A river of terrestrial dissolved organic matter in the upper waters of the central Arctic Ocean

The Transpolar Drift (TPD) is a mechanism for the rapid transport of shelf-modified Siberian river waters across the Arctic Ocean and out through Fram Strait. We present results from three trans-Arctic research cruises in August-September 2014-2016 to investigate the distribution and dynamics of dissolved organic matter (DOM) in the upper waters across the North Pole, from Svalbard to the Mackenzie River mouth, and in two important outflow gateways of the Arctic Ocean (Fram Strait and Lancaster Sound). Fluorescence measurements of DOM obtained using in situ sensor and laboratory-based spectroscopic analyses, coupled with parallel factor analysis (PARAFAC) were used to map components of DOM at high spatial resolution. The optical properties showed a completely different composition with a much stronger humic-like signal observed in surface waters in the Makarov Basin than in the adjacent Canada Basin, likely due to the substantial amount of Siberian runoff transported by the TPD. The high levels of humic-like in TPD-influenced surface waters were traced from southern Makarov shelves up to the Lomonosov Ridge near the North Pole. Lower DOM levels were observed in the eastern Amundsen basin waters, likely the result of mixing with terrestrial-poor DOM Atlantic waters. The annual flux of humic-like C2 transported to the Atlantic through Fram Strait was estimated at 1816 & PLUSMN;926 r.u. km3. This study reveals the importance of shelf processes and TPD in supplying humic-like material to the central Arctic Ocean to Fram Strait.