Description of methods from cruise plans and project proposal:

Triaxus and CTD operations were conducted from the R/V Point Sur within the Santa Barbara Channel. Samples were collected for particulates and dissolved constituents. Determinations of phytoplankton productivity were made using 14C, 15NO3 and 32Si incorporation using on-deck incubator. Measurements of microbial activity, biomass and DNA. 3H-Leucine were used to assess bacterial production. Deck board incubation experiments were also conducted.

The Triaxus survey was used to assess fluorescence and to target the areas of water collection for experimental work. A 24-station CTD grid was performed on each cruise. A full suite of particulate and dissolved nutrients were measured, along with bacterial and phytoplankton productivity measurements. Two large incubation experiments were conducted onboard using deck incubators. 

Assays of nutrient stress: Phytoplankton nutrient stress at each grid station were quantified by measuring the uptake rate of silicic acid and nitrate at the ambient concentration and then again after the addition of a saturating level of the nutrient. Tracers, 15NO3 or 32Si(OH)4, were added to replicate subsamples. One of the subsamples was unaltered to yield the rate of nitrate or Si uptake under ambient nutrient concentrations. The second sample in each pair received a saturating addition of the nutrient whose uptake was being monitored, yielding the uptake rate under conditions of nutrient sufficiency.

Isotopic 14C tracer experiments: The methods of Lancelot and Mathot (1985) were modified to track primary production (PP), dissolved organic Carbon (DOC) extracellular release, fraction of released DOC incorporated by bacterioplankton and the fraction that’s resistant to rapid remineralization.