River water fraction plotted against neodymium isotope composition ( Nd ). Error bars for Nd and [Nd] represent 2 standard deviations from measurements, while those for f RIV account for both measurement errors and endmember variability. Black arrows indicate admixture of individual riverine Nd sources (Lena, YenOb) to Arctic Atlantic Water (AAW). PS94 cruise samples collected in the Makarov Basin, outside the freshwater-rich part of the Transpolar Drift, are highlighted with dashed circles. One MOSAiC sample from the Fram Strait, influenced by unradiogenic Nd from Greenland (Supplementary Text 2 ), deviates from the data envelope in the f RIV - Nd space and is excluded from our analysis. MOSAiC data symbols are color-coded by sampling depth.
