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      New Production Regulates Export Stoichiometry in the Ocean

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          Abstract

          The proportion in which carbon and growth-limiting nutrients are exported from the oceans’ productive surface layer to the deep sea is a crucial parameter in models of the biological carbon pump. Based on >400 vertical flux observations of particulate organic carbon (POC) and nitrogen (PON) from the European Arctic Ocean we show the common assumption of constant C:N stoichiometry not to be met. Exported POC:PON ratios exceeded the classical Redfield atomic ratio of 6.625 in the entire region, with the largest deviation in the deep Central Arctic Ocean. In this part the mean exported POC:PON ratio of 9.7 (a:a) implies c. 40% higher carbon export compared to Redfield-based estimates. When spatially integrated, the potential POC export in the European Arctic was 10–30% higher than suggested by calculations based on constant POC:PON ratios. We further demonstrate that the exported POC:PON ratio varies regionally in relation to nitrate-based new production over geographical scales that range from the Arctic to the subtropics, being highest in the least productive oligotrophic Central Arctic Ocean and subtropical gyres. Accounting for variations in export stoichiometry among systems of different productivity will improve the ability of models to resolve regional patterns in carbon export and, hence, the oceans’ contribution to the global carbon cycle will be predicted more accurately.

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          Production of macroaggregates from dissolved exopolymeric substances (EPS) of bacterial and diatom origin.

          Exopolymeric substances (EPS) isolated from a pure culture of the marine bacterium Marinobacter sp. and the marine diatom Skeletonema costatum (axenic) were partially purified, chemically characterized and used as dissolved organic matter (DOM) for the production of macroaggregates. The role of organic particles such as transparent exopolymeric particles (TEP) and Coomassie stained particles (CSP) in the production of macroaggregates was experimentally assessed. Three experimental rolling tanks containing sterile medium with: (1) EPS, (2) EPS + live diatom cells and (3) EPS + killed bacteria, and three control tanks without any added EPS were used for macroaggregate production. Changes in abundance and average size of macroaggregates were monitored using image analysis, whereas TEP and CSP were enumerated microscopically. In the presence of microbial EPS, macroaggregates of a size of 23-35 mm(2) were produced. Aggregate size and abundance considerably varied with both time and source of EPS. No correlation was observed for macroaggregate size and abundance with either TEP or CSP. One-way ANOVA demonstrated significant differences in the variance of particle abundance and size in tanks having only EPS or EPS in combination with live diatom cells. Our data suggest that production of macroaggregates was influenced by polymer chemistry and surface properties of colliding particles, whereas TEP and CSP concentrations were influenced by molecular weight of EPS and the presence of growing cells. Interestingly, macroaggregates were formed in the near absence of TEP and CSP, highlighting the role of other unknown processes in the transformation of DOM to particulate organic matter (POM) in aquatic environments.
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            Author and article information

            Contributors
            Role: Editor
            Journal
            PLoS One
            PLoS ONE
            plos
            plosone
            PLoS ONE
            Public Library of Science (San Francisco, USA )
            1932-6203
            2013
            16 January 2013
            : 8
            : 1
            : e54027
            Affiliations
            [1 ]Department of Arctic and Marine Biology, University of Tromsø, Tromsø, Norway
            [2 ]Institute of Ecology and Earth Sciences, University of Tartu, Tartu, Estonia
            [3 ]SINTEF Fisheries and Aquaculture, Trondheim, Norway
            Institute of Marine Research, Norway
            Author notes

            Competing Interests: The authors have declared that no competing interests exist.

            Conceived and designed the experiments: TT MR. Analyzed the data: TT DS KO. Contributed reagents/materials/analysis tools: TT MR KO DS PW. Wrote the paper: TT MR KO.

            [¤]

            Current address: Institute of Marine Sciences-CSIC, Barcelona, Catalonia, Spain

            Article
            PONE-D-12-30236
            10.1371/journal.pone.0054027
            3546974
            23342065
            5306992b-da86-4365-8e52-d0a9dd88eb51
            Copyright @ 2013

            This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

            History
            : 2 October 2012
            : 7 December 2012
            Page count
            Pages: 8
            Funding
            This study was financed by the Research Council of Norway ( http://www.forskningsradet.no) through the project 184860/S30 MERCLIM (T.T., D.S., P.W.) and by Tromsø forskningsstiftelse through the project CONFLUX (M.R., D.S.). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
            Categories
            Research Article
            Biology
            Ecology
            Ecosystems
            Ecosystem Functioning
            Ecosystem Modeling
            Biogeochemistry
            Earth Sciences
            Marine and Aquatic Sciences
            Oceanography
            Biological Oceanography
            Water Column
            Oceans
            Arctic Ocean
            Marine Ecology

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            Uncategorized

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