Re: [asa] Global Warming on Mars, Jupiter, Saturn, Pluto, Venus, ...?

Gas clathrates are stable only under high pressure and low temperature. If
pressure decreases or temperature increases enough, they will dissociate.
This also makes it difficult to study them, since they have to be kept at
high pressure and low temperature.

Whether they might catastrophically dissociate would depend on the exact
conditions in the deep ocean. Increasing sea level from melting glaciers
would increase the pressure a bit. A shift in production of deep ocean
water from the present-day cold salty sources (North Atlantic, re-chilled
around Antarctica) to warm salty sources (e.g., the Mediterranean and the
Red Sea) would drastically raise deep-sea temperature. Changing ocean
currents and climate could bring this shift about. Basically, increasing
saltiness or decreasing temperature (until barely above the freezing point)
increases seawater density. Masses of water of sufficiently different
density tend to move over or under each other rather than fully
mixing. Thus, there is a global pattern of dense water forming near the
surface, sinking down, and very gradually changing as it circles the globe
and encounters other water and the seafloor until finally coming to the
surface, currently taking about 300 years. One ongoing change that could
greatly modify the present-day pattern is the increasing meltwater entering
the Arctic is already decreasing the salinity of the water that currently
forms deep ocean water. (Increasing high-latitude precipitation would
contribute also and is a likely consequence of global warming but I don't
know if that particular change has been demonstrated to be happening). I
don't know if anyone knows about the relative responses of methane-producing
and methane-using bacteria to climate change. Many other factors can also
play a role, e.g. the amount of deep-sea volcanic activity. Exactly how all
the different factors will interact is open to plenty of speculation.

Methane is a more effective greenhouse gas than carbon dioxide, so it is of
particular concern.

Methane comes from a variety of sources. Some of it forms abiotically.
Some forms from the breakdown of organic compounds, such as much natural
gas. Some forms by the action of methanogenic bacteria. Because of the
complexity of the biochemical reactions involved, each one slightly favoring
the marginally lighter molecules with 12C rather than the heavier 13C or
14C, bacterially-generated methane is extremely deficient in heavy isotopes
of carbon, even more drastic than the large deficiency caused by similar
processes in photosynthesis. This makes it easy to detect isotopically.

Without looking into the data in more detail, I couldn't say what the
proposed non-clathrate source for methane would be, but most anoxic
environments (marshes, intestines, etc.) and the decay of organisms can
release methane. I would guess that the large increase in marshy tundra
habitat that follows glacial melting would provide some increase in methane
but don't know if that was the identified source.

-- 
Dr. David Campbell
425 Scientific Collections
University of Alabama
"I think of my happy condition, surrounded by acres of clams"
To unsubscribe, send a message to majordomo@calvin.edu with
"unsubscribe asa" (no quotes) as the body of the message.