites de la région permet donc d’approcher les spécificités de l’élevage, de la chasse et de la consommation carnée des populations protohistoriques, en un mot, de la relation entre elles et les populations animales. Par le prisme de l’archéozoologie, la vallée du Rhône apparaît comme un espace parfaitement intégré au reste de la Gaule. Ainsi, au premier âge du Fer, les pratiques alimentaires et d’élevage montrent une partition de la région entre l’influence des mondes nord-alpin et celtique méditerranéen. Au second, les pratiques impliquant des animaux et des produits d’origine animale présentent des évolutions, parmi lesquelles une augmentation plus ou moins forte de la part des porcs dans l’alimentation. Ces changements correspondent à ceux qui s’observent dans l’ensemble de la Gaule et qui sont sans doute en lien avec une réorganisation de la société. La morphologie des espèces domestiques et son évolution, de même que la pratique de la chasse, sont également plus ou moins similaires à celles du reste de la Gaule, du VIIIe au Ier siècle av. J.-C. L’influence des cultures grecque et italique, en matière alimentaire, semble être anecdotique, du point de vue des produits d’origine animale, les évolutions semblant davantage liées à l’organisation et à la démographie des populations. L’alimentation rhodanienne nous offre donc l’image d’une région pleinement intégrée aux cultures alimentaires celtiques et présente des évolutions moins liées à celles de l’environnement qu’à des problématiques sociales et économiques.
Climate change pushes us to consider old and new hypotheses of reading the
past. Today's events show similarities with the events of the centuries that have us
preceded. Movements of peoples, pandemic events and the collapse of powerful and extensive non-civilizations
they seem to be disjointed from causes that draw on natural, climatic and geological history.
Climate reconstructions over the last millennium are essential to estimate natural and anthropogenic forcing. Here we present a stalagmite δ¹⁸O record from southwestern China, which characterizes changes in the Asian Summer Monsoon (ASM) precipitation over the past 1350 years. Wet climate is clearly identified during the Dark Age Cold Period (DACP) and Little Ice Age (LIA); dry climate is clearly identified during the Medieval Warm Period (MWP) and Current Warm Period (CWP). These precipitation oscillations, except that over the CWP, are remarkably similar to, but strongly antiphase with, those in northwestern China. Over the CWP, our δ¹⁸O record, similar to other stalagmite records in East Asia, also exhibits a gradually increasing trend. This trend has been assumed to be caused by anthropogenic temperature warming. Here a better correlation is identified between our record and atmospheric temperature change during the preindustrial and industrial eras. This correlation provides solid evidence for the consistent modulation of the temperature on the ASM precipitation without and with the human-induced forcing. However, this modulation may act in a different manner during the industrial era, which results in the same δ¹⁸O variation across East Asia. In sum, our record provides a clear spatial variation of the ASM precipitation and highlights persistent temperature modulation on the ASM without and with anthropogenic emissions.
This work aimed to study the cyclicity of the geochemical chemical parameters and the carbonate percentages along a 59 cm core from the sebkha of Mchiguig, Central Tunisia. In fact, from the bottom upwards, six climatic phases were recorded including the Warming Present (Great Acceleration), the Late Little Ice Age (Anthropocene), the Early Little Ice Age, the Medieval Climatic Anomaly, the Dark Age, and the Roman Warm Period. In fact, the spectral analysis of the studied parameters visualized many cycles. Those cycles are related to sun activity, oceanographic, and atmospheric factors. Solar activity generated 500 yr cycles; however, the oceanographic circulation generated other cycles of 1500 yr and 700-800 yr. The 1500 yr cycle may be the result of the solar activity and NAO-like circulation.
The characterization of organic matter (OM) composition, physico-chemical, geochemical, and mineralogical studies of sedimentary core can help to better understand the paleoclimates and the depositional environments. The purpose of this work is to identify the factors monitoring the mineralogical composition and the sedimentation of sebkha Mhabeul sediments (southeastern Tunisia), during the Holocene. A 100.5 cm core (Mh 1) collected from this sebkha was analyzed for the determination of chemical composition by X-ray fluorescence (XRF), carbonate content by Bernard calcimetry, grain-sized sediments by AFNOR sieves, OM content by Rock-Eval 6 Pyrolysis, and mineralogical composition by X-ray diffraction (XRD), scanning electronic microscope (SEM), and infrared spectroscopy (IR). The sedimentary fillings of this sebkha, constituted by fine fractions, are characterized by the dominance of the detrital minerals (72–96 %) with high quartz percentages (42.2–91.5 %). The mineralogical composition of the studied sediments included detrital minerals (clay minerals, quartz, and feldspars), carbonate minerals (ankerite, dolomite, and calcite), and evaporitic minerals (halite, bassanite). The clay minerals (11–14%) are composed of a mixture of kaolinite, illite and palygorskite. Fourier transform infrared (FTIR) absorption spectra of all sediment samples confirm the mineralogical composition obtained by XRD and the existence of OM, by defining the band assignments for OM and different minerals as quartz, feldspar, clay, and carbonate minerals. The Rock Eval pyrolysis shows that the OM is immature and has a mixed origin (terrestrial and aquatic). The statistical analyses prove the results of geochemical and mineralogical studies. Indeed, the principal component analysis (PCA) of geochemical and mineralogical data and the depth help to prove the relationships between minerals and chemical elements. Moreover, the negative correlation between the Rock Eval Pyrolysis parameters and the depth shows a homogenous statistical group.
