The stable isotope composition of authigenic calcites in a core from Lake Tilo, a small crater lake in the Ethiopian Rift Valley, provides a subcentury scale record of lake response to climatic change over the last 8850 14C yrs (9850 cal. yrs). An unusually high range of δ18O and δ13C values (~15,) is attributed, in part, to major changes in hydrothermal groundwater flux. Although hydrothermal groundwater influx to the lake was high during the early Holocene, its flow rate was relatively stable and thus climatically induced changes to the water budget can be inferred from variations in δ18O and δ13C ratios. A major decline in hydrothermal groundwater input from ~5500 14C yrs BP increased lakewater residence time and led to substantial increases in δ18O and δ13C, before the mid-Holocene transition to more arid conditions. During the last ~2700 14C years diagenetic processes have resulted in extremely varied δ18O and δ13C values. The Holocene isotope record from Lake Tilo challenges the widely held assumption that crater lakes act as ’gigantic rain gauges’, sensitive only to changes in precipitation/evaporation ratios.
Aitken, M.J.1990: Science-based dating in archaeology. London: Longman .
2.
Bottinga, Y.1969: Calculated fractionation factors for carbon and hydrogen isotope exchange in the system calcite-CO2-graphite-methanehydrogen and water vapour . Geochimica et Cosmochimica Acta33, 49-64 .
3.
Brady, G.S. and Robertson, D.1870: The Ostracoda and Foraminifera of tidal rivers . Annals and Magazine of Natural History, Series 4, 9, 48-70 .
4.
Cerling. T.E. , Bowman, J.R. and O'Neil, J.R.1988: An isotopic study of a fluvial-lacustrine sequence: the Plio-Pleistocene Koobi Fora sequence, East Africa . Palaeogeography, Palaeoclimatology, Palaeoecology63, 335-356 .
5.
Cerling, T.E. , Johnston, T.C. , Halfman, J.D. and Lister, C.1985: Pore water chemistry of an alkaline Rift Valley lake: Lake Turkana, Kenya . Geological Society of America Abstracts with Program17, 541–541 .
6.
Chivas, A.R. , De Dekker, P. , Cali, J.A. , Chapman, A. , Kiss, E. and Shelly, J.M.G.1993: Coupled stable isotope and trace element measurements of lacustrine carbonates as palaeoclimatic indicators . In Swart, P.K., Lohmann, K.C., McKenzie, J.A. and Savin, S., editors, Climate change in continental isotopic records, Geophysical Monograph78, 113-122 .
7.
Cole, J.J. , Caraco, N.F. , Kling, G.W. and Kratz, T.K.1994: Carbon dioxide supersaturation in the surface waters of lakes . Science265, 1568-1570 .
8.
Craig, H. , Gordon, L. and Horibe, Y.1963: Isotopic exchange effects in the evaporation of water. 1. Low-temperature experimental results . Journal of Geophysical Research68, 5079-5087 .
9.
Craig, H. , Lupton, J.E. and Horowitz, R.M.1977: Isotopic geochemistry and hydrology of geothermal waters in the Ethiopian Rift Valley. La Jolla, California: Scripps Institute of Oceanography, SIO77-14.
10.
Darling, W.G. 1996: The geochemistry of fluid processes in the eastern branch of the East African Rift system. Unpublished PhD thesis, Open University.
11.
Dean, W.E. Jr1974: Determination of carbonate and organic matter in calcareous sediments and sedimentary rocks by loss on ignition: comparison with other methods . Journal of Sedimentary Petrology44, 242-248 .
12.
Delibrias, G. and Guillier, M.-T.1988: GIF natural radiocarbon measurements XI . Radiocarbon30, 61-124 .
13.
F.A.O.1984: Agroclimatological data for Africa, volume 1. FAO Plant Production and Protection Series No. 22. Rome: Food and Agriculture Organization of the United Nations .
14.
Fontes, J-C. and Gasse, F.1991: PALHYDAF (Palaeohydrology in Africa) program: objectives, methods, major results . Palaeogeography, Palaeoclimatology, Palaeoecology84, 191-215 .
15.
Gamachu, D.1977: Aspects of climate and water budget in Ethiopia. A technical monograph. Addis Ababa: Addis Ababa University Press .
16.
Gasse, F. and Descourtieux, C.1979: Diatomees et évolution de trois milieux Ethiopiens d'altitude différente, au cours du Quaternaire supérieur . Palaeoecology of Africa11, 117-134 .
17.
