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The Indo-Pacific Warm Pool (IPWP) exerts a dominant role in global climate by releasing huge amounts of water vapour and latent heat to the atmosphere and modulating upper ocean heat content (OHC), which has been implicated in modern climate change1. The long-term variations of IPWP OHC and their effect on monsoonal hydroclimate are, however, not fully explored. Here, by combining geochemical proxies and transient climate simulations, we show that changes ofIPWP upper (0-200 m) OHC over the past 360,000 years exhibit dominant precession and weaker obliquity cycles and follow changes in meridional insolation gradients, and that only 30%-40% ofthe deglacial increases are related to changes in ice volume. On the precessional band, higher upper OHC correlates with oxygen isotope enrichments in IPWP surface water and concomitant depletion in East Asian precipitation as recorded in Chinese speleothems. Using an isotope-enabled air-sea coupled model, we suggest that on precessional timescales, variations in IPWP upper OHC, more than surface temperature, act to amplify the ocean-continent hydrological cycle via the convergence of moisture and latent heat. From an energetic viewpoint, the coupling of upper OHC and monsoon variations, both coordinated by insolation changes on orbital timescales, is critical for regulating the global hydroclimate.
A key feature of anthropogenic climate change is that heat associated with the present energy imbalance is mainly (approximately 90%) absorbed by the world's oceans1. Indeed, a substantial slowdown in surface warming between 2002 and 2012 CE2-3 has been attributed to an increased subsurface ocean heat uptake, through increased subduction in shallow overturning cells in the Pacific Ocean and enhanced heat convergence in the equatorial thermocline4. Increased upper OHC might have fuelled and intensified La Niña, monsoon and tropical cyclone activities during the last decade5-7. Given the time-limited and transient response seen in modern observations (for example, the shift in the 1970s), it is critical to gain knowledge of the relationships between variations in equatorial Pacific OHC and tropical hydroclimate from palaeoclimate records8,9.
The IPWP, defined by a sea surface temperature (SST) of greater than 28 °C (Fig. 1a), is the largest reservoir of warm water on Earth and serves as a 'steam and heat engine' for global climate today, and its upper OHC has a particularly important role in the energy flow and hydrological...