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This study assesses marine biological production of organic carbon based on the diel variability of bio-optical properties monitored by two BioGeoChemical-Argo (BGC-Argo) floats. Experiments were conducted in two distinct Mediterranean systems, the Northwestern Ligurian Sea and the Central Ionian Sea during summer months. We derived particulate organic carbon (POC) stock and gross community production integrated within the surface, euphotic and subsurface chlorophyll maximum (SCM) layers, using an existing approach applied to diel cycle measurements of the particulate beam attenuation (cp) and backscattering (bbp) coefficients. The diel cycle of cp provided a robust proxy for quantifying biological production in both systems; that of bbp was comparatively less robust. Derived primary production estimates vary by a factor of 2 depending upon the choice of the bio-optical relationship that converts the measured optical coefficient to POC, which is thus a critical step to constrain. Our results indicate a substantial, yet variable, contribution to the water column production of the SCM layer (16–42%). In the Ligurian Sea, the SCM is a seasonal feature that behaves as a subsurface biomass maximum (SBM) with the ability to respond to episodic abiotic forcing by increasing production. In contrast, in the Ionian Sea, the SCM is permanent, induced by phytoplankton photoacclimation and contributes moderately to water column production. These results emphasize the strong potential for transmissometers deployed on BGC-Argo profiling floats to quantify non-intrusively in situ biological production of organic carbon in the water column of stratified oligotrophic systems with recurring or permanent SCMs, which are widespread features in the global ocean.

As commonly observed in oligotrophic stratified waters, a subsurface (or deep) chlorophyll maximum (SCM) frequently characterizes the vertical distribution of phytoplankton chlorophyll in the Mediterranean Sea. Occurring far from the surface layer “seen” by ocean colour satellites, SCMs are difficult to observe with adequate spatio-temporal resolution and their biogeochemical impact remains unknown. Biogeochemical-Argo (BGC-Argo) profiling floats represent appropriate tools for studying the dynamics of SCMs. Based on data collected from 36 BGC-Argo floats deployed in the Mediterranean Sea, our study aims to address two main questions. (1) What are the different types of SCMs in the Mediterranean Sea? (2) Which environmental factors control their occurrence and dynamics? First, we analysed the seasonal and regional variations in the chlorophyll concentration (Chl a), particulate backscattering coefficient (bbp), a proxy of the particulate organic carbon (POC) and environmental parameters (photosynthetically active radiation and nitrates) within the SCM layer over the Mediterranean Basin. The vertical profiles of Chl a and bbp were then statistically classified and the seasonal occurrence of each of the different types of SCMs quantified. Finally, a case study was performed on two contrasted regions and the environmental conditions at depth were further investigated to understand the main controls on the SCMs. In the eastern basin, SCMs result, at a first order, from a photoacclimation process. Conversely, SCMs in the western basin reflect a biomass increase at depth benefiting from both light and nitrate resources. Our results also suggest that a variety of intermediate types of SCMs are encountered between these two endmember situations.

International audience; Stratified oceanic systems are characterized by the presence of a so-called Deep Chlorophyll a Maximum (DCM) not detectable by ocean color satellites. A DCM can either be a phytoplankton (carbon) biomass maximum (Deep Biomass Maximum, DBM), or the consequence of photoacclimation processes (Deep photoAcclimation Maximum, DAM) resulting in the increase of chlorophyll a per phytoplankton carbon. Even though these DCM (further qualified as either DBMs or DAMs) have long been studied, no global-scale assessment has yet been undertaken and large knowledge gaps still remain in relation to the environmental drivers responsible for their formation and maintenance. In order to investigate their spatial and temporal variability in the open ocean, we use a global data set acquired by more than 500 Biogeochemical-Argo floats given that DCMs can be detected from the comparative vertical distribution of chlorophyll a concentrations and particulate backscattering coefficients. Our findings show that the seasonal dynamics of the DCMs are clearly region-dependent. High-latitude environments are characterized by a low occurrence of intense DBMs, restricted to summer. Meanwhile, oligotrophic regions host permanent DAMs, occasionally replaced by DBMs in summer, while subequatorial waters are characterized by permanent DBMs benefiting from favorable conditions in terms of both light and nutrients. Overall, the appearance and depth of DCMs are primarily driven by light attenuation in the upper layer. Our present assessment of DCM occurrence and of environmental conditions prevailing in their development lay the basis for a better understanding and quantification of their role in carbon budgets (primary production and export).

International audience; Evidence of water reflectance saturation in extremely turbid media is highlighted based on both field measurements and satellite data corrected for atmospheric effects. This saturation is obvious in visible spectral bands, i.e., in the blue, green and even red spectral regions when the concentration of suspended particulate matter (SPM) reaches then exceeds 100 to 1000 g.m −3. The validity of several bio-optical semi-analytical models is assessed in the case of highly turbid waters, based on comparisons with outputs of the Hydrolight radiative transfer model. The most suitable models allow to reproduce the observed saturation and, by inversion, to retrieve information on the SPM mass-specific inherent optical properties.

