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André Morel

Bio: André Morel is an academic researcher from Pierre-and-Marie-Curie University. The author has contributed to research in topics: Ocean color & Coastal Zone Color Scanner. The author has an hindex of 69, co-authored 114 publications receiving 24229 citations. Previous affiliations of André Morel include Centre national de la recherche scientifique.


Papers
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Journal ArticleDOI
TL;DR: In this paper, the spectral dependence law of absorption appears to vary within a restricted range, and an average law can be considered representative of rapid measurements at one selected wavelength, and the concentration appears influenced predominantly by natural and industrial land discharges.
Abstract: Spectral values of absorption of light by dissolved organic matter were measured in samples originating from diverse parts of the ocean, quite different with respect to pigment and particle content. The use of llO-cm cells and then of lo-cm cells, with a highly sensitive spectrophotometer, allowed measurement throughout the UV-visible range (200-700 nm) even for the low concentrations of yellow substance encountered in the open sea. The concentration appears influenced predominantly by natural and industrial land discharges. In oceanic waters, it remains low and seems to be related to the biological activity averaged over a long period rather than to the local and temporary phytoplankton content. However, even at such low concentrations, yellow substance in the open sea may have an effect on absorption and hence on ocean color similar to that of low or moderate algal biomass. The spectral dependence law of absorption appears to vary within a restricted range, and an average law can be considered representative of rapid measurements at one selected wavelength.

1,491 citations

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TL;DR: In this paper, a pigment-dependent optical model is developed to predict the propagation of visible radiant energy within the ocean or the backscattered radiation from the upper layer to be predicted as a function of the local phytoplanktonic content.
Abstract: The aim of the present study is to review and tentatively to interpret the optical behavior of oceanic case I waters, those waters for which phytoplankton and their derivative play a predominant role in determining their optical properties. Chlorophyll-like pigment concentration is used as the index to quantify the algal material (living and detrital), and statistical relationships between this index and the depth of the euphotic layer, the spectral values of the attenuation coefficient for downwelling irradiance, or the scattering coefficient are investigated. On the basis of these statistical relationships a pigment-dependent optical model is developed. It allows the propagation of the visible radiant energy within the ocean or the backscattered radiation from the upper layer to be predicted as a function of the local phytoplanktonic content. Other geophysical or geochemical applications are derived which concern the heating rate due to penetrating visible radiations or the rate of energy storage due to photosynthesis. The nonlinear trends observed in the algal biomass-attenuation relationships are analyzed by (1) considering the rather regular change of the living-to-detrital organic carbon ratio which seems to occur in oceanic waters ranging from oligotrophic to eutrophic, and (2) accounting for the respective contributions of absorption (by pigmented cells) and of scattering (by all kind of particulates) in the attenuation process of radiant energy.

1,385 citations

Journal ArticleDOI
TL;DR: In this article, the chlorophyll (chl) a-specific absorption coefficients of living phytoplankton aph*(λ) were analyzed using a data set including 815 spectra determined with the wet filter technique in different regions of the world ocean.
Abstract: Variability in the chlorophyll (chl) a-specific absorption coefficients of living phytoplankton aph*(λ) was analyzed using a data set including 815 spectra determined with the wet filter technique in different regions of the world ocean (covering the chlorophyll concentration range 0.02–25 mg m−3). The aph* values were observed to decrease rather regularly from oligotrophic to eutrophic waters, spanning over more than 1 order of magnitude (0.18 to 0.01 m2 mg−1) at the blue absorption maximum. The observed covariation between aph*(λ) and the field chl a concentration (chl) can be explained considering (1) the level or pigment packaging and (2) the contribution of accessory pigments to absorption. Empirical relationships between aph*(λ) and 〈chl〉 were derived by least squares fitting to power functions. These relationships can be used to produce aph* spectra as a function of 〈chl〉. Such a simple parameterization, if confirmed with further data, can be used, e.g., for refining estimates of the carbon fixation rate at global or regional scales, such as those obtained by combining satellite pigment concentration maps with primary production models based on physiological parameters, among which aph* is an important one.

1,064 citations

Book
16 Nov 1983
TL;DR: In this article, an assessment of the state-of-the-art of remote, (satellite-based) Coastal Zone Color (CZCS) scanning of color variations in the ocean due to phytoplankton is presented.
Abstract: An assessment is presented of the state-of-the-art of remote, (satellite-based) Coastal Zone Color (CZCS) Scanning of color variations in the ocean due to phytoplankton. Attention is given to physical problems associated with ocean color remote sensing, in-water algorithms for the correction of atmospheric effects, constituent retrieval algorithms and application of the algorithms to CZCS imagery. The applicability of CZCS to both near-coast and mid-ocean waters is considered, and it is concluded that while differences between the two environments are complex, universal algorithms can be used for the case of mid-ocean waters, and site-specific algorithms are adequate for CZCS imaging of the near-coast oceanic environment. A short description of CVCS and some sample photographs are provided in an appendix.

