Chemical characterization of individual particles from the nepheloid layer in the Atlantic Ocean |
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| Authors: | James KB Bishop Pierre E Biscaye |
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| Institution: | Lamont-Doherty Geological Observatory of Columbia University, Palisades, NY 10964,U.S.A. |
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| Abstract: | Particulate matter samples filtered from near-bottom, 30-liter water samples collected during the GEOSECS Atlantic cruise were analyzed by the Computer Evaluated Scanning Electron Microscope Image (CESEMI-2) system. This system permitted automated discrete particle analysis for the elements Al, Si, P, S, K, Ca, and Fe by energy-dispersive X-ray spectrometry and for particle size. Approximately 2000 particles in the size range 1–20 μm, representative of several milliliters of seawater, were analyzed per sample and yielded discrete size and chemical analysis of the major classes of particulate matter—opal, calcium carbonate, and clay—as well as some regularly occurring subclasses of clay and other minor classes.The distributional patterns of the major classes matched both in chemistry and abundance their general distributional patterns in sediments. Clay particles reflected high- and low-latitude sources; opal particles, patterns of diatom productivity; and carbonate, patterns of productivity as well as the calcite saturation chemistry of the water column. Superimposed on these features was evidence for long-range transport of particles in well-defined bottom water masses such as the Antarctic Bottom Water. Such transport is believed to occur through a series of resuspension events, in which case particle distributions match the properties of the sediments. Cases were found where near-bottom particles did not match the sediments, especially in quiescent environments. |
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