Abrupt variations in South American monsoon rainfall during the Holocene based on a speleothem record from central-eastern Brazil.

Abstract

Well-dated high-resolution oxygen isotope records of speleothems in central-eastern Brazil spanning from 1.3 to 10.2 kyr B.P. reveal that the occurrence of abrupt variations in monsoon precipitation is not random. They show a striking match with Bond events and a significant pacing at ∼800 yr, a dominant periodicity present in sea surface temperature records from both the North Atlantic and equatorial Pacific Oceans that is possibly related to periods of low solar activity (high 14C based on the atmospheric Δ14C record). The precipitation variations over central-eastern Brazil are broadly antiphased with the Asian and Indian Monsoons during Bond events and show marked differences in duration and structure between the early and late Holocene. Our results suggest that these abrupt multicentennial precipitation events are primarily linked to changes in the North Atlantic meridional overturning circulation (AMOC). Anomalous cross-equatorial flow induced by negative AMOC phases may have modulated not only the monsoon in South America but also affected El Niño−like conditions in the tropical Pacific during the Holocene.