1,018 citations

Journal ArticleDOI
TL;DR: In this article, the spectral attenuation for downward irradiance Kd(X) and irradiance reflectance R(X), as well as a bio-optical model of the upper layer was developed.
Abstract: The apparent optical properties (AOPs) of oceanic case 1 waters were previously analyzed [Morel, 1988] and statistically related to the chlorophyll concentration ([Chl]) used as a global index describing the trophic conditions of water bodies. From these empirical relationships a bio-optical model of the upper layer was developed. With objectives and structure similar to those of the previous study the present reappraisal utilizes AOPs determined during recent Joint Global Ocean Flux Study cruises, namely, spectral attenuation for downward irradiance Kd(X) and irradiance reflectance R(X). This revision also benefits from improved knowledge of inherent optical properties (lOPs), namely, pure water absorption coefficients and particle scattering and absorption coefficients, and from better pigment quantification (via a systematic use of highperformance liquid chromatography). Nonlinear trends, already observed between optical properties and algal biomass, are fully confirmed, yet with numerical differences. The previous Kd(X) model, and subsequently the R(X) model, is modified to account for these new relationships. The R(X) values predicted as a function of [Chl] and the predicted ratios of reflectances at two wavelengths, which are commonly used in ocean color algorithms, compare well with field values (not used when developing the reflectance model). This good agreement means that semianalytical ocean color algorithms can be successfully applied to satellite data. Going further into purely analytical approaches, ideally based on radiative transfer computations combined with a suite of relationships between the lOPs and [Chl], remains presently problematic, especially because of the insufficient knowledge of the phase function and backscattering efficiency of oceanic particles.

1,007 citations


Cited by
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Journal ArticleDOI
10 Jul 1998-Science
TL;DR: Integrating conceptually similar models of the growth of marine and terrestrial primary producers yielded an estimated global net primary production of 104.9 petagrams of carbon per year, with roughly equal contributions from land and oceans.
Abstract: Integrating conceptually similar models of the growth of marine and terrestrial primary producers yielded an estimated global net primary production (NPP) of 104.9 petagrams of carbon per year, with roughly equal contributions from land and oceans. Approaches based on satellite indices of absorbed solar radiation indicate marked heterogeneity in NPP for both land and oceans, reflecting the influence of physical and ecological processes. The spatial and temporal distributions of ocean NPP are consistent with primary limitation by light, nutrients, and temperature. On land, water limitation imposes additional constraints. On land and ocean, progressive changes in NPP can result in altered carbon storage, although contrasts in mechanisms of carbon storage and rates of organic matter turnover result in a range of relations between carbon storage and changes in NPP.

4,873 citations

Journal ArticleDOI
Peter M. Cox1, Richard Betts1, Chris D. Jones1, S. A. Spall1, I. Totterdell 
09 Nov 2000-Nature
TL;DR: Results from a fully coupled, three-dimensional carbon–climate model are presented, indicating that carbon-cycle feedbacks could significantly accelerate climate change over the twenty-first century.
Abstract: The continued increase in the atmospheric concentration of carbon dioxide due to anthropogenic emissions is predicted to lead to significant changes in climate. About half of the current emissions are being absorbed by the ocean and by land ecosystems, but this absorption is sensitive to climate as well as to atmospheric carbon dioxide concentrations, creating a feedback loop. General circulation models have generally excluded the feedback between climate and the biosphere, using static vegetation distributions and CO2 concentrations from simple carbon-cycle models that do not include climate change. Here we present results from a fully coupled, three-dimensional carbon–climate model, indicating that carbon-cycle feedbacks could significantly accelerate climate change over the twenty-first century. We find that under a 'business as usual' scenario, the terrestrial biosphere acts as an overall carbon sink until about 2050, but turns into a source thereafter. By 2100, the ocean uptake rate of 5 Gt C yr-1 is balanced by the terrestrial carbon source, and atmospheric CO2 concentrations are 250 p.p.m.v. higher in our fully coupled simulation than in uncoupled carbon models, resulting in a global-mean warming of 5.5 K, as compared to 4 K without the carbon-cycle feedback.

