Sounds like a job for Geochemists' Workbench (or PHREEQC), which I have
access to. I'd be glad to do some runs if data is available. Temperature
effects I bet are minor as mentioned, and partial pressure of CO2 should be
a main driver for depositional events of calcite "snow". These depositional
events happen in lakes, too.
Just for the record, this is Neal Hines (NSS 47827), relatively new to
Texas (Austin), having moved here from Minnesota with my wife who is in
music grad. school at UT. I've met several cavers already and I look
forward to getting underground a bit more.
-Neal
On Feb 13 2012, George Veni wrote:
Measurements I made of soil and cave air carbon dioxide during my
dissertation research in the Honey Creek area show a strong positive
correlation between spring-summer plant growth and increases in cave air
carbon dioxide. Studies in other areas have shown the same thing.
You are correct that the water temperature has an effect, as do seasonal
changes in water chemistry, both of which I didn't mention for the sake of
brevity. I would expect that a decrease in temperature would result in
dissolution of the rafts rather than the precipitation we see. However,
because the water temperature has usually come close to equilibrating with
the temperature of the surrounding mass of rock and water by the time we
see
it in the areas where rafts are deposited, I would also expect any
temperature effects to be minor given the small decrease in temperature. I
have measured significant changes in carbon dioxide and know that is
certainly a major factor.
It would be interesting to run a "standard" example of the cave's water
chemistry values through a geochemical model and tweak the temperature and
carbon dioxide levels over a series of iterations to predict how much of a
change in temperature or carbon dioxide would be needed to affect raft
deposition one way or the other.
George
***************************
George Veni, Ph.D.
Executive Director
National Cave and Karst Research Institute
400-1 Cascades Avenue
Carlsbad, New Mexico 88220-6215 USA
Office: 575-887-5517
Mobile: 210-863-5919
Fax: 575-887-5523
gv...@nckri.org
www.nckri.org
-----Original Message-----
From: Diana Tomchick [mailto:diana.tomch...@utsouthwestern.edu]
Sent: Monday, February 13, 2012 12:40
To: <gv...@nckri.org>
Cc: texas cavers
Subject: Re: [Texascavers] Honey Creek sand observation
The degree to which the sand accumulates or is noticed at any given time
depends mostly on:
. How much time has passed since the last flood, which determines
how many rafts will accumulate floating on the water;
. How severe the flood was, and did it just sink the floating
rafts where they can be seen, or wash them away or bury them under silt and
clay where they will not be seen;
. The chemistry of the cave's water and atmosphere to create
favorable conditions for raft development. Kurt is right that they usually
form more quickly in the winter because the cave atmosphere has less carbon
dioxide at that time, allowing more carbon dioxide to degas from the water,
driving the water to supersaturation with respect to calcite, and promoting
calcite raft development.
Does the cave atmosphere have less carbon dioxide due to lesser amounts of
degradation of biomass in the ground over the cave in the winter (due to
the
lower surface air temperatures), or is it due to a reduction in temperature
of the creek water in the cave? Because the solubility of carbon dioxide
increases as the temperature of water decreases.
Diana
* * * * * * * * * * * * * * * * * * * * * * * * * * * * Diana R. Tomchick
Professor University of Texas Southwestern Medical Center Department of
Biochemistry
5323 Harry Hines Blvd.
Rm. ND10.214B
Dallas, TX 75390-8816, U.S.A.
Email: diana.tomch...@utsouthwestern.edu
214-645-6383 (phone)
214-645-6353 (fax)
________________________________
UT Southwestern Medical Center
The future of medicine, today.
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