SwePub
Sök i SwePub databas

  Utökad sökning

Träfflista för sökning "L773:0924 7963 OR L773:1879 1573 "

Sökning: L773:0924 7963 OR L773:1879 1573

  • Resultat 1-50 av 88
Sortera/gruppera träfflistan
   
NumreringReferensOmslagsbildHitta
1.
  • Pers, Charlotta, et al. (författare)
  • Changes in apparent oxygen removal in the Baltic proper deep water
  • 2000
  • Ingår i: Journal of Marine Systems. - 0924-7963 .- 1879-1573. ; 25:3-4, s. 421-429
  • Tidskriftsartikel (refereegranskat)abstract
    • By developing a steady state diagnostic model for a stratified deep-water mass, one is able to quantify both the mass flows and apparent oxygen removal in the Baltic proper deep water. The model is based on continuity of the assumed conservative observable volume, salinity and temperature. Second degree polynomials are fitted to observed vertical profiles of temperature as well as oxygen concentration to give a functional correspondence with the used spatial variable salinity. These relations are used in the model that calculate the water flows, oxygen flows and oxygen removal during four periods between 1959 and 1997. The model forms a boundary value problem, which is solved with a finite difference scheme. The model seems to give reasonable estimates of the flows. The oxygen removal is mainly balanced by inflow of oxygen with incoming water. The oxygen consumption is 4-8 ╡1 O2 1-1 day -1, which corresponds to a degradation of organic matter in the range 30-60 g C m-2 year-1. (C) 2000 Elsevier Science B.V.
  •  
2.
  • Ahlgren, Joakim, et al. (författare)
  • Temperature, DOC level and basin interactions explain the declining oxygen concentrations in the Bothnian Sea
  • 2017
  • Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 170, s. 22-30
  • Tidskriftsartikel (refereegranskat)abstract
    • Hypoxia and oxygen deficient zones are expanding worldwide. To properly manage this deterioration of the marine environment, it is important to identify the causes of oxygen declines and the influence of anthropogenic activities. Here, we provide a study aiming to explain the declining oxygen levels in the deep waters of the Bothnian Sea over the past 20 years by investigating data from environmental monitoring programmes. The observed decline in oxygen concentrations in deep waters was found to be primarily a consequence of water temperature increase and partly caused by an increase in dissolved organic carbon (DOC) in the seawater (R-Adj(2). = 0.83) as well as inflow from the adjacent sea basin. As none of the tested eutrophication-related predictors were significant according to a stepwise multiple regression, a regional increase in nutrient inputs to the area is unlikely to explain a significant portion of the oxygen decline. Based on the findings of this study, preventing the development of anoxia in the deep water of the Bothnian Sea is dependent on the large-scale measures taken to reduce climate change. In addition, the reduction of the nutrient load to the Baltic Proper is required to counteract the development of hypoxic and phosphate-rich water in the Baltic Proper, which can form deep water in the Bothnian Sea. The relative importance of these sources to oxygen consumption is difficult to determine from the available data, but the results clearly demonstrate the importance of climate related factors such as temperature, DOC and inflow from adjacent basins for the oxygen status of the sea.
  •  
3.
  • Algesten, Grete, et al. (författare)
  • Organic carbon budget for the Gulf of Bothnia
  • 2006
  • Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 63:3-4, s. 155-161
  • Tidskriftsartikel (refereegranskat)abstract
    • We calculated input of organic carbon to the unproductive, brackish water basin of the Gulf of Bothnia from rivers, point sources and the atmosphere. We also calculated the net exchange of organic carbon between the Gulf of Bothnia and the adjacent marine system, the Baltic Proper. We compared the input with sinks for organic carbon; permanent incorporation in sediments and mineralization and subsequent evasion of CO2 to the atmosphere. The major fluxes were riverine input (1500 Gg C year(-1)), exchange with the Baltic Proper (depending on which of several possible DOC concentration differences between the basins that was used in the calculation, the flux varied between an outflow of 466 and an input of 950 Gg C year(-1)), sediment burial (1100 Gg C year) and evasion to the atmosphere (3610 Gg C year(-1)). The largest single net flux was the emission of CO2 to the atmosphere, mainly caused by bacterial mineralization of organic carbon. Input and output did not match in our budget which we ascribe uncertainties in the calculation of the exchange of organic carbon between the Gulf of Bothnia and the Baltic Proper, and the fact that CO2 emission, which in our calculation represented 1 year (2002) may have been overestimated in comparison with long-term means. We conclude that net heterotrophy of the Gulf of Bothnia was due to input of organic carbon from both the catchment and from the Baltic Proper and that the future degree of net heterotrophy will be sensible to both catchment export of organic carbon and to the ongoing eutrophication of the Baltic Proper.
  •  
4.
  • Almroth Rosell, Elin, 1977, et al. (författare)
  • A new approach to model oxygen dependent benthic phosphate fluxes in the Baltic Sea
  • 2015
  • Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 144, s. 127-141
  • Tidskriftsartikel (refereegranskat)abstract
    • The new approach to model the oxygen dependent phosphate release by implementing formulations of the oxygen penetration depths (OPD) and mineral bound inorganic phosphorus pools to the Swedish Coastal and Ocean Biogeochemical model (SCOBI) is described. The phosphorus dynamics and the oxygen concentrations in the Baltic proper sediment are studied during the period 1980-2008 using SCOBI coupled to the 3D-Rossby Centre Ocean model. Model data are compared to observations from monitoring stations and experiments. The impact from oxygen consumption on the determination of the OPD is found to be largest in the coastal zones where also the largest OPD are found. In the deep water the low oxygen concentrations mainly determine the OPD. Highest modelled release rate of phosphate from the sediment is about 59 x 10(3) t P year(-1) and is found on anoxic sediment at depths between 60-150 m, corresponding to 17% of the Baltic proper total area. The deposition of organic and inorganic phosphorus on sediments with oxic bottom water is larger than the release of phosphorus, about 43 x 10(3) t P year(-1). For anoxic bottoms the release of total phosphorus during the investigated period is larger than the deposition, about 19 x 10(3) t P year(-1). In total the net Baltic proper sediment sink is about 23.7 x 10(3) t P year(-1). The estimated phosphorus sink efficiency of the entire Baltic Sea is on average about 83% during the period.
  •  
5.
  • Andersson, Andreas, et al. (författare)
  • Using eddy covariance to estimate air-sea gas transfer velocity for oxygen
  • 2016
  • Ingår i: Journal of Marine Systems. - : Elsevier. - 0924-7963 .- 1879-1573. ; 159, s. 67-75
  • Tidskriftsartikel (refereegranskat)abstract
    • Air-sea gas transfer velocity for O2 is calculated using directly measured fluxes with the eddy covariance technique. It is a direct method and is frequently used to determine fluxes of heat, humidity, and CO2, but has not previously been used to estimate transfer velocities for O2, using atmospheric eddy covariance data. The measured O2 fluxes are upward directed, in agreement with the measured air-sea gradient of the O-2 concentration, and opposite to the direction of the simultaneously measured CO2 fluxes. The transfer velocities estimated from measurements are compared with prominent wind speed parameterizations of the transfer velocity for CO2 and O2, previously established from various measurement techniques. Our result indicates stronger wind speed dependence for the transfer velocity of O2 compared to CO2 starting at intermediate wind speeds. This stronger wind speed dependence appears to coincide with the onset of whitecap formation in the flux footprint and the strong curvature of a cubic wind -dependent function for the transfer velocity provides the best fit to the data. Additional data using the measured O2 flux and an indirect method (based on the Photosynthetic Quotient) to estimate oxygen concentration in water, support the stronger wind dependence for the transfer velocity of O2 O-2 to CO2.
  •  
6.
  • Armbrecht, Linda, et al. (författare)
  • Comparison of the cross-shelf phytoplankton distribution of two oceanographically distinct regions off Australia
  • 2015
  • Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 148, s. 26-38
  • Tidskriftsartikel (refereegranskat)abstract
    • The coastline of Australia spans tropical to temperate latitudes and encompasses a highly diverse phytoplankton community. Yet little is known about environmental driving forces of compositional and distributional patterns in natural phytoplankton communities of Australia. We investigate the relationships of phytoplankton (pico-, nano-, microphytoplankton, determined by microscopy and CHEMTAX) with a variety of environmental variables along cross-shelf gradients. Case studies were conducted in two highly distinct oceanographic regions of Australia (2010/2012): the tropical-temperate Coffs Harbour region (similar to 30 degrees S, 153 degrees E), where the shelf is narrow (similar to 30 km), and the tropical Kimberley region (similar to 16 degrees S, 122 degrees E), where the shelf is-wide (similar to 200 km). We distinguished three water masses in both study regions: relatively cold, nutrient-rich inshore waters; oligotrophic, stratified offshore waters; and cold, nutrient-rich deep waters. Most phytoplankton taxa (cyanobacteria, cryptophytes, dinoflagellates, haptophytes and prasinophytes) showed group-specific relationships with similar environmental variables in both regions. Diatoms occurred in nutrient-rich inshore waters in the Kimberley, whereas they were widely spread across the narrow continental shelf at Coffs Harbour. Off Coffs Harbour, a senescent bloom of the diatom Leptocylindrus danicus probably caused shelf-scale surface nutrient depletion. While microphytoplankton clearly increased, pico- and nanophytoplankton decreased with distance from the coast over the wide shelf in the Kimberley region. In contrast, the abundance of individual phytoplankton size-classes remained relatively constant across the narrow Coffs Harbour shelf. We conclude that general similarities exist between the relationship of phytoplankton and cross-shelf environmental variables in the two sites and assign differences primarily to the varying spatial resolution of our case studies.
  •  
7.
  • Björk, Göran, 1956, et al. (författare)
  • Seasonal oxygen depletion in a shallow sill fjord on the Swedish west coast
  • 2017
  • Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 175, s. 1-14
  • Tidskriftsartikel (refereegranskat)abstract
    • During the summer of 2008, oxygen depleted water, between 5 and 12 m depth, was discovered in Sannasfjord on the Swedish west coast. The resulting sediments were black, benthic macrofauna were absent and Beggiatoa bacterial mats were a characteristic feature. This phenomenon, which was observed several years in a row, appears to be a relatively new phenomenon starting in the mid-1980s. In this study we attempt to find the underlying causes by investigating climatic effects (temperature, wind and precipitation), the local supply of nutrients from land, ecosystem change and the supply of organic material from the open Skagerrak. An analysis of long meteorological time series indicates that climatic effects are contributory, but probably not a dominating factor leading to hypoxia. Results from an advection-diffusion model solving for oxygen show that the observed increase in the river supply of nutrients has a high potential to generate hypoxia. Although complex and more difficult to quantify, it appears that ecosystem changes, with higher abundance of filamentous algae, may have played an important role. It is also possible that an enhanced supply of organic material from the open Skagerrak has contributed. (C) 2017 Elsevier B.V. All rights reserved.
