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The Marine Biogeochemistry of Molybdenum

出版	Massachusetts Institute of Technology, 2003
URL	http://books.google.com.hk/books?id=aykeAQAAIAAJ&hl=&source=gbs_api

註釋Prevailing wisdom holds that the vertical distribution of molybdenum (Mo) in the open ocean is conservative, despite Mo's important biological role and association with Mn oxides and anoxic sediments. Mo is used in both nitrogenase, the enzyme responsible for N2 fixation, and nitrate reductase, which catalyzes assimilatory and dissimilatory nitrate reduction. Laboratory culture work on two N2 fixing marine cyanobacteria, Trichodesmium and Crocosphaera, and a marine facultative denitrifier, Marinobacter hydrocarbanoclasticus, showed that Mo cell quotas in these organisms were positively correlated with Mo-containing enzyme activity. Mo concentrations in Crocosphaera dropped almost to blank levels when not fixing N2 suggesting daily synthesis and destruction of the entire nitrogenase enzyme and release of Mo. Trichodesmium cultures, however, retained a pool of cellular Mo even when not fixing N2. Colonies of Trichodesmium collected in the field have Mo:C tenfold higher than seen in culture, these Mo:C ratios were reflected in SPM samples from the same region. Fe:C ratios for Trichodesmium were between 12-160 pmol:mol in field and culured samples. The Fe:C ratio of Crocosphaera was established to be 15.8 =/+ 11.3 under N2 fixing conditions. Mo cellular concentrations in cultured organisms were too small to significantly influence dissolved Mo distributions, but may slightly affect Suspended Particulate Matter (SPM) distributions. Mean SPM Mo:C ratios were slightly elevated in regions of N2 fixation and denitrification. A high precision (=/+ 0.5%) isotope dilution ICP-MS method for measuring Mo was developed to re-evaluate the marine distribution of Mo in the dissolved and particulate phase.