Gradients 4 - TN397 - 14C NPP - Arrays

Standard HOT protocols were used to measure in vitro primary productivity (PP) via the 14C radiotracer method [Karl et al., 1996]. Water samples were collected via CTD before dawn at certain depths, treated, and then redeployed on an array to the depths from which the water was sampled. A time zero sample was taken at each station to ensure acidification was complete.  Following 12-hr dawn to dusk incubations in situ, the arrays were recovered and each sample was filtered onto a 25mm glass fiber filter. Filters were acidified with 1 ml of 2N hydrochloric acid in a fume hood for 12 hr to remove inorganic 14C after which 10 ml of Ultima Gold scintillation fluid was added to each sample. Radioactivity was determined using a Perkins Elmer 2600 liquid scintillation counter. The rate of primary productivity was calculated by multiplying the percent of carbon labeled by the total carbon available for photosynthesis (e.g. dissolved inorganic carbon, DIC, calculated from SST and salinity measured at each station as per Lee et al. [2006]) and dividing by incubation time (t = 1 day).  Time stamp is in UTC.