ORGANIC MATTER CHARACTERISATION ALONG A RIVER DELTA TO SHELF TRANSECT IN EASTERN SIBERIA

The Arctic Ocean receives an estimated amount of 40 × 1012 g organic carbon (OC) through inflow of rivers every year (Holmes et al., 2012; McClelland et al., 2016). A large part of the Arctic Ocean watershed is underlain by permafrost that experiences widescale warming exposing more OC to thaw and degradation (Biskaborn et al., 2019). Arctic Rivers will be increasingly affected by the hydrological and biogeochemical effects of thawing permafrost. During transport, permafrost-OC can be degraded into greenhouse gasses and potentially add to further climate warming (Schuur et al., 2015). However, a significant amount of this OC is transported all the way to the shelf and is buried in marine sediments, attenuating greenhouse gas emissions (Vonk & Gustafsson, 2013). The East Siberian Arctic Shelf is the largest and shallowest shelf in the Arctic Ocean (Stein & MacDonald, 2004). It receives significant amounts of terrestrial OC, delivered through coastal erosion and fluvial input (Gustafsson et al., 2011; Sanchez-Garcia et al., 2011; Vonk et al., 2012). This region is also warming rapidly, and is strongly affected by the loss of sea ice, increasing the open water extent and wave, storm and tidal impact on the coast (Biskaborn et al., 2019; IPCC, 2014). In this study, we focus on the biogeochemical cycling of OC along the river-shelf continuum of the Kolyma river, the largest river completely underlain by continuous permafrost. To quantify the flux of OC and to link its source to its potential sink in the East Siberian Sea, we have sampled dissolved OC, particulate OC and sediment OC along a transect from an active permafrost thaw site near Cherskiy towards the outer Kolyma delta near Ambarchik. On all of these samples isotopic (δ13C, Δ14C) and molecular (lipid biomarkers, lignin phenols) analyses will be used to characterise the OC and assess its degradation status. This, in combination with published data from the East Siberian Shelf close to the Kolyma delta and earlier studies on the Kolyma river, will give us insight in the complete pathway of permafrost-OC from the moment of thaw to degradation during transport and ultimate storage in marine sediments.