References of "Deep-Sea Research Part I, Oceanographic Research Papers"
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See detailEffects of samples conservation on photosynthetic efficiency assessment of phytoplankton using PAM fluorometry
Garrido, Marie ULg; Cecchi, Philippe; Vaquer, André et al

in Deep-Sea Research Part I, Oceanographic Research Papers (2013), 71

Pulse Amplitude Modulated (PAM) fluorometry is now a widely used method for the assessment of phytoplankton fitness, with an increasing popularity in field assessments. It is usually recommended to carry ... [more ▼]

Pulse Amplitude Modulated (PAM) fluorometry is now a widely used method for the assessment of phytoplankton fitness, with an increasing popularity in field assessments. It is usually recommended to carry out measurements swiftly after collection, but the number of samples and analytical procedures needed to obtain valuable datasets sometimes makes immediate analysis impracticable, forcing delays between fluorescence measurements. Conservation conditions of samples before analysis may potentially affect their photosynthetic performances but no formal study documenting such impacts appears available in the literature. The aim of this study was to investigate the effects of storage conditions (temperature, duration) on photosynthetic parameters in different phytoplankton communities (characterized in situ by a BBE fluoroprobe) sampled during summer in different environmental locations in a Mediterranean lagoon (Biguglia lagoon, Corsica, France). PAM-fluorescence parameters were measured after three different conservation durations (2h to 4h, 6h to 8h and 10h to 12h after collection) on samples stored at three different temperatures (15°C, 25°C and 35°C). Results showed that storage at the highest temperature severely impacted photosynthetic parameters, with cumulative effects as storage duration increased. For phytoplankton samples collected in warm or tropical environments, storage at “room temperature” (25°C) only appeared a valid option if measurements have to be carried out strictly within a very short delay. Inversely, cooling the samples (i.e. conservation at 15°C) did not induce significant effects, independently of storage duration. Cooling appeared the best solution when sampling-to-analysis delay goes over a few hours. Long-term storage (>8h) should definitively be avoided. [less ▲]

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See detailBiogeochemistry and carbon mass balance of a coccolithophore bloom in the northern Bay of Biscay (June 2006)
Harlay, Jérôme ULg; Chou, Lei; De Bodt, Caroline et al

in Deep-Sea Research Part I, Oceanographic Research Papers (2011), 58(2), 111-127

Primary production (PP), calcification (CAL), bacterial production (BP) and dark community respiration (DCR) were measured along with a set of various biogeochemical variables, in early June 2006, at ... [more ▼]

Primary production (PP), calcification (CAL), bacterial production (BP) and dark community respiration (DCR) were measured along with a set of various biogeochemical variables, in early June 2006, at several stations at the shelf break of the northern Bay of Biscay. The cruise was carried out after the main spring diatom bloom that, based on the analysis of a time-series of remotely sensed chlorophyll-a (Chl-a), peaked in mid-April. Remotely sensed sea surface temperature (SST) indicated the occurrence of enhanced vertical mixing (due to internal tides) at the continental slope, while adjacent waters on the continental shelf were stratified, as confirmed by vertical profiles of temperature acquired during the cruise. The surface layer of the stratified water masses (on the continental shelf) was depleted of inorganic nutrients. Dissolved silicate (DSi) levels probably did not allow significant diatom development. We hypothesize that mixing at the continental slope allowed the injection of inorganic nutrients that triggered the blooming of mixed phytoplanktonic communities dominated by coccolithophores (Emiliania huxleyi) that were favoured with regards to diatoms due to the low DSi levels. Based on this conceptual frame, we used an indicator of vertical stratification to classify the different sampled stations, and to reconstruct the possible evolution of the bloom from the onset at the continental slope (triggered by vertical mixing) through its development as the water mass was advected on-shelf and stratified. We also established a carbon mass balance at each station by integrating in the photic layer PP, CAL and DCR. This allowed computation at each station of the contribution of PP, CAL and DCR to CO2 fluxes in the photic layer, and how they changed from one station to another along the sequence of bloom development (as traced by the stratification indicator). This also showed a shift from net autotrophy to net heterotrophy as the water mass aged (stratified), and suggested the importance of extracellular production of carbon to sustain the bacterial demand in the photic and aphotic layers. [less ▲]

