Carbon cycling on the East Siberian Arctic Shelf – a change in air-sea CO2 flux induced by mineralization of terrestrial organic carbon

• Main Authors: Gustafsson, Erik, Humborg, Christoph, Björk, Göran, Stranne, Christian, Anderson, Leif G., Geibel, Marc C., Mörth, Carl-Magnus, Sundbom, Marcus, Semiletov, Igor P., Thornton, Brett F., Gustafsson, Bo G.
• Format: Text
• Language: English
• Published: 2018
• Subjects: Arctic; Arctic Ocean; SWERUS-C3
• Online Access: https://doi.org/10.5194/bg-2017-115; https://www.biogeosciences-discuss.net/bg-2017-115/

Measurements from the SWERUS-C3 and ISSS-08 Arctic expeditions were used to calibrate and validate a new physical-biogeochemical model developed to quantify key carbon cycling processes on the East Siberian Arctic Shelf (ESAS). The model was used in a series of experimental simulations with the specific aim to investigate the pathways of terrestrial dissolved and particulate organic carbon (DOC ter and POC ter ) supplied to the shelf. Rivers supply on average 8.5 Tg C yr −1 dissolved inorganic carbon (DIC), and further 8.5 and 1.1 Tg C yr −1 DOC ter and POC ter respectively. Based on observed and simulated DOC concentrations and stable isotope values (δ 13 C DOC ) in shelf waters, we estimate that only some 20 % of the riverine DOC ter is labile. According to our model results, an additional supply of approximately 14 Tg C yr −1 eroded labile POC ter is however required to describe the observed stable isotope values of DIC (δ 13 C DIC ). Degradation of riverine DOC ter and POC ter results in a 1.8 Tg C yr −1 reduction in the uptake of atmospheric CO 2 , while degradation of eroded POC ter results in an additional 10 Tg C yr −1 reduction. Our calculations indicate nevertheless that the ESAS is an overall small net sink for atmospheric CO 2 (1.7 Tg C yr −1 ). The external carbon sources are largely compensated by a net export from the shelf to the Arctic Ocean (31 Tg C yr −1 ), and to a smaller degree by a permanent burial in the sediments (2.7 Tg C yr −1 ).