Radiocarbon in Particulate Matter from the Eastern Sub-Arctic Pacific Ocean: Evidence of a Source of Terrestrial Carbon to the Deep Sea

Abstract

Carbon isotope ratios were measured in organic and inorganic carbon of settling particulate matter collected with a sediment trap at Ocean Station “P” in the Gulf of Alaska from March to October, 1983. Dissolved inorganic carbon (DIG) in surface sea water collected during two different seasons in 1984 were analyzed using large gas proportional counters and revealed a minimum seasonal Δ14C variation of 14‰. Results show that the Δ14C of calcium carbonate scdimenting to the deep sea is the same as that measured in surface water DIC. In contrast, particulate organic carbon (POC) had significantly higher Δ14C values (by 25–70‰) than that in surface water DIC. Also, the δ13C of the POC was markedly lower than previously reported values from other trap stations and marine particulate matter in general. Results from this study suggest that a significant amount of the POC settling to the deep sea at this pelagic station is of terrestrial origin, not strictly of marine origin as had previously been believed.