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See detailAbundance and size distribution of transparent exopolymer particles (TEP) in a coccolithophorid bloom in the northern Bay of Biscay
Harlay, Jérôme ULg; De Bodt, Caroline; Engel, Anja et al

in Deep-Sea Research Part I, Oceanographic Research Papers (2009), 56(8), 1251-1265

The distribution of transparent exopolymer particles (TEP) was investigated during a coccolithophorid bloom in the northern Bay of Biscay (North Atlantic Ocean) in early June 2006. MODIS chlorophyll-a ... [more ▼]

The distribution of transparent exopolymer particles (TEP) was investigated during a coccolithophorid bloom in the northern Bay of Biscay (North Atlantic Ocean) in early June 2006. MODIS chlorophyll-a (Chl-a) and reflectance images before and during the cruise were used to localize areas of important biological activity and high reflectance (HR). TEP profiles along the continental margin, determined using microscopic (TEPmicro) and colorimetric (TEPcolor) methods, showed abundant (6.1 x 10(6)-4.4 x 10(7) L-1) and relatively small (0.5-20 mu m) particles, leading to a low total volume fraction (0.05-2.2 ppm) of TEPmicro and similar vertical profiles of TEPcolor Estimates of carbon content in TEP (TEP-C) derived from the microscopic approach yielded surface concentration of 1.50 mu mol CL-1. The contribution of TEP-C to particulate organic carbon (POC) was estimated to be 12% (molar C ratio) during this survey. Our results suggest that TEP formation is a probable first step to rapid and efficient export of C during declining coccolithophorid blooms. (C) 2009 Elsevier Ltd. All rights reserved. [less ▲]

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See detailModelling the habitat suitability of cetaceans:Example of the sperm whale in the northwestern Mediterranean Sea
Praca, Emilie; Gannier, Alexandre; Das, Krishna ULg et al

in Deep-Sea Research Part I, Oceanographic Research Papers (2009), (56), 648657

Cetaceans are mobile and spend long periods underwater. Because of this, modelling their habitat could be subject to a serious problem of false absence. Furthermore, extensive surveys at sea are time and ... [more ▼]

Cetaceans are mobile and spend long periods underwater. Because of this, modelling their habitat could be subject to a serious problem of false absence. Furthermore, extensive surveys at sea are time and money consuming, and presence–absence data are difficult to apply. This study compares the ability of two presence–absence and two presence-only habitat modelling methods and uses the example of the sperm whale (Physeter macrocephalus) in the northwestern Mediterranean Sea. The data consist of summer visual and acoustical detections of sperm whales, compiled between 1998 and 2005. Habitat maps were computed using topographical and hydrological eco-geographical variables. Four methods were compared: principal component analysis (PCA), ecological niche factor analysis (ENFA), generalized linear model (GLM) and multivariate adaptive regression splines (MARS). The evaluation of the models was achieved by calculating the receiver operating characteristic (ROC) of the models and their respective area under the curve (AUC). Presence–absence methods (GLM, AUC=0.70, and MARS, AUC=0.79) presented better AUC than presence-only methods (PCA, AUC=0.58, and ENFA, AUC=0.66), but this difference was not statistically significant, except between the MARS and the PCA models. The four models showed an influence of both topographical and hydrological factors, but the resulting habitat suitability maps differed. The core habitat on the continental slope was well highlighted by the four models, while GLM and MARS maps also showed a suitable habitat in the offshore waters. Presence–absence methods are therefore recommended for modelling the habitat suitability of cetaceans, as they seem more accurate to highlight complex habitat. However, the use of presence-only techniques, in particular ENFA, could be very useful for a first model of the habitat range or when important surveys at sea are not possible. [less ▲]

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See detailSpace and time distributions of phosphate in the Mediterranean Sea
Karafistan, A.; Martin, J. M.; Rixen, M. et al

in Deep-Sea Research Part I, Oceanographic Research Papers (2002), 49(1), 67-82

Statistical modelling was applied to a large number of historical nutrient data to assess the significance of human perturbations in the Mediterranean Sea. All available phosphate data were grouped into ... [more ▼]

