The sea is characterized by the low water temperatures, which ranges from in the north to in the south-eastern parts. The medium water layer is warmer, up to 1.5 °С because it is fed by the warm Atlantic waters. It takes them 2.5–3 years to reach the Laptev Sea from their formation near Spitsbergen. The deeper layer is colder at about −0.8 °С. In summer, the surface layer in the ice-free zones warms up by the sun up to 8–10 °С in the bays and 2–3 °С in the open sea, and remains close to 0 °С under ice. The water salinity is significantly affected by the thawing of ice and river runoff. The latter amounts to about 730 km3 and would form a 135 cm freshwater layer over the entire sea; it is the second largest in the world after the Kara Sea. The salinity values vary in winter from 20 to 25‰ (parts per thousand) in the south-east to 34‰ in the northern parts of the sea; it decreases in summer to 5–10‰ and 30–32‰ respectively.