Large Lakes Observatory at the University of Minnesota - Duluth
Home > People > Tom Johnson

Tom Johnson

Regents Professor

Large Lakes Observatory
University of Minnesota Duluth
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, focusing on tropical East Africa.
  • Sedimentary processes in large lakes, including lake floor morphology, sediment erosion and redeposition by bottom currents, and pore water geochemistry.
  • Acoustic remote sensing of large lake basins, using high-resolution seismic reflection profiling, side scan sonar and multi-beam sonar.
  • Water sustainability and climate in the Great Lakes region of East Africa.

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.
  • Sedimentary processes in large lakes: turbidity plumes and the effects of surface and internal waves on sediment dynamics.

OPPORTUNITIES FOR GRADUATE STUDENTS

Funding is available for graduate 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 co-advise 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 1.2 million years. We also triple cored the north basin of the lake, recovering a high-resolution record spanning roughly the past 75,000 years. Analyses continue on this unique, long record from tropical Africa.

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, spanning the past 1.2 million years.
  • 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
  • Analyses of Lake Superior sediments for past carbon and nitrogen input.
  • Tephrochronology of the Malawi drill core.
  • Modern process studies linking climate forcing to sediment composition in tropical African lakes.

RECENT PUBLICATIONS

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

Slate, J. E., Johnson, T. C., and Moore, T. C., 2012. Potential impact of pre-Columbian agriculture, climate change, and tectonic activity inferred from a 5700-year paleolimnological record from Lake Nicaragua. Journal of Paleolimnology, in review.

Castaņeda*, I., Werne, J.P., Johnson, T. C., and Oberem*, L., 2011. Organic Geochemical Records from Lake Malawi (East Africa) of the last 700 years, part II: Biomarker Evidence for Recent Changes in Primary Productivity. Palaeogeography, Palaeoclimatology, Palaeoecology. v. 303, pp. 140-154.

Johnson, Thomas T. C., Brown, E. T., and *Shi, J., 2011. Biogenic silica deposition in Lake Malawi, East Africa, over the past 150,000 years. Palaeogeography, Palaeoclimatology, Palaeocecology , v. 303, p. 103-109.

Konecky, B., J.M. Russell, T.C. Johnson, E.T. Brown, M.A. Berke*, J.P. Werne, and Y. Huang, 2011. Atmospheric circulation patterns during late Pleistocene climate changes at Lake Malawi, Africa. Earth and Planetary Science Letters. v. 312, pp 318-326.

*Powers, L., Werne, J., *Castaneda, I., Johnson, T. C., Hopmans, E., Sinninghe Damste, S., and Schouten, S., 2011. 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, v. 303, p. 133 - 139.

Johnson, T. C. and Scholz, C. A., 2010. Coping with Lake Kivu, East Africa, EOS, Transactions of the American Geophyscial Union, v. 91, pp 264.

*Breckenridge, A. and Johnson, T. C., 2009. Paleohydrology of the upper Laurentian Great Lakes from the late glacial to early Holocene. Quaternary Research, v. 71, pp 397 - 408.

*Castaņeda, I., Werne, J. P., Johnson, T. C., and Filley, T. R., 2009. Late Quaternary vegetation history of southeast Africa: the molecular isotopic record from Lake Malawi. Palaeogeography, Palaeoclimatology, Palaeocecology, v. 275, pp 100 - 112

Johnson, T. C. and Malala, J. O., 2009. 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.

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: pp 1622-1632.