A speleothem record of South Pacific Convergence Zone dynamics during MIS 3 - Evidence for non-stationary coupling between the southern tropical Pacific and Greenland?

Abstract:

The South Pacific Convergence Zone (SPCZ) is the largest component of the Intertropical Convergence Zone (ITCZ), and its impact on global climate rivals that of the deep convection at the heart of the Western Pacific Warm Pool. Rapid glacial climate fluctuations, such as Dansgaard-Oeschger (D-O) Events, would have triggered a reorganization of tropical systems such as the SPCZ, manifesting as significantly altered rainfall across the tropical south Pacific. However, a critical lack of high-resolution glacial records from this region means the dynamics of the SPCZ are largely unknown.

We present a decade-resolution, absolute-dated speleothem rainfall record from the Island of Niue in the southern Tropical Pacific spanning 25-45 ka. Sr, Mg, δ¹⁸O and δ¹³C variations show that Niue experienced large, rapid fluctuations in rainfall lasting up to 1200 years. Between 40 and 45 ka, these show a remarkable concordance with the timing, duration and shape of D-O events 9-11. Rapid warming in Greenland was accompanied by a sudden increase in rainfall in Niue, implying that the SPCZ was strongly coupled with climate in the high Northern latitudes. These changes are not consistent with a wholesale northward shift in the SPCZ, which would have resulted in drying in Niue, and instead imply that the SPCZ underwent a more complex reorganization, perhaps rotating around its western edge in a manner analogous to modern-day extreme ENSO events.

The speleothem record between 25-40 ka also shows large changes in rainfall, with D-O events identifiable. However, these changes are less well matched to Greenland, and include events not captured by the ice cores. It is clear that the SPCZ response to global climate change is complex: while it can closely couple with high-northern latitude climate for periods, this coupling may not be stationary with time. We speculate that this might result from changing precession, influencing which teleconnections dominate climate changes in the south tropical Pacific.