EGU24-149, updated on 08 Mar 2024
EGU General Assembly 2024
© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.

Quantifying permafrost organic carbon remineralization after redeposition on the ocean floor, using  δ13C and F14C.

Manuel Ruben1, Jens Hefter1, Torben Gentz1, Florence Schubotz2,3, Bingbing Wei1, Bo Liu1, Michael Fritz4, Anna Maria Irrgang4, Anabel von Jackowski5, Walter Geibert1, and Gesine Mollenhauer1,2,3
Manuel Ruben et al.
  • 1Alfred-Wegener Institut, Marine Geoscience, Germany
  • 2University of Bremen, Bibliothekstraße 1, 28359 Bremen, Germany
  • 3MARUM - Center for Marine Environmental Sciences, University of Bremen, Leobener Straße 8, 28359 Bremen, Germany
  • 4Alfred Wegener Institute Helmholtz Centre for Polar- and Marine Research, Telegrafenberg, 14473 Potsdam, Germany
  • 5CNRS/Sorbonne Université, UMR7621 Laboratoire d’Océanographie Microbienne, Banyuls-sur-Mer, France

Arctic permafrost is a critical global tipping element in a warming climate. Annually, the erosion of coastal permafrost discharges an estimated 5 to 14 Tg of organic carbon (OC) into the Arctic Ocean. Although this previously stored OC has the potential to be reintroduced into the atmosphere, thus accelerating human-induced climate change, little is known about the benthic remineralization processes of permafrost OC after erosion and redeposition on the ocean floor. Our research quantified fluxes of dissolved inorganic carbon (DIC) and analyzed its isotopic composition of nearshore sediments in the Canadian Beaufort Sea, specifically off Herschel Island. Our findings showed a DIC release of 0.217 mmo/m²/d, with an average signature of δ13C = -22.44 ± 72 ‰ and F14C = 0.548 ± 0.007. Utilizing a model that combines two carbon isotopes, we estimate that approximately 38 ± 10% of the released DIC is a result of subsurface degradation of redeposited permafrost OC, with an additional 15 ± 12% originating from redeposited active layer OC. Additionally, isotopic endmember analysis was utilized on bacterial membrane lipids from live sedimentary bacteria to determine the relative utilization of OC sources in bacterial communities within shallow subsurface sediment (<25 cm). Our results indicate that, on average, these communities obtain 73 ± 10% of their OC from recent marine primary production, 11 ± 6% from permafrost OC, and 16 ± 11% from active layer OC. This study is the first direct quantitative assessment of the release of permafrost OC into the active carbon cycle after it has been redeposited on the ocean floor, as far as we know. The data suggest that the redeposited permafrost OC is easily accessible and utilized by subsurface bacteria. Considering the immense size and vulnerability of the eroding coastal permafrost OC pool, 27 to 53% of it contributing to benthic DIC fluxes could have a prolonged effect on the world's climate, worsening the climate emergency.

How to cite: Ruben, M., Hefter, J., Gentz, T., Schubotz, F., Wei, B., Liu, B., Fritz, M., Irrgang, A. M., von Jackowski, A., Geibert, W., and Mollenhauer, G.: Quantifying permafrost organic carbon remineralization after redeposition on the ocean floor, using  δ13C and F14C., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-149,, 2024.