Ocean color satellite sensors are powerful tools to study and monitor the dynamics of suspended particulate matter (SPM) discharged by rivers in coastal waters. In this study, we test the capabilities of Landsat-8/Operational Land Imager (OLI), AQUA&TERRA/Moderate Resolution Imaging Spectroradiometer (MODIS) and MSG-3/Spinning Enhanced Visible and Infrared Imager (SEVIRI) sensors in terms of spectral, spatial and temporal resolutions to (i) estimate the seawater reflectance signal and then SPM concentrations and (ii) monitor the dynamics of SPM in the Rhône River plume characterized by moderately turbid surface waters in a micro-tidal sea. Consistent remote-sensing reflectance (Rrs) values are retrieved in the red spectral bands of these four satellite sensors (median relative difference less than ~16% in turbid waters). By applying a regional algorithm developed from in situ data, these Rrs are used to estimate SPM concentrations in the Rhône river plume. The spatial resolution of OLI provides a detailed mapping of the SPM concentration from the downstream part of the river itself to the plume offshore limits with well defined small-scale turbidity features. Despite the low temporal resolution of OLI, this should allow to better understand the transport of terrestrial particles from rivers to the coastal ocean. These details are partly lost using MODIS coarser resolutions data but SPM concentration estimations are consistent, with an accuracy of about 1 to 3 g·m-3 in the river mouth and plume for spatial resolutions from 250 m to 1 km. The MODIS temporal resolution (2 images per day) allows to capture the daily to monthly dynamics of the river plume. However, despite its micro-tidal environment, the Rhône River plume shows significant short-term (hourly) variations, mainly controlled by wind and regional circulation, that MODIS temporal resolution failed to capture. On the contrary, the high temporal resolution of SEVIRI makes it a powerful tool to study this hourly river plume dynamics. However, its coarse resolution prevents the monitoring of SPM concentration variations in the river mouth where SPM concentration variability can reach 20 g·m-3 inside the SEVIRI pixel. Its spatial resolution is nevertheless sufficient to reproduce the plume shape and retrieve SPM concentrations in a valid range, taking into account an underestimation of about 15%–20% based on comparisons with other sensors and in situ data. Finally, the capabilities, advantages and limits of these satellite sensors are discussed in the light of the spatial and temporal resolution improvements provided by the new and future generation of ocean color sensors onboard the Sentinel-2, Sentinel-3 and Meteosat Third Generation (MTG) satellite platforms.

Quantifying Colored Detrital Matter (CDM) from satellite observations can improve our knowledge of carbon dynamics in coastal areas and the open oceans. Several bio-optical inversion models have been developed for this purpose. However, care must be taken when they are applied to waters where optical properties significantly differ from model assumptions, which is the case in the Mediterranean Sea. Algorithm testing and validation are thus required before routine use. Here, in situ radiometric measurements collected in the NW Mediterranean Sea (BOUSSOLE site) are used to evaluate three bio-optical inversion models that retrieve the CDM light absorption coefficients at 443 nm (a(cdm)(443)). Although all methods reproduced the CDM seasonal cycles at the surface, comparisons of predicted and in situ acdm(443) coefficients showed that the Quasi-Analytical Algorithm version 6 (QAAv6) and a locally-adapted version of the Garver-Siegel-Maritorena model (GSM-Med) were the two best algorithms. Applying these two models to SeaWiFS remote sensing reflectances, collected between 2003 and 2010, reproduced with good accuracy the acdm(443) coefficients retrieved from field radiometric measurements at the BOUSSOLE site, with seasonal patterns consistent with previous observations. Finally, bio-optical relationships derived from satellite-retrieved a(cdm)(443) and chlorophyll values confirmed the higher-than-average CDM contribution for a given chlorophyll concentration in the Mediterranean Sea as compared to many oceanic regions. (C) 2016 Elsevier Inc. All rights reserved.

International audience; The present study proposes a novel method that merges satellite ocean color bio-optical products with Argo temperature-salinity profiles to infer the vertical distribution of the particulate backscattering coefficient (bbp). This neural network-based method (SOCA-BBP for Satellite Ocean-Color merged with Argo data to infer the vertical distribution of the Particulate Backscattering coefficient) uses three main input components: (1) satellite-based surface estimates of bbp and chlorophyll a concentration matched up in space and time with (2) depth-resolved physical properties derived from temperature-salinity profiles measured by Argo profiling floats and (3) the day of the year of the considered satellite-Argo matchup. The neural network is trained and validated using a database including 4725 simultaneous profiles of temperature-salinity and bio-optical properties collected by Bio-Argo floats, with concomitant satellite-derived products. The Bio-Argo profiles are representative of the global open-ocean in terms of oceanographic conditions, making the proposed method applicable to most open-ocean environments. SOCA-BBP is validated using 20% of the entire database (global error of 21%). We present additional validation results based on two other independent data sets acquired (1) by four Bio-Argo floats deployed in major oceanic basins, not represented in the database used to train the method; and (2) during an AMT (Atlantic Meridional Transect) field cruise in 2009. These validation tests based on two fully independent data sets indicate the robustness of the predicted vertical distribution of bbp. To illustrate the potential of the method, we merged monthly climatological Argo profiles with ocean color products to produce a depth-resolved climatology of bbp for the global ocean.

We investigated 32 net primary productivity (NPP) models by assessing skills to reproduce integrated NPP in the Arctic Ocean. The models were provided with two sources each of surface chlorophyll‐a concentration (chlorophyll), photosynthetically available radiation (PAR), sea surface temperature (SST), and mixed‐layer depth (MLD). The models were most sensitive to uncertainties in surface chlorophyll, generally performing better with in situ chlorophyll than with satellite‐derived values. They were much less sensitive to uncertainties in PAR, SST, and MLD, possibly due to relatively narrow ranges of input data and/or relatively little difference between input data sources. Regardless of type or complexity, most of the models were not able to fully reproduce the variability of in situ NPP, whereas some of them exhibited almost no bias (i.e., reproduced the mean of in situ NPP). The models performed relatively well in low‐productivity seasons as well as in sea ice‐covered/deep‐water regions. Depth‐resolved models correlated more with in situ NPP than other model types, but had a greater tendency to overestimate mean NPP whereas absorption‐based models exhibited the lowest bias associated with weaker correlation. The models performed better when a subsurface chlorophyll‐a maximum (SCM) was absent. As a group, the models overestimated mean NPP, however this was partly offset by some models underestimating NPP when a SCM was present. Our study suggests that NPP models need to be carefully tuned for the Arctic Ocean because most of the models performing relatively well were those that used Arctic‐relevant parameters., Key Points The models reproduced primary productivity better using in situ chlorophyll‐a than satellite valuesThe models performed well in low‐productivity seasons and in sea ice‐covered/deep‐water regionsNet primary productivity models need to be carefully tuned for the Arctic Ocean

