HOLIVAR2006 Abstracts
Palaeoclimate record in the River Nile catchment (0-25 kyr) as recorded by 87Sr/86Sr in a marine core under the Nile plume.
Matthew Box1, Michael Krom1, Robert Cliff1, Ahuva Almogi-Labin2, Miryam Bar-Matthews2, Martine Paterne3, Bettina Schilman2, Avner Ayalon2 and Jean-Daniel Stanley4
1Dept. Earth Sciences, Leeds University, Leeds, UK
2Geological Survey of Israel, Jerusalem, Israel
3LSCE-CNRS-CEA Gif sur Yvett, France
4Smithsonian Institute, Washington D.C., USA
Contact: Matthew Box (m.box@earth.leeds.ac.uk)
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Core 9509 (32°02'N, 34°17'E) was raised from 884 m water depth off the coast of Israel. The core site is located under the pre-Aswan (1965) Nile plume and represents an almost pure Nile sediment record over the studied period of the past 25 kyr (gross sedimentation rate ~167 mm/kyr). We carried out strontium isotope (87Sr/86Sr) analysis on the <20 µm lithogenic fraction and major element analysis on the bulk <20 µm fraction for interpretation with previously determined δ18OG. ruber and total organic carbon (TOC) measurements from the same sample depths. Core 9509 is dated through comparison of its δ18O curve to that of a well dated (U/Th) speleothem from Soreq cave in the Judean Mountains of Israel.
Strontium isotopes have been used as a relative measure of Blue Nile (0.7055) versus White Nile (0.7105) sediment. Lithogenic 87Sr/86Sr ratios are controlled by the amount and provenance of sediment reaching the Nile delta which is, in turn, controlled by climate change over the Nile catchment and particularly the movement of the Intertropical Convergence Zone (ITCZ); which brings the monsoon rains to the Ethiopian Highlands.
We find that a close correspondence between the east Africa climate and the δ18OG. ruber record, which is a proxy for the changing sea-surface temperature (SST) of east Mediterranean Sea and terrestrial temperature as well as global ice volume. There is also close correspondence with short climatic events. The 87Sr/86Sr and δ18O records reveal a large, rapid change (from 0.7082 to 0.7102 and +0.35 to -1.65 respectively) at the base of the sapropel (c. 9.2 kyr BP) reflecting simultaneous climate change in the eastern Mediterranean and Nile catchment areas, simultaneous changes also occur during the Younger Dryas and H1 events.
Core 9509 also yields evidence for sub-millennial Holocene climate changes in the Nile catchment at c. 2.0 kyr BP which may be related to a major increase in grazing or other anthropogenic activity increasing the physical erosion rate in the Ethiopian Highlands. Evidence of Nile catchment climate change is also present at c. 4.2 kyr BP. and 8.2 kyr BP. A single datum exists for the 4.2 kyr climate event in the 87Sr/86Sr record which indicates that the Nile suffered drying out at this time. This local minimum signal corresponds to a 87Sr/86Sr minimum observed in the profile from a brackish water (Lake Manzala) Nile delta core (S21). Analysis is currently being carried out a freshwater Nile core (S86) to examine the past 6 kyr in more detail.