Exercise 2 solution

When seawater freezes, the ice crystals are almost pure water, and most of the salt is rejected into the liquid water below (as cold, salty brine). The water under the ice therefore becomes saltier. It is already at the freezing point (about minus 1.9 degrees), so it is very cold as well. Cold and salty both increase density, so the water becomes dense enough to sink down the continental slope and form Antarctic Bottom Water.

A large flow of glacier meltwater would add fresh water, lowering salinity and so density. The surface water would be less able to sink, which would weaken the formation of bottom water. This is the reason scientists watch the freshening of polar seas.