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The anthropogenically forced expansion of coastal hypoxia is a
major environmental problem affecting coastal ecosystems and biogeochemical
cycles throughout the world. The Baltic Sea is a semi-enclosed shelf sea
whose central deep basins have been highly prone to deoxygenation during its
Holocene history, as shown previously by numerous paleoenviro...
Contexts in source publication
Context 1
... despite the contrasting bot- tom water oxygenation between adjacent sub-basins in the area ( Virtasalo et al., 2005), the long-term trends in envi- ronmental conditions are largely congruent over the entire Archipelago Sea, excluding areas close to prominent nutri- ent point sources (Suomela, 2011). Two replicate sediment cores (HAV-KU-5 and HAV-KU- 6) were retrieved using a 5 m long piston corer onboard R/V Aurelia of the Archipelago Research Institute in June 2015 (Table 1). The coring device was adjusted to start the core retrieval with the piston positioned 1-2 decimeters above the sediment-water interface, in order to capture the sediment surface as intact as possible. ...
Context 2
... to disturbance of the uppermost sediments in the reference half of HAV-KU-6 during split- ting of the core, the subsampling for X-radiography for the topmost 170 cm was done for the replicate core HAV-KU- 5. For the bottom part, the subsampling was conducted for HAV-KU-6 due to the longer core retrieval (Table 1). The cores were correlated visually based on the occurrence of the laminated intervals and the boundaries of the lithological units described below. ...
Citations
... However, only short-term (usually <50 years) and temporally discontinuous monitoring data exist, thus our understanding of hypoxia events in estuaries is biased toward intervals with heavy anthropogenic influences. Limitations in the duration of observational data, therefore, make it challenging to identify whether current episodes of hypoxia are more severe or frequent than those that occurred prior to human disturbances 14 . This also leads to difficulties in discerning the role of climate variability in driving hypoxia, even though climate is potentially a key vector for developing hypoxia in estuaries 10,15,16 . ...
Many large estuaries are threatened by intensifying hypoxia. However, due to the limited duration of available observations, uncertainties persist regarding the level of contemporary hypoxia intensity in a longer-term context and the relative contributions of climate versus human factors. Here we present sediment records for the hypoxia intensity and associated environmental parameters in the Yangtze Estuary over the past three centuries. The results show that the hypoxia intensity has been increasing during the last half century due to anthropogenic eutrophication, but the current hypoxia condition is not as severe as some preindustrial periods due to weaker stratification in the water column. Our findings suggest that if anthropogenic and climatic forcing coincide in the foreseeable future, the hypoxia intensity of the Yangtze Estuary may reach unprecedented levels.
... Five different oxygen regimes were used to simulate various conditions that mussels may encounter in their natural habitat, including normoxia (~90-100% of air saturation), short-term hypoxia (1 day at ~0.1% of air saturation), long-term hypoxia (7 days at ~0.1% of air saturation), short-term reoxygenation (1 h of normoxia following 7 days of hypoxia), and long-term reoxygenation (24 h of normoxia following 7 days of hypoxia). Short-term and long-term hypoxia conditions were selected to represent possible scenarios that mussels may encounter in eutrophicated estuaries and coastal dead areas during seasonal hypoxia (Conley et al., 2011;Diaz and Rosenberg, 2008;Fennel and Testa, 2019;Jokinen et al., 2018), and are consistent with methodologies employed in previous studies (Haider et al., 2020). The recovery durations were chosen because the molecular and cellular stress responses associated with reoxygenation typically occur within minutes to hours after the return of oxygen (Andrienko et al., 2017;Bundgaard et al., 2019;Ivanina and Sokolova, 2016;Sokolova et al., 2019). ...
... The Småholmen station (60.24° N, 22.04° E) close to Haverö in the Archipelago Sea is 20 m deep and has been seasonally anoxic or hypoxic at the seafloor for at least seven decades 65 . The low oxygen conditions and lack of bioturbation have resulted in the formation of laminated sediment at this site. ...
