THE RESPONSE OF GREAT BASIN CLIMATE TO MILANKOVITCH FORCING, DANSGAARD-OESCHGER (D-O) AND HEINRICH (H) EVENTS, AND THE PACIFIC DECADAL OSCILLATION (PDO)

Published studies of Great Basin lake-based climate records indicate that the hydrologic cycle has exhibited variability on scales ranging from seasonal to multicentennial. In particular, climate appears to have responded not only to slowly varying Milankovitch forcing but also to abrupt, millennial-scale changes that have been documented in Greenland ice-core records.

Milankovitch forcing influenced the hydrologic and cryologic balances of the Owens River surface-water system during the past 140,000 years. The influence of solar forcing on pollen records from coastal California also has been demonstrated.

A Summer Lake paleomagnetic record has been correlated with D-O events found in the GISP oxygen-18 record, and it has been suggested that D-O events may have affected the hydrologic and cryologic balances of four Great Basin surface-water systems. Lowstands of Mono Lake appear to have accompanied H events, and Lake Bonneville appears to have increased in size during the Younger Dryas interval.

The rise and fall of Great Basin lake systems between 35 and 13 calendar (cal) ka appear to be associated with shifts in the position of the polar jet stream. The lakes achieved their highstand states at about the same time (15 cal ka) as Sierran alpine glaciers began to recede.

The Holocene was characterized by a very dry period between 8 and 3 cal ka. During this time, Owens Lake desiccated, Lake Tahoe fell below its spill point, and trees grew at elevations below the present lake level. Relative to the past 100 years, climate between 8 and 3 cal ka was ~30% drier.

An Oxygen-18 record from Pyramid Lake indicates the presence of 18 oscillations during the past 2760 years with drought intervals sometimes persisting for a century. Two of the persistent droughts occurred during the Medieval Climatic Anomaly and were previously documented in the tree-stump record of Mono Lake. A comparison of tree-ring-based precipitation and runoff records from the Sierra Nevada with tree-ring-based reconstructions of the PDO for the past 300 years indicate that major periods of drought occurred during positive phases of the PDO.