Dataset: Diatom silica productivity rates

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). 

Diatom rate processes were quantified using 32Si and PDMPO tracers.  Samples were incubated in acrylic incubators cooled with continually flowing surface water under a series of neutral density screens to simulate light levels at the depth of collection.  Four 250-mL bottle replicates were taken for each measurement, two for a 12-hour incubation (in daylight) and two for a 24-hour incubation; Si(OH)4 one replicate for each incubation duration was amended by +20 uM (i.e. Enrichment or “E” samples).  

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