Fluctuations in Closed-Basin Lakes as An Indicator of Past Atmospheric Circulation Patterns

Abstract

At the present day, maxima in the areal extent of lakes are associated with the latitudinal mean positions of the equatorial trough and the mid-latitude westerlies. This association is applied to variations in the relative extent of lakes during the last 18 000 years in order to deduce past changes in atmospheric circulation. The analysis is based on a large number of ¹⁴C-dated lake-level sequences from Africa and western Eurasia. We infer that the period following the glacial maximum at ca. 18 000 yr BP was characterized by increasing aridity in the tropics, culminating at around 14 000 – 12 500 yr BP when atmospheric moisture convergence and runoff reached minimum values over almost the entire study area. Between 12 500 and 5000 yr BP, a broad belt of expanded lakes developed in Africa and Arabia. It migrated irregularly northwards to a latitude of 16.5 N and then disintegrated rapidly after 5000 – 4000 yr BP. This early postglacial intensification of the continental hydrological cycle is attributed primarily to an enhanced monsoonal circulation over Africa and Arabia, probably accompanied by a northward shift of the mean ITCZ. It was interrupted by two episodes of prolonged drought centred on 10 200 and 7400 yr BP. The causes of these abrupt climatic events are discussed.