A TALE OF TWO PHILIPPINES SPELEOTHEM RECORDS: THE RELATIONSHIP BETWEEN SOUTHEAST ASIAN SUMMER AND WINTER MONSOON SYSTEMS DURING THE LATE HOLOCENE

The Indo-Pacific Warm Pool (IPWP) exhibits complex hydroclimate dynamics with high variability and is therefore a critical force in the global hydrologic cycle. This hydroclimate variability is largely influenced by the southeast Asian Southwest Summer (SWM) and Northeast Winter Monsoons (NEM), yet there is very little understanding of the relationship between the two monsoon systems. Positive correlation between the two systems have been found on orbital scales, but additional studies are necessary to disentangle the evolution of the correlation into the Holocene and on shorter timescales.

This study utilizes speleothems to reconstruct precipitation in the Philippines that can be linked to southeast Asian regional monsoon seasons. We compare the stable isotope (¹⁸O and ¹³C) and trace element (Mg/Ca, Sr/Ca, Ba/Ca) records of two speleothems from two different caves in the Philippines – Ari-0 Cave in Cagayan (ARI-0-CS2 – 18.1994°N, 121.8897°E) and Puerto-Princesa Subterranean River National Park in Palawan (GG1 – 10.167°N, 118.917°E). Ari-0 Cave lies in the northeast Philippines and Palawan lies in the southwest and, based on ongoing monitoring efforts, these two caves are largely affected by the NEM and SWM, respectively.

Stalagmite GG1 grew between 1 and 4 ka and stalagmite CS2 grew between 1 and 5 ka. ¹⁸O results of the speleothem records show anti-correlated hydroclimate conditions of the NEM and SWM on millennial timescales. Trace element analyses were conducted to gain insight into the driving factors of the stable isotope records. Preliminary trace element results suggest potential external factors influencing the stable isotope records of GG1. We are doing further analysis to determine whether this is true, and if necessary, correction methods will be applied to the stable isotope records to ensure we are recording the climate signals. The coeval growth allows for an intra-speleothem comparison to better understand regional differences of monsoon dynamics during the late Holocene in the Philippines. Further, comparisons to other speleothem records in the IPWP show regional agreement in the northeast as well as in the southwest. The results from this study will improve our understanding of the southeast Asian monsoon system and their regional effects on IPWP hydroclimate variability.