Persistent Shelf‐to‐Basin Export of Bioavailable Dissolved Organic Carbon in the Arctic Ocean

Abstract

Microbial carbon demand often exceeds local primary production in the oligotrophic central Arctic Ocean. Whether shelf‐derived dissolved organic carbon (DOC) provides a persistent carbon subsidy to reconcile this imbalance remains unclear. Here, we combine amino acid‐based molecular tracers and hydrographic analyses to trace the transport and transformation of bioavailable DOC from the Beaufort shelf into the Canada Basin. Semi‐labile DOC dominated the upper 200 m (15–36 μmol L ⁻¹ ), whereas labile DOC was scarce (<1.4 μmol L ⁻¹ ) and spatially heterogeneous. Along halocline transport pathways, semi‐labile DOC declined by 25%–28%, accompanied by progressive microbial alteration. Off‐shelf export of semi‐labile DOC could offset up to 32% of the annual microbial carbon deficit in the Canada Basin. These findings identify the halocline as an important conduit linking shelf production to microbial metabolism in the basin interior. Such lateral carbon subsidies may decline as warming alters halocline structure and accelerates microbial degradation.