  •  
8.
  • Chndrasekhararao, A. V., et al. (författare)
  • Phytoplankton response to the contrasting physical regimes in the eastern Arabian Sea during north east monsoon
  • 2018
  • Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573.
  • Tidskriftsartikel (refereegranskat)abstract
    • Phytoplankton abundance and composition in two contrasting physical regimes - convective mixing in the northeastern Arabian Sea (NEAS) and Arabian Sea mini warm pool (ASMWP) in the southeastern Arabian Sea(SEAS) - were investigated during the northeast monsoon (NEM) of 2015 and 2017. Observations in 2015 were carried out late during the season, and only one station in the north (at 21°N latitude) fell within the zone of convective mixing where microplankton was dominated by diatoms. In 2017, convective mixing occurred even at 16°N latitude, but the microplankton contribution was low, presumably due to low Si/N ratios. Within the convective mixing regime of the NEAS, chlorophyll (Chl) concentrations were higher in 2015 (maximum1080 ng L-1; average 493 ng L-1) than in 2017 (maximum 673 ng L-1; average 263 ng L-1). In contrast, picophytoplankton was dominant in the ASMWP of the SEAS with peak abundance associated with the subsurface chlorophyll maximum. A warm core eddy was present in 2015 in the SEAS where four times higherProchlorococcus counts were found within the core of the eddy than at its periphery. This study provides the first description of the phytoplankton community in the ASMWP. Our results clearly demonstrate phytoplankton response to the contrasting physical conditions, highlighting the role of biophysical coupling in the productivity of the Arabian Sea
  •  
9.
  • Christaki, Urania, et al. (författare)
  • Microzooplankton diversity and potential role in carbon cycling of contrasting Southern Ocean productivity regimes
  • 2021
  • Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 219
  • Tidskriftsartikel (refereegranskat)abstract
    • Microzooplankton play an important role in aquatic food webs through their multiple interactions with other organisms and their impact on carbon export. They are major predators of phytoplankton and bacteria while being preyed on by higher trophic levels. Microzooplankton diversity (Dinoflagellates, DIN and Ciliates, CIL), community structure, interaction with phytoplankton and its potential in channeling carbon to higher trophic levels were studied in contrasting productivity regimes (off- and on-plateau, the latter been naturally fertilized by iron) around the Kerguelen islands in the Southern Ocean (SO). DIN and CIL diversity was sampled in late summer (February–March 2018; project MOBYDICK) and at the onset-of the bloom (KEOPS2 cruise), and assessed by Illumina sequencing of 18S rDNA amplicons and microscopic observations. The diversity obtained by the two approaches could be compared at a relatively high taxonomic level (i.e., often to family level). In particular for DIN, relative abundances and ranking of dominant taxa differed between sequencing and microscopy observations. CIL were always recorded at considerably lower abundances than DIN, the median of their abundances across stations and seasons being 350 and 1370 cells L−1, respectively. During late summer, DIN and CIL biomasses were about 1.5 times higher on- than in off-plateau waters, while community composition was spatially similar. The most abundant DIN at all stations and during both seasons were small Gymnodinium (<20 μm). During late summer, ciliates Lohmaniella oviformis (<20 μm) and Cymatocylis antarctica (20-40 μm) dominated on- and off-plateau, respectively. Dilution experiments suggested significant grazing of microzooplankton on phytoplankton as phytoplankton net growth (k) was lower than microzooplankton grazing (g) at all stations (mean k = 0.16 ± 0.05 d−1, g = 0.36 ± 0.09 d−1) in late summer. Despite having great potential as a phytoplankton grazer, microzooplankton occurred at low biomass and showed little temporal variability, suggesting that it was controlled by copepod predation. Microzooplankton is a key component of the SO as an intermediate trophic level mediating carbon transfer from primary producers to higher trophic levels.
  •  
10.
  • Conley, Daniel, et al. (författare)
  • Past, present and future state of the biogeochemical Si cycle in the Baltic Sea
  • 2008
  • Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 73:3-4, s. 338-346
  • Tidskriftsartikel (refereegranskat)abstract
    • The Baltic Sea is one of many aquatic ecosystems that show long-term declines in dissolved silicate (DSi) concentrations due to anthropogenic alteration of the biogeochemical Si cycle. Reductions in DSi in aquatic ecosystems have been coupled to hydrological regulation reducing inputs, but also with eutrophication, although the relative significance of both processes remains unknown for the observed reductions in DSi concentrations. Here we combine present and historical data on water column DSi concentrations, together with estimates of present river DSi loads to the Baltic, the load prior to damming together with estimates of the long-term accumulation of BSi in sediments. In addition, a model has been used to evaluate the past, present and future state of the biogeochemical Si cycle in the Baltic Sea. The present day DSi load to the Baltic Sea is 855 ktons y(-1). Hydrological regulation and eutrophication of inland waters can account for a reduction of 420 ktons y(-1) less riverine DSi entering the Baltic Sea today. Using published data on basin-wide accumulation rates we estimate that 1074 ktons y(-1) of biogenic silica (BSi) is accumulating in the sediments, which is 36% higher than earlier estimates from the literature (791 ktons y(-1)). The difference is largely due to the high reported sedimentation rates in the Bothnian Sea and the Bothnian Bay. Using river DSi loads and estimated BSi accumulation, our model was not able to estimate water column DSi concentrations as burial estimates exceeded DSi inputs. The model was then used to estimate the BSi burial from measured DSi concentrations and DSj load. The model estimate for the total burial of BSi in all three basins was 620 ktons y(-1), 74% less than estimated from sedimentation rates and sediment BSi concentrations. The model predicted 20% less BSi accumulation in the Baltic Proper and 10% less in the Bothnian Bay than estimated, but with significantly less BSi accumulation in the Bothnian Sea by a factor of 3. The model suggests there is an overestimation of basin-wide sedimentation rates in the Bothnian Bay and the Bothnian Sea. In the Baltic Proper, modelling shows that historical DSi concentrations were 2.6 times higher at the turn of the last century (ca. 1900) than at present. Although the DSi decrease has leveled out and at present there are only restricted areas of the Baltic Sea with limiting DSi concentrations, further declines in DSi concentrations will lead to widespread DSi limitation of diatoms with severe implications for the food web.
  •  
11.
  • Dahlgren Strååt, Kim, et al. (författare)
  • Future export of particulate and dissolved organic carbon from land to coastal zones of the Baltic Sea
  • 2018
  • Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 177, s. 8-20
  • Tidskriftsartikel (refereegranskat)abstract
    • The Baltic Sea is a semi-enclosed brackish sea in Northern Europe with a drainage basin four times larger than the sea itself. Riverine organic carbon (Particulate Organic Carbon, POC and Dissolved Organic Carbon, DOC) dominates carbon input to the Baltic Sea and influences both land-to-sea transport of nutrients and contaminants, and hence the functioning of the coastal ecosystem. The potential impact of future climate change on loads of POC and DOC in the Baltic Sea drainage basin (BSDB) was assessed using a hydrological-biogeochemical model (CSIM). The changes in annual and seasonal concentrations and loads of both POC and DOC by the end of this century were predicted using three climate change scenarios and compared to the current state. In all scenarios, overall increasing DOC loads, but unchanged POC loads, were projected in the north. In the southern part of the BSDB, predicted DOC loads were not significantly changing over time, although POC loads decreased in all scenarios. The magnitude and significance of the trends varied with scenario but the sign (+ or -) of the projected trends for the entire simulation period never conflicted. Results were discussed in detail for the middle CO2 emission scenario (business as usual, a1b). On an annual and entire drainage basin scale, the total POC load was projected to decrease by ca 7% under this scenario, mainly due to reduced riverine primary production in the southern parts of the BSDB. The average total DOC load was not predicted to change significantly between years 2010 and 2100 due to counteracting decreasing and increasing trends of DOC loads to the six major sub-basins in the Baltic Sea. However, predicted seasonal total loads of POC and DOC increased significantly by ca 46% and 30% in winter and decreased by 8% and 21% in summer over time, respectively. For POC the change in winter loads was a consequence of increasing soil erosion and a shift in duration of snowfall and onset of the spring flood impacting the input of terrestrial litter, while reduced primary production mainly explained the differences predicted in summer. The simulations also showed that future changes in POC and DOC export can vary significantly across the different sub-basins of the Baltic Sea. These changes in organic carbon input may impact future coastal food web structures e.g. by influencing bacterial and phytoplankton production in coastal zones, which in turn may have consequences at higher trophic levels.
  •  
12.
  • Danielsson, Åsa, et al. (författare)
  • Alterations in nutrient limitations - Scenarios of a changing Baltic Sea
  • 2008
  • Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 73:3-4, s. 263-283
  • Tidskriftsartikel (refereegranskat)abstract
    • Previous trend studies have shown increasing nitrogen and phosphorus as well as decreasing silica concentrations ill the water mass of the Baltic Sea. This has had an impact on the amount of primary production, but also on the quality and succession of plankton species. Present study examines the spatial and temporal patterns of potential nutrient limitations in the Baltic Sea for the time period 1970-2000. Generally, low concentrations of DSi can limit the diatom blooms and such conditions are found in the Gulf of Riga and Gulf of Finland during spring and summer. Nutrient ratios, DSi:DIN, DSi:DIP and DIN:DIP, are often used to determine which nutrient may limit the primary production. Annual long-term temporal trends of silica to inorganic nitrogen and phosphorus respectively show consistent decreasing patterns. The largest slopes are detected during spring and summer for DSi: DIN and during spring for DSi:DIP ratios. For the DIN:DIP ratio significant slopes are only found in a few locations despite increasing levels for both nutrients, displaying a large variation in trends. In the open Baltic Proper the present trends are positive during winter and negative during spring and autumn. Gulf of Finland and Gulf of Riga are areas where both DSi:DIP and DSi:DIN ratios are found close to the Redfield ratios for diatoms. Together with the evaluated trends these suggest that the Gulfs may become silica limited in a relatively near future. These findings give some implications on the development and impact of changing nutrient concentrations.
  •  
13.
