Decoupling of seasonal temperature and precipitation over the western Pacific during the early mid-Holocene

This paper considers seasonal patterns of temperature and precipitation over the western Pacific during the early mid-Holocene through an analysis of seasonal variations in sea surface temperature (SST, reconstructed from coral Sr/Ca ratios) and seawater O-18 (O-18(sw), generated from coral Sr/Ca and O-18 ratios) in both modern corals and fossil corals from the early mid-Holocene (ca. 6.7-6.5ka Before Present (BP)). The modern coral, from the northern South China Sea (SCS) in the northwest Pacific, shows relatively negative O-18(sw) values during the warmer seasons (May-December), but relatively positive values during the colder seasons (January-April). In contrast, the fossil coral shows relatively negative O-18(sw) values during the cold seasons (February-May), but relatively positive values during the warm seasons (June-October). This contrast is also evident in the Vanuatu corals from the southwest Pacific. In detail, the modern coral record shows low O-18(sw) values during most of the year, but with a positive O-18(sw) peak in October (cold season), while the two early mid-Holocene corals record a positive O-18(sw) peak in February (summer) and a negative peak in August (winter). Seasonal patterns preserved in coral O-18(sw) series reflect seasonal variations in precipitation, both in the northern SCS and Vanuatu; consequently, their contrasting seasonal coral O-18(sw) variations during the early mid-Holocene and at present indicate that the configuration of temperature and precipitation during the early mid-Holocene differed to the present-day situation. This decoupling of seasonal temperature and precipitation variations occurred over the western Pacific, which means that it was a regional, rather than simply a local climate phenomenon. This seasonal decoupling may have resulted from the synchronous northward shift of both the Intertropical Convergence Zone and South Pacific Convergence Zone during the early mid-Holocene, which seems to be controlled by orbital forcing.