Different sources and degradation state of dissolved, particulate, and sedimentary organic matter along the Eurasian Arctic coastal margin

Abstract

Thawing Arctic permafrost causes massive fluvial and erosional releases of dissolved and particulate organic carbon (DOC and POC) to coastal waters. Here we investigate how different sources and degradation of remobilized terrestrial carbon may affect large‐scale carbon cycling, by comparing molecular and dual‐isotope composition of waterborne high molecular weight DOC (>1 kD, aka colloidal OC), POC, and sedimentary OC (SOC) across the East Siberian Arctic Shelves. Lignin phenol fingerprints demonstrate a longitudinal trend in relative contribution of terrestrial sources to coastal OC. Wax lipids and cutins were not detected in colloidal organic carbon (COC), in contrast to POC and SOC, suggesting that different terrestrial carbon pools partition into different aquatic carrier phases. The Δ14C signal suggests overwhelmingly contemporary sources for COC, while POC and SOC are dominated by old C from Ice Complex Deposit (ICD) permafrost. Monte Carlo source apportionment (δ13C, Δ14C) constrained that COC was dominated by terrestrial OC from topsoil permafrost (65%) and marine plankton (25%) with smaller contribution ICD and other older permafrost stocks (9%). This distribution is likely a result of inherent compositional matrix differences, possibly driven by organomineral associations. Modern OC found suspended in the surface water may be more exposed to degradation, in contrast to older OC that preferentially settles to the seafloor where it may be degraded on a longer timescale. The different sources which partition into DOC, POC, and SOC appear to have vastly different fates along the Eurasian Arctic coastal margin and may possibly respond on different timescales to climate change.

Contrasting composition of terrigenous organic matter in the dissolved, particulate and sedimentary organic carbon pools on the outer East Siberian Arctic Shelf

“…Those ratios showed decreasing trends off the Lena River plume with higher ratios in the Laptev Sea and W-ESS. The same pattern and similar ratios were observed in the inner shelf of the ESAS (Karlsson et al, 2016). Moreover, these values are in the same range as OC / TN ratios of DOC in Eurasian Arctic rivers, which varied between 23 and 69 (Lobbes et al, 2000), and the high OC / TN ratios (> 40) of DOC collected from the Kara Sea (Köhler et al, 2003;Opsahl et al, 1999).…”

“…The SOC also depicts older signatures near the New Siberian Islands. A recent study from the same area at the land-ocean interface presented older signatures in the POC than in the DOC (Karlsson et al, 2016), suggesting that thawing permafrost was transported preferentially within the POC pool. Therefore, our results support the hypothesis that remobilized permafrost preferentially settles out close to land, and then it is transported off-shelf through sediment resuspension-redeposition events.…”

“…It seems that different pools of Terr-OC have different behavior and fate during remobilization and transport. DOC and POC pools have much younger 14 C ages than the deposited sedimentary OC (Guo et al, 2007;Karlsson et al, 2011Karlsson et al, , 2016. Compound-specific radiocarbon analyses of lipid molecules and lignin phenols of surface sediments and POC from major river mouths in the Arctic revealed marked age offsets between different Terr-OC pools (Feng et al, 2013;Vonk et al, 2010), but POC in the Eurasian rivers is not well characterized.…”

The spatial and interannual dynamics of the surface water carbonate system and air–sea CO<sub>2</sub> fluxes in the outer shelf and slope of the Eurasian Arctic Ocean

“…How climate change impacts the contemporary carbon cycle in the Eurasian Arctic seas, including its consequences for transformation and fluxes, has been the subject of intense interest during the last decade (Anderson et al, 2011;Bischoff et al, 2016;Bröder et al, 2016;Charkin et al, 2015;Gustafsson et al, 2011;Karlsson et al, 2016;Macdonald et al, 2008;Sánchez-García et al, 2014;Tesi et al, 2014;Vonk et al, 2014). Small changes in the largest marine carbon pool, the dissolved inorganic carbon (DIC) pool, can have profound impacts on the CO 2 flux between the ocean and the atmosphere and the feedback of this flux to climate.…”

Towards the Marine Arctic Component of the Pan-Eurasian Experiment

“…Despite the importance of this process, our present knowledge on submarine 30 permafrost distribution, its thermal state, rates of greenhouse gas liberation and transport up into the atmosphere is meager (Ping et al, 2011). Also there is an evidence that terrestrial matter dominates in both water column and surface sediment of Arctic rivers compared to marine matter released from the sea floor (Karlsson et al 2016). Bottom temperature, and water Atmos.…”