Abstract
A 6,500-year diatom stratigraphy has been used to infer hydrochemical changes in Lake Awassa, a topographically closed oligosaline lake in the Ethiopian Rift Valley. Conductivity was high from ~6400-6200 BP, and from 5200-4000 BP, with two brief episodes of lower conductivity during the latter period. Although the timing of the conductivity changes is similar to the timing of lake-level change in the nearby Zwai-Shalla basin, their directions are the reverse of that expected from a climatic cause. Dissolution of the tephras which precede both phases of high conductivity cannot explain the increases in salinity, because rhyolitic tephras are only sparingly soluble. Instead, the pulsed input of groundwater made saline by the reaction of silicate minerals and volcanic glass with carbonic acid, formed from the solution of carbon dioxide degassed from magma under the Awassa Caldera, is suggested as a plausible mechanism for the observed change in lake chemistry. Diatom-inferred hydrochemistry cannot therefore be used to reconstruct climate change in Lake Awassa.
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Abella, S. E. B, 1988. The effect of the Mt. Mazama ashfall on the planktonic diatom community of Lake Washington. Limnol. Oceanogr. 33: 1376-1385.
Barker, P. A., N. Roberts, H. F. Lamb, S. van der Kaars & A. Benkaddour, 1994. Interpretation of Holocene lake-level changes from diatom assembalages in Lake Sidi Ali, Middle Atlas, Morocco. J. Paleolim. 12: 223-234.
Baross, J. A., C. N. Dahm, A. K. Ward, M. D. Lilley & J. R. Sedell, 1982. Initial microbiological response in lakes to the Mt. St. Helens eruption. Nature 296: 49-52.
Battarbee, R. W., 1986. Diatom analysis. In Berglund, B.E., (ed) Handbook of Holocene Palaeoecology and Palaeohydrology. John Wiley & Sons, Chichester: 527-570.
Berhanu G., 1996. The origin of high bicarbonate and fluoride concentrations of the Main Ethiopian Rift Valley, East African Rift system. J. Afr. Earth Sci. 22: 391-402.
Bischoff, J. L. & R. J. Rosenbauer, 1996. The alteration of rhyolite in CO2 charged water at 200 and 350°C-the unreactivity of CO2 at higher temperature. Geochim. Cosmochim. 60: 3859-3867.
Broecker, W. S., R. Wanninkhof, G. Mathieu, T. H. Peng, S. Stine, S. Robinson, A. Herczeg & M. Stuiver, 1988. The radiocarbon budget for Mono Lake: An unsolved mystery. Earth planetary Sci Lett. 88: 16-26.
Darling, W. G., Berhanu G. & M. K. Arusei, 1996. Lake-groundwater relationships and fluid-rock interactions in the East African Rift Valley: isotopic evidence. J. Afr. Earth Sci. 22: 423-431.
Dawson, J.B., 1966. Oldoinyo Lengai-an active volcano with sodium carbonatite lava flows. In Tuttle, O. F. & J. Gittins (eds), Carbonatites. J. Wiley & Sons, NY. 155-168.
Dean, W. E., 1974. Determination of carbonate and organic matter in calcareous sediments and sedimentary rocks by loss on ignition: Comparison with other methods. J. sedimentary Petrol. 44: 242-248.
Di Paola, G. M., 1972. The Ethiopian Rift Valley (between 7°00′ and 8°40′lat North). Bull. Vulcanol. 36: 517-560.
Elizabeth K., Zinabu G.-M. & I. Ahlgren, 1994. The Ethiopian Rift Valley lakes: Chemical characteristics of a salinity-alkalinity series. Hydrobiologia 288: 1-12.
FAO, 1984. Agroclimatological data for Africa. Food and Agriculture Organization of the United Nations, Rome.
