Dataset: Bacterial cell counts and DOC
Deployment: AT39-06

Bioassays were conducted at each station using water collected within 10 m depth horizon. Water was gently gravity-filtered serially through 142 mm PC filtration cartridges loaded with either a 1.2- or a 0.2-µm mixed cellulose ester membrane filter. The 1.2 µm filtrate was retained as a bacterioplankton inoculum with diluted large phytoplankton and nanoflagellate grazers while the 0.2 µm fraction was retained as particle-free DOM substrate. When possible, the filtration rig was directly attached to Niskin bottles with platinum-cured silicon tubing and the filtrate was collected into PC carboys. Otherwise, unfiltered water from the Niskin was first drawn into a PC carboy and then filtered into another PC carboy. Each bioassay was initiated by combining the 1.2 µm filtrate with the 0.2 µm filtrate in a 30:70 ratio. A pair of incubation bottles were then rinsed with this water and subsequently filled. Ammendments were added if applicable. 8 pre-combusted (4 hours at 450°C) 40 mL EPA borosilicate glass incubation vials were also rinsed and filled with initial incubation water. Bioassays were maintained in Fisherbrand Isotemp BOD refrigerated incubators. They were kept in darkness for up to 81 days at temperatures as near in situ as logistically possible (±1.5°C). Incubation bottles were sampled over the duration of each campaign, while vials were sacrificially sampled for organic carbon during and beyond the duration of each campaign. Bacterioplankton carbon (BC, µmol C / L) refers to the carbon content of a population at any given time. BC at the initial and stationary growth conditions of each bioassay were estimated by applying empirical carbon conversion factors (CCFs, fg C / cell) to POC estimates. The dissolved organic carbon (DOC) fraction in a bioassay, was estimated by subtracting bacterioplankton cell carbon (µmol C / L) from TOC measurements.