Fluctuations in marine radiocarbon reservoir age in the western Pacific: Evidence of reduced E-W Pacific gradient over the past 6000 years

Abstract

Radiocarbon (14 C) is a useful tracer for surface ocean circulation and mixing, which reflects air-sea CO 2 exchange. We present radiocarbon marine reservoir ages (R) and corrections (ΔR) in Holocene inferred from 18 paired 14 C and 230 Th ages on fossil corals from Lanyu Island offshore eastern Taiwan. The results show large fluctuations in the ΔR value, with averages of-330 and-5 14 C yr for 6000-5100 yr BP and the past 150 years, respectively. The extremely young R in the mid-Holocene indicate a well-equilibrated North Equatorial Current (NEC), likely stemmed from enhanced air-sea interactions and strengthened Pacific Walker circulation. This suggests a larger E-W gradient across the Equatorial Pacific and hence a La Niña-like condition, consistent with both model simulations and other paleo-proxy records. Combining the ΔR records in the northern South China Sea, the results imply an increasing influence of the NEC water on the subtropical western Pacific since the mid-Holocene.