Dynamics Of The Intertropical Convergence Zone Over The Western Pacific During The Little Ice Age

Abstract:

Both palaeoclimate reconstructions and climate modeling have demonstrated that precipitation in low latitudes is primarily controlled by north- south migration of the global Intertropical Convergence Zone on millennial to orbital timescales. These migrations are associated with the occurrence of opposite rainfall variations between the two hemispheres. However, the pattern of rainfalls around the marine-continental tropical western Pacific region over the last millennium remains unclear. Several recent studies suggest a southward migration of the Intertropical Convergence Zone during the Little Ice Age (~AD 1400-1850). Concomitantly, dry Little Ice Age conditions should have occurred in the northern extent of the Intertropical Convergence Zone and wet conditions around the southern limit. However, our synthesis of proxy hydrology records from the Asian-Australian monsoon area documents a distinctly different rainfall pattern that violates this expectation, suggesting instead the occurrence of synchronous retreat of the East Asian Summer Monsoon and the Australian Summer Monsoon during the Little Ice Age. Thus we propose an alternative dynamic scenario: rather than strict north-south migration, the apparent mode of multi-decadal to centennial change for the western Pacific Intertropical Convergence Zone is contraction/expansion in response to external forcings such as solar irradiance variation and large volcanic eruptions.