Seawater neodymium isotope composition ( Nd ) 88, with major compositional trends depicted by colored circles that reflect the relative proportions of the two riverine endmembers Lena and Yenisei/Ob (YenOb>>Lena: pronounced excess of Yenisei/Ob water compared to Lena water; YenObLena: nearly equal contributions of these endmembers; see also Figs. 3 e and 4b for interpretation). The dashed black circle in ( a ) marks the formation region of first-year ice, for which no seawater data are available. However, river water composition in this region, indicated in ( c ), is inferred from the first-year ice data. The pathway of the freshwater-rich Transpolar Drift, showing fluctuating river water contributions, is represented by a thick, solid black arrow in ( c ), while the advection of low amounts of Yenisei/Ob water along the Nansen Basin, likely exported from the northwestern Laptev Sea, is shown in the same map with a dashed grey arrow and a grey dashed circle around relevant stations. The drift tracks of the ice floes are shown as dashed black lines in all maps, while the recorded growth and drift of first-year ice are represented by a solid black line. The intervals i)iv) shown in c correspond to major trends in river water proportions in the sea ice. The maps were created using ODV 82 and modified manually.
