TY - JOUR
T1 - Late Pleistocene and Holocene drought events at Lake Tana, the source of the Blue Nile
AU - Marshall, Michael H.
AU - Lamb, Henry F.
AU - Huws, Dei
AU - Davies, Sarah J.
AU - Bates, Richard
AU - Bloemendal, Jan
AU - Boyle, John
AU - Leng, Melanie J.
AU - Umer, Mohammed
AU - Bryant, Charlotte
N1 - Funding Information:
MHM was in receipt of a University of Wales Aberystwyth Postgraduate Research Studentship. Fieldwork and analytical costs were supported by grants from the Natural Environment Research Council (NERC Grant NER/B/S/2002/00540 ), the Leverhulme Trust , and the Royal Geographical Society . Support for ten of the AMS radiocarbon dates was obtained through NERC's Radiocarbon Steering Committee (Allocation No. 1200.1006). Dr Paul Coombes is acknowledged for field assistance and Carol Arrowsmith for the organic geochemistry analyses. We thank the Amhara Region Agricultural Research Institute for logistical support while at Lake Tana. Constructive comments and suggestions by two anonymous reviewers and the editor greatly improved the final manuscript.
PY - 2011/8/31
Y1 - 2011/8/31
N2 - Magnetic and geochemical core data spanning the last 17,000 years are correlated with new seismic stratigraphy from Lake Tana, Ethiopia, to infer past lake-level change and hence effective precipitation. The data confirm that low lake-level coincides with Heinrich Event 1 (H1) in the North Atlantic, as previously shown from diatom and pollen evidence (Lamb et al., 2007). The lake deepened at 15.3 cal kyr BP and abruptly returned to freshwater conditions, when the lake overflowed into the Blue Nile. Low runoff and lake levels and therefore rainfall are inferred between 13.0 and 12.5 cal kyr BP and may represent southerly suppression of the ITCZ and the associated monsoon front at the time of the Younger Dryas. Two drought episodes occurred at 8.4 and 7.5 cal kyr BP, and are also interpreted as a southward shift in the monsoon front. The first of these events appears to have preceded and been more significant than the 8.2 cal kyr BP. Precipitation declined after 6.8 cal kyr BP, although we do not see an abrupt end to the African Humid Period. This period culminated in a dry episode at ~ 4.2 cal kyr BP, supporting the view that reduced Nile flow was a contributing factor to the demise of the Egyptian Old Kingdom.
AB - Magnetic and geochemical core data spanning the last 17,000 years are correlated with new seismic stratigraphy from Lake Tana, Ethiopia, to infer past lake-level change and hence effective precipitation. The data confirm that low lake-level coincides with Heinrich Event 1 (H1) in the North Atlantic, as previously shown from diatom and pollen evidence (Lamb et al., 2007). The lake deepened at 15.3 cal kyr BP and abruptly returned to freshwater conditions, when the lake overflowed into the Blue Nile. Low runoff and lake levels and therefore rainfall are inferred between 13.0 and 12.5 cal kyr BP and may represent southerly suppression of the ITCZ and the associated monsoon front at the time of the Younger Dryas. Two drought episodes occurred at 8.4 and 7.5 cal kyr BP, and are also interpreted as a southward shift in the monsoon front. The first of these events appears to have preceded and been more significant than the 8.2 cal kyr BP. Precipitation declined after 6.8 cal kyr BP, although we do not see an abrupt end to the African Humid Period. This period culminated in a dry episode at ~ 4.2 cal kyr BP, supporting the view that reduced Nile flow was a contributing factor to the demise of the Egyptian Old Kingdom.
KW - Ethiopian highlands
KW - Holocene
KW - Mineral magnetics
KW - Nile
KW - Seismics
KW - XRF
UR - http://hdl.handle.net/2160/8480
UR - http://www.scopus.com/inward/record.url?scp=80052170135&partnerID=8YFLogxK
U2 - 10.1016/j.gloplacha.2011.06.004
DO - 10.1016/j.gloplacha.2011.06.004
M3 - Article
SN - 1872-6364
VL - 78
SP - 147
EP - 161
JO - Global and Planetary Change
JF - Global and Planetary Change
IS - 3-4
ER -