THE LAST DEGLACIATION IN WESTERN NORTH AMERICA: THE VIEW FROM THE PACIFIC OCEAN

The complex climate change Western North America associated with the last deglaciation is best understood with regional grids of information, including data from the eastern Pacific Ocean. Pacific ocean temperatures guide and respond to wind fields and the Pacific is the ultimate source of water for North America west of the Rocky Mountains. In addition, continental margin sediments from the Pacific Ocean preserve climate signals from the western margin of North America to augment other paleoclimate data.

Along the coast of North America, there is a distinctive pattern of ocean temperature change, where very cold waters advected from the subarctic Pacific at the last glacial maximum met waters of near-modern temperature in the Southern California Borderlands and formed a strong temperature gradient near Cape Conception. The gradient formed because the Southern California Borderlands region began warming about 25 thousand years ago, and reached Holocene temperatures by the last glacial maximum. In contrast, records from the Oregon margin show maximum cold temperatures prior to the glacial maximum, but only warm slowly until Holocene temperatures were reached at about 10 thousand years ago. Such a pattern of temperatures within the California Current would not have occurred if the storm tracks were consistently displaced south of their present position.

Coupled with the temperature records there are also coastal pollen and productivity records from the North American margin extending for 500,000 years or more. These records show that deglaciations are consistently associated with a coastal wet interval on the coast. Only records for the last 2 glaciations are available from southern California, but show that the deglacial wet intervals in the south consistently are older than those from central California through Oregon, and during the last deglaciation, only the southern Calfiornia wet interval aligns in time with high lake levels in Lakes Bonneville and Lahontan. The data suggest that precipitation in the Great Basin derives from the tropical Pacific, not from a southerly displacement of temperate storm tracks.