Moisture variability in the southwestern United States linked to abrupt glacial climate change

Many regions of the world experienced abrupt climate variability during the last glacial period (75-15 thousand years ago(1,2)). These changes probably arose from interactions between Northern Hemisphere ice sheets and circulation in the North Atlantic Ocean(3), but the rapid and widespread propagation of these changes requires a large-scale atmospheric response whose details remain unclear(4-7). Here we use an oxygen isotope record from a speleothem collected from the Cave of the Bells, Arizona, USA, to reconstruct aridity in the southwestern United States during the last glacial period and deglaciation. We find that, during this period, aridity in the southwestern United States and climate in the North Atlantic region show similar patterns of variability. Periods of warmth in the North Atlantic Ocean, such as interstadials and the Bolling-Allerod warming, correspond to drier conditions in the southwestern United States. Conversely, cooler temperatures in the high latitudes are associated with increased regional moisture. We propose that interstadial warming of the North Atlantic Ocean diverted the westerly storm track northward, perhaps through weakening of the Aleutian Low, and thereby reduced moisture delivery to southwestern North America. A similar response to future warming would exacerbate aridity in this already very dry region.