DID THE PACIFIC STORM TRACK REACH NORTHEAST MEXICO DURING THE LAST GLACIAL MAXIMUM?

Increased winter precipitation during the Last Glacial Maximum from a strengthened Pacific westerly storm track is well documented in California paleoclimate records. However, we have limited understanding of the spatial extent of increased winter precipitation due to discrepancies in paleo-tuned climate models (PMIP3) and the paucity of paleoclimate records from Northern Mexico. Here, we provide the first multi-proxy (d¹⁸O, d¹³C and Mg/Ca) U-Th dated speleothem record from Tamaulipas, Mexico which records precipitation between 4,000 and 60,000 years BP. As the longest and highest temporally resolved paleoclimate record in Mexico, we have the exclusive opportunity to explore the significance of the intensified Pacific storm track on a larger spatial scale.

Over 2400 stable isotope and trace element measurements at a median resolution of 26 years provide context of the overall response of precipitation during the LGM. Interestingly, there is a decoupling of proxies during this time period. Speleothem d¹⁸O, interpreted to reflect precipitation amount, demonstrates no increase of precipitation in comparison to background glacial conditions. However, speleothem d¹³C and Mg/Ca ratios demonstrate a negative shift of -2‰ and -10 mmol/mol respectively, representing significantly wetter conditions. Results from an active cave monitoring program, precipitation isotope analyses, a suite of back-trajectory moisture analyses and freshwater-forced paleoclimate models will be used to explain these discrepancies and elucidate the dominant drivers of hydrological change in Northern Mexico during the LGM. Ultimately this work serves to highlight similarities, and differences, of precipitation throughout North America, providing a pathway to improve the predictability of precipitation under future climate scenarios.