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Particulate Biogenic Silica
Particle Filtration
FTP View Data
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Analytical Method

Samples for elemental analyses of Particulate biogenic silica were collected into 4L polyethylene carboys; filtered through 47 mm polycarbonate filter holders; onto 47 mm polycarbonate, membrane filters; and placed into 50 ml polypropylene centrifuge tubes. Time course subsamples (1.5, 3, 4.5, 6.5 and 24 hours) were measured colorimetrically to distinguish Lithogenic-Si from Biogenic-Si (DeMaster, 1981). The average precisions during 2007 determined from duplicate analyses are presented in the Table below.


PSi
Cruise mean CV
(%)
mean SD
(ng/l)
N
189 7.3 1.124 1
190 10.4 1.651 2
191 1.7 0.194 2
193 16.0 2.574 2
194 9.7 1.499 2
195 8.4 1.308 2
196 12.3 2.143 2
197 4.4 0.912 1
198 20.7 3.995 2
Mean 10.1 1.711 9



Results

Particulate biogenic silica (PSi) concetrations in the surface ocean over the last 11 years of the program are shown in Figure 68 and Figure 69. PSi typically ranges from < 10 to about 25 nmol kg-1 in the upper 100 m of the water column. During the summer months in 1998, 2000 and 2005, PSi increased dramatically in the upper 50 m of the water. This feature appears associated with a large bloom of diatomes, as evidenced from the sharp increases in fucoxanthin (Figure 48)