  • Demina, Ludmila, et al. (författare)
  • Some features of the trace metal biogeochemistry in the deep-sea hydrothermal vent fields (Menez Gwen, Rainbow, Broken Spur at the MAR and 9°50'N at the EPR) : A synthesis
  • 2013
  • Ingår i: Journal of Marine Systems. - : Elsevier. - 0924-7963 .- 1879-1573. ; 126:SI, s. 94-105
  • Tidskriftsartikel (refereegranskat)abstract
    • Along with summarizing the published literature and our own data some new results on properties of the trace metal biogeochemistry in the deep-sea hydrothermal ecosystems at the Mid-Atlantic Ridge (MAR) and East Pacific Rise (EPR) are shown. Differences in mean concentrations of big group of trace metals (Fe, Mn, Zn, Cu, Ni, Cr, Co, As, Pb, Cd, Ag, Hg) between the biotope water of the low- and high-temperature hydrothermal vent fields were firstly revealed. The same trace metals were studied in different groups of organisms within different temperature zones at one and the same vent field (9°50′N EPR), as well as in fauna inhabiting geochemically different vent sites. Distribution patterns of Fe, Mn, Zn, Cu, Cd, Pb, Ag, Ni, Cr, Co, As, Se, Sb, and Hg in different taxa gave an evidence of the influence of environmental and biological parameters on their bioaccumulation in organisms. Among the animals a particular “champion” with respect to the trace metal content was found to be a polychaeta Alvinella pompejana that inhabits the hottest places of the vent sulfide chimneys of the 9°50′N field, EPR. New data on the trace metal distribution between soft tissues and carbonate shell let us estimate a role of biomineralization in the accumulation of metals in the Bathimodiolus mussels. Contrasting geochemical behavior was revealed for Cu that is enriched in soft tissues of mussels and depleted in shells, on the one hand, and Mn that is accumulated almost totally in mussel shells, on the other hand.Deep-sea hydrothermal biological communities demonstrate a strong concentration function, and bioconcentration factors (BCF) of trace metals estimated for Bathimodiolus mussels collected at the four hydrothermal fields vary within the limits of n102–n105 and are similar to that of the littoral mussels. Due to this and to the high values of biomasses per square meter, the hydrothermal fauna may be considered as a newly discovered biological filter of the oceans.
  •  
14.
  • Ehrnsten, Eva, et al. (författare)
  • Benthic-pelagic coupling in coastal seas - Modelling macrofaunal biomass and carbon processing in response to organic matter supply
  • 2019
  • Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 196, s. 36-47
  • Tidskriftsartikel (refereegranskat)abstract
    • Benthic macrofauna is an important component linking pelagic and benthic ecosystems, especially in productive coastal areas. Through their metabolism and behaviour, benthic animals affect biogeochemical fluxes between the sediment and water column. Mechanistic models that quantify these benthic-pelagic links are imperative to understand the functioning of coastal ecosystems. In this study, we develop a dynamic model of benthic macrofauna to quantify the relationship between organic matter input and benthic macrofaunal biomass in the coastal zone. The model simulates the carbon dynamics of three functional groups of benthic macrofauna and their sediment food sources and is forced by a hydrodynamic-biogeochemical model simulating pelagic physical and biological dynamics. The model reproduces measured time-series of macrofaunal biomass from two coastal sites with contrasting sedimentation in the Baltic Sea in 1993-2005 with comparatively high accuracy, including a major increase at one of the sites dominated by the bivalve Limecola (Macoma) balthica. This shift in community composition suggests altered pathways of organic matter degradation: 39% of simulated sedimentation was mineralised by macrofauna in 2005 compared to 10% in 1995. From the early 2000s onward macrofaunal biomass seems to be food-limited, as ca 80% of organic carbon sedimentation was processed by the deposit-feeding macrofauna at both sites. This model is a first step to help quantify the role of macrofauna in marine coastal ecosystem functioning and biogeochemical cycles and build predictive capacity of the effects of anthropogenic stressors, such as eutrophication and climate change, on coastal ecosystems.
  •  
15.
  • Eilola, K., et al. (författare)
  • Evaluation of biogeochemical cycles in an ensemble of three state-of-the-art numerical models of the Baltic Sea
  • 2011
  • Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 88:2, s. 267-284
  • Tidskriftsartikel (refereegranskat)abstract
    • Three state-of-the-art coupled physical-biogeochemical models, the BAltic sea Long-Term large-Scale Eutrophication Model (BALTSEM), the Ecological Regional Ocean Model (ERGOM), and the Swedish Coastal arid Ocean Biogeochemical model coupled to the Rossby Centre Ocean circulation model (RCO-SCOBI), are used to calculate changing nutrient and oxygen dynamics in the Baltic Sea. The models are different in that ERGOM and RCO-SCOBI are three-dimensional (3D) circulation models while BALTSEM resolves the Baltic Sea into 13 dynamically interconnected and horizontally integrated sub-basins. The aim is to assess the simulated long-term dynamics and to discuss the response of the coupled physical-biogeochemical models to changing physical conditions and nutrient loadings during the period 1970-2005. We compared the long-term seasonal and annual statistics of inorganic nitrogen, phosphorus, and oxygen from hindcast simulations with those estimated from observations. We also studied the extension of hypoxic bottom areas covered by waters with O(2)<2 ml O(2) l(-1) and cod reproductive volumes comprising waters with salinity >11 and O(2)>2 ml O(2) l(-1). The models reproduce much of the nutrient biogeochemical cycling in the Baltic proper. However, biases are larger in the Bothnian Sea and Bothnian Bay. No model shows outstanding performance in all aspects but instead the ensemble mean results are better than or as good as the results of any of the individual models. Uncertainties are primarily related to differences in the bioavailable fractions of nutrient loadings from land and parameterizations of key processes like sediment fluxes that are presently not well known. Also the uncertainty related to the initialization of the models in the early 1960s influence the modeled biogeochemical cycles during the investigated period.
  •  
16.
  • Ekeroth, Nils, et al. (författare)
  • Effects of oxygen on recycling of biogenic elements from sediments of a stratified coastal Baltic Sea basin
  • 2016
  • Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 154, s. 206-219
  • Tidskriftsartikel (refereegranskat)abstract
    • Benthic nutrient dynamics in the coastal basin Kanholmsfjarden, NW Baltic proper, were studied by in situ flux measurements and sediment samplings in 2010-2013. The benthic release of NH4 and DIP from anoxic sediments in Kanholmsfjarden were calculated to renew the standing stock inventories of DIN and DIP in the overlying water in roughly 1 year. Starting in summer 2012, mixing of oxygen-rich water into the deep part of the basin temporarily improved the oxygen conditions in the deep water. During the 1 year oxygenated period, the total phosphorus inventory in the surficial sediment increased by 0.4 g P m(-2) or 65%. This was most likely due to stimulated bacterial P assimilation under oxygenated conditions. By July 2013, the bottom water had again turned anoxic, and DIP and DSi fluxes were even higher than earlier in the study period. These high fluxes are attributed to degradation of sedimentary pools of P and Si that had accumulated during the bottom water oxygenation in 2012. The strong correlation between DIP and DSi fluxes and the similar dynamics of DIP and DSi in the sediment pore water and near bottom water, suggest a similar redox dependency of benthic-pelagic exchange for these nutrients.
  •  
17.
  • Gustafsson, Erik, et al. (författare)
  • Carbon cycling in the Baltic Sea - The fate of allochthonous organic carbon and its impact on air-sea CO2 exchange
  • 2014
  • Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 129, s. 289-302
  • Tidskriftsartikel (refereegranskat)abstract
    • A coupled physical-biogeochemical model (BALTSEM) is used to estimate carbon fluxes in the Baltic Sea over the 1980-2006 period. Budget calculations for organic carbon indicate that of the total allochthonous organic carbon (TOCT) supplied to the system, on average 56% is mineralized, 36% is exported out of the system, and the remainder is buried. River discharge is the main source of dissolved inorganic carbon (DIC) to the Baltic Sea. However, model results indicate that in the Gulf of Bothnia (northern Baltic Sea), the contribution to the DIC stock by TOCT mineralization is of the same order as direct river input of DIC In the Kattegat and Danish Straits (southwestern Baltic Sea) on the other hand, net uptake of atmospheric CO2 comprises the major DIC source. Despite large variations within the system, with net outgassing from some sub-basins and net absorption in others, the Baltic Sea as a whole was estimated to be a net sink for atmospheric CO2. Mineralization of allochthonous dissolved organic carbon (DOCT) influences air-sea CO2 exchange. A sensitivity study indicates that depending on the labile fraction of DOCT, the contribution from CO2 absorption to total external DIC sources can amount to 10-25%.
  •  
18.
  • Gustafsson, Erik, et al. (författare)
  • Future acidification of the Baltic Sea - A sensitivity study
  • 2020
  • Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 211
  • Tidskriftsartikel (refereegranskat)abstract
    • Future acidification of coastal seas will depend not only on the development of atmospheric CO2 partial pressure (pCO(2)), but also on changes in the catchment areas, exchange with the adjacent ocean, and internal cycling of carbon and nutrients. Here we use a coupled physical-biogeochemical Baltic Sea model to quantify the sensitivity of pH to changes both in external forcing and internal processes. The experiments include changes in runoff, supply of dissolved inorganic carbon (DIC) and total alkalinity (A(T)), nutrient loads, exchange between the Baltic and North Seas, and atmospheric pCO(2). We furthermore address the potential different future developments of runoff and river loads in boreal and continental catchments, respectively. Changes in atmospheric pCO(2) exert the strongest control on future pH according to our calculations. This CO2-induced acidification could be further enhanced in the case of desalination of the Baltic Sea, although increased concentrations of A(T) in the river runoff due to increased weathering to some extent could counteract acidification. Reduced nutrient loads and productivity would reduce the average annual surface water pH but at the same time slightly increase wintertime surface water pH (the annual pH minimum). The response time of surface water pH to sudden changes in atmospheric pCO(2) is approximately one month, whereas response times to changes in e.g. runoff and A(T)/DIC loads are more related to residence times of water and salt (> 30 years). It seems unlikely that the projected future increase in atmospheric pCO(2) and associated pH reduction could be fully counteracted by any of the other processes addressed in our experiments.
  •  
19.
