Biogenic Silica

Methods

Biogenic silica collection and analysis

In-situ bSi samples were transferred to 1 L polycarbonate bottles and filtered onto 47 mm 0.6 um polycarbonate filters, which were then dried in the oven at 60˚C for 24 hours and stored for on-shore analysis. Incubation bSi samples used 400-900 mL seawater, depending on availability, and were filtered and dried similarly. Samples were digested in 4 mL 0.2 N NaOH in HF-clean teflon tubes at 95˚C for 40 minutes and then cooled in an ice bath and neutralized with 1 mL 1 N HCl. After centrifuging 10 min at 1100 x g, 4 mL were withdrawn, diluted and measured at 810 nm for reactive silicate via the colorimetric ammonium molybdate method (Brzezinski & Nelson, 1995; Paasche, 1973; Strickland & Parsons, 1977), where a 10 mL sample was added to a 4 mL molybdate solution and allowed to stand 10 minutes before being quenched by a reducing reagent of a metol-sulfite solution, oxalic acid and sulfuric acid.