INVESTIGATING THE CAUSES OF PLUVIAL CONDITIONS IN THE SOUTHEASTERN BASIN AND RANGE DURING MIS2 USING CLUMPED ISOTOPE PALEOTHERMOMETRY OF CARBONATES IN LACUSTRINE AND WETLAND SEDIMENTS

The last Deglacial interval (~19-11 ka) was marked by major perturbations to Earth’s climate, featuring a coupled increase in atmospheric temperature and CO₂ concentration, approaching modern levels by the early Holocene. Several discharges of freshwater into the North Atlantic caused by melting and collapse of continental ice sheets affected ocean circulation and sea-surface temperatures, in turn triggering abrupt changes in terrestrial climate worldwide. While the timing and amount of associated temperature changes at high latitudes have been quantified from ice core records, corresponding reconstructions from lower latitudes are comparatively sparse and concentrated along coastlines, at high elevations, and in tropical and mesic regions. This is problematic for efforts to improve the reliability of long-term climate forecasts, reliant on models lacking sufficient validation by reconstructions from interior drylands—presently covering nearly half of Earth’s land surface.

Evidence of past hydroclimatic changes in arid regions comes from the geomorphic shoreline records of ancient lake-surface area in internally-drained basins, reflecting spatial and temporal variations in effective moisture. However, the utility of these records depends on our relatively limited ability to deconvolve the contributions of temperature and precipitation to these changes. Here we explore the influence of temperature on past hydroclimate in the southern Basin and Range using clumped isotope paleothermometry from biogenic and sedimentary carbonates in lacustrine and wetland deposits spanning the Last Glacial Maximum (~23-19 ka) and ensuing deglaciation. Specifically, we compare estimates of past changes in surface-water temperature and δ¹⁸O to seasonal output from coupled-climate models in the PMIP3 ensemble.