Search

The consequences of global change on the ocean are multiple such as increase in temperature and sea level, stronger storms, deoxygenation, impacts on ecosystems. But the detection of changes and impacts is still difficult because of the diversity and variability of marine environments. While there has been a clear increase in the number of marine and coastal observations, whether by in situ, laboratory or remote sensing measurements, each data is both costly to acquire and unique. The number and variety of data acquisition techniques require efficient methods of improving data availability via interoperable portals, which facilitate data sharing according to FAIR principles for producers and users. ODATIS, the ocean cluster of Data Terra, the French research infrastructure for Earth data, is the entry point to access all the French Ocean observation data (Ocean Data Information and Services ; www.odatis-ocean.fr/en/). The first challenge of ODATIS is to get data producers to share data. To that purpose, ODATIS offers several services to help them define Data Management Plan (DPM), implement the FAIR principles, make data more visible and accessible by being referenced in the ODATIS catalog, and better tracked and cited through a Digital Object Identifier (DOI). ODATIS also offers a service for publishing open scientific data on the sea, through SEANOE (www.seanoe.org) that provides a DOI that can be cited in scientific articles in a reliable and sustainable way. In parallel to the informatic development of the ocean cluster, further communication and training are needed to inform the research community of these new tools. Through technical workshops, Odatis offers data providers practical experience and support in implementing data access, visualization and processing services. Finally, ODATIS relies on scientific consortia in order to promote and develop innovative processing methods and products for remote, airborne, or in situ observations of the ocean and its interfaces (atmosphere, coastline, seafloor) with the other clusters of the RI Data Terra.

A new methodology has been developed in order to improve the description of the spatial and temporal variability of not well-resolved oceanic variables from other well-observed high-resolution oceanic variables. The method is based on the cross-scale inference of information, incorporating the common features of different multifractal high-resolution variables into a coarser one. An exercise of validation of the methodology has been performed based on the outputs of coupled physical-biogeochemical Regional Ocean Modeling System adapted to the eastern boundary upwelling systems at two spatial resolutions. Once the algorithm has been proved to be effective in increasing the spatial resolution of modeled partial pressure of CO2 at the surface ocean (pCO2), we have investigated the capability of our methodology when it is applied to remote sensing data, focusing on the improvement of the temporal description. In this regard, we have inferred daily pCO2 maps at high resolution (4 km, i.e., 1/24°) fusing monthly pCO2 data at low resolution (100 km, i.e., 1°) with the small-scale features contained in daily high-resolution maps of satellite sea surface temperature and Chlorophyll-a. The algorithm has been applied to the South Eastern Atlantic Ocean opening the possibility to obtain an accurate quantification of the CO2 fluxes in relevant coastal regions, such as the eastern boundary upwelling systems. Outputs of our algorithm have been compared with in situ measurements, showing that daily maps inferred from monthly products are in average 6 $\mu $ atm closer to the in situ values than the original coarser monthly maps. Furthermore, values of pCO2 have been improved in points close to the coast with respect to the original input data.

Transient mesoscale oceanic eddies in Eastern Boundary Upwelling Systems are thought to strongly affect key regional scale processes such as ocean heat transport, coastal upwelling and productivity. Understanding how these can be modulated at low-frequency is thus critical to infer their role in the climate system. Here we use 26 years of satellite altimeter data and regional oceanic modeling to investigate the modulation of eddy kinetic energy (EKE) off Peru and Chile by ENSO, the main mode of natural variability in the tropical Pacific. We show that EKE tends to increase during strong Eastern Pacific (EP) El Niño events along the Peruvian coast up to northern Chile and decreases off central Chile, while it is hardly changed during Central Pacific El Niño and La Niña events. However the magnitude of the EKE changes during strong EP El Niño events is not proportional to their strength, with in particular the 1972/1973 El Niño event standing out as an extreme event in terms of EKE increase off Peru reaching an amplitude three times as large as that during the 1997/1998 El Niño event, and the 2015/2016 El Niño having instead a weak impact on EKE. This produces decadal changes in EKE, with a similar pattern than that of strong EP El Niño events, resulting in a significant negative (positive) long-term trend off Peru (central Chile).

In the Gulf of Mexico (GoM), the upper 300 m of the water column contains a mixture of water types derived from water masses from the North Atlantic and the Caribbean Sea, namely Caribbean Surface Water (CSW), Subtropical Underwater (SUW), Gulf Common Water (GCW), and Tropical Atlantic Central Water (TACW). These are mainly altered by mesoscale processes and local evaporation, which modulate biogeochemical cycles. In this study, we improve our understanding of water mass dynamics by including biogeochemical data when evaluating the T-S relationship to define water-mass boundaries, particularly when the observed thermohaline characteristics overlap. The variables considered were apparent oxygen utilization (AOU), nitrate, and dissolved inorganic carbon (DIC). The data were obtained from eight cruises carried out in the central and southern regions of the GoM and an additional cruise that covered the entire coastal-ocean region. The new proposed boundaries were instrumental in clarifying the dynamics of surface waters. Of note, GCW on the western side of the GoM is not formed from the mixing of CSW and SUW but by the mixing of remnant CSW with TACW. In winter, a remnant of CSW mixed with GCW, and the biogeochemical composition of surface waters was affected, as observed from an increase in nitrate and DIC concentrations and positive AOU values. CSW was mainly detected at the surface during summer with negative AOU values, low DIC values, and almost undetectable nitrate concentrations. The presence or absence of CSW modulated the depth of the nitracline and likely influenced primary productivity.

