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© Nature Publishing Group1981
© Nature Publishing Group1981
Glacial and interglacial wind regimes over the Eastern subtropical Atlantic and North-West Africa.
Abstract
Analysis was made of aeolo-marine dust deposits in the subtropical eastern Atlantic in order to determine the mechanisms of climatic change affecting the late Quaternary and present Saharan arid belt. Grain-size data were obtained from deep-sea samples using two approaches. The strengths of the major wind patterns that existed during the late Quaternary were quantified. The climatic changes were found to be related to the varying strength of the tropical disturbances and the varying supply of water vapour from the equatorial Atlantic. Mechanisms controlling the climate in North-west Africa during the present phase of the interglacial, were found to be more closely related to that of the last glacial than to that of the Holocene climatic optimum. (H.C.B.)
... Per analogy to Sarnthein et al. (1981) we have somewhat simplified our routine search for an excess portion of clay by means of EM analysis to process routinely the grain size spectra of a large number of sediment samples (Figs. 2 and 3). EM modeling algorithms extract pertinent information from grain-size distribution datasets such as provenance, transport and sedimentation processes subsequently to be used to reconstruct past climate variability (Prins and Weltje, 1999;Prins et al., 2002;Van Hateren et al., 2018). ...
... End-member analysis forms the backbone of our study to distinguish fluvial and eolian portions in the terrigenous sediment fraction at ODP Site 1144 (Figs. 2 and 4). On the one hand, fine-silt EM1 (modal size of 6 μm; Fig. 4c) presents dominant clay and fine silt characteristic of flu- vial input (Sarnthein et al., 1981), a tracer of monsoon precipitation during summer (Fig. 1d). This conclusion is corroborated by results from mapping different siliciclastic grain size fractions over the South China Sea (Fig. 3; Wang et al., 1999). ...
... On the other hand, EM 2 of coarse silt (modal size of 24 μm; Fig. 4c) reflects eolian dust deposits, consistent with the modal size of Chinese loess (Sun et al., 2004;Kang et al., 2020;Liu et al., 2020), in the South China Sea mainly advected by northeasterly monsoon winds during winter. Also, this grain size mode comes close to that of wind-blown dust in East Atlantic sediments close to the Sahara Desert (Sarnthein et al., 1981). EM analysis-based spectra of silt grain size for ODP Site 1144 are compared to those of neighbor ODP Site 1146, where we traced similar endmembers of 5 μm for riverine sediments and of 22 μm for eolian dust based on grain size data of Boulay et al. (2007) (Fig. 4). ...
Glacial-to-interglacial variations in East Asian summer and winter monsoon are widely ascribed to orbital and/or global ice-sheet forcing. However, the relative impact of orbital and millennial-scale factors on Pleistocene variations in East Asian monsoon still remains controversial. To better constrain the differential response of seasonal monsoon winds over the last million years we present paired records of siliciclastic silt grain sizes, pollen, minerals, and geochemical tracers obtained from high-sedimentation rate deposits at ODP Sites 1144 and 1146 in the northern South China Sea. The proxy records show that loess-style eolian dust supply of winter monsoon was dominant and fluvial input reduced during peak glacials over the last 900 kyr, moreover, during Heinrich stadials, while abundant fluvial mud marked interglacial regimes as result of enhanced summer monsoon, then completely overlying the weakened dust input of winter monsoon. Likewise, an excess of fluvial mud suppressed the eolian dust signal during the initial part of most glacial stages during and after the Mid-Pleistocene Transition (MPT), in part possibly induced by long-term groundwater reserves and/or unknown climate forcings linked to the southern Hemisphere. Prior to the MPT, during glacial stages 24–32, prolonged groundwater reserves and/or a more limited extent of northern-Hemisphere ice sheets, or unknown southern Hemisphere forcing may have controlled an ongoing interglacial-style humid monsoon climate in East Asia. In summary, our findings suggest that the sediment record of seasonal East Asian monsoon variability in part may have been more sensitive to secondary factors of groundwater storage, plant cover, as well as to the redistribution of insolation energy amongst various climate subsystems than to direct orbital and/or northern ice-sheet forcing.
... The Sahara and Sahel regions of Africa are thought to be the most important sources of LRT dust in the world today (Prospero et al., 2002;Goudie and Middleton, 2006;Mahowald et al., 2006;Kohfeld and Tegen, 2007). One important dust pathway from these source regions is the northeasterly trade wind belt (Fig. 1a), which occurs at low altitudes year-round (Pye, 1987;Sarnthein et al., 1981;Stein and Sarnthein, 1984;Stuut et al., 2005). Along this trajectory, dust from the westernmost Sahara is transported to the eastern Atlantic Ocean off the coast of northwestern Africa. ...
