Abstract
The southern hemisphere tropical climate response to glacial/interglacial climate transitions is poorly understood because there are relatively few quantitative reconstructions of climate in these regions. To gain insight into tropical climate during the last glacial period and over the transition into the Holocene we measured the stable isotope ratios of fluid inclusions from U/Th dated speleothems from southwestern Madagascar ( approximately 24 degrees S). These data provide estimates of the isotopic composition of precipitation and, when combined with measurements of the isotopic composition of speleothem calcite, paleotemperatures for the last approximately 60,000 years. Preliminary results show the delta (super 18) O (sub fi) and delta D (sub fi) composition of fluid inclusion water falls within error (95%) of the modern local meteoric water line, based on station data collected from the capital, Antananarivo. One exception is a modern sample, which falls above the line. Other recent samples have delta (super 18) O (sub fi) values from -4.13 ppm to -5.93 ppm and delta D (sub fi) values from -21.41 ppm to -28.69 ppm, while Holocene delta (super 18) O (sub fi) and delta D (sub f) i values are more enriched, -3.86 ppm and -19.37 ppm. The LGM has a range of delta (super 18) O (sub fi) and delta D (sub fi) values from -3.13 to -6.09 ppm, and -21.37 to -24.97 ppm respectively. The rest of our record has even greater variability with a range of delta (super 18) O (sub fi) and delta D (sub fi) values from -2.11 to -5.58 ppm, and -8.13 to -37.51 ppm respectively. Combining the delta (super 18) O of speleothem carbonate along with the delta (super 18) O of fluid inclusions and assuming equilibrium precipitation, we can calculate cave calcification temperatures, which are generally considered to yield MAAT. Initial data suggest approximately 10 degrees C of warming from the last glacial period to the Holocene in southwestern Madagascar. The onset of warming, approximately 20 kya agrees with organic biomarker temperature records from East Africa lakes, albeit the degree of warming is greater in our Madagascar record, possibly due to being situated further south or differences in what the proxies represent (i.e. lake surfaces vs cave interiors). Future work will focus on additional fluid inclusion measurements to extend this record and provide higher resolution estimates of southern hemisphere tropical temperatures and hydrologic changes from the last glacial period to today.