Supported by the National Natural Science Foundation of China (Grant No. 42188102, 91958208, 41976047 and 42176053), Prof. Zhimin Jian and his research group from the State Key Laboratory of Marine Geology (Tongji University) have achieved important progress in underlying mechanisms of how the low-latitude Indo-Pacific regulate Asian monsoonal energy and moisture changes on orbital timescales. The related research was titled "Warm pool ocean heat content regulates ocean-continent moisture transport" and published in Nature recently.

Article link: http://www.nature.com/articles/s41586-022-05302-y.

Since the industrial revolution, approximately 90% of the heat caused by anthropogenic source of CO2 has been absorbed by the ocean. The Indo-Pacific Warm Pool (IPWP) is the region with the highest sea surface temperature (SST) and the largest reservoir of warm water on Earth and serves as a ‘steam and heat engine’ for global climate today. Combination of geochemical proxies and climate simulations is an efficient approach to study the past change of ocean heat content (OHC) and its regulation on the ocean-continental energy/water cycle, which could remedy the shortage of instrument observations, however, the difficulties lie in the lack of long-term records of thermocline water temperatures (TWT) and quantitative methods to calculate the past upper OHC.

In this study, Zhimin Jian and his research group reconstructed sea surface temperature (SST) and thermocline water temperature (TWT) on the basis of the Mg/Ca ratios of the tests of planktonic foraminifera species Globigerinoides ruber and Pulleniatina obliquiloculata, respectively, from ten deep-sea sediment cores. The calcification depths of P. obliquiloculata are estimated at 110-160 m water depth (upper thermocline). Further, they reconstruct upper (0-200 m) OHC in the IPWP for the last 360,000 yr based on the SSTs and TWTs. This proxy reconstruction is generally comparable with the simulated annual mean upper OHC changes from the Community Earth System Model, in terms of both the amplitude and the pattern. At the same time, the residual δ18O of surface seawater (δ18Osw, with the ice-volume effect removed) reconstructed from G. ruber is not only consistent with the OHC change in the IPWP but also are out-of-phase of precession cycle with Chinese speleothem δ18O, and further confirmed by transient simulation with the water isotope climate model GISS_ModelE2-R.

By combining modern observations, geochemical proxies, and numerical simulation with isotope-enabled air–sea coupled model, this study explored the moisture and latent heat transport using upper OHC (more than surface temperature) from the warm pool, and measured the monsoonal hydrological cycle intensity via ocean–continent oxygen isotope gradient. This research demonstrated the great role of low-latitude climate and upper ocean dynamics in regulating global climate changes from an energetic viewpoint for the first time, which not only broadens a new research area of energetics in paleoceanography and paleoclimate, but also provides a new approach to predict modern and future climate changes.