This study explores the paleoenvironmental changes of the Acholla coast over the last 2000 years by means of subsurface sediment analyses of lagoonal deposits via a multiproxy approach. A sequence of 5 steps is shown to have shaped the coastal development at Acholla and includes (i) the settlement of an open marine embayment during the Upper Pleistocene (substage 5e) in response to a transgressive event as evidenced by the deposition of carbonate sandstones rich in mollusc associations and marine elemental ratios Sr/Al, Ca/Al, Cl/Al, and S/Al; (ii) a sea-level rise towards183 AD, after a long period of emergence of the coast, leading to transgressive deposits of poorly sorted fine sands that are rich in diversified mollusc and ostracod taxa; (iii) a high-energy event (towards 417AD) with a peculiar biofacies characterized by coarse bioclastic mollusc-rich sands, charcoal particles, Tyrrhenian lithoclasts, and high values of marine elemental ratios Cl/Al, S/Al, and Ca/Al; (iv) a progradation of coastal habitats (between 417 and 1577 AD), favored by a period of flooding/detrital input and longshore current drifts, resulting in the development of an extensive sandspit and the formation of the Acholla lagoon. The construction of a Roman pier, originally constructed to protect the Acholla harbor from sedimentation, was counterproductive and favored the expansion of coastal swash bars and extension of the sandspit, ultimately resulting in the abandonment of the Acholla harbor; (v) the closure of the lagoon (from 1577 AD onward) and the built-up of well-sorted silt deposits are marked by the decrease of detrital elemental ratios (Ti/Al, Si/Al, and K/Al) and by reduced ostracod species richness values. The inferred scenario for the evolution at Acholla coast matches those for Sfax and Skhira coast in the Gulf of Gabes (Tunisia). Unlike Sfax and Skhira, however, the Acholla coast has been subjected to uplift by active faults, resulting in a time shift of depositional patterns.
La cisterna monumentale romana di Formiae (I sec. a.C.): storia della "riscoperta" degli ambienti ipogei nel sottosuolo di un quartiere popo-lare e considerazioni di carattere idraulico The monumental Roman tank of Formiae (1 st century B.C.): history of the rediscoverey of hypogean places in the underground of a popular neighborhood and hydraulic considerations MIELE Paolo (*) Geologo, libero professionista RIASSUNTO-La cisterna monumentale di Formiae, del I sec. a.c. (nota localmente come il "cisternone"), relegata nell'oblio per secoli dopo la caduta di Roma ed il conseguente declino della città, è stata casualmente "riscoperta" nel 1860 a seguito di una perlustrazione del pittore Pasquale Mattej, che ci fornisce una prima descrizione dell'ipogeo. A questa ha fatto seguito, nel 1930, una seconda relazione da parte del podestà di Formia, Felice Tonetti. Solo dalla seconda metà degli anni '80 del secolo scorso, tuttavia, se ne ha una migliore conoscenza,dettagliata-mente documentata a seguito delle esplorazioni di un gruppo locale spontaneo di giovani studiosi, che si occuparono di rile-vare una planimetria e tracciare alcune sezioni oltre che, natu-ralmente, produrre una ricca documentazione fotografica del sito. A seguito di questo lavoro di documentazione la cisterna fu finalmente oggetto di un intervento di recupero e quindi, dal 2003, aperta al pubblico. Appare ancora poco chiara tuttavia la funzionalità idraulica dell'opera, che doveva rifornire con continuità e con ingenti portate idriche, una porzione impor-tante dell'antica Formiae nel suo periodo di massimo sviluppo. In particolare appare fortemente inadeguata al rifornimento la sorgente indicata dai primi esploratori come possibile fonte di rifornimento. Per contro viene proposta una linea di ricerca al-ternativa, che prevede la possibilità di uno sfruttamento della falda poco profonda e/o il drenaggio delle acque di infiltra-zione superficiale. PAROLE CHIAVE: Formia, Castellone, Cisternone romano, Ci-sterna monumentale, Idrogeologia. ABSTRACT-The monumental tank of Formiae (1 st century. B.C.) locally called "cisternone", relegated to oblivion for centuries after the fall of Rome and the consequent decline of the city, it was accidentally "rediscovered" in 1860 following a patrol of the painter Pasquale Mattej, who provides us with first description of the hypogeum. This was followed in 1930 by a second report by Felice Tonetti. Only from the second half of the 80s of the last century, however , we have a better knowledge of it, documented in detail following the explorations of a spontaneous local group of young scholars, who took care of detecting a plan and tracing some sections as well as, of course, produce a rich photographic documentation of the site. Following this documentary work, the tank was finally subject to recovery and therefore, since 2003, open to the public. However, the hydraulic functionality of the work is still unclear, which had to supply continuously and with large water flows, an important portion of the ancient Formiae in its period of maximum development. In particular, the spring indicated by the first explorers as a possible supply source appears to be highly inadequate. On the other hand, an alternative research line is proposed, which provides for the possibility of exploiting the shallow water table and / or the drainage of surface infiltration waters.
The temperate desert in arid central Asia (ACA) is located along the Silk Road, an ancient land route used for economic and cultural exchange between the East and the West. In this paper, we survey of 145 surface pollen samples and related modern vegetation sample plots along an east-west desert transect in the eastern ACA in order to relate surface pollen assemblages to specific desert vegetation types. Results reveal that (1) the surface pollen assemblages reflect the modern vegetation composition in terms of dominant taxa, (2) three zonal vegetation belts are recognizable by the surface pollen assemblages, and even the six desert vegetation types with mosaic distribution are also distinct, and (3) the ratio of Chenopodiaceae and Artemisia provides no resolution in further identifying the different desert vegetation types. These findings allow us to develop a new approach for reconstructing past vegetation succession and desert ecosystem formation. Applying these calibrate ancient datasets to palaeoecologic analysis offers a method to improve the resolution at which different desert vegetation types can be distinguished and to more precisely understand the composition of desert ecosystems. The new approach is, not only, applicable to the Quaternary, but also to Neogene whose taxa are almost the same at the genus and/or family level.
This work is based on a marine sediment core retrieved from 250 m column of water depth near the landfall island Andaman isalands.
