Australia: The Land Where Time Began

A biography of the Australian continent 

North Atlantic Forcing of Amazonian Precipitation During the Last Ice Age

Multiple abrupt reorganisations of the circulation of the oceans and the atmosphere took place during the last glacial period (1). At times when the Atlantic meridional overturning circulation slowed, which it does on 1,000-year timescales, such periods were associated with high northern latitude cooling, and northern warming has been associated with periods of strengthened circulation (Cruz et al., 2005; Fritz et al., 2010). These events on a millennial scale were primarily reflected in the tropics as changed precipitation patterns (Petersen et al., 2000). Along the Atlantic seaboard and the high Andes (Fritz et al., 2010) ecological changes were induced by these hydrologic fluctuations, though less is known about the response of the Amazon Basin. In this paper the authors¹ reconstruct precipitation in the region of the Amazon in Ecuador for the past 94,000 years by the use of a δ¹⁸O record compiled from speleothems from Santiago Cave, western Amazonia, interpreting as changes of source and amount of precipitation, the variability of the δ¹⁸O record. Abrupt high-frequency changes coincide with shifts of the North Atlantic circulation, with the exception of the period between 40,000 and 17,000 years ago, which indicates a high-latitude influence on Amazonian precipitation over millennial timescales. A relationship to precessional changes in the orbit of the Earth on longer timescales is shown by the record. The authors¹ conclude that western Amazonian ecosystems have not experienced prolonged drying in the last 94,000 years, as the records do not show periods of extreme aridity.

Sources & Further reading

1. Mosblech, Nicole A. S., Mark B. Bush, William D. Gosling, David Hodell, Louise Thomas, Peter van Calsteren, Alexander Correa-Metrio, et al. "North Atlantic Forcing of Amazonian Precipitation During the Last Ice Age." Nature Geosci 5, no. 11 (11//print 2012): 817-20.