Millennial-scale interhemispheric asymmetry of low-latitude precipitation: Speleothem evidence and possible high-latitude forcing

During the last glacial period, global climate was characterized by numerous millennial-scale abrupt changes. Mechanisms of these events, however, are not yet resolved. Here, we use phasing information between climate records from different localities to distinguish between mechanisms. We establish a 90,000 year-long oxygen isotopic record of cave calcite, with our previously reported and newly obtained data from Caverna Botuverá, southern Brazil. The record was precisely dated with uranium-series methods. Using independent absolute-dated chronologies, we compare the southern Brazil record with contemporaneous oxygen isotopic records of cave calcite from eastern China and the record of speleothem growth periods from northeastern Brazil. Our record anti-correlates remarkably with the eastern China profile, while it correlates positively with the northeastern Brazil one, on both millennial and orbital scales. Thus, rainfall patterns are antiphased between southern Brazil and eastern China but in-phase between the two Brazilian regions. The in-phase Brazilian relationship argues against a Super El Niño-Southern Oscillation (Super-ENSO) mechanism as modern rainfall at these sites is out of phase during ENSO years. Rather, the relationship among the three records is likely related to displacement in the mean position of the intertropical convergence zone and associated asymmetry in Hadley circulation, which leads to an interhemispheric anti-phasing of rainfall between the southern and northern low latitudes. The abrupt climate events during the last glacial-interglacial cycle are probably triggered by meridional overturning circulation changes initiated in the high latitudes and then amplified through air-sea dynamics, resulting in the observed pattern of low-latitude precipitation.