Quantifying Degradative Loss of Terrigenous Organic Carbon in Surface Sediments Across the Laptev and East Siberian Sea

Lisa Bröder; August Andersson; Tommaso Tesi; Igor Semiletov; Örjan Gustafsson

doi:10.1029/2018GB005967

Quantifying Degradative Loss of Terrigenous Organic Carbon in Surface Sediments Across the Laptev and East Siberian Sea

Lisa Bröder^*, August Andersson, Tommaso Tesi, Igor Semiletov, Örjan Gustafsson

^*Corresponding author for this work

Earth and Climate

Research output: Contribution to Journal › Article › Academic › peer-review

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
Pages (from-to)	85-99
Number of pages	15
Journal	Global Biogeochemical Cycles
Volume	33
Issue number	1
DOIs	https://doi.org/10.1029/2018GB005967
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
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

UN SDGs

This output contributes to the following UN Sustainable Development Goals (SDGs)

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10.1029/2018GB005967

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title = "Quantifying Degradative Loss of Terrigenous Organic Carbon in Surface Sediments Across the Laptev and East Siberian Sea",

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. ",

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AU - Bröder, Lisa

AU - Andersson, August

AU - Tesi, Tommaso

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AU - Gustafsson, Örjan

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AB - 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.

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JF - Global Biogeochemical Cycles

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Quantifying Degradative Loss of Terrigenous Organic Carbon in Surface Sediments Across the Laptev and East Siberian Sea

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Keywords

UN SDGs

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