Studies in laboratory-based experimental evolution have demonstrated that phytoplankton species can rapidly adapt to higher temperatures. However, adaptation processes and their pace remain largely unknown under natural conditions. Here, by comparing resurrected Skeletonema marinoi strains from the Baltic Sea during the past 60 years, we show that modern S. marinoi have increased their temperature optima by 1 °C. With the increasing ability to grow in higher temperatures, growth rates in cold water decreased. Modern S. marinoi modified their valve:girdle ratio under warmer temperatures, which probably increases nutrient uptake ability. This was supported by the upregulation of several genes related to nitrate metabolism in modern strains grown under high temperatures. Our approach using resurrected strains demonstrates the adaptation potential of naturally occurring marine diatoms to increasing temperatures as global warming proceeds and exemplifies a realistic pace of evolution, which is an order of magnitude slower than estimated by experimental evolution.
... Nowadays, the Baltic Sea comprises areas with high degrees of eutrophication (Murray et al., 2019) that expand the natural hypoxic and anoxic bottoms conditions in its central part, i.e., the Baltic Proper (Carstensen et al., 2014;Conley et al., 2011). The initiation of coastal hypoxia in the 20th century was an unprecedented event in the latest 1500 years (Jokinen et al., 2018) and the volume of the central Baltic Sea with hypoxic conditions increased tenfold since the early 1900s and from 15% to 26% since 1960 (Hansson et al., 2018). This trend, which is widely recognized to be linked to eutrophication (Carstensen et al., 2014), will be amplified with global warming (Kabel et al., 2012), and will extend the present-day area of accumulation of organicrich sediments mapped in the deep Baltic Sea Zillen et al., 2008). ...
... Previous works reported similar high TOC values in the Baltic Proper (ca. 10 wt%) Zillen et al., 2008;Struck et al., 2000;Leipe et al., 2011) and radiometric dating revealed that these sediments were deposited during the modern warm period of the Baltic Proper (latest 100 years) . Their age and occurrence in areas showing present-day hypoxia or anoxia, and deoxygenation trends of the water column since early 1900s (Carstensen et al., 2014), indicate that these organic-rich sediments are a result of the modern warm period amplified by the historical eutrophication during the past 120 years, and the consequent increased primary productivity (notably marine-derived, phytoplankton) (Jokinen et al., 2018;Struck et al., 2000) and poor degradation of organic matter in the oxygen-depleted water column (Zillen et al., 2008;Jokinen et al., 2018;Jonsson and Carman, 1994). Homogeneous, light brown and grey mud deposits (i.e., post-glacial clay; av. ...
... Previous works reported similar high TOC values in the Baltic Proper (ca. 10 wt%) Zillen et al., 2008;Struck et al., 2000;Leipe et al., 2011) and radiometric dating revealed that these sediments were deposited during the modern warm period of the Baltic Proper (latest 100 years) . Their age and occurrence in areas showing present-day hypoxia or anoxia, and deoxygenation trends of the water column since early 1900s (Carstensen et al., 2014), indicate that these organic-rich sediments are a result of the modern warm period amplified by the historical eutrophication during the past 120 years, and the consequent increased primary productivity (notably marine-derived, phytoplankton) (Jokinen et al., 2018;Struck et al., 2000) and poor degradation of organic matter in the oxygen-depleted water column (Zillen et al., 2008;Jokinen et al., 2018;Jonsson and Carman, 1994). Homogeneous, light brown and grey mud deposits (i.e., post-glacial clay; av. ...
... Studies of Zilleń et al. (2008) and Zillen and Conley (2010) proposed that the growth of the surrounding population and their agriculture during the MCA may have increased the nutrient loads and, thereby, the hypoxic area. However, these conclusions are challenged by empirical studies finding no evidence that hypoxia in the open Baltic Sea during the Medieval Climate Anomaly was caused by human activities on land (Jokinen et al., 2018;Ning et al., 2018;Norbäck Ivarsson et al., 2019;van Helmond et al., 2020). In addition, other modeling studies such as Kabel et al. (2012) argued for a temperature-dependent hypoxia response during the MCA. ...
