Coherent pan‐Asian climatic and isotopic response to orbital forcing of tropical insolation

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Abstract
The oxygen‐18 isotope composition of calcite in stalagmites across southern and eastern Asia are highly correlated to one another on orbital time scales: large negative excursions are coincident with maxima in summer insolation in the subtropics of the Northern Hemisphere (NH). These isotopic excursions reflect changes in the precipitation‐weighted isotopic composition of precipitation, δ18Op. We present results from two core experiments using an isotope‐enabled climate model—the“high‐insolation” and “low‐insolation” experiments—in which the model is forced by extrema in NH summer insolation. Compared to the low‐insolation experiment, the high‐insolation climate features profound, large‐scale changes in the pattern of monsoon precipitation spanning from Africa to Southeast Asia that are due to changes in the relative contributions of temperature and moisture to the near‐surface equivalent potential temperature θe. Under high insolation, a more rapid increase in land surface temperature in early summer causes the greatest θe (and hence precipitation) to shift from the oceans in low insolation (such as today) to be over land in high insolation (such as the early Holocene). The model captures the general pattern of isotopic excursions seen in caves spanning from Israel to western China, including large drops in δ18Op over eastern Tibet (−7‰), the Arabian Peninsula, and northeast Africa (−4‰). Although there are large changes in precipitation over Tibet, the change in δ18Op is due to changes in the δ18O of water vapor that is delivered and subsequently precipitated; it does not inform on local precipitation amount or intensity.

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