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. --------------------------------------------------------------------- Visit our website: http://texascavers.com To unsubscribe, e-mail: texascavers-unsubscr...@texascavers.com For additional commands, e-mail: texascavers-h...@texascavers.com
