Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Data Files
• Related Publications
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

This dataset includes kinetic experiments, using 32Si and PDMPO, to determine the degree of Si uptake limitation by ambient silicic acid.  The data include total silicic acid, gross silica production, and biomass-normalized measurements, concentrations of phosphate, nitrate+nitritie, total chlorophyll, chlorophyll a, phaeopigments, and CTD measurements (e.g. temperature, salinity).

PDMPO = 2-(4-pyridyl)-5-((4-(2-dimethylaminoethylaminocarbamoyl)methoxy)phenyl)oxazole

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.

BCO-DMO Data Manager Processing Notes:
* added a conventional header with dataset name, PI name, version date
* modified parameter names to conform with BCO-DMO naming conventions
* blank values replaced with no data value 'nd'
* added minus sign to longitudes
* -999 changed to "nd"
* SEQ_NUM(CAST) added so it can be matched with CTD bottle and profile data
* added ISO_DateTime_UTC
* changed cruise value from DYEatom to PS13-12 to be consistent with CTD files
* params starting 32Si changed to Si32 due to unsupported names with leading number.
* data version 2018-03-12 replaces version 2017-08-17.  In data version 2018-03-12 the following data parameters were added: Total_SiOH4, Si32_Rho, Si32_Vb, PDMPO_Rho

This study will examine the distribution of silica production among diatom species, using a novel combination of existing approaches, to evaluate the contributions of specific species or genera to total diatom silica production. Specific hypotheses regarding the distribution of silica production among species of diatoms will be tested by exploiting the strong contrasts in diatom community structure and silica production between a coastal upwelling system and in an oligotrophic subtropical gyre. Several lines of evidence support the idea that the diatoms responsible for the majority of silica production shifts from the most numerically abundant species in coastal systems to relatively rare, but very large, cells in offshore oligotrophic environments. This shift alters the role of diatoms in regional food webs and because many processes determining the role of phytoplankton groups in biogeochemical cycles are a function of cell size, such a shift has strong implications for regional differences in the contribution of diatoms to upper-ocean carbon cycling and the biological pump. 

This study also seeks to understand of the role of silicon limitation in regulating diatom silica production at the species level. Si limitation of silica production has been detected in every system examined to date, ranging from the high Si waters of the Antarctic, to coastal upwelling systems and the oligotrophic subtropical gyres. Field studies of Si limitation are rarely accompanied by examination of the species present. When studies do have taxonomic data the lack of information on the performance of individual species makes it impossible to allocate the measured rates among cells, potentially leading to erroneous conclusions about the contribution of specific diatom groups to community composite rates.

The project will test five hypotheses. Each is related to the general theme of using species-specific data to improve understanding of the factors regulating diatoms' role in marine food webs. By combining bulk measures of silica production using the radioisotope 32Si with quantitative measures of silicon deposition rates by individual cells using the fluorescent probe 2-(4-pyridyl)-5((4-(2-dimethylaminoethyl-aminocarbamoyl)-methoxy)phenyl)oxazole, or PDMPO, the following will be determined: species-specific diatom contributions to total community silica production, regional differences in the distribution of silica production among diatom species as a function of cell size, species-specific kinetic parameters governing the ability of species to compete for dissolved silicon, and whether dominance of a particular diatom group or species can be explained by knowledge of their capacity to utilize Si and their numerical abundance (as opposed to other factors such as grazing or limitation by other nutrients).