| 1. |
- Alekseeva, Irina, et al.
(författare)
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Reproducing the Aral Sea water budget and sea-groundwater dynamics between 1979 and 1993 using a coupled 3-D sea-ice-groundwater model
- 2009
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Ingår i: Journal of Marine Systems. - : Elsevier. - 0924-7963. ; 76:3, s. 296-309
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Tidskriftsartikel (refereegranskat)abstract
- We have developed the 3-D sea-ice model, ECOSMO, into a coupled sea-ice–groundwater model and investigated the factors that may have influenced the groundwater–seawater interactions and the water balance of the shrinking Aral Sea. During the simulation period, 1979–1993, the model successfully reproduced the rapid Aral Sea level drop, surface area decrease, coastline position changes and increasing salinization of the Aral Sea. Model predictions of evaporation and groundwater inflow were also consistent with independent estimations. Model results indicated that the net groundwater inflow to the Aral Sea may have increased by 10% or more as a direct effect of the sea level lowering. Furthermore, model scenario tests showed that in comparison with a basic scenario, in which salinity effects were accounted for, not accounting for such effects resulted in considerable changes in ice formation and winter thermal conditions, which in turn influenced the thermo- and hydrodynamics and fresh water air-sea fluxes in the Aral Sea. As a result, the zero-salinity scenario predicted higher evaporation rates and an accelerated sea level lowering by up to 2 cm/yr, in comparison with the basic scenario. Model results showed that increased groundwater inflow to the sea may have influenced the Aral Sea salinity distribution since the 1990's. Our results emphasise the importance of taking into account both baroclinic hydrodynamics, sea-ice dynamics and as well as potentially increased future groundwater-related salinity effects in order to accurately estimate the Aral Sea water balance. More generally, models that can handle such highly dynamic systems may have a realistic potential for making detailed assessments of sea characteristics under the influence of climate and hydrological cycle changes.
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| 2. |
- Bieser, Johannes, et al.
(författare)
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The 3D biogeochemical marine mercury cycling model MERCY v2.0 – linking atmospheric Hg to methylmercury in fish
- 2023
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Ingår i: Geoscientific Model Development. - 1991-959X .- 1991-9603. ; 16:9, s. 2649-2688
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Tidskriftsartikel (refereegranskat)abstract
- Mercury (Hg) is a pollutant of global concern. Due to anthropogenic emissions, the atmospheric and surface ocean Hg burden has increased substantially since preindustrial times. Hg emitted into the atmosphere gets transported on a global scale and ultimately reaches the oceans. There it is transformed into highly toxic methylmercury (MeHg) that effectively accumulates in the food web. The international community has recognized this serious threat to human health and in 2017 regulated Hg use and emissions under the UN Minamata Convention on Mercury. Currently, the first effectiveness evaluation of the Minamata Convention is being prepared, and, in addition to observations, models play a major role in understanding environmental Hg pathways and in predicting the impact of policy decisions and external drivers (e.g., climate, emission, and land-use change) on Hg pollution. Yet, the available model capabilities are mainly limited to atmospheric models covering the Hg cycle from emission to deposition. With the presented model MERCY v2.0 we want to contribute to the currently ongoing effort to improve our understanding of Hg and MeHg transport, transformation, and bioaccumulation in the marine environment with the ultimate goal of linking anthropogenic Hg releases to MeHg in seafood.Here, we present the equations and parameters implemented in the MERCY model and evaluate the model performance for two European shelf seas, the North and Baltic seas. With the model evaluation, we want to establish a set of general quality criteria that can be used for evaluation of marine Hg models. The evaluation is based on statistical criteria developed for the performance evaluation of atmospheric chemistry transport models. We show that the MERCY model can reproduce observed average concentrations of individual Hg species in water (normalized mean bias: HgT 17 %, Hg0 2 %, MeHg −28 %) in the two regions mentioned above. Moreover, it is able to reproduce the observed seasonality and spatial patterns. We find that the model error for HgT(aq) is mainly driven by the limitations of the physical model setup in the coastal zone and the availability of data on Hg loads in major rivers. In addition, the model error in calculating vertical mixing and stratification contributes to the total HgT model error. For the vertical transport we find that the widely used particle partitioning coefficient for organic matter of log(kd)=5.4 is too low for the coastal systems. For Hg0 the model performance is at a level where further model improvements will be difficult to achieve. For MeHg, our understanding of the processes controlling methylation and demethylation is still quite limited. While the model can reproduce average MeHg concentrations, this lack of understanding hampers our ability to reproduce the observed value range. Finally, we evaluate Hg and MeHg concentrations in biota and show that modeled values are within the range of observed levels of accumulation in phytoplankton, zooplankton, and fish. The model performance demonstrates the feasibility of developing marine Hg models with similar predictive capability to established atmospheric chemistry transport models. Our findings also highlight important knowledge gaps in the dynamics controlling methylation and bioaccumulation that, if closed, could lead to important improvements of the model performance.
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| 3. |
- Chafik, Léon, 1985-, et al.
