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

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 μM, 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 CO2. This process should be considered as a geographically dislocated carbon‐climate coupling where thawing of vulnerable permafrost carbon on land is eventually adding CO2 above the ocean. Key Points Strong influence of terr‐OC in the Laptev and W‐East Siberian seas waters Quantitative constraint of the POC inventory in the Laptev and East Siberian seas Strong nonconservative behavior of POC (mainly degradation and sedimentation)