International audience; André Morel (1933-2012) was a prominent pioneer of modern optical oceanography, enabling significant advances in this field. Through his forward thinking and research over more than 40 years, he made key contributions that this field needed to grow and to reach its current status. This article first summarizes his career and then successively covers different aspects of optical oceanography where he made significant contributions, from fundamental work on optical properties of water and particles to global oceanographic applications using satellite ocean color observations. At the end, we share our views on André's legacy to our research field and scientific community. Expected final online publication date for the Annual Review of Marine Science Volume 6 is January 03, 2014. Please see http://www.annualreviews.org/catalog/pubdates.aspx for revised estimates.

Miniaturized radiance cameras measuring underwater multispectral radiances in all directions at high-radiometric accuracy (CE600) are presented. The camera design is described, as well as the main steps of its optical and radiometric characterization and calibration. The results show the excellent optical quality of the specifically designed fish-eye objective. They also show the low noise and excellent linearity of the complementary metal oxide semiconductor (CMOS) detector array that is used. Initial results obtained in various oceanic environments demonstrate the potential of this instrument to provide new measurements of the underwater radiance distribution from the sea surface to dimly lit layers at depth. Excellent agreement is obtained between nadir radiances measured with the camera and commercial radiometers. Comparison of the upwelling radiance distributions measured with the CE600 and those obtained with another radiance camera also shows a very close agreement. The CE600 measurements allow all apparent optical properties (AOPs) to be determined from integration of the radiance distributions and inherent optical properties (IOPs) to be determined from inversion of the AOPs. This possibility represents a significant advance for marine optics by tying all optical properties to the radiometric standard and avoiding the deployment of complex instrument packages to collect AOPs and IOPs simultaneously (except when it comes to partitioning IOPs into their component parts).

Spectral reflectances of the ocean, R, as derived from ocean color remote sensing data at four wavelengths (412, 443. 490, and 555 nm), can be used to form two ratios of spectral reflectance, namely R(412)/R(443), and R(490)/R(555), thereafter denoted R-443(412) and R-555(490). The former is mainly sensitive to the colored dissolved organic material (CDOM), albeit influenced by the a [gal content as depicted by the chlorophyll concentration, ([Chl]); in contrast, the latter is essentially depending on [Chl], although it is also influenced by CDOM. Therefore the signatures of CDOM and [Chl] which are not truly separable. can nevertheless be identified by considering simultaneously the two ratios. The concomitant variations in these ratios can be established via a bio-optical model developed for Case I waters. This model implicitly includes a ``mean'' relationship between CDOM and [Chl], and thus produces a unique curve relating R-443(412) and R-555(490). Deviations with respect to this mean relationship can be introduced through a factor (phi), with (phi)>1 (excess) or

When the nominal algorithms commonly in use in Space Agencies are applied to satellite Ocean Color data, the retrieved chlorophyll concentrations in the Mediterranean Sea are recurrently notable overestimates of the field values. Accordingly, several regionally tuned algorithms have been proposed in the past to correct for this deviation. Actually, the blueness of the Mediterranean waters is not as deep as expected from the actual (low) chlorophyll content, and the modified algorithms account for this peculiarity. Among the possible causes for such a deviation, an excessive amount of yellow substance (or of chromophoric dissolved organic matter, CDOM) has been frequently cited. This conjecture is presently tested, by using a new technique simply based on the simultaneous consideration of marine reflectance determined at four spectral bands, namely at 412, 443, 490, and 555 nm, available on the NASA-SeaWiFS sensor (Sea–viewing Wide Field-of-view Sensor). It results from this test that the concentration in yellow colored material (quantified as ay, the absorption coefficient of this material at 443 nm) is about twice that one observed in the nearby Atlantic Ocean at the same latitude. There is a strong seasonal signal, with maximal ay values in late fall and winter, an abrupt decrease beginning in spring, and then a flat minimum during the summer months, which plausibly results from the intense photo-bleaching process favored by the high level of sunshine in these areas. Systematically, the ay values, reproducible from year to year, are higher in the western basin compared with those in the eastern basin (by about 50%). The relative importance of the river discharges into this semi-enclosed sea, as well as the winter deep vertical mixing occurring in the northern parts of the basins may explain the high yellow substance background. The regionally tuned [Chl] algorithms, actually reflect the presence of an excess of CDOM with respect to its standard (Chl-related) values. When corrected for the presence of the actual CDOM content, the [Chl] values as derived via the nominal algorithms are restored to more realistic values, i.e., approximately divided by about two; the strong autumnal increase is smoothed whereas the spring bloom remains as an isolated feature.

Field measurements and Mie calculations of the particulate light-scattering coefficient (bp, in m-1) in the near-infrared and visible spectral domains are combined to quantify and model the effect of particulate absorption on the bp spectral variations. The case of particles of coastal origin and assumed to follow a Junge-type size distribution is considered. A simple power-law function closely reproduces the near-infrared bp spectral variations, with a spectral slope varying in the range 0.1-1.4. In the visible (e.g., 440 nm), particulate absorption effects systematically lead to bp values 5-30% lower than values predicted using a power-law function fitted in the near infrared and extrapolated to 440 nm. The respective influences of the particle size distribution and composition are investigated for both mineral and organic particle populations. Finally, an empirical model derived from theoretical calculations closely reproduces the actual bp spectral variations from near-infrared to short visible wavelengths, taking into account particulate absorption effects.

