TY - JOUR
T1 - Climatic and non-climatic effects on the δ18O and δ13C compositions of Lake Awassa, Ethiopia, during the last 6.5 ka
AU - Lamb, Angela L.
AU - Leng, Melanie J.
AU - Lamb, Henry F.
AU - Telford, Richard J.
AU - Mohammed, Mohammed Umer
N1 - Funding Information:
The authors would like to thank Dr. Solomon Tadesse and Professor Getaneh Assefa from the Department of Geology and Geophysics, University of Addis Ababa for help with many aspects of fieldwork in Ethiopia. Dr Elias Dadebo and Dr Zinabu Gebre-Mariam from the Awassa College of Agriculture also kindly arranged fieldwork permits and assisted with fieldwork. Special thanks are also due to Seifu Kedebe, Wolde Selassie, Geoff Duller and Nick Pearce for help in the field. Hilary Sloane and Carol Arrowsmith (NERC Isotope Geosciences Laboratory) provided technical assistance with isotope analysis and Vicky Hards (British Geological Survey) provided help and advice with XRD analysis. Sarah Metcalfe and an anonymous reviewer are thanked for their useful comments on the manuscript. This research was supported by an NERC case studentship with the NERC Isotope Geosciences Laboratory, a NERC research grant (GR3/10767) and an EEC research contract (STD3-TS3-CT92-0076) NIGL publication number 467.
PY - 2002/11/12
Y1 - 2002/11/12
N2 - A comparison of a 6450 14C yr δ18O and δ13C record of authigenic calcite from Lake Awassa, Ethiopia, with other proxy climate records in the area suggests that the lake records long-term regional climate changes. Co-varying and increasing δ18O and δ13C values from ∼4800 BP suggest an aridification of climate after the early Holocene insolation maximum. After 4000 BP, humid conditions return until after ∼2800 BP when δ18O increases again, reflecting more arid conditions recorded elsewhere in Ethiopia. In addition to these long-term changes, there are abrupt decreases in both δ18Ocalcite and δ13Ccalcite immediately after tephra layers. The likeliest explanation for these abrupt decreases in isotopes is the effect of tephra on the lake's catchment vegetation. δ18O, δ13C and lake-level measurements from Lake Awassa since the 1970s suggest that the lake is currently isotopically sensitive to short-term (annual–decadal) climate change. However, during this period, the catchment has undergone progressive deforestation that may have caused an increase in runoff. Caution is therefore required when reconstructing palaeoclimates as a contemporary lake may not always be a good analogue for lake hydrology in the past.
AB - A comparison of a 6450 14C yr δ18O and δ13C record of authigenic calcite from Lake Awassa, Ethiopia, with other proxy climate records in the area suggests that the lake records long-term regional climate changes. Co-varying and increasing δ18O and δ13C values from ∼4800 BP suggest an aridification of climate after the early Holocene insolation maximum. After 4000 BP, humid conditions return until after ∼2800 BP when δ18O increases again, reflecting more arid conditions recorded elsewhere in Ethiopia. In addition to these long-term changes, there are abrupt decreases in both δ18Ocalcite and δ13Ccalcite immediately after tephra layers. The likeliest explanation for these abrupt decreases in isotopes is the effect of tephra on the lake's catchment vegetation. δ18O, δ13C and lake-level measurements from Lake Awassa since the 1970s suggest that the lake is currently isotopically sensitive to short-term (annual–decadal) climate change. However, during this period, the catchment has undergone progressive deforestation that may have caused an increase in runoff. Caution is therefore required when reconstructing palaeoclimates as a contemporary lake may not always be a good analogue for lake hydrology in the past.
UR - http://www.scopus.com/inward/record.url?scp=0038138087&partnerID=8YFLogxK
U2 - 10.1016/S0277-3791(02)00087-2
DO - 10.1016/S0277-3791(02)00087-2
M3 - Article
AN - SCOPUS:0038138087
SN - 0277-3791
VL - 21
SP - 2199
EP - 2211
JO - Quaternary Science Reviews
JF - Quaternary Science Reviews
IS - 20-22
ER -