3,816 citations

Journal ArticleDOI
TL;DR: The 6S code has still limitations; it cannot handle spherical atmosphere and as a result, it cannot be used for limb observations, and the decoupling the authors are using for absorption and scattering effects does not allow to use the code in presence of strong absorption bands.
Abstract: Remote sensing from satellite or airborne platforms of land or sea surfaces in the visible and near infrared is strongly affected by the presence of the atmosphere along the path from Sun to target (surface) to sensor. This paper presents 6S (Second Simulation of the Satellite Signal in the Solar Spectrum), a computer code which can accurately simulate the above problems. The 6S code is an improved version of 5S (Simulation of the Satellite Signal in the Solar Spectrum), developed by the Laboratoire d'Optique Atmospherique ten years ago. The new version now permits calculations of near-nadir (down-looking) aircraft observations, accounting for target elevation, non lambertian surface conditions, and new absorbing species (CH/sub 4/, N/sub 2/O, CO). The computational accuracy for Rayleigh and aerosol scattering effects has been improved by the use of state-of-the-art approximations and implementation of the successive order of scattering (SOS) algorithm. The step size (resolution) used for spectral integration has been improved to 2.5 nm. The goal of this paper is not to provide a complete description of the methods used as that information is detailed in the 6S manual, but rather to illustrate the impact of the improvements between 5S and 6S by examining some typical remote sensing situations. Nevertheless, the 6S code has still limitations. It cannot handle spherical atmosphere and as a result, it cannot be used for limb observations. In addition, the decoupling the authors are using for absorption and scattering effects does not allow to use the code in presence of strong absorption bands.

2,955 citations

Journal ArticleDOI
TL;DR: In this paper, a light-dependent, depth-resolved model for carbon fixation (VGPM) was developed to understand the critical variables required for accurate assessment of daily depth-integrated phytoplankton carbon fixation from measurements of sea surface pigment concentrations (Csat)(Csat).
Abstract: We assembled a dataset of 14C-based productivity measurements to understand the critical variables required for accurate assessment of daily depth-integrated phytoplankton carbon fixation (PP(PPeu)u) from measurements of sea surface pigment concentrations (Csat)(Csat). From this dataset, we developed a light-dependent, depth-resolved model for carbon fixation (VGPM) that partitions environmental factors affecting primary production into those that influence the relative vertical distribution of primary production (Pz)z) and those that control the optimal assimilation efficiency of the productivity profile (P(PBopt). The VGPM accounted for 79% of the observed variability in Pz and 86% of the variability in PPeu by using measured values of PBopt. Our results indicate that the accuracy of productivity algorithms in estimating PPeu is dependent primarily upon the ability to accurately represent variability in Pbopt. We developed a temperature-dependent Pbopt model that was used in conjunction with monthly climatological images of Csat sea surface temperature, and cloud-corrected estimates of surface irradiance to calculate a global annual phytoplankton carbon fixation (PPannu) rate of 43.5 Pg C yr‒1. The geographical distribution of PPannu was distinctly different than results from previous models. Our results illustrate the importance of focusing Pbopt model development on temporal and spatial, rather than the vertical, variability.

2,471 citations

Journal ArticleDOI
TL;DR: In this article, a large data set containing coincident in situ chlorophyll and remote sensing reflectance measurements was used to evaluate the accuracy, precision, and suitability of a wide variety of ocean color algorithms for use by SeaWiFS (Sea-viewing Wide Field-of-view Sensor).
Abstract: A large data set containing coincident in situ chlorophyll and remote sensing reflectance measurements was used to evaluate the accuracy, precision, and suitability of a wide variety of ocean color chlorophyll algorithms for use by SeaWiFS (Sea-viewing Wide Field-of-view Sensor). The radiance-chlorophyll data were assembled from various sources during the SeaWiFS Bio-optical Algorithm Mini-Workshop (SeaBAM) and is composed of 919 stations encompassing chlorophyll concentrations between 0.019 and 32.79 μg L−1. Most of the observations are from Case I nonpolar waters, and ∼20 observations are from more turbid coastal waters. A variety of statistical and graphical criteria were used to evaluate the performances of 2 semianalytic and 15 empirical chlorophyll/pigment algorithms subjected to the SeaBAM data. The empirical algorithms generally performed better than the semianalytic. Cubic polynomial formulations were generally superior to other kinds of equations. Empirical algorithms with increasing complexity (number of coefficients and wavebands), were calibrated to the SeaBAM data, and evaluated to illustrate the relative merits of different formulations. The ocean chlorophyll 2 algorithm (OC2), a modified cubic polynomial (MCP) function which uses Rrs490/Rrs555, well simulates the sigmoidal pattern evident between log-transformed radiance ratios and chlorophyll, and has been chosen as the at-launch SeaWiFS operational chlorophyll a algorithm. Improved performance was obtained using the ocean chlorophyll 4 algorithm (OC4), a four-band (443, 490, 510, 555 nm), maximum band ratio formulation. This maximum band ratio (MBR) is a new approach in empirical ocean color algorithms and has the potential advantage of maintaining the highest possible satellite sensor signal: noise ratio over a 3-orders-of-magnitude range in chlorophyll concentration.

2,441 citations