Energy, commons and the rest

Thoughts on energy as a commons, science and other stuffs by Cecile Blanchet

Moroccan margin

 

Sedimentation and climate on the NW Moroccan Margin

von Suchodoletz,H., H. Oberhänsli, D. Faust, M. Fuchs, C. Blanchet, T. Goldhammer and L. Zöller (2009). The evolution of Saharan dust input on Lanzarote (Canary Islands) – influenced by human activity in the Northwest Sahara during the early Holocene? The Holocene (doi:10.1177/0959683609350385)

An overall Holocene increase of Saharan dust input to the Canary Islands and to the North Canary Basin is accompanied by a strong coarsening of Saharan dust in loess-like sediments deposited on Lanzarote from ~7–8 ka. No similar coarsening events are indicated in investigations of the sedimentological record for
the last 180 ka, a period showing several dramatic climate changes. Therefore a mobilisation of Holocene dust by anthropogenic activity in the northwest Sahara east of the Canary Islands is assumed. Although scarce archaeological data from the coastal area of that region does not point to strong anthropogenic activity during the early Holocene, a high density of unexplored archaeological remains is reported from the coastal hinterlands in the Western Sahara. Thus, the hypothesis of early anthropogenic activity cannot be excluded.

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Blanchet, C.L., Broder, T., Goldhammer, T., Freudenthal, T. and Stuut, J.-B. (2009) Sedimentary patterns on Cape Ghir margin (Morocco) during the past 30 kyr deciphered by their magnetic and geochemical properties.
Poster presented at the European Geophysical Union Annual Meeting in April 2009 (Vienna) (sent on request)

The sediments deposited on the Cape Ghir margin (Morocco) contain detailed records of Holocene oceanic and climatic regimes. Based on these results, the newly designed drill-rig MeBO has retrieved two pushed-cores on the continental margin (R.V. Maria S. Merian, 2007): cores GeoB11804 (355 m water depth) and GeoB11807 (908 m water depth). Since this corer allows deeper penetration in the sequence, we can extent the paleo-record further back in time. Also, the sedimentation in this region is known to be greatly fed by aeolian dust which can be traced using the magnetic properties of sediments, and eventually compared to the upwelling activity.
A set of 26 calibrated 14C ages show that core GeoB11804 covers the last 30 kyr. Correlation of magnetic susceptibility pro.files and delta 18O measurements on planktonic foraminifers indicate that core GeoB11807 spans the last 20 kyr. Both cores exhibit mean sedimentation rates of ca. 110 cm/ka, therefore providing a time resolution of ca. 20 years. Very low terrigenous and magnetic contents are recorded between 30 and 18 ka, indicating the predominance of marine input on the margin during the Last Glacial Maximum (25-20 ka). The deglaciation is marked by pulses of magnetite (Fe3O4) and greigite (Fe3S4) at 18 and 12 ka, probably related to rapid sea level rises. These pulses are superimposed on a steady increase in terrigenous and magnetic contents between 18 and 10 ka, which could indicate a progressively stronger terrigenous contribution (from winds or rivers) due to sea level rise and/or climatic change. The Younger Dryas event (YD, 12-11 ka) is here recorded as an abrupt decrease in terrigenous sediment delivery. The hematite (Fe2S3) and goethite (FeOOH) contents rapidly and step-wisely increase after the YD and stabilize at ca. 8 ka. At ca. 1.7 ka, the magnetic contents abruptly increase, which might be related to diagenetic processes around the Sulfate-Methane transition. The top 1500 yrs are enriched in magnetic minerals of rather low grain-size in both cores, that might constitute the pristine present-day sedimentary assemblage. Further work is needed to elucidate the sedimentary changes occurring during the Holocene, and particularly at times of drastic changes in the Saharan environment (e.g. the African Humid Period).

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