A multi-proxy stalagmite reconstruction of the climate of southwestern North America from the Middle to Late Holocene

The seasonal balance of moisture has a significant effect on natural ecosystems and culture in southwestern North America (SWNA), and it thus is necessary to understand the cause of this moisture variability in order to better predict the scope of potential future changes. Studies of modern SWNA climate indicate that most of the annual moisture at this site comes from monsoonal summer precipitation and a lesser amount of Pacific winter moisture. The climate of the Holocene is of particular interest for constraining natural variability of interglacial climates prior to any anthropogenic influence. An overall transition to a wetter Late Holocene climate in SWNA has been established by different climate proxies, and a definable shift in climate around 4.2 ka is observed in records from various locations around the world. However, the lack of highly resolved records in SWNA limits our ability to determine the mechanisms and timing of this climate shift in this region. In this study we present a high-resolution U-Th dated speleothem record from ~6500 to ~1000 yr BP of oxygen and carbon stable isotopes, Sr and Ba trace elements, grayscale, and 234U/238U isotope ratios from two caves in southeastern New Mexico. Our data suggests the climate of the Middle Holocene was warmer and dominated by monsoonal precipitation, and the Late Holocene was cooler and experienced an increase in winter precipitation. Our record further suggests this shift occurred around 4.2 ka. High-frequency climate variability observed in SWNA during the Late Holocene has been attributed to an active ENSO/PDO system, yet this was limited by lack of direct comparison with the Middle Holocene. Spectral and wavelet analyses from this study show interdecadal and decadal variation observed in the Late Holocene that is not observed in the Middle Holocene, suggesting that strengthened ENSO/PDO activity is responsible for the increased moisture observed in SWNA during the Late Holocene by increasing winter precipitation