Dataset: Particulate silica, standing stocks, and productivity rates
Deployment: AE1228

Bottle samples were collected from CTD casts in the upper 200 m of the water column during R/V Atlantic Explorer cruises, some of which were Bermuda Atlantic Time-series cruises. Cruise AE1218 was BATS283, AE1228 was BATS286, and AE1322 was validation cruise BVAL048.

Silicic acid Si(OH)4 was analyzed using a sensitive manual colorimetric analysis as done previously in this region [Brzezinski and Nelson, 1995].  Approximately 3 liters of water were filtered for particulate silica concentration through two successive in-line filter holders (47 mm diameter) with pore sizes of 3.0 um followed by 0.4 um, filters were dried at sea, and analyzed on shore using sequential NaOH and HF digestions [Brzezinski and Nelson, 1995], but using Teflon tubes for the digestions [Krause et al., 2009] which provide low and stable blank values. 

The rate of biogenic silica production in both size classes was measured using the radioisotope tracer 32Si.  300 mL samples were incubated with high specific activity 32Si(OH)4 (>40 kBq umol / Si).  Rate samples were incubated on a surface-tethered array or in acrylic incubators cooled with continually flowing surface water since in situ arrays were not logistically feasible; a series of neutral density screens were used to simulate light levels at depth.  After incubation, samples were processed immediately by filtering through 3.0 um and 0.4 um filters sequentially and drying filters on a nylon planchette. 

Once dry, the filters and nylon planchette were covered with mylar and secured with a nylon ring.  After secular equilibrium was achieved between 32Si and its daughter isotope, 32P (~120 days), sample activity was quantified via gas proportional counting using a GM Multicounter (Riso National Laboratory, Technical University of Denmark); this methodology [Krause et al., 2011] allows for higher precision and a lower detection limit than liquid scintillation counting and is useful for resolving small analytical signals in the picoplankton size fraction.

These data were published in Global Biogeochemical Cycles:
Krause, J.W., Brzezinski, M.A., Baines, S. B., Collier, J. L., Twining, B. S., Ohnemus, D. C.  Picoplankton contribution to biogenic silica stocks and production rates in the Sargasso Sea.  2017.  Global Biogeochemical Cycles.  doi: 10.1002/2017GB005619

References: 

Brzezinski, Mark A., and David M. Nelson. "The annual silica cycle in the Sargasso Sea near Bermuda." Deep Sea Research Part I: Oceanographic Research Papers 42.7 (1995): 1215-1237. http://dx.doi.org/10.1016/0967-0637(95)93592-3

Krause, Jeffrey W., David M. Nelson, and Michael W. Lomas. "Biogeochemical responses to late-winter storms in the Sargasso Sea, II: Increased rates of biogenic silica production and export." Deep Sea Research Part I: Oceanographic Research Papers 56.6 (2009): 861-874. http://dx.doi.org/10.1016/j.dsr.2009.01.002

Krause, Jeffrey W., Mark A. Brzezinski, and Janice L. Jones. "Application of low-level beta counting of 32 Si for the measurement of silica production rates in aquatic environments." Marine Chemistry 127.1 (2011): 40-47. http://dx.doi.org/10.1016/j.marchem.2011.07.001