Past glaciation in the tropics

Abstract

Tropical glaciers are considered along three meridional profiles, for the Australasian sector, Africa and the Americas. Evaluated are the annual mean freezing level 0 °C, modern equilibrium line altitude MEL, and past equilibrium line altitude PEL. The calculation of 0 °C is based on a 1958–1997 global data set; MEL refers to estimates concerning the first half of the 20th century; and the timing of the PEL is not generally known. 0 °C stands around 4000–5000 m, with lower levels in the outer tropics. MEL is reached in the Australasian sector on four mountains, and in Africa on three mountains, near the Equator, near or above 0 °C. In the American cordilleras many peaks are still glaciated, above 0 °C, but in the arid southern tropical Andes even summits above 6000 m do not reach MEL. The PEL stands between 3000 m and 5000 m, high in the equatorial zone, but highest in the arid southern tropical Andes. The height difference between MEL and PEL is of order 1000 m, with regional differences. Deglaciation dates range between 15,000 and 8000 years BP, with later timing towards the higher elevations. This synopsis suggests priority targets for further research: morphological mapping and age determination in the High Atlas of Morocco; timing of deglaciation in the High Semyen of Ethiopia and the Altos de Cuchumatanes of Guatemala; exploration in the highlands of Lesotho and of the Dominican Republic; and glaciation in the arid southern tropical Andes.