Primary productivity samples are taken each day shortly before local apparent noon (LAN). Primary production is estimated from 14C uptake using a simulated in-situ technique. Light penetration is estimated from the Secchi depth (assuming that the 1% light level is three times the Secchi depth). The depths with ambient light intensities corresponding to light levels simulated by the on-deck incubators are identified and sampled on the rosette upcast. Occasionally an extra bottle or two are tripped in addition to the usual 20 levels sampled in the combined rosette-productivity cast in order to maintain the normal sampling depth resolution. Triplicate samples (two light and one dark control) are drawn from each productivity sample depth into 250 ml polycarbonate incubation bottles.
Complete methods for primary productivity determination can be found here.
Samples are inoculated with 43.19 µCi of 14C as NaHCO3 (200 µl of 216 µCi/ml stock) prepared in a 0.3 g/liter solution of sodium carbonate (Fitzwater et al., 1982). Samples are incubated from LAN to civil twilight in seawater-cooled incubators with neutral-density screens which simulate in situ light levels. At the end of the incubation, the samples are filtered onto Millipore HA filters and placed in scintillation vials. One half ml of 10% HCl is added to each sample. The sample is then allowed to sit, without a cap, at room temperature for 12 hours (after Lean and Burnison, 1979). Following this, 10 ml of scintillation cocktail are added to each sample and the samples are returned to SIO where the radioactivity is determined with a scintillation counter.