The oceanic carbon cycle has traditionally been viewed as a reversible, one step reduction-oxidation reaction (CO2CH2O). Principle pathways were thought to involve eukaryotic photoautotrophy and oxygen-dependent bacterial respiration, respectively. However, prokaryotic (cyanobacterial) photoautotrophy is now well documented and has even been proposed as a major carbon pathway1-6. In a previous study of the mesopelagic zone in the North Pacific Ocean7, the observed downward fluxes of organic carbon, nitrogen, ATP and RNA suggested production in situ of new particulate organic carbon at 700-900 m. Here we present evidence that this is indeed the case and that it is mediated by bacterial chemolithotrophy. Energy for this process may be in part provided by detrital NH+4 derived from the downward flux of large particles.
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