Protactinium-231 and thorium-230 abundances and high scavenging rates in the western arctic ocean     

HN Edmonds  SB Moran  JA Hoff  JN Smith  RL Edwards 《Science (New York, N.Y.)》1998,280(5362):405-407

The Canadian Basin of the Arctic Ocean, largely ice covered and isolated from deep contact with the more dynamic Eurasian Basin by the Lomonosov Ridge, has historically been considered an area of low productivity and particle flux and sluggish circulation. High-sensitivity mass-spectrometric measurements of the naturally occurring radionuclides protactinium-231 and thorium-230 in the deep Canada Basin and on the adjacent shelf indicate high particle fluxes and scavenging rates in this region. The thorium-232 data suggest that offshore advection of particulate material from the shelves contributes to scavenging of reactive materials in areas of permanent ice cover.  相似文献   

Applications of the acetylene-ethylene assay for measurement of nitrogen fixation     

R.W.F. Hardy  R.C. Burns  R.D. Holsten 《Soil biology & biochemistry》1973,5(1):47-81

A comprehensive report of the acetylene reduction assay for measurement of N₂ fixation is presented. The objective is to facilitate the effective use and identify some potential limitations of the method. The report is based on more than 200 accounts of the use of this technique in 15 countries during the last 5 years. Methods of measurement of N₂ fixation are compared. Nomenclature, e.g., N₂[C₂H₂] fixed, is introduced to identify values of N₂ fixation determined by C₂H₂-C₂H₂ assay. The biochemical basis of the assay is described along with relevant characteristics including K_m, C₂H₂/N₂ conversion factor, and specific N₂[C₂H₂]-fixing activities obtained with various systems. Effects of combined nitrogen, temperature, light, pO₂, N₂, pC₂H₂ and water on activity are summarized. Available methods for sample preparation, assay chamber, gas phase, assay condition, termination of reaction, C₂H₄ analysis and expression of results are compared. The many uses of the C₂H₂-C₂H₄ assay for investigations of the biochemistry of nitrogenase and physiology of N₂-fixing organisms, definition of N₂-fixing organisms and measurement of field N₂ fixation by legume, non-legume, soil, marine, rhizosphere, phylloplane and mammalian samples are tabulated.  相似文献