... Near Africa, the SAL reaches altitudes as high as 5e7 km, above the trade wind zone. Sarnthein et al. (1981), Stein and Sarnthein (1984), Tetzlaff and Peters (1986), and Pye (1987) point out that although the main direction of dust transport in the SAL is to the west at latitudes between~15 N and~21 N, south of the Canary Islands (Fig. 1b), a south-to-north component of flow can occur in the lee of an easterly wave. Thus, a "hook-like" trajectory of dust movement from the Sahel to the vicinity of the Canary Islands via the SAL is observed (Figs. ...
... 1a and 2). Evidence presented by Sarnthein et al. (1981) and Grousset et al. (1998) indicates that both the trade winds and the SAL were situated approximately where they are now during the last glacial maximum,~20,000 yr B.P., but dust fluxes may have been greater. In more recent studies, McGee et al. (2013) and Dust-bearing wind paths generalized from Dubief (1979), Kalu (1979), Sarnthein et al. (1981), McTainsh and Walker (1982), Stein and Sarnthein (1984), Tetzlaff and Peters (1986), Pye (1987), Stuut et al. (2005), and Schwanghart and Schütt (2008). ...
Africa is the most important source of dust in the world today and dust storms from that continent frequently deposit sediment on the nearby Canary Islands. Many investigators have inferred African dust inputs to Canary Islands paleosols based only on the presence of quartz. However, some local rocks do contain this mineral, so quartz alone is insufficient proof of dust deposition. Further, it is not known whether the Sahara Desert or the Sahel region is more important as a dust source. We address these issues by study of sequences of Pleistocene aeolian sands on the islands of Lanzarote and Fuerteventura. Aeolian sands are composed mostly of marine carbonate minerals and locally derived volcanic minerals. They date from the early-middle Pleistocene to the Holocene. Trace element geochemistry shows that the soils formed from both locally derived basalt and African dust. Major element geochemistry and clay mineralogy indicate that dust additions to the Canary Islands likely come from both the Sahara and Sahel. Dust delivered from the Sahel indicates that droughts in that region have had a history extending through much of the Quaternary. Accretionary-inflationary profile development, from dust accretion, is evident in the upward growth of Canary Islands paleosols.
... The NSAS is composed of two major hydrological units: the sandstone-dominated Nubian aquifer system (NAS) and the overlying carbonate-dominated post-Nubian aquifer system (PNAS; (M Bakhbakhi, 2006). The NSAS was largely recharged during previous pluvial periods in the Quaternary by intensification of paleomonsoons (Prell and Kutzbach, 1987;Sarnthein et al., 1981;Yan and Petit-Maire, 1994) or paleowesterlies (Abouelmagd et al., 2014;Sturchio et al., 2004;Sultan et al., 1997). At present, the aquifer is receiving modest local recharge in the 9 southern highlands (e.g., Gebel Darfur in Sudan and Gebel Tibesti in Chad; Fig. 1) where the Nubian Sandstone crops out and where precipitation reaches up to 96 mm/yr. ...
... The NSAS is believed to have been largely recharged in previous wet climatic periods by intensification of monsoons (Prell and Kutzbach, 1987;Sarnthein et al., 1981;Yan and Petit-Maire, 1994) or paleowesterlies Abouelmagd et al., 2014;Sturchio et al., 2004;Sultan et al., 1997), yet it is still receiving modern recharge locally over the Nubian Sandstone outcrops at the foothills of mountains that are receiving high (> 96 mm/yr) precipitation . Examples of such areas include the Nuba and Darfur mountains (southern Sudan, North Sudan Platform), the Tibesti and Sherif mountains (eastern Chad, southern Kufra subbasin). ...
https://scholarworks.wmich.edu/dissertations/3668
... Egyptian J. Desert Res., 73, No. 2, 629-653 (2023) was replenished thousands to millions of years ago by an intensification of paleomonsoons (Sarnthein et al., 1981;Prell and Kutzbach, 1987;Yan andPetit-Maire 1994 andMohamed et al., 2022). Therefore, monitoring groundwater quality and level fluctuation is crucial to assessing the sustainability of fossil nonrenewable groundwater as a sole public water supply source. ...
