In article
,
Alan writes:
When the main body of a shallow sea, such as the Southern North Sea,
reaches 4C does the SST cool faster because the maximum density has
been reached?

Presumably, but cooling a body of water as deep as the North Sea
(calling it "shallow" is strictly relative) to 4C throughout its depth
takes a lot of doing. Until that happens, water cooled at the surface
will be denser than water below and tend to sink, to be replaced by less
cold water. Also less cold water will tend to invade from the north from
the North Atlantic. I suspect that in recent decades only in 1946-7 and
1962-3 would what you envisage have occurred. ISTR reading that by the
end of the 1946-7 winter there were ice floes off the coast of Belgium
and/or Holland.
--
John Hall
"Acting is merely the art of keeping a large group of people
from coughing."
Sir Ralph Richardson (1902-83)