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Abstract: Optical water types were identified from an in situ data set of concomitant biogeochemical and optical parameters collected in contrasted turbid coastal areas of the eastern English Channel, southern North Sea and French Guiana at different seasons (211 stations). Four optical classes have been defined using a clustering approach performed on the spectrally normalized reflectance spectra. Normalization of the reflectance spectra was carried out during the statistical analysis to emphasize the shape of the reflectances rather than their magnitude. Each optical water type is associated with a specific bio-optical environment, in agreement with previous works. Two classes present a very marked optical character, one being mostly determined by strong phytoplankton and dissolved material loads, and the other one by a high proportion of mineral particles. The two remaining classes are related to optically mixed situations although there are some differences in the relative proportion of particulate mineral material. Applying this optical typology to the SeaWiFS daily reflectance data, we emphasized the high representativeness of these 4 optical water types which allow to describe about two thirds of the reflectance spectra found within the development sites whatever the season. The adequacy of optical water type definition for monitoring the spatio-temporal variability of coastal water masses optical quality, which reflects the impact of biological and hydrodynamic processes occurring at different time scales (i.e. from high frequency to seasonal processes), has been demonstrated. The four optical classes'' typology has been shown to remain highly representative at global scale. This underlines the effective optical vicinity of some parts of the coastal ocean during some periods of the year, in spite of the recognized high optical diversity of coastal waters. This further demonstrates the high pertinence of class-based approach for large scale coastal applications. Finally, the potential for class-based inversion algorithms for improving ocean color products retrieval, as well as the applicability of such class-specific algorithms with respect to satellite information have been illustrated from the estimation of the suspended matter concentration. This work provides very encouraging evidence of the potential and adequacy of class-based inversion methods for deriving bio-optical products in optically complex waters such as the coastal ocean. [Copyright &y& Elsevier]

Abstract: Knowledge of the oceanic particulate organic carbon (POC) pool and of its spatio-temporal variability is important for understanding the oceanic carbon cycle. Until now, POC estimates from space have been restricted to the surface layer. An empirical algorithm is developed to derive the POC content integrated over the euphotic layer () from the near-surface POC concentration (). The relationship follows a power-law distribution, , with A and B depending on the type of waters (stratified or well-mixed) and on the near-surface chlorophyll concentration. A global climatology of and is generated from the SeaWiFS archive between 1998 and 2006. The global patterns of and follow the major gyre systems and other large-scale circulation features. High surface and integrated POC content, around and , are encountered at high latitude, whereas low content, and , are observed in subtropical gyres. The mean global values of and over the global ocean are and . The standing stocks of POC are and over the first penetration and euphotic depth, respectively. [Copyright &y& Elsevier]

The in-water radiance field has been computed in typical Case 2 waters by using radiative transfer models and appropriate inherent optical properties (IOPs) combined with realistic boundary conditions. In particular, the bi-directional structure of the subsurface upward flux has been investigated in view of remote sensing applications related to ocean colour. In Case 2 waters, the IOPs are not controlled by the phytoplankton (or chlorophyll) concentration; rather they are essentially determined by the abundance of terrigenous optically active materials, either particulate or dissolved. Based on field data and related IOPs, two extreme situations were selected as representative instances of sedimentdominated and yellow-substance-dominated Case 2 waters. This study shows that even in very turbid natural waters, the upward radiance field is not isotropic and remains Sun-angle dependent. More than 100 successive events are needed to reach a quasi-isotropic, illumination independent, upward radiance field. In contrast, with a high yellow substance content resulting in high absorption (compared to scattering), single scattering prevails in such waters and this leads to strongly featured radiance fields that are heavily dependent on the Sun's position. It is necessary to account for these effects when interpreting waterleaving radiances as detected from space, and, perhaps more importantly, when carrying out at-sea radiometric measurements in support of calibration of remote ocean colour sensors. For this purpose, a practical approach and mean values of relevant coefficients are proposed to describe the bi-directional structure of the upward radiance field in the two extreme situations of strongly scattering or strongly absorbing waters. [ABSTRACT FROM AUTHOR]

