HEMIARID BASIN RESPONSES TO ABRUPT CLIMATIC-CHANGE - PALEOLAKES OF THE TRANS-PECOS CLOSED BASIN

Western North American hemiarid basins situated along a climate bounda ry zone, or threshold, that separates regions of different climate reg imes exhibit greater variability to changes in hydroclimatic variables . The Trans-Pecos Closed Basin study examines how global paleoclimatic factors and intrinsic geographic controls act in determining the thre shold between stares of hydroclimatic equilibria. Geomorphic, radiocar bon, and limnetic evidence identifies four major highstands for late P leistocene Lake King during the Last Glacial Maximum (LGM). Patterns i n the resulting model limnograph for Lake King suggest that runoff con tributions from basin catchments to the inundated area were limited by precipitation rather than evaporation. Timing of the onset of lacustr ine transgressive events corresponds with the later stages of cooling events recorded in the Greenland ice and North Atlantic deep-sea sedim entary record. Correlation of Trans-Pecos lacustrine environments with North Atlantic cooling implies that full pluvial conditions in the ba sin were limited to those periods when those cooling events resulted i n extreme equatorward shifts of the LGM subpolar winter storm tracks, providing a moisture source to the basin. By comparing timing, intensi ty, and direction of climate change over a widely spaced array of hemi arid basins, the global implications of climatic events are better und erstood.