Time series measurements of 14C-based primary production (>0.2 um) in the subtropical North Pacific Ocean

Over a 3-year period (April 2010-April 2013), we measured primary production from vertical profiles at near-monthly time scales in the subtropical North Pacific Ocean. Production measurements were based on 14C-assimilation into  >0.2 um plankton biomass.  Seawater for the productivity measurements was collected from predawn CTD hydrocasts into acid-cleaned 500-ml polycarbonate bottles. A total of four replicate 500 ml bottles were subsampled per depth and each bottle was spiked with ~1.85 MBq 14C-bicarbonate. One hundred milliliters from one replicate per depth was immediately vacuum filtered through a polycarbonate filter as a time zero blank. These filters were placed in 20 ml glass scintillation vials and stored at -20oC until shore-based laboratory processing. The remaining three bottles were hung on a free-drifting array, deployed before dawn, and incubated at their initial collection depths throughout the photoperiod (typically 11-13 hours). After sunset the array was recovered, and 100 ml subsamples of all bottles were filtered under gentle vacuum onto 0.2 um polycarbonate filters that were then placed in scintillation vials and frozen. The total radioactivity added to each sample bottle was determined by subsampling 250 µl aliquots into scintillation vials containing 500 µl of β-phenylethylamine. At the shore-based laboratory, filters were acidified, passively vented, and the resulting radioactivity was determined using liquid scintillation counting.