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During the last decades, the Baltic Sea has been among the fastest warming seas in the world. The warming is mainly driven by increasing air temperatures but deeper water layers can also be warmed by lateral advection of heat. By analyzing a 159 years long (1850–2008) hindcast simulation of the Baltic Sea, we link the exceptionally strong bottom water warming in the western Baltic Sea to a shift in the seasonality of saltwater inflows from the North Sea to the Baltic Sea. Over the model period, warm summer and early autumn inflows have increased while cold winter inflows have decreased. Sensitivity experiments reveal that these changes were partly driven by a shift in river runoff seasonality. The strong warming could lead to faster oxygen depletion in the affected layers and thus have ecological consequences., Plain Language Summary: The Baltic Sea is home to various marine and freshwater species and an important economic factor for the surrounding countries. Like other seas, the Baltic Sea is getting warmer due to climate change. The water at the surface warms especially fast because it takes up heat from the warming atmosphere. After some time, temperatures also increase in deeper layers. However, some deep parts in the western Baltic Sea are warming even faster than the sea surface. In our study, we investigate if the exceptional warming can be explained by an increase in warm saltwater inflows from the North Sea. Hence, we use a model simulation of the Baltic Sea for over 150 years to compare long time series of warm inflows and the temperatures in the deep layers of the western Baltic Sea. We find a strong correlation. Thus, we can link the exceptional warming in the deep layers of the western Baltic Sea during the last decades to an increase in warm inflows. The warming has ecological consequences since in warmer water, the oxygen is consumed faster and the deep water layers of the Baltic Sea are suffering from low oxygen concentrations., Key Points: Summer and early autumn salt import into the Baltic Sea increased significantly since 1851 compared to the annual salt import. Salt import between June and October is highly correlated with the annual sub‐thermocline temperature maximum in the western Baltic Sea. The shift in inflow seasonality was partly caused by seasonal changes in river runoff., https://doi.io-warnemuende.de/10.12754/data-2023-0006, https://doi.io-warnemuende.de/10.12754/data-2018-0004

Benthic oxygen dynamics and the exchange of oxygen and other solutes across the sediment‐water interface play a key role for the oxygen budget of many limnic and shallow marine systems. The sediment‐water fluxes are largely determined by two factors: sediment biogeochemistry and the thickness of the diffusive boundary layer that is determined by near‐bottom turbulence. Here, we present a fully coupled benthic‐pelagic modeling system that takes these processes and their interaction into account, focusing especially on the modulation of the sediment‐water fluxes by the effects of near‐bottom turbulence and stratification. We discuss the special numerical methods required to guarantee positivity and mass conservation across the sediment‐water interface in the presence of rapid element transformation, and apply this modeling system to a number of idealized scenarios. Our process‐oriented simulations show that near‐bottom turbulence provides a crucial control on the sediment‐water fluxes, the oxygen penetration depth, and the re‐oxidation of reduced compounds diffusing upward from the deeper benthic layers especially on time scales of a few days, characterizing oceanic tides, internal seiching motions in lakes, and mesoscale atmospheric variability. Our results also show that the response of benthic‐pelagic fluxes to rapid changes in the forcing conditions (e.g., storm events) can only be understood with a fully coupled modeling approach., Plain Language Summary: Oxygen is one of the most relevant ecosystem parameters in marine systems and in lakes. In shallow systems, the overall oxygen budget is often controlled by the sedimentary oxygen demand, and it is therefore crucial to account for the exchange of oxygen and other solutes between the sediment and the water column. In this, context, a thin (millimeter‐scale) “diffusive sublayer,” located immediately above the sediment surface, is known to play an especially important role as it may form a bottleneck for the solute exchange. As the thickness of this sublayer is controlled by hydrodynamic processes, sediment‐water fluxes are affected by complex feedbacks between physical and biogeochemical processes. Here, we describe a fully coupled numerical modeling system that takes these feedback mechanisms into account, including advanced numerical methods guaranteeing that the total mass of all solutes is conserved (even if these are transformed) and that their concentrations do not become negative. Using a series of idealized examples, it is shown that near‐bottom hydrodynamic processes have an important impact on the sediment‐water fluxes, the depth to which oxygen penetrates into the upper sediment layers, and the re‐oxidation of reduced chemical compounds in the sediments. These feedbacks are particularly important for processes with time scales of a few days, like ocean tides, internal oscillations in lakes, and short‐term atmospheric disturbances (e.g., storm events)., Key Points: First fully coupled benthic‐pelagic modeling system accounting for the effects of near‐bottom turbulence on sediment‐water solute fluxes. Hydrodynamic effects control benthic biogeochemistry and fluxes especially on time scales of a few days, and during extreme events. New numerical methods that guarantee mass conservation and positivity across the sediment‐water interface., Leibniz Association, German Research Foundation, Swiss National Science Foundation, UK Natural Environment Research Council, Department for Environment Food and Rural Affairs, https://gotm.net/, https://github.com/fabm-model, https://doi.org/10.5281/zenodo.7950383, https://doi.org/10.5281/zenodo.7950866

