The Quaternary History of Nile Paleofloods Recorded in the Eastern Mediterranean Deep-Sea Sediments
Abstract
Grain-size analyses, coupled with end-member modeling, have been performed on the detrital fraction of core MD90-964 located on the distal part of the Nile deep-sea fan, to provide new insights into the significance of grain-size variability in the eastern Mediterranean and to reconstruct variations in paleofloods of the Nile from the early Quaternary to the present. End-member modeling of siliciclastic grain-size distributions shows that the grain-size distributions of core MD90-964 can be divided into three end-members, with modal grain size values of ca. 50 μm, 10 μm, and 3 μm, respectively. The coarsest end-member EM1 generally varies from 0% to 20% in normal marls, but can reach as high as 60% to 90% in sapropels. It reflects changes in coarse grains carried by Nile paleofloods. The end-member with the median modal grain size (EM2) primarily reflects changes in Saharan-derived dust through time. The finest, EM3, represents clayey inputs from the Nile River. The EM1/EM3 ratios have been adopted as a proxy of Nile paleofloods to reconstruct its variations through time. Elevated values of EM1/EM3 ratios in sapropelic layers indicate that the occurrences of paleofloods are closely related to increased African monsoon precipitation in North Africa during boreal summer insolation maxima. A period with more frequent Nile paleoflood events is observed between 1500 and 1050 ka. A possible explanation for this is the increase in African monsoon precipitation in North Africa induced by decreased SST in the tropical Atlantic. In addition, our results also show that Saharan dust contributes up to 30 - 50% of the sediment influx in the study area. Influx of dust to the eastern Mediterranean basin is calculated to vary between 0 and 3 g/cm2/kyr during the Quaternary. Such a range is comparable to the range of dust influx to the Arabian Sea and the tropical Atlantic Ocean observed in previous studies.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMOS43F..07Z
- Keywords:
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- 3022 MARINE GEOLOGY AND GEOPHYSICS / Marine sediments: processes and transport;
- 4914 PALEOCEANOGRAPHY / Continental climate records