RUI: High-resolution sediment records of late Holocene paleohydrology from the summer and winter rainfall regions of South Africa.

Paul Smith'S College Of Arts And Sciences, Paul Smiths NY

Investigators

Abstract

Paleoclimatic research in Africa has relied heavily upon analysis of lake sediment cores and has provided abundant evidence of dramatic climate fluctuations during the late Quaternary. However, much of that work has suffered from several important limitations, including (1) coarse temporal resolution of time series, (2) gaps due to discontinuous sedimentation or loss of soft upper sediments during coring, (3) complications in sediment dating, (4) a scarcity of continuous lake records from the southern hemisphere, and (5) difficulty in teasing out the relative contributions of rainfall and temperature to inferred environmental changes. These limitations have reduced the clarity of climate reconstructions and hindered the development of robust regional and global-scale models of rainfall dynamics, especially for the late Holocene. Under this RUI grant, the PI and undergraduate students analyze diatoms (algae with glassy shells) and geochemical records in lake sediment cores representing the last 2000 years that were recently collected in South Africa in collaboration with American and African students and colleagues. These cores represent key sites in the southern summer and winter rainfall regions of the continent and they contain clear evidence of paleohydrological fluctuations. The central goal is to clarify the nature and causes of African rainfall variability during the late Holocene. Intellectual merit: The fine temporal resolution of these analyses, conducted at annual to decadal increments and dated with 14C, 210Pb, 137Cs, and pollen indicators is unusually high for African cores. These detailed time series help to refine the nature and timing of key paleoclimate events in southern Africa in relation to records from equatorial and polar latitudes. They also provide continuous paleohydrological records leading into modern times, and help to clarify the interpretations of pollen- and isotope-based studies in the region. These findings are used to evaluate models of rainy season responses to past global warmings and coolings, of African-Antarctic teleconnections, and of solar influences on African rainfall during the last two millennia. Transfer functions are used to convert diatom data into the longest and most detailed reconstructions of Holocene water chemistry parameters that have ever been obtained in South Africa. Results are compared to other records ranging from equatorial to polar latitudes, putting the climatic history of South Africa into a global context. Broader impacts: Rainfall has much greater ecological and societal impacts in Africa than temperature alone does. By clarifying the recent hydrological history of South Africa, this study supports efforts to model and predict rainfall dynamics, as well as the roles of Antarctic and solar influences (and, indirectly, greenhouse warming) in relation to past and future African climate changes. Two undergraduate students are helping to collect and analyze cores for their senior capstone projects at Paul Smith's, a small college in an under-served rural region of upstate New York. Collaborations with paleoecologists in South Africa and Britain enhances PI and student access to research facilities, professional networks, and expertise, and the data is archived at the NOAA World Data Center. The internationally syndicated "Natural Selections" radio program broadcasts the results of this work widely and also makes podcasts available from the North Country Public Radio website.