Dark dissolved inorganic carbon (DIC) fixation in the ocean is mediated by chemoautotrophs and mixotrophs, as well as heterotrophs via anaplerotic metabolism. Organic carbon production by dark DIC fixation processes has long been thought to be negligible compared to phytoplankton primary production. Yet, recent studies indicate that dark DIC fixation in the mesopelagic waters is in the same order of magnitude as heterotrophic prokaryotic production. We investigated the spatial distribution of bulk dark DIC fixation in the Atlantic and Pacific Ocean and the cell-specific bicarbonate uptake rates determined by microautoradiography. Higher bulk DIC fixation and relative abundance of prokaryotes taking up DIC were found in epipelagic waters (~30% of total prokaryotes) than in mesopelagic waters. Meso- and bathypelagic prokaryotes exhibited nearly equal cell-specific DIC uptake rates than the epipelagic communities even though only ~1-5% of prokaryotes took up DIC. These results indicate an active fraction of DIC fixing prokaryotes down to bathypelagic layers.

Primary Presenter: Chie Amano, University of Vienna (chie.amano@univie.ac.at)

Authors:

Chie Amano, University of Vienna  (chie.amano@univie.ac.at)

Ulrike Willhelm, University of Vienna  (a12115076@unet.univie.ac.at)

Theres Koch, University of Vienna  ()

Thomas Reinthaler, University of Vienna  (thomas.reinthaler@univie.ac.at)

Eva Sintes, Centre Oceanogràfic de les Balears - Instituto Español de Oceanografía, CSIC  (eva.sintes@ieo.csic.es)

Roberta L. Hansman, Woods Hole Oceanographic Institution  (rhansman@whoi.edu)

Gerhard J. Herndl, University of Vienna  (gerhard.herndl@univie.ac.at)

Federico Baltar, University of Vienna  (federico.baltar@univie.ac.at)