Over the last 1,000 years, changing climate strongly influenced the ecosystem of coastal oceans such as the Baltic Sea. Sedimentary records revealed that changing temperatures could be linked to changing oxygen levels, spreading anoxic, oxygen-free areas in the Baltic Sea. However, the attribution of changing oxygen levels remains to be challenging. This work simulates a preindustrial period of 850 years, covering the Medieval Climate Anomaly (MCA) and the Little Ice Age using a coupled physical-biogeochemical model. We conduct a set of sensitivity studies that allow us to disentangle the contributions of different biogeochemical processes to increasing hypoxia during the last millennium. We find that the temperature-dependent mineralization rate is a key process contributing to hypoxia formation during the MCA. Faster mineralization enhances the vertical phosphorus flux leading to higher primary production. Our results question the hypothesis that increased cyanobacteria blooms are the reason for increased hypoxia in the Baltic Sea during the MCA. Moreover, the strong contribution of the mineralization rate suggests that the role of temperature-dependent mineralization in current projections should be revisited.
... The inferred bottom water oxygen depletion during the second half of the 19th century including the deoxygenation event in the mid-19th century (Fig. 4) agrees well with historical accounts of increased humaninduced environmental perturbations (Zillén et al., 2008) and changes in sedimentary archives in deeper waters of the Baltic Sea at that time (e.g., Zillén and Conley, 2010;Kabel et al., 2012;Jokinen et al., 2018). Mn/Ca shell values increased shortly after the start of the Industrial Revolution in NW Europe (around 1850), which was associated, among others, with major land-use changes (cropland expansion on deforested land), accelerating population growth and a significantly increased flux of nutrients into the Baltic Sea (Zillén et al., 2008;Andrén, 1999). ...
... However, the onset of dark laminated sediments with high organic carbon content, for instance, in cores from the Gotland Basin and the Gulf of Finland suggest large areas of the Baltic Sea were affected by severe oxygen depletion since approx. the mid-19th century (Jonsson et al., 1990;Zillén and Conley, 2010;Kabel et al., 2012;Jokinen et al., 2018). ...
The Baltic Sea serves as a model region to study processes leading to oxygen depletion. Reconstructing past low-oxygen occurrences, specifically hypoxia, is crucial to understand current ecological disturbances and developing future mitigation strategies. The history of dissolved oxygen (DO) concentration in some Baltic Sea basins has been investigated in previous studies, but temporally well-constrained, inter-annual and better resolved DO reconstructions are still scarce. Here, we present precisely dated, high-resolution DO record since the mid-19th century reconstructed from Mn/Cashell values of Arctica islandica (Bivalvia) collected in the Mecklenburg Bight. According to the data, this area experienced similar low oxygenation during the second half of the 19th century and the late 20th century, but DO variability increased: A 12-15-yr oscillation prevailed in the 19th century, but a 4-6-year period dominated in the late 20th century. Shortly after the onset of the Industrial Revolution around 1850, Mn/Cashell values increased, indicating a DO decrease, probably caused by strong anthropogenic nutrient input. More recently, phosphate levels and inflows of oxygen-rich North Sea water have been identified as major factors controlling the bottom water oxygenation. For example, the increase in DO in the mid-1990s was linked to the decrease in phosphate content and several Major Baltic Inflows. The strong Ba/Cashell rise between the 1860s and the turn of the century most likely reflects changes in diatom community structure rather than a bloom of mass phytoplankton. This is supported by largely unchanged Mn/Cashell and shell growth. Decadal and multi-decadal cycles of shell growth rate correlated strongly with the Atlantic Multidecadal Variability, likely reflecting changes in atmospheric circulation patterns, precipitation rate and riverine nutrient supply. To further improve the management and protection of ecosystems in the Baltic Sea, a larger number of such high-resolution retrospective studies covering long periods of time and large regions are needed.
... Eutrophication is often linked to climate change and present-day land-use changes (e.g., Jokinen et al., 2018;Rabalais et al., 2009); however, our work shows that historical land use may play a larger T A B L E 2 Predicted future nutrient contribution potential for Umstead State Park headwater channels resulting from the up-valley expansion of the drainage network. Results, by average soil horizon thickness and in aggregate rely on the average erosion volume, the assumption that 50% of modified fourth-order streams will migrate (90,419 AE 56,838 m 3 , calculated in Table 1), a soil bulk density of 1300 kg/m 3 (Bradley, 2020), and nutrient values from Figure 12 role than typically appreciated, in part and specifically through the reestablishment of equilibrium channel head locations. ...
