Department of Earth System Science

A small but significant depletion of radiocarbon activity () is present in surface, meso-, bathy- and abyssopelagic fishes and crustaceans collected from depth in the North Central Pacific (NCP) and in the Northeast Pacific (NEP) in the 1960s and 1970s compared to average values for dissolved inorganic carbon (DIC) and zooplankton found in the euphotic zone during this period. These low ¹⁴C activities are postulated to result from (1) the ¹⁴C gradient in DIC in the euphotic zone, and (2) the incorporation of low activity, pre-bomb peakcarbon (pre-1969) from the surface ocean into chronologically old organisms. Based on the relative increase of ¹⁴C activity in surface and deep organisms, maximum estimates of the turnover times range from 1< to 9 years for the organic carbon in surface and mesopelagic animals and 4–18 years for bathy- ad abyssopelagic animals from the NCP and NEP. These data suggest that the main source of dietary carbon for deep-sea organisms is from rapidly sinking organic detritus from the surface and from active (animal mediated) transport of living carbon. There may be a minor contribution (15%) to bathypelagic organisms from low ¹⁴C activity chemolithotrophically der ived organic carbon, from heterotrophic uptake of mid-depth DIC or from recycled carbon.