This work aims to study the relation between the geological history of Sidi El Hani saline environment and its response to the climatic variability. To achieve this goal, a multidisciplinary work compiled in the individual chapters' compilation thesis format was done. Added to chapter zero, this work is made up of seven chapters. Each of them has its own local purpose serving the global purpose of the work. In chapter zero, the aim is to show scientific arguments for compiling this work in English and to give the scientific name of Sidi El Hani saline environment according to the Anglophone terminology. This terminology gives a name to a saline environment according to its geologic features and the speciality of study. For instance, hydrogeologically, Sidi El Hani saline environment is a discharge playa; hydrologically, it is playa; and sedimentologically, it is a clay pan. Chapter one aims, by introducing the specific context of Sidi El Hani saline environment, to show the further increasing need for a multidisciplinary study, to give a bird's eyes sight on the coming chapters and to comment the thesis format. In chapter two, the focus was meant to be on the interaction between the global, the regional and the local frameworks on the one hand and the geodynamic context of Sidi El Hani saline environment on the other; such interaction proves vital in deciding whether the saline environment will be commanded by its geological history or by the climatic variability. Thus, on the basis of a cross-interpretation of previous works, results showed that the geological history is more likely to dominate by providing a salty context in the subsurface of Sahel area. This study proposed its own model of a saline environment inherited from the Messinian Salinity Crisis (MSC). By doing so, this study proposes two hypotheses as origin of salt: the Triassic intrusions and the Messinian Salinity Crisis. In chapter three, on the basis of a hydrological, hydrogeological and geochemical study, the aim was to reinforce the idea of a strong deep influence of somewhere domes of salt and/or salty water probably inherited from the Triassic domes and/or the Messinian Salinity Crisis (MSC) and to deduce that the climatic factor has been taking minor role since the opening of Sidi El Hani discharge playa. By proposing its own model about the groundwater contribution, this study found out that, as a consequence of the dominance of a salty groundwater contribution, the effect of the climate is considered as minor. In chapter four, the aim was to give some precision to previous studies and to examine the depositional environment of sediments in Sidi El Hani watershed, which may feed the saline environment after their erosion by wind or water. Accordingly, some outcropping sediments from the vicinities were sampled and studied. Three crania found also somewhere near the playa have permitted this study declaring Sidi El Hani zone as archeological site; and they may be an efficient tool for dating. In chapter five, the Visual Core Description focused on three reference sandy bands and on the concept of grey scale variability in order to infer the clay pan response to the climatic variability during the last two millennia. Actually, this study established its own concept of the major grey scale variability. This line of attack permitted the classification of Sidi El Hani cores according to their major grey scales variability. Only cores with high major grey scales variability were indeed useful to infer the climatic variability in Sidi El Hani clay pan. Correlations of these cores, on the basis of the major grey scale variability and the occurrence of the three reference sandy bands, were done with a known reference core from sebkha Mhabeul (southeast Tunisia) in order to guess the last 2000 years clay pan climatic history. In chapter six, cores were the object of descriptive classifications of the grain size distribution, which were meant to describe the grain size continuous variability within cores and to correlate between them. The statistical treatment of the crude data was done on the basis of two different methods (the method of Moments Statistics and the method of Inclusive Graphic Statistics) to compute statistical parameters of the grain size distribution such as mean and median. The correlations between cores were done on the basis of sand/silt/clay percentages. Eventhough it has given special care to test different methods of studying the grain size distribution, this study was not deviated from its primary purpose of investigating the filling of the playa; correlations between different cores were meant to infer their sedimentary dynamics. In chapter seven, the synthesis was done by giving a complete map of the saline environment of Sidi El Hani summing up the hydrological, hydrogeological and sedimentological features of its vicinities and its fillings. This Master opens new perspectives concerning the chaos theory and studying the organic matter. Another serious promise for research is in comparing Sidi El Hani saline environment with other saline environments in Tunisia and with analogous locations in planet Mars.
Although environmental factors such as precipitation and temperature are
recognized as influencing pollen production, the impact of rising atmospheric
carbon dioxide concentration ([CO2]) on the
potential growth and pollen production of hay-fever-inducing plants is
unknown. Here we present measurements of growth and pollen production of
common ragweed (Ambrosia artemisiifolia L.) from
pre-industrial [CO2] (280 mol
mol–1) to current concentrations (370 mol
mol–1) to a projected 21st century concentration
(600 mol mol–1). We found that exposure to current
and elevated [CO2] increased ragweed pollen
production by 131 and 320%, respectively, compared to plants grown at
pre-industrial [CO2]. The observed
stimulations of pollen production from the pre-industrial
[CO2] were due to an increase in the number
(at 370 mol mol–1) and number and size (at 600 mol
mol–1) of floral spikes. Overall, floral weight as
a percentage of total plant weight decreased (from 21% to 13%),
while investment in pollen increased (from 3.6 to 6%) between 280 and
600 mol mol–1 CO2. Our
results suggest that the continuing increase in atmospheric
[CO2] could directly influence public health
by stimulating the growth and pollen production of allergy-inducing species
such as ragweed.
Spectral estimation procedures which employ several prolate spheroidal sequences as tapers have been shown to yield better than standard single-taper spectral analysis when used on a variety of engineering data. We apply the adaptive multitaper spectral estimation method of Thomson (1982) to a number of high-resolution digital seismic records and compare the results to those obtained using standard single-taper spectral estimates. Single-taper smoothed-spectrum estimates are plagued by a trade-off between the variance of the estimate and the bias caused by spectral leakage. Applying a taper to reduce bias discards data, increasing the variance of the estimate. Using a taper also unevenly samples the record. Throwing out data from the ends of the record can result in a spectral estimate which does not adequately represent the character of the spectrum of nonstationary processes like seismic waveforms. For example, a discrete Fourier transform of an untapered record (i.e., using a boxcar taper) produces a reasonable spectral estimate of the large-amplitude portion of the seismic source spectrum but cannot be trusted to provide a good estimate of the high frequency roll-off.A discrete Fourier transform of the record multiplied by a more severe taper (like the Hann taper) which is resistant to spectral leakage leads to a reliable estimate of high-frequency roll-off, but this estimate weights the analyzed data unequally. Therefore single-taper estimators which are less affected by leakage not only have increased variance but also can misrepresent the spectra of nonstationary data. The adaptive multiplier algorithm automatically adjusts between these extremes. We demonstrate its advantages using 16-bit seismic data recorded by instruments in the Anza Telemetered Seismic Network. We also present an analysis demonstrating the superiority of the multitaper algorithm in providing low-variance spectral estimates with good leakage resistance which do no overemphasize the central portion of the record.
