| 1. |
- Conley, Daniel, et al.
(författare)
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Hypoxia-Related Processes in the Baltic Sea
- 2009
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 43:10, s. 3412-3420
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Tidskriftsartikel (refereegranskat)abstract
- Hypoxia, a growing worldwide problem, has been intermittently present in the modern Baltic Sea since its formation ca. 8000 cal. yr BP. However, both the spatial extent and intensity of hypoxia have increased with anthropogenic eutrophication due to nutrient inputs. Physical processes, which control stratification and the renewal of oxygen in bottom waters, are important constraints on the formation and maintenance of hypoxia. Climate controlled inflows of saline water from the North Sea through the Danish Straits is a critical controlling factor governing the spatial extent and duration of hypoxia. Hypoxia regulates the biogeochemical cycles of both phosphorus (P) and nitrogen (N) in the water column and sediments. Significant amounts of P are currently released from sediments, an order of magnitude larger than anthropogenic inputs. The Baltic Sea is unique for coastal marine ecosystems experiencing N losses in hypoxic waters below the halocline. Although benthic communities in the Baltic Sea are naturally constrained by salinity gradients, hypoxia has resulted in habitat loss over vast areas and the elimination of benthic fauna, and has severely disrupted benthic food webs. Nutrient load reductions are needed to reduce the extent, severity, and effects of hypoxia.
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| 2. |
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| 3. |
- Hallfors, Heidi, et al.
(författare)
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Vertical and temporal distribution of the dinoflagellates Dinophysis acuminata and D. norvegica in the Baltic Sea
- 2011
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Ingår i: Boreal environment research. - 1239-6095 .- 1797-2469. ; 16:2, s. 121-135
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the distributions of the toxic dinoflagellates Dinophysis acuminata and D. norvegica in the brackish Baltic Sea, and found them to differ both regarding their seasonality and their vertical distribution. Dittophysis acuminata was considerably more abundant, especially in the Gulf of Finland, where we observed an August peak of 14 300 cells l(-1). It occurred in elevated abundances during or after periods of high phytoplankton biomass in early and late summer. Dinophysis norvegica was abundant during a shorter period, peaking one month after the first D. acuminata maximum. While D. norvegica probably is restricted by both salinity and temperature in the northern Baltic Sea, the more tolerant D. acuminata thrives. The results presented here expand the wide range of scenarios in which D. acuminata may bloom worldwide. Both species mainly formed population maxima either in the mixed surface waters or near the thermocline. Dinophysis acuminata usually occurred in the illuminated and nutrient-poor mixed surface layer, but in the presence of light and a nutricline it formed distinct subsurface peaks. Dinophysis norvegica was not as sensitive to darkness and predominantly formed subsurface peaks, even below the euphotic zone. These occurrences were promoted by shallow stratification, and the combination of a deep mixed layer and cool surface waters drew the D. norvegica population closer to the surface. When D. acuminata and D. norvegica co-occurred, their abundances peaked at different depths; this was observed even when both species formed maxima in the surface layer.
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| 4. |
- Lehtoranta, Jouni, et al.
(författare)
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Atmospheric forcing controlling inter-annual nutrient dynamics in the open Gulf of Finland
- 2017
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Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 171, s. 4-20
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Tidskriftsartikel (refereegranskat)abstract
- The loading of P into the Gulf of Finland has decreased markedly, but no overall trend in the concentration of P has been observed in the open Gulf, where the concentrations of both inorganic N and P still have a pronounced inter annual variability. Our main aim was to study whether the internal processes driven by atmospheric forcing can explain the variation in the nutrient conditions in the Gulf during the period 1992-2014. We observed that the long-term salinity variation of the bottom water in the northern Baltic Proper controls that in the Gulf, and that the deep-water concentrations of oxygen and nutrients are significantly correlated between the basins. This imposes preconditions regarding how atmospheric forcing may influence deep water flows and stratification in the Gulf on a long-term scale. We found that over short timescales, winter winds in particular can control the in- and outflows of water and the vertical stratification and mixing, which to a large extent explained the inter-annual variation in the DIN and TP pools in the Gulf. We conclude that the inter-annual variation in the amounts, ratios, and spatial distribution of nutrients sets variable preconditions for the spring and potential blue-green algae blooms, and that internal processes were able to mask the effects of the P load reductions implemented across the whole Gulf. The transportation of P along the bottom from the northern Baltic Proper and its evident uplift in the Gulf highlights the fact that the nutrient reductions are also needed in the entire catchment of the Baltic Sea to improve the trophic status of the open Gulf.
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| 5. |
- Myrberg, Kai, et al.