Depth-integrated primary productivity (PP) estimates obtained from satellite ocean color-based models (SatPPMs) and those generated from biogeochemical ocean general circulation models (BOGCMs) represent a key resource for biogeochemical and ecological studies at global as well as regional scales. Calibration and validation of these PP models are not straightforward, however, and comparative studies show large differences between model estimates. The goal of this paper is to compare PP estimates obtained from 30 different models (21 SatPPMs and 9 BOGCMs) to a tropical Pacific PP database consisting of ∼ 100014C measurements spanning more than a decade (1983-1996). Primary findings include: skill varied significantly between models, but performance was not a function of model complexity or type (i.e. SatPPM vs. BOGCM); nearly all models underestimated the observed variance of PP, specifically yielding too few low PP (< 0.2 g C m- 2d- 1) values; more than half of the total root-mean-squared model-data differences associated with the satellite-based PP models might be accounted for by uncertainties in the input variables and/or the PP data; and the tropical Pacific database captures a broad scale shift from low biomass-normalized productivity in the 1980s to higher biomass-normalized productivity in the 1990s, which was not successfully captured by any of the models. This latter result suggests that interdecadal and global changes will be a significant challenge for both SatPPMs and BOGCMs. Finally, average root-mean-squared differences between in situ PP data on the equator at 140°W and PP estimates from the satellite-based productivity models were 58% lower than analogous values computed in a previous PP model comparison 6 years ago. The success of these types of comparison exercises is illustrated by the continual modification and improvement of the participating models and the resulting increase in model skill. © 2008 Elsevier B.V.

The very clear waters of the South Pacific Gyre likely constitute an end-member of oligotrophic conditions which remain essentially unknown with respect to its impact on carbon fixation and exportation. We describe a non-intrusive bio-optical method to quantify the various terms of a production budget (Gross community production, community losses, net community production) in this area. This method is based on the analysis of the diel cycle in Particulate Organic Carbon (POC), derived from high frequency measurements of the particle attenuation coefficient cp. We report very high integrated rates of Gross Community Production within the euphotic layer (average of 846±484 mg C m−2 d−1 for 17 stations) that are far above any rates determined using incubation techniques for such areas. Furthermore we show that the daily production of POC is essentially balanced by the losses so that the system cannot be considered as net heterotrophic. Our results thus agree well with geochemical methods, but not with incubation studies based on oxygen methods. We stress to the important role of deep layers, below the euphotic layer, in contributing to carbon fixation when incident irradiance at the ocean surface is high (absence of cloud coverage). These deep layers, not considered up to know, might fuel part of the heterotrophic processes in the upper layer, including through dissolved organic carbon. We further demonstrate that, in these extremely clear and stratified waters, integrated gross community production is proportional to the POC content and surface irradiance via an efficiency index ψ GCP*, the water column cross section for Gross Community Production. We finally discuss our results in the context of the role of oligotrophic gyre in the global carbon budget and of the possibility of using optical proxies from space for the development of growth community rather than primary production global models.

International audience; The spatial and temporal variations of oceanic new primary production have a crucial importance for the study of biogeochemical fluxes in the ocean; however, they have been poorly documented. In this paper, we propose a revision of the ``shift-up'' new production model developed for upwelling areas by Dugdale et al. (1989), and later adapted by Kudela and Dugdale (1996), using ocean color and sea surface temperature satellite data as inputs. The major improvement of the model is that the estimation of nitrogen uptake rates takes into account the phytoplankton community size structure, estimated for each pixel using the method of Uitz et al. (2006). Appropriate physiological parameters are then used for each size class. This revised model has been applied to Medium-Resolution Imaging Spectrometer and Advanced Along Track Scanning Radiometer data acquired over the year 2003, using the Benguela upwelling area as a test site. The combination of the new production model with a total production model allows the seasonal variations of new and total productions (including the respective contributions of the three size classes) to be estimated and compared. Even though microphytoplankton are generally considered to be responsible for new production, our results show that the contribution of small cells should not be overlooked in the upwelling-affected areas.

International audience; The match-up of satellite-derived reflectances with in situ observations is crucial to evaluate their quality and temporal stability. To contribute to this effort, a project has been set up to collect a data set of in situ radiometric and bio-optical quantities, in support to satellite ocean color calibration and validation. The project has been named ''BOUSSOLE'', and one of its key elements is a deep-sea optics mooring collecting data on a near-continuous basis since September 2003. This buoy is deployed in the deep clear waters of the northwestern Mediterranean Sea, and is visited on a monthly basis for servicing and acquisition of complementary data. The characteristics of the work area establish the site as a satisfactory location for validating satellite ocean color observations. A description of the data processing protocols is provided, followed by an analysis of the uncertainty of the buoy radiometry measurements. The results of a match-up analysis of the marine reflectances, diffuse attenuation coefficients, and chlorophyll concentrations for three major missions, i.e., MERIS, SeaWiFS, and MODIS-A, are then analyzed. They show poor performances for the bluest band (412 nm) of the three sensors, and performances within requirements at 443 and 490 nm for SeaWiFS and MODIS-A. These results suggest that a vicarious calibration should be introduced for the MERIS sensor. This analysis also demonstrates that a major effort is still required to improve atmospheric correction procedures whatever the mission.

International audience; Empirical algorithms based on first order relationships between ocean color and the chlorophyll concentration ([ChI]; mg m(-3)) are widely used, but cannot explain the statistical dispersion or ``anomalies'' around the mean trends. We use an empirical approach that removes the first order effects of [ChI] from satellite ocean color, thus allowing us to quantify the impact on the ocean color signal of optical anomalies that vary independently of the global mean trends with remotely sensed [ChI]. We then present statistical and modeling analyses to interpret the observed anomalies in terms of their optical sources (i.e. absorption and backscattering coefficients). We identify two main sources of second order variability for a given [ChI]: 1) the amount of non-algal absorption, especially due to colored dissolved organic matter; and 2) the amplitude of the backscattering coefficient of particles. The global distribution of the anomalies displays significant regional and seasonal trends, providing important information for characterizing the marine optical environment and for inferring biogeochemical influences. We subsequently use our empirically determined anomalies to estimate the backscattering coefficient of particles and the combined absorption coefficient for colored detrital and dissolved materials. This purely empirical approach provides an independent assessment of second order optical variability for comparison with existing methods that are generally based on semi-analytical models. (C) 2008 Elsevier Inc. All rights reserved.

