From: farrar@datasync.com (Paul D. Farrar)
Newsgroups: sci.environment
Subject: Re: precipitation and greenhouse trends (was Re: nuclear fusion)
Date: Fri, 26 May 2000 03:10:42 GMT

In article <392C34E9.5562369C@xirr.com>, Wed, 24 May 2000 15:00:41
-0500, Dennis Towne writes:

>The reaction I was referring to was the combination of carbon dioxide
>dissolved in the water with calcium, which precipitates out and falls to
>the ocean floor.  This does not require the interaction of life, and is
>believed to have removed most of the CO2 from the atmosphere of the
>early earth.

The reaction actually goes the other direction. When you dissolve CO2
in water it consumes CO3(--) ions, including by dissolving CaCO3
already present on the seafloor. The reaction is

CO2(gas) + H2O + CaCO3 > Ca(++) + 2*HCO3(-)

This equation is the net of several reactions, not a literal reaction.

Weathering of silicate rock, followed by carbonate deposition, can
draw down atmospheric CO2 without being limited by bottom sediments.
(Since it creates them.)

CaSiO3 + CO2(gas) > SiO2 + CaCO3

as can pyrite weathering. Once again the equation is a net result.

>
>Your point is taken however, in that higher temperatures reduce the
>amount of CO2 in the water; but it also increases the rate of
>precipitation as I recall (up to a point anyway.)  Beyond a certain
>temperature this process would doubtless cease to be effective.
>
>Why would the oceans be a source?  I don't understand that statement.

The deep ocean is oversaturated with respect to the current
atmosphere, mainly because of the biota, which fix CO2 near the
surface, die, sink, and are oxidized by bacteria at a greater depth
than where they started. Still, becoming a source is pretty unlikely;
but a reduced sink (relative to the present) is definitely possible.

>
>-dennis towne

--
Paul D. Farrar
http://www.datasync.com/~farrar