Articles | Volume 13, issue 5
Ocean Sci., 13, 735–748, 2017

Special issue: Climate–carbon–cryosphere interactions in the...

Ocean Sci., 13, 735–748, 2017

Research article 18 Sep 2017

Research article | 18 Sep 2017

Carbon geochemistry of plankton-dominated samples in the Laptev and East Siberian shelves: contrasts in suspended particle composition

Tommaso Tesi1,2,3, Marc C. Geibel1,2, Christof Pearce2,4,5, Elena Panova6, Jorien E. Vonk7, Emma Karlsson1,2, Joan A. Salvado1,2, Martin Kruså1,2, Lisa Bröder1,2, Christoph Humborg1,2, Igor Semiletov6,8,9, and Örjan Gustafsson1,2 Tommaso Tesi et al.
  • 1Department of Environmental Science and Analytical Chemistry (ACES), Stockholm University, Stockholm, Sweden
  • 2Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden
  • 3Institute of Marine Sciences, National Research Council (ISMAR-CNR), Bologna, Italy
  • 4Department of Geological Sciences, Stockholm University, Stockholm, Sweden
  • 5Department of Geoscience, Aarhus University, Aarhus, Denmark
  • 6Tomsk Polytechnic University, Tomsk, Russia
  • 7Vrije Universiteit Amsterdam (VU), Amsterdam, the Netherlands
  • 8Pacific Oceanological Institute FEB RAS, Vladivostok, Russia
  • 9University of Alaska Fairbanks, Fairbanks, USA

Abstract. Recent Arctic studies suggest that sea ice decline and permafrost thawing will affect phytoplankton dynamics and stimulate heterotrophic communities. However, in what way the plankton composition will change as the warming proceeds remains elusive. Here we investigate the chemical signature of the plankton-dominated fraction of particulate organic matter (POM) collected along the Siberian Shelf. POM (> 10 µm) samples were analysed using molecular biomarkers (CuO oxidation and IP25) and dual-carbon isotopes (δ13C and Δ14C). In addition, surface water chemical properties were integrated with the POM (> 10 µm) dataset to understand the link between plankton composition and environmental conditions.

δ13C and Δ14C exhibited a large variability in the POM (> 10 µm) distribution while the content of terrestrial biomarkers in the POM was negligible. In the Laptev Sea (LS), δ13C and Δ14C of POM (> 10 µm) suggested a heterotrophic environment in which dissolved organic carbon (DOC) from the Lena River was the primary source of metabolisable carbon. Within the Lena plume, terrestrial DOC probably became part of the food web via bacteria uptake and subsequently transferred to relatively other heterotrophic communities (e.g. dinoflagellates). Moving eastwards toward the sea-ice-dominated East Siberian Sea (ESS), the system became progressively more autotrophic. Comparison between δ13C of POM (> 10 µm) samples and CO2aq concentrations revealed that the carbon isotope fractionation increased moving towards the easternmost and most productive stations.

In a warming scenario characterised by enhanced terrestrial DOC release (thawing permafrost) and progressive sea ice decline, heterotrophic conditions might persist in the LS while the nutrient-rich Pacific inflow will likely stimulate greater primary productivity in the ESS. The contrasting trophic conditions will result in a sharp gradient in δ13C between the LS and ESS, similar to what is documented in our semi-synoptic study.

Short summary
Recent Arctic studies suggest that sea-ice decline and permafrost thawing will affect the phytoplankton in the Arctic Ocean. However, in what way the plankton composition will change as the warming proceeds remains elusive. Here we show that the carbon composition of plankton might change as a function of the enhanced terrestrial organic carbon supply and progressive sea-ice thawing.