A Younger Dryas Icecap in the Equatorial Andes

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 km 2 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 14 C yr B.P. Tephras and the age of organic deposits at the plateau edge indicate ice-free conditions before 11,800 14 C yr B.P. This interval was followed by the expansion of an ca. 140 km 2 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 14 C 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.