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 δ18O (δ18Osw, generated from coral Sr/Ca and δ18O ratios) in both modern corals and fossil corals from the early mid-Holocene (ca. 6.7–6.5 ka Before Present (BP)). The modern coral, from the northern South China Sea (SCS) in the northwest Pacific, shows relatively negative δ18Osw 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 δ18Osw 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 δ18Osw values during most of the year, but with a positive δ18Osw peak in October (cold season), while the two early mid-Holocene corals record a positive δ18Osw peak in February (summer) and a negative peak in August (winter). Seasonal patterns preserved in coral δ18Osw series reflect seasonal variations in precipitation, both in the northern SCS and Vanuatu; consequently, their contrasting seasonal coral δ18Osw 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.
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