Dataset: Kinetics of Silicon uptake
Deployment: PS1312

Multiple hydrocasts conducted at stations denoted in the bottle file meta data.  A SeaBird CTD was used with redundant sensors for temperature and conductivity; the instrument package was owned and operated by the R/V Point Sur (Moss Landing Marine Laboratories, Moss Landing, California).  All hydrocast data was processed to1-m bins.  Prior to the cruise, the transmissometer was not calibrated and many data anomalies were observed; therefore, these data are suspect and not reported with the bottle data. 

Samples were collected in the euphotic zone, or just below, to a maximum of ~60 m.  Water was filtered (0.6 um pore size) for dissolved inorganic nutrient analysis (N+N, SRP, Si(OH)4), and analyzed at the University of California Santa Barbara Marine Science Institute’s Analytical Laboratory using flow injection techniques on a QuickChem 8000 analyzer (Lachat Instruments Division, Zellweger Analytics) as described in Brzezinski and Washburn (2011).  Chlorophyll a was also quantified using the protocol followed in Brzezinski and Washburn (2011).  ~175 – 350 mL of seawater was filtered through a 0.45 um-pore 47mm diameter HAWP Millipore filter, immediately frozen until analysis on shore (<2 weeks) via extracting with 90% acetone for 24 hours at -20C and quantification of fluorescence on a calibrated Turner Designs 10AU fluorometer with and without acidification.  For biogenic silica analysis, 630 mL of seawater was filtered through a 1.2 um-pore polycarbonate filter (47 mm diameter) and frozen immediately.  On shore, filters were dried and analyzed using a NaOH digestion in Teflon tubes which provide low and stable blank values (Krause et al., 2009). 

For the cruise, three kinetic experiments were set up by filling eight 250-mL bottles and adding increasing enrichments of Si(OH)4 (to create a gradient from ambient to +20 uM).  The rate of biogenic silica production in both size classes was measured using the radioisotope tracer 32Si with high specific activity (>40 kBq µmol/Si) as described in Krause et al. (2012).  After incubation, samples were processed immediately as described in Krause et al. (2011).  For PDMPO uptake, 48 uL of dye was added to each 250 mL bottle (e.g. 12-hr, 24-hr, ambient or enriched Si(OH)4 ) and incubated in the same conditions as the 32Si samples.  After incubation, samples were processed as in McNair et al. (2015) to quantify the bulk PDMPO uptake.  

Note: no ionophore rinse was used during the DYEatom cruise, this was added later in the McNair et al. (2015) protocol.