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Summary Ports are open systems with direct connection to the sea, therefore any potential impact on port waters may have implications for the health of adjacent marine ecosystems. European WFD addressed ports in the category of Heavily Modified Water Bodies (HMWBs) and promoted implementation of protocols to monitor and improve their ecological status. TRIX index, which incorporates the main variables involved in the trophism of marine ecosystems (Nitrogen, Phosphorus, Chlorophyll a, Dissolved Oxygen), is widely utilized in European coastal areas to evaluate trophic status. The relationships between the variables involved in TRIX computation, particularly Chlorophyll a concentration, and water spectral reflectance provides an alternative method to evaluate the quality and ecological status of the port water. Hyperspectral (380–710 nm) water reflectance data were recorded by a portable radiometric system in five ports from the Western and Eastern Mediterranean Basin. The spectral distance between samples was measured by two metrics using both the original and reduced spectra and was implemented within a hierarchical clustering algorithm. The four spectral classes that emerged from this operation were statistically analysed versus standard water quality descriptors and phytoplankton community features to evaluate the ecological significance of the information obtained. The results indicated a substantial coherence of different indicators with more than 60% of the total TRIX variability is accounted for by the proposed classification of reflectance spectra. This classification is therefore proposed as a promising Rapid Assessment Technique of ports water ecological quality, which can serve as an effective monitoring tool for sustainable management of ports.

Recent research has demonstrated that the TRophic IndeX (TRIX) is informative on the ecological quality of Mediterranean port waters and can be estimated by the processing of multispectral observations collected in situ. The current study investigates the alternative use of multispectral data acquired by medium-high spatial resolution optical satellite sensors, i.e. the Landsat-8 (L8) Operational Land Imager (OLI) and the Sentinel-2 (S2) MultiSpectral Instrument (MSI). The study analyzes the impact of the main factors influencing TRIX estimation using datasets collected in several Mediterranean ports and particularly in those of Civitavecchia and Viareggio (Central Italy). The experimental results indicate that the spectral configurations of OLI and MSI have a marginal impact on TRIX estimation, while major effects are caused by the different spatial and temporal features of the two sensors. The enhanced spatial properties of MSI are important particularly in the smaller port of Viareggio; the higher acquisition frequency of this sensor brings significant advantages for operational monitoring applications. Overall, the accuracy of TRIX estimation based on in situ spectral measurements is reduced significantly by the use of OLI images and only marginally by that of MSI images. Both image types represent an advancement for the operational monitoring of port waters.

This study examines the relationships linking methanesulfonic acid (MSA, arising from the atmospheric oxidation of the biogenic dimethylsulfide, DMS) in atmospheric aerosol, satellite-derived chlorophyll a (Chl-a), and oceanic primary production (PP), also as a function of sea ice melting (SIM) and extension of the ice free area in the marginal ice zone (IF-MIZ) in the Arctic. MSA was determined in PM10 samples collected over the period 2010-2012 at two Arctic sites, Ny Ålesund (78.9°N, 11.9°E), Svalbard islands, and Thule Air Base (76.5°N, 68.8°W), Greenland. PP is calculated by means of a bio-optical, physiologically based, semi-analytical model in the potential source areas located in the surrounding oceanic regions (Barents and Greenland Seas for Ny Ålesund, and Baffin Bay for Thule). Chl-a peaks in May in the Barents sea and in the Baffin Bay, and has maxima in June in the Greenland sea; PP follows the same seasonal pattern of Chl-a, although the differences in absolute values of PP in the three seas during the blooms are less marked than for Chl-a. MSA shows a better correlation with PP than with Chl-a, besides, the source intensity (expressed by PP) is able to explain more than 30% of the MSA variability at the two sites; the other factors explaining the MSA variability are taxonomic differences in the phytoplanktonic assemblages, and transport processes from the DMS source areas to the sampling sites. The taxonomic differences are also evident from the slopes of the correlation plots between MSA and PP: similar slopes (in the range 34.2-36.2 ng m-3of MSA/(gC m-2 d-1)) are found for the correlation between MSA at Ny Ålesund and PP in Barents Sea, and between MSA at Thule and PP in the Baffin Bay; conversely, the slope of the correlation between MSA at Ny Ålesund and PP in the Greenland Sea in summer is smaller (16.7 ng m-3of MSA/(gC m-2 d-1)). This is due to the fact that DMS emission from the Barents Sea and Baffin Bay is mainly related to the MIZ diatoms, which are prolific DMS producers, whereas in the Greenland Sea the DMS peak is related to an offshore pelagic bloom where low-DMS producer species are present. The sea ice dynamic plays a key role in determining MSA concentration in the Arctic, and a good correlation between MSA and SIM (slope = 39 ng m-3 of MSA/106 km2 SIM) and between MSA and IF-MIZ (slope = 56 ng m-3 of MSA/106 km2 IF-MIZ) is found for the cases attributable to bloomings of diatoms in the MIZ. Such relationships are calculated by combining the data sets from the two sites and suggest that PP is related to sea ice melting and to the extension of marginal sea ice areas, and that these factors are the main drivers for MSA concentrations at the considered Arctic sites. © 2016 The Authors.

