Extrapolar cold reversal during the last deglaciation

The last deglaciation is characterized by large changes in atmospheric CO2, bi-hemispherical warming, dramatic changes in ocean circulation and hydrologic regimes in the tropics and subtropics. Deciphering the interplay between these changes has remained a challenge, in part, due to the lack of precisely-dated hemispherical-scale records of climate variability. Speleothem records, given their excellent preservation, and in many instances their suitability for precise chronology coupled with multiple climate proxies offer special opportunities, especially if they can be obtained from regions that are sensitive to large-scale climate variability. Here, we present a speleothem-based high precision δ18O record from the western interior of North America, Fort Stanton Cave (AH-1), New Mexico, with a mean 2-σ age uncertainty of about 70 years, linked to Northern Hemisphere atmospheric temperature (NHT) variability. The record matches the Greenland ice core records of the last glacial period, including the timing and relative amplitudes of Dansgaard-Oeschger (DO) events, except for part of the last deglaciation. Our data, combined with data from across the globe, show a dramatic cold reversal during the last deglaciation, starting at about 18.65 ka, which we refer to as the Extrapolar Cold Reversal (ECR). This event is not fully expressed in ice core records from either pole, while it is the most prominent feature in high-resolution tropical and subtropical climate proxies. The initiation of the ECR coincides with the beginning of the sudden rise in atmospheric CO2, likely due to upwelling in the Southern Ocean and the near collapse of the Atlantic Meridional Overturning Circulation (AMOC). We attribute the wide-spread extrapolar cooling to upwelling of cold deep waters from the Southern Ocean. This is supported by a variety of isotopic and elemental proxies from large regions of the Atlantic and North Pacific basins showing the incursion of deep Southern Ocean waters into the tropics and the subtropics. Regional climate-hydrologic variability across the extrapolar regions occurring during the ECR interval, such as the large reduction in the strength of the Asian monsoon and large change in the season balance of precipitation of the Southwestern United States, can now be understood in the context of the ECR event.