Temporal Variability of Ocean Colour Derived Products in the European Seas

The ten-year record of ocean colour data provided by the SeaWiFS mission is an important asset for monitoring and research activities conducted on the optically-complex European seas. This study mainly makes use of the SeaWiFS data set of normalized water leaving radiances LWN to study the major characteristics of temporal variability associated with optical properties across the entire European domain. Specifically, the time series of LWN, band ratios, diffuse attenuation coefficient Kd(490) and concentration of chlorophyll a Chla are decomposed into terms representing a fixed seasonal cycle, irregular variations and trends, and the contribution of these components to the total variance is described for the various basins. The diversity of the European waters is fully reflected by the range of results varying with regions and wavelengths. Generally, the Mediterranean and Baltic seas appear as two end-members with, respectively, high and low contributions of the seasonal component to the total variance. The existence of linear trends affecting the satellite products is also explored for each basin. The interpretation of the trends observed for LWN and band ratios is not straightforward, but it circumvents the limitations resulting from the levels of uncertainty, very variable in space and often high, that characterize derived products such as Chla in European waters. Results for Kd(490) and Chla are also analyzed. Statistically significant, and in some cases large, trends are detected in the Atlantic Ocean west of the European western shelf, the central North Sea, the English Channel, the Black Sea, the northern Adriatic, and various regions of the Mediterranean Sea and the northern Baltic Sea, revealing changes in the concentrations of optically significant constituents in these regions.JRC.H.3-Global environement monitorin

Multi-Year Analysis of Standard Ocean Colour Products for the European Seas

A 10-year time series of ocean colour products has been assembled for the European Seas from the SeaWiFS and MODIS full resolution satellite imagery. The JRC ocean colour archive is first briefly described. Then the study focuses on the analysis of the spatial and temporal variability of standard products such as the chlorophyll a pigment concentration and the diffuse attenuation coefficient. The European seas are partitioned into a set of specific regions for which average time series are derived and analysed in terms of seasonal and inter-annual variability. Finally, a statistical analysis yields a decomposition of the series into seasonal, irregular and linear trend components, thus providing a classification of the European waters on the basis of their temporal variations.JRC.H.3-Global environement monitorin

Selected UV Photochemical and Photobiological Impacts on Marine Ecosystems: General Characteristics and Sensitivity Analyses

In the recent years, numerous efforts have been performed in order to characterize the impacts of UVR on marine photobiology and photochemistry. The quantification of these UV-dependent processes through modelling approaches requires (i) an accurate description of UV underwater light field (ii) an adapted parameterization of the response of marine water compounds and/or organisms to spatio-temporal changes in solar radiations. The spatial and temporal variability of the absorption coefficient of the colored detrital material, which is a key element for studying undersea UV climate, has been characterized in the two basins selected for this study (the Mediterranean Sea and the Norwegian Seas) using the SeaWiFS products archive recently achieved for the period 1998-2006. Moreover, the various models currently available for the description of selected optical (CDOM photobleaching), photochemical (CO and DIC production) and photobiological (primary production inhibition) effects of UVR on marine waters have been described. Further, the general characteristics of these UV-dependent processes have been presented focusing, in particularly, on their variability along the daily, vertical and spectral dimensions. Several sensitivity analyses have been performed in order to define the relative importance of the various inputs of the spectral and depth resolved model on the final estimations. Finally, some of the straightforward models recently proposed in order to estimate some of the UV impacts at large temporal and or spatial scales have been tested and their limits of application have been discussed.JRC.H.3-Global environement monitorin

