Trade winds drive pronounced seasonality in carbonate chemistry in a tropical Western Pacific island cave—Implications for speleothem paleoclimatology

Abstract Carbon dioxide concentrations in caves are a primary driver of rates of carbonate dissolution and precipitation, exerting strong control on speleothem growth rate and geochemistry. Long‐term cave monitoring studies in midlatitude caves have observed seasonal variability in cavepCO2,whereby airflow is driven by temperature contrasts between the surface and subsurface. In tropical settings, where diurnal temperature cycles are larger than seasonal temperature cycles, it has been proposed that caves will ventilate on daily time scales, preventing cavepCO2from increasing substantially above atmosphericpCO2. By contrast, the relatively small temperature difference between the surface and subsurface may be insufficient to drive complete ventilation of tropical caves. Here we present results of an 8 year cave monitoring study, including observations of cavepCO2and carbonate chemistry, at Jinapsan Cave, Guam (13.4°N, 144.5°E). We find that cavepCO2in Jinapsan Cave is both relatively high and strongly seasonal, with cavepCO2ranging from 500 to 5000 ppm. The seasonality of cavepCO2cannot be explained by temperature contrasts, instead we find evidence that seasonal trade winds drive cave ventilation and modulate cavepCO2. Calcite deposition rates at seven drip sites in Jinapsan Cave are shown to be seasonally variable, demonstrating that speleothem growth rates in Jinapsan Cave are strongly affected by seasonal variations in cavepCO2. These results highlight the importance that advection can have on cave ventilation processes and carbonate chemistry. Seasonality in carbonate chemistry and calcite deposition in this cave affect the interpretation of speleothem‐based paleoclimate records.