Gasse, F. and Fontes, J-C.1989: Palaeoenvironments and palaeohydrology of a tropical closed lake (Lake Asal, Djibouti) since 10,000 yr BP . Palaeogeography, Palaeoclimatology, Palaeoecology69, 67-102 .
18.
Gasse, F. and Fontes, J-C.1992: Climatic changes in northwest Africa during the last deglaciation (16-7 Ka BP). In Bard, E. and Broeker, W. , editors, The last deglaciation: absolute and radiocarbon chronologies, NATO ASI series 12, Dordrecht: Kluwer , 295-325.
19.
Gasse, F. and Street, F.A.1978: Late Quaternary lake-level fluctuations and environments of the northern Rift Valley and Afar region (Ethiopia and Djibouti) . Palaeogeography, Palaeoclimatology, Palaeoecology24, 279-325 .
20.
Gat, J.R.1980: Isotope hydrology of very saline lakes. In Nissenbaum, A. , editor, Hypersaline brines and evaporitic environmentsAmsterdam: Elsevier , 1-8.
21.
Gillespie, R. , Street-Perrott, F.A. and Switsur, R. , 1983: Post-glacial arid episodes in Ethiopia have implications for climate prediction . Nature306, 680-682 .
22.
Gizaw, B. 1989: Geochemical investigation of the Aluto-Langano geothermal field, Ethiopian Rift Valley. Unpublished M Phil thesis, University of Leeds.
23.
Griffiths, J.F.1972: Climates of Africa, world survey of climatology, volume 10. Amsterdam: Elsevier .
24.
IAEA1990: World survey of isotope concentrations in precipitation. Technical Report Series 311. Vienna: International Atomic Energy Agency .
25.
IAEA1992: Statistical treatment of isotopes in precipitation. Vienna: International Atomic Energy Agency .
26.
Krabbenhoft, D.P. , Bowser, C.J. , Anderson, M.P. and Valley, J.W.1990: Estimating groundwater exchange with lakes. 1. The stable isotope mass balance method . Water Resources Research26, 2445-2453 .
27.
Kutzbach, J.E.1983: Monsoon rains of the late Pleistocene and early Holocene: patterns, intensity and possible causes of changes. In Street-Perrott, F.A. et al., editors, Variations in the global water budget, Dordrecht: D. Reidel , 371-389.
28.
Leng, M.J. , Lamb, A.L. , Lamb, H.F. and Telford, R.J.1999: Palaeoclimatic implications of isotopic data from modern and early Holocene shells of the freshwater snail Melanoides tuberculata, from lakes in the Ethiopian Rift Valley . Journal of Paleolimnology21, 97-106 .
29.
Li, H.-C. and Ku, T.-L.1997: Sδ13C-δ18O covariance as a paleohydrological indicator for closed-basin lakes . Palaeogeography, Palaeoclimatology, Palaeoecology133, 69-80 .
30.
Lister, G.S. , Kelts., K. , Zao, C.K. , Yu, J.K. and Niessen, K.1991: Lake Qinghai, China: closed basin lake levels and the oxygen isotope record for ostracoda since the Late Pleistocene . Palaeogeography, Palaeoclimatology, Palaeoecology84, 141-162 .
31.
Martens, K.1990: Revision of African Limnocythere s. s. Brady, 1867 (Crustacea, Ostracoda), with special reference to the Eastern Rift Valley lakes: morphology, taxonomy, evolution and (palaeo)ecology . Archiv für Hydrobiologie, Supplementen83, 453-524 .
32.
McCrea, J.M.1950: On the isotopic chemistry of carbonates and a palaeotemperature scale . Journal of Chemical Physics18, 849-857 .
33.
McKenzie, J.A.1985: Carbon isotopes and productivity in the lacutstrine and marine environment. In Stumm, W. , editor, Chemical processes in lakes, New York: Wiley , 99-118.
34.
McKenzie, J.A.1993: Pluvial conditions in the eastern Sahara following the penultimate deglaciation: implications for changes in atmospheric circulation patterns with global warming . Palaeogeography, Palaeoclimatology, Palaeoecology103, 95-105 .
35.
Menking, K.M. , Bischoff, J.L. , Fitzpatrick, J.A. , Burdette, J.W. and Rye, R.O.1997: Climatic/hydrologic oscillations since 155,000 yr BP at Owens Lake, California, reflected in abundance and stable isotope composition of sediment carbonate . Quaternary Research48, 58-68 .
36.
O'Neil, J.R. , Clayton, R.N. and Mayeda, T.K.1969: Oxygen isotope fractionation in divalent metal carbonates . Journal of Chemical Physics5, 5547-5558 .
