| Understanding and predicting climate change is a major scientific challenge, particularly with regard to climate-induced environmental changes and their impact on human society. Models to predict future climate change are based in part on what we know of past climate variability, from recent instrumental and historical records as well as from geological climate archives. However, the study of palaeoclimates is limited by our ability to accurately determine past temperature variability, especially on the continents. We are currently developing a proxy for lake surface-water temperature based on fossilized crenarchaeotal membrane lipids. The calibration based on analyses of surface sediments of large lakes is remarkably similar to the one we obtained for marine settings, indicating that this palaeotemperature proxy is independent of salinity. We are using this new proxy to reconstruct the post-glacial temperature history of equatorial East Africa from the continuous and finely laminated sediment record of Lake Challa, a crater lake on the lower East slope of Mt. Kilimanjaro. This reconstruction is aided by an analysis of a set of core-top sediments from the present-day lake. First results indicate that surface and down-core sediments indeed contain fossil crenarchaeotal membrane lipids, and have recorded a substantial warming during the deglaciation period. |
