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Silica production in the Monterey, California, upwelling system
Author(s) -
Brzezinski Mark A.,
Phillips Dennis R.,
Chavez Francisco P.,
Friederich Gernot E.,
Dugdale Richard C.
Publication year - 1997
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.1997.42.8.1694
Subject(s) - upwelling , silicic acid , biogenic silica , oceanography , plume , bay , new production , dissolved silica , phytoplankton , geology , diatom , chemistry , nutrient , meteorology , physics , organic chemistry , dissolution
Silica cycling was examined during a major upwelling event in Monterey Bay, California. Strong upwelling‐favorable winds blew for 6 d with speeds up to 15 m s −1 just prior to the study. A survey of the region near the end of the wind event showed newly upwelled water at the north end of the bay, with silicic acid concentrations up to 29.8 µ M. Silicic acid concentrations decreased to a minimum of 15 µ M along the upwelling plume. Biogenic silica concentrations in the upwelling plume were generally between 2 and 5 µ mol Si liter −1 . Specific rates of biogenic silica production were <0.2 d −1 in the freshly upwelled waters a increased to >1.0 d −1 downplume. Kinetic experiments indicated that silicic acid concentrations throughout the upwelling plume supported maximal rates of silica production. Silica production rates were ~1 µ mol Si liter −1 d −1 at the upwelling source, increasing to 7 µ mol liter −1 d −1 downplume. The upwelling event was followed by several days of calm winds, creating ideal conditions for a phytoplankton bloom. Integrated biogenic silica concentrations between the surface and the 0.1% light depth during the calm period ranged from 56 to 566 mmol Si m −2 , w th 8 of 11 stations exhibiting concentrations >100 mmol Si m −2 . Specific production rates of biogenic silica were generally >1 d −1 , with production rates between 10 and 30 µ mol Si liter −1 d −1 . Integrated silica production rates averaged 205 mmol Si m −2 d −1 (range 13–1,140 mmol m 2 d −1 ), which is four times greater than the average rate observed for other coastal upwelling systems. The maximum value observed (1,140 mmol m −2 d −1 ) is nearly four times greater than levels ever observed before in the sea. The high silica production rates seemed to result from an inefficient silicate pump. On average, 72% of the biogenic silica produced in the upwelling plume was retained in the surface waters, resulting in biogenic silica concentrations of 6.7–13.7 µ mol Si liter −1 at stations where integrated production rates were >200 mmol Si m −2 d −1 . Ambient silicic acid concentrations in these same waters were generally >8 µ M. Kinetic studies showed that these silicic acid concentrations supported nearly maximal rates of sil ca production. Substrate limitation of silica production became readily detectable at 5 µ M Si(OH) 4 . By that time, 80 to >90% of the silicic acid and ~90% of the nitrate in the upwelled waters had been consumed, indicating that substrate limitation of silica production played only a minor role in controlling the magnitude of both net silica production and new production by diatoms.