Factors influencing the stable carbon isotopic composition of suspended and sinking organic matter in the coastal Antarctic sea ice environment
Other literature type, Unknown, Article
Henley, S. F.
Annett, A. L.
Ganeshram, R. S.
Carson, D. S.
Fallick, A. E.
- Publisher: Copernicus Publications
(issn: 1726-4189, eissn: 1726-4189)
Carbon dioxide | Sediment trap | Southern Ocean | /dk/atira/pure/subjectarea/asjc/1100/1105 | Ecology, Evolution, Behavior and Systematics | Antarctica | /dk/atira/pure/subjectarea/asjc/1900/1904 | Global and Planetary Change | Diatoms | Organic Chemistry | Sea ice | Carbon concentrating mechanisms | Oceanography | Biochemistry | Phytoplankton | Organic matter | /dk/atira/pure/subjectarea/asjc/1300/1303 | /dk/atira/pure/subjectarea/asjc/1900/1910 | Carbon isotopes | /dk/atira/pure/subjectarea/asjc/2300/2306 | Earth-Surface Processes | /dk/atira/pure/subjectarea/asjc/1600/1605
A high resolution time-series analysis of stable carbon isotopic signatures
in particulate organic carbon (δ<sup>13</sup>C<sub>POC</sub>) and associated
biogeochemical parameters in sea ice and surface waters provides an insight
into the factors affecting δ<sup>13</sup>C<sub>POC</sub> 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 <i>Proboscia inermis</i> is strongly correlated with a large
~10 ‰ negative isotopic shift in δ<sup>13</sup>C<sub>POC</sub> that cannot
be explained by a concurrent change in concentration or isotopic signature
of CO<sub>2</sub>. We hypothesise that the δ<sup>13</sup>C<sub>POC</sub> shift may be
driven by the contrasting biochemical mechanisms and utilisation of
carbon-concentrating mechanisms (CCMs) in different diatom species.
Specifically, very low δ<sup>13</sup>C<sub>POC</sub> in <i>P. inermis</i> may be caused by the
lack of a CCM, whilst some diatom species abundant at times of higher
δ<sup>13</sup>C<sub>POC</sub> may employ CCMs. These short-lived yet pronounced
negative δ<sup>13</sup>C<sub>POC</sub> excursions drive a 4 ‰ decrease in the
seasonal average δ<sup>13</sup>C<sub>POC</sub> 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<sup>13</sup>C<sub>POC</sub> variability and, as such, we invoke phytoplankton species
changes as a potentially important factor influencing sedimentary δ<sup>13</sup>C<sub>POC</sub>. We also find significantly higher δ<sup>13</sup>C<sub>POC</sub> 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<sub>3</sub><sup>−</sup> 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<sup>13</sup>C<sub>POC</sub> in
Antarctic coastal environments and underlying sediments, with consequences
for the utility of diatom-based δ<sup>13</sup>C<sub>POC</sub> in the sedimentary