Se han realizado anilisis palinologicos, de foraminiferos y sedimentologicos asi como dataciones radiometricas en sedimentos del estuario del Bidasoa (sureste del Golfo de Bizkaia). Los resultados obtenidos y su comparacion con otros provenientes de la region cantabrica (norte de Espafia) han permitido relacionar la sucesion de la vegetacion y los cambios relativos del nivel del mar durante el Holoceno. La expansion de Alnus en esta region, entre 6000 y 4500 BP, es contemporanea con una fase de retirada del mar que ha sido identificada en la parte suroriental del Golfo de Bizkaia entre S800 y 4900 BP. Esta retirada de la influencia marina produjo amplias zonas de agua dulce favorables para el desarrollo de las alisedas.
To adequately manage the fragile and changing environments of semiarid regions it is essential to disentangle human from climate or other environmental impacts over longer timescales than human memory. We investigated sediment cores from Salada Chiprana, a saline lake in the central Ebro basin in Spain, using pollen, charcoal, sedimentological, geochemical and radiometric dating techniques. The sequence indicates a rapid evolution from an ephemeral playa lake during the Late Holocene to a permanent saline lake a few centuries ago. The limnological evolution correlates with changes in agricultural practices and provides evidence of the strong impact of irrigation on the lake's hydrological balance from the XVth century. The work demonstrates that the Salada Chiprana, the only permanent, relatively deep, hypersaline lake in Spain has been created by a long history of human interaction with the landscape.
Solar total and ultraviolet (UV) irradiances are reconstructed annually from 1610 to the present. This epoch includes the Maunder Minimum of anomalously low solar activity (circa 1645-1715) and the subsequent increase to the high levels of the present Modern Maximum. In this reconstruction, the Schwabe (11-year) irradiance cycle and a longer term variability component are determined separately, based on contemporary solar and stellar monitoring. The correlation of reconstructed solar irradiance and Northern Hemisphere (NH) surface temperature is 0.86 in the pre-industrial period from 1610 to 1800, implying a predominant solar influence. Extending this correlation to the present suggests that solar forcing may have contributed about half of the observed 0.55°C surface warming since 1860 and one third of the warming since 1970.
Palaeoclimatology provides our only means of assessing climatic variations before the beginning of instrumental records. The various proxy variables used, however, have a number of limitations which must be adequately addressed and understood. Besides their obvious spatial and seasonal limitations, different proxies are also potentially limited in their ability to represent climatic variations over a range of different timescales. Simple correlations with instrumental data over the period since ad 1881 give some guide to which are the better proxies, indicating that coral- and ice-core-based reconstructions are poorer than tree-ring and historical ones. However, the quality of many proxy time series can deteriorate during earlier times. Suggestions are made for assessing proxy quality over longer periods than the last century by intercomparing neighbouring proxies and, by comparisons with less temporally resolved proxies such as borehole temperatures. We have averaged 17 temperature reconstructions (representing various seasons of the year), all extending back at least to the mid-seventeenth century, to form two annually resolved hemispheric series (NH10 and SH7). Over the 1901–91 period, NH10 has 36% variance in common with average NH summer (June to August) temperatures and 70% on decadal timescales. SH7 has 16% variance in common with average SH summer (December to February) temperatures and 49% on decadal timescales, markedly poorer than the reconstructed NH series. The coldest year of the millennium over the NH is ad 1601, the coldest decade 1691–1700 and the seventeenth is the coldest century. A Principal Components Analysis (PCA) is performed on yearly values for the 17 reconstructions over the period ad 1660–1970. The correlation between PC1 and NH10 is 0.92, even though PC1 explains only 13.6% of the total variance of all 17 series. Similar PCA is performed on thousand-year-long General Circulation Model (GCM) data from the Geophysical Fluid Dynamics Laboratory (GFDL) and the Hadley Centre (HADCM2), sampling these for the same locations and seasons as the proxy data. For GFDL, the correlation between its PC1 and its NH10 is 0.89, while for HADCM2 the PCs group markedly differently. Cross-spectral analyses are performed on the proxy data and the GFDL model data at two different frequency bands (0.02 and 0.03 cycles per year). Both analyses suggest that there is no large-scale coherency in the series on these timescales. This implies that if the proxy data are meaningful, it should be relatively straightforward to detect a coherent near-global anthropogenic signal in surface temperature data.
Some examples of postglacial and modern European vegetation are presented as starting points for a discussion on the pattern and processes of the late-Holocene recession of forests. Predictive modern vegetation models are considered; they indicate that deciduous forest may not at present be the dominant vegetation type in northern Europe and in part of central Europe. A comparison of pollen diagrams at a supraregional scale shows that the beginning of deforestation in northern Europe was contemporaneous with expansion of forests in Italy. Some Holocene pollen records, compared with the classical interglacial-cycle models, seem to indicate that, at least in some regions of Europe, the present interglacial might already be in the terminal phase, namely open conifer-dominated woodlands. On the basis of these observations, the hypothesis is suggested that late-Holocene natural openings in the forests, predictable at the end of the interglacials, favouring the diffusion of grasses, produced environments suitable for human settlements, agriculture and pastoral activity.
This paper discusses the research carried out to check the climatic characteristics of the late Maunder Minimum (LMM) (AD 1675–1715) in the southwestern part of the Iberian Peninsula and as an aid towards pressure patterns reconstruction in the NE Atlantic and Europe. Documentary evidence reveals that interannual precipitation variability was similar to the present one, although some very severe dry periods occurred (particularly one in 1694). On the other hand, during the LMM there was a higher percentage of cold winter months, some of them with snowfall. A brief comparison is made with other areas from the Mediterranean. The relationships between weather similarities and differences for particular months is analysed in the light of the reconstructed synoptical patterns, and further research into historical climatic change of southern Europe is suggested.
