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  • Articles  (9)
  • Wiley  (9)
  • Frontiers Media
  • ZBW - Deutsche Zentralbibliothek für Wirtschaftswissenschaften, Leibniz-Informationszentrum Wirtschaft Kiel, Hamburg
  • Journal of Geophysical Research JGR - Oceans  (6)
  • Journal of Geophysical Research: Oceans  (3)
  • 7529
Collection
  • Articles  (9)
Source
Publisher
  • Wiley  (9)
  • Frontiers Media
  • ZBW - Deutsche Zentralbibliothek für Wirtschaftswissenschaften, Leibniz-Informationszentrum Wirtschaft Kiel, Hamburg
  • American Geophysical Union  (10)
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  • 1
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    Optical properties of the Dead Sea (2013)
    Wiley
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    Publication Date: 2013-02-13
    Description: [1]  The Dead Sea, located in the rift valley between Jordan and Israel, is a hypersaline lake, resulting in unique biogeochemistry and optical properties. In the spring of 2004 we conducted two days of physical and optical measurements in the lake. Because of the significant effect of dissolved salts onthe optical propertiesof water,our analysis required a novel processing approach to obtain dissolved and total inherent optical properties from the measurements. In addition, we show that the lake's salinity can be estimated from measurements of hyper-spectral absorption or attenuation spectra in the red and infrared parts of the spectrum, using published values of specific absorption of dissolved NaCl, despite the fact that the lake's salt chemistry is complex. In situ observations demonstrated that the lake has a two-layer structure with a warm and more turbid layer at the top 20-30 m and a clearer colder layer below. Both the particulate and dissolved absorption are well approximated by exponentially decreasing functions with the spectral slope of the particulate absorption about half that of the dissolved fraction and consistent with other aquatic environments. Both have relatively low and similar magnitudes in the blue (O(0.15 m -1 )). Mean particle size was observed to increase with depth consistent with precipitating salt crystals (observed in past campaigns) shown here toplay a major role in the lake's optical properties.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 2
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    Bio-optical observations of the 2004 Labrador Sea phytoplankton bloom (2011)
    Wiley
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    Publication Date: 2011-11-24
    Description: A unique time series of moored bio-optical measurements documented the 2004 spring-summer bloom in the southern Labrador Sea. In situ and satellite chlorophyll data show that chlorophyll levels in the 2004 bloom were at the upper end of those typically observed in this region. Satellite chlorophyll and profiling float temperature/salinity data show that the main bloom, which typically peaks in June/July, is often preceded by ephemeral mixed layer shoaling and a lesser, short-lived bloom in May; this was the case in 2004. The particulate backscatter to beam attenuation ratio (bbp[470 nm]/Cp[660 nm]) showed peaks in the relative abundance of small particles at bloom initiation and during the decline of the bloom, while larger particles dominated during the bloom. Chlorophyll/Cp and bbp/chlorophyll were correlated with carbon export and dominated by changes in the pigment per cell associated with lower light levels due to enhanced attenuation of solar radiation during the bloom. An NPZ (nutrients, phytoplankton, zooplankton) model captured the phytoplankton bloom and an early July peak in zooplankton. Moored acoustic Doppler current profiler (ADCP) data showed an additional mid-June peak in zooplankton biomass which was attributed to egg-laying copepods. The data reported here represent one of the few moored time series of Cp, bbp and chlorophyll extending over several months in an open ocean region. Interpretation of data sets such as this will become increasingly important as these deployments become more commonplace via ocean observing systems. Moreover, these data contribute to the understanding of biological-physical coupling in a biogeochemically important, yet poorly studied region.
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    Topics: Geosciences , Physics
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  • 3
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    Observations of the sensitivity of beam attenuation to particle size in a coastal bottom boundary layer (2011)
    Wiley
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    Publication Date: 2011-02-16
    Description: The goal of this study was to test the hypothesis that the aggregated state of natural marine particles constrains the sensitivity of optical beam attenuation to particle size. An instrumented bottom tripod was deployed at the 12-m node of the Martha's Vineyard Coastal Observatory to monitor particle size distributions, particle size-versus-settling-velocity relationships, and the beam attenuation coefficient (cp) in the bottom boundary layer in September 2007. An automated in situ filtration system on the tripod collected 24 direct estimates of suspended particulate mass (SPM) during each of five deployments. On a sampling interval of 5 min, data from a Sequoia Scientific LISST 100x Type B were merged with data from a digital floc camera to generate suspended particle volume size distributions spanning diameters from approximately 2 μm to 4 cm. Diameter-dependent densities were calculated from size-versus-settling-velocity data, allowing conversion of the volume size distributions to mass distributions, which were used to estimate SPM every 5 min. Estimated SPM and measured cp from the LISST 100x were linearly correlated throughout the experiment, despite wide variations in particle size. The slope of the line, which is the ratio of cp to SPM, was 0.22 g m−2. Individual estimates of cp:SPM were between 0.2 and 0.4 g m−2 for volumetric median particle diameters ranging from 10 to 150 μm. The wide range of values in cp:SPM in the literature likely results from three factors capable of producing factor-of-two variability in the ratio: particle size, particle composition, and the finite acceptance angle of commercial beam-transmissometers.
