[U-02] 人新世・第四紀の気候および水循環

[U02-P02] Paleoceanographic Implications of Holocene Marine Reservoir Age Variations in the Taiwan Strait

*李 岳洋¹、王 興麟¹、沈 川洲¹、顏 一勤²、劉 司捷^1,3、徐 澔德¹ (1.國立臺灣大學、2.顏一勤應用地質技師事務所、3.財團法人中興工程顧問社深地質研究專案辦公室)

キーワード：放射性炭素年代測定、U-Th年代測定、ΔR、珊瑚、完新世、エルニーニョ・南方振動

The long residence time for carbon in the marine reservoir results in a radiocarbon reservoir age in the surface seawater, making radiocarbon ages of marine samples older than their true values. Reservoir age varies both spatially and temporally, and site-specific corrections (ΔR) are necessary for accurate ages of marine samples. Previous studies on ΔR in the western Pacific Ocean, especially in the Taiwan Strait, were limited. In this study, we present reservoir ages and ΔR values over the past 7000 years using paired U-Th and radiocarbon dates of 47 pristine Holocene coral samples, with less than 1% calcite, collected from two sites, including Hengchun on the southernmost tip of Taiwan and the Penghu Islands located in the middle of the Taiwan Strait. In the Taiwan Strait, we calculated a weighted mean ΔR of -155 ± 10 ¹⁴C yr since the Mid-Holocene. Clear temporal trends were observed, including a period of high ΔR variability before 5500 cal BP, after which ΔR variability decreased. Two periods of low ΔR values reaching below -250 ¹⁴C yr around 3500 and 1500 cal BP were also identified, while high ΔR values of -47 ¹⁴C yr occurred around 2500 cal BP. The concurrency of ΔR records in the Taiwan Strait and the South China Sea (SCS) suggests a shared source, likely driven by the Kuroshio Intrusion, which transports Pacific water into both regions. Internal waves generated by the intrusion facilitate mixing of Kuroshio water with SCS water before the waters are transported north into the Taiwan Strait and south into the SCS basin. Similarly, ΔR records from the Great Barrier Reef in the Southern Pacific Ocean exhibit comparable trends, further supporting the Pacific origin of reservoir age variations. The broad spatial distribution and similarities with ENSO variability imply ENSO may play a key role in shaping ΔR variations across the tropical Pacific.