... This temporal interval may be analogously juxtaposed with global climatic events beyond the geographical boundaries of India. Specifically, during the LGM, the climatic conditions prevailing in India and the broader intertropical regions were characterized by a state of cold, dry, and windy, as documented by various studies (Williams, 1975(Williams, , 1985(Williams, , 2006Prell et al., 1980;Cullen, 1981;Sarnthein et al., 1981;Duplessy, 1982;Kutzbach, 1987;Hoelzmann et al., 2004). Insights from Prell et al. (1980) research suggest that the period known as Marine Isotope Stage 1 (MIS-1) was marked by warmth and increased moisture content from ~14 ka to the present, coinciding with a global increase in moisture availability and a strengthening of the Indian summer monsoon (ISM), as depicted in Fig. 7. MIS-3 through MIS-1 are included Field photograph at Belan Baraudha section, the river bed rocks exposed, at Ayodhya section, the alluvial cliff developed along the left bank of Belan River. ...
The Marginal Gangetic Plain is the southernmost segment of the Ganga Plain, formed by Himalayan Orogen thrust fold stress flexing the Indian lithosphere. Rivers originating in the Himalayas have received much attention (i.e., Ganga, Yamuna, Kosi, Ghagra, etc.). In contrast, the tributaries draining from the peripheral bulge of the foreland basin have not been studied in detail, although it bears signatures of seismic activity in the basement of the craton. The Belan River, a tributary of the Tons River and sub-tributary of the Ganga River, drains through the Marginal Gangetic Plain. Various tectonic-induced geomorphic signatures have been identified using Landsat Images, such as fluvial incision, river shifting, gorges channel formation, etc., in the Belan River Basin. Geomorphic indices of active tectonics (asymmetry factor, SL index, basin elongation ratio, and long profile), drainage pattern, and lineament study have been performed for the Belan River Basin. These parameters indicate slope adjustment due to the uplift and subsidence of the parts of the basin area. The most recent and extensive valley fills started accumulating at ∼51 ± 7 ka and persisted until around ∼22 ± 2 ka. The aggradation was accompanied by a weakening summer monsoon, followed by incision after 22 ± 2 ka, indicating a return to warmer and wetter conditions and a stronger summer monsoon after the Last Glacial Maximum (LGM). Tectonic exhumation in the southern and south-eastern parts of the Belan River Basin revealed by geomorphic indices. These findings indicate that the drainage networks of the Belan River Basin were built over a tectonically controlled valley and that denudational processes have been transforming the basin for a considerable period.
... Moreover, the polymodality also suggests that the sediments were not well mixed in the suspension. Multivariate approaches to distinguish the subpopulations of GSDs include, among others, cluster analysis (CA) and principal component analysis (PCA) (Sarnthein et al., 1981;East, 1985East, , 1987. However, the application of cluster analysis on GSDs focused on provenance studies and stratigraphic analysis. ...
Grain size distribution is one of the paleoenvironmental proxies that provide insight statistical distribution of size fractions within the sediments. Multivariate statistics have been used to investigate the depositional process from the grain size distribution. Still, the direct application of the standard multivariate methods is not straightforward and can yield misleading interpretations due to the compositional nature of the raw grain size data. This paper is a methodological framework for grain size data characterization through the centered log ratio transformation and euclidean data, coupled with principal component analysis, cluster analysis, and linear discriminant analysis to examine Quaternary sediments from Tövises bed in the southeast Great Hungarian Plain. These approaches provide statistically significant and sedimentologically interpretable results for both datasets. However, the details by which they supplemented the conceptual model were significantly different, and this discrepancy resulted in a different temporal model of the depositional history.
... Beyond terrestrial traps (loess, ice, soils), 'subaquatic' dust (Stuut, 2014) is preserved in marine and lacustrine sediments. Dust has been recovered from Cenozoic marine sediments from regions sufficiently remote that the transport medium must have been eolian (e.g., Sarnthein et al., 1981;Hovan et al., 1989;Rea, 1994;deMenocal et al., 2000;Stuut et al., 2002). Such truly oceanic archives from remote regions are scarce for the pre-Cretaceous deep-time record, owing to the young age of ocean crust, excepting rare examples of obducted assemblages in ophiolite complexes (e.g., Japan Akiyoshi; Patterson et al., 2011). ...
