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" Optical properties of the marine cyanobacteria Trichodesmium: "
A. Subramaniam
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Latin Dissertation
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| Language of Document
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English
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| Record Number
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1113433
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TLpq304206190
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| Main Entry
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A. Subramaniam
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| Title & Author
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Optical properties of the marine cyanobacteria Trichodesmium:\ A. Subramaniam
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| College
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State University of New York at Stony Brook
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| Date
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1995
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| student score
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1995
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| Degree
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Ph.D.
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| Page No
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180
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| Abstract
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Trichodesmium spp. are nitrogen fixing marine cyanobacteria that are frequently the most abundant phytoplankton in tropical oligotrophic waters. This study calculated that Trichodesmium supply the Northern Caribbean Sea usd4.1\times10\sp9usd gN/day via nitrogen fixation, more than any other source of new nitrogen there. The importance of the role Trichodesmium play in the world oceans can be assessed using satellite imagery, but this requires algorithms that can distinguish Trichodesmium from other phytoplankton. The absorption properties of Trichodesmium are key to developing a remote sensing algorithm. But there are discrepancies in reports in the literature of their absorption spectra. This study, using measurements of absorption, fluorescence and oxygen evolution action spectra, determined that the discrepancies were due to real physiological variability and hypothesizes a new model to explain the variability. Trichodesmium was found to change the ratio of phycourobilins to phycoerythrobilins to adapt to the available light, demonstrating State transitions in nature. Under high light, near the surface around noon for example, light absorbed by phycourobilin was not transferred to Photosystem II, increasing fluorescence around 565 nm. Therefore, algorithms for detecting Trichodesmium need to incorporate low absorption around 550 nm and high fluorescence at 565 nm. A remote sensing reflectance model was developed using measured backscattering and absorption spectra. The measurements of chlorophyll-specific absorption showed that "secondary packaging", the effect of self-shading in colonial phytoplankton, was an important factor in quantifying Trichodesmium chlorophyll biomass. This study calculated an underestimation by at least a factor of 4 of Trichodesmium chlorophyll biomass by standard satellite chlorophyll algorithms. The model results showed that the combination of the high backscatter, absorption, and fluorescence, determined for Trichodesmium, could be used to distinguish moderate to high concentrations (>1 mg Ch1/m of Trichodesmium from other phytoplankton. Surface scum blooms of Trichodesmium have high reflectance in the near infrared. Satellite algorithms often use water leaving radiance around 750 nm for cloud detection and so flags have to be established in these algorithms to distinguish the relatively high albedo due to Trichodesmium blooms from that due to clouds. This study developed an algorithm based on the remote sensing reflectance model that was successful in identifying Trichodesmium blooms in CZCS imagery. The remote sensing reflectance model was also used to develop an "Albedo Vegetation Index" similar to the Normalized Difference Vegetation Index. This used the visible and infrared channels of the AVHRR to map surface blooms of Trichodesmium in the Arabian Sea.
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Applied sciences
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Biological sciences
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Earth sciences
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nitrogen fixing
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Oceanography
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Pure sciences
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