Dataset: Biogenic and lithogenic silica in Southern Ocean marine suspended particulate material (0-1000 m)
Deployment: NBP1102

Water (2-10.9 liters) from each GO-Flo was filtered over a 47-millimeter (mm) diameter, 0.4-micrometer (µm) pore size PCTE filter (Measures et al., 2008). Samples were stored in new Whatman petri slides, double-bagged, at room temperature until ready for processing. The filters were subdivided into thirds or quarters using a ceramic rotary blade on a clean acrylic panel.

One subsection (1/3 or 1/4) was processed for biogenic and lithogenic silica concentrations, according to Krause et al. (2009) and Brzezinski and Nelson (1995). In brief, the filter subsample was submerged in 0.2 N NaOH for 2 hours in Teflon tubes to dissolve the silica. The resulting solution was reacted with ammonium molybdate, metol, and oxalic acid to produce silicomolybous acid, the absorbance of which was measured spectrophotometrically.

Lithogenic silica concentrations were determined using a subsample of the original NaOH digest solution, which was diluted with DI water and centrifuged. The supernatant was taken to dryness then digested again using HF over 48 hours. Boric acid was added to the HF solution, which was then reacted and analyzed in the same way as the biogenic silica digest solutions.

Concentrations were determined using matrix-matched standards for both the biogenic and lithogenic digest solutions.