A simple method to identify turbid, sediment-loaded, waters within satellite ocean color imageries was recently proposed (A. Morel and S. Belanger, Remote Sensing of Environment, 102, (2006), 237-249). Systematic application of this method to the level-3 composites obtained from three ocean color sensors shows that the ``turbid'' flag is often raised in the open ocean, especially in the sub-tropical oligotrophic gyres, where turbidity is unlikely. In addition these flagged zones migrate with season, and clearly follow the sun declination course. The combination of low chlorophyll waters with a residual sun-glint is at the origin of this artifact. Simple approaches for eliminating such a misleading detection are proposed. The identification and elimination of the bias are also needed in particular for an unambiguous detection of the presence of calcite (coccolithophores) in open waters. (C) 2008 Published by Elsevier Inc.

Optical measurements within both the visible and near ultraviolet (UV) parts of the spectrum (305-750 nm) were recently made in hyperoligotrophic waters in the South Pacific gyre (near Easter Island). The diffuse attenuation coefficients for downward irradiance, K-d(lambda), and the irradiance reflectances, R(lambda), as derived from hyperspectral (downward and upward) irradiance measurements, exhibit very uncommon values that reflect the exceptional clarity of this huge water body. The K-d(lambda) values observed in the UV domain are even below the absorption coefficients found in current literature for pure water. The R(A) values (beneath the surface) exhibit a maximum as high as 13% around 390 nm. From these apparent optical properties, the absorption and backscattering coefficients can be inferred by inversion and compared to those of (optically) pure seawater. The total absorption coefficient (a(tot)) exhibits a flat minimum (similar to 0.007 m(-1)) around 410-420 nm, about twice that of pure water. At 310 nm, a(tot) may be as low as 0.045 m(-1), i.e., half the value generally accepted for pure water. The particulate absorption is low compared to those of yellow substance and water and represents only similar to 15% of a(tot) in the 305-420-nm domain. The backscattering coefficient is totally dominated by that of water molecules in the UV domain. Because direct laboratory determinations of pure water absorption in the UV domain are still scarce and contradictory, we determine a tentative upper bound limit for this elusive coefficient as it results from in situ measurements.

International audience; The third primary production algorithm round robin (PPARR3) compares output from 24 models that estimate depth-integrated primary production from satellite measurements of ocean color, as well as seven general circulation models (GCMs) coupled with ecosystem or biogeochemical models. Here we compare the global primary production fields corresponding to eight months of 1998 and 1999 as estimated from common input fields of photosynthetically-available radiation (PAR), sea-surface temperature (SST), mixed-layer depth, and chlorophyll concentration. We also quantify the sensitivity of the ocean-color-based models to perturbations in their input variables. The pair-wise correlation between ocean-color models was used to cluster them into groups or related output, which reflect the regions and environmental conditions under which they respond differently. The groups do not follow model complexity with regards to wavelength or depth dependence, though they are related to the manner in which temperature is used to parameterize photosynthesis. Global average PP varies by a factor of two between models. The models diverged the most for the Southern Ocean, SST under 10 degrees C, and chlorophyll concentration exceeding 1 mg Chlm(-3). Based on the conditions under which the model results diverge most, we conclude that current ocean-color-based models are challenged by high-nutrient low-chlorophyll conditions, and extreme temperatures or chlorophyll concentrations. The GCM-based models predict comparable primary production to those based on ocean color: they estimate higher values in the Southern Ocean, at low SST, and in the equatorial band, while they estimate lower values in eutrophic regions (probably because the area of high chlorophyll concentrations is smaller in the GCMs). Further progress in primary production modeling requires improved understanding of the effect of temperature on photosynthesis and better parameterization of the maximum photosynthetic rate. (c) 2006 Elsevier Ltd. All rights reserved.

Case 1 waters with high chlorophyll content can be encountered as soon as the nutrient availability is high enough and the terrestrial influence by land drainage is negligible. Offshore oceanic blooms and upwelling zones along and coasts are instances of such waters. Their bio-optical properties are less documented compared to those of mesotrophic or oligotrophic waters. A coherent set of measurements of bio-geochemical properties (algal pigments, suspended particulate matter), inherent optical properties (absorption and scattering by water bodies and by particulate material), and apparent optical properties (hyperspectral reflectance and diffuse attenuation coefficients) was obtained within the Benguela Current, i.e. in an upwelling area with and climate and no runoff. These data allow the bio-optical relationships in eutrophic Case 1 waters to be analyzed, and their natural variability to be compared with that previously observed in less productive waters. In addition, a comparison between eutrophic Case 1 waters and yellow substance dominated Case 2 waters can be made, since such waters are also present in the area under investigation. The coherence between the inherent and apparent optical properties is also analyzed via inversion. Despite some deficiencies in their parameterization, the existing bio-optical models for Case 1 waters were proven to be valid such that they can be extended without significant discontinuities toward the domain of high concentration (up to 30 mg m(-3)). In particular, those models in use for the interpretation of remotely sensed ocean color continue to apply, even if the sensitivity of current algorithms for the chlorophyll retrieval weakens owing to inescapable physical limitations in the case of high concentrations. (c) 2006 Published by Elsevier Ltd.

