Inventories and behavior of particulate organic carbon in the Laptev and East Siberian seas

Abstract

Fluvial and erosional release processes in permafrost-dominated Eurasian Arctic cause transport of large amounts of particulate organic carbon (POC) to coastal waters. The marine fate of this terrestrial POC (terr-POC), water column degradation, burial in shelf sediments, or export to depth, impacts the potential for climate-carbon feedback. As part of the International Siberian Shelf Study (ISSS-08; August-September 2008), the POC distribution, inventory, and fate in the water column of the extensive yet poorly studied Eurasian Arctic Shelf seas were investigated. The POC concentration spanned 1-152 mM, with highest values in the SE Laptev Sea. The POC inventory was constrained for the Laptev (1.32 0.09 Tg) and East Siberian seas (2.85 0.20 Tg). A hydraulic residence time of 3.5 2 years for these Siberian shelf seas yielded a combined annual terr-POC removal flux of 3.9 1.4 Tg yr -1 . Accounting for sediment burial and shelf-break exchange, the terr-POC water column degradation was 2.5 1.6 Tg yr -1 , corresponding to a first-order terr-POC degradation rate constant of 1.4 0.9 yr -1 , which is 5-10 times faster than reported for terr-DOC degradation in the Arctic Ocean. This terr-POC degradation flux thus contributes substantially to the dissolved inorganic carbon excess of 10 Tg C observed during ISSS-08 for these waters. This evaluation suggests that extensive decay of terr-POC occurs already in the water column and contributes to outgassing of CO 2 . This process should be considered as a geographically dislocated carbon-climate coupling where thawing of vulnerable permafrost carbon on land is eventually adding CO 2 above the ocean.