Paleoclimates Off Northwest Africa (28°–35°N) about 18,000 yr B.P. Based on Continental Eolian Deposits

Abstract

Most conceptual models of atmospheric circulation deduced from bottom sediments or isopollen maps off NW Africa assume the occurrence of intensified NNE trade winds about 18,000 yr B.P. in latitudes of 28°–35°N, and oversimplify the glacial atmospheric circulation over Africa. An alternative method for reconstructing paleowinds of the last glacial maximum in these latitudes was recently put forward, and uses sedimentological records from the Canary Islands and coastal regions of Morocco. The continental data do not agree with the previous models and show the prevalence of westerlies. All the data from deep sea cores (reduction of sea surface temperature, increase of biogenic opal accumulation, distribution patterns of pollen or dinoflagellate cysts, and xeric conditions on the adjacent continent) can be explained without increased activity of the trade winds, but with a discharge current of cold meltwater from the European and North American ice sheets. The model is backed up by a comparison with the present-day Humboldt Current off subtropical South America.