To adequately manage the fragile and changing environments of semiarid regions it is essential to disentangle human from climate or other environmental impacts over longer timescales than human memory. We investigated sediment cores from Salada Chiprana, a saline lake in the central Ebro basin in Spain, using pollen, charcoal, sedimentological, geochemical and radiometric dating techniques. The sequence indicates a rapid evolution from an ephemeral playa lake during the Late Holocene to a permanent saline lake a few centuries ago. The limnological evolution correlates with changes in agricultural practices and provides evidence of the strong impact of irrigation on the lake's hydrological balance from the XVth century. The work demonstrates that the Salada Chiprana, the only permanent, relatively deep, hypersaline lake in Spain has been created by a long history of human interaction with the landscape.
It has long been believed that the 20th warming was preceded by the "Little Ice Age" and the "Medieval Warm Period" as a result
of the natural variability of climate. But as
Bradley
explains in this Perspective, recent research has shown that these climate patterns may not have been global, and are much
more variable in time and space than previously assumed. However, one fact remains indisputable, namely that end-20th century
temperatures were higher than at any time during the last millenium.
Based on a quantitative study of the common fluctuations of 14 Ca nd10Be production rates, we have derived a time series of the solar magnetic variability over the last 1200 years. This record is converted into irradiance variations by linear scaling based on previous studies of sun-like stars and of the sun’s behavior over the last few centuries. The new solar irradiance record exhibits low values during the well-known solar minima centered at about 1900, 1810 (Dalton) and 1690 ad (Maunder). Further back in time, a rather long period between 1450 and 1750 ad is characterized by low irradiance values. A shorter period is centered at about 1200 ad, with irradiance slightly higher or similar to present day values. It is tempting to correlate these periods with the so-called ‘‘little ice age’’ and ‘‘medieval warm period’’, respectively. An accurate quantification of the climatic impact of this new irradiance record requires the use of coupled atmosphere‐ocean general circulation models (GCMs). Nevertheless, our record is already compatible with a global cooling of about 0.5‐1°C during the ‘‘little ice age’’, and with a general cooling trend during the past millenium followed by global warming during the 20th century (Mann et al., 1999).
Seventy-one sensitivity experiments have been performed using a two-dimensional sectoraveragedglobal climate model to assess the potential impact of six different factors on the lastmillennium climate and in particular on the surface air temperature evolution. Both natural(i.e, solar and volcanism) and anthropogenically-induced (i.e. deforestation, additional greenhousegases, and tropospheric aerosol burden) climate forcings have been considered.Comparisons of climate reconstructions with model results indicate that all the investigatedforcings are needed to simulate the surface air temperature evolution. Due to uncertainties inhistorical climate forcings and temperature reconstructions, the relative importance of a particularforcing in the explanation of the recorded temperature variance is largely function of theforcing time series used. Nevertheless, our results indicate that whatever the historical solar andvolcanic reconstructions may be, these externally driven natural climate forcings are unable togive climate responses comparable in magnitude and time to the late–20th-century temperaturewarming while for earlier periods combination of solar and volcanic forcings can explain theLittle Ice Age and the Medieval Warm Period. Only the greenhouse gas forcing allows themodel to simulate an accelerated warming rate during the last three decades. The best guesssimulation (largest similarity with the reconstruction) for the period starting 1850 AD requireshowever to include anthropogenic sulphate forcing as well as the impact of deforestation toconstrain the magnitude of the greenhouse gas twentieth century warming to better fit theobservation. On the contrary, prior to 1850 AD mid-latitude land clearance tends to reinforcethe Little Ice age in our simulations. DOI: 10.1034/j.1600-0870.2002.00287.x
New evidence from deep-sea sediment cores in the subpolar North Atlantic demonstrates that a significant component of sub-Milankovitch climate variability occurs in distinct 1-2 kyr cycles. We have traced that cyclicity from the present to within marine isotope stage 5, an interval spanning more than 80 kyrs. The most robust indicators of the cycle are repeated increases in the percentages of two petrologic tracers, Icelandic glass and hematite-stained grains. Both are sensitive measures of ice rafting episodes associated with ocean surface coolings. The petrologic tracers exhibit a consistent relation to Heinrich events, implying that mechanisms forcing Heinrich events were closely linked to those forcing the cyclicity. Our records further suggest that Dansgaard/Oeschger events may be amplifications of the cycle brought about by the impact of iceberg (fresh water) discharges on North Atlantic thermohaline circulation. The tendency of thermohaline circulation to undergo threshold behavior only when fresh water input is relatively large may explain the absence of Dansgaard/Oeschger events in the Holocene and their long pacings (thousands of years) in the early part of the glaciation. Finally, evidence from cores near Newfoundland confirms previous suggestions that the Little Ice Age was the most recent cold phase of the 1-2 kyr cycle and that the North Atlantic tended to oscillate in a muted Dansgaard/Oeschger-like mode during the Holocene.
Palaeoecological evidence from a pollen sequence in eastern Spain does not support the notion of potential vegetation as employed by the floristic-phytosociological approach of vegetation classification. A middle Holocene replacement of Pinus forest by Quercus-dominated communities is interpreted as the result of increased fires in the surroundings of the site and suggests that sclerophyllous scrub in the region could not have been determined by climatic conditions as previously assumed. Therefore it cannot be considered to be a climax state of vegetation. The possible role of anthropogenic and random processes in this change should not be underestimated.
A peat core from a bog in northwest Spain provides a record of the net accumulation of atmospheric mercury since 4000 radiocarbon
years before the present. It was found that cold climates promoted an enhanced accumulation and the preservation of mercury
with low thermal stability, and warm climates were characterized by a lower accumulation and the predominance of mercury with
moderate to high thermal stability. This record can be separated into natural and anthropogenic components. The substantial
anthropogenic mercury component began ∼2500 radiocarbon years before the present, which is near the time of the onset of mercury
mining in Spain. Anthropogenic mercury has dominated the deposition record since the Islamic period (8th to 11th centuries
A.D.). The results shown here have implications for the global mercury cycle and also imply that the thermal lability of the
accumulated mercury can be used not only to quantify the effects of human activity, but also as a new tool for quantitative
paleotemperature reconstruction.
