Collaborative Research: Developing Continental Paleoclimate Records from Soils Using Pedogenic Carbonate

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This NSF support will allow the investigators to complete the first critical phase of what they think should be a detailed view into the climate of the mid North American continent over the past hundred thousand years. This record comes from arid soils of the Wind River Basin in Wyoming. The vast majority of high resolution (~ hundred to thousand year time windows) past climate data comes from oceanic sediments, and the chemical record provides information on the temperature and volume of the oceans over time. While this record is very important to understand how the Earth's climate has varied, and how past warm periods can inform us how the Earth might respond to present greenhouse gas increases, these records do not tell us directly what was happening on the continents, and how climate patterns on land changed with global ocean changes. There is arguably only one "high resolution" land-based paleoclimate record on land: the so-called Devil's Hole limestone accumulation that formed by ground water in the desert of the California/Nevada border. The oxygen isotopes in the limestone provide detailed changes in the land temperature of the southern Great Basin over multiple glacial and interglacial climates. To date, this remains arguably the most detailed land record on Earth, and is formed in a very unique geological setting that is not found in many other locations. For the past two decades, the investigators have been studying the growth rings of calcium carbonate in Wind River Basin soils. During this time interval, there has been a revolution in the ability to study these growth rings in microscopic detail: lasers can volatilize the minerals at a micron scale and new generations of mass spectrometers can both determine the age of the mineral and its oxygen isotope composition (which is a guide to the temperature and the source of rainfall in the region). They have been able to collect multiple samples from the field, and through numerous selection criteria, have found growth rings that are continuous over hundred thousand year time scales. Six of these have been dated, and one has been sent to the NSF SIMS isotope facility in Madison WI for preliminary oxygen isotope analyses. The oxygen isotope data, when linked with the sample age, indicate that these thin (~ 2 cm or less) growth rings span nearly two hundred thousand years, and that the oxygen isotope pattern is likely temporally comparable to that of Devil's Hole. The preliminary record shows both similarities and dissimilarities to Devil's Hole (as might be expected for the distance between the two locations), suggesting insights into the precipitation sources of the mid-continent. Additionally, since desert (and carbonate bearing soils) cover ~20% of the Earth, the extension of this technique to a wide variety of locations seems promising, opening new insights into the climate history of the Earth's land surface over the last few glacial cycles. This project requests the funds to support an advanced PhD student for one year to (1) make two trips to the SIMS facility in Wisconsin to collect carbon and oxygen isotope profiles on the remaining dated laminations, (2) write a research paper on the results of the work, and (3) use the results as the basis for a request for longer term support to expand the record to other locations.