Evidence for connectivity between Siberian river runoff and the lower limb of the Atlantic meridional overturning circulation

Freshwater originating from the central Arctic Ocean participates in the globally important Atlantic Meridional Overturning Circulation (AMOC). However, the origins of this freshwater contribution are currently unknown. Here, we use high-resolution, in-situ observations of dissolved organic matter (DOM) fluorescence to trace the origins of freshwater and organic carbon in the densest component of the AMOC, namely the Denmark Strait Overflow Water (DSOW). We find a distinct terrestrial DOM signal in DSOW that can be traced upstream to the Siberian shelves in the central Arctic Ocean. This implies a riverine origin of freshwater in DSOW, and we estimate a 0.94 % contribution of Siberian Shelf water to DSOW. Modelling confirms the large-scale connectivity between high Arctic rivers and the deep water in the AMOC inferred from observations. Our results demonstrate biogeochemical connectivity on large regional scales and offers a potential to monitor freshwater and organic carbon export in the AMOC, which will be vital for enhancing our understanding climate variability, particularly given the anticipated changes in the coming decades.