Different sources and degradation state of dissolved, particulate and sedimentary organic matter along the Eurasian Arctic coastal margin
(English)Manuscript (preprint) (Other academic)
Thawing of permafrost in the Eurasian Arctic causes massive fluvial and erosional releases of both dissolved and particulate organic carbon (DOC and POC) to coastal waters. Here we investigate how different sources and extent of degradation of remobilized terrestrial carbon pools imprint on major recipient carbon pools and thereby affect large-scale carbon cycling. The molecular and dual-isotope composition is compared with source end-member composition in waterborne high-molecular weight DOC (>1kD, a.k.a. colloidal OC), POC and in sedimentary OC (SOC) along coastal Kara, Laptev and East Siberian Seas.
The lignin phenol fingerprint demonstrates a clear geospatial trend in the relative contribution of different terrestrial sources to coastal OC in going from the west to the east. The wax lipids and cutins were much less abundant in the COC compared to in the POC and SOC compartment, suggesting that different terrestrial carbon pools partition into different aquatic carrier phases. The Δ14C signal suggests that the COC is overwhelmingly derived from contemporary carbon sources. Furthermore, degradation proxies based on terrestrial lignin phenol biomarkers suggest a highly degraded COC composition. Monte Carlo based source apportionment simulations of the δ13C/Δ14C composition constrained that the COC is dominated by terrestrial OC from topsoil permafrost (65%) and marine plankton (25%) with smaller contribution from Ice Complex Deposit (ICD) and other older stocks of permafrost carbon (9%). This contrasts starkly to the POC and especially the SOC compartment, which are dominated by old C from ICD-OC permafrost.
These results combine with other recent studies to suggest a pattern along the East Siberian Arctic margin of SOC being constantly older yet less degraded than water column POC. This study also extends this perspective spatially along the Eurasian Arctic seaboard and also to the large COC (HMW DOC) pool, which is even younger yet even more degraded than the POC. An implication is that DOC and POC pools need to be treated separately in assessments of effects on the large-scale carbon cycle (and climate feedback) of old carbon released from thawing permafrost to aquatic receptors across the Eurasian Arctic coast.
organic carbon, terrestrial biomarkers, acyl lipids, lignin phenols, radiocarbon, Eurasian Arctic shelf, East Siberian Sea, Laptev Sea, Lena River, colloidal matter, particulate matter, sedimentary matter
Earth and Related Environmental Sciences
Research subject Applied Environmental Science
IdentifiersURN: urn:nbn:se:su:diva-116871OAI: oai:DiVA.org:su-116871DiVA: diva2:809314