  • Gustafsson, Erik, et al. (författare)
  • Modelling the C-13 and C-12 isotopes of inorganic and organic carbon in the Baltic Sea
  • 2015
  • Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 148, s. 122-130
  • Tidskriftsartikel (refereegranskat)abstract
    • In this study, C-12 and C-13 contents of all carbon containing state variables (dissolved inorganic and organic carbon, detrital carbon, and the carbon content of autotrophs and heterotrophs) have for the first time been explicitly included in a coupled physical-biogeochemical Baltic Sea model. Different processes in the carbon cycling have distinct fractionation values, resulting in specific isotopic fingerprints. Thus, in addition to simulating concentrations of different tracers, our new model formulation improves the possibility to constrain the rates of processes such as CO2 assimilation, mineralization, and air-sea exchange. We demonstrate that phytoplankton production and respiration, and the related air-sea CO2 fluxes, are to a large degree controlling the isotopic composition of organic and inorganic carbon in the system. The isotopic composition is further, but to a lesser extent, influenced by river loads and deep water inflows as well as transformation of terrestrial organic carbon within the system. Changes in the isotopic composition over the 20th century have been dominated by two processes the preferential release of C-12 to the atmosphere in association with fossil fuel burning, and the eutrophication of the Baltic Sea related to increased nutrient loads under the second half of the century.
  •  
20.
  • Gutiérrez Loza, Lucia, et al. (författare)
  • Air–sea CO2 exchange in the Baltic Sea—A sensitivity analysis of the gas transfer velocity
  • 2021
  • Ingår i: Journal of Marine Systems. - : Elsevier. - 0924-7963 .- 1879-1573. ; 222
  • Tidskriftsartikel (refereegranskat)abstract
    • Air–sea gas fluxes are commonly estimated using wind-based parametrizations of the gas transfer velocity. However, neglecting gas exchange forcing mechanisms – other than wind speed – may lead to large uncertainties in the flux estimates and the carbon budgets, in particular, in heterogeneous environments such as marginal seas and coastal areas. In this study we investigated the impact of including relevant processes to the air–sea CO2 flux parametrization for the Baltic Sea. We used six parametrizations of the gas transfer velocity to evaluate the effect of precipitation, water-side convection, and surfactants on the net CO2 flux at regional and sub-regional scale. The differences both in the mean CO2 fluxes and the integrated net fluxes were small between the different cases. However, the implications on the seasonal variability were shown to be significant. The inter-annual and spatial variability were also found to be associated with the forcing mechanisms evaluated in the study. In addition to wind, water-side convection was the most relevant parameter controlling the air–sea gas exchange at seasonal and inter-annual scales. The effect of precipitation and surfactants seemed negligible in terms of the inter-annual variability. The effect of water-side convection and surfactants resulted in a reduction of the downward fluxes, while precipitation was the only parameter that resulted in an enhancement of the net uptake in the Baltic Sea.
  •  
21.
  • Humborg, Christoph, et al. (författare)
  • Changes in dissolved silicate loads to the Baltic Sea : The effects of lakes and reservoirs
  • 2008
  • Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 73:3-4, s. 223-235
  • Tidskriftsartikel (refereegranskat)abstract
    • We tested the hypothesis that dissolved silicate (DSi) yields [kg km− 2 yr− 1] of 82 major watersheds of the Baltic Sea can be expressed as a function of the hydraulic load (HL) as a measure of water residence time and the total organic carbon (TOC) concentration, both variables potentially increasing the DSi yield. Most boreal rivers fitted a linear regression model using HL as an independent variable to explain the DSi yield. Rivers with high HL, i.e., shortest residence times, showed highest DSi yields up to 2300 kg km− 2 yr− 1. This is most likely caused by an excess supply of DSi, i.e., the geochemical sources prevail over biological sinks in these boreal watersheds. The DSi yield for regulated and unregulated larger rivers of the boreal watersheds constituting about 40% of the total water discharge and of the total DSi load to the Baltic Sea, respectively, can be expressed as: DSi yield = 190 + 49.5 HL[m yr− 1] + 0.346 TOC [µM] (R2 = 0.80). Since both HL and TOC concentrations have decreased after damming, the DSi yields have decreased significantly in the regulated boreal watersheds, for the River Luleälven we estimated more than 30%. The larger eutrophic watersheds draining cultivated landscape of the southern catchment of the Baltic Sea and representing about 50% of the annual water discharge to the Baltic Sea, deviated from this pattern and showed lower DSi yields between 60–580 kg km− 2 yr− 1. DSi yields showed saturation curve like relationship to HL and it appears that DSi is retained in the watersheds efficiently through biogenic silica (BSi) production and subsequent sedimentation along the entire river network. The relationship between HL and DSi yields for all larger cultivated watersheds was best fitted by a Freundlich isotherm (DSi = 115.7HL109; R2 = 0.73), because once lake and reservoir area exceeds 10% of the watershed area, minimum DSi yields were reached. To estimate an uperturbed DSi yield for the larger eutrophic southeastern watersheds is still difficult, since no unperturbed watersheds for comparison were available. However, a rough estimate indicate that the DSi flux from the cultivated watersheds to the Baltic Sea is nowadays only half the uperturbed flux. Overall, the riverine DSi loads to the Baltic Sea might have dropped with 30–40% during the last century.
  •  
22.
  • Humborg, Christoph, et al. (författare)
  • Silicon and the Baltic Sea Long-term Si decrease in the Baltic Sea - A conceivable ecological risk?
  • 2008
  • Ingår i: Journal of Marine Systems. - : Elsevier. - 0924-7963 .- 1879-1573. ; 73:3-4, s. 221-222
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • Since the pioneering work of Schelske and Stoermer (1971) and Schelske et al., 1983 C.L. Schelske, E.F. Stoermer, D.J. Conley, J.A. Robbins and R.M. Glover, Early eutrophication in the Lower Great-Lakes — new evidence from biogenic silica in sediments, Science 222 (1983), pp. 320–322. View Record in Scopus | Cited By in Scopus (56)Schelske et al. (1983) it has been known that eutrophication of aquatic systems leads to depletion in dissolved silicate (DSi). Early studies on the Nile River have shown that the construction of dams leads to DSi decrease downstream due to the formation of additional deposition sites of biogenic silica (BSi) that was thought to consist mainly of diatoms. In the Baltic Sea there was a perception in the scientific community that DSi concentrations were high and therefore, that DSi concentrations were not limiting for diatom growth. Long-term trend analyses on DSi concentrations in the Baltic have shown decreasing trends in the 1970s and 1980s, whereas similar analysis for the 1990s concluded that DSi concentrations were no longer decreasing, but rather levelling off. Consequently, observations of reduced abundance of diatoms in the early 1990s were attributed to mild winters rather than low DSi concentrations, i.e., a low turbulence regime in the water column favouring non-siliceous algae. However, decadal nutrient trends in the Baltic Sea are significantly influenced by the large and varying internal Si pools in the sediments and deep water masses similar to that described for P dynamics in the Baltic Sea. No one seriously addressed the longer trends in DSi concentrations over the last century, whereas many studies estimated these changes for N and P.The EU funded research project SIBER (Silicate and Baltic Sea Ecosystem Response; EVK3-CT-2002-00069) began in 2002 with the objectives of understanding the major changes in Si dynamics in the Baltic Sea during the last century. The SIBER project addressed various aspects of the biogeochemical Si cycle in the Baltic Sea including constraining Si budgets for the Baltic Sea and its catchment, experiments describing the growth characteristics of Baltic diatoms related to the long-term trends in monitoring data of Baltic Sea diatoms.Si budgets are addressed by several papers in this special issue. Humborg et al. and Sferratore et al. describe riverine Si fluxes. Pastuszak et al. address estuarine Si fluxes. Redfield ratios including DSi and their development in the Baltic Sea are described by Danielsson et al.Possible ecosystem effects of changes in Redfield nutrient ratios are analysed in the paper by Olli et al. who examine phytoplankton responses in the Gulf of Riga and by Wasmund et al. who investigate long-term trends in phytoplankton species in the Kiel Bight. Spilling and Markager describe growth characteristics of Baltic Sea diatoms. Finally, in their paper Conley et al. present a long-term Si budget for the entire Baltic Sea for the first time.The Baltic Sea biogeochemical Si cycle has been fundamentally changed within the last century not only as a consequence of river regulation and lake eutrophication, but also through increases in the sediment accumulation of BSi (Conley et al.). Sediment accumulation of BSi has increased by a factor on 1.9 due to increased diatom growth from marine eutrophication. Results from the SIBER project indicate that DSi concentration were ca. 36 µM a century ago in the Baltic proper compared to ca. 13 µM observed today (Conley et al.). In fact, DSi concentrations have changed much more dramatically compared to N and P regarding the total changes in the available nutrient stocks. Similar changes have occurred in other large water bodies with respect to size and volume, i.e. the North American Great Lakes with long residence times where DSi decreased from 80–100 µM to ca. 25 µM. Surprisingly, such a major change in nutrient inventories has not been reported earlier in this well investigated coastal system. We are only starting to understand the possible ecological consequences, such as the occurrence of different diatom species that are less silicified and its implication for the sedimentation fluxes and carbon flux to benthic communities. The SIBER project has shown that a dramatic change in DSi concentrations is possible within a very short time period, although the situation appears stable today, perhaps since the drivers for this change, i.e. eutrophication and river regulation, have not changed within the last 30 years. However, even a slight increase in N and P loads and/or further damming of rivers may drive the Baltic Sea into Si-limitation.
  •  
23.
  • Håkanson, Lars, et al. (författare)
  • Modelling phosphorus and suspended particulate matter in Ringkobing Fjord to understand regime shifts
  • 2007
  • Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 68:1-2, s. 65-90
  • Tidskriftsartikel (refereegranskat)abstract
    • The focus in this work is on the conditions in Ringkøbing Fjord (Denmark), where there have been major regime shifts during the last 30 years. The regime shift in the 1990s is discussed in this paper and concerns reductions in nutrient input from land and changes in salinity. The changes in these abiotic have drastically influenced the structure and functioning of the ecosystem [e.g., in phytoplankton production, water clarity, macrophyte cover and biomass of clams]. This work concerns the modelling and understanding of such changes and the aim is also to consider patterns in variability in the data that may explain the regime shift. The model used is a general, dynamic process-based mass-balance model for total phosphorus (TP) and suspended particulate matter (SPM). The model uses ordinary differential equations (the ecosystem scale). The calculation time is 1 month to reflect seasonal variations. We quantify, e.g., sedimentation, resuspension, diffusion, mixing and retention. The model has previously been tested for coastal areas of different character and shown to predict TP, SPM, Secchi depth, chlorophyll and the oxygen saturation in the deep-water zone very well (within the uncertainty bands of the empirical data). We show that the model, with new calculation routines for macrophytes and clams, also describes the conditions in Ringkøbing Fjord well, which means that the model is a useful general tool for interpretations of changes in coastal ecosystems. The model is simple to apply in practice since all driving variables may be readily accessed from maps or regular monitoring programs.