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    Topics: Geosciences , Physics
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  • 4
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    Temporal and Vertical Variations of Particulate and Dissolved Optical Properties in the South China Sea (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract Two Bio‐Argo floats measured the concentration of chlorophyll‐a, the backscattering coefficient, the fluorescence of humic‐like dissolved organic matter, dissolved oxygen, and temperature and salinity in the northern and central basins of the South China Sea for over 2 years. Temporal evolutions of bio‐optical properties were analyzed at surface, subsurface, and in the whole water column, respectively. It was found that (1) The seasonal variability of the surface chlorophyll‐a was highly controlled by photoacclimation, especially in the central basin; (2) backscattering in the upper 150 m was nearly constant, exhibiting no distinct seasonality; (3) with vertical mixing, particles from the deep chlorophyll maxima were entrained into the mixed layer resulting in enhanced surface chlorophyll during the early winter. This phenomenon may mislead a study based on satellite data which is likely to interpret it as blooming rather than a redistribution of phytoplankton within the water column; (4) analysis of a winter bloom and an anticyclonic eddy reveal that physical entrainment and biological photoacclimation modulated the vertical distributions of chlorophyll‐a and particles and potentially also changes of phytoplankton community composition; and (5) fluorescent dissolved organic matter was found to be highly coupled to phytoplankton dynamics in both basins, with a maximum (after removing the contribution of physical convective mixing) located at the depth of chlorophyll‐a subsurface maximum.
    Print ISSN: 2169-9275
    Electronic ISSN: 2169-9291
    Topics: Geosciences , Physics
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  • 5
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    Southern Ocean Biogeochemical Float Deployment Strategy, With Example From the Greenwich Meridian Line (GO‐SHIP A12) (2019)
    Wiley
    Details
    Publication Date: 2019
    Description: Abstract Biogeochemical Argo floats, profiling to 2,000‐m depth, are being deployed throughout the Southern Ocean by the Southern Ocean Carbon and Climate Observations and Modeling program (SOCCOM). The goal is 200 floats by 2020, to provide the first full set of annual cycles of carbon, oxygen, nitrate, and optical properties across multiple oceanographic regimes. Building from no prior coverage to a sparse array, deployments are based on prior knowledge of water mass properties, mean frontal locations, mean circulation and eddy variability, winds, air‐sea heat/freshwater/carbon exchange, prior Argo trajectories, and float simulations in the Southern Ocean State Estimate and Hybrid Coordinate Ocean Model (HYCOM). Twelve floats deployed from the 2014–2015 Polarstern cruise from South Africa to Antarctica are used as a test case to evaluate the deployment strategy adopted for SOCCOM's 20 deployment cruises and 126 floats to date. After several years, these floats continue to represent the deployment zones targeted in advance: (1) Weddell Gyre sea ice zone, observing the Antarctic Slope Front, and a decadally‐rare polynya over Maud Rise; (2) Antarctic Circumpolar Current (ACC) including the topographically steered Southern Zone chimney where upwelling carbon/nutrient‐rich deep waters produce surprisingly large carbon dioxide outgassing; (3) Subantarctic and Subtropical zones between the ACC and Africa; and (4) Cape Basin. Argo floats and eddy‐resolving HYCOM simulations were the best predictors of individual SOCCOM float pathways, with uncertainty after 2 years of order 1,000 km in the sea ice zone and more than double that in and north of the ACC.
