wrote:

There is a reason why it is around 28.4 degrees F at high
latitudes, see below.

Here is an explanation of latent heat of fusion:

http://en.wikipedia.org/wiki/Latent_heat_of_fusion

About three and one-half degrees F below the freezing point of pure
water.

I am familiar with the concept of freezing point suppression.

Regarding the Arctic ice cap being freshwater, that is partly
because when seawater freezes the salts are mostly 'excreted'
(for want of a better term) from the ice. Some of the Arctic
ice cap is freshwater because it is formed by precipitation
on top of the sea ice.

Based on the following information it would appear that today the
freezing point of seawater is around 28.4 degrees F.

http://en.wikipedia.org/wiki/Freezing-point_depression
http://en.wikipedia.org/wiki/Sea_water
http://www.newton.dep.anl.gov/askasc...9/gen99263.htm
http://www.csgnetwork.com/h2ofreezecalc.html

If the salinity were twice what it is today then the freezing
point would be about 25 degrees F. That does not agree well
with the assertion that the average ocean temperature was
30 to 40 degrees cooler ten thousand years ago, or ever.


I'm not a great fan of Wikipedia; but even the articles you cite say
that salinity varies a lot. If the water near Iceland really freezes at
28.4, then that's probably because those same waters are some of the
freshest. Although, as I understand what I've read, no one suggests
that the sea is freezing around Iceland or Greenland. Rather,
freshwater glaciers form at high altitudes, away from the sea, flow
downhill toward the sea, and then break into icebergs. If the sea water
cold really freeze at 28.4, then there'd be coastal ice around Northern
places in winter, just like you see in lakes and ponds. I'm not aware
that any such thing exists, or ever has existed.

In places where salinity is high, freezing points will be much
lower. And, as I said earlier, when lots of the Earth's total water
turns to ice, then there's less liquid water to contain the same amounts
of salt. Salinity rises, freezing points drop, and you still have only
fresh water in a solid state, with sea water increasingly resistant to
cold. In fact, it occurs to me that there may be some self-governing
mechanism at work. No matter how cold it gets, there might ALWAYS be
liquid water on Earth. Each little bit of sea water that evaporates,
freezes, and then returns to Earth in a fresh and frozen state, leaves
its salts behind in the water that remains liquid, thereby protecting
that liquid from freezing. It's possible that even the most extreme
cold that can occur on this planet won't be cold enough to freeze all
the water, or to freeze out all the life-forms.

That would also work if sea water actually "excretes" its salt,
though I've never heard of that before, and have a hard time seeing how
it could work.

I don't think heat of fusion has much to do with overall
temperatures. That's really just a little bit of hysteresis in the
freeze/melt cycle. But heat that has to be withdrawn from water to
solidify it also has to be returned before the water can re-liquify. A
zero sum game. And, since Earth's water is part liquid, and part solid,
the game is always giving at the same time it's taking. I can't see how
that would make much difference in average temperature. It might make a
tiny difference in how much water is solid, and how much is liquid, at
any given temperature; but it doesn't change the total kinetic energy
involved. Certainly, any effect it might have would zero out over the
length of a complete warming cooling cycle.

KG