README file  NGDC/WDC MGG Data Set: 94075001
Large Lakes Observatory (LLO) 
Biogenic Silica Data and 14C dates from Lake Victoria Sediments

The LLO operates in conjunction with the Limnological Research Center (LRC) in 
working towards fulfilling the objectives of the International Decade for the 
East African Lakes (IDEAL) to study the East African Lakes.  The Lake Victoria 
project is funded by NSF.  Like Lake Victoria, extensive work is being 
continued on Lake Malawi, Lake Turkana, and Lake Edward.   In addition to the 
East African lakes, the LLO is working on Lake Issyk Kul’, Lake Nicaragua, 
and Lake Superior.

SUMMARY

The Biogenic Silica Data file contains data for 5 cores taken from various 
sites in Lake Victoria.  The data include ship, coring date, water depth, 
latitude/longitude, sampling device, sampled interval, % biogenic silica, and 
14C dates. Cores were sampled at 10 cm intervals for biogenic silica analysis. 
 Samples taken for 14C dating were prepared at the LRC Laboratory and sent to 
an outside AMS Facility for analysis.  Pollen, charcoal, and plant 
macrofossils were dated.

Method for Biogenic Silica Analysis:

Biogenic Silica analysis was done using a timed, wet extraction technique 
adapted from D. J. DeMaster (1979).  The analysis was done using 0.5 M NaOH at 
85 0C. 

References:

DeMaster, D.J. (1979) , The Marine Budgets of Silica and 32Si. Ph. D. Thesis, 
Yale University. pp 246-264.
 
Johnson, T. C.,  C. A. Scholz, M. R. Talbot, K. Kelts, R. D. Ricketts, G.
Ngobi, K. Beuning, I. Ssemmanda and J. McGill, 1996.  Late Pleistocene
desiccation of Lake Victoria and rapid evolution of cichlid fishes.
Science, v.273, p. 1091-1093...

Beuning, K., K. Kelts and T. C. Johnson, in press.  Paleohydrology of Lake
Victoria,  East Africa inferred from 18O/16O ratios in sediment cellulose.
Geology.

Johnson, T. C., Y. Chan, K. Beuning, K. Kelts, G. Ngobi and D. Verschuren,
in press.  Biogenic silica profiles in Holocene cores from Lake Victoria:
implications for lake level history and initiation of the Victoria Nile.
In: Lehman, J. T. (Editor), Environmental Change and Response in East 
African Lakes. Kluwer Press,  Amsterdam.

Verschuren, D., D. N. Edgington, H. J. Kling and T. C. Johnson, in press.
The eutrophication of Lake Victoria: sedimentary signals at offshore
stations. Journal of Gt. Lakes Research.

Scholz, C. A., T. C. Johnson, P. Cattaneo, H. Malinga and S. Shana, in
press. Initial results of 1995 IDEAL seismic reflection survey of Lake
Victoria, Uganda and Tanzania.   In:  Lehman, J. T. (Editor),
Environmental Change and Response in East African Lakes. Kluwer Press,
Amsterdam.

Data produced by:

Large Lakes Observatory
University of Minnesota, Duluth
213 Research Laboratory Building
2205 East 5th Street
Duluth, MN 55812-2401
email: tcj@d.umn.edu
URL: http://www.d.umn.edu/llo/

Data available from:

NOAA/National Geophysical Data Center
& collocated
World Data Center for Marine Geology & Geophysics
E/GC3 325 Broadway
Boulder, CO USA 80305
phone: 303-497-6338
fax: 303-497-6513
url: http://www.ngdc.noaa.gov/mgg/geology/llo.html