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Three million years of monsoon variability over the northern Sahara

Three million years of monsoon variability over the northern Sahara
Three million years of monsoon variability over the northern Sahara
We present a 3 million year record of aeolian dust supply into the eastern Mediterranean Sea, based on hematite contents derived from magnetic properties of sediments from Ocean Drilling Program Site 967. Our record has an average temporal resolution of ?400 years. Geochemical data validate this record of hematite content as a proxy for the supply of aeolian dust from the Sahara. We deduce that the aeolian hematite in eastern Mediterranean sediments derives from the eastern Algerian, Libyan, and western Egyptian lowlands located north of the central Saharan watershed (?21°N). In corroboration of earlier work, we relate dust flux minima to penetration of the African summer monsoon front to the north of the central Saharan watershed. This would have enhanced soil humidity and vegetation cover in the source regions, in agreement with results from "green Sahara" climate models. Our results indicate that this northward monsoon penetration recurred during insolation maxima throughout the last 3 million years. As would be expected, this orbital precession-scale mechanism is modulated on both short (?100-kyr) and long (?400-kyr) eccentricity time scales. We also observe a strong expression of the ?41-kyr (obliquity) cycle, which we discuss in terms of high- and low-latitude mechanisms that involve Southern Hemisphere meridional temperature contrasts and shifts in the latitudes of the tropics, respectively. We also observe a marked increase in sub-Milankovitch variability around the mid-Pleistocene transition (?0.95 Ma), which suggests a link between millennial-scale climate variability, including monsoon dynamics, and the size of northern hemisphere ice sheets.
0930-7575
689-698
Larrasoana, J.C.
9201c9da-a9fc-4f3b-86a8-83fda450084e
Roberts, A.P.
4497b436-ef02-428d-a46e-65a22094ba52
Rohling, E.J.
a2a27ef2-fcce-4c71-907b-e692b5ecc685
Winklhofer, M.
70de02f9-51b3-4d4a-89c6-b4ef634407dc
Wehausen, R.
2917ec4a-8570-4ee1-9c98-6ba534a3a5ce
Larrasoana, J.C.
9201c9da-a9fc-4f3b-86a8-83fda450084e
Roberts, A.P.
4497b436-ef02-428d-a46e-65a22094ba52
Rohling, E.J.
a2a27ef2-fcce-4c71-907b-e692b5ecc685
Winklhofer, M.
70de02f9-51b3-4d4a-89c6-b4ef634407dc
Wehausen, R.
2917ec4a-8570-4ee1-9c98-6ba534a3a5ce

Larrasoana, J.C., Roberts, A.P., Rohling, E.J., Winklhofer, M. and Wehausen, R. (2003) Three million years of monsoon variability over the northern Sahara. Climate Dynamics, 21 (7-8), 689-698. (doi:10.1007/s00382-003-0355-z).

Record type: Article

Abstract

We present a 3 million year record of aeolian dust supply into the eastern Mediterranean Sea, based on hematite contents derived from magnetic properties of sediments from Ocean Drilling Program Site 967. Our record has an average temporal resolution of ?400 years. Geochemical data validate this record of hematite content as a proxy for the supply of aeolian dust from the Sahara. We deduce that the aeolian hematite in eastern Mediterranean sediments derives from the eastern Algerian, Libyan, and western Egyptian lowlands located north of the central Saharan watershed (?21°N). In corroboration of earlier work, we relate dust flux minima to penetration of the African summer monsoon front to the north of the central Saharan watershed. This would have enhanced soil humidity and vegetation cover in the source regions, in agreement with results from "green Sahara" climate models. Our results indicate that this northward monsoon penetration recurred during insolation maxima throughout the last 3 million years. As would be expected, this orbital precession-scale mechanism is modulated on both short (?100-kyr) and long (?400-kyr) eccentricity time scales. We also observe a strong expression of the ?41-kyr (obliquity) cycle, which we discuss in terms of high- and low-latitude mechanisms that involve Southern Hemisphere meridional temperature contrasts and shifts in the latitudes of the tropics, respectively. We also observe a marked increase in sub-Milankovitch variability around the mid-Pleistocene transition (?0.95 Ma), which suggests a link between millennial-scale climate variability, including monsoon dynamics, and the size of northern hemisphere ice sheets.

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Published date: 2003

Identifiers

Local EPrints ID: 11191
URI: https://eprints.soton.ac.uk/id/eprint/11191
ISSN: 0930-7575
PURE UUID: 271b5afe-42a7-42d1-ab1b-b8c6b8cd457c
ORCID for E.J. Rohling: ORCID iD orcid.org/0000-0001-5349-2158

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Date deposited: 28 Oct 2004
Last modified: 06 Jun 2018 13:06

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