Hydroclimate response in Texas and Gulf of Mexico to rapid warming during the last deglacial: High-resolution speleothem proxy and monitoring evidence

Abstract

Cave calcite (i.e., speleothem) proxy records that span abrupt warming events, such as those of the last deglacial, may prologue regional responses of hydroclimate to 21st century warming. Proxy reliability is advanced by an understanding of the modern hydrologic system and controls on calcite growth. Here we integrate monitoring of Cave CWN in central Texas with high-resolution imaging and δ18O analysis of Stalagmite CWN-4 to understand how regional hydroclimate changed during a rapid deglacial warming event - the transition from Heinrich Stadial 1 (HS1) to the Bølling-Allerød (BA) warm period. This event is recorded in CWN-4 as a rapid negative δ18O excursion of 1.7‰ over ∼210 years (HS1-BA δ18O excursion = ‘HBO’), followed by a 6-fold growth rate increase.Monitoring demonstrates that modern calcite grows during cool seasons, growth rates follow drip rate, and drip water and calcite δ18O reflect the δ18O of recharge. Because drip waters have interannual epikarst residence times, their δ18O values are well-mixed averages of their Gulf of Mexico (GoM) moisture source δ18O values, which rapidly decreased during Laurentide Ice Sheet (LIS) melting events. Confocal laser fluorescence microscopy imaging indicates that growth lamina are seasonal within U-series age constraints. The timing of the HBO (14.75 ± 0.08 to 14.54 ± 0.08 ka), corresponds with 1) the onset of Bølling warming in Greenland (14.64 ka), 2) AMOC reinvigoration (∼14.61–14.25 ka), 3) Meltwater Pulse 1a (14.65–14.31 ka), and 4) Meltwater Flood 3 (MWF-3) - the most intense episode of LIS meltwater discharge into the GoM (14.97–14.46 ka). The rapid increase in growth rates following the HBO indicates an abrupt transition to a wetter hydroclimate in central Texas following these regional and global events.The HBO δ18O excursion occurred monotonically, consistent with meltwater discharge being continuous. This excursion also corresponds with climate change recognized across the HS1-BA transition in marine and terrestrial records influenced by changes in North Atlantic climate, AMOC, and ITCZ migrations. We infer that central Texas deglacial hydroclimate largely followed changes in AMOC, linked via meltwater input to the GoM. Periods of fast (slow) speleothem growth coincide with warmer (cooler) North Atlantic episodes, with the exception of the HS1 to BA transition. For this transition, slow growth rates during MWF-3 may reflect protracted cooling of GoM SST and corresponding atmospheric moisture reduction. The common timing and duration of the HBO with shifts toward wetter conditions across the HS1-BA transition in many northern Hemisphere climate records supports common ocean-atmosphere teleconnections related to AMOC intensity.