| 1. |
- Pers, Charlotta, et al.
(författare)
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Changes in apparent oxygen removal in the Baltic proper deep water
- 2000
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Ingår i: Journal of Marine Systems. - 0924-7963 .- 1879-1573. ; 25:3-4, s. 421-429
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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.
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| 2. |
- Ahlgren, Joakim, et al.
(författare)
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Temperature, DOC level and basin interactions explain the declining oxygen concentrations in the Bothnian Sea
- 2017
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Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 170, s. 22-30
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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.
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| 3. |
- Algesten, Grete, et al.
(författare)
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Organic carbon budget for the Gulf of Bothnia
- 2006
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Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 63:3-4, s. 155-161
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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.
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| 4. |
- Almroth Rosell, Elin, 1977, et al.
(författare)
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A new approach to model oxygen dependent benthic phosphate fluxes in the Baltic Sea
- 2015
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Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 144, s. 127-141
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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.
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| 5. |
- Andersson, Andreas, et al.
(författare)
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Using eddy covariance to estimate air-sea gas transfer velocity for oxygen
- 2016
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Ingår i: Journal of Marine Systems. - : Elsevier. - 0924-7963 .- 1879-1573. ; 159, s. 67-75
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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.
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| 6. |
- Armbrecht, Linda, et al.
(författare)
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Comparison of the cross-shelf phytoplankton distribution of two oceanographically distinct regions off Australia
- 2015
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Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 148, s. 26-38
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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.
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| 7. |
- Björk, Göran, 1956, et al.
(författare)
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Seasonal oxygen depletion in a shallow sill fjord on the Swedish west coast
- 2017
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Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 175, s. 1-14
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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.
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| 8. |
- Chndrasekhararao, A. V., et al.
(författare)
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Phytoplankton response to the contrasting physical regimes in the eastern Arabian Sea during north east monsoon
- 2018
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Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573.
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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
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| 9. |
- Christaki, Urania, et al.
(författare)
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Microzooplankton diversity and potential role in carbon cycling of contrasting Southern Ocean productivity regimes
- 2021
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Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 219
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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.
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| 10. |
- Conley, Daniel, et al.
(författare)
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Past, present and future state of the biogeochemical Si cycle in the Baltic Sea
- 2008
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Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 73:3-4, s. 338-346
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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.
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