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Guzman L.,Estacion de Investigaciones Marinas de Margarita EDIMAR | Varela R.,Estacion de Investigaciones Marinas de Margarita EDIMAR | Muller-Karger F.,University of South Florida | Lorenzoni L.,University of South Florida
Journal of Marine Systems | Year: 2016

The bio-optical changes of the water induced by red tides depend on the type of organism present, and the spectral characterization of such changes can provide useful information on the organism, abundance and distribution. Here we present results from the bio-optical characterization of a non-toxic red tide induced by the autotrophic ciliate Mesodinium rubrum. Particle absorption was high [ap(440) = 1.78 m-1], as compared to measurements done in the same region [ap(440) = 0.09 ± 0.06 m-1], with detrital components contributing roughly 11% [ad(440) = 0.19 m-1]. The remainder was attributed to absorption by phytoplankton pigments [aph(440) = 1.60 m-1]. These aph values were ~15 times higher than typical values for these waters. High chlorophyll a concentrations were also measured (52.73 μg L-1), together with alloxanthin (9.52 μg L-1) and chlorophyll c (6.25 μg L-1). This suite of pigment is typical of the algal class Cryptophyceae, from which Mesodinium obtains its chloroplasts. Remote sensing reflectance showed relatively low values [Rrs(440) = 0.0007 sr-1], as compared to other Rrs values for the region under high bloom conditions [Rrs(440) = 0.0028 sr-1], with maxima at 388, 484, 520, 596 and 688 nm. Based on the low reflection in the green-yellow, as compared to other red tides, we propose a new band ratio [Rrs(688)/Rrs(564)] to identify blooms of this particular group of organisms. © 2016 Elsevier B.V.

Lorenzoni L.,University of South Florida | Benitez-Nelson C.R.,University of South Carolina | Thunell R.C.,University of South Carolina | Hollander D.,University of South Florida | And 4 more authors.
Marine Geology | Year: 2012

A sediment density flow was observed in the eastern Cariaco Basin during September 2008. Evidence suggests that this flow was likely triggered by a magnitude 5.2 earthquake that occurred on August 11, 2008, with an epicenter located at 10.51°N, 64.17°W (off the city of Cumaná, Venezuela). Elevated suspended sediments near the bottom were observed at the mouth of the Manzanares Canyon (>90gm -2, over a depth of 165m) and decreased to ~11gm -2 (over a depth of 40m) 42km away from the canyon's mouth at the CARIACO Ocean Time-Series site. The sediment flux associated with this single event was ~10% of the total annual sediment flux that typically reaches the Cariaco Basin deep seafloor. Carbon to nitrogen ratios and isotope composition confirm that most of the organic matter transferred by the sediment flow was of continental origin (C/N ratios of ~17.67, δ 13C of -27.04‰, and δ 15N of 6.83‰). Our observations contribute to the growing body of evidence that suggests that submarine canyons are rapid, efficient sediment conduits of particles from shallow to deep waters, and that they should be included in efforts to constrain estimates of sediment and terrestrially derived carbon transport from the continental shelves to the deep ocean. © 2011 Elsevier B.V.

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