Although environmental factors such as precipitation and temperature are recognized as influencing pollen production, the impact of rising atmospheric carbon dioxide concentration ([ CO2]) on the potential growth and pollen production of hay- fever- inducing plants is unknown. Here we present measurements of growth and pollen production of common ragweed (Ambrosia artemisiifolia L.) from pre- industrial [CO2] (280 mu mol mol(-1)) to current concentrations (370 mu mol mol(-1)) to a projected 21st century concentration (600 mu mol mol(-1)). We found that exposure to current and elevated [CO2] increased ragweed pollen production by 131 and 320%, respectively, compared to plants grown at pre- industrial [CO2]. The observed stimulations of pollen production from the pre- industrial [CO2] were due to an increase in the number (at 370 mu mol mol(-1)) and number and size (at 600 mu mol mol(-1)) of floral spikes. Overall, floral weight as a percentage of total plant weight decreased (from 21% to 13%), while investment in pollen increased (from 3.6 to 6%) between 280 and 600 mu mol mol(-1) CO2. Our results suggest that the continuing increase in atmospheric [CO2] could directly influence public health by stimulating the growth and pollen production of allergy- inducing species such as ragweed.
The measurement of power spectra is a problem of steadily increasing importance which appears to some to be primarily a problem in statistical estimation. Others may see it as a problem of instrumentation, recording and analysis which vitally involves the ideas of transmission theory. Actually, ideas and techniques from both fields are needed. When they are combined, they provide a basis for developing the insight necessary (i) to plan both the acquisition of adequate data and sound procedures for its reduction to meaningful estimates and (ii) to interpret these estimates correctly and usefully. This account attempts to provide and relate the necessary ideas and techniques in reasonable detail — Part I of this article appeared in the January, 1958 issue of THE BELL SYSTEM TECHNICAL JOURNAL.
1 Pollen diagrams from four peatbogs and a marshland located in the Atlantic and Mediterranean zones of north-central Spain are described, and their correlation is used to define a Holocene pollen reference sequence for the region. 2 Two main variants may be defined for the reference sequence: a northern variant, characterized by the predominance of deciduous trees, corresponds to sites under Atlantic temperate and moist climatic influence and a southern variant, with lower deciduous tree diversity, corresponds to sites under Mediterranean and continental climatic conditions. A vegetation gradient from the Atlantic to the Mediterranean side may be inferred from the pollen analysis. 3 A compilation of $^{14}C$ dated pollen diagrams from the northern Iberian Peninsula is used to plot maps for the Holocene spread of the principal tree genera. 4 Quercus, Corylus, Alnus, Taxus and Pinus had a wide distribution in the northern Iberian Peninsula during pre-Holocene times, as patchy refugia situated at medium elevations. They spread from these refugia at different times depending on climatic, geomorphological and successional conditions. Fagus, Abies and Carpinus could have spread through the Pyrenees. 5 Anthropogenic disturbance at the range limit of Fagus, Abies and Carpinus is probably responsible for their present geographical distribution. 6 The present-day Pinus silvestris forests growing in the Iberian Cordillera, southern Pyrenees and Cantabrian Cordillera have a local origin and may constitute the Mediterranean mountain pine forest altitudinal zone, not previously described for the Iberian Peninsula.
High-resolution sequential analysis of the upper 380 mm of a sediment core from Lake Sanabria, an oligotrophic freshwater lake in the granitic zone of the NW Iberian Peninsula, shows four lacustrine sedimentary episodes, some of which have been interpreted as the Little Ice Age (LIA). Radiometric dating of the core (C-14 Accelerator Mass Spectrometry (AMS)) gives an age of 875 AD for the oldest sedimentary episode. Subsequent variations are attributed to human influence on the catchment of Lake Sanabria: agricultural activity of the San Martı́n de Castañeda monastery during the Middle Ages, the breached Vega de Tera dam in January 1959, or the designation of Lake Sanabria as a natural park in 1978.
Pollen, plant macrofossil. charcoal, sedimentary analyses and magnetic susceptibility measurements have been carried out on a C-14 dated sediment sequence from Las Pardillas Lake (1850 m a.s.l., Iberian Mountain Chain). The interpretation of the pollen diagram has been assisted by the analysis of an altitudinal transect of moss-polsters collected in the same area. After 9310 BP, a Pinus-Betula-Quercus open woodland developed. Between c. 9000 BP and 7100 BP, the woodland became a mixed forest with Pinus vylvestris. The beginning of the continuous curve of Corylus c. 9000 BP dated the local population expansion of this tree and is 1000 years earlier than the age previously attributed to its expansion in north-central Spain. At c. 7400 BP a local fire is associated with a possible first establishment of Fagu.s in the area. From c. 7100 BP to c. 3700 BP, Taxus, Rex and Hedera were present in the forest vegetation. During this interval, the pollen and sedmentological record indicated a stable period of rich, mixed Quercus forest. At the same time, the community of floating-leaved aquatics was replaced by submerged plants, suggesting that a rise in lake water level may have occurred between 7200 and 6400 BP. Fagus became continuously present in the Las Pardillas Lake area c. 3200 BP. As Fagus is fire-sensitive, the expansion and stand scale establishment may be linked to an increase in fire regime, a type of disturbance which has facilitated the spread of this taxon elsewhere in Europe. A significant forest reduction, involving all the trees, took place c. 1500 BP. Between 1000 and 400 BP, Pinus and Fugus re-expanded associated with the first clear evidence of agricultural activity. The well-represented, mixed Quercus forest around Las Pardillas Lake, and the early development of Coryluw compared to other Mediterranean zones, suggests that oceanic conditions prevailed on the northern slopes of these mountains in north-central Spain.
