Dataset: Biogenic Silica - Profiles

Samples for standing stock and biological rate determinations were collected during early morning hydrocasts (~02:00 local time) using Niskin bottles on a CTD rosette. Experimental bottles were filled directly from the rosette bottles, placed into mesh bags, secured to an in situ array and the array deployed for 24 hours. Incubated samples were processed immediately after array recovery. Seawater samples (1.0 L) for biogenic silica analysis, were filtered through 0.6-um polycarbonate membranes, placed in cryovials, and dried in an oven for ~24 h. On shore, quantification of biogenic silica concentration was done using a NaOH digestion procedure in Teflon tubes, which provides low and stable blanks. The rate of net biogenic silica production was determined by the difference between biogenic silia concentration in initial whole seawater samples (no nutrient amendments or dilution, processed immediately) relative to those incubated for 24 h on the drift array. In small-volume bottles (i.e., <4 L) with a high surface-area to volume ratio, the biogenic silica adsorption to the bottle walls can be quantitatively significant, and without correction can lead to systematic errors in the calculated net rates. To minimize these effects for biogenic silica filtrations (i.e. initial or final), the bottles were rinsed three times with ~50 mL of 0.1-um filtered seawater per rinse, and the rinse volume was added to the volumes filtered.