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Iron and silicic acid concentrations together regulate Si uptake in the equatorial Pacific Ocean
Author(s) -
Brzezinski Mark A.,
Dumousseaud Cynthia,
Krause Jeffrey W.,
Measures Christopher I.,
Nelson David M.
Publication year - 2008
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.2008.53.3.0875
Subject(s) - silicic acid , saturation (graph theory) , limiting , upwelling , analytical chemistry (journal) , diatom , silicic , chemistry , kinetic energy , silicon , zoology , mineralogy , geology , environmental chemistry , biology , oceanography , physics , volcano , mechanical engineering , mathematics , organic chemistry , combinatorics , quantum mechanics , seismology , engineering
The effects of added Si and Fe on the rate of silicic acid uptake were examined during two cruises to the equatorial Pacific upwelling zone between 110°W and 140°;W. Maximum uptake rates of Si ( V max ) were highly consistent with a mean of 0.026 ± 0.007 h −1 (n = 29), implying maximum diatom growth rates of ~0.6 d −1 . Half‐saturation constants for Si uptake ( K S ) also showed little variance, averaging 1.7 ± 0.7 mmol L −1 Si(OH) 4 . No ecologically significant spatial or temporal patterns for either V max or K S were observed. Comparison of Si uptake rates at the ambient silicic acid concentration ( V amb ) with V max indicated that the ambient [Si(OH) 4 ] restricted V amb to an average of 63% ± 13% of V max . Fe additions also caused significant increases in both V max and V amb , indicating that the rate of Si uptake was also regulated by the ambient [Fe]. Fe additions had a variable effect on K S , but they consistently increased both V max and the initial slope of the kinetic curve ( V max : K S ), and thus the diatom assemblages’ ability to take up Si(OH) 4 at low concentrations. Added Fe or Si increased Si uptake rates by 87% ± 59% and 69% ± 31%, respectively, indicating nearly equal roles for the two elements in limiting rates of Si uptake in situ. The largest average increase in Si uptake rates, 172% ± 43%, was observed when both Si and Fe were added, implying that together Si and Fe restricted Si uptake rates by almost a factor of three.