Investigating Sensitivity of East Asian Monsoon to Orbital Forcing During the Late Pliocene Warm Period

摘要

The Late Pliocene climate (3.264-3.025 Ma) is thought to be relatively warmand stable compared with the Pleistocene, but with clear orbital-scale climate variability. Using the Community Earth System Model, we investigate the sensitivity of East Asian monsoon to realistic orbital forcing during the Late Pliocene. Initial evaluation shows that theCommunity Earth SystemModel broadly capturesmodern East Asianmonsoon climatology and reproduces the reconstructed stronger (weaker) East Asian summer (winter) monsoon in the Late Pliocene under the PRISM3D (Pliocene Research, Interpretation and Synoptic Mapping) boundary conditions that use present-day orbital configurations. Sensitivity experiments indicate that summer and winter temperatures averaged over the East Asia continent remain higher for different orbital configurations in the Late Pliocene than the preindustrial, but with different warming magnitude. Variation of East Asian summer monsoon is significantly modulated by orbital forcing in the Late Pliocene. Under several extreme orbital configurations, the summermonsoon becomes weaker relative to the preindustrial. This is attributed to the fact that the orbitally induced decrease in land-sea thermal contrast exceeds the increase arising fromthe PRISM3D boundary conditions. East Asian winter monsoon exhibits a relatively stable feature and remains weaker in the Late Pliocene even with extreme orbital forcing, as the effect of PRISM3D boundary conditions that lead to reduced land-sea thermal contrast overwhelms the influence of orbital forcing. Given limitations of snapshot time slab simulation and different model sensitivity, the orbital-scale variability of East Asian monsoon in the Late Pliocene should be further explored using transient simulation and with other coupled models.