European‐American settlement of the southeastern U.S. introduced agricultural practices that included extensive clearing of forested hillslopes to support food and cash‐crop agriculture. This land disturbance has long‐term effects on stream morphology by displacing channel heads down‐valley, impacting downstream sediment and nutrient supply as channel heads migrate back up‐valley towards their pre‐disturbance locations. This study investigates 40 stream channels in William B. Umstead State Park in the Piedmont of North Carolina using relationships between local slope and contributing drainage areas to predict channel head locations and compare these to their observed positions. Further, expected eroded sediment and nutrient contributions are quantified using migration distances and sampled soils near channel heads. Of the 40 investigated channel heads, 23 are located down‐valley from their predicted location by an average of 174.4 m ± 109.6 (1‐σ). Using this distance and average channel cross‐sectional area, 1.6 ± 1.4 m2 (1‐σ), the expected future erosion per channel is 282.6 ± 177.6 m3 (1‐σ). Drainage density was used to extrapolate volumes to the 23 km2 park using a conservative estimate that 50% of the first‐order channel heads will migrate up‐valley, implying an additional 90.4 ± 56.8 x 103 m3 (1‐σ) of sediment is expected to erode from the study area. Finally, scaling these volume estimates to sampled soil nutrient values indicates that approximately 1,053 ± 662 t (68% conf.) of carbon, 51 ± 32 t of total nitrogen, and 15 ± 9 t of phosphorus are anticipated to enter the fluvial system in response to channel head migration from within the confines of this state park, representing only 1% of the land area in Wake County. These findings suggest that regional water quality challenges posed by suspended sediments and nutrients will persist for hundreds to perhaps thousands of years from non‐point sources as first‐order channels continue to erode headward towards their equilibrium landscape positions.
... Since oxygen consumption at the sediment-water interface can have a large share in depth-integrated respiration (Boynton et al., 2018), separation of the near-bottom layer from the waters above may accelerate oxygen depletion in the NBL. For instance, Jokinen et al. (2018) suggested that a decrease in the water volume between the pycnocline and the seabed increased the probability of hypoxia occurrences in a shallow basin of the Archipelago Sea (Haverö). We suggest that besides the strong seasonal stratification and reduced vertical mixing, the haline stratification in the deep layer that already existed in spring was a crucial precondition for hypoxia development in 2018. ...
The Gulf of Riga is a relatively shallow bay connected to the deeper central Baltic Sea (Baltic Proper) via straits with sills. The decrease in the
near-bottom oxygen levels from spring to autumn is a common feature in the gulf, but in 2018, extensive hypoxia was observed. We analyzed
temperature, salinity, oxygen, and nutrient data collected in 2018, along with historical data available from environmental
databases. Meteorological and hydrological data from the study year were compared with their long-term means and variability. We suggest that
pronounced oxygen depletion occurred in 2018 due to a distinct development of vertical stratification. Seasonal stratification developed early and
was stronger in spring–summer 2018 than on average due to high heat flux and weak winds. Dominating northeasterly winds in early spring and summer
supported the inflow of saltier waters from the Baltic Proper that created an additional deep pycnocline restricting vertical transport between the
near-bottom layer (NBL) and the water column above. The estimated oxygen consumption rate in the NBL in spring–summer 2018 was about
1.7 mmolO2m-2h-1, which exceeded the oxygen input to the NBL due to advection and vertical mixing. Such a consumption rate leads
to near-bottom hypoxia in all years when vertical mixing in autumn reaches the seabed later than on average according to the long-term (1979–2018)
meteorological conditions. The observed increase in phosphate concentrations in the NBL in summer 2018 suggests a significant sediment phosphorus
release in hypoxic conditions counteracting the mitigation measures to combat eutrophication. Since climate change projections predict that
meteorological conditions comparable to those in 2018 will occur more frequently, extensive hypoxia would be more common in the Gulf of Riga and
other coastal basins with similar morphology and human-induced elevated input of nutrients.
