Graduation Year
2023
Document Type
Thesis
Degree
M.S.
Degree Name
Master of Science (M.S.)
Degree Granting Department
School of Geosciences
Major Professor
Bogdan P. Onac, Ph.D.
Committee Member
Philip Van Beynen, Ph.D.
Committee Member
Viorel N. Atudorei, Ph.D.
Committee Member
Matthew S. Lachniet, Ph.D.
Keywords
El Malpais National Monument, lava tubes, New Mexico, paleoclimate, stable isotopes
Abstract
A small number of caves and lava tubes worldwide host perennial ice deposits, which occur at elevations well below those of mountain glaciers and in areas outside the permafrost climatic belt, where no surface glaciation exists. These settings make any of the ice deposits in caves or lava tubes particularly susceptible to the current warming trend, leading to the imminent loss of some untapped cryospheric paleoenvironmental archives.
The present work is the result of a paleoclimate study based on ice deposits accumulated within lava tubes in El Malpais National Monument (ELMA, western New Mexico). The ice cores span from 7,000 to 1,000 cal yr BP and their oxygen isotopic (δ18O) values vary from −12.5 to −3.54 ‰, reflecting the isotopic composition of the precipitation. The ice deposits consist mainly of spring-melted winter snow of whose abundance is determined by the interplay of several large-scale atmospheric circulation patterns (e.g., El Niño-Southern Oscillation, Pacific Decadal Oscillation (PDO), Pacific/North American pattern). At times when the North American Monsoon-related rainfall was abundant during summer in the investigated region, its 18O-enriched waters played a critical role in increasing the δ18O values of ice. Back to 3,000 cal yr BP, the ice core (LT 29) reflects the alternation of summer and winter precipitation which, in turn, can be affected by the source of moisture (Gulf of Mexico and Gulf of California versus Pacific). From 7,000 to 3,000 cal yr BP the ice core (LT 91) records winter precipitation coming either from the subtropical or north Pacific.
The lava tubes in ELMA also provide evidence for human visitation during periods of prolonged drought, as evidenced from the local tree ring record, documented by the presence of charcoal fragments. These are the product of man-made fires or wildfires that occurred within or above the lava tubes, respectively. During periods of enhanced La Niña conditions (less snow over the winter), the following summers are drier. Such conditions are exacerbated when La Niña is in phase with negative PDO and weak North American Monsoon.
Scholar Commons Citation
Calabrò, Laura, "Ice-Core Reveals Flavors of Hydroclimate Extremes in the American Southwest" (2023). USF Tampa Graduate Theses and Dissertations.
https://digitalcommons.usf.edu/etd/10465
