T154 Characterization of Karst Aquifers Using Chemical, Biological, and Hydrogeological Data

Tuesday, 17 October 2023
8:00 AM - 12:00 PM
310 / 311

WHAT IT TAKES TO DEVELOP SPELEOTHEM RECORDS: A DEEP-DIVE INTO THE TRANSFER FUNCTIONS BETWEEN CLIMATE AND GEOCHEMISTRY IN TROPICAL CAVE SYSTEMS FROM THE PHILIPPINES

Paper number: T154-2
Program: Technical Sessions
Time: 8:05 AM – 8:25 AM

Authors

Abstract

Speleothem growth is sensitive to multiple in-cave specific factors in addition to regional and local hydroclimate variability. Developing paleoclimate records using the geochemistry of speleothem growth layers often relies on a detailed understanding of modern cave systematics. Continuous and long-term monitoring of cave systems helps disentangle relationships between regional hydroclimate, karst aquifer hydrology, and cave microclimate. Understanding these empirical relationships is crucial ‘prior’ to the development and interpretation of speleothem records from cave systems across the world. South-east Asia and more precisely, the Philippines, stands out as a region with abundant karst landscape and by extension, multiple cave systems and speleothems, yet has negligible monitoring of these systems.

This work reports the first seasonal monitoring effort across multiple cave systems spanning an approximately 10° latitudinal spread in the Philippines. Bangalau (18.2158° N, 121.8762° E); Maningning Cave (MC, 15.1071° N, 121.0773° E) in Biak-na-Bato National Park; and Puerto Princesa Underground River (PPUR, 10.1926° N, 118.9266° E) in Puerto Princesa Subterranean River National Park were monitored for (1) drip rate, water δ18O, water δ2H, and elemental (cations and anions) composition, (2) monthly or bimonthly modern cave calcite δ18O, δ13C, and elemental (Ca, Mg, Sr) composition, and (3) continuous cave atmosphere pCO2, relative humidity and temperature.

Our preliminary results indicate that the geochemistry of the speleothems extracted from the monitored cave sites will likely reflect paleoclimate variability rather than in-cave processes. Variability of cave atmosphere pCO2 suggests cave ventilation and ideal condition for seasonal growth of calcite. δ18O and δ2H of cave dripwater fall along the Global Water Meteoric Water Line for all the monitored sites suggesting minimal impact of evaporation. Further, regression analyses of δ18O and δ13C in farmed cave calcite suggest sensitivity to rainfall and cave-air temperature. Lastly, slopes of cave dripwater ln(Sr/Ca) and ln(Mg/Ca) largely fall within 0.85+/-0.16 (Sinclair et al., 2012) indicating that prior calcite precipitation, a proxy for local hydrological activity, is driving variations in alkali-earth metals.

Geological Society of America Abstracts with Programs. Vol. 55, No. 6

doi: 10.1130/abs/2023AM-392442

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