Ice Deposits in Lava Tubes from West-Central New Mexico as Archives of Past Volcanic Eruptions and Climate Change
The Southwest of the United States is currently in a megadrought phase. Recent studies have shown that three of the most severe droughts of the last two millennia have occurred in the last 120 years, while geo-archaeological evidence suggests there were five megadroughts just from 150 to 950 CE. To...
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| Format: | Thesis |
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Digital Commons @ University of South Florida
2022
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| Online Access: | https://digitalcommons.usf.edu/etd/10364 https://digitalcommons.usf.edu/context/etd/article/11651/viewcontent/VitelliHawkins_usf_0206M_17431.pdf |
| Summary: | The Southwest of the United States is currently in a megadrought phase. Recent studies have shown that three of the most severe droughts of the last two millennia have occurred in the last 120 years, while geo-archaeological evidence suggests there were five megadroughts just from 150 to 950 CE. To try to better understand the causes of the droughts across the Southwest, a 110-cm long ice core was drilled from an ice deposit in a lava tube (Cave 29) from El Malpais National Monument in west-central New Mexico. The δ18O values in the ice core (ranging from −11.78 to −3.54‰) indicate that the overall strength of the summer rainfall, the North American Monsoon (NAM), is responsible for increases in the values. The changes in the stable isotope values also helped determine the effects of the Southwest’s winter climate variability related to the El Niño Southern Oscillation, the Pacific/North American pattern, and the positional trend of the Intertropical Convergence Zone (ITCZ). Cave 29’s record shows megadrought periods typically corresponding with La Niña phases triggered by a northward shift in the ITCZ and the addition of weak NAMs. During these extensive droughts, Ancestral Puebloan communities across El Malpais melted the ice from the lava tubes. The abundance of charcoal deposits throughout Cave 29 is evidence of ice harvesting activities and their presence helps establish a chronology using radiocarbon dating. Additionally, since major volcanic eruptions release sulfur dioxide into the stratosphere, major ion geochemistry was also applied to the Cave 29 ice core to measure the non-sea-salt sulfate content to infer past volcanic eruptions. Recent data indicates an increase in El Niño events and an overall southward migration of the ITCZ since the Middle Holocene; therefore, the Southwest should currently be undergoing wetter conditions. However, the current megadrought demonstrates that this is not a result of a natural climactic cycle but may be an effect of anthropogenic warming. Furthermore, ... |
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