A 30,000-YR CONTINENTAL PALEOTEMPERATURE RECORD DERIVED FROM NOBLE-GASES DISSOLVED IN GROUNDWATER FROM THE SAN-JUAN BASIN, NEW-MEXICO

Paleotemperatures for the last glacial maximum (LGM) have been derived from noble gases dissolved in C-14-dated groundwater of the Ojo Alamo and the Nacimiento formations in the San Juan Basin, northwestern New Mexico. The difference in mean annual (ground) temperature between th e Holocene and the LGM was determined to be 5.5 +/- 0.7 degrees C. A p ractically identical result, 5.2 +/- 0.7 degrees C, has been obtained previously from the Carrizo aquifer in southern Texas. This suggests t hat the southwestern United States was uniformly cooler during the LGM and that the mean annual temperature gradient along a transect from t he Gulf of Mexico to northwestern New Mexico has been unchanged since the LGM. The noble gas paleotemperatures are supported by paleoecologi cal evidence in the region. The Holocene/LGM temperature difference of 5.4 degrees C indicates that a simple lapse rate calculation may be a pplied to convert the 1000-m glacial depression of snowlines in the Co lorado Front Range into a temperature decrease. A continental temperat ure change of 5.4 +/- 0.7 degrees C is inconsistent with a temperature change of about 2 degrees C determined for the surface waters of the Gulf of Mexico. (C) 1995 University of Washington.