The geomorphic, oceanographic, terrestrial and anthropogenic attributes of the European coastal zone are described and published data on ecosystem function (primary production and respiration) are reviewed. Four regions are considered: the Baltic Sea, Mediterranean Sea, Black Sea and the European Atlantic coast including the North Sea. The metabolic database (194 papers) suffers from a non-homogeneous geographical coverage with no usable data for the Black Sea which was therefore excluded from this part of our study. Pelagic gross primary production in European open shelves is, by far, the most documented parameter with an estimated mean of 41 mmol C m-2 d-1, the lowest value is reported in the Mediterranean Sea (21 mmol C m-2 d-1) and the highest one in the Atlantic/North Sea area (51 mmol C m-2 d-1). Microphytobenthic primary production, mostly measured in shallow areas, is extrapolated to the entire 0–200 m depth range. Its contribution to total primary production is low in all regions (mean: 1.5 mmol C m-2 d-1). Although macrophyte beds are very productive, a regional production estimate is not provided in this study because their geographical distribution along the European coastline remains unknown. Measurements of pelagic community respiration are clearly too sparse, especially below the euphotic zone, to yield an accurate picture of the fate of organic matter produced in the water column. With a mean value of 17 mmol C m-2 d-1, benthic community respiration consumes approximately 40% of the pelagic organic matter production. Estuaries generally exhibit high metabolic rates and a large range of variation in all parameters, except microphytobenthic primary production. Finally, the problem of eutrophication in Europe is discussed and the metabolic data obtained in the framework of the Land–Ocean Interactions in the Coastal Zone (LOICZ) project are compared with available direct measurements of net ecosystem production.

International audience; A spectral model of the inherent optical properties (IOP) of oceanic case 1 waters, as previously developed for studying the near-surface bidirectional reflectance, provides the input parameters for the present computations of radiative transport (RT), now extended throughout the water column (three times the euphotic zone). All spectral apparent optical properties (AOP) are computed at each of the levels (30) for six chlorophyll values (from 0.03 to 10 mg m(-3)) and for six values of the zenith Sun angle (from 0degrees to 75degrees). The Raman emission is accounted for. From the irradiances and radiances values the various attenuation coefficients (K), the average cosines ((mu) over bar), and the reflectance ( R) are derived for all depths and layers. Their variations resulting from the Sun's position are also studied, which removes the static character of previous empirical models inasmuch as the diurnal changes of the parameters describing the in-water light field can be predicted. The AOPs observed within the deepest levels are also compared to values independently derived from an asymptotic ( iterative) solution of the RT. The rate of approach to the asymptotic regime is numerically analyzed; this rate is actually governed by tau(b), i.e., this fraction of tau ( the optical thickness) that corresponds only to scattering. Practical applications of these systematic computations are examined, such as the change (with solar position) of the euphotic depth, the time- and wavelength-dependent scalar irradiance that controls during the day the energy available for photosynthesis (or the heating rate), and the interpretation of radiometric field experiments involving upward and downward irradiance measurements. Some approximate expressions relating AOPs to IOPs are examined in the light of exact computations.

A system was designed for the continuous surface monitoring of hydrological, bio-optical, and biogeochemical properties in the vicinity of the Almeria-Oran jet-front system (Northwestern Mediterranean Sea). This system included a thermosalinograph, a fluorometer, an optical particle counter, and an absorbance-attenuance meter (AC9), allowing the estimation of the absorption [a(l), (m 21 )] and scattering [b(l), (m 21 )] coefficients at nine wavelengths. More than 500 multivariate records were acquired over a transect crossing the jet-front system three times and encompassing the diversity of water types encountered in this area. A method is proposed to retrieve relevant biogeochemical or bio-optical quantities, among which are the chlorophyll a concentration [from a(676)], the particulate carbon concentration [from b(555)], the colored dissolved organic matter [CDOM, from a(412)], and the chlorophyll-specific scattering coefficient at 555 nm, b*(555) (m 2 mg Chl a 21 ). The analyses of these various quantities with respect to the surface hydrodynamic fields reveal two main features. First, the particle pool displays highly dynamic quantitative variations across the frontal structure. Qualitatively, flagellate-dominated populations are associated with moderate density waters and maximal jet velocity, while diatoms are recorded at the narrow limit between the jet-front and the Mediterranean waters, where jet velocity is minimal. Second, the CDOM pool presents remarkable covariations with the surface-density field. In particular, the lowest aCDOM(412) values are reproducibly associated with the highest density values, which track upwelled flow associated with the frontal circulation; accumulation of CDOM is always observed inside the frontal waters, at a density value of 27.2 kg m 23 . These CDOM variations suggest that the frontal system is the place of enhanced biological activity.

A correlation analysis based on the concept of singular-value decomposition of a matrix is applied here to an atmospheric aerosol data set, for twelve metals (Al, Ca, Cd, Co, Cu, Fe, Mg, Mn, Na, Ni, Pb and Zn),in the Ligurian Sea coastal environment. An iterative procedure allows atypical samples to be discarded, i.e. samples with characteristics significantly different to those of the whole data set. After five atypical samples have been objectively discarded, the general characteristics of the data set are better described and some features are enhanced according to a decreasing order of importance, For example, the mineral dust character of almost every metal is shown, which points out that the marine recycling component is negligible. Marine (Mg, Na) and anthropogenic (Cd, Cu, Pb, Zn) contributions are assessed as well. There is also evidence of some peculiar behaviours: among others, Fe clearly exhibits an anthropogenic component; the remainder of automotive Pb is still apparent; Ni exhibits a relatively high crustal component; Zn, despite its recognized anthropogenic character, is not clearly correlated with other anthropogenic metals., Une analyse de corrélation, basée sur le concept de décomposition d'une matrice en valeurs singulières, permet de décrire le comportement de douze métaux (Al, Ca, Cd, Co, Cu, Fe, Mg, Mn, Na, Ni, Pb et Zn) dans l'aérosol atmosphérique de la mer Ligure. Une procédure itérative permet d’écarter les échantillons atypiques, c'est-à-dire ceux dont les caractéristiques sont sensiblement différentes des tendances générales du lot de données. Après que cinq échantillons atypiques aient été écartés objectivement, les caractéristiques générales des échantillons sont décrites et quelques particularités sont mises en valeur, selon un ordre décroissant d'importance. Par exemple, le caractère crustal de chaque métal est mis en évidence, ce qui signifie que la composante de recyclage marin est négligeable. Les contributions à caractère marin (Mg, Na) et anthropique (Cd, Cu, Pb, Zn) sont également évaluées. Certains comportements particuliers sont mis en évidence : entre autres, il existe une composante anthropique de Fe ; le reliquat de Pb automobile est encore largement détectable ; Ni a un caractère détritique relativement fort ; Zn, bien que présentant un caractère anthropique marqué, n'est pas clairement corrélé avec les autres métaux liés aux activités humaines.

