For the past 30 years my students and I have been interested in reconstructing the history of East African climate and ecosystems through sediment cores taken from lake deposits. Initially we restricted our studies to the Quaternary, but increasingly we are becoming interested in even longer records extending back into the Neogene. Much of our work has been conducted at Lake Tanganyika (photo A) where we have looked at variability in complex ecosystems and the response of ecosystems to lake level and climate change during the Holocene (e.g. Alin and Cohen (2003); Alin and Cohen (2004)), and have studied high resolution, varved records to understand linkages between climate and lacustrine productivity (Cohen et al (2006)).
At Lake Malawi (photos B and C), my colleagues, students and I have been engaged over the past few years in a very exciting effort, the Lake Malawi Scientific Drilling Project. This drilling project recovered almost 700m of core in 2005, the longest of which (382m) provides a record of climate and environmental change for tropical Africa over the past 1.25 million years (Scholz et al., 2007; Cohen et al., 2007; Stone et al., 2011; Ivory et al., 2011).
Since 2006 I have been investigating the paleolimnological history of Lake Rukwa and its past hydrologic connections with Lake Tanganyika. This work was spurred by our interest in the presence of endemic Tanganyikan molluscs and crustaceans in the fossils of the Rukwa basin (photo D). (Cohen et al., in press 2013, Palaeogeog., Palaeoclim., Palaeoecol.)
Long term plans in my lab include extending the evolutionary ecological record of African lakes through additional drill core studies, potentially including Lake Tanganyika (Cohen et al., 2011.)
Key Recent Publications
Scholz, CA, Johnson, TC, Cohen, AS, King, JW, Peck, J, Overpeck, JT, Talbot, MR, Brown, ET, Kalindekafe, L, Amoako, P, et al. 2007, East African megadroughts between 135-75 kyr ago and implications for early human history Proc. Nat. Acad. Sci. 104:16416-16421.
Cohen, A.S., Stone, J.R., Beuning, K.R., Park, L.E., Reinthal, P.N., Dettman, D., Scholz, C.A., Johnson, T.C., King, J.W., Talbot, M.R., Brown, E.T., and Ivory, S.J., 2007 Ecological Consequences of Early Late-Pleistocene Megadroughts in Tropical Africa. Proc. Nat. Acad. Sci. 104:16422-16427.
McGlue, M.M., Lezzar, K.E., Cohen, A.S., Russell, J.M., Tiercelin, J.J., Felton, A.A., Mbede, E., Nkotagu, H.H., 2007 Seismic records of late Pleistocene aridity in Lake Tanganyika, tropical East Africa J Paleolimnol DOI 10.1007/s10933-007-9187-x.
Tierney, J.E., Russell, J.M., Huang, Y., Sinninghe Damsté, J.S., Hopmans, E.C., and Cohen, A.S., 2008, Northern Hemisphere Controls on Tropical Southeast African Climate During the Past 60,000 Years. Science 10 October 2008 322: 252-255.
Mcglue, M.M., Soreghan, M.J., Michel, E., Todd, J.A., Cohen, A.S., Mischler, J., O’Connell, C.S., Castaneda, O.S., Hartwell, R.J.,. Nkotagu, H.N., and Lezzar, K.E., 2009 Environmental Controls On Rift Lake Shell Carbonates: A View From Lake Tanganyika’s Littoral. Palaios 25:426-438.
Tierney, J.E., Mayes, M.M., Meyer, N., Johnson, C., Swarzenski, P., Cohen, A.S., and Russell, J.M. 2010, The Unprecedented Warming of Lake Tanganyika. Nature Geoscience 16 May 2010 DOI: 10.1038/NGEO865
Scholz, C.A., Cohen, A.S., Johnson, T.C., King, J., Talbot, M.R. and Brown, E.T., 2011 Scientific Drilling in the Great Rift Valley: The 2005 Lake Malawi Scientific Drilling Hemisphere East Africa. Palaeogeog., Palaeoclim. Palaeoecol. 303:3-19, doi: 10.1016/j.palaeo.2010.10.030.
Stone, J.R., Westover, K.S. and Cohen, A.S., 2011, Late Pleistocene Diatom Paleoecology of the Central Basin of Lake Malawi, Africa. Palaeogeog., Palaeoclim. Palaeoecol. 303:51-70, doi:10.1016/j.palaeo.2010.01.012
Beuning, K.M., Zimmerman, K.A.,. Ivory, S.J., and Cohen, A.S. 2011, Vegetation response to glacial-interglacial climate variability near Lake Malawi in the southern African tropics. Palaeogeog., Palaeoclim. Palaeoecol. 303:81-92, doi: 10.1016/j.palaeo.2010.01.025.
Park. L.E., and Cohen, A.S., 2011 Paleoecological Response of Ostracods to Early-Late Pleistocene Lake Level Changes in Lake Malawi, East Africa. Palaeogeog., Palaeoclim. Palaeoecol. 303:71-80, doi:10.1016/j.palaeo.2010.02.038.
Reinthal, P. N., Cohen, A.S. and Dettman, D. L., 2011 Fish fossils as paleo-indicators of ichthyofauna composition and climatic change in Lake Malawi, Africa. Palaeogeog., Palaeoclim. Palaeoecol. 303:126-132, doi:10.1016/j.palaeo.2010.01.004.
Cohen, A.S., 2011, Scientific drilling and evolution in ancient lakes: Lessons learned and recommendations for the future. Hydrobiologia. doi 10.1007/s10750-010-0546-7.
Ivory, S.J., Cohen, A.S. and Lézine, A.-M., 2011, Effect of aridity and rainfall seasonality on vegetation in East Africa during the Late Pleistocene. Quaternary Research. doi:10.1016/j.yqres.2011.11.005.
Russell, J.M., Cohen, A.S., Johnson, T.C., and Scholz, C.A., 2012, Scientific Drilling in the East African Lakes: A strategic planning workshop. Scientific Drilling n.14:49-54.
Cohen, A.S., Van Bocxlaer, B., Todd, J.A., McGlue, M., Michel, E., Nkotagu, H., Grove, A.T., and Delvaux, D., Quaternary ostracodes and molluscs from the Rukwa Basin (Tanzania) and their evolutionary and paleobiogeographic implications. In press, Palaeogeography, Palaeoclimatology, Palaeoecology..
A. A storm over the Mahale Mountains at Lake Tanganyika.
B. The Lake Malawi Scientific Drilling Project Viphya Barge with the SEACORE drill
rig mounted in port at Lake Malawi. Note the large blue dynamic positioning
thruster engines mounted on the two forward corners of the barge.
C. Retrieving the hydraulic piston corer on the Viphya deck during
drilling at Lake Malawi.
D. With Hudson Nkotagu and two Tanzanian game rangers at Katavi National Park.
We have just located the point where paleolake Rukwa overspilled into the Lake
Tanganyika Basin during the Early Holocene. Water on the left today flows to
Lake Tanganyika, whereas water on the right flows to Lake Rukwa.