THE HOLOCENE CLIMATE OF THE GREAT BASIN

Because many of the lakes in the western Great Basin are fed by Sierran snowmelt, their records of hydrologic variability are transferable to streams that drain the western slope of the Sierra Nevada. Therefore, records of climate change obtained from the Great Basin can be used to evaluate the frequency and severity of droughts that may impact the agriculturally critical Central Valley of California.

Oxygen-18 and TIC records indicate that Owens Lake was shallow or dry between 7.7 and 3.2 calendar ka. Oxygen-18 and magnetic susceptibility records from Pyramid Lake indicate that Lake Tahoe did not spill most of the time between 6.5 and 3.7 ka, indicating that the middle Holocene was ~30% drier than the average climate of the past 100 years. Using radiocarbon, Susan Lindstrom has dated tree stumps submerged in Lake Tahoe and showed that the lake was below its spill point from at least 6.3 to 4.8 ka. Studies of the Ruby Marshes by Bob Thompson, southern Nevada black mats by Jay Quade, Homestead Cave harvest mice by Don Grayson, and textiles found in Lahontan Basin rock shelters by Gene Hattori and Susan McCabe all reinforce the concept of a dry middle Holocene in the Great Basin.

Cores taken from the deep eastern and southern basins of Mono Lake indicate that Paoha Island emerged ~1700 AD, shedding sediment that blanketed both basins. A 300-year climate record of change in the hydrologic balance of Mono Lake can be correlated with tree-ring records of changes in discharge and precipitation from the northern and southern Sierra Nevada. All three records of climate change indicate that major periods of drought occurred during positive phases of the Pacific Decadal Oscillation.

Cores from Pyramid Lake show that during the past 2740 years, 18 multiyear droughts occurred with intervals between droughts ranging from 80 to 230 years. Two multidecadal droughts centered on 1150 and 1280 AD were previously documented in the tree-stump record of Mono Lake by Scott Stine. These droughts affected much of the western U.S. and are associated with Native American migration out of the central San Juan Basin, New Mexico, followed later by abandonment of the Four Corners region.