Precession forcing of the Holocene moisture transfer between tropical western Pacific and Indian Ocean

Precipitation, evaporation and moisture transport within the oceans are the main components of the global hydrological cycle. However, the evolution of the oceanic hydrological cycle over the Holocene remains a knowledge gap. In this study, through compiling paired planktonic foraminiferal δ¹⁸O and Mg/Ca sea surface temperature reconstructions from 98 locations in the tropical ocean, we calculate the fluctuation of sea surface δ¹⁸O and residual δ¹⁸O for the Holocene period. We notice a striking feature that the residual δ¹⁸O records of the tropical western Pacific and eastern Indian Ocean show a different change over the Holocene. The mean residual δ¹⁸O of the tropical western Pacific was about 0.2‰ heavier than that of the eastern Indian Ocean during the early-mid Holocene (11.5～6.0 kaBP), but they were almost identical over the late Holocene (2.0～0 kaBP). Combined with the transient climate simulations, we suggest that precession forcing is responsible for this different pattern through modulating a set of climate processes. The lower precession over the early Holocene drove a net atmospheric moisture transport from the western Pacific to the eastern Indian Ocean and lowered precipitation δ¹⁸O over the eastern Indian Ocean. Moreover, the strengthened South Asian monsoon delivered large amounts of diluted freshwater into the Bay of Bengal via river systems. All these three mechanisms contribute to a relatively negative excursion of residual δ¹⁸O in the eastern Indian Ocean. In contrast, the lower precession resulted in a decrease of net precipitation in the open western Pacific and a loss of freshwater via the atmospheric transport, thus generating heavier residual δ¹⁸O values. Through combining seawater δ¹⁸O reconstructions from a large spatial extent with the isotope-enabled simulations, this study has provided a reliable picture of the moisture transfer between different ocean basins and unveiled the underlying mechanisms regulated by precession.