9506425 Stute One of key questions in paleoclimate research is the degree of change in tropical surface temperatures between today and the last glacial maximum (LGM). Most sea surface temperature records suggest small (<1oC) glacial/interglacial temperature changes, while continental records indicate considerably larger temperature changes. A resolution of this conflict is crucial for a reliable reconstruction of past and prediction of future climate change. We plan to address this issue by improving the continental climate record in the tropics at low altitude, which at this stage is less quantitative than the sea surface temperature record. We will use the concentrations of atmospheric noble gases dissolved in groundwater as paleothermometer ('noble gas thermometer') and confined aquifer as archive of climate change. We request funds for collection and evaluation of geochemical data (He, Ne, Ar, Kr, Xe, 14 C, 13 C, D , 18 O 34 S and major dissolved ions) from two groundwater flow systems in the tropics, the Mekong Delta aquifers in southern Vietnam and the Rio Guayas aquifers in Ecuador. Noble gas paleotemperature records from these aquifers will allow quantitative reconstruction of paleotemperature records for the continental tropics covering the past 30,000 years. The aquifers are located at altitudes less than 100 aaaaam a.s.l. and close to the eastern and western coasts of the Pacific. The records obtained from these aquifers will therefore allow us to directly compare continental and oceanic paleotemperatures during the last glaciation.