Atmospheric dust constitutes particles <100 μm, or deposits thereof (continental or marine); dust includes ‘loess,’ defined as continental aeolian silt (4–62.5 μm). Dust is well-known from Earth's near-time (mostly Quaternary) record, and recognized as a high-fidelity archive of climate, but remains under-recognized for deep time. Attributes such as thickness, grain size, magnetism, pedogenesis, and provenance of dust form valuable indicators of paleoclimate to constrain models of atmospheric dustiness. Additionally, dust acts as an agent of climate change via both direct and indirect effects on radiative forcing, and on productivity, and thus the biosphere and carbon cycling. Dust from the late Paleozoic of western equatorial Pangea reflects ultimate derivation from orogens (ancestral Rocky Mountains, Central Pangean Mountains), whereas dust from southwestern Pangea (Bolivia) reflects both proximal volcanism and crustal material. Records of dust conducive to cyclostratigraphic analysis, such as data on dust inputs from carbonate sections, or magnetism in paleo-loess, reveal dust cyclicity at Milankovitch timescales, but resolution is compromised if records are too brief, or irregular in interval or magnitude of the attribute being measured. Climate modeling enables identification of the primary regions of dust sourcing in deep time, and impacts of dust on radiative balance and biogeochemistry. Deep-time modeling remains preliminary, but is achievable, and indicates principal dust sources in the Pangean subtropics, with sources increasing during colder climates. Carbon cycle modeling suggests that glacial-phase dust increases stimulated extreme productivity, potentially increasing algal activity and perturbing ecosystem compositions of the late Paleozoic.
In this contribution we report the first systematic study of zircon U-Pb geochronology and δ18O-εHf(t) isotope geochemistry from ten islands of the hot-spot related Galapagos Archipelago. The data extracted from the zircons allow them to be grouped into three types: 1) young zircons (0 – ~4 Ma) with εHf(t) (~5 – 13) and δ18O (~4 – 7) isotopic mantle signature with crystallization ages dating the islands, 2) zircons with εHf(t) (~5 – 13) and δ18O (~5 – 7) isotopic mantle signature (~4 to 164 Ma) which are interpreted to date the time of plume activity below the islands (~164 Ma is the minimum time of impingement of the plume below the lithosphere), and 3) very old zircons (~213 to 3000 Ma) with mostly continental (but also juvenile) εHf(t) (~ -28 – 8) and δ18O (~5 – 11) isotopic values documenting potential contamination from a number of sources. The first two types with similar isotopic mantle signature define what we call the Galápagos Plume Array (GPA). Given lithospheric plate motion, this result implies that GPA zircon predating the Galápagos lithosphere (i.e., >14 – 164 Ma) formed and were stored at sublithospheric depths for extended periods of time. In order to explain these observations, we performed 2D and 3D thermo-mechanical numerical experiments of plume-lithosphere interaction which show that dynamic plume activity gives rise to complex asthenospheric flow patterns and results in distinct long-lasting mantle domains beneath a moving lithosphere. This demonstrates that it is physically plausible that old plume-derived zircons survive at asthenospheric depths below ocean islands.
Savanna ecosystems were the landscapes for human evolution and are vital to modern Sub-Saharan African food security, yet the fundamental drivers of climate and ecology in these ecosystems remain unclear. Here we generate plant-wax isotope and dust flux records to explore the mechanistic drivers of the Northwest African monsoon, and to assess ecosystem responses to changes in monsoon rainfall and atmospheric pCO 2. We show that monsoon rainfall is controlled by low-latitude insolation gradients and that while increases in precipitation are associated with expansion of grasslands into desert landscapes, changes in pCO 2 predominantly drive the C 3 /C 4 composition of savanna ecosystems.
Reconstructions of aeolian dust flux to West African margin sediments can be used to explore changing atmospheric circulation and hydroclimate over North Africa on millennial to orbital timescales. Here, we extend West African margin dust flux records back to 37 ka in a transect of sites from 19° to 27°N, and back to 67 ka at Ocean Drilling Program (ODP) Hole 658C, in order to explore the interplay of orbital and high‐latitude forcings on North African climate and make quantitative estimates of dust flux during the core of the Last Glacial Maximum (LGM). The ODP 658C record shows a Green Sahara interval from 60 to 50 ka during a time of high Northern Hemisphere summer insolation, with dust fluxes similar to levels during the early Holocene African Humid Period, and an abrupt peak in flux during Heinrich event 5a (H5a). Dust fluxes increase from 50 to 35 ka while the high‐latitude Northern Hemisphere cools, with peaks in dust flux associated with North Atlantic cool events. From 35 ka through the LGM dust deposition decreases in all cores, and little response is observed to low‐latitude insolation changes. Dust fluxes at sites from 21° to 27°N were near late Holocene levels during the LGM time slice, suggesting a more muted LGM response than observed from mid‐latitude dust sources. Records along the northwest African margin suggest important differences in wind responses during different stadials, with maximum dust flux anomalies centered south of 20°N during H1 and north of 20°N during the Younger Dryas.
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