Climate change in the Indo-Pacific basin from mid- to late Holocene

Abstract

Changes in climate mean state profoundly impact climate variability. Here, we quantify slow changes in the mean climate induced by the variations in the Earth’s orbit from mid- to late Holocene, and their feedback on the main modes of climate variability. We focus on the Indo-Pacific system and show that mid-Holocene conditions favored the dominance of an equatorial dipole mode in the Indian Ocean (IO), independent of the El Niño Southern Oscillation (ENSO) and different from the IO Dipole (IOD) observed today. Mean state changes induced a gradual shift to an IO basin mode that along with the IOD modulates most of the IO variance at present. The climate modes evolution and their connectivity changes are investigated over 6000 years using a complex network methodology and principal component analysis. To uncover the causal link between a constantly evolving mean state and such changes in variability we consider two independent analyses. First, we explore changes in the mean state by quantifying the departure of 500-year annual mean snapshots from the annual mean conditions averaged over the mid-Holocene. Second, we leverage ideas from dynamical system theory and characterize the nature of the Indo-Pacifc transition, in a state space representation, by accounting for its spatiotemporal and multivariable dependency. The analysis reveals that a strengthening of the Walker circulation, driven by enhanced convection over the central Pacific and by the weakening of the Asian monsoon, set the stage for a shift in modes in both basins.