Bronwen Konecky, Research Scientist, Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder
The tropical water cycle is projected to undergo substantial changes under a warming climate, but direct meteorological observations to contextualize these changes are rare prior to the modern satellite era. The cooler, lower-CO2 conditions of the Last Glacial Maximum (LGM) provide a natural testbed to investigate the mechanisms by which greenhouse gases, ice sheets, and other climate forcings affect tropical rainfall. However, many land-based proxy records from the tropics disagree on the sign and magnitude of glacial hydroclimate changes, making it difficult to tease apart possible mechanisms. Here, I present proxy records from the Indo-Pacific Warm Pool region that track three key aspects of LGM climate: vegetation, surface runoff, and precipitation δ18O and δD. Records are derived from a combination of sedimentary and calcite archives, with special focus given to lake sediment reconstructions from Indonesia where these three aspects of hydroclimate can be examined side-by-side. I interpret these records with the aid of new, single- and combined-forcing model experiments of LGM climate using the water isotope-enabled Community Earth System Model. Model results are integrated with proxy data and modern observations in order to assess the stable O- and H- isotopic “fingerprint” of individual climate forcings on the tropical water cycle, from the geologic past to today.