Blooms of Noctiluca miliaris in the Arabian Sea—An in situ and satellite study

Gomes, Helga do Rosário; Goés, Joaquim I.; Matondkar, S.G.P.; Parab, Sushma G.; Al-Azri, Adnan; Thoppil, Prasad G.

doi:10.1016/j.dsr.2008.03.003

Cited by 101 publications

(78 citation statements)

References 26 publications

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“…Most contemporary estimates of phytoplankton biomass (estimated as Chlorophyll a, Chl a), productivity and carbon cycling have come from satellite-based observations 4,5 or coupled biophysical models 6 . Beginning in 2003, our field studies have provided large datasets of the taxonomic structure 4,5,7 of winter phytoplankton communities which show a drastic shift from diatom-dominated blooms to thick and widespread blooms composed primarily of the green dinoflagellate, N. scintillans. Unlike the red form reported mostly in temperate coastal waters worldwide 8 , this Arabian Sea N. scintillans is green because of its large endosymbiotic population of free-swimming cells of Pedinomonas noctilucae (Class Prasinophyceae, Division Chlorophyta) 9,10 (Fig.…”

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Massive outbreaks of Noctiluca scintillans blooms in the Arabian Sea due to spread of hypoxia

et al. 2014

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In the last decade, the northern Arabian Sea has witnessed a radical shift in the composition of winter phytoplankton blooms, which previously comprised mainly of diatoms, the unicellular, siliceous photosynthetic organisms favoured by nutrient-enriched waters from convective mixing. These trophically important diatom blooms have been replaced by widespread blooms of a large, green dinoflagellate, Noctiluca scintillans, which combines carbon fixation from its chlorophyll-containing endosymbiont with ingestion of prey. Here, we report that these massive outbreaks of N. scintillans during winter are being facilitated by an unprecedented influx of oxygen deficient waters into the euphotic zone and by the extraordinary ability of its endosymbiont Pedinomonas noctilucae to fix carbon more efficiently than other phytoplankton under hypoxic conditions. We contend that N. scintillans blooms could disrupt the traditional diatom-sustained food chain to the detriment of regional fisheries and long-term health of an ecosystem supporting a coastal population of nearly 120 million people.

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Massive outbreaks of Noctiluca scintillans blooms in the Arabian Sea due to spread of hypoxia

et al. 2014

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“…Though these regions are of great interest to the scientific community, resource managers and climatologists, due to errors in atmospheric correction, possibilities of determination of full spectra of water-leaving radiance are very limited and L w (412) < 0.2 mW cm −2 µm −1 sr −1 are often excluded to minimize the impacts from atmospheric overcorrection in causing negative or significantly reduced waterleaving radiance (Siegel et al, 2002). This eventually leads to a tremendous loss of information for ocean colour work (Doerffer et al, 2008).…”

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confidence: 99%

“…The process of removing the atmospherically scattered signal in order to retrieve the desired ocean colour signal (i.e. water-leaving radiance L w ) is referred to as atmospheric correction (Gordon, 1997). Since simultaneous measurements of atmospheric optical properties are not available, the atmospheric correction algorithm developed for SeaWiFS and MODIS (also referred to as SeaDAS atmospheric correction algorithm) assumes negligible L w in the bands centred at 765 and 865 nm (748 and 869 nm in case of MODIS) in order to derive aerosol optical properties and extrapolate these into the visible spectrum (Gordon and Wang, 1994).…”

Section: Introductionmentioning

confidence: 99%

“…water-leaving radiance L w ) is referred to as atmospheric correction (Gordon, 1997). Since simultaneous measurements of atmospheric optical properties are not available, the atmospheric correction algorithm developed for SeaWiFS and MODIS (also referred to as SeaDAS atmospheric correction algorithm) assumes negligible L w in the bands centred at 765 and 865 nm (748 and 869 nm in case of MODIS) in order to derive aerosol optical properties and extrapolate these into the visible spectrum (Gordon and Wang, 1994). This procedure is termed as the dark-pixel atmospheric correction scheme which has been widely used for clear ocean waters, where satisfactory results have been found with uncertainties <5 % in L w and <35 % in chlorophyll-a (Chl-a) concentrations from SeaW204 P. Shanmugam: CAAS: an atmospheric correction algorithm for the remote sensing of complex waters down for optically more complex waters that are classified in the context of the present study into four types: (1) waters in the presence of intense aerosols (absorbing and nonabsorbing), (2) waters with dense phytoplankton blooms, (3) waters with high particulate (suspended matter-SS) and dissolved substances (CDOM), and (4) waters with combination of the above types and nature (all these categories belong to Case 2 waters).…”

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CAAS: an atmospheric correction algorithm for the remote sensing of complex waters

Shanmugam

2012

Ann. Geophys.

