AFP - Valles Caldera Sediment Study Show Past Multicentury SW Droughts, Increases Up To 14F

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Layers in the 260-foot-long sediment core were easily distinguishable, and were bounded by distinct layers of volcanic ash that allowed for very accurate dating. Researchers looked at chemical constituents trapped within the layers as well as plant and pollen debris to characterize the climate conditions of the time.

The sediment layers from beneath the South Mountain Lake covered two "interglacial" periods. Such periods are significant because they represent a time between ice ages when warmer temperatures mimicked present-day temperatures. The ancient interglacial period, known as Marine Isotope Stage 11-MIS 11 for short-lasted about 50,000 years and included, among several periods of climatic variation, one definitive megadrought period followed by a cooler period.

Prior to the study, detailed data about MIS 11 had been scarce because most of the information was gathered from Antarctic ice cores or marine sediments. The terrestrial record obtained beneath South Mountain Lake revealed a bounty of information that nicely details the ancient climate.

The oldest warm period in MIS 11 appears somewhat analogous to the present-day Holocene interglacial period, which has been ongoing for about the past 10,000 years. During MIS 11, the ancient climate warmed dramatically by about 14 degrees Fahrenheit.

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http://www.terradaily.com/reports/Dry_Lake_Reveals_Evidence_Of_Southwestern_Megadroughts_999.html