Abrupt reorganization of North Pacific and western North American climate during the last deglaciation

Dramatic hydroclimate shifts occurred in western North America during the last deglaciation, but the timing and mechanisms driving these changes are uncertain and debated, and previous modeling has largely relied on linear interpolations between equilibrium snapshot simulations. Using a published transient climate simulation and a range of proxy records, we analyze the region's climate evolution in order to identify the mechanisms governing hydroclimate shifts. A rapid loss of ice around 14,000 years ago causes an abrupt reorganization of the circulation, which precipitates drying and moistening of southwestern and northwestern North America, respectively. The atmospheric circulation transitions between two states on a timescale of decades to centuries, during which time the westerly jet shifts north by about 7 degrees. In contrast to previous studies, we find that changes in the water budget of western North America prior to this event are not attributable to variations in the position of the jet, but rather to the intensity of moisture transport into the continent.