NORTHERN HEMISPHERE PENULTIMATE GLACIAL MAXIMUM AND TERMINATION FROM SOUTHWESTERN UNITED STATES SPELEOTHEM RECORDS

Accurately dated time series from speleothems are being used to better characterize the rapid and large climate swings associated with glacial terminations. High resolution speleothem records spanning the last northern hemisphere glacial period (NH Glacial-I) and termination (T-I) have revealed the timing and nature of rapid climate changes that occurred in the northern hemisphere, and have established links between glacial terminations and Southwestern United States (SW USA) precipitation regime changes. Our understanding of such timing and precipitation regime responses associated with previous glacial maxima and terminations in the SW USA remains vague. Here we present high resolution carbon and oxygen isotope time series spanning the NH Glacial-II (Penultimate) maximum and T-II from two stalagmites collected from Fort Stanton Cave (FS-TR3) and Carlsbad Caverns National Park, New Mexico (MSC-3).

δ¹⁸O time series of stalagmite FS-TR3 best defines the NH Glacial-II maximum occurring during low values between ~140 to 130 ka. A growth hiatus marks the end of the NH Glacial-II maximum and places T-II at 130.3 ka. T-II in stalagmite MSC-3 is defined by the cessation of stalagmite growth at 128.7 ka. T-II as indicated by both of these stalagmites coincides with a two-step termination defined by China stalagmites at 128.95 and 130.3 ka (Cheng et al. 2009 ref 1). Stalagmite MSC-3 shows a sharp rise in both δ¹³C and δ¹⁸O at 130.3 ka, coeval with the FS-TR3 growth hiatus, but continues to grow an additional 1600 years. The low δ¹⁸O values during this 1600 years of extra growth in stalagmite MSC-3 suggest that the SW USA glacial precipitation regime was pacific-based even though summer insolation at 132.5 ka started rising and was increasing up to the final step of T-II. NH Glacial-II maximum is punctuated by one Heinrich Event (HE-11) lasting ~5 kyr and is devoid of a pronounced warming event equivalent to the Bølling-Allerød event. The growth hiatuses in these stalagmites support a rapid onset of drying conditions in the SW USA probably due to a rapid northern hemisphere glacial termination at T-II likely driven by summer insolation.

1. Cheng, H., Edwards, L., Broecker, W., Denton, G., Kong, X., Wang, Y., Zhang, R. & Wang, X. Ice Age Terminations. Science 326, 248-252 (2009).