Abstract
A small but significant depletion of radiocarbon activity ( Δ 14 C 0 00 ) 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.
Highlights
IN A study of radiocarbon activities in marine organisms from the equatorial and North Pacific, WILLIAMS and L1NICK(1975) concluded that bomb radiocarbon was removed more or less rapidly from the euphotic zone into the deep water depending upon particular food chain mechanisms
PEARCYand STUIVER(1983) reported a decrease with depth in the organic-14C content of meso- and bathypelagic and abyssobenthic animals (500-5180 m) in the Northeastern Pacific Ocean off Oregon. They suggested that rapidly sinking, recently produced particles from the upper mixed layer are not the principal source of dietary organic carbon for deep-sea fishes and large benthic invertebrates. They concluded that "large and nutritious particles do sink into the deep sea, but they are not from surface waters, and they do not have high 14C levels because non-refractory organic carbon is regenerated and recycled many times in the euphotic zone, [and] fecal pellets that sink into deep-sea sediment traps are mainly produced by larger mesopelagic animals that consume such recycled and 'aged' carbon." They estimated a residence time of about 18-35 years for the dietary organic carbon pool for meso- and bathypelagic and abyssobenthic animals
We report here a re-analysis of their data, plus additional organic-14C activities for meso, bathy- and abyssopelagic fishes and crustaceans collected in the North Central Pacific (NCP) and the Northeastern Pacific (NEP)
Summary
IN A study of radiocarbon activities in marine organisms from the equatorial and North Pacific, WILLIAMS and L1NICK(1975) concluded that bomb radiocarbon was removed more or less rapidly from the euphotic zone into the deep water depending upon particular food chain mechanisms. PEARCYand STUIVER(1983) reported a decrease with depth in the organic-14C content of meso- and bathypelagic and abyssobenthic animals (500-5180 m) in the Northeastern Pacific Ocean off Oregon. They suggested that rapidly sinking, recently produced particles from the upper mixed layer (euphotic waters) are not the principal source of dietary organic carbon for deep-sea fishes and large benthic invertebrates. (DIC) in the mixed layer, combined with the chronological age of the organisms themselves are primarily responsible for the decrease in biocarbon-t4C activities with depth
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