Farrar, C. D., M. L. Sorey, W. C. Evans, J. F. Howle, B. D. Kerr, B. M. Kennedy, C.-Y. King & J. R. Southon, 1995. Forest-killing diffuse CO2 emission at Mammoth Mountain as a sign of magmatic unrest. Nature 376: 675-678.
Foucault, A., & D. J. Stanley, 1989. Late Quaternary paleoclimatic oscillations in East-Africa recorded by heavy minerals in the Nile Delta. Nature 339: 44-46.
Freeze, R. A. & J. A. Cherry, 1979. Groundwater. Prentice-Hall, Englewood Cliffs, 604pp.
Gasse, F., 1977. Evolution of Lake Abhé (Ethiopia and TFAI) from 70,000 b.p. Nature 265: 42-45.
Gasse, F., 1986. East African diatoms: Taxonomy, ecological distribution. Bibliotheca Diatomologica, Band 11. Cramer, Berlin, 201pp.
Gasse, F. & C. Descourtieux, 1979. —Diatomées et évolution de trois milieux Ethiopiens d'altitude différente, au cours du Quaternaire supérieur. Palaeoecol. Africa 11: 117-134.
Gasse, F. & F.A. Street, 1978. Late Quaternary lake-level fluctuations and environments of the northern Rift Valley and Afar region (Ethiopia and Djibouti). Palaeogeogr. Palaeoclim. Palaeoecol. 24: 279-325.
Gasse, F., S. Juggins & K. Ben Khelifa, 1995. Diatom-based transfer functions for inferring past hydrochemical characteristics of African lakes. Palaeogeogr. Palaeoclim. Palaeoecol. 117: 31-54.
Gasse, F., P. Barker, P.A. Gell, S.C. Fritz & F. Chalié, 1997. Diatominferred salinity in palaeolakes: An indirect tracer of climatic change. Quat. Sci. Rev. 16: 547-563.
Gasse, F., R. Téhet, A. Durand, E. Gilbert & J.Ch. Fontes, 1990. The arid-humid transition in the Sahara and the Sahel during the last deglaciation. Nature 346: 141-156.
Gillespie, R., F. A. Street-Perrott & R. Switsur, 1983. Post-glacial arid episodes in Ethiopia have implications for climate prediction. Nature 306: 680-683.
Gittins, J., 1966. Summaries and bibliography of carbonatite complexes. In Tuttle, O. F. & J. Gittins (eds), Carbonatites. J. Wiley & Sons, NY. 417-540.
Grimm, E.C, 1987. CONISS: a FORTRAN 77 program for stratigraphically constrained cluster analysis by the method of incremental sum of squares. Computers Geosci. 13: 13-35.
Grove, A. T., F. A. Street & A. S. Goudie, 1975. Former lake levels and climatic change in the rift valley of southern Ethiopia. Geograph. J. 141: 177-202.
Haberyan, K. A. & R. E. Hecky, 1987. The late Pleistocene and Holocene stratigraphy and paleolimnology of Lakes Kivu and Tanganyika. Palaeogeogr. Palaeoclim. Palaeoecol. 61: 169-197.
Hecky, R. E. & P. Kilham, 1973. Diatoms in alkaline, saline lakes: ecology and geochemical implications. Limnol. Oceanogr. 18: 53-71.
Hickman, M. & M. A. Reasoner, 1994. Diatom responses to late Quaternary vegetation and climate change, and to deposition of two tephras in an alpine and a sub-alpine lake in Yoho National Park, British Columbia. J. Paleolim. 11: 173-188.
Inbar, M., H. A. Ostera, C. A. Parica, M. B. Remesal & F. M. Salani, 1995. Environmental assessment of 1991 Hudson volcano eruption ashfall effects on southern Patagonia region, Argentina. Economic Geol. 25: 119-125.
Johnson, M. C., A. T. Anderson & M. J. Rutherford, 1994. Preeruptive volatile contents of magmas. Re-views in Mineralogy 30: 281-330.