Challenges and New Advances in Ocean Color Remote Sensing of Coastal Waters

Knowing that coastal areas concentrate about 60% of the world's population (within 100 km from the coast), that 75-90% of the global sink of suspended river load takes place in coastal waters in which about 15% of the primary production occurs, the ecological, societal and economical value of these areas are obvious (fish resources, aquaculture, water quality information, recreation areas management, global carbon budget, etc). In that context, precise assessment of suspended particulate matter (SPM) concentrations and of the phenomena controlling its temporal variability is a key objective for many research fields in coastal areas. SPM which encompasses organic (living and non-living) and inorganic matter controls the penetration of light into the water and brings new nutrients into the system, both key parameters influencing phytoplankton primary production. Concentrations and availability of SPM are also known to control rates of food intake, growth and reproduction for various filter feeder organisms. Phytoplankton is highly sensitive to environmental perturbations (such as nutrient inputs, light, and turbulence). The abundance, biomass and dynamics of phytoplankton in coastal areas therefore reflect the prevailing environmental conditions and represent key parameters for assessing information on the ecological conditions, as well as on the coastal water quality. Because phytoplankton is highly sensitive to environmental perturbations [1], its distribution patterns and temporal variability represent good indicators of the ecological conditions of a defined region [2, 3]. Coastal waters also host complex ecosystems and represent important fishery areas that support industry and provide livelihood to coastal settlements. The food chain in the coastal ocean is generally short (especially in upwelling systems, having as low as three trophic levels) whereas the open ocean food web presents up to six trophic levels [4]. As a result, when compared to the open ocean, a relative lower fraction of the primary production gets respired in the coastal ocean while a higher fraction reaches the uppermost trophic level (fish) [5] or is exported to adjacent areas (coastal or open sea)..

Inter-annual variations in the SeaWiFS global chlorophyll-a concentration (1997-2007)

The SeaWiFS data set covering the period 1997-2007 is used to develop a framework for a comprehensive description of the inter-annual variations in chlorophyll-a concentration (Chla). For each grid cell, the monthly Chla series is decomposed into seasonal, irregular and trend-cycle terms with the Census X-11 technique that is an iterative band-pass filter algorithm. This approach allows variations in the annual cycle, while the trend-term isolates the multi-annual evolution in the mean level of the signal. The patterns with relatively large inter-annual variations are selected using the variance due to the trend-term with respect to the total variance, and are compared with maps of monotonic trends derived by a non-parametric Kendall analysis. Most of these patterns are identified in the subtropical domain (30S-30N), even though there are patterns with strong variations at mid-latitudes, particularly in the Northeast Atlantic and South of Australia. The time series found within each pattern of interest are found coherent. Conversely, the ensemble of spatially averaged time series of Chla trend-terms shows a diversity of evolutions, with rather monotonic changes for all or part of the period, abrupt shifts or low-frequency oscillations, sometimes coupled with a modification in the amplitude of the annual cycle. Some of these series are correlated with climate indices, and those in subtropical regions usually show a negative correlation with the equivalent trend-term calculated for sea surface temperature. The identified inter-annual signals should be further monitored with longer time series and can serve as test cases for biogeochemical models.JRC.H.5-Land Resources Managemen

Temporal Variability in SeaWiFS Derived Apparent Optical Properties in European Seas

The ten-year record of ocean color data provided by the SeaWiFS mission is an important asset for monitoring and research activities conducted on the optically-complex European seas. This study makes use of the SeaWiFS data set of normalized water leaving radiances LWN to study the major characteristics of temporal variability associated with optical properties across the entire European domain. Specifically, the time series of LWN and associated band ratios are decomposed into terms representing a fixed seasonal cycle, irregular variations and trends, and the contribution of these components to the total variance is described for the various basins. The diversity of the European waters is fully reflected by the range of results varying with regions and wavelengths. Generally, the Mediterranean and Baltic seas appear as two end-members with, respectively, high and low contributions of the seasonal component to the total variance. The existence of linear trends affecting the satellite products is also explored for each basin. By focusing the analysis on LWN and band ratios, the validity of the results is not limited by the varying levels of uncertainty that characterize derived products such as the concentration of chlorophyll a in optically complex waters. Statistically significant, and in some cases large, trends are detected in the Atlantic Ocean west of the European western shelf, the central North Sea, the English Channel, the Black Sea, the northern Adriatic, and various regions of the Mediterranean Sea and the northern Baltic Sea, revealing changes in the concentrations of optically significant constituents in these regions.JRC.H.5-Land Resources Managemen

Temporal Variability of 10-Year Global SeaWiFS Time-Series of Phytoplankton Chlorophyll a Concentration