(författare)
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Validation of three-dimensional hydrodynamic models of the Gulf of Finland
- 2010
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Ingår i: Boreal environment research. - 1239-6095 .- 1797-2469. ; 15:5, s. 453-479
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Tidskriftsartikel (refereegranskat)abstract
- A model-intercomparison study was conducted, the first of its kind for the Baltic Sea, whose aim was to systematically simulate the basic three-dimensional hydrographic properties of a realistic, complex basin. Simulations of the hydrographic features of the Gulf of Finland for the summer autumn of 1996 by six three-dimensional hydrodynamic models were compared. Validation was undertaken using more than 300 vertical hydrographic profiles of salinity and temperature. The analysis of model performance, including averaging of the ensemble results, was undertaken with a view to assessing the potential suitability of the models in reproducing the physics of the Baltic Sea accurately enough to serve as a basis for accurate simulations of biogeochemistry once ecosystem models are incorporated. The performance of the models was generally satisfactory. Nevertheless, all the models had some difficulties in correctly simulating vertical profiles of temperature and salinity, and hence mixed layer dynamics, particularly in the eastern Gulf of Finland. Results emphasized the need for high resolution in both vertical and horizontal directions in order to resolve the complex dynamics and bathymetry of the Baltic Sea. Future work needs to consider the choice of mixing and advection schemes, moving to higher resolution, high-frequency forcing, and the accurate representation of river discharges and boundary conditions.
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| 6. |
- Paczkowska, Joanna, 1983-
(författare)
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Phytoplankton drivers in a marine system influenced by allochthonous organic matter – the Baltic Sea
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Climate change scenarios predict that seawater temperature and precipitation will increase in the Baltic Sea region during the next century. In the northern part of the Baltic Sea, increasing inflows of the terrestrial allochthonous dissolved organic matter (ADOM) are expected to be a major consequence of elevated rainfall, which can alter light and nutrient availability for phytoplankton. The aim of my thesis was to elucidate effects of ADOM on phytoplankton production, community, size-structure and nutritional strategy along offshore south-north gradients in the Baltic Sea, as well as in estuarine systems exposed to seasonal variation in river discharge. Field studies, a mesocosm experiment and a modeling study were used to explore these issues.Results from the field studies and mesocosm experiment illustrated that the nutritional strategy, size-structure and cellular pigment content of the phytoplankton were governed by changes in ADOM, and thus in light and nutrient availability. A summer study along an offshore south-north gradient showed that the proportion of mixotrophic phytoplankton increased towards the north. In this area the concentrations humic substances (proxy for ADOM) were high, while the light availability and phosphorus concentrations were relatively low. The phytoplankton cells responded to reduced light availability by increasing their chlorophyll a: carbon ratio. Additionally, the levels of photoprotective pigments decreased from south to north, as a result of acclimation to a low-light environment and reduced exposure to ultraviolet radiation. According to ecological assumptions picophytoplankton should be favored in light- and nutrient-limited environments. However, the results did not follow that pattern, the proportion of picophytoplankton being highest in the relatively nutrient rich Baltic Proper. The study was performed during the decline of an extensive bloom of filamentous cyanobacteria, a successional phase in which picophytoplankton often dominate the phytoplankton community.The estuarine studies performed in the Bothnian Bay (Råne estuary) and in the Bothnian Sea (Öre estuary) showed different successions. In the Råne estuary no spring phytoplankton bloom occurred and highest primary production was observed during the summer. This absence of a spring bloom was explained by low phosphorus and high ADOM concentrations, while the summer maximum could be explained by higher temperature and nutrient concentrations. In the Öre estuary a marked phytoplankton spring bloom was observed as well as an ADOM sustained bacterial production phase. The later secondary peak of bacterial production observed in summer, concomitant with an extended secondary primary production peak, suggests that autochthonous dissolved organic matter supported the bacterial growth Furthermore, the photosynthetic efficiency (i.e. phytoplankton growth rates) was lower during spring, indicating that high ADOM, and thus lower light and phosphorus availability, disfavored phytoplankton growth.Our modeling study showed that climate change can impact the food web; however effects will be different between basins. In the southern Baltic Sea elevated temperature and nutrient discharge may promote nutrient recycling and oxygen consumption, potentially extending anoxic areas, sediment nutrient release and cyanobacteria blooms. In the north, increased inflow of ADOM may promote heterotrophic bacterial production and decrease primary production due to light attenuation and lower phosphorus availability. This will favor the heterotrophic microbial food web and consequently lead to lower food web efficiency of the ecosystem.
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| 7. |
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| 8. |
- Viitasalo, Markku, et al.
(författare)
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Environmental Impacts—Marine Ecosystems
- 2015
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Ingår i: Second Assessment of Climate Change for the Baltic Sea Basin. - London : Springer. - 9783319160061 - 9783319160054 ; , s. 363-380
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Increase in sea surface temperature is projected to change seasonal succession and induce dominance shifts in phytoplankton in spring and promote the growth of cyanobacteria in summer. In general, climate change is projected to worsen oxygen conditions and eutrophication in the Baltic Proper and the Gulf of Finland. In the Gulf of Bothnia, the increasing freshwater discharge may increase the amount of dissolved organic carbon (DOC) in the water and hence reduce phytoplankton productivity. In winter, reduced duration and spatial extent of sea ice will cause habitat loss for ice-dwelling organisms and probably induce changes in nutrient dynamics within and under the sea ice. The projected salinity decline will probably affect the functional diversity of the benthic communities and induce geographical shifts in the distribution limits of key species such as bladder wrack and blue mussel. In the pelagic ecosystem, the decrease in salinity together with poor oxygen conditions in the deep basins will negatively influence the main Baltic Sea piscivore, cod. This has been suggested to cause cascading effects on clupeids and zooplankton.
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