Out of the Tropics: The Pacific, Great Basin Lakes, and Late Pleistocene Water Cycle in the Western United States

Abstract

The water cycle in the western United States changed dramatically over glacial cycles. In the past 20,000 years, higher precipitation caused desert lakes to form which have since dried out. Higher glacial precipitation has been hypothesized to result from a southward shift of Pacific winter storm tracks. We compared Pacific Ocean data to lake levels from the interior west and found that Great Basin lake high stands are older than coastal wet periods at the same latitude. Westerly storms were not the source of high precipitation. Instead, air masses from the tropical Pacific were transported northward, bringing more precipitation into the Great Basin when coastal California was still dry. The changing climate during the deglaciation altered precipitation source regions and strongly affected the regional water cycle.

Seasonality of Groundwater Recharge in the Basin and Range Province, Western North America

“…This finding is corroborated from studies of paleolake shores in the modern day Great Basin desert (Lyle et al, 2012). Meanwhile, paleo-vegetation recorded in packrat middens in the Mojave Desert indicate that between 6,800 and 5,060 years ago, the region was drier than the present (Spaulding 1991).…”

“…The δ 18 O of calcite record at Devils Hole in southern Nevada indicates that prior to 17.5 years BP, the climate of the western U.S. was warmer and wetter (Winograd et al, 2006). This finding is corroborated from studies of paleolake shores in the modern day Great Basin desert (Lyle et al, 2012 (Dansgaard, 1964). Because the region has been both wetter and drier in the time frame in which present day groundwater recharged, it is difficult to say if their might be a bias in the winter recharge fraction estimations.…”

Increased aridity in southwestern Africa during the warmest periods of the last interglacial

“…We use pollen and charcoal as terrestrial tracers, and δ 18 O from benthic foraminifera as a marine tracer. Vegetation reconstructions from marine records have contributed to our understanding of ocean-land interactions in many regions of the world, including the Iberian Peninsula (Sánchez Goñi et al, 2000), the eastern subtropical Pacific (Lyle et al, 2012), and the tropical Atlantic (González and Dupont, 2009). Studies from the African margin (e.g.…”

Spatially explicit analysis sheds new light on the Pleistocene megafaunal extinction in North America

“…The higher precipitation and lower temperature of this region changed and became more comparable to modern climate ca. 9000 cal yr BP (Metcalfe et al 2000;Lyle et al 2012), matching the timing of the megafaunal extinction predicted in that area by our ordinary kriging model. In the Great Lakes region, the predominant biome from 14,000 to 10,000 cal yr BP was cool mixed forest, a noanalogue biome composed of conifers (Pinus, Picea, Tsuga) and the broadleaved Quercus and Betula (Williams et al 2004;Gill et al 2009;Gonzales and Grimm 2009;Blois et al 2011).…”

“…Of greatest interest are the areas with unusually recent last appearances, as they may represent refugia, areas insulated against the more extreme climate changes of northern latitudes. These surfaces, too, match with unique precipitation and biotic changes: from 11,000 to 10,000 cal yr BP, an influx of tropical storms from the eastern Pacific Ocean led to higher precipitation in Mexico and southern Texas, with a noanalogue Pleistocene biome most comparable to modern southern Idaho (Metcalfe et al 2000;Hall and Goble 2012;Lyle et al 2012;Albert 2015). The higher precipitation and lower temperature of this region changed and became more comparable to modern climate ca.…”