Krammer, K. & H. Lange-Bertalot, 1986. Band 2/1: Bacillariophyceae. 1. Teil: Naviculaceae. Süßwasserflora von Mitteleuropa. Gustav Fischer Verlag, Stuttgart, 876pp.
Krammer, K. & H. Lange-Bertalot, 1988. Band 2/2: Bacillariophyceae. 2. Teil: Bacillariaceae, Epithemiaceae, Surirellaceae. Süßwasserflora von Mitteleuropa. Gustav Fischer Verlag, Stuttgart, 576pp.
Krammer, K. & H. Lange-Bertalot, 1991. Band 2/3: Bacillariophyceae. 1. Teil: Centrales, Fragilariaceae, Eunotiaceae. Süßwasserflora von Mitteleuropa. Gustav Fuscher Verlag, Stuttgart, 596pp.
Laird, K. R., S. C. Fritz, E. C. Grimm & P.G. Mueller, 1996. Centuryscale paleoclimatic reconstruction from Moon Lake, a closedbasin lake in the Northern Great-Plains. Limnol. Oceanogr. 41: 890-902.
Leng, M. J., A. L. Lamb, H. F. Lamb & R. J. Telford, In press. Palaeoclimatic implications of isotopic data from modern and early Holocene shells of the freshwater snail Melanoides tuberculata, from lakes in the Ethiopian Rift Valley. J. Paleolim.
Lotter, A. F., H. J. B. Birks & B. Zolitschka, 1995. Late-glacial pollen and diatom changes in response to two different environmental perturbations: volcanic eruption and Younger Dryas cooling. J. Paleolim. 14: 23-47.
Makin, M. J., T. J. Kingham, A. E. Waddams, C. J. Birchall & T. Teferra, 1975. Development prospects in the Southern Rift Valley, Ethiopia. Land Resources Study 21, Land Resources Division, U.K. Ministry of Overseas Development, Tolworth, 266 pp.
Samuel F., 1983. Review of fishery development potential in Ethiopia. Trade focus (Addis Ababa) 2: 29-36.
Sanford, W. E. & W. W. Wood, 1991. Brine evolution and mineral deposition in hydrologically open evaporite basins. Am. J. Sci. 291: 687-710.
Seyoum M. & C. H. Fernando, 1991. Seasonality and abundance of some dominant crustacean zooplankton in Lake Awasa, a tropical rift valley lake in Ethiopia. Hydrobiologia 226: 137-152.
Sturchio, N. C., P. N. Dunkley & M. Smith, 1993. Climate-driven variations in the geothermal activity in the northern Kenya rift valley. Nature 362: 233-234.
von Damm, K. L. & J. M. Edmond, 1984. Reverse weathering in the closed-basin lakes of the Ethiopian rift. Am. J. Sci. 284: 835-862.
Wissmar, R. C., A. H. Devol, J. T. Staley & J. R. Sedell, 1982. Biological responses of lakes in the Mount St. Helens blast zone. Science 216: 178-181.
Woldegabriel, G., J. L. Aronson & R. C. Walter, 1990. Geology, geochronology, and rift basin development in the central sector of the Main Ethiopian Rift. Geol. Soc. Am. Bull. 102: 439-458.
Wood, R. B. & J. F. Talling, 1988. Chemical and algal relationships in a salinity series of Ethiopian inland waters. Hydrobiologia 158: 29-67.
Wright, H. E., D. H. Mann & P. H. Glaser, 1983. Piston corers for lake and wetland sediments. Ecology 65: 657-659.
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Telford, R.J., Lamb, H.F. & Umer Mohammed, M. Diatom-derived palaeoconductivity estimates for Lake Awassa, Ethiopia: evidence for pulsed inflows of saline groundwater. Journal of Paleolimnology 21, 409–422 (1999). https://doi.org/10.1023/A:1008092823410
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DOI: https://doi.org/10.1023/A:1008092823410