Preprints
https://doi.org/10.5194/bg-2022-183
https://doi.org/10.5194/bg-2022-183
 
09 Sep 2022
09 Sep 2022
Status: this preprint is currently under review for the journal BG.

Particulate organic matter in the Lena River and its Delta: From the permafrost catchment to the Arctic Ocean

Olga Ogneva1,2,3, Gesine Mollenhauer1,3, Bennet Juhls2, Tina Sanders4, Juri Palmtag5,a, Matthias Fuchs2, Hendrik Grotheer1, Paul J. Mann5, and Jens Strauss2 Olga Ogneva et al.
  • 1Marine Geochemistry Section, Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven, 27570, Germany
  • 2Permafrost Research Section, Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Potsdam, 14473, Germany
  • 3Faculty of Geosciences, University of Bremen, Bremen, 28359, Germany
  • 4Institute for Carbon Cycles, Helmholtz Centre Hereon, Geesthacht, 21502, Germany
  • 5Department of Geography and Environmental Sciences, Northumbria University, Newcastle-upon-Tyne, NE1 8ST, UK
  • anow at: Department of Human Geography, Stockholm University, Stockholm, Sweden

Abstract. Rapid Arctic warming accelerates permafrost thaw, causing an additional release of terrestrial organic matter (OM) into rivers, and ultimately, after transport via deltas and estuaries, to the Arctic Ocean nearshore. The majority of our understanding of nearshore OM dynamics and fate has been developed from freshwater rivers, despite the likely impact of highly dynamic estuarine and deltaic environments on transformation, storage, and age of OM delivered to coastal waters. Here, we studied OM dynamics within the Lena River main stem and Lena Delta along an approximately ∼1600 km long transect from Yakutsk, downstream to the delta disembogue into the Laptev Sea. We measured particulate organic carbon (POC), total suspended matter (TSM), and carbon isotopes (δ13C and ∆14C) in POC to compare riverine and deltaic OM composition and changes in OM source and fate during transport offshore. We found that TSM and POC concentrations decreased by 55 and 70 %, respectively, during transit from the main stem to the delta and Arctic Ocean. We found deltaic POC to be strongly depleted in 13C relative to fluvial POC, indicating a significant phytoplankton contribution to deltaic POC (∼68 ±6 %). Dual-carbon (∆14C and δ13C) isotope mixing model analyses suggested an additional input of permafrost-derived OM into deltaic waters (∼18 ±4 % of deltaic POC originates from Pleistocene deposits vs ∼ 5 ±4 % in the river main stem). Despite the lower concentration of POC in the delta than in the main stem (0.41 ±0.10 vs. 0.79 ±0.30 mg L-1, respectively ), the amount of POC derived from Pleistocene deposits in deltaic waters was almost twice as large as POC of Yedoma origin in the main stem (0.07 ±0.02 and 0.04 ±0.02 mg L-1, respectively). We assert that estuarine and deltaic processes require consideration in order to correctly understand OM dynamics throughout Arctic nearshore coastal zones and how these processes may evolve under future climate-driven change.

Olga Ogneva et al.

Status: open (until 21 Oct 2022)

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  • RC1: 'Comment on bg-2022-183', Anonymous Referee #1, 22 Sep 2022 reply

Olga Ogneva et al.

Olga Ogneva et al.

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Short summary
We characterized organic matter along the Lena River over a transect from Yakutsk north to the Lena Delta (approximately 1640 km). We identified the distribution, main sources, and transformation of organic carbon on its way from the permafrost catchment to the Arctic Ocean. We show that the Lena Delta as the interface between the Lena River and the Arctic Ocean plays a crucial role in determining the qualitative and quantitative composition of organic matter discharged into the Arctic Ocean.
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