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A younger dryas icecap in the Equatorial Andes

Abstract:

Morphologic and stratigraphic evidence shows that a late-glacial ice cap existed on part of the Eastern Cordillera of Ecuador (Lat. 0° 20′ S) on ground with a mean elevation of 4200 m where none exists now. An outlet glacier from an ca. 800 km2 ice cap terminated at 3850 m altitude in the Papallacta valley on the eastern side of the plateau. Radiocarbon dates show that moraines formed by this advance were ice-free by 13,200 14C yr B.P. Tephras and the age of organic deposits at the plateau edge indicate ice-free conditions before 11,800 14C yr B.P. This interval was followed by the expansion of an ca. 140 km2 ice cap that discharged glaciers into adjacent valleys where terminal moraines were built at 3950 m altitude. AMS and conventional radiocarbon dates from macrofossils, peat, and gyttja above and below till of the readvance indicate that the ice cap formed between ca. 11,000 and 10,000 14C yr B.P. and was thus coeval with the European Younger Dryas event. The ice cap developed in response to a surface temperature cooling of at least 3°C in the tropical Andes, a finding that is consistent with a coupled equatorial/high latitude North Atlantic climate system operating at the late-glacial/Holocene transition. These results are further evidence that Younger Dryas cooling may have been a global event. © 1997 University of Washington.