• Arctic shelves;
  • freshwater;
  • sea-ice melt;
  • sea-ice brines;
  • river discharge;
  • oxygen isotope ratio;
  • Laptev Sea (71°N 110°E 78°N 150°E)

[1] Hydrographic and stable isotope (δ18O) data from four summer surveys in the Laptev Sea are used to derive fractions of sea-ice meltwater and river water. Sea-ice meltwater fractions are found to be correlated to river water fractions. While initial heat of river discharge is too small to melt the observed 0–158 km3 of sea-ice meltwater, arctic rivers contain suspended particles and colored dissolved organic material that preferentially absorb solar radiation. Accordingly, heat content in surface waters is correlated to river water fractions. But in years when river water is largely absent within the surface layer, absolute heat content values increase to considerably higher values with extended exposure time to solar radiation and sensible heat. Nevertheless, no net sea-ice melting is observed on the shelf in years when river water is largely absent within the surface layer. The total freshwater volume of the central-eastern Laptev Sea (72–76°N, 122–140°E) varies between ~1000 and 1500 km3 (34.92 reference salinity). It is dominated by varying river water volumes (~1300–1800 km3) reduced by an about constant freshwater deficit (~350–400 km3) related to sea-ice formation. Net sea-ice melt (~109–158 km3) is only present in years with high river water budgets. Intermediate to bottom layer (>25 salinities) contain ~60% and 30% of the river budget in years with low and high river budgets, respectively. The average mean residence time of shelf waters was ~2–3 years during 2007–2009.