CENTENNIAL TO MILLENNIAL-SCALE CLIMATE CHANGE AND ECOSYSTEM RESPONSE DURING THE MIDDLE PLEISTOCENE FROM THE VALLES CALDERA, NEW MEXICO

Millennial-scale climate change during the last glacial period is well characterized from a variety of paleoclimate records. However, our understanding of millennial-scale climate change from earlier in the Pleistocene comes primarily from Antarctic ice cores and deep-sea proxy records, and is not as well studied in terrestrial settings. We present here a high-resolution, multiproxy record of climate and vegetation change from the Valles Caldera, NM. A strong pattern of warm interstadials and cold stadials at centennial to millennial timescales is evident during MIS 12 (480-426 ka), one of the coldest glacial periods of the Pleistocene. Proxies including physical sedimentary properties, pollen, diatoms, scanning XRF data, and biomarker paleotemperature estimates show 14 prominent Dansgaard-Oeschger oscillations, spaced 2-5 kyr apart, with a sawtooth pattern of abrupt warming (~50 yrs) and more gradual cooling (thousands of years). Within individual D-O events, significant centennial-scale variability is also present, although not as prominent as that of the millennial-scale. Valles Caldera Stadials (VCS) are marked by cold mean annual temperatures, high percentages of boreal-type pollen taxa (Picea, Abies, high-elevation Pinus), lake highstands, and local minima in clastic sediment input relative to organic sediment components. Several prominent cold events, including the strongest right before Termination V, appear to correlate with Heinrich Events in the North Atlantic Ocean. Interstadials are characterized by warmer MATs, lake lowstands, and more open canopy vegetation in the watershed resulting in enhanced erosion and clastic flux into the lake. The pattern of stadial highstands and interstadial lowstands is best explained by a southward / northward migration of the winter jet stream in response to changes in the elevation and size of the Laurentide ice Sheet and enhanced evaporation during the warmer interstadials.