Abstract: Particulate suspended matter concentration (SPM) were estimated over a 8 year time period (2002–2010) in the coastal waters of French Guiana from a regional algorithm applied to the MODIS monthly reflectance measurements. Comparison between SPOT images and MODIS-SPM maps revealed the strong spatio-temporal coupling between in water SPM and the dynamics of local (i.e. Kourou and Cayenne) mud banks. Highest MODIS SPM values (>13 g m−3 approximately) can be significantly associated with the subtidal part of the banks as well as to the related turbid plume. The migration of these mud banks induces strong interannual changes in SPM reaching up to 6% year−1 within increasing and decreasing patchy areas distributed alternatively along the coastline of French Guiana. Mud banks migration rates derived from MODIS SPM data reach in average about 2 km year−1 in agreement with previous studies. The MODIS time series have allowed for a detailed description of the seasonality and interannual variations in the in-water SPM loads. Seasonal changes in SPM are related to the onset of the trade wind season. Marked non-linear patterns including a sharp evolution in the SPM values around 2005 as well as additional high frequency modulations have been emphasized within the upward and downward SPM trend regions. Concurrent temporal variations in the frequency of northward swells (favoring mud banks migration and reworking) as well as interannual changes in the amount of sediment delivered by the Amazon River have been shown to play a major role in the SPM temporal patterns observed in the French Guiana coastal waters. Our results clearly demonstrate the advantage for ocean color data to describe mud banks dynamics through the assessment of in water SPM temporal variability. [Copyright &y& Elsevier]

Coastal waters of the English Channel and the North Sea are affected by a massive spring phytoplankton bloom event of the prymnesiophyte Phaeocystis globosa every year. The impact of this bloom on DOM dynamics in coastal waters of the western English Channel was investigated through a 45 d long mesocosm experiment and field survey (2012-2014). Our results highlight that, over short time scales, marine production of DOM mostly affects CDOM absorption properties in the UV domain. Specifically, it has been evidenced that the acdom spectral slope between 320 nm and 412 nm ( S320-412) can be used as a relevant indicator of the DOM marine origin. The presence of a strong linear relationship between S320-412 and the DOC specific absorption coefficient in phytoplankton bloom conditions reveals that this optical parameter provides complementary information to those obtained from the spectral slope between 275 nm and 295 nm, S275-295 which has been recently described as a relevant tracer of the terrestrial DOM and a good descriptor of the specific absorption coefficient of dissolved organic carbon variability in the confining river-influenced ocean margins. This study has further demonstrated that the joint use of S275-295 and S320-412 significantly improves the estimation DOC-specific absorption coefficient in the presence of varying contribution of marine and terrestrial DOM. While such bands are still not available on ocean color sensors, this methodology represents a valuable tool for estimating DOC concentration from CDOM absorption measurements from in situ data obtained from classical discrete measurements or from autonomous platforms equipped with adapted spectrophotometer. [ABSTRACT FROM AUTHOR]

Abstract: The PHYSAT method, which enables identification of four different phytoplankton groups from their impact on the normalized water-leaving radiance (nLw) spectra, is applied to coincident in situ measurements of both chlorophyll concentration (Chl ) and nLw. Observations show that measurements acquired in waters dominated by haptophytes, diatoms and Synechococcus-like cyanobacteria have optical properties that deviate significantly from the mean OC4V4 bio-optical model, which is currently used as the standard for global ocean color processing. A specific OC4v4-like relationship, i.e., Chl as a 4th-order polynomial of the “maximum band ratio”, was fitted for each dominant phytoplankton group identified by PHYSAT. The resulting OC4-SD bio-optical model thus starts from a classification of the dominant phytoplankton group, followed by a species-dependent estimate of Chl . It has been applied to global daily SEAWIFS data of the year 2001. Monthly mean maps of Chl derived from OC4-SD or OC4v4 show large regional differences that can reach 50% at high latitudes. The new algorithm leads to lower concentrations in regions where the standard model retrievals are known to be too high, such as the Mediterranean Sea. Conversely, higher concentrations are retrieved in regions dominated by diatom blooms, such as the northern North Atlantic in summer, where previous studies have demonstrated a low bias in standard SEAWIFS Chl . [Copyright &y& Elsevier]