37.
Rhodes, T.E. , Gasse, F. , Ruifen, L. , Fontes, J.-C. , Keqin, W. , Betrand, P. , Gibert, E. , Mélières, F. , Tucholka, P. , Zhixiang, W. and Zhi-Yuan, C.1996: A late Pleistocene-Holocene lacustrine record from Lake Manas, Zunggar (northern Xinjiang, Western China) . Palaeogeography, Palaeoclimatology, Palaeoecology120, 105-121 .
38.
Ricketts, D.R. and Johnson, T.C.1996: Climate change in the Turkana basin deduced from a 4000 year long δ18O record . Earth and Planetary Science Letters142, 7-17 .
39.
Roselle, P.1982: Quantitative mineralogical analysis of carbonate sediments by X-ray diffraction: a new, automatic method for sediments with low carbonate content . Sedimentology29, 595-600 .
40.
Rozanski, K. , Araguás-Araguás, L. and Gonfiantini, R.1993: Isotopic patterns in modern global precipitation. In Swart, P.K. , Lohmann, K.C. , McKenzie, J.A. and Savin, S. , editors, Climate change in continental isotopic records, Geophysical Monograph 78, 1-36.
41.
Street, F.A. 1979: Late Quaternary lakes in the Ziway-Shala basin, Southern Ethiopia. Unpublished PhD thesis, Cambridge University.
42.
Street-Perrott, F.A. and Roberts, N.1983: Fluctuations in closed-basin lakes as an indicator of past atmospheric circulation patterns. In Street-Perrott, F.A. et al., editors, Variations in the global water budtget, Dordrecht: D. Reidel , 331-345.
43.
Stuiver, M. and Reimer, P.J.1993: Extended 14C data base and revised CALIB 3.0 14C age calibration program . Radiocarbon35, 215-230 .
44.
Talbot, M.R.1990: A review of the palaeohydrological interpretation of carbon and oxygen isotopic ratios in primary lacustrine carbonates . Chemical Geology (Isotope Geoscience Section)80, 261-279 .
45.
Talbot, M.R. and Kelts, K.1986: Primary and diagenetic carbonates in the anoxic sediments of Lake Bosumtwi, Ghana . Geology14, 912-916 .
46.
Talbot, M.R. and Kelts, K.1990: Paleolimnological signatures from carbon and oxygen isotopic ratios in carbonates from organic carbon-rich lacustrine sediments. In Katz, B.J. , editor, Lacustrine basin exploration, AAPG Memoir 50, 99-112.
47.
Telford, R.J. and Lamb, H.F.1999: Groundwater-mediated response to Holocene climatic change recorded by the diatom stratigraphy of an Ethiopian crater lake . Quaternary Research52, 63-75 .
48.
Telford, R.J. , Lamb, H.F. and Mohammed, M.U.1999: Diatom-derived palaeoconductivity estimates for Lake Awassa, Ethiopia: evidence for pulsed inflows of saline groundwater?Journal of Paleolimnology, 21, 409-421 .
49.
Tesfaye, Chernet1982: Hydrogeology of the lakes region, Ethiopia. Memoir no. 7 – Ministry of Mines and Energy. Addis Ababa: Ethiopian Institute of Geological Surveys .
50.
Tietze, K. , Geyh, M. , Muller, H. , Schroder, L.Stahl, W. and Wehner, H.1980: The genesis of the methane in Lake Kivu (Central Africa) . Geologische Rundschau69, 452-472 .
51.
Whiticar, M.J. , Faber, E. and Schoell, M.1986: Biogenic methane formation in marine and freshwater environments: CO2 reduction vs acetate fermentation . Geochimica et Cosmochimica Acta50, 693-709 .
52.
Williams, M.A.J. , Dunkerley, D.L. , De Dekker, P. , Kershaw. A.P. and Stokes, T.1993: Quaternary environments. London: Edward Arnold .
53.
Wood, R.B. , Prosser, M.V. and Baxter, R.M.1976: The seasonal pattern of thermal characteristics of four of the Bishoftu crater lakes, Ethiopia . Freshwater Biology6, 519-530 .
54.
Wright, H.E. , Mann, D.H. and Glasser, P.H.1983: Piston corers for lakes and wetland sediments . Ecology65, 657-659 .
55.
Wright, V.P.1990: Lacustrine sediments. In Tucker, M.E. and Wright, V.P. , editors, Carbonate sedimentology, Oxford: Blackwell Scientific Publications , 164-190.