Marine primary production (PP) is a key factor in the regulation of the global carbon cycle, with important potential feedback on climate. Seventy percent of marine PP is generated by phytoplankton photosynthesis. However, the phytoplankton productivity rate is dependent on the photo-physiological state of phytoplankton cells, as well as other environmental conditions. To consider these variables appropriately, refine the current estimates of PP, and reduce the laboursome and lengthy methodologies of radiocarbon estimates, we have created “Phyto-VFP” (Variable Fluorescence Phytoplankton Production), a new bio-optical model classified as a Wavelength and Depth-resolved (WDR) model. The model integrates the effect of the photo-acclimation processes on the “active” fraction of the phytoplankton population with the dynamic of the water column, parametrised through a series of laboratory experiments based on in vivo variable fluorescence measures on the marine diatom Skeletonema costatum (Greville) Cleve. The performance of Phyto-VFP was compared with concurrent estimates of radiocarbon (14C) uptakes, under different dynamic and optical conditions, during two oceanographic cruises (SAMCA3 and SAMCA4) in the Mediterranean Sea. The low Root Mean Square Differences (RMSDs) show that Phyto-VFP performs well when estimating phytoplankton PP. When compared to other bio-optical models, Phyto-VFP estimates of PP in coastal waters were closer to radiocarbon measurements than other models could predict [e.g., the Morel model (MM)]. The application of Phyto-VFP to the SAMCA dataset and its comparison to MM allowed the assessment of model performance under three different physical and biological conditions, in which it was possible to analyse how photo-physiological responses of phytoplankton influence PP.

Three algorithms based on MODIS imagery were evaluated for the estimation of Chlorophyll-a concentration ([CHL]) in the Western Mediterranean Sea. The first algorithm (OC3M) is usually applied at global scale, while the second (MedOC3), has been used in the Mediterranean basin. The third algorithm (SAM_LT), specifically developed for the Ligurian and North Tyrrhenian Seas, is here described and applied, in its updated version. The three algorithms were assessed through comparison with 240 sea [CHL] samples collected during the 2002-2011 decade. The results obtained show that OC3M is the most accurate algorithm when used for the entire Western Mediterranean, but is outperformed by SAM_LT in the area where this was originally developed. The impact of different MODIS quality flags on the three algorithms has been finally evaluated, providing guidelines for their operational application in the study area.

We investigated the composition of diatom communities in annual fast ice and their variations over time during the 1999 austral spring in Terra Nova Bay (Ross Sea, Antarctica). Diatoms varied along the ice core in both cell abundance and species composition, with a minimum in the lower layer and a peak in the platelet ice. Planktonic species constituted in total about 98% of the diatom assemblage in the surface layers of the ice core down to the thickness of 220 cm. In the bottom ice and the underlying platelet-ice layer, the contribution of planktonic diatoms was lower (60% and 65%, respectively) at the beginning of the sampling period, and then decreased further to reach 30% in the bottom ice, where a remarkable biomass increase over time was caused by in situ growth and accumulation of benthic species. By contrast in the platelet-ice layer only small changes were recorded in the composition of the diatom assemblage, which was mainly constituted by the bloom of Fragilariopsis nana. The benthic species are generally not found in the water column, while species in the platelet-ice layer presumably constitute the seed for the initial plankton bloom during the ice-free periods in Terra Nova Bay.