Sun-stimulated chlorophyll a fluorescence has been measured in situ, within the upward and downward light fields, in oceanic waters with chlorophyll concentrations of 0.04-3 mg m(-3). We combined these signals with phytoplankton absorption spectra to derive the fluorescence quantum yield, phi (number of photons emitted by fluorescence/number of absorbed photons). phi was derived separately from hyperspectral (upward and downward) irradiance measurements (with a LI-COR Instruments spectroradiometer) and fi om nadir radiance near 683 nn (with a Biospherical Instruments profiler). The contribution of inelastic Raman scattering to the signal in the red band was assessed and subtracted. Raman-corrected phi values derived from the two instruments compared well. Vertical phi profiles were strongly structured, with maximal (5-6%) values at depth, whereas phi was congruent to1% in near-surface waters (measurements made approximately at solar noon). These near-surface values are needed for interpretation of remotely sensed fluorescence signals. This optical study shows that the fluorescence yield of algae in their natural environment can be accurately derived in a nonintrusive way with available instrumentation and adequate protocols. (C) 2000 Optical Society of America OCIS codes: 010.4450, 260.2510.

International audience; Temperature and salinity of Mediterranean deep water have been increasing, based on observations extending back to 1959. Over the 1940-1995 period, the corresponding changes in heat and water budgets across the sea surface have been estimated to be 1.74 Wm(-2) for the greenhouse effect change, 0.5 degrees C and 0.4 degrees C for mean air and sea-surface temperature increases, respectively, and an increase of 0.1 m (or 11%) in the freshwater deficit, which is due partly to human activities and partly to climatic changes.

26th International Liege Colloquium on Ocean Hydrodynamics - The Coastal Ocean in a Global Change Perspective, LIEGE, BELGIUM, MAY 05-09, 1994-1995; At great scales of time and space, the dynamics of the Mediterranean Sea, a concentration basin, are mainly linked to its freshwater budget. This budget is subject to evolutions due to man's use of freshwater and to climatic changes affecting precipitation and/or evaporation. Marine dynamics and Atlantic, atmospheric and terrestrial inputs are strong constraints for the geochemical behaviour of the Mediterranean Sea. From measurements made during the last decades in the deep western water, it appeared that temperature, salinity, nutrients and trace metal concentrations were changing with time. In spite of its depth, the Mediterranean Sea looks like a coastal ocean, according to its coast length, watershed and number of inhabitants and to its fast response to climatic and environmental changes. The changes discovered in deep homogeneous waters are signatures of evolutions occurred in the surface layer. But in this layer and particularly in coastal waters, climatic and/or environmental trends may be masked by seasonal and interannual variabilities of not only physical and chemical characteristics but also climatic forcing or anthropic inputs. Analyses of river runoff, atmospheric inputs or climatic trends together with marine evolutions indicate constraints concerning probable changes in the coastal sea and/or in the surface water and processes involved at the interfaces. Moreover, changes observed in coastal or deep-water constitute new constraints for the modelling of the marine circulation and the transfer of matter.

The bidirectional reflectance of oceanic waters is conveniently described in a normalized way by forming the ratio of the upwelling irradiance E(sub u) to any upwelling radiance L(sub u)(theta prime, phi). This ratio, Q (theta prime, theta(sub 0), (phi(sub 0) - phi), where theta prime, phi are the nadir and azimuth angles for the upward radiance and theta(sub 0), phi(sub 0) are the zenith and azimuth angles of the Sun, has been determined from measurements at sea and computed via Monte Carlo simulations using the inherent optical properties measured in the field and appropriate boundary conditions (clear sky, no wind, varying Sun angle). Experimental ad computed Q values are in excellent agreement. This successful comparison confirms the importance of the bidirectional character of ocean reflectance, already pointed out from a purely numerical approach without field validation, and corroborates the extended range of the Q variations. The later point is of importance when interpreting the marine signals detected by an ocean color satellite-borne sensor. The validation is extended by considering the historical data for the radiance distributions in Lake Pend Oreille determined at various depths. The closure issue in ocean optics is examined by solving the direct problem of radiative transfer and through a model-data comparison in terms of radiance field.