Statistical modelling was applied to a large number of historical nutrient data to assess the significance of human perturbations in the Mediterranean Sea. All available phosphate data were grouped into subsets representative of averaged values of the measured vertical profiles in the surface and deep water layers. In contrast to earlier predictions, the statistical analysis of the phosphate concentrations in a deep water layer does not indicate any particular trend in time for the last 30 years. These data sets were then used as an input to an inverse model and a 3D primitive equation model (PEM). The former redistributes the measured concentrations by means of a variational principle and reconstructs average horizontal space distributions of the phosphate data fields as gridded solutions over the whole area. The spatial and temporal distributions thus obtained are visualised graphically and compared with other existing data, providing the first overall view of phosphate in the whole Mediterranean Sea and revealing an increasing oligotrophy towards the eastern basin. The primitive equation model is then used to assess the variability and upwelling fluxes. (C) 2001 Elsevier Science Ltd. All rights reserved. [less ▲]

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See detailDiagnosis of vertical velocities with the QG Omega equation: a relocation method to obtain pseudo-synoptic data sets
Rixen, Michel; Beckers, Jean-Marie ULg; Allen, J. T.

in Deep-Sea Research Part I, Oceanographic Research Papers (2001), 48(6), 1347-1373

The quantification of vertical motion and vertical fluxes is essential in our ability to predict and tolerate climate change. However, diagnostic estimations might be affected by the errors arising from ... [more ▼]

The quantification of vertical motion and vertical fluxes is essential in our ability to predict and tolerate climate change. However, diagnostic estimations might be affected by the errors arising from the necessary compromise between spatio-temporal resolution and cost of hydrographic surveys. Observations of a numerical ocean model have been made in order to test the accuracy of different sampling strategies and their possible a-posteriori corrections. A simple first-order correction method, computing a pseudo-synoptic data set from a non-synoptic data set and involving a geostrophic relocation of the stations is shown to correct significantly the synopticity error in hydrographic data, derived QG vertical motion and vertical temperature fluxes. Sensitivity analyses also show that the lack of synopticity is more critical than other factors, including the sampling resolution, the level of no-motion and the analysis. (C) 2001 Elsevier Science Ltd. All rights reserved. [less ▲]

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See detailExport production in the Bay of Biscay as estimated from barium - barite in settling material: a comparison with new production
Dehairs, F.; Fagel, Nathalie ULg; Antia, A. et al

in Deep-Sea Research Part I, Oceanographic Research Papers (2000), 47(4), 583-601

We present barium data for sediment traps deployed in a northeast Atlantic margin environment (Bay of Biscay). Fluxes of excess barium were measured with the objective of calculating carbon export ... [more ▼]

We present barium data for sediment traps deployed in a northeast Atlantic margin environment (Bay of Biscay). Fluxes of excess barium were measured with the objective of calculating carbon export production rates from the surface mixed layer and thus contribute to the understanding of organic carbon transport in a margin environment. Therefore, it was necessary to properly understand the different processes that affected the barium fluxes in this margin environment. Seasonal variability of POC/Ba flux ratios and decrease of barium solubilisation in the trap cups with increasing depth in the water column probably indicate that the efficiency of barite formation in the organic micro-environment varies with season and that the process is relatively slow and not yet completed in the upper 600 m of water column. Thus barite presence in biogenic aggregates will significantly depend on water column transit time of these aggregates. Furthermore, it was observed that significant lateral input of excess-Ba can occur, probably associated with residual currents leaving the margin. This advected excess-Ba affected especially the recorded fluxes in the deeper traps (>1000 m) of the outer slope region. We have attempted to correct for this advected excess-Ba component, using Th (reported by others for the same samples) as an indicator of enhanced lateral flux and assigning a characteristic Ba/Th ratio to advected material, Using transfer functions relating excess-Ba flux with export production characteristic of margin areas, observed Ba fluxes indicate an export production between 7 and 18 g C m(-2) yr(-1). Such values are 3-7 times lower than estimates based on N-nutrient uptake and nutrient mass balances, but larger and more realistic than is obtained when a transfer function characteristic of open ocean systems is applied. The discrepancy between export production estimates based on excess-Ba fluxes and nutrient uptake could be resolved if part of the carbon is exported as dissolved organic matter. Results suggest that margin systems function differently from open ocean systems, and therefore Ba-proxy rationales developed for open ocean sites might not be applicable in margin areas. (C) 2000 Elsevier Science Ltd. All rights reserved. [less ▲]