Analyses of pollen, non-pollen microfossils and carbonaceous particles from a valley mire in the Lozoya Valley in the Sierra de Guadarrama, which forms part of the Spanish Central System, are presented. The sedimentary sequence, which covers the last 8500 years, provides one of the oldest records in the central sector of this mountain chain. The core displays evidence of well developed Pinus sylvestris forests coupled with the presence of taxa such as Castanea or Olea in the early Holocene, highlighting the value of near-tree-line montane enclaves in the reconstruction of vegetation dynamics. The results show that the Lozoya Valley was an important refugial area for thermophilous taxa and that taxa like Olea and Castanea were present in pre-Roman times in this part of the Central System. In contrast to other areas of Spain and elsewhere in Europe where Quercus replaces Pinus in the early Holocene, evidence is presented of a natural pine belt in the Iberian continental montane system throughout the Holocene. The first signs of human impact are recorded in the pollen record at about 3740 BP, but major deforestation of the montane forests belts in the Sierra de Guadarrama is not visible until c. 1000 BP. This date is similar to dates for maximum human pressure in other Iberian environments and appears to be synchronous with a flourishing socioculture in Spain
In this article a stationary model for the calculation of residual flow and mixing of water in a ria, on the basis of contribution of fresh water and salinity as a tracer, is presented. The model is applied to the ria of Vigo, whose circulation is similar to that of a partially stratified estuary. This ria is divided into five boxes and a system of 20 equations is proposed whose solutions are the residual outflows and inflows, and the rise and mixing fluxes, which occur in the ria. In the winter the velocities of the residual currents are from 4 to 8 cm s-1, and the exit of fresh water is high for the northern mouth of the ria. The flows diminish and the mixing of water increases in the ria (2 3 m day-1 in box 2) as the contribution of fresh water decreases in the spring and summer. The presence of northerly winds increases the residual circulation threefold in the summer, there being an out-flow of 106 kg s-1 to the ocean. However, southerly winds retain the water in the ria and the proposed model can only be applied to the ria's inner and middle sections.
In this study we compare seasonal pollen and spore assemblages in river waters from the Mississippi River at Vicksburg, Mississippi to those downstream at Belle Chasse, Louisiana and in a distributary, the Atchafalaya River at Morgan City, Louisiana. Assemblages of pollen in waters at Vicksburg and Belle Chasse are similar to each other, but distinctively different from those in the Atchafalaya River. Local pollen inputs are more important in the anastomosing Atchafalaya River channel, as compared to the meandering main stem Mississippi channel which discharges through the bird-foot delta. Riverine pollen and spore assemblages are also compared to those of surface sediments from the Louisiana continental shelf in the vicinity of the Mississippi River plume. In this area the primary source of marine pollen and spore assemblages appears to be the discharge from the main stem Mississippi, with limited input from the Atchafalaya. Thus, pollen deposited in these coastal waters provides a record of vegetation in the Mississippi drainage basin, rather than local coastal areas. Pollen assemblages on the continental shelf vary with distance from the river source, but not in a systematic manner. The pattern is explained by biological controls on fine-particle deposition in marine waters, i.e., deposition of pollen in copepod fecal pellets. As copepod grazing is dependent upon phytoplankton production, pollen deposition from the river plume will be limited by high turbidities proximal to the river mouth. We hypothesize that in neritic environments, pollen is preferentially deposited in areas corresponding to high phytoplankton production, which are characterized by reduced turbidity and high nutrient availability.
We describe new reconstructions of northern extratropical summer
temperatures for nine subcontinental-scale regions and a composite
series representing quasi "Northern Hemisphere" temperature change over
the last 600 years. These series are based on tree ring density data
that have been processed using a novel statistical technique (age band
decomposition) designed to preserve greater long-timescale variability
than in previous analyses. We provide time-dependent and
timescale-dependent uncertainty estimates for all of the
reconstructions. The new regional estimates are generally cooler in
almost all precalibration periods, compared to estimates obtained using
earlier processing methods, particularly during the 17th century. One
exception is the reconstruction for northern Siberia, where 15th century
summers are now estimated to be warmer than those observed in the 20th
century. In producing a new Northern Hemisphere series we demonstrate
the sensitivity of the results to the methodology used once the number
of regions with data, and the reliability of each regional series,
begins to decrease. We compare our new hemisphere series to other
published large-regional temperature histories, most of which lie within
the 1σ confidence band of our estimates over most of the last 600
years. The 20th century is clearly shown by all of the palaeoseries
composites to be the warmest during this period.
SUMMARY - The period of pollination of Quercus in Extremadura was analyzed over four years, monitoring atmospheric pollen levels. There were clear interannual differences in both recorded concentrations and phenology. Significant correlations were found with temperatures between January and May, rainfall from February to April, and the date of the last frost, which would explain the aforementioned differences.
We analyse the series of the Wolf sunspot number in the frequency domain to determine the dimension of the solar cycle system by using the properties of its strange attractor and to study the stability in time of this dimensionality and of the main quasi-periodicities. The two classical methods of time series analysis, Fourier harmonic and Blackman-Tukey spectral analysis, have been applied first to the series of the annual Wolf sunspot numbers to determine its overall character. To detect stationarity, periodic regression based upon the three most statistically significant quasi-periods and especially a moving form the maximum entropy spectrum analysis (MESA) have been used. Both analyses show a splitting of the 11-year cycle before 1800, when a ± 55-year cycle is dominant, and a single 11-year and ± 100-year peak after 1800. Moreover, these quasi-periods are very sensitive to the time interval over which the analysis is carried out. The reason is that the sunspot numbers constitute a widely non-stationary process, which therefore implies that Fourier techniques are not useful to predict solar activity and must be used as fitting procedure only. The minimum cross-entropy method serves to improve the maximum entropy spectrum. With a good a priori estimate and data containing a low noise level, this method allows the detection of very close peaks and the refinement of the main frequencies; it does not split nor introduce artificial peaks. The Thomson model was also applied for its superior bias control, its excellent leakage resistance and a better statistical information. The same methods were then used to study the 22-year magnetic cycle, which is formed by taking into account the change in polarity of the succeeding 11-year cycle. The moving form of MESA confirms the 22-year cycle to be highly stable in contrast to the instability in the period of the 11-year sunspot series. This suggests the importance of working with the more invariant 22-year magnetic series to explain the complex, non-stationary behaviour of the sunspot series and of the solar-terrestrial interactions. Finally, we tried to see if the system generated by the sunspot data was allowing the existence of an attractor and tried to determine the minimum number of variables necessary to describe this system. It is shown that the dimension of the attractor is highly unstable varying from 2.21 to 4.95 in a quasi-cyclic way.
