Even though the meso- and bathypelagic regions beneath the euphotic zone contain nearly all of the oceans volume, little is known about the biogeochemical processes that function in this region. For this reason, a PI from Scripps Institute of Oceanography will collaborate with a PI from Harvard University to determine which carbon sources fuel prokaryotic production in the meso- and bathypelagic ocean. Specifically, the PIs wish to address the following two questions: (1) Is freshly-produced organic matter the primary dissolved organic carbon (DOC) pool that is accessible to deep ocean heterotrophic prokaryotes or is "old" DOC also bioavailable?; and (2) Is chemoautotrophic fixation of inorganic carbon by planktonic archaea an important component of the deep ocean carbon cycle? To address these questions, the PIs plan to measure the radiocarbon (14C) concentration of the carbon source pools and the resulting prolaryotic (bacterial and archaeal) biomass at the surface, meso (500-600 m) and bathypelagic (>900 m) depths. In addition, fluorescent in-situ hybridization (FISH) and genetic diversity analysis by denaturing gradient gel electrophorsis (DGGE) will provide a complementary picture of the biological community. Lastly, to obtain the large quantities of biomass-derived carbon needed for this study, the PIs plan to develop an in-situ, battery powered, submersible pump capable of pumping 20,000L of seawater per deployment during the first year of the study.
