North Atlantic forcing of Amazonian precipitation during the last ice age

摘要

The last glacial period was marked by multiple, abrupt reorganizations of ocean and atmosphere circulation. On thousand-year timescales, slowing of the Atlantic meridional overturning circulation was associated with cooling in the high northern latitudes, whereas strengthened circulation was linked to northern warming. In the tropics, these millennial-scale events were primarily reflected in altered patterns of precipitation. These hydrologic fluctuations induced ecological changes in the Atlantic seaboard and the high Andes, but less is known about the Amazon Basin. Here we reconstruct precipitation over Amazonian Ecuador over the past 94,000 years using a δ 18 O record from speleothems collected in Santiago Cave in western Amazonia. We interpret the variability of the δ 18 O record as changes in the source and amount of precipitation. With the exception of the period between 40,000 and 17,000 years ago, abrupt, high-frequency changes coincide with shifts in North Atlantic circulation, indicating a high-latitude influence on Amazonian precipitation over millennial timescales. On longer timescales, the record shows a relationship to precessional changes in the Earth's orbit. In light of the lack of extreme aridity in our records, we conclude that ecosystems in western Amazonia have not experienced prolonged drying over the past 94,000 years.