  •  
24.
  • Isaev, A. V., et al. (författare)
  • Model estimates of the impact of bioirrigation activity of Marenzelleria spp. on the Gulf of Finland ecosystem in a changing climate
  • 2017
  • Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 171, s. 81-88
  • Tidskriftsartikel (refereegranskat)abstract
    • Drastic changes have occurred in the Eastern Gulf of Finland ecosystem after recent invasion and establishment of polychaete Marenzelleria spp. Possible mechanisms of these changes are explored with the help of three-dimensional ecosystem model SPBEM. Relative significance of bioirrigation activity is studied by comparison of two climate change scenario simulations, which include or disregard Marenzelleria effects. The novel results obtained with this approach demonstrate that on a system level biogeochemical consequences of both implemented climate changes scenario and polychaete activity are equivalent to a weakening of vicious circle of the Baltic Sea eutrophication. The eutrophication-mitigating effects of the Marenzelleria invasion into the Eastern Gulf of Finland, revealed by the long-term field measurements, are explained by simulation-based considerations.
  •  
25.
  • Johansson, Olov, et al. (författare)
  • Variation of groundwater salinity in the partially irrigated Amudarya river delta, Uzbekistan
  • 2009
  • Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 76:3, s. 287-295
  • Tidskriftsartikel (refereegranskat)abstract
    • The Amudarya delta region contains surface and groundwater resources that discharge into the shrinking Large Aral Sea and ultimately control its future fate. These freshwater resources are prerequisites for sustaining the population of the region. However, salinization and pollution caused by agricultural irrigation is a key problem for these water systems. Here, we report results from a recent field measurement campaign conducted during April 2005 which included 24 monitoring wells located in an irrigated region of the Amudarya delta, thereby extending the historical data set of groundwater levels and salinity measurements. This data set is combined with corresponding data from a downstream, non-irrigated region that was formerly irrigated (together covering 16,100km2 between the Uzbek cities of Nukus and Muynak). This comparison shows that in the downstream region, which is currently not irrigated, shallow groundwaters are far more saline (average 23g l− 1) than the currently irrigated region (average 3g l− 1). We estimate that the unconfined aquifer within the 13,500km2 non-irrigated zone of study area contains 9billion tons of salt, or almost as much salt as the entire Aral Sea (containing 11billion tons of salt and covering an area of 20,000km2 in year 2000). Within the non-irrigated zone, there are statistically significant large-scale spatial correlations between groundwater salinity and distance to the Amudarya River, irrigation canals and surface water bodies when distance is measured along the modelled regional groundwater flow direction. Generally, groundwater salinities are lower downstream of surface water bodies in the non-irrigated zone. Annual fluctuations in groundwater salinity are too large to be explained by input from surface water (Amudarya) or wind-blown salt from the dried Aral Sea sediments. Salt transport by groundwater is the only plausible remaining explanation for these changes.
  •  
26.
  • Jönsson, Anders, et al. (författare)
  • Evaluation of the Stockholm archipelago, northwestern Baltic Sea proper, as a trap for freshwater-runoff organic carbon
  • 2005
  • Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 56:1-2, s. 167-178
  • Tidskriftsartikel (refereegranskat)abstract
    • Time-series data on the freshwater inflow of total organic carbon (TOC) to the Stockholm Archipelago, Baltic Sea, covering four full years, showed a distinct seasonal pattern with six times higher monthly flow in winter–spring than in the summer with an annual freshwater TOC input of 28 Gg year−1. Estimation of burial flux and source apportionment of sedimentary OC in the Inner Archipelago (IA) was based on extensive sediment sampling of seismically surveyed accumulation bottom areas. The resulting IA-averaged OC content was 56±16 mg g dw−1 sediment, yielding an IA-wide bottom sediment deposition for the 1992–1995 period of 3.1 Gg year−1. The sediments in the eastern Lake Mälaren (LM), IA, and Outer Archipelago (OA) were geochemically distinguishable based on their stable carbon isotope signatures (δ13C). The δ13C values were −28.2±0.6, −25.4±1.0, and −23.6±0.3, respectively, for LM (n=15), IA (n=17), and OA (n=31). These spatial trends were consistent with the C:N ratios, which were 9.96±1.2, 9.29±0.73, and 9.13±0.22 for the same subsystems. Using a simple isotopic mass balance model, it was deduced that about one-third (39%) of the OC burial in the IA sediments was of Lake Mälaren runoff origin. Hence, a low archipelago-trapping efficiency of only 4% for the runoff TOC was found to be accumulating in the sediments underlying the approximately 30 km transect through the IA eastward of Stockholm. This scenario suggests that the organic matter and associated substances added by the Lake Mälaren outflow, passing through urban Stockholm, are largely either remineralised and released to the IA water column, or transported with the currents to more pristine offshore Baltic ecosystems.
  •  
27.
  • Kari, Elina, et al. (författare)
  • Development of under-ice stratification in Himmerfjärden bay, north-western Baltic proper, and their effect on the phytoplankton spring bloom
  • 2018
  • Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 186, s. 85-95
  • Tidskriftsartikel (refereegranskat)abstract
    • Seasonal sea ice cover reduces wind-driven mixing and allows for under-ice stratification to develop. These under-ice plumes are a common phenomenon in the seasonal sea ice zone. They stabilize stratification and concentrate terrestrial runoff in the top layer, transporting it further offshore than during ice-free seasons. In this study, the effect of sea ice on spring stratification is investigated in Himmerfjärden bay in the NW Baltic Sea. Distinct under-ice plumes were detected during long ice seasons. The preconditions for the development of the under-ice plumes are described as well as the typical spatial and temporal dimensions of the resulting stratification patterns. Furthermore, the effect of the under-ice plume on the timing of the onset and the maximum of the phytoplankton spring bloom were investigated, in terms of chlorophyll-a (Chl-a) concentrations. At the head of the bay, bloom onset was delayed on average by 18 days in the event of an under-ice plume. However, neither the maximum concentration of Chl-a nor the timing of the Chl-a maximum were affected, implying that the growth period was shorter with a higher daily productivity. During this period from spring bloom onset to maximum Chl-a, the diatom biomass was higher and Mesodinium rubrum biomass was lower in years with under-ice plumes compared to years without under-ice plumes. Our results thus suggest that the projected shorter ice seasons in the future will reduce the probability of under-ice plume development, creating more dynamic spring bloom conditions. These dynamic conditions and the earlier onset of the spring bloom seem to favor the M. rubrum rather than diatoms.
  •  
28.
  • Kononets, Mikhail Y, 1978, et al. (författare)
  • In situ incubations with the Gothenburg benthic chamber landers : Applications and quality control
  • 2021
  • Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 214
  • Tidskriftsartikel (refereegranskat)abstract
    • In situ incubations of sediment with overlying water provide valuable and consistent information about benthic fluxes and processes at the sediment-water interface. In this paper, we describe our experiences and a variety of applications from the last 14 years and 308 deployments with the Gothenburg benthic chamber lander systems. We give examples of how we use sensor measurements for chamber leakage control, in situ chamber volume determination, control of syringe sampling times, sediment resuspension and stirring quality. We present examples of incubation data for in situ measurements of benthic fluxes of oxygen, dissolved inorganic carbon, nutrients, metals and gases made with our chamber landers, as well as manipulative injection experiments to study nitrogen cycling (injections of N-15 nitrate), phosphate retention (injections of marl suspension) and targeted sediment resuspension. Our main goal is to demonstrate the possibilities that benthic chamber lander systems offer to measure solute fluxes and study processes at the sediment-water interface. Based on our experience, we recommend procedures to be used in order to obtain high quality data with benthic chamber landers.
  •  
29.
  • Kumar Das, Supriyo, et al. (författare)
  • Connecting pigment composition and dissolved trace elements to phytoplankton population in the southern Benguela Upwelling zone (St. Helena Bay)
  • 2017
  • Ingår i: Journal of Marine Systems. - : ELSEVIER SCIENCE BV. - 0924-7963 .- 1879-1573. ; 176, s. 13-23
  • Tidskriftsartikel (refereegranskat)abstract
    • Rich in upwelled nutrients, the Southern Benguela is one of the most productive ecosystems in the world ocean. However, despite its ecological significance the role of trace elements influencing phytoplankton population in the Southern Benguela Upwelling System (SBUS) has not been thoroughly investigated. Here, we report pigment composition, macronutrients (nitrate, phosphate and silicate) and concentrations of dissolved Cd, Co, Fe and Zn during late austral summer and winter seasons in 2004 to understand the relationship between the selected trace elements and phytoplankton biomass in St. Helena Bay (SHB), which falls within the southern boundary of the SBUS. Chlorophyll a concentrations indicate higher phytoplankton biomass associated with high primary production during late summer in SHB where high diatom population is inferred from the presence of fucoxanthin. Diminished phytoplankton biomass and a shift from diatoms to dinoflagellates as the dominant phytoplankton taxa are indicated by diagnostic pigments during late winter. Dissolved trace elements (Cd, Co and Zn) and macronutrients play a significant role in phytoplankton biomass, and their distribution is affected by biological uptake and export of trace elements. Continuous uptake of Zn by diatoms may cause an onset of Zn depletion leading to a period of extended diatom proliferation during late summer. Furthermore, the transition from diatom to dinoflagellate dominated phytoplankton population is most likely facilitated by depletion of trace elements (Cd and Co) in the water column.
  •  
30.
