Abstract
Ongoing permafrost thaw in the Arctic may remobilize large amounts of old organic matter. Upon transport to the Siberian shelf seas, this material may be degraded and released to the atmosphere, exported off-shelf, or buried in the sediments. While our understanding of the fate of permafrost-derived organic matter in shelf waters is improving, poor constraints remain regarding degradation in sediments. Here we use an extensive data set of organic carbon concentrations and isotopes (n = 109) to inventory terrigenous organic carbon (terrOC) in surficial sediments of the Laptev and East Siberian Seas (LS + ESS). Of these ~2.7 Tg terrOC about 55% appear resistant to degradation on a millennial timescale. A first-order degradation rate constant of 1.5 kyr −1 is derived by combining a previously established relationship between water depth and cross-shelf sediment-terrOC transport time with mineral-associated terrOC loadings. This yields a terrOC degradation flux of ~1.7 Gg/year from surficial sediments during cross-shelf transport, which is orders of magnitude lower than earlier estimates for degradation fluxes of dissolved and particulate terrOC in the water column of the LS + ESS. The difference is mainly due to the low degradation rate constant of sedimentary terrOC, likely caused by a combination of factors: (i) the lower availability of oxygen in the sediments compared to fully oxygenated waters, (ii) the stabilizing role of terrOC-mineral associations, and (iii) the higher proportion of material that is intrinsically recalcitrant due to its chemical/molecular structure in sediments. Sequestration of permafrost-released terrOC in shelf sediments may thereby attenuate the otherwise expected permafrost carbon-climate feedback.
Original language | English |
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Pages (from-to) | 85-99 |
Number of pages | 15 |
Journal | Global Biogeochemical Cycles |
Volume | 33 |
Issue number | 1 |
DOIs | |
Publication status | Published - 1 Jan 2019 |
Funding
1Department of Environmental Science and Analytical Chemistry, Stockholm University, Stockholm, Sweden, 2Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden, 3Department of Earth Sciences, Vrije Universiteit Amsterdam, Amsterdam, Netherlands, 4Institute of Marine Sciences – National Research Council, Bologna, Italy, 5International Arctic Research Center, University Alaska Fairbanks, Fairbanks, USA, 6Pacific Oceanological Institute, Russian Academy of Sciences, Vladivostok, Russia, 7National Research Tomsk Polytechnic University, Tomsk, Russia We thank crew and personnel of the RV Yakob Smirnitskyi, the TB0012, and the IB ODEN. The International Siberian Shelf Study 2008 (ISSS‐08) and the SWERUS‐C3 2014 expeditions were supported by the Knut and Alice Wallenberg Foundation, Headquarters of the Far Eastern Branch of the Russian Academy of Sciences, the Swedish Research Council (VR contract 621‐2007‐4631, 621‐2013‐5297, and 2017‐05687), the European Research Council (ERC‐AdG CC‐TOP project 695331 to Ö. G.), the US National Oceanic and Atmospheric Administration (OAR Climate Program Office, NA08OAR4600758/Siberian Shelf Study), the Swedish Polar Research Secretariat, the Nordic Council of Ministers, and the U.S. National Science Foundation (OPP ARC‐0909546 and 1023281). L. B. and Ö. G. also acknowledge financial support from the Climate Research School of the Bolin Centre for Climate Research. T. T. also acknowledges EU financial support as a Marie Curie fellow (contract PIEF‐GA‐2011‐ 300259), contribution number 1988 of ISMAR‐CNR Sede di Bologna. I. S. further thanks the Russian Government for financial support (megagrant 14.Z50.31.0012). Aron Varhelyi contributed valuable support with laboratory work. All data used in this study are provided in the supporting information as Tables S1– S3. They can also be found as Excel files at the Bolin Centre Database (https:// bolin.su.se/data/Broder‐2019).
Funders | Funder number |
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Climate Research School of the Bolin Centre for Climate Research | |
Headquarters of the Far Eastern Branch of the Russian Academy of Sciences | |
IB ODEN | |
ISMAR-CNR Sede di Bologna | |
ISMAR‐CNR Sede di Bologna | |
International Siberian Shelf Study | ISSS‐08 |
National Science Foundation | 300259, 1023281, 0909546, 695331, OPP ARC‐0909546 |
National Oceanic and Atmospheric Administration | |
Office of AIDS Research | |
Polarforskningssekretariatet | |
European Commission | PIEF‐GA‐2011‐ 300259 |
European Research Council | |
Knut och Alice Wallenbergs Stiftelse | |
Nordisk Ministerråd | |
Vetenskapsrådet | 621‐2007‐4631, 2017‐05687, 621‐2013‐5297 |
Keywords
- Arctic shelves
- carbon fluxes
- degradation
- marine sediments
- permafrost