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Article Dans Une Revue Biogeosciences Année : 2012

Factors influencing the stable carbon isotopic composition of suspended and sinking organic matter in the coastal Antarctic sea ice environment

K. Weston
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X. Crosta
A. Tait
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J. Dougans
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A. E. Fallick
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Résumé

A high resolution time-series analysis of stable carbon isotopic signatures in particulate organic carbon (δ 13 C POC) and associated biogeochemical parameters in sea ice and surface waters provides an insight into the factors affecting δ 13 C POC in the coastal western Antarctic Peninsula sea ice environment. The study covers two austral summer seasons in Ryder Bay, northern Marguerite Bay between 2004 and 2006. A shift in diatom species composition during the 2005/06 summer bloom to near-complete biomass dominance of Proboscia inermis is strongly correlated with a large ∼10 ‰ negative isotopic shift in δ 13 C POC that cannot be explained by a concurrent change in concentration or isotopic signature of CO 2. We hypothesise that the δ 13 C POC shift may be driven by the contrasting biochemical mechanisms and utilisation of carbon-concentrating mechanisms (CCMs) in different diatom species. Specifically, very low δ 13 C POC in P. inermis may be caused by the lack of a CCM, whilst some diatom species abundant at times of higher δ 13 C POC may employ CCMs. These short-lived yet pronounced negative δ 13 C POC excursions drive a 4 ‰ decrease in the seasonal average δ 13 C POC signal, which is transferred to sediment traps and core-top sediments and consequently has the potential for preservation in the sedimentary record. This 4 ‰ difference between seasons of contrasting sea ice conditions and upper water column stratification matches the full amplitude of glacial-interglacial Southern Ocean δ 13 C POC variability and, as such, we invoke phytoplankton species changes as a potentially important factor influencing sedi-mentary δ 13 C POC. We also find significantly higher δ 13 C POC in sea ice than surface waters, consistent with autotrophic carbon fixation in a semi-closed environment and possible contributions from post-production degradation, biological utilisation of HCO − 3 and production of exopolymeric substances. This study demonstrates the importance of surface water diatom speciation effects and isotopically heavy sea ice-derived material for δ 13 C POC in Antarctic coastal environments and underlying sediments, with consequences for the utility of diatom-based δ 13 C POC in the sedimentary record.
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Dates et versions

hal-02105642 , version 1 (21-04-2019)

Identifiants

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S. F. Henley, A. L. Annett, R. S. Ganeshram, D. S. Carson, K. Weston, et al.. Factors influencing the stable carbon isotopic composition of suspended and sinking organic matter in the coastal Antarctic sea ice environment. Biogeosciences, 2012, 9 (3), pp.1137-1157. ⟨10.5194/bg-9-1137-2012⟩. ⟨hal-02105642⟩

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