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The evolution of Saharan dust input on Lanzarote (Canary Islands) – influenced by human activity in the Northwest Sahara during the early Holocene?
(2009)
- 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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Soil moisture fluctuations recorded in Saharan dust deposits on Lanzarote (CanaryIslands) over the last 180 ka
(2010)
- Aeolian sediments trapped in volcanically dammed valleys on Lanzarote, Canary Islands, were investigated in order to reveal environmental changes over the last 180 ka. Clay content and frequency dependent magnetic susceptibility were used as proxies for pedogenesis and palaeo-soil moisture. During the last 180 ka, these proxies showed a general pattern of enhanced soil moisture during glacials and stadials and more arid conditions during interglacials and interstadials. Comparisons of these results with proxies from regional palaeoclimate studies identified a positive correlation with proxies of trade wind strength off northwest Africa and inverse correlations with both sea surface temperatures in the northeast Atlantic and the extent of Mediterranean vegetation. Possible causes for the observed pattern include a glacial enhancement of precipitation from westerly cyclones, a change in relative humidity due to fluctuating air temperatures and an occasional influence of the African summer monsoon. Although it is not yet possible to clearly differentiate among these factors, it is clear that the first two factors must have been primarily dominant. These results represent the first quasi-continuous terrestrial data testifying to environmental changes in the northwest African coastal area for the last 180 ka and complement the abundant data derived from marine cores of the region. High latitude dynamics had a major influence in this area and were intermediated by North Atlantic sea surface temperatures. A possible negative correlation can also be observed with the orbital obliquity cycle with a 10 ka time lag, which is similar to the lag recorded from North Atlantic sea surface temperatures.
