USING CENTRAL TEXAS SPELEOTHEMS TO IDENTIFY REGIONAL MOISTURE DISTRIBUTION DURING THE LAST DEGLACIATION

The SW US is a moisture limited and drought-prone region. Understanding the timing and magnitude of changes in moisture source during the last deglaciation, and in particular, abrupt warming (Bolling-Allerod, BA, 14.7 – 12.9 ka) and cooling events (Younger Dryas, YD, 12.9-11.5 ka), can provide insight into how changes in global climate affect moisture distribution in this region. SW US speleothem δ¹⁸O values and growth rates may serve as proxies for source and amount of rainfall. In central Texas, a speleothem δ¹⁸O and growth rate record (sample CWN-4; Feng et al., 2014) appears to predominantly reflect moisture source (e.g. Gulf of Mexico vs. Pacific moisture), and a concomitant increase in rainfall amount, during the BA. This is based on similarities in changes in CWN-4 δ¹⁸O values from Gulf of Mexico (GoM) seawater proxy records before and during the BA. CWN-4 records a hiatus in growth from 12.3 – 10.1 ka, while two speleothem records from a cave in New Mexico and in Arizona (Asmerom et al., 2010; Wagner et al., 2010), also show a cessation in growth near the end of the YD. The consistent cessation in growth between all three records could suggest a more arid climate in the SW US as the climate transitioned from the colder YD to warmer Holocene climate. Here we present speleothem records from two other caves in central Texas (McN-1; IC-2) which grew during the YD and span the CWN-4 growth hiatus interval, extending later into the Holocene. Similar to CWN-4, and the New Mexico and Arizona records, McN-1 has a slower growth rate near the termination of the YD, potentially indicating drier conditions. Consistent drops in the δ¹⁸O records of ~ -1‰ during the YD in both the GoM seawater and McN-1 and IC-2 records suggest that the speleothem δ¹⁸O records are recording changes in moisture source δ¹⁸O values. Deglacial GoM-sourced moisture was influenced by input from isotopically light meltwater via the Mississippi River drainage system, where δ¹⁸O values from GoM seawater proxy records are suggested to proxy meltwater outflow (Flowers et al., 2004; Williams et al., 2012). These drops in the δ¹⁸O records could also indicate meltwater outflow into the GoM due to increasing temperatures associated with the end of the YD.