Holocene variation of radiocarbon reservoir age offshore western Taiwan, derived from paired charcoals and mollusks

Abstract

We use the carbon content of charcoals from coastal sediments to evaluate the magnitude of alteration, and apply this as a screening criterion for radiocarbon dating. Charcoals with carbon yields <2% indicate significant carbon loss and likely reworking. Reliable age estimates for sedimentary deposition can be achieved by eliminating these highly altered charcoals. We compare radiocarbon dates from well preserved (terrestrial) charcoals with marine mollusk fragments from the same, or similar sediment horizons, to calculate radiocarbon reservoir ages during the Holocene in the Taiwan Strait, western Taiwan. The early Holocene radiocarbon reservoir age (R) estimated from our study site is similar to early Holocene R values from the South China Sea (SCS). However, we find a large increase in R, in excess of 1000 14C years, between 3000 and 4000 cal BP. After this time the late Holocene R value from our site returns to the SCS pre-bomb value. These west coast R values are lower than those from offshore northeastern Taiwan, and reinforce the need to document site-specific R values through time to achieve reliable 14C dates.