The climate of tropical Africa transitioned from an interval of pronounced, orbitally-paced megadroughts to more humid and stable conditions approximately 70,000years ago (Scholz et al., 2007). The regional atmospheric circulation patterns that accompanied these climatic changes, however, are unclear due to a paucity of continental paleoclimate records from tropical Africa extending into the last interglacial. We present a new 140-kyr record of the deuterium/hydrogen isotopic ratio of terrestrial leaf waxes (δDwax) from drill cores from Lake Malawi, southeast Africa, that spans this important climatic transition. δDwax shifts from highly variable and relatively D-depleted to more stable and D-enriched around 56ka, contemporary with the onset of more humid conditions in the region. Moisture source and transport history dominate the δDwax signal at Lake Malawi, with local rainfall amount playing a secondary role for much of the paleorecord. Analysis of modern moisture sources for Lake Malawi suggests that D-depletion of waxes during the megadroughts may have been caused by an enhanced contribution of the drier, D-depleted air mass currently located in central southern Africa to the Lake Malawi catchment. This D-depleted air mass is associated with the descending limb of the Hadley cell, which implies significant changes in the Hadley circulation during the megadroughts and related changes in the position of the Intertropical Convergence Zone over Africa. These findings demonstrate the ability of δDwax to serve as an atmospheric tracer when used in conjunction with additional proxy records for moisture balance, and elucidate potential mechanisms for pronounced hydrological change in southeast Africa during the late Pleistocene.
Bibliographical noteFunding Information:
This research was funded by NSF-EAR Grant 0639474 to J. Russell, the Geological Society of America's 2009 Charles A. and June R.P. Ross Research Award to B. Konecky, by an NSF Graduate Research Fellowship to B. Konecky, and by NSF Grants EAR-0602454 and EAR-902714 to T. Johnson. Core storage and sampling assistance were provided by the National Lacustrine Core Repository. Martijn Woltering provided lipid extracts for several samples from MAL05-2A. Customized SCIAMACHY datasets were provided by Christian Frankenberg (NASA-JPL) and Remco Scheepmaker (SRON). We thank two anonymous reviewers for helpful feedback on this manuscript. We wish to acknowledge Candice Bousquet and Michaeline Nelson for laboratory assistance, Rafael Tarozo for technical support, and Lynn Carlson for assistance with spatial datasets.
- East Africa
- Hydrogen isotopes
- Lake Malawi
- Leaf waxes