Identifying the Extent of River‐Influenced Waters of the Transpolar Drift With In Situ Measurements of Dissolved Organic Matter Fluorescence and Seawater Density

Abstract The oceanic component of the Transpolar Drift (TPD) is a key component of Arctic Ocean surface circulation. However, our understanding of its spatial extent and influence on the underlying water column remains limited. This study leverages a unique high spatial resolution oceanographic transect from August 2022 (late summer), first to identify in‐situ criteria to define the extent of the river‐influenced waters of the TPD and then to investigate its characteristics in the western Eurasian Basin. The section stretches from northeast of Greenland across the Amundsen and Nansen Basins to the continental slope north of Svalbard. Large contrasts are observed between the Amundsen and Nansen Basin, including a fresher surface ocean in the Amundsen Basin. By combining hydrography with in‐situ measurements of dissolved organic matter fluorescence and dissolved oxygen, we characterize the water masses associated with the oceanic TPD. In our multi‐parameter analysis, we find that the combination of the isopycnal 26 kg m −3 and elevated humic‐like fluorescent dissolved matter can be used to identify the vertical and eastward extents of the oceanic TPD dominated by river‐influenced waters. The upper halocline beneath the TPD core contains denitrified water with high Apparent Oxygen Utilization, suggesting a contribution from the Chukchi shelf. The interplay between the TPD and underlying water layers is complex: the TPD influences halocline strength but does not appear to affect the depth of the Atlantic Water core. Understanding this interplay is important, as ongoing climate‐driven changes in surface circulation and freshwater distribution may alter the TPD, potentially impacting Arctic ecosystem dynamics.