46-1 Evidence of Increasing Aridification in the Southern United States since the Last Glacial: Leveraging Advances in Tooth Enamel Triple Oxygen Isotopes and Revisiting Paleontological and Archaeological Collections

Session: Old Collections, New Tricks (Posters)

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Abstract:

Since the Last Glacial Maximum (LGM, ~21,000 years before present), North America has experienced hydroclimate reorganization, changes in floral and faunal communities, and expansion of pre-Columbian societies. Model results from TraCE-21K (“Transient Climate Evolution of the Last 21,000 Years”), a coupled ocean-atmospheric-land climate model, suggest that since the LGM, changes in regional atmospheric conditions (e.g., temperature, relative humidity) and water balance (i.e., precipitation minus evaporation; P-E) occurred not only at high latitudes, but also across the southern United States (US). Specifically, in northern Texas, TraCE-21K suggests that since the LGM, relative humidity decreased from 70% to 60% and P-E decreased from 2.0 mm/day to ~0.8 mm/day, consistent with aridification. If these large, rapid changes can be independently confirmed, these results will have implications for better understanding the role of hydroclimate change on widespread megafaunal extinctions, grasslands expansion, and patterns of human activity in the southern US at this time.

Here, we use geochemical proxy data from fossils collected from seven sites in northern Texas to test whether aridification is corroborated by terrestrial proxies. Our dataset encompasses paleontological and archaeological sites representing four general age groups: before LGM, LGM, after LGM, and Holocene. Site excavations were mostly performed prior to municipal infrastructure projects during the 1950s-1970s. We leverage analytical and conceptual advances in tooth enamel triple oxygen isotopes (paired δ¹⁷O-δ¹⁸O values) to reconstruct a history of regional hydroclimate change in northern Texas spanning the last ~30,000 years. Based on studies of enamel triple oxygen isotopes in modern taxa, we expect that, under different hydroclimate states, the range of observed enamel triple oxygen isotope values across all taxa will either be reduced during humid, wetter conditions, or expanded under drier, arid conditions. For each site in this study, we measured enamel triple oxygen isotope values for a variety of extinct and extant taxa (e.g., mammoth, mastodon, deer, pronghorn, camelid, bison, and beaver). Our preliminary data indicate that before and during the LGM, conditions in northern Texas were relatively wet, followed by more arid conditions during the Holocene into the present. These results broadly corroborate TraCE-21K model data for this region. Together, our results combine cutting-edge isotope data with exceptional museum collections to investigate linkages between global climate, regional hydrology, and terrestrial ecosystems in novel ways.

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