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  • 6
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    Estimation of Phytoplankton Accessory Pigments From Hyperspectral Reflectance Spectra: Toward a Global Algorithm (2017)
    Wiley
    Details
    Publication Date: 2017-11-22
    Description: Phytoplankton community composition in the ocean is complex and highly variable over a wide range of space and time scales. Able to cover these scales, remote-sensing reflectance spectra can be measured both by satellite and by in situ radiometers. The spectral shape of reflectance in the open ocean is influenced by the particles in the water, mainly phytoplankton and co-varying non-algal particles. We investigate the utility of in situ hyperspectral remote-sensing reflectance measurements to detect phytoplankton pigments by using an inversion algorithm that defines phytoplankton pigment absorption as a sum of Gaussian functions. The inverted amplitudes of the Gaussian functions representing pigment absorption are compared to coincident High Performance Liquid Chromatography measurements of pigment concentration. We determined strong predictive capability for chlorophylls a, b, c 1 + c 2 , and the photoprotective carotenoids. We also tested the estimation of pigment concentrations from reflectance-derived chlorophyll a using global relationships of co-variation between chlorophyll a and the accessory pigments. We found similar errors in pigment estimation based on the relationships of co-variation versus the inversion algorithm. An investigation of spectral residuals in reflectance data after removal of chlorophyll-based average absorption spectra showed no strong relationship between spectral residuals and pigments. Ultimately, we are able to estimate concentrations of three chlorophylls and the photoprotective carotenoid pigments, noting that further work is necessary to address the challenge of extracting information from hyperspectral reflectance beyond the information that can be determined from chlorophyll a and its co-variation with other pigments.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 7
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    Biogeochemical sensor performance in the SOCCOM profiling float array (2017)
    Wiley
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    Publication Date: 2017-07-06
    Description: The Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) program has begun deploying a large array of biogeochemical sensors on profiling floats in the Southern Ocean. As of February 2016, 86 floats have been deployed. Here the focus is on 56 floats with quality controlled and adjusted data that have been in the water at least 6 months. The floats carry oxygen, nitrate, pH, chlorophyll fluorescence, and optical backscatter sensors. The raw data generated by these sensors can suffer from inaccurate initial calibrations and from sensor drift over time. Procedures to correct the data are defined. The initial accuracy of the adjusted concentrations is assessed by comparing the corrected data to laboratory measurements made on samples collected by a hydrographic cast with a rosette sampler at the float deployment station. The long-term accuracy of the corrected data is compared to the GLODAPv2 data set whenever a float made a profile within 20 km of a GLODAPv2 station. Based on these assessments, the fleet average oxygen data are accurate to 1±1%, nitrate to within 0.5±0.5 µmol kg −1 , and pH to 0.005±0.01, where the error limit is 1 standard deviation of the fleet data. The bio-optical measurements of chlorophyll fluorescence and optical backscatter are used to estimate chlorophyll a and particulate organic carbon concentration. The particulate organic carbon concentrations inferred from optical backscatter appear accurate to with 35 mg C m −3 or 20%, whichever is larger. Factors affecting the accuracy of the estimated chlorophyll a concentrations are evaluated.
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  • 8
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    Revisiting Ocean Color algorithms for chlorophyll a and particulate organic carbon in the Southern Ocean using biogeochemical floats (2017)
    Wiley
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    Publication Date: 2017-07-06
    Description: The Southern Ocean (SO) ecosystem plays a key role in the carbon cycle by sinking a major part (43%) of the ocean uptake of anthropogenic CO2, and being an important source of nutrients for primary producers. However, undersampling of SO biogeochemical properties limits our understanding of the mechanisms taking place in this remote area. The Southern Ocean Carbon and Climate Observions and Modeling project (SOCCOM) has been deploying a large number of autonomous biogeochemical floats to study the SO (as of December 2016, 74 floats out of 200 have been deployed). SOCCOM floats measurements can be used to extend remote sensing chlorophyll a (chla) and particulate organic carbon (POC) products under the clouds or during the polar night as well as adding the depth dimension to the satellite-based view of the SO. Chlorophyll a concentrations measured by fluorometers embedded on the floats and POC concentrations derived from backscattering coefficients were calibrated with samples collected during the floats' deployment cruise. Float chla and POC were compared with products derived from observations of MODIS and VIIRS sensors. We find the Ocean Color Index (OCI) global algorithm to agree well with the matchups (within 9%, on average, for the Visible Infrared Imaging Radioneter Suite (VIIRS) and 12%, on average, for the Moderate Resolution Imaging Spectroradiometer Aqua (MODIS)). SO specific algorithms estimating chla are offset by ∼45% south of the Sea Ice Extent Front (∼ 60°S). In addition, POC estimates based on floats agree well with NASA's POC algorithm.
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  • 9
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    Southern Ocean Phytoplankton Blooms Observed by Biogeochemical Floats (2019)
    Wiley
    Details
    Publication Date: 2019
    Description: Abstract The spring bloom in the Southern Ocean is the rapid‐growth phase of the seasonal cycle in phytoplankton. Many previous studies have characterized the spring bloom using chlorophyll estimates from satellite ocean color observations. Assumptions regarding the chlorophyll‐to‐carbon ratio within phytoplankton and vertical structure of biogeochemical variables lead to uncertainty in satellite‐based estimates of phytoplankton carbon biomass. Here, we revisit the characterizations of the bloom using optical backscatter from biogeochemical floats deployed by the Southern Ocean Carbon and Climate Observations and Modelling (SOCCOM) and Southern Ocean and Climate Field Studies with Innovative Tools (SOCLIM) projects. In particular, by providing a three‐dimensional view of the seasonal cycle, we are able to identify basin‐wide bloom characteristics corresponding to physical features; biomass is low in Ekman downwelling regions north of the Antarctic Circumpolar Current (ACC) region, and high within and south of the ACC.
    Print ISSN: 2169-9275
    Electronic ISSN: 2169-9291
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