Isotopic and pollen analyses of an eastern Atlantic core permit the first direct correlation of substages 5e and 5c of the marine climatostratigraphical system with the Eemian and St Germain I, respectively, of the classical Grande Pile pollen sequence (north-east France). The vegetational sequences during the warm intervals of the last interglacial complex (125,000-75,000 yr BP) indicate that climatic deterioration occurred late on the mid-European continent after the initiation of glaciation over continental masses in high latitudes.
Historic documentation containing a record of rogation ceremonies carried out in response to environ mental factors allows an initial assessment of the pluviometric regime in the Iberian Peninsula during the late Maunder Minimum, climatically one of the most interesting periods of the 'Little Ice Age'. The data indicate an increase in precipitation with regional variation in its intensity related to the more frequent passage of low- pressure systems over the peninsula.
The equivalent spectral analysis methods of linear prediction, autoregression, and maximum entropy are reviewed. Their properties are listed and examples from speech and EEG given which illustrate the methods. The techniques of data extrapolation to improve spectral resolution and to predict the data beyond the range of observation are mentioned.
This book includes discussion of the following topics: man's awareness of climatic changes; evidence of past weather and climate; climate and the long history of the earth; climatic in historical times; man-made climate changes; and, approaches to the problem of forecasting.
This paper is based upon palynological data from Carihuela Cave (Granada, southeastern Spain), that support the presence of walnut (Juglans regia L.) in the western Mediterranean during the early and middle last-glacial stage. Pollen records of Juglans L. are closely associated with Mediterranean evergreen assemblages. particularly Quercus L., Oleaceae and other thermophilous taxa. Palaeo-climatic reconstruction, supported by sedimentological and palaeontological information, points to a further relationship between Juglans appearances and climatic improvements. Growth in refuges close to the site is proposed, perhaps in intramontane river valleys of the Betic ranges. Finally, the possibility of early diversification in the western Mediterranean is evaluated taking into account both the classical viewpoint about its allegedly first arrival during Roman times. and other palynological data suggesting a native character for walnut within the area. Some problems are discussed concerning the poorly understood relationship between cultivated and wild relatives.
The focus of this paper is the conversion of radiocarbon ages to calibrated (cal) ages for the interval 24,000–0 cal BP (Before Present, 0 cal BP = AD 1950), based upon a sample set of dendrochronologically dated tree rings, uranium-thorium dated corals, and varve-counted marine sediment. The 14 C age–cal age information, produced by many laboratories, is converted to Δ 14 C profiles and calibration curves, for the atmosphere as well as the oceans. We discuss offsets in measured l4 C ages and the errors therein, regional 14 C age differences, tree–coral 14 C age comparisons and the time dependence of marine reservoir ages, and evaluate decadal vs . single-year 14 C results. Changes in oceanic deepwater circulation, especially for the 16,000–11,000 cal BP interval, are reflected in the Δ 14 C values of INTCAL98.
Annual pollen influx has been monitored in short transects across the altitudinal tree limit in four areas of the Swiss Alps with the use of modified Tauber traps placed at the ground surface. The study areas are Grindelwald (8 traps), Aletsch (8 traps), Simplon (5 traps), and Zermatt (5 traps). The vegetation around the traps is described. The results obtained are: (1) Peak years of pollen influx (one or two in seven years) follow years of high average air temperatures during June-November of the previous year for Larix and Picea, and less clearly for Pinus non-cembra, but not at all for Pinus cembra and Alnus viridis. (2) At the upper forest limit, the regional pollen influx of trees (trees absent within 100 m of the pollen trap) relates well to the average basal area of the same taxon within 10-15 km of the study areas for Pinus cembra, Larix, and Betula, but not for Picea, Pinus non-cembra, and Alnus viridis. (3) The example of Zermatt shows that pollen influx characterises the upper forest limit, if the latter is more or less intact. (4) Presence/absence of Picea, Pinus cembra, Larix, Pinus non-cembra, and Alnus viridis trees within 50-100 m of the traps is apparent in the pollen influx in peak years of pollen influx but not in other years, suggesting that forest-limit trees produce significant amounts of pollen only in some years. (5) Pollen influx averaged over the study period correlates well with the abundance of plants around the pollen traps for conifer trees (but not deciduous trees), Calluna, Gramineae, and Cyperaceae, and less clearly so Compositae Subfam. Cichorioideae and Potentilla-type. (6) Influx of extra-regional pollen derived from south of the Alps is highest in Simplon, which is open to southerly winds, slightly lower in Aletsch lying just north of Simplon, and lowest in Zermatt sheltered from the south by high mountains and Grindelwald lying north of the central Alps.
The focus of this paper is the conversion of radiocarbon ages to calibrated (cal) ages for the interval 24,000-0 cal BP (Before Present, 0 cal BP = AD 1950), based upon a sample set of dendrochronologically dated tree rings, uranium-thorium dated corals, and varve-counted marine sediment. The 14C age-cal age information, produced by many laboratories, is converted to Δ14C profiles and calibration curves, for the atmosphere as well as the oceans. We discuss offsets in measured 14C ages and the errors therein, regional 14C age differences, tree-coral 14C age comparisons and the time dependence of marine reservoir ages, and evaluate decadal vs. single-year 14C results. Changes in oceanic deepwater circulation, especially for the 16,000-11,000 cal BP interval, are reflected in the Δ14C values of INTCAL98.