  • Laznik, M, et al. (författare)
  • Riverine input of nutrients to the Gulf of Riga - temporal and spatial variation
  • 1999
  • Ingår i: Journal of Marine Systems. - 0924-7963 .- 1879-1573. ; 23:1-3, s. 11-25
  • Tidskriftsartikel (refereegranskat)abstract
    • Riverine transport is the, most important pathway for input of nutrients to the Gulf of Riga. The present study focused on updating existing estimates of the riverine nutrient contributions and on improving the favailable information on temporal and spatial variation in such input. The results show that the gulf received an average of 113,300 tons of nitrogen, 2050 tons of phosphorus and 64,900 tons of dissolved silica (DSi) annually during the time period 1977-1995. There was large interannual variation in loads, e.g., a factor two difference was found between the two most extreme years (1984 and 1990), this was attributed mainly to natural variation in water discharge. The seasonal distribution of nutrient loads exhibited a distinct pattern for practically all studied constituents, especially nitrate. Loads were high during the spring-flow and relatively low during the low-flow summer period. Examination of the spatial variation of nutrient loads showed that the Daugava River alone accounted for approximately 60% of the total riverine load. The highest area-specific loads of nitrate and phosphate were observed in the agriculturally dominated Lielupe River, and the highest loads of organic-nitrogen (org-N) and total phophorus (tot-P) were found in the Parnu River. However, the values for all the studied rivers and constituents were rather low (phosphorus) or moderate (nitrogen and silica) compared to those reported for many other drainage areas of the Baltic Sea. This was true despite the inefficient sewage treatment and intensive agriculture in the studied basins in the 1970s and 1980s. (C) 1999 Elsevier Science B.V. All rights reserved.
  •  
31.
  • Lehtoranta, Jouni, et al. (författare)
  • Atmospheric forcing controlling inter-annual nutrient dynamics in the open Gulf of Finland
  • 2017
  • Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 171, s. 4-20
  • 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.
  •  
32.
  • Limburg, Karin E., et al. (författare)
  • In search of the dead zone : Use of otoliths for tracking fish exposure to hypoxia
  • 2015
  • Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 141, s. 167-178
  • Tidskriftsartikel (refereegranskat)abstract
    • Otolith chemistry is often useful for tracking provenance of fishes, as well as examining migration histories. Whereas elements such as strontium and barium correlate well with salinity and temperature, experiments that examine manganese uptake as a function of these parameters have found no such correlation. Instead, dissolved manganese is available as a redox product, and as such, is indicative of low-oxygen conditions. Here we present evidence for that mechanism in a range of habitats from marine to freshwater, across species, and also present ancillary proxies that support the mechanism as well. For example, iodine is redox-sensitive and varies inversely with Mn; and sulfur stable isotope ratios provide evidence of anoxic sulfate reduction in some circumstances. Further, S may be incorporated trophically whereas other elements appear to be taken up directly from water. This research suggests a potential means to identify individual fish exposure to hypoxia, over entire lifetimes. With further testing and understanding, in the future fish may be able to be used as "mobile monitors" of hypoxic conditions. (C) 2014 The Authors. Published by Elsevier B.V.
  •  
33.
  • Medina-Silva, Renata, et al. (författare)
  • Microbial diversity from chlorophyll maximum, oxygen minimum and bottom zones in the southwestern Atlantic Ocean
  • 2018
  • Ingår i: Journal of Marine Systems. - : Elsevier. - 0924-7963 .- 1879-1573. ; 178, s. 52-61
  • Tidskriftsartikel (refereegranskat)abstract
    • Conspicuous physicochemical vertical stratification in the deep sea is one of the main forces driving microbial diversity in the oceans. Oxygen and sunlight availability are key factors promoting microbial diversity throughout the water column. Ocean currents also play a major role in the physicochemical stratification, carrying oxygen down to deeper zones as well as moving deeper water masses up towards shallower depths. Water samples within a 50-km radius in a pockmark location of the southwestern Atlantic Ocean were collected and the prokaryotic communities from different water depths - chlorophyll maximum, oxygen minimum and deep-sea bottom (down to 1355 m) - were described. At phylum level, Proteobacteria were the most frequent in all water depths, Cyanobacteria were statistically more frequent in chlorophyll maximum zone, while Thaumarchaeota were significantly more abundant in both oxygen minimum and bottom waters. The most frequent microorganism in the chlorophyll maximum and oxygen minimum zones was a Pelagibacteraceae operational taxonomic unit (OTU). At the bottom, the most abundant genus was the archaeon Nitrosopurnilus. Beta diversity analysis of the 16S rRNA gene sequencing data uncovered in this study shows high spatial hetero-geneity among water zones communities. Our data brings important contribution for the characterisation of oceanic microbial diversity, as it consists of the first description of prokaryotic communities occurring in different oceanic water zones in the southwestern Atlantic Ocean.
  •  
34.
  • Müller-Karulis, Bärbel, et al. (författare)
  • Modeling the long-term dynamics of nutrients and phytoplankton in the Gulf of Riga
  • 2011
  • Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 87:3-4, s. 161-176
  • Tidskriftsartikel (refereegranskat)abstract
    • The long term dynamics of nitrogen, phosphorus, and phytoplankton in the Gulf of Riga were simulated with a biogeochemical box model that resolved seasonal cycles. The model was calibrated using a numerical optimization procedure that adjusted 37 parameters to maximize the model data fit for field observations from 1973 to 2000 and validated with an independent dataset covering 2001-2007. Both the long-term increase and subsequent decline in winter nitrogen concentrations, as well as the continuous increase in winter phosphate levels were well reproduced by the model, which also gave reasonable representations of the seasonal dynamics of nutrients and phytoplankton. Starting from the mid-1990s, the model simulated an increase in cyanobacteria growth sustained by internal phosphorus loading. While nitrogen was efficiently removed by denitrification from the Gulf of Riga, comparatively slow export to the Baltic Proper was the main removal pathway of phosphorus. Modeled residence times were 5.4 years for nitrogen and 38 years for phosphorus. Scenario simulations indicated that the Gulf of Riga responds to phosphorus load reductions with a gradual decrease in primary production and cyanobacteria growth, while the effect of nitrogen load reductions is largely offset by nitrogen fixation.
  •  
35.
  • Norman, Maria, 1973-, et al. (författare)
  • Impact of improved air–sea gas transfer velocity on fluxes and water chemistry in a Baltic Sea model
  • 2013
  • Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 111, s. 175-188
  • Tidskriftsartikel (refereegranskat)abstract
    • The air–sea exchange of gases is largely controlled by the efficiency of the transfer across the interface (parameterized by the transfer velocity). A biogeochemical model of the Baltic Sea is used to study the impact of an improved formulation of the transfer velocity on the air–sea fluxes and water chemistry. Two parameterizations using the concept of resistance are applied in the model for calculating carbon dioxide and oxygen air–sea fluxes. One parameterization includes the water-side convection, which has demonstrated to increase the transfer velocity during unstable atmospheric stratification and at great mixing depths. Including the water-side convection changes the seasonal cycle of CO2 and O2 fluxes, although the changes are relatively small due to feedback processes in the model. When not taking the feedback processes into account, the impact of water-side convection on the fluxes is significantly greater, with a maximum difference in the order of 20%. The vertical water profiles are also slightly modified when including water-side convection, the accumulated effect being greatest in the deeper part of the basin. Furthermore, CO2 uptake and O2 emissions decrease by 6.5% and 4.5%, respectively, when water-side convection is included in the model. Compared to the great difference between previous studies, the differences between the model runs in the present study are small, indicating that the choice of formulation for the transfer velocity in a model is not crucial although it is more physically correct.
  •  
36.
  • Pastuszak, Marianna, et al. (författare)
  • Silicon dynamics in the Oder estuary, Baltic Sea
  • 2008
  • Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 73:3-4, s. 250-262
  • Tidskriftsartikel (refereegranskat)abstract
    • Studies on dissolved silicate (DSi) and biogenic silica (BSi) dynamics were carried out in the Oder estuary, Baltic Sea in 2000-2005. The Oder estuary proved to be an important component of the Oder River-Baltic Sea continuum where very intensive seasonal DSi uptake during spring and autumn, but also BSi regeneration during summer take place. Owing to the regeneration process annual DSi patterns in the river and the estuary distinctly differed; the annual patterns of DSi in the estuary showed two maxima and two minima in contrast to one maximum- and one minimum-pattern in the Oder River. F)Si concentrations in the river and in the estuary were highest in winter (200-250 mu mol dm(-3)) and lowest (often less than 1 mu mol dm(-3)) in spring, concomitant with diatom growth; such low values are known to be limiting for new diatom growth. Secondary DSi summer peaks at the estuary exit exceeded 100 mu mol dm(-3), and these maxima were followed by autumn minima coinciding with the autumn diatom bloom. Seasonal peaks in BSi concentrations (ca. 100 mu mol dm(-3)) occurred during the spring diatom bloom in die Oder River. Mass balance calculations of DSi and BSi showed that DSi + BSi import to the estuary over a two year period was 103.2 kt and that can be compared with the DSi export of 98.5 kt. The difference between these numbers gives room for ca. 2.5 kt BSi to be annually exported to the Baltic Sea. Sediment cores studies point to BSi annual accumulation on the level of 2.5 kt BSi. BSi import to the estuary is on the level of ca. 10.5 kt, thus ca. 5 kt of BSi is annually converted into the DSi, increasing the pool of DSi that leaves the system. BSi concentrations being ca. 2 times higher at the estuary entrance than at its exit remain in a good agreement with the DSi and BSi budgeting presented in the paper.
  •  
37.
  • Rutgersson, Anna, 1971-, et al. (författare)
  • Enhancement of CO2 transfer velocity due to water-side convection
  • 2010
  • Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 80:1-2, s. 125-134
  • Tidskriftsartikel (refereegranskat)abstract
    • The exchange of CO2 between ocean and atmosphere is controlled by the air-sea difference in partial pressure of CO2 and by the efficiency of the transfer processes, the efficiency can be represented by a resistance of the surface and expressed by transfer velocity, k.Measurements made at the Östergarnsholm field station in the Baltic Sea indicate that the CO2 transfer velocity is also a function not only of wind speed, but also of the mixed-layer depth of the water and, to a lesser degree, of the stratification of the atmosphere. The transfer velocity is significantly enhanced by a large mixed-layer depth, the enhancement increasing as the surface cooling increases. The impact of mixed layer depth is expressed by the convective velocity scale of the water (analogous to atmospheric convective scaling).Enhancement due to convection is an important factor affecting the diurnal cycle of air-sea fluxes. Large air-sea temperature differences also occur due to air mass advection. Here water-side convection at wind speeds between 2.5 and 6.5 m s-1 is investigated.The enhancement due to convection can be added to the traditional transfer velocity.
  •  
38.