We used simplifying assumptions to derive analytical formulae expressing the reflectance of shallow waters as a function of observation depth and of bottom depth and albedo. These formulae also involve two apparent optical properties of the water body: a mean diffise attenuation coefficient and a hypothetical reflectance which would be observed if the bottom was infinitely deep. The validity of these approximate formulae was tested by comparing their outputs with accurate solutions of the radiative transfer obtained under the same boundary conditions by Monte Carlo simulations. These approximations were also checked by comparing the reflectance spectra for varying bottom depths and compositions determined in coastal lagoons with those predicted by the formulae. These predictions were based on separate determinations of the spectral albedos of typical materials covering the floor, such as coral sand and various green or brown algae. The simple analytical expressions are accurate enough for most practical applications and also allow quantitative discussion of the limitations of remote-sensing techniques for bottom recognition and bathymetry. As early as 1944, Duntley used a spectrograph mounted in a glass-bottomed boat or flown in an airplane to analyze radiances emerging from the ocean and shallow waters. He evidenced the influence of the water depth on the spectral composition of the upward flux (Duntley 1963). Using a Monte Carlo technique, Plass and Kattawar (1972) calculated the radiative field in the atmosphere+cean system and in particular examined the dependence of the upward flux on the albedo of the ocean floor. Gordon and Brown (1974) studied the diffuse reflectance of a shallow ocean using Monte Carlo simulations and a probabilistic approach. Gordon and Brown provided an analysis based on photon history of the light field as modified by the presence of a reflecting bottom. In, addition, Ackleson and Klemas (1986) developed a two-flow model that simulated the light field within a canopy of bottom-adhering plants. A single scattering approximation for irradiance reflectance was also

An objective correlation analysis based on the concept of singular-value decomposition of a matrix is proposed here for the field of metallic traces in the atmospheric aerosol. On the basis of an atmospheric sampling at Cap Ferrat (southeastern coast of France), the method is applied to the airborne concentrations of Al, Pb, Cd, Cu, and Zn. The data matrix is decomposed in two series of singular vectors. These vectors are orthogonal and classified in decreasing importance, according to the percentage of the total variance that they explain. Such a method is easy to apply and, if compared with a standard correlation analysis, it exhibits such advantages as (i) atypical points can be objectively discarded in order to improve the description of the general characteristics of the data set; (ii) all the elements are simultaneously taken into account by the analysis, which permits the enhancement of the features of the data set involving one or several metals; (iii) the importance of these independent features in the variability of the data set is measured.

Seven models for computing underwater radiances and irradiances by numerical solution of the radiative transfer equation are compared. The models are applied to the solution of several problems drawn from optical oceanography. The problems include highly absorbing and highly scattering waters, scattering by molecules and by particulates, stratified water, atmospheric effects, surface-wave effects, bottom effects, and Raman scattering. The models provide consistent output, with errors (resulting from Monte Carlo statistical fluctuations) in computed irradiances that are seldom larger, and are usually smaller, than the experimental errors made in measuring irradiances when using current oceanographic instrumentation. Computed radiances display somewhat larger errors.

Mediterranean nutrient studies differ from one another by their rates of exchange with the Atlantic Ocean and by atmospheric and terrestrial sources, which sometimes vary by six times. During the Medatlante cruises (in 1988 and 1989), increases of phosphate and nitrate concentrations were confirmed in deep western waters and may be related to increasing agricultural, industrial and urban activities around the sea since the 1960s. In a non-steady-state model, this evolution of deep water concentrations constrains uncertainties in the nutrient budgets; we propose a reduced range for atmospheric and terrestrial sources of nutrients. In the Western Basin in the late 1980s the total atmospheric and terrestrial source amounted to 8–10 × 109 mol y−1 of phosphate, and 190–220 × 109 mol y−1 of nitrate; about two-fold greater than estimates based on measurements of atmospheric and terrestrial inputs (the latter is calculated from the Rhone river concentrations over the 1971–1988 period). Consequently, phosphate budgets suggest that some of the riverine particulate input of phosphorus dissolves when entering the sea and constitutes a main source of phosphate, a scenario proposed by Froelich (1988). Likewise, dissolved inorganic nitrogen budgets require biological fixation of molecular nitrogen by plankton species and seagrasses. This process may constitute the main nitrogen source and explain the peculiar molar ratio N/P in the Mediterranean Sea (about 21–23) instead of about 15 in the global ocean.

THE western Mediterranean Sea comprises three water masses: a surface layer (from 0 to ∼150 m depth), an intermediate layer (∼150–400 m) issuing from the eastern basin, and a deep water mass at depths below 400 m. The deep water is homogeneous and has maintained a more or less constant temperature and salinity from the start of the century until recently1. Here we report measurements from the Medatlante cruises of December 1988 and August 1989, which show the deep layer to be 0.12 °C warmer and ∼0.03 p.s.u. more saline than in 1959. Taking these data together with those from earlier cruises, we find a trend of continuously increasing temperatures over the past three decades. These deep-water records reflect the averaged evolution of climate conditions at the surface during the winter, when the deep water is formed. Consideration of the heat budget and water flux in the Mediterranean2,3 leads to the possibility that the deep-water temperature trend may be the result of greenhouse-gas-induced local warming.

Characterizing phytoplankton distribution and dynamics in the world's open oceans requires in situ observations over a broad range of space and time scales. In addition to temperature/salinity measurements, Biogeochemical-Argo (BGC-Argo) profiling floats are capable of autonomously observing at high frequency bio-optical properties such as the chlorophyll fluorescence, a proxy of the chlorophyll a concentration (Chla), the particulate backscattering coefficient (bbp), a proxy of the stock of particulate organic carbon, and the light available for photosynthesis. We analyzed an unprecedented BGC-Argo database of more than 8,500 multi-variable profiles collected in various oceanic conditions, from subpolar waters to subtropical gyres. Our objective is to refine previously established Chla vs bbp relationships and gain insights into the sources of vertical, seasonal and regional variability in this relationship. Despite some nuances in the relationship considering one or another water column layer or region, a general covariation occurs at a global scale. We distinguish two main contrasted situations: (1) concomitant changes in Chla and bbp that correspond to actual variations in phytoplankton biomass, e.g. in subpolar regimes; (2) a decoupling between the two variables attributed to photoacclimation or changes in the relative abundance of non-algal particles, e.g. in subtropical regimes. The variability in the bbp:Chla ratio in the surface layer appears to be essentially influenced by the type of particles and photoacclimation processes. The dense BGC-Argo database helps identifying the spatial and temporal scales at which this ratio is predominantly driven by one or the other of these two factors.