The SeaWiFS global data set now offers a 10-year time-series of a consistent, well calibrated, ocean colour record suitable for temporal analysis. The relative importance of the seasonal term in the Chla signal is first assessed using statistical techniques of temporal decomposition. The emphasis is on the Census Method II (X-11) approach that allows year-to-year variations of the seasonal component. The seasonality found in the SeaWiFS Chla record is analyzed through a generic province-based classification of marine ecosystems and at global scale, and is found very variable in space. Working with 5¿-resolution gridded Chla products, the contribution of the seasonal component derived from X-11 amounts to 64% of the total variance, as compared to only 36% if a fixed annual cycle is assumed. The capacity of X-11 of capturing the interannual variations in seasonality is used for diagnosing the stability of the Chla seasonal cycle. Finally, linear changes in Chla concentration observed after a decade of continuous ocean colour record are globally in line with previous observations on shorter series. Signigicant changes of both signs are detected in various regions of the world¿s oceans, foremost a general decrease of Chla in the mid-ocean gyres.JRC.H.3-Global environement monitorin

How optically diverse is the coastal ocean?

Coastal regions are a resource for societies while being under severe pressure from a variety of factors. They also show a large diversity of optical characteristics, and the potential to optically classify these waters and distinguish similarities between regions is a fruitful application for satellite ocean color. Recognizing the specificities and complexity of coastal waters in terms of optical properties, a training data set is assembled for coastal regions and marginal seas using full resolution SeaWiFS global remote sensing reflectance RRS data that maximize the geographic coverage and seasonal sampling of the domain. An unsupervised clustering technique is operated on the training data set to derive a set of 16 classes that cover conditions from very turbid to oligotrophic. When applied to a global seven-year SeaWiFS data set, this set of optical water types allows an efficient classification of coastal regions, marginal seas and large inland water bodies. Classes associated with more turbid conditions show relative dominance close to shore and in the mid-latitudes. A geographic partition of the global coastal ocean serves to distinguish general optical similarities between regions. The local optical variability is quantified by the number of classes selected as dominant across the period, averaging 5.2 classes if the cases accounting for 90% of the data days are considered. Optical diversity is more specifically analyzed with a Shannon index computed with the class memberships. Regions with low optical diversity are the most turbid waters as well as closed seas and inland water bodies. Oligotrophic waters also show a relatively low diversity, while intermediate regions between coastal domain and open ocean are associated with the highest diversity, which has interesting connections with ecological features.JRC.H.1-Water Resource

Caractérisation bio-optique des eaux côtières en Manche Orientale pour l'estimation de la production primaire et le suivi des poussées phytoplanctoniques (application à la télédétection satellitaire "couleur de l'eau" en milieu côtier)

CALAIS-BU Sciences (621932101) / SudocSudocFranceF

Phytoplankton Diel and Vertical Variability in Photobiological Responses at a Coastal Station in the Mediterranean Sea

Photophysiological parameters provide useful insights into the effects of environmental forcings on phytoplankton physiology. We present data on the short-term photoacclimative responses of phytoplankton throughout the water column during a diel sampling (every 1.5-3 h for 33 h) at a coastal station in the Gulf of Naples (Italy) in November 1996. Liposoluble pigments (HPLC), variable fluorescence (Prim-Prod probe) and picoplankton cell counts and autofluorescence (flow cytometry) were investigated every 1.5 to 3 h over a period of 33 hours. The phytoplankton was phased to the alternation of light and dark and also showed acclimation to the different light intensities. Photoprotective pigments were synthesized during the day at the surface (0 to 20 m), and were significantly correlated with light intensity changes, as well as with the effective quantum yield of fluorescence. At night, recovery of photosystems from excess light was observed as was redistribution of nutrients and algae due to vertical convective motions caused by thermal dissipation. Equations linking photobiological parameters and time or light evolution were inferred to obtain kinetic coefficients. These were then used as biological tracers of vertical mixing whose velocity in the surface layer was estimated to be <0.05 cm sec-1.JRC.H.3-Global environement monitorin