Energy budget analysis of the Western Pacific Warm Pool highlights the pivotal role of heat transport by the South Equatorial Current during the last deglaciation

The Western Pacific Warm Pool (WPWP) is a region in the Western Pacific where the annual average sea surface temperature (SST) exceeds 28^oC. With its substantial heat storage capacity, the WPWP plays a critical role in both oceanic and atmospheric circulations, acting as the primary source of heat and moisture for the Earth’s system. While extensive studies have been conducted on the connections between the WPWP and subtropical or mid-to-high latitudes in modern observations and global warming simulations, discussions of these mechanisms on geological timescales, especially millennial timescales, remain limited.

Here we present the energy budget of the WPWP from the Last Glacial Maximum (LGM) to pre-industrial using transient simulations TraCE (Transient Climate Evolution) – 21ka. During the glacial terminations, the shortwave radiation received by the WPWP is approximately balanced by longwave radiation, latent heat flux, and sensible heat flux. Variations in ocean heat content (OHC) trends during these periods, as well as millennial-scale fluctuations, are primarily driven by ocean heat transport (OHT), whose variation is about ten times larger than the net effect of radiation and surface heat flux.

By defining the North-South-West-East (20^oN - 12 ^oS , 110 ^oE - 165 ^oE) four boundaries of the WPWP, we computed the OHT across each boundary and identified the southern boundary as the dominant contributor to both long-term trends and millennial-scale fluctuations. The northward meridional OHT at the southern boundary increased during relatively cold periods in the Northern Hemisphere (e.g., Heinrich Event I and the Younger Dryas, with 29% and 47% OHT increase compared to LGM) and decreased during relatively warm periods (e.g., Bølling–Allerød, with only 24% increase compared to LGM). These variations are associated with changes in the New Guinea Coastal Undercurrent (NGCUC), a downstream branch of the South Equatorial Current.

Our findings highlight a significant connection between the WPWP and the South Pacific during glacial terminations and across millennial timescales. These results provide valuable insights into the WPWP's role in modulating past climate dynamics and its broader implications for ocean-atmosphere interactions.