Ana Prohaska, Alistair Seddon, Bernd Meese, Katherine Willis, John Chiang, Dirk Sachse

The mean state of the tropical Pacific ocean-atmosphere climate, in particular its east-west asymmetry, has profound consequences for regional climates and for the El Niño/ Southern Oscillation variability. Here we present a new high-resolution paleohydrological record using the stable-hydrogen-isotopic composition of terrestrial-lipid biomarkers (δDwax) from a 1,400-year-old lake sedimentary sequence from northern Philippines. Results show a dramatic and abrupt increase in δDwax values around 1630 AD with sustained high values until 1900 AD. We interpret this change as a shift to sustained El Niño-like mean state conditions, and consequently, significantly drier conditions in the western tropical Pacific during the second half of the Little Ice Age. Our findings highlight the prominent role of the tropical Pacific in shaping the hydrology of the Tropics during the Little Ice Age and demonstrate that a marked transition in the tropical Pacific mean state can occur within a human lifetime.