According to recommendations of the international community of phytoplankton functional type algorithm developers, a set of experiments on marine algal cultures was conducted to (1) investigate uncertainties and limits in phytoplankton group discrimination from hyperspectral light absorption properties of assemblages with mixed taxonomic composition, and (2) evaluate the extent to which modifications of the absorption spectral features due to variable light conditions affect the optical discrimination of phytoplankton. Results showed that spectral absorption signatures of multiple species can be extracted from mixed assemblages, even at low relative contributions. Errors in retrieved pigment abundances are, however, influenced by the co-occurrence of species with similar spectral features. Plasticity of absorption spectra due to changes in light conditions weakly affects interspecific differences, with errors

In remote marine areas, biogenic productivity and atmospheric particulate are coupled through dimethylsulfide (DMS) emission by phytoplankton. Once in the atmosphere, the gaseous DMS is oxidized to produce H2SO4 and methanesulfonic acid (MSA), both species can affect the formation of cloud condensation nuclei. This study analyses eight years of biogenic aerosol evolution and variability at two Arctic sites: Thule (76.5&deg, N, 68.8&deg, W) and Ny &Aring, lesund (78.9&deg, N, 11.9&deg, E). Sea ice plays a key role in determining the MSA concentration in polar regions. At the beginning of the melting season, in April, up to June, the biogenic aerosol concentration appears inversely correlated with sea ice extent and area, and positively correlated with the extent of the ice-free area in the marginal ice zone (IF-MIZ). The upper ocean stratification induced by sea ice melting might have a role in these correlations, since the springtime formation of this surface layer regulates the accumulation of phytoplankton and nutrients, allowing the DMS to escape from the sea to the atmosphere. The multiyear analysis reveals a progressive decrease in MSA concentration in May at Thule and an increase in July August at Ny &Aring, lesund. Therefore, while the MSA seasonal evolution is mainly related with the sea ice retreat in April, May, and June, the IF-MIZ extent appears as the main factor affecting the longer-term behavior of MSA.

We investigated the physical conditions of the Spring pack ice environment at Terra Nova Bay to understand their influence on the structure and physiology of sympagic microalgae. Bio-optical methods were used to study the availability and spectral quality of solar radiation, both inside and underneath the ice cover. Pack ice thickness was around 2.5 m, with a temperature between −2 and −7°C. On average, only 1.4% of surface PAR penetrated to the bottom ice and less than 0.6% below platelet ice level. Surface UV-B radiation under the bottom ice was 0.2–0.4%. Biomass concentrations up to 2400 mg Chl a m−3, dominated by two species of diatoms (Entomoneis kjellmannii and Nitschia cf. stellata), showed marked spatial and temporal patterns. Maximum values were in the platelet ice during the first half of November, and in the bottom ice two weeks later. Strong shade adaptation characteristics emerged clearly and explained the relevant abundance of microalgae within the sea ice, with specific absorption coefficients (a*) as low as 0.005 m2 (mg Chl a)−1 and the photo-acclimation index (Ek) in the range of in situ irradiance. The biomass specific production values were low, around 0.12–0.13 mg C mg Chl a−1 h−1. The hypothesis suggesting bottom ice colonization by platelet ice microalgae is supported here.

