Large Lakes Observatory

Tom Johnson

Professor

Large Lakes Observatory
University of Minnesota
2205 E. 5th St.,
Research Laboratory Building 204
Duluth, MN 55812

Tel. (218) 726-8128

Fax: (218) 726-6979

email: tcj at d.umn.edu

RESEARCH INTERESTS

• Paleoclimatology based on the analysis of lake sediment cores, on time scales ranging from decades to millennia.
• Sedimentary processes in large lakes, including lake floor morphology, sediment erosion and redeposition by bottom currents, pore water geochemistry.
• Acoustic remote sensing of large lake basins, using high-resolution seismic reflection profiling, side scan sonar and multi-beam sonar.

EDUCATION

Scripps Institution of Oceanography, Ph.D.
University of Washington, B.S.

RESEARCH AREAS

• The nature of tropical climate change in East Africa based on analysis of sediment cores from the large lakes of the Rift Valley.
• Developing new analytical approaches for improving our interpretation of lake sediment records in terms of past environmental conditions and refining the geochronology in lake sediment cores.
• Deep drilling in Lake Malawi, East Africa: obtaining a record of past climate change in the tropics spanning the past million years.
• Carbon cycles in large lakes.
• Sedimentary processes in large lakes: turbidity plumes and the effects of surface and internal waves on sediment dynamics.

OPPORTUNITIES FOR GRADUATE STUDENTS

I welcome applications for new graduate students, for enrollment in Fall 2008. Funding is available for students who qualify for my program, as either Teaching Assistants in Geology or as Research Assistants, subject to availability of funds. I welcome applications from students with B.S. or M.S. degrees in geology (through the Department of Geological Sciences at UMD or the Department of Geology and Geophysics on the Twin Cities Campus) or with B.S. or M. S. degrees in any of the sciences and engineering (through the graduate program in Water Resource Sciences ). I collaborate with other LLO scientists in paleoclimatology and sedimentology. Doug Ricketts leads LLO's efforts on lakes in central and east Asia. Steve Colman is conducting paleoclimatic and sedimentological studies on Lake Superior and Lake Qinghai in China. Joe Werne and I co-advise students who are applying organic geochemical analysis to paleoclimate studies. Nigel Wattrus and Steve Colman provide a variety of geophysical techniques (airguns, multi-beam sonar, CHIRP high resolution profiling, side scan sonar) for mapping the geology of lake basins. Erik Brown and I are co-advising students who are applying scanning XRF analyses to sediment cores, to generate high-resolution records of past climate change.

In collaboration with scientists from four other universities, we completed a major drilling program on Lake Malawi, East Africa, in early 2005, recovering a 385 m sequence of sediments from the central basin of the lake, that is providing an intriguing record of past climate change in tropical Africa extending back several hundred thousand years. We also triple cored the north basin of the lake, recovering a high-resolution record spanning roughly the past 75,000 years. Our first publications based on analyses of these unique sediment cores are just beginning to appear in the journals -- see list of recent publications, below. Lake Malawi Drilling Project website

I am currently advising or assisting in the advisement of graduate students addressing the following thesis topics:

• High-resolution paleoclimate records in Lake Malawi sediments: linking climate to sediment signals, especially organic biomarkers.
• Application of the new paleothermometer for lacustrine sediment, TEX86, and organic biomarker signals of past aridity to the analysis of sediment cores from African tropical lakes
• Analysis of drill cores recovered from Lake Malawi in early 2005 to generate a several hundred thousand year history of climate variability in tropical East Africa.
• Paleoclimate analyses of Minnesota lake cores using scanning XRF and organic biomarkers to elucidate the nature of the mid-Holocene climatic optimum and the Medieval Warm Period.
• Analyses of Lake Superior sediments for past nitrogen input.

RECENT GRADUATES - Where did they end up?

My graduate students have all succeeded in obtaining good positions in the geosciences upon completion of their degree requirements. Recent examples are:

• Chad Wittkop, Ph.D., 2004 , Assistant Professor, Minnesota State University at Mankato
• James Russell, Ph.D., 2004, Assistant Professor, Brown University, Providence, RI
• Andy Breckenridge, Ph.D., 2005, Assistant Professor, Mercyhurst College, Erie, PA
• Lindsay Powers, Ph.D., 2005, Research Associate, Mzuzu University, and Co-Owner/Manager of a coal mine, Mzuzu, Malawi (East Africa)
• Jon Van Alstine, M.S., 2006, Staff scientist, EPA Environmental Laboratory, Duluth, MN
• Isla Castaneda, Ph.D., 2007, Post-doctoral Research Scientist, Netherlands Institute for Sea Research, Texel, the Netherlands

RECENT PUBLICATIONS

(* refers to graduate student or post-doc advisee)

Johnson, T. C. and McCave, I. N., 2008. Transport mechanism and paleoclimatic significance of terrigenous silt deposited in varved sediments of an African rift lake. Limnology and Oceanography, v. 53: p. 1622-1632.

Johnson, T. C. and Malala, J. O., in press. Lake Turkana and its link to the Nile. In: Dumont, H. (ed.), The Nile, Origin, Environments, Limnology and Human Use. Springer Science, Berlin, pp. 287 - 304.

*Breckenridge, A. and Johnson, T. C., in press. Paleohydrology of the upper Laurentian Great Lakes from the late glacial to early Holocene. Quaternary Research.

*Castaneda, I., Werne, J. P., Johnson, T. C., and Filley, T. R., in press. Late Quaternary vegetation history of southeast Africa: the molecular isotopic record from Lake Malawi. Palaeogeography, Palaeoclimatology, Palaeocecology.

Johnson, Thomas C., Brown, E. T., *Shi, J., in review. Biogenic silica deposition in Lake Malawi, East Africa, over the past 150,000 years. Palaeogeography, Palaeoclimatology, Palaeocecology special issue on the Malawi Drilling Project.

*Oberem, L. P., Werne, J., *Castaneda, I., Johnson, T. C., Hopmans, E., Sinninghe Damste, S., and Schouten, S., in review. Organic geochemical records of environmental variiability in Lake Malawi (East Africa) during the last 700 years, Paart I: the TEX86 temperature record. Palaeogeography, Palaeoclimatology, Palaeocecology special issue on the Malawi Drilling Project.

*Woltering, M., Johnson, T. C., Werne, J. P., Schouten, S., Sinninghe Damste, in review. Late Pleistocene temperature history of southeast Africa: A TEX86 temperature record from Lake Malawi. Palaeogeography, Palaeoclimatology, Palaeocecology special issue on the Malawi Drilling Project.