CENTENNIAL AND MILLENNIAL-SCALE CLIMATE CHANGE DURING A MID-PLEISTOCENE GLACIAL (MIS 12): A LACUSTRINE RECORD FROM THE VALLES CALDERA, NEW MEXICO

Millennial-scale climate change during the last glacial period is well characterized from a variety of paleoclimate records including ice cores, marine sediment cores, and terrestrial records (lakes, speleothems, loess). However, our understanding of millennial-scale climate change from earlier Pleistocene glacials comes primarily from Antarctic ice cores and marine records, and is not as well studied in terrestrial settings. We present here a multi-proxy, high-resolution lacustrine record of centennial and millennial scale climate change from MIS 12, one of the coldest glacials of the Pleistocene. The record comes from the Valles Caldera, a large Pleistocene volcanic caldera complex in northern NM. High resolution proxies including pollen, scanning XRF data, sediment density, magnetic susceptibility (MS), and biomarker paleotemperature proxies including MBT/CBT, show 14 prominent stadial-interstadial oscillations in this glacial period. These are spaced 3-4 ka apart and are characterized by gradual coolings followed by abrupt warmings, similar to Dansgaard-Oeschger events in the Greenland ice core record. Stadials in the VC-3 record are characterized by cold MATs (-2 to -4^oC), high percentages of boreal taxa pollen (Piceaand Abies), relative lows in density, MS, and Ti counts from scanning XRF. Several prominent cold events, including one at Termination V, likely correlate with Heinrich-like events in the North Atlantic. Interstadials are marked by increases in MATs by up to 4 to 6^oC, abrupt increases in clastic sediment fluxes as shown by Ti count, by abrupt decreases in boreal taxa pollen and increases in non-arboreal pollen (NAP). Each of the 14 abrupt warming events is characterized by a short-lived, dramatic increase in Cyperaceae (Sedge) pollen, indicating a shallower lake with a broad marshy margin. The high interstadial NAP values show a more open canopy in the lake watershed allowing greater erosion and thus higher clastic input to the lake. Within these stadial-interstadial oscillations, some proxies (e.g., Ti, large Pine and Piceapollen percentages) show significant centennial-scale variations, although not as prominent as the millennial-scale variability. The Valles Caldera record shows a robust expression of millennial-scale climate and vegetation change during MIS 12.