Paleohydrology

 
 

Climate models consistently predict that subtropical and midlatitude arid regions will become drier in response to greenhouse warming, but the magnitude and spatial distribution of this response are poorly understood. In the U.S., there is particular interest in understanding controls on water availability in the Great Basin, a drought-prone region that has experienced substantial population growth over the last two decades. Paleorecords provide a key complement to models of future changes by characterizing the region’s responses to a wide variety of initial conditions and forcings.

During the last glacial period, the U.S. Great Basin experienced much greater effective precipitation, allowing lakes to fill most of its subbasins (lower figure). The largest of these lakes was Lake Bonneville, a lake at the northeastern edge of the Great Basin that was approximately the size of modern Lake Michigan. Though Lake Bonneville’s history has been studied for over a century, substantial uncertainties remain about the precise timing and rate of the lake’s rise and fall and the lake’s response to the abrupt climate changes of the last glacial period.

We have identified lacustrine carbonates precipitated in a series of caves flooded by Lake Bonneville that are capable of being dated with great precision by both U-Th and 14C methods. Beginning and end dates for the deposits precisely record the lake’s rise and fall past each cave site, while stable isotope data provide high-resolution records of the basin’s water balance.

We are also developing complementary records from stalagmites from a high-elevation cave on the western edge of the basin. These deposits record much of the past 400,000 years, including the last 3 interglacials, promising new insights into the region’s water balance during past warm periods.

 

New cave records of past water balance changes in the U.S. Great Basin

Schematic map of lake levels in the U.S. Great Basin during the last glacial period. Lake Bonneville, the largest of these lakes, is shown at the northeastern edge of the Great Basin. Figure courtesy Ken Adams, DRI.

Sampling lacustrine cave carbonates in Craners Cave.

One of the stalagmites from the western edge of the basin used to reconstruct past changes in precipitation.

Inside Cathedral Cave, the site of the best-developed lacustrine cave carbonates.

Lake Bonneville