A long record of environmental change from bat guano deposits in Makangit Cave, Palawan, Philippines

We present the first record of Holocene and Pleistocene environmental change derived from the chemical and stable-isotope composition of a tropical cave guano sequence from Makangit Cave in northern Palawan (Philippines). The 180 cm sequence of guano, derived predominantly from insectivorous bats and birds, consists of two distinct units. An upper section of reddish-brown oxidised guano to 110 cm was deposited since the mid-Holocene while a lower section of black, reduced guano was deposited through the Last Glacial Maximum (LGM) to > 30 000 BP. Carbon-isotope (VC) values in guano deposited during the LGM bare as high as -13.5 parts per thousand indicating that a C-4-dominated grassland existed in the area around the cave at this time. Guano delta C-13 values of -25 parts per thousand to -28 parts per thousand suggest that this open vegetation was replaced by C-3-dominated closed tropical forest, similar to that of the present, by the mid-Holocene. The results suggest that the climate of northern Palawan was substantially drier at the LGM than is currently the case.