Holocene Paleoclimate Reconstruction Inferred from Proxy Records in Speleothems from the Mechara Karst Area and Lake Archives From Tilo and Awassa Lakes, Ethiopia

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Addis Ababa Universty


Holocene palaeoclimate records recovered from Bero_1 stalagmite of Holocene age, and, modern stalagmite samples Asfa_3, Ach_1 and Merc_1 and from lake Tilo and lake Awassa were compared in order to see the trends and nature of correlation and variability between the records. The major proxies used are the 18O of Bero_1 stalagmite together with the lamina width variation and the 18O of authigenic calcite from the lake records, and lake level variations reconstructed from the Ziway-Shalla lakes. The 18O proxy data was chosen because it varies with the variation in the precipitation amount and P/E ratios. The comparison made between 18O values of stalagmites showed they are poorly correlated. The comparison of 18O values between the Lake records and Bero_1 stalagmite again showed poor correlation. But the over all trend of isotopic variation between the lake and stalagmite records in the Holocene was similar in such a way that it is similar with the general early-middle-late Holocene moisture variation previously recovered from Paleo-lake level variations of the Ziway-Shalla lakes. The stalagmite 18O time series showed five major trends at a time scale of 100-120 years between 7800-7500, 7400-7300, 5400-5300, 4860-4800, and 4550-4470 yr BP and smaller variations at 10-20 years time scale within the major trends. Relatively enriched 18O values in Bero_1 stalagmite around 7650-7370 yr BP, 5300-5400, 4801-4860 and 4470-4530 yr BP and the recent late Holocene peak at the end of the growth phase correspond to the relatively lower precipitation periods in the Holocene. Similarly, the depleted 18O values between 7590-7450, 5890-5860, 5290-5320 corresponds to relatively wetter periods. Thicker stalagmite lamina deposited during relatively wet seasons and thinner lamina records during relatively dry periods further support the 18O trends with the precipitation amount variation. The 18O of authigenic carbonates from lake Tilo and Awassa also showed similar relatively depleted 18O values in the early Holocene wet period, and enriched values were recorded in dryer periods in response to the increased lake water evaporation effect. This study shows the comparison made between lake and stalagmite records follow similar trends through out the Holocene but with different magnitude of change; and the stalagmite records are further more important in providing a high resolution multi proxy records in order to understand the precipitation amount variability in the Holocene.



Holocene palaeoclimate