Geoscience Reference
In-Depth Information
13
Desert glaciations
The glacier glistens. A distant snow peak scours the mind, but a
snow peak in the tropics draws the heart to a fine shimmering
painful point of joy.
Peter Matthiessen & Eliot Porter
The Tree where Man was Born:
The African Experience (1972)
13.1 Introduction
In Chapters 11 and 12 , we reviewed the long history of the debate over whether
or not pluvials and glacials were synchronous in the drier regions of the world. We
concluded that in North America, there was good evidence that many desert lake levels
were high around the time of the Last Glacial Maximum and subsequent deglacial, as
were Lake Lisan (the Late Pleistocene precursor of the Dead Sea) and Lake Konya in
semi-arid Anatolia in Turkey, both of which reflect more intense winter rainfall at that
time.
However, this did not seem to be the case in the tropical northern deserts of
Africa and Asia, which showed highest lake levels in the early to mid-Holocene
and relatively low glacial maximum lake levels. Indeed, in one recent study of the
Quaternary sediments at Dakhla Oasis in the Western Desert of Egypt, Brookes
( 2010 ) argued that the record of former temperature maxima at this latitude could
be used to date Quaternary pluvial events in this hyper-arid region over the past
800 ka. His reasoning was based on what he called 'the well-validated premise that
temperature cycles in the north African dry belt drive those of precipitation within the
seasonally migratory ITCZ' (op. cit., p. 253), although he did note that there could
be 'a complication arising from delayed surface discharge of pluvially recharged
groundwater' (op. cit., p. 253). That the last interglacial (MIS 5e) was warmer than
the Holocene postglacial is shown by current best estimates for eustatic sea level at
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