(författare)
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On the spatial structure and temporal variability of poleward transport between Scotland and Grennland :
- 2014
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Ingår i: Journal of Geophysical Research: Oceans. - 2169-9291. ; 119:2, s. 824-841
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Tidskriftsartikel (refereegranskat)abstract
- [1] The flow north of warm subtropical water though the northeastern Atlantic is known to have many pathways that vary over time. Here we use a combination of upper ocean current measurements between Greenland and Scotland near 60°N and satellite altimetry to examine the space-time variability of poleward transport. The high-resolution scans of currents in the top 400 m show that the Reykjanes Ridge serves as a very effective separator of flow toward the Nordic and Labrador Seas, respectively. Whereas the Labrador Sea branch exhibits two mean flows to the north on the western slope of the Reykjanes Ridge, the eastern branch flows north in roughly equal amounts over the deep Maury channel and east of Hatton Bank including the Slope Current. There is also a well-defined southward flow along the eastern slope of the Reykjanes Ridge. The satellite altimetric sea surface height (SSH) data show good overall agreement with geostrophically determined -level difference from the repeat ADCP sections (1999–2002), but are unable to resolve the fine structure of the topographically defined mean circulation. The altimetric data show that variations in poleward flow west and east of the Reykjanes Ridge are strongly anticorrelated. They further reveal that the two eastern subbranches also exhibit anticorrelated variability, but offset in time with respect to the Labrador Sea branch. Remarkably, all these variations cancel out for the entire Greenland-Scotland section leaving a gradual decrease in sea-level difference of about 0.06 m over the 1993 to the end of 2010 observation period.
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| 4. |
- Friedland, René, et al.
(författare)
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Effects of Nutrient Management Scenarios on Marine Eutrophication Indicators : A Pan-European, Multi-Model Assessment in Support of the Marine Strategy Framework Directive
- 2021
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Ingår i: Frontiers in Marine Science. - : Frontiers Media SA. - 2296-7745. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- A novel pan-European marine model ensemble was established, covering nearly all seas under the regulation of the Marine Strategy Framework Directive (MSFD), with the aim of providing a consistent assessment of the potential impacts of riverine nutrient reduction scenarios on marine eutrophication indicators. For each sea region, up to five coupled biogeochemical models from institutes all over Europe were brought together for the first time. All model systems followed a harmonised scenario approach and ran two simulations, which varied only in the riverine nutrient inputs. The load reductions were evaluated with the catchment model GREEN and represented the impacts due to improved management of agriculture and wastewater treatment in all European river systems. The model ensemble, comprising 15 members, was used to assess changes to the core eutrophication indicators as defined within MSFD Descriptor 5. In nearly all marine regions, riverine load reductions led to reduced nutrient concentrations in the marine environment. However, regionally the nutrient input reductions led to an increase in the non-limiting nutrient in the water, especially in the case of phosphate concentrations in the Black Sea. Further core eutrophication indicators, such as chlorophyll-a, bottom oxygen and the Trophic Index TRIX, improved nearly everywhere, but the changes were less pronounced than for the inorganic nutrients. The model ensemble displayed strong consistency and robustness, as most if not all models indicated improvements in the same areas. There were substantial differences between the individual seas in the speed of response to the reduced nutrient loads. In the North Sea ensemble, a stable plateau was reached after only three years, while the simulation period of eight years was too short to obtain steady model results in the Baltic Sea. The ensemble exercise confirmed the importance of improved management of agriculture and wastewater treatments in the river catchments to reduce marine eutrophication. Several shortcomings were identified, the outcome of different approaches to compute the mean change was estimated and potential improvements are discussed to enhance policy support. Applying a model ensemble enabled us to obtain highly robust and consistent model results, substantially decreasing uncertainties in the scenario outcome. ABSTRACT A novel pan-European marine model ensemble was established, covering nearly all seas under the regulation of the Marine Strategy Framework Directive (MSFD), with the aim of providing a consistent assessment of the potential impacts of riverine nutrient reduction scenarios on marine eutrophication indicators. For each sea region, up to five coupled biogeochemical models from institutes all over Europe were brought together for the first time. All model systems followed a harmonised scenario approach and ran two simulations, which varied only in the riverine nutrient inputs. The load reductions were evaluated with the catchment model GREEN and represented the impacts due to improved management of agriculture and wastewater treatment in all European river
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| 5. |
- Schmitt, Lou, 1942, et al.
(författare)
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Why they came; The colonization of the coast of Western Sweden and its environmental context at the end of the last glaciation
- 2006
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Ingår i: Oxford Journal of Archaeology. - : Wiley. - 0262-5253 .- 1468-0092. ; 25:1
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Tidskriftsartikel (refereegranskat)abstract
- Summary. In this paper we will bring into view new aspects of Late Palaeolithic and early Mesolithic research on the west coast of Sweden. In doing so, we make use of oceanography and tidal modelling, in conjunction with basic research in the fields of archaeology and palynology. The focus of research concerns the Hensbacka culture group in central Bohuslän, a group of hunter-gatherers which visited the area between c.10,300–9300 bp (10,200/10,000–8500 cal BC). Recent investigations indicate that the frequency of Hensbacka sites in the archipelago of central Bohuslän, which at that time had a total land area of c.500 sq km, might well represent the highest site density area in northern Europe during a c.1000-year period of time at the close of the Late Glacial and beginning of the early Post Glacial. In the pages that follow, we will discuss how, and why, this ‘seasonal colonization’ was possible.
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