Cirque morphology and palaeo-climate indications along a south-north transect in High Mountain Asia

Abstract

Cirques preserve important palaeo-climate information and have been investigated in various areas around the world. High Mountain Asia (HMA) contains the largest modern glacier inventory outside of polar regions, and tens of thousands of cirques. We analyzed 2831 largely ice-free cirques from five areas along a south-north transect in HMA, including central Himalayas (C. Himalayas), western Gangdise (W. Gangdise), eastern Tian Shan (E. Tian Shan), southern Altai (S. Altai), and northern Altai (N. Altai). These cirques are large relative to those in many parts of the world, and in the Himalayas, Tian Shan, and Altai their vertical dimensions are considerable. Their size variations show weakly allometric relations. The poleward decreasing trend in cirque floor altitudes is consistent with the reducing temperature trend toward high latitudes. Although just north of C. Himalayas, W. Gangdise is in their precipitation shadow and its cirque floors are higher. Relatively shallow cirques in W. Gangdise probably reflect low subglacial erosion associated with limited precipitation received from either the Indian monsoon or Westerlies due to this orographic effect. Lower cirque floor altitudes for north-facing cirques were likely caused by their lesser receipt of solar radiation. Because most mountains rose well above equilibrium-line altitudes of glaciers and were heavily glaciated, cirque aspects show symmetric vector strengths except in the lowest area, N. Altai. Eastward aspects in N. and S. Altai show the strong effects of Westerly winds in the past, as for present glaciers. Similarly, cirque aspects in C. Himalayas are more northeast-ward than modern glacier aspects, suggesting a stronger west wind influence in the past. North-facing cirques are lower and more frequent than south-facing, showing the general importance of solar radiation receipt, which is especially dominant in E. Tian Shan.