The Bay of Biscay and the English Channel, in the North-eastern Atlantic, are considered as a natural laboratory to explore the coastal dynamics at different spatial and temporal scales. In those regions, the coastal circulation is constrained by a complex topography (e.g. varying width of the continental shelf, canyons), river runoffs, strong tides and a seasonally contrasted wind-driven circulation. Based on different numerical model experiments (from 400m to 4km spatial resolution, from 40 to 100 sigma vertical layers using 3D primitive equation ocean models), different features of the Bay of Biscay and English Channel circulation are assessed and explored. Both spatial (submesoscale and mesoscale) and temporal (from hourly to monthly) scales are considered. Modelled spatial scales, with a specific focus on the variability of fine scale features (e.g. fronts, filaments, eddies), are compared with remotely sensed observations (i.e. Sea Surface Temperature). Different methodologies as singularity and Lyapunov exponents allow describing fine scales features and are applied on both modelled and observed datasets. For temporal scales, in situ high frequency surface temperature measurements from coastal moorings (from COAST-HF observing network) provide a reference for the temporal variability to be modelled. Exploring differences in the temporal scales (from an Empirical Mode Decomposition) advises on the efficiency of our coastal modelling approach. This result overview in the Bay of Biscay and the English Channel aims illustrating the input of coastal modelling activities in understanding multi-scale interactions (spatial and temporal).

The past few decades have seen a marked acceleration in the amount of marine observation data derived using both in situ and remote sensing measurements. For example, high-frequency monitoring of key physical-chemical parameters has become an essential tool for assessing natural and human-induced changes in coastal waters as well as their consequences on society. The number and variety of data acquisition techniques require efficient methods of improving data availability. The challenge is to make ocean data available via interoperable portals, which facilitate data sharing according to Findable, Accessible, Interoperable, and Reusable (FAIR) principles for producers and users. Ocean DAta Information and Services (ODATIS) aims to become a unique gateway to all French marine data, regardless of the discipline (e.g., physics, chemistry, biogeochemistry, biology, sedimentology). ODATIS is the ocean cluster of the Data Terra research infrastructure for Earth data, which relies on a network of data and service centers (DSC) supported by the major French oceanic research organizations (CNRS, CNES, Ifremer, IRD, SHOM; Marine Universities). ODATIS, through its components, is involved in European and international initiatives such as Copernicus, SeaDataCloud, and EMODnet. The first challenge of ODATIS is to catalog all open ocean and coastal data and facilitate data collection and access (discovery, visualization, extraction) through its web portal. A specific task is to develop tools for handling large amounts of data and generate products for policymakers, practitioners, and academics. This study presents the strategy used by ODATIS to implement the FAIR and CoreTrustSeal requirements in each of its DSCs and promote adherence within the scientific community (the main data producer) regarding the upload and/or use of data and suggestion of new products. A second challenge is to cover the end-user needs ranging from proximity to the producer to cross-analysis of data from all Earth compartments. This involves defining and organizing a classification of DSCs in the network, which will be developed within the framework of the French Data Terra research infrastructure, the only framework capable of providing the necessary IT and human resources.

International audience; The frontal activity in coastal regions remains a research field where a large number of open questions needs to be addressed to quantify the potential impact of these processes on dependent systems (e.g.biogeochemical activity). Spatial and seasonal distributions of Sea Surface Temperature (SST) fronts (∼1-100 km) in the vicinity of main French rivers, Gironde and Loire, are explored over the continental shelf North of 45°N in the Bay of Biscay. A highresolution (1km spatial and daily temporal resolutions) dataset of 11 years (2003 to 2013) remotely sensed SST by MODIS sensor onboard Aqua and Terra satellites has been investigated and compared with coastal numerical model experiments. The detection and characterization fronts with fluctuating amplitudes is achieved through the Singularity Analysis (i.e. the process of calculating the degree of regularity or irregularity of a function at each point in a domain). Seasonality of frontal activity in the Bay of Biscay is then described based on the long-term satellite SST archive and coastal operational model simulations. The identifiedhot spots of higher frontal occurrences correspond on one hand to previously observed features (e.g. tidal fronts) but also reveal new features. These are investigated to identify fine-scale dynamical drivers. In winter, density fronts are prominent in a coastal strip where freshwater influence is important. In spring, this strip diminishes as plumes detach from the coast, while tidal fronts become apparent in other regions. In summer, tidal fronts in Ushant region and internal wave activity along the shelf break dominate. In autumn, coastal density fronts due to freshwater inputs reappear as these inputs increase, and reduced stratification causes a weakening of the Ushant and shelf break fronts.Additional information and an effort to dynamically interpret these fronts, based on a systematic investigation of the whole seasonