Africa’s first ice core record

Melting of low-latitude glaciers in Africa is so rapid that, unless they are cored soon, their content of long-term climate data may soon be gone forever.  So the first detailed isotopic record from Africa’s highest glacier on Kilimanjaro is cause for some relief.  Intrepid glaciologist Lonnie Thompson welded a large team together for this important task (Thompson, L. 2002. Kilimanjaro ice core records: evidence of Holocene climate change in tropical Africa.  Science, v. 298, p. 589-593).  The annually layered ice goes back only about 12 ka, but nonetheless gives a precious account of climate change at the heart of the continent, far more detailed than sparse lake-bed cores from various places.

The core confirms a broad pattern of warm, wet conditions from 11 to 4 ka, before the long-term cooling and drying of historical times.  These reflect likely weakening of monsoonal conditions in the late Holocene.  However, assigning precise ages to depth in the cores is not as easy as in those from high-latitude ice sheets, because of a lack of good layering (presumably) and dateable carbon.  At about 5200 years ago, the record shows an abrupt fall in d18O, a sign of drying and cooling that took place over perhaps a matter of decades.  This correlates with disruption of early civilisations in India, Egypt and the Middle East, and probably stemmed from cooling in the North Atlantic.  However, an equally rapid deterioration occurred around 6300 years bp, although not so extreme, to presage a millennium of arid conditions at the heart of Africa.  Important as these data are, the team’s estimates of current retreat rates of the Kilimanjaro glaciers are alarming.  Quite probably, the white cap of Africa’s highest mountain will have disappeared within the next 20 years.

Lonnie Thompson is obviously both keyed- and clued up about extracting climatic data from ice at high elevations.  So much so, that Science has printed a lengthy account of his exploits, mainly on low-latitude glaciers (Krajick, K. 2002.  Ice man: Lonnie Thompson scales the peaks for science.  Science, v. 298, p. 518-522

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