low Mediterranean native Larrasoaña

Core/Site name:

ODP987

Country/Region:

Mediterranean

Elevation:

-2553

Archive:

marine sediments (downcore)

Proxy measurement:

isothermal remanent magnetization

Sampling resolution:

centennial

Climate sensitivity:

dust

Dating resolution:

no dates

Dating information:

sapropel occarance, nannofossil datums, d18o strat

Startyear:

3029065 BP

Endyear:

0 BP

All uncertainties:

Large age uncertainty

Description:

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 (~21ºN). In corroboration of earlier work, we relate dust flux minima to penetration of the African summermonsoon 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 variabilityaround 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."

Data entered by name:

Delia Oppo

Data entered by email:

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Main reference(s):

Larrasoaña, J.C., A.P. Roberts, E.J. Rohling, M. Winklhofer, and R. Wehausen. 2003.Three million years of monsoon variability over the northern Sahara. Climate Dynamics, 21, 689-698.

Link to reference 1:

http://www.springerlink.com/content/d1q3956eegky68ym/

Data storage link 1:

http://hurricane.ncdc.noaa.gov/pls/paleox/f?p=519:1:4323658048257285::::P1_STUDY_ID:6412

Comments:

Probably not appropriate for Ocean 2k effort.

Current dating method:

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Annual snow acc rate:

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Category: Ocean2k