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Abstract. The current SeaDAS atmospheric correction algorithm relies on the computation of optical properties of aerosols based on radiative transfer combined with a nearinfrared (NIR) correction scheme (originally with assumptions of zero water-leaving radiance for the NIR bands) and several ancillary parameters to remove atmospheric effects in remote sensing of ocean colour. The failure of this algorithm over complex waters has been reported by many recent investigations, and can be attributed to the inadequate NIR correction and constraints for deriving aerosol optical properties whose characteristics are the most difficult to evaluate because they vary rapidly with time and space. The possibility that the aerosol and sun glint contributions can be derived in the whole spectrum of ocean colour solely from a knowledge of the total and Rayleigh-corrected radiances is developed in detail within the framework of a Complex water Atmospheric correction Algorithm Scheme (CAAS) that makes no use of ancillary parameters. The performance of the CAAS algorithm is demonstrated for MODIS/Aqua imageries of optically complex waters and yields physically realistic water-leaving radiance spectra that are not possible with the SeaDAS algorithm. A preliminary comparison with in-situ data for several regional waters (moderately complex to clear waters) shows encouraging results, with absolute errors of the CAAS algorithm closer to those of the SeaDAS algorithm. The impact of the atmospheric correction was also examined on chlorophyll retrievals with a Case 2 water bio-optical algorithm, and it was found that the CAAS algorithm outperformed the SeaDAS algorithm in terms of producing accurate pigment estimates and recovering areas previously flagged out by the later algorithm. These findings suggest that the CAAS algorithm can be used for applications focussing in quantitative assessments of the biological and biogeochemical properties in complex waters, and can easily be extended to other sensors such as OCM-2, MERIS and GOCI.

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Heterotrophic bacteria as major nitrogen fixers in the euphotic zone of the Indian Ocean

Shiozaki

Ijichi

Kodama

et al. 2014

Global Biogeochemical Cycles

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Diazotrophy in the Indian Ocean is poorly understood compared to that in the Atlantic and Pacific Oceans. We first examined the basin-scale community structure of diazotrophs and their nitrogen fixation activity within the euphotic zone during the northeast monsoon period along about 69°E from 17°N to 20°S in the oligotrophic Indian Ocean, where a shallow nitracline (49-59 m) prevailed widely and the sea surface temperature (SST) was above 25°C. Phosphate was detectable at the surface throughout the study area. The dissolved iron concentration and the ratio of iron to nitrate + nitrite at the surface were significantly higher in the Arabian Sea than in the equatorial and southern Indian Ocean. Nitrogen fixation in the Arabian Sea (24.6-47.1 μmolN m À2 d À1 ) was also significantly greater than that in the equatorial and southern Indian Ocean (6.27-16.6 μmolN m À2 d À1 ), indicating that iron could control diazotrophy in the Indian Ocean. Phylogenetic analysis of nifH showed that most diazotrophs belonged to the Proteobacteria and that cyanobacterial diazotrophs were absent in the study area except in the Arabian Sea. Furthermore, nitrogen fixation was not associated with light intensity throughout the study area. These results are consistent with nitrogen fixation in the Indian Ocean, being largely performed by heterotrophic bacteria and not by cyanobacteria. The low cyanobacterial diazotrophy was attributed to the shallow nitracline, which is rarely observed in the Pacific and Atlantic oligotrophic oceans. Because the shallower nitracline favored enhanced upward nitrate flux, the competitive advantage of cyanobacterial diazotrophs over nondiazotrophic phytoplankton was not as significant as it is in other oligotrophic oceans.

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Blooms of Noctiluca miliaris in the Arabian Sea—An in situ and satellite study

Cited by 101 publications

References 26 publications

Massive outbreaks of Noctiluca scintillans blooms in the Arabian Sea due to spread of hypoxia

Massive outbreaks of Noctiluca scintillans blooms in the Arabian Sea due to spread of hypoxia

CAAS: an atmospheric correction algorithm for the remote sensing of complex waters

Heterotrophic bacteria as major nitrogen fixers in the euphotic zone of the Indian Ocean

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