Temporal Variations of Radiocarbon Reservoir Ages in the South Pacific Ocean during the Holocene

Abstract

This article discusses the magnitude and rate of change of radiocarbon reservoir ages from the surface ocean in the South Pacific during the Holocene. 14C reservoir ages are calculated from paired U/Th and 14C measurements. Seventeen pairs of coral dates were determined from samples collected on Rendova and Tetepare Islands, in the Solomon Islands, and from Espiritu Santo Island, Vanuatu. The samples are all Holocene in age, with 230Th ages ranging from about 400 to 9400 BP. Samples were collected as drill cores or surface outcrops. About half of the surface samples appear to have incorporated modern carbon through postdepositional recrystallization. Two of the core samples were also affected by carbon exchange. The Holocene 14C reservoir ages observed in this data set show stable values for the last 3000 yr, and substantial variability from 5000–6000 BP (~100 to ~950 14C yr). Persistent low values (<200 14C yr) were observed for samples from 7000–8000 BP. We attribute these variations to temporal changes in lateral advection and vertical mixing, and possibly to local environmental conditions related to the interplay between sea-level rise and episodic uplift, characteristic of all the coral localities.