CENTURY-TO-MILLENNIAL SCALE CLIMATIC VARIABILITY IN LAKE MALAWI REVEALED BY ISOTOPE RECORDS

Abstract

Diatom-based oxygen isotope data (δ18Odiatom) from Lake Malawi show multi-centennial scale wet-dry intervals spaced approximately every 2.3 ka throughout a 25 ka sequence. The δ18Odiatom record is supported by a lower resolution deuterium (δDpa)isotope curve derived from palmitic acid. We interpret these isotope data in terms of major shifts in precipitation and evaporation moderated by seasonal controls on the host organisms. Dry periods marked by relatively positive isotope values, represent the extension of abrupt Holocene events noted from northern and equatorial Africa to 10-15°S. These events in Lake Malawi correspond to cool episodes in Greenland, thereby demonstrating teleconnections generated by meridional temperature gradients. Sea surface temperatures are likely to be the primary transmitter of deglacial climate changes, although trade wind strength and direction is critical in controlling precipitation patterns in tropical regions. Conversely, the global hydrological cycle, driven by low latitude regions represents an important positive feedback amplifying deglacial processes. © 2007.