  • Rutgersson, Anna, 1971-, et al. (författare)
  • The annual cycle of carbon dioxide and parameters influencing the air-sea carbon exchange in the Baltic Proper
  • 2008
  • Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 74:1-2, s. 381-394
  • Tidskriftsartikel (refereegranskat)abstract
    • A land-based field station, two moored buoys and data from the Finnpartner ship were used to investigate the variability of the air-sea CO2-flux and parameters controlling the flux during one year in the Baltic Sea region.The agreement between the sea surface partial pressure of CO2 measured near the tower and from the ship in the central parts of the Baltic Proper was relatively good during most of the period.But, during periods with intense biological activity or strong upwelling there were significant differences.The flux of CO2 was measured with the eddy-correlation method.The transfer velocity was calculated from the flux measurements and the instrumental uncertainty in calculations of the hourly values of transfer velocity was of the order of 20%.The calculated value of the transfer velocity increased with increasing the wind speed.The relation showed, however, great scatter and no clear wind-dependent relation could be determined.It was shown that for the measured flux and for transfer velocities estimated from measurements it is important to know the variability of pCO2w in the footprint area.This is of particular importance when investigating the processes influencing the flux.When calculating the air-sea flux of CO2 the greatest uncertainty is in the determination of the transfer velocity, but it was shown that also the partial pressure of CO2 in the surface water is crucial to determine with good accuracy.
  •  
39.
  • Sanchez-Garcia, Laura, et al. (författare)
  • Geochemical signature in off-shore sediments from the Gulf of Cadiz inner shelf Sources and spatial variability of major and trace elements
  • 2010
  • Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 80:04-mar, s. 191-202
  • Tidskriftsartikel (refereegranskat)abstract
    • The geochemical characterization of 15 surficial sediments from the Gulf of Cadiz (GoC) inner shelf was assessed by examining their granulometric, mineralogic and major-minor elemental composition, in order to evaluate the sources of contaminants and describe environmental conditions. The study involved the comparison of the geochemical signature of the shelf sediments with that of surficial sediments from the main fluvial systems of the region: Guadiana, Piedras, Tinto and Odiel. Although the major supply of sedimentary material in this area is discharged by the Guadiana River, the high absolute concentration of elements associated to sulphide deposits (P, As, Cu, Hg, Pb and Zn) observed in some sediments indicated the important influence of the historically polluted Tinto-Odiel fluvial system in certain locations. The significant levels (>99%) of positive correlation observed between Al, Fe, K, Ni, V and, in a lesser extent, Na and Ba, suggested the association of these elements in the form of aluminous clay minerals. No correlation was observed between Al and Si (0.20), in contrast to the strong positive correlation found for the latter and Ti (0.91). On the other hand, an inverse relationship occurred between terrigenous-detrital sources and carbonate fractions, presumably related to biogenic origins, according to the significant negative correlations (> 99%) observed for Si, respect to Ca (-0.82), Mg (-0.96) and total inorganic carbon (-0.81). The general enrichment of As, Cu, Hg, Pb and Zn detected in the shelf sediments, together with strong and moderate positive correlations observed among these metals and P, Suggested a common origin for all these elements, potentially related to pollutant-anthropogenic activities developed in the industrial area of Huelva city. Those sediments situated closer to the Tinto-Odiel mouth displayed enrichment factors (EF) equal or higher than 2 for As, Cu, Hg, Pb and Zn, particularly evident in one sample (S7), which showed EF of 2.7, 18.7, 8.7, 4.0 and 5.7, respectively. Cluster and Principal Components Analyses allowed us to differentiate four groups of shelf sediments governed by similar geochemical patterns: (i) a first group including the sediments under the Guadiana river influence, formed by coarser siliclastic sediments, with dominant terrigenous-detrital signatures and enrichment of Co and Mn: (ii) a second group of off-shore muddy sediments. Ni-associated, showing moderate enrichment of Cu, Hg, Pb and Zn, as well as important contribution of carbonate forms, which represent the transition towards a dominant marine source; (iii) sample S7, formed by muddy materials and enriched in sulphide associated-heavy metals and phosphorous, according to its proximity to the Tinto-Odiel fluvial system; and (iv) the coarsest sample S13, with high concentration of carbonates and moderate enrichment of heavy metals, which reflects a mixed signature between the detritic influence from Guadiana and Piedras rivers and marine-biogenic sources.
  •  
40.
  • Sandman, Antonia, et al. (författare)
  • Spatial predictions of Baltic phytobenthic communities : Measuring robustness of generalized additive models based on transect data
  • 2008
  • Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 74:Supplement 1, s. S86-S96
  • Tidskriftsartikel (refereegranskat)abstract
    • The spatial distributions of benthic surface sediments and phytobenthic plant species were modelled at a high spatial resolution using generalized additive models together with field data from diving transects. The efficiency of different modelling options was validated using independent datasets, and model fit versus predictive power was analysed. For rock/boulder, sand and mud/clay increasing complexity of the model resulted in higher Reciever Operating Characteristics (ROC) values for the model fit, but lower ROC values for the independent validation. The same pattern was found for hard substrate algae species, whereas it was not true for the rooted plant species. As high model ROC values were often found to be connected to low predictive power of the models, this implies that internal model validation results should be treated cautiously. In general, the models should be kept simple, as the performance of the explanation model increases with increasing complexity, while the predictive power of the model generally decreases. Only by using external validation datasets, the true predictive capacity of an explanation model can be reliably measured, as internal validation schemes tend to over-estimate model performance. Our results also indicate that the Akaike Information Criterion is a more reliable model selection method than Cross-selection when there are few predictor variables.
  •  
41.
  • Schneider, Bernd, et al. (författare)
  • Control of the mid-summer net community production and nitrogen fixation in the central Baltic Sea : An approach based on pCO2 measurements on a cargo ship
  • 2014
  • Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 136, s. 1-9
  • Tidskriftsartikel (refereegranskat)abstract
    • Automated measurements of the surface CO2 partial pressure, pCO2, were performed since 2003 on a cargo ship along a transect between Helsinki in the Gulf of Finland and Lübeck/Gdynia in the southwest of the Baltic Sea. The temporal and spatial resolution of the measurements amounted to 2–4 days and about 2 nautical miles, respectively. Based on temperature and salinity records and on the mean alkalinity, the total CO2 concentrations, CT, were calculated from the mean pCO2 in the northeastern Gotland Sea. The CT data were used to establish a CO2 mass balance for the period from mid-June to the beginning of August in 2005, 2008, 2009 and 2011. Taking into account the air–sea CO2 gas exchange, the mass balance yielded the net organic matter (Corg) production which is fuelled by nitrogen fixation at this time of the year. Several production events were detected with rates up to 8 μmol-C L− 1 d− 1. The production rates were not related to temperature, but showed a distinct correlation with the rate of the temperature increase. This led to the conclusion that the exposure of nitrogen fixing cyanobacteria to irradiance is the dominating control for the Corg production. Therefore, we suggest using the ratio of irradiance to the mixed layer depth as a variable for the parameterization of nitrogen fixation in biogeochemical models. The Corg production and thus the nitrogen fixation rates remained almost constant as long as continuous rising temperatures indicated favorable irradiation conditions. A limitation of the rates by phosphate or any other factor could not be detected. Based on the C/N ratio of particulate organic matter during a cyanobacteria bloom, the Corg production was used to estimate the mid-summer nitrogen fixation. The values varied from 102 mmol m− 2 to 214 mmol m− 2 (mean: 138 mmol m− 2) for the different years and did not show any correlation with the phosphate excess after the spring nitrate depletion.
  •  
42.
  • Sferratore, Agata, et al. (författare)
  • Modelling nutrient fluxes from sub-arctic basins : Comparison of pristine vs. dammed rivers
  • 2008
  • Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 73:3-4, s. 236-249
  • Tidskriftsartikel (refereegranskat)abstract
    • The deterministic Riverstrahler model of river functioning is applied for the first time to sub-arctic catchments. Seasonal nutrient (N, P, Si) deliveries to the coastal zone are simulated, and nutrient annual fluxes are established for the nearly pristine river Kalix (hereafter called Kalixalven) and the heavily dammed river Lule, (hereafter called Lulealven) both located in Northern Sweden and draining into the Bothnian Bay, Baltic Sea. For Kalixalven simulations are performed with a runoff calculated from precipitation, evapo-transpiration and temperature data for the period 1990-1999, using a hydrological model calibrated on observed monthly discharges at the river outlet. The same hydrological parameters are used to calculate specific runoff for the Lulealven basin in absence of dam regulation. Reservoir filling and emptying are simulated using a simplified representation of their management rules. Diffuse sources of nutrient are evaluated according to land cover of the catchment. The simulated seasonal trends are within the range of the observed data, in particular for discharge, dissolved silica, total phosphorus, inorganic nitrogen and total organic carbon. Specific runoff is 50% higher in the Lulealven than in the Kalixalven watershed due to higher altitudes and precipitations. Average silica, nitrate and phosphorus concentrations are much lower in Lulealven than in Kalixalven. Comparison of model results for the Lulealven with and without dams shows a reduction of respectively 25% and 30% in silica and phosphorus fluxes delivered at the outlet, while nitrogen delivery is increased by 10% in the dammed vs. undammed river system. The model allows assessing the respective role of reservoir trapping of nutrient in the reservoir through algal uptake and sedimentation, and of changes in the vegetation induced by flooding the valley formerly covered by forests and wetlands.
  •  
43.
  • Skogen, Morten D., et al. (författare)
  • Eutrophication status of the North Sea, Skagerrak, Kattegat and the Baltic Sea in present and future climates : A model study
  • 2014
  • Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 132, s. 174-184
  • Tidskriftsartikel (refereegranskat)abstract
    • A method to combine observations and an ensemble of ecological models has been used to assess eutrophication. Using downscaled forcing from two GCMs under the A1B emission scenario, an assessment of the eutrophication status was made for a control (19702000) and a future climate (20702100) period. By using validation results from a hindcast to compute individual weights between the models, an assessment of eutrophication is done using a set of threshold values. The final classification distinguishes between three categories: problem area, potential problem area, and non-problem area, in accordance with current management practice as suggested by the Oslo and Paris Commissions (OSPAR) and the Helsinki Commission (HELCOM). For the control run the assessment indicates that the Kattegat, the Danish Straits, the Gulf of Finland, the Gotland Basin as well as main parts of the Arkona Basin, the Bornholm Basin, and the Baltic proper may be classified as problem areas. The main part of the North Sea and also the Skagerrak are non-problem areas while the main parts of the Gulf of Bothnia, Gulf of Riga and the entire southeastern continental coast of the North Sea may be classified as potential problem areas. In the future climate scenarios most of the previous potential problem areas in the Baltic Sea have become problem areas, except for the Bothnian Bay where the situation remain fairly unchanged. In the North Sea there seems to be no obvious changes in eutrophication status in the projected future climate.
  •  
44.
