Great Basin hydrology, paleoclimate, and connections with the North Atlantic: A speleothem stable isotope and trace element record from Lehman Caves, NV

We present a record of speleothem stable isotope (δ¹⁸O, δ¹³C) and trace element (Mg/Ca, Sr/Ca) variations from Lehman Caves, Nevada for an interval of time (139-128 ka) that encompasses the penultimate glacial termination, Termination II (T-II). Additional growth phases provide data from about 123 ka, a time that correlates with Marine Isotope Stage (MIS) 5e, and about 84 ka and between 82 and 81 ka (MIS 5a). Chronologies from two new stalagmites are anchored by thirty-six uranium-thorium dates. We also present new trace element data from stalagmite LC-2, which has a previously published uranium-thorium chronology and stable isotope record of T-II (Shakun et al., 2011). Our T-II δ¹⁸O record broadly replicates that of the Shakun et al. (2011) and Lachniet et al. (2014) records of this time, recording low values from 139 to 135 ka followed by an approximately 3.5‰ increase over an extended interval between 134 and 129 ka. This rise in δ¹⁸O values occurs during Heinrich Stadial 11 and the associated Weak Monsoon Interval observed in Chinese caves; our record broadly follows the marine termination, rising boreal summer insolation, and the rise in atmospheric CO₂. We infer that this shift results from temperature increase due to increasing atmospheric CO₂ and potentially a change in moisture source or precipitation seasonality from greater influence of the North American Monsoon accompanying summer insolation increase. It is also plausible that the melting of the ice sheet itself may have contributed to both temperature and precipitation seasonality changes. Trace element ratios and δ¹³C values are largely decoupled from δ¹⁸O values, showing minimal variation between 139 and 130 ka, for the duration of the Chinese Weak Monsoon Interval. However, these values increase sharply between 130 and 128 ka, which we interpret as increased prior calcite precipitation driven by a transition from wet to dry conditions. This abrupt drying event coincides within dating uncertainties with the abrupt strengthening of the East Asian summer monsoon, which marks the end of both the Weak Monsoon Interval and Heinrich Stadial 11. Our records demonstrate a link between North Atlantic climate and Great Basin moisture during this time that is consistent with the interpretation of data from the last glacial period and may result from abrupt shifts in Atlantic Meridional Overturning Circulation affecting the strength of the Aleutian Low.