Upper ocean dynamics is characterized by a strong variability, at different scales, both in direction and structure of the flow. Mesoscale variability, which is ubiquitous in the world ocean, is often the dominant component in the variance spectrum of velocity with relevant implications on water mass mixing and transformation and on the carbon transfer in the marine food web. Mesoscale activity is manifested through the formation of instabilities, meanders and eddies. Eddies generate either a doming of isopycnals (cyclones) or a central depression (anticyclones). This in turn modifies, among the others, nutrient and organism distributions in the photic zone eventually enhancing or depressing photosynthetic activity and other connected biological responses. The mechanism is similar to what has been thoroughly studied for the warm and cold core rings but at different spatial and temporal scales. The enhancement of phytoplankton growth and the modification of photosynthetic parameters has been shown to occur in situ by means of a modulated fluorescence probe. More recently, an attempt to estimate the magnitude of this specific forcing on nutrient fluxes and primary production has also been conducted at different scales by modeling exercises, though with contrasting estimates the relative importance concerns. Because phytoplankton growth takes place when light, nutrients and cells are found at the same place, the increase in primary production favored by mesoscale eddies cannot be easily predicted. The incident light, the seasonality, the life-time of the structure, its intensity etc. can all influence the final yield. In addition, it has still to be determined which component of the community reacts faster and takes advantage of the new nutrients and how efficiently the new carbon is channeled in the food web. For what remote sensing is concerned, the detectability form the space of such structures is certainly dependent on the depth at which the upward distortion of isopycnals takes places. It can be supposed that a change in bio-optical signature of the whole structure could occur because of the 3-D dynamics of the eddy. If this holds true, then color remote sensing coupled with sea level topography and sea surface temperature should be a powerful tool to track such transient structures. The ALT-SYMPLEX program has been designed to better understand the relationship between short living eddies and carbon transfer in the food web. This is based on several experiments aimed to integrate remote sensing data (ocean color and surface topography) and in situ data in order to evaluate the relationship between surface and sub-surface physical dynamics and its relations on chemical and biological aspects in presence of mesoscale features.

International audience; Measurements of in vivo spectral absorption, a(lambda), and fluorescence excitation, F-m(lambda), of phytoplankton were performed in two contrasted situations (oligotrophic and mesotrophic) of the tropical North Atlantic, during October 1991. The vertical and inter-site variability of these properties, and the relative fluorescence yield (F-m/a)(lambda) were investigated, in relation to light conditions and to the pigment and taxonomic composition of the natural populations. The large vertical variations in the chi-specific absorption coefficients (a*) at the oligotrophic site appear to be related to both the decrease of the non-photosynthetic pigment concentration, and the increase of the package effect with depth. At the mesotrophic site, lower a* coefficients are observed, likely originating from the larger average size of the phytoplanktonic organisms, which induces a larger package effect. Both vertical and intersite variation of the chi-specific fluorescence (F-m*) shows opposite trends compared to a*. The variable presence of non-photosynthetic carotenoids (mainly zeaxanthin) is revealed to be the most clearly identifiable source of variation for the relative fluorescence yield, with a drop in the blue-green region. Prochlorococcus, Synechococcus and picoeukaryotes show a strong photoacclimation capacity to low irradiances. In addition there is evidence in the phytoplankton communities for a complementary chromatic adaptation process to the prevailing spectral irradiance conditions at both sites. Copyright (C) 1996 Elsevier Science Ltd

Absorption spectra of laboratory cultures of eight species of phytoplankton were studied. These spectra, normalized per unit of chlorophyll a concentration (specific absorption) show variability in magnitude and spectral form. Specific absorption at 440 nm varied over a factor of three. Spectra of phytoplankton belonging to the same taxonomic group tended to have similar forms. Over 95% of the variability in specific absorption could be explained in terms of changes in cell size, intracellular pigment concentration, and the relative importance of auxiliary pigments. Shape was not an important factor for this sample set. The spectral characteristics of absorption by intact cells of phytoplankton have been the subject of various studies because of their importance in primary production, radiative transfer in seawater, and in passive remote-sensing of phytoplankton. At sufficiently low concentrations, the total absorption coefficient a of a given substance at a given wavelength X can be expressed as a product of a specific absorption coefficient a*c and the concentration of the substance C. That is

The growth rate of a diatom (Chaetoceros protubcram) was followed during transfers from moderate to higher or lower irradianccs (PAR) with differing spectral compositions (“white,” “blue,” and “green” light). Chlorophyll-specific and carbon-specific absorption coefficients of the algae were monitored, allowing changes in the quantum yield for growth (@),) to be assessed. All the parameters appear to be practically unaffected by chromatic conditions, provided that the photosynthetically usable radiation (PUR) is made equal. Diatoms respond to the energy level whatever the color. Nevertheless, due to opposite influences of the modifications in the “package” eflt thereafter it remains low and steady. Conversely the enhanced value observed just after transfer to low irradiance is not maintained beyond 2 or 3 d; after that, a’, is restored practically to its initial value.