Brzezinski/Nelson - AESOPS Silica data Methodology

Silicic acid concentrations ([Si(OH)4]) were measured by high-sensitivity manual colorimetric analysis, as described by Brzezinski and Nelson (1989). The analysis has a detection limit of 0.05 uM. Its precision is 0.05 uM for concentrations <5 uM, and 1% for concentrations = or >5 uM. Biogenic particulate silica concentrations (BSi) were measured by the alkaline digestion method of (Paasche, 1973), on material collected on 0.6 um polycarbonate membrane filters. Sample volume was usually 625 ml. Data were corrected for interference from lithogenic particulate silica as described by Brzezinski and Nelson (1989). The detection limit for biogenic silica in 625-ml samples by this method is 0.004 umol Si per liter and the precision is 0.004 umol per liter or 5%, whichever uncertainty is greater. Biogenic silica production rates ("Vb" and "rho") were measured in 24-hr incubation experiments using the radioisotope 32Si (Treguer et al., 1991). Sample volume was 300 ml. All samples were incubated on deck under natural sunlight at sea-surface temperature, which was maintained by continuous flow of surface seawater. Irradiance was matched to that at the depth from which each sample was collected, using combinations of blue and neutral-density photographic screening (e.g. Smith et al., 1996). Rate calculations were as described by Brzezinski and Phillips (1997). The references cited are as follows:

Brzezinski, M.A. and D.M. Nelson. 1989. Seasonal changes in the silicon cycle within a Gulf Stream warm-core ring. Deep-Sea Res. 36: 1009-1030.

Brzezinski, M.A. and D.R. Phillips. 1997. Evaluation of 32Si as a tracer for measuring silica production rates in marine waters. Limnol. Oceanogr. 42: 856-865.

Paasche, E. 1973. Silicon and the ecology of marine planktonic diatoms. I. Thalassiosira pseudonana (Cyclotella nana) grown in a chemostat with silicate as the limiting nutrient. Mar. Biol. 19: 117-126.

Smith, W.O., Jr., D.M. Nelson, G.R. DiTullio and A.R. Leventer. 1996. Temporal and spatial patterns in the Ross Sea: Phytoplankton biomass, elemental composition, productivity and growth rates. J.Geophys. Res. 101: 18,455-18,465.

Treguer, P., L. Lindner, A.J. van Bennekom, A. Leynaert, M. Panouse and G. Jacques. 1991. Production of biogenic silica in the Weddell-Scotia Seas measured with 32Si. Limnol. Oceanogr. 36: 1217-1227.