The Radiocarbon Signature of Microorganisms in the Mesopelagic Ocean

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The Radiocarbon Signature of Microorganisms in the Mesopelagic Ocean

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Title: The Radiocarbon Signature of Microorganisms in the Mesopelagic Ocean
Author: Hansman, Roberta L.; Griffin, Sheila; Watson, Jordan T.; Druffel, Ellen R. M.; Ingalls, Anitra E.; Pearson, Ann; Aluwihare, Lihini I.

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Citation: Hansman, Roberta L., Sheila Griffin, Jordan T. Watson, Ellen R. M. Druffel, Anitra E. Ingalls, Ann Pearson, and Lihini I. Aluwihare. 2009. The radiocarbon signature of microorganisms in the mesopelagic ocean. Proceedings of the National Academy of Sciences of the United States of America 106(16): 6513-6518.
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Abstract: Several lines of evidence indicate that microorganisms in the meso- and
bathypelagic ocean are metabolically active and respiring carbon. In addition, growing evidence suggests that archaea are fixing inorganic carbon in this environment. However, direct quantification of the contribution from deep ocean carbon sources to community production in the dark ocean remains a challenge. In this study, carbon flow through the microbial community at 2 depths in the mesopelagic zone of the North Pacific Subtropical Gyre was examined by exploiting the unique radiocarbon signatures (Δ14C) of the 3 major carbon sources in this environment. The radiocarbon content of nucleic acids, a biomarker for viable cells, isolated from size-fractionated particles (0.2– 0.5 μm and >0.5 μm) showed the direct incorporation of carbon delivered by rapidly sinking particles. Most significantly, at the 2 mesopelagic depths examined (670 m and 915 m), carbon derived from in situ autotrophic fixation supported a significant fraction of the free-living
microbial community (0.2– 0.5 μm size fraction), but the contribution
of chemoautotrophy varied markedly between the 2 depths. Results further showed that utilization of the ocean’s largest reduced carbon reservoir, 14C-depleted, dissolved organic carbon, was negligible in this environment. This isotopic portrait of carbon assimilation by the in situ, free-living microbial community, integrated over >50,000 L of seawater, implies that recent, photosynthetic carbon is not always the major carbon source supporting microbial community production in the mesopelagic realm.
Published Version: doi:10.1073/pnas.0810871106
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