Identifying regional moisture source during the last deglaciation through analysis of central Texas speleothems

Precipitation in the drought-prone Southwest US is principally sourced from the Gulf of Mexico (GoM) and/or Pacific Ocean, each with distinctive δ18O compositions. Temporal changes in moisture source in this region have been reconstructed from speleothem proxies for the last deglaciation ( 19 - 11 ka). In this study we focus on how moisture sources in Texas speleothem records varied in response to abrupt deglacial warming/cooling events, namely the Bølling-Allerod (BA) interstadial (14.7-14.1 ka) and the Younger Dryas stadial (12.9-11.5 ka). A recent speleothem oxygen isotope record (CWN-4) in a stalagmite from Cave Without A Name near Boerne, Texas, suggests that both the magnitude and timing of changes in δ18O values during the deglaciation closely match δ18O values from a seawater proxy record based on GoM foraminifera (Feng et al., 2014; Flower et al., 2004). A distinct negative δ18O excursion of -3‰ is observed in both records at the onset of the BA, with a subsequent 3‰ increase occurring at the end of the BA. Based on these similarities, regional moisture was hypothesized to be predominantly sourced from the GoM. In order to test the hypothesis that the CWN-4 record captures a regional climate signal, as opposed to recording local variations in in-cave processes, we analyze multiple central Texas speleothem δ18O records. We present oxygen isotope records of a flowstone (IC-2) from a cave 130 km WSW of CWN and a stalagmite (McN-1) from a cave 140 km NE of CWN, with both records spanning the onset of the deglaciation through the Holocene. The IC-2 δ18O record is consistent with that of CWN-4, however, the age model relies on several dates with high uncertainties related to elevated concentrations of detritus containing common Th. The McN-1 record is anticipated to have a more robust age model as it appears to contain less detrital material based on low 232Th concentrations (< 0.009 ppb) in the growth layers that have been selected for U-series analysis. Preliminary δ18O values for the pre-BA period of McN-1 cover a similar range of δ18O values (-4.5 to -2.5‰) compared with the pre-BA portions of the CWN-4 and IC-2 records. These results are consistent with the regional climate hypothesis, which will be tested further by building a complete, high-resolution oxygen isotope time series for McN-1.