... This deficit of knowledge is largely attributed to incomplete instrumental data and lack of suitable high-resolution archives. Whereas DO trends on time-scales of centuries and millennia can be reconstructed from sediment cores (Jokinen et al., 2018), annually and better resolved, temporally well-constrained archives are still scarce. Besides fish otoliths (Limburg et al., 2011) and foraminifera (Groeneveld and Filipsson, 2013), shells of the marine bivalve mollusk, Arctica islandica have recently been identified as interannually to seasonally resolved in-situ archives of oxygen deficiency with manganese-to-calcium molar ratios serving as a proxy for DO in the overlying water body (DO measured some decimeters away from the seafloor) (Schöne et al., 2021). ...
An increasing area of shallow-marine benthic habitats, specifically in the Baltic Sea, is affected by seasonal oxygen depletion. To place the current spread of oxygen deficiency into context and quantify the contribution of anthropogenic ecosystem perturbation to this development, high-resolution archives for the pre-instrumental era are needed. As recently demonstrated, shells of the bivalve mollusk, Arctica islandica fulfil this task with molar Mn/Cashell ratios as proxies for dissolved oxygen (DO) levels in the water column. Since the ocean quahog is inhomogeneously distributed in the Baltic Sea and may not be present in museum collections or found throughout sedimentary sequences, the present study evaluated whether two other common bivalves, Astarte elliptica and Astarte borealis can be used interchangeably or alternatively as proxy DO recorders. Once mathematically resampled and corrected for shell growth rate-related kinetic effects and (some) vital effects, Mn/Cashell data of all three species (age ten onward in A. islandica) were statistically significantly (p < 0.0001) linearly and inversely correlated to DO concentration in the free water column above seafloor (r = –0.66 to –0.75, corresponding to 43 to 56% explained variability). A. elliptica may provide slightly more precise DO data (1σ error of ±1.5 mL/L) than A. islandica or A. borealis ( ± 1.6 mL/L), but has a shorter lifespan. Both Astarte species show a stronger correlation with DO than A. islandica, because their biomineralization seems to be less severely hampered by oxygen and salinity stress. In turn, A. islandica grows faster resulting in less time-averaged data. During youth, the ocean quahog typically incorporates a disproportionately large amount of manganese into its shell, possibly because food intake occurs directly at the sediment-water interface where Mn-rich porewater diffuses out of the sediment. With increasing age, however, A. islandica seems to generate a gradually stronger inhaling water current and takes in a larger proportion of water farther away from the fluffy layer. As demonstrated here, all three studied species can be used as DO archives, though species-specific limitations should be kept in mind.
... In Finland, the soil materials that form AS soils have a sedimentary origin, and consist of mineral and organic soil materials that contain sulfide minerals. Although nowadays the sulfidization continues in the sediments of the current Baltic Sea (Jokinen et al., 2018;Jokinen et al., 2020), most of the sulfidic sediments were formed in the preceding Littorina Sea (Fig. 1) (Palko, 1994;Yli-Halla et al., 1999;Kivinen, 1950;Purokoski, 1959;Erviö, 1975;Puustinen et al., 1994). After the glaciation, the isostatic land uplift has led to these sediments emerging above the current sea level. ...
Acid sulfate soils are one of the most environmentally harmful soils existing in nature. This is because they produce sulfuric acid and release metals, which may cause several ecological damages. In Finland, the occurrence of this type of soil in the coastal areas constitutes one of the major environmental problems of the country. To address this problem, it is essential to precisely locate acid sulfate soils. Thus, the creation of occurrence maps for these soils is required. Nowadays, different machine learning methods can be used following the digital soil mapping approach. The main goal of this study is the evaluation of different supervised machine learning techniques for acid sulfate soil mapping. The methods analyzed are Random Forest, Gradient Boosting and Support Vector Machine. We show that Gradient Boosting and Random Forest are suitable methods for the classification of acid sulfate soils, the resulting probability maps have high precision. However, the accuracy of the probability map created with Support Vector Machine is lower because this method overestimates the non-AS soils occurrences. We also compare these modeled probability maps with the conventionally produced occurrence map. In general, the modeled maps are more objective and accurate than the conventional maps. Moreover, the mapping process using machine learning techniques is faster and less expensive.
