The transcriptional mechanism of precession signal of the stalagmite <italic>δ</italic>¹⁸O from Eastern China: Insolation-modulated rainout effect in the moisture source region—Decoding the global climate heat engine archive

The orbital-scale long sequence of stalagmite δ18O in Eastern China exhibits an almost perfect match with the precessional cycling solar radiation, which has sparked significant interest and attention in the paleoclimate scientific community. Since stalagmites and loess coexist in Eastern China, using the stalagmite δ18O, which shows no difference between glacial and interglacial periods within the precession cycle, as an indicator of summer monsoon circulation clearly contradicts the paleoclimatic fact that " loess development during glacial periods indicates a weak summer monsoon." This then raises a new question: if the δ18O signal reflects " neither rainfall nor wind, " where and by what mechanisms is the precessional insolation signal transcribed into the stalagmite δ18O in Eastern China? Based on recently published terrestrial and marine datasets, we find that the underlying mechanism is most likely the insolation-modulated " isotopic rainout effect" in the moisture source region of the Indo-Pacific Warm Pool (IPWP). The precession-paced insolation delivers energy to the ocean heat content (OHC) of the IPWP, the variations in OHC, in turn, operate changes in the Walker Circulation through air-sea interactions and, together with the Walker Circulation, co-drive the water cycle over the ocean within IPWP. Within the water cycle over the ocean, the precession-paced " rainout" produces large-amplitude negative shifts in the vapor δ18O of atmospheric moisture storage and corresponding positive shifts in seawater δ18O. The precessional δ18O signal recorded by the stalagmites in Eastern China is therefore transcribed in the moisture source region. The monsoon circulation that transports heat and moisture to Eastern China does not generate but load the signals. Furthermore, the predominance of frontal-type summer precipitation in Eastern China allows the faithful transmissions of the isotopic signal from the source-region. We further analyze an episode in which the stalagmite δ18O " derails" (rapid, large-magnitude shifts opposite to the direction of insolation changes) and find that the stalagmite δ18O responds to global climate events more like a monitor that is independent of the climatic system. In this sense, the stalagmite δ18O from Eastern China is a geological archive that documents the operating state of the global climate heat engine and may provide new insights into the long-standing " energy puzzle" of glacial-interglacial cycles.