  • Svedén, Jennie B., 1980-, et al. (författare)
  • The bloom of nitrogen-fixing cyanobacteria in the northern Baltic Proper stimulates summer production
  • 2016
  • Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 163, s. 102-112
  • Tidskriftsartikel (refereegranskat)abstract
    • In the northern Baltic Sea Proper, total nitrogen (TN) increases during the summer bloom of filamentous heterocystous cyanobacteria. To follow the fate of the nitrogen they fix, we studied several N fractions during the bloom. We measured cyanobacterial biomass, TN, particulate organic N (PON, two size fractions), dissolved organic N (DON), and PON sedimentation in two areas in 2011. TN increased mainly due to increasing PON, but also to DON. Cyanobacteria contributed about 20% of the PON increase and ~ 10% of the TN increase. About half the PON changes (increase, then decrease) could be explained by the sum of cyanobacteria, other autotrophs (> 2 μm) and zooplankton, indicating that the bloom stimulates primary and secondary production. TN decreased after the bloom mainly due to declining PON > 10 μm, but sedimentation rates did not increase and could explain little of the post-bloom N-loss. There was little settling of undecomposed cyanobacteria.The seasonal development of Aphanizomenon sp. and N pools was similar among stations and areas. For Nodularia spumigena between-station variability increased once patchy surface accumulations developed. A brief Dolichospermum spp. bloom indicated that sampling frequency may be more important than spatial resolution for capturing dynamics of this bloom.
  •  
45.
  •  
46.
  • Timmermann, Karen, et al. (författare)
  • Modelling macrofaunal biomass in relation to hypoxia and nutrient loading
  • 2012
  • Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 105-108, s. 60-69
  • Tidskriftsartikel (refereegranskat)abstract
    • Nutrient loading of aquatic ecosystems results in more food for benthic macrofaunal communities but also increases the risk of hypoxia, resulting in a reduction or complete loss of benthic biomass. This study investigates the interaction between eutrophication, hypoxia and benthic biomass with emphasis on the balance between gains and loss of benthic biomass due to changes in nutrient loadings. A physiological fauna model with 5 functional groups was linked to a 3D coupled hydrodynamic-ecological Baltic Sea model. Model results revealed that benthic biomass increased between 0 and 700% after re-oxygenating bottom waters. Nutrient reduction scenarios indicated improved oxygen concentrations in bottom waters and decreased sedimentation of organic matter up to 40% after a nutrient load reduction following the Baltic Sea Action Plan. The lower food supply to benthos reduced the macrofaunal biomass up to 35% especially in areas not currently affected by hypoxia, whereas benthic biomass increased up to 200% in areas affected by eutrophication-induced hypoxia. The expected changes in benthic biomass resulting from nutrient load reductions and subsequent reduced hypoxia may not only increase the food supply for benthivorous fish, but also significantly affect the biogeochemical functioning of the ecosystem.
  •  
47.
  • Wesslander, Karin, 1976, et al. (författare)
  • Observed carbon dioxide and oxygen dynamics in a Baltic Sea coastal region
  • 2011
  • Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 86:1-2, s. 1-9
  • Tidskriftsartikel (refereegranskat)abstract
    • In April 2006, diurnal variations of carbon dioxide (CO2) and oxygen (O2) in the surface water east of Gotland in the Baltic Sea were investigated with a unique multitechnology approach. Several parameters were measured simultaneously providing an overviewof the CO2 system.Moored instrumentswere continuously recording partial pressure of CO2 in the surface water (pCO2 w), currents,mixing,waves, salinity, temperature and O2. Measurements of total alkalinity (AT) and dissolved inorganic carbon (CT) were taken from R/V Skagerak. These measurements were converted to pCO2 w to support the continuous pCO2 w data and also calculate the air–sea exchange of CO2. Additionally, the time derivatives of O2 and CT concentrations in the water were determined using incubations and a Productivity Autosampler (PA). O2 and pCO2 w were significantly anti-correlated and periods dominated of either biological processes, mixing, air–sea exchange or a combination of these were detected. O2 and pCO2 w had a daily cycle and variations occurred on the 1 h time scale. In April 2006, the seawas a CO2 sink and the averaged parameterized air–sea exchange was −1.0±0.6 mmol m−2 h−1.
  •  
48.
  • Rahm, Lars, et al. (författare)
  • Nitrogen fixation in the Baltic proper : An empirical study
  • 2000
  • Ingår i: Journal of Marine Systems. - 0924-7963. ; 25:3-4, s. 239-248
  • Tidskriftsartikel (refereegranskat)abstract
    • Nitrogen as the limiting nutrient for primary production in the eutrophic Baltic proper has been under debate. Based on only a limited number of actual measurements, nitrogen fixation has been assumed to be the only significant internal nitrogen source. It is then assumed that about one fifth of the net nitrogen load to the Baltic proper comes from nitrogen fixation by cyanobacteria. An alternative or additional source is utilisation of dissolved organic nitrogen (DON). In the present study, we hypothesise that nitrogen fixation is the only internal source for inorganic nitrogen. This was done in order to investigate its potential to maintain net primary production during summer. If inorganic nitrogen is depleted after the spring bloom and if inorganic phosphorus still remains in significant concentrations, then a continuous decrease in phosphorus may be coupled to the net nitrogen fixation rate by cyanobacteria. The estimated phosphorus consumption is adjusted for external and internal inputs. An estimate of the assumed net annual nitrogen fixation based on the proper Redfield ratio in the surface layer down to the seasonal thermocline is calculated for a number of monitoring stations in the Baltic proper. Typical values of nitrogen fixation are in the range 10–130 μmol m−3 day−1. A simple integration over the Baltic proper gives an internal load in the range 30–260×103 ton N year−1. Another result is an east–west gradient in fixation rate that may reflect the nitrogen load.
  •  
49.
  • Alekseeva, Irina, et al. (författare)
  • Reproducing the Aral Sea water budget and sea-groundwater dynamics between 1979 and 1993 using a coupled 3-D sea-ice-groundwater model
  • 2009
  • Ingår i: Journal of Marine Systems. - : Elsevier. - 0924-7963. ; 76:3, s. 296-309
  • 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.
  •  
50.
  • Almroth Rosell, Elin, 1977, et al. (författare)
  • Transport of fresh and resuspended particulate organic material in the Baltic Sea — a model study
  • 2011
  • Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963. ; 87:1, s. 1-12
  • Tidskriftsartikel (refereegranskat)abstract
    • A fully coupled high-resolution 3-dimensional biogeochemical–physical ocean model including an empirical wave model was used to investigate the long-term average (1970–2007) distributions and transports of resuspended matter and other types of suspended organic matter in the Baltic Sea. Modelled bottom types were compared to observations and the results showed that the model successfully managed to capture the horizontal, as well as the vertical, distribution of the different bottom types: accumulation, transport and erosion bottoms. The model also captured well the nutrient element contents in the sediments. On average the largest contribution of resuspended organic carbon to the transport of total organic carbon is found at erosion and transport bottoms. Although the relative transport of resuspended organic carbon at deeper accumulation bottoms in general is low (< 10% of total), the central parts of the sub-basins act on average as sinks that import organic matter while the more shallow areas and the coastal regions acts as sources of organic carbon in the water column. This indicates that the particulate organic matter produced in erosion and transport areas might be kept in suspension long enough to be transported and settle in less energetic areas, i.e. on accumulation bottoms.
  •  
Skapa referenser, mejla, bekava och länka
  • Resultat 1-50 av 88
Typ av publikation
tidskriftsartikel (86)
forskningsöversikt (1)
recension (1)
Typ av innehåll
refereegranskat (86)
övrigt vetenskapligt/konstnärligt (2)
Författare/redaktör
Björk, Göran, 1956 (4)
Omstedt, Anders, 194 ... (4)
Walve, Jakob (3)
Aigars, Juris (3)
Chierici, Melissa, 1 ... (2)
Grimvall, Anders (2)
visa fler...
Wikner, Johan (2)
Jarsjö, Jerker (2)
Nilsson, J. (1)
Andersson, K (1)
Olsen, A (1)
Kortelainen, Pirkko (1)
Bonaglia, Stefano (1)
Linderholm, Hans W., ... (1)
Lundberg, Peter (1)
Wulff, Angela, 1963 (1)
Håkanson, Lars (1)
Chen, Deliang, 1961 (1)
Rudels, B. (1)
Dillen, Wout (1)
Kelly, Aodhan (1)
Sichani, Anna-Maria (1)
Gustafsson, Örjan (1)
Larsson, Ulf (1)
Jansson, Mats (1)
Kautsky, Hans (1)
Lundälv, Tomas, 1944 (1)
Bergström, Ulf (1)
Ahlborg, Helene, 198 ... (1)
Michael, Kavya, 1985 (1)
Unsworth, Samuel Joh ... (1)
Hategekimana, Sylver ... (1)
Osunmuyiwa, Olufolah ... (1)
Åberg, Anna, 1978 (1)
Hultman, Martin, 197 ... (1)
Lindström, Martin (1)
Ahlgren, Joakim (1)
Tranvik, Lars (1)
Rolff, Carl (1)
Löfgren, Stefan (1)
Holm, Nils (1)
Elmgren, Ragnar (1)
Dahlbo, Kim (1)
Sallée, Jean-Baptist ... (1)
Neumann, T (1)
Destouni, Georgia (1)
Ödalen, Malin (1)
Alekseeva, Irina (1)
Schrum, Corinna (1)
Bornmalm, Lennart, 1 ... (1)
visa färre...
Lärosäte
Stockholms universitet (32)
Göteborgs universitet (30)
Uppsala universitet (13)
Linköpings universitet (11)
Lunds universitet (8)
Chalmers tekniska högskola (5)
visa fler...
Sveriges Lantbruksuniversitet (4)
Umeå universitet (2)
Linnéuniversitetet (2)
Högskolan i Borås (2)
Örebro universitet (1)
Mittuniversitetet (1)
visa färre...
Språk
Engelska (87)
Svenska (1)
Forskningsämne (UKÄ/SCB)
Naturvetenskap (70)
Samhällsvetenskap (5)
Lantbruksvetenskap (2)
Teknik (1)
Medicin och hälsovetenskap (1)
Humaniora (1)

År

Kungliga biblioteket hanterar dina personuppgifter i enlighet med EU:s dataskyddsförordning (2018), GDPR. Läs mer om hur det funkar här.
Så här hanterar KB dina uppgifter vid användning av denna tjänst.

 
pil uppåt Stäng

Kopiera och spara länken för att återkomma till aktuell vy