Rapid Down‐Slope Transport of Fresh Dissolved Organic Matter to the Deep Ocean in the Eastern North Atlantic

Abstract Intense convective mixing in the central North Atlantic is a major gateway for dissolved organic matter (DOM) into the deep ocean, sustaining elevated dissolved organic carbon (DOC) concentrations. Rapid down‐slope transport on adjacent Irish and Hebrides Margins represents another, less‐explored mechanism contributing to the deep‐sea DOM reservoir. Our analyses of solid‐phase extractable DOM (SPE‐DOM) in bottom waters in this region showed 7–11 μM higher DOC concentration and 190–330 years youngerSPE‐DOM radiocarbon ages compared to similar depths in the open eastern North Atlantic. We estimated a down‐slope DOC flux of 43 Tg C yr−1 from the Irish and Hebrides shelves. During transport, conservative mixing, dominated by physical rather than biological/chemical processes, determined the molecular DOM composition, while minor particulate organic matter degradation introduced less‐refractory DOM with terrigenous characteristics. Thus, rapid down‐slope transport emerges as an efficient conduit for delivering fresh DOM into the deep ocean.