We analyze multidecadal temperature fluctuations of the Atlantic Ocean and their influence on Northern Europe, focusing on the Baltic Sea, without a priori assuming a linear relationship of this teleconnection. Instead, we use the method of low-frequency component analysis to identify modes of multidecadal variability in the Baltic Sea temperature signal and relate this signal to the Atlantic climate variability. Disentangling the seasonal impact reveals that a large fraction of the variability in Baltic Sea winter temperatures is related to multidecadal temperature fluctuations in the North Atlantic, known as Atlantic Multidecadal Variability (AMV). The strong winter response can be linked to the interaction between the North Atlantic Oscillation and the AMV and is maintained by oceanic inertia. In contrast, the AMV does not influence the Baltic Sea's summer and spring water temperatures., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

The Baltic Sea is a semi-enclosed brackish sea located in Northern Europe. Due to some natural features (limited exchange with the World Ocean and permanent halocline) and anthropogenic forcing (nutrient loads from agriculture), the Baltic Sea experiences accelerating hypoxia and anoxia (bottom O2 concentrations less than 2 and 0 ml/l, respectively). Apart from the vertical oxygen fluxes across the pycnocline, the only natural ventilation mechanism in the Baltic Sea are the saltwater inflows from the North Sea transporting salty and oxygen-reach water to the central Baltic Sea. In this study, we utilized a 3-dimensional coupled ocean model to investigate the 29 biggest oxygen inflows within the 4 basins of the central Baltic Sea (the Bornholm Basin, the eastern Gotland Basin, the northern Gotland Basin, and the western Gotland Basin) happening from 1948 to 2018. We found a significant decline in inflows’ lifetimes for all basins, especially for the remote northern and western Gotland Basins, where oxygen supply via the inflows has been reducing since the 1970s and almost stopped during the last decade. Since no trend in the inflows’ strength was found, the overall decline in ventilation was attributed to the elevated oxygen consumption in the region, which was observed in the model. It was found that ventilation by inflows triggers the same processes consuming oxygen regardless of the system’s trophic state, mainly the mineralization of particulate organic matter (specifically detritus) in the sediments., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

The western Baltic Sea is impacted by various anthropogenic activities and stressed by high riverine and atmospheric nutrient loads. Atmospheric deposition accounts for up to a third of the nitrogen input into the Baltic Sea and contributes to eutrophication. Amongst other emission sources, the shipping sector is a relevant contributor to the atmospheric concentrations of nitrogen oxides (NOX) in marine regions. Thus, it also contributes to atmospheric deposition of bioavailable oxidized nitrogen into the Baltic Sea. In this study, the contribution of shipping emissions to the nitrogen budget in the western Baltic Sea is evaluated with the coupled three-dimensional physical biogeochemical model MOM–ERGOM (Modular Ocean Model–Ecological ReGional Ocean Model) in order to assess the relevance of shipping emissions for eutrophication. The atmospheric input of bioavailable nitrogen impacts eutrophication differently depending on the time and place of input. The shipping sector contributes up to 5 % to the total nitrogen concentrations in the water. The impact of shipping-related nitrogen is highest in the offshore regions distant from the coast in early summer, but its contribution is considerably reduced during blooms of cyanobacteria in late summer because the cyanobacteria fix molecular nitrogen. Although absolute shipping-related total nitrogen concentrations are high in some coastal regions, the relative contribution of the shipping sector is low in the vicinity of the coast because of high riverine nutrient loads.

Paula C. Barata, University of Guelph, Charlene Y. Senn, University of Windsor, Misha Eliasziw, Tufts University, H. Lorraine Radtke, University of Calgary, Wilfreda E. Thurston, University of Calgary, and Karen L. Hobden, University of Windsor Can a successful Sexual Assault Resistance Program Also Reduce IPV? Exploring IPV Reduction as an Outcome of the EAAA Program