What is the timing of orbital-scale monsoon changes?

Abstract

A major (but little noted) divergence of opinion has developed among climate scientists over the orbital-scale periodicity and phasing of tropical monsoon variations. Kutzbach (1981. Monsoon climate of the early Holocene: climate experiment with Earth's orbital parameters for 9000 years ago. Science 214, 59–61) proposed that monsoons are driven by northern summer insolation at the precession period, but Clemens and Prell (1990. Late Pleistocene variability of Arabian Sea summer monsoon winds and continental aridity: eolian records from the lithogenic component of deep-sea sediments. Paleoceanography 5, 109–145; 2003. A 350,000-year summer-monsoon multi-proxy stack from the Owen Ridge, Northern Arabian Sea. Marine Geology 201, 35–51) inferred a more complicated response tied to latent heat transfer from the Southern Hemisphere. Because tropical monsoons affect climate over a vast area, resolving this divergence is an important task for the climate community. The purpose of this note is to highlight definitive evidence from high-resolution dating of speleothem calcite that provides unambiguous support for the Kutzbach hypothesis.