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See detailNutrient utilisation and particulate organic matter changes during summer in the upper mixed layer (Ross Sea, Antarctica).
Catalano, Giulio; Povero, Paolo; Fabiano, Mauro et al

in Deep-Sea Research Part I, Oceanographic Research Papers (1997), 44(1), 97-112

The relationships among vertical stability, estimated nutrient utilisation and particulate organic matter in the Ross Sea are analysed from data collected during two cruises in the summers of 1987 - 88 ... [more ▼]

The relationships among vertical stability, estimated nutrient utilisation and particulate organic matter in the Ross Sea are analysed from data collected during two cruises in the summers of 1987 - 88 and 1989 - 90. In the upper mixed layer (UML), identified through the vertical stability E(Z(UML)), nutrient consumption is calculated as the difference between the « diluted » nutrient value and the mean calculated from the integrated value in the UML. The nutrient utilisation ratio and E(Z(UML)) are linearly related for E(Z(UML)) < 25, whereas for values > 25, the distribution pattern is more scattered and independent of E(Z(UML)). For E(Z(UML)) > 25, utilisation values were > 4, 0.4 and 10 mmol m-3 for nitrate, phosphate and silicate, respectively. Significant relationships between nutrient depletion and both particulate organic carbon (POC) and particulate protein / particulate carbohydrate ratios (PPRT/PCHO) are found. The analysis of particulate matter distribution vs nutrient utilisation shows that the stations could be divided into two groups having different characteristics. The first group includes coastal stations, where high nutrient utilisation, POC and PPRT / PCHO are typical of areas with high production. In the second group (pelagic stations), nutrient utilisation, POC and PPRT / PCHO are lower. The vertical stability can be used to discriminate among the factors that influence primary production. [less ▲]

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See detailSeasonal temperature and salinity fields in the Mediterranean Sea: Climatological analyses of a historical data set
Brasseur, P.; Beckers, Jean-Marie ULg; Brankart, J. M. et al

in Deep-Sea Research Part I, Oceanographic Research Papers (1996), 43(2), 159-192

Climatological analyses of a historical data base have been carried out with the aim of reconstructing the three-dimensional temperature and salinity fields in the Mediterranean Sea. Seasonal and monthly ... [more ▼]

Climatological analyses of a historical data base have been carried out with the aim of reconstructing the three-dimensional temperature and salinity fields in the Mediterranean Sea. Seasonal and monthly distributions of hydrographic properties have been computed by a variational inverse method as an alternate to the standard Gandin (1969; Objective analysis of meterological fields, Israeli Program for Scientific Translation, Jerusalem) procedure. The spline solutions of the minimization problem are demonstrated to be numerically and theoretically equivalent to field estimates obtained by conventional objective analysis. The application of a finite-element technique allows analysis to be performed in the model space rather than in the observational space, which substantially improves the numerical efficiency of the procedure. The parameters of the scheme are adjusted according to the statistics of the climatological data. The results,realized as gridded data sets (horizontal resolution of 0.25 degrees), show some trends in seasonal variability affecting the properties of water masses. As expected, the upper layer is subject to a well-defined seasonal signal affecting both the temperature and salinity fields. Error maps, reflecting the degree of uncertainty in the analyses, have been systematically produced. The present work is conceived as a basic support to more advanced studies such as diagnostic calculations, initialization of dynamical models, assimilation of hydrological data into primitive equation models, or planning of experimental surveys. New versions of the climatological fields will be released as data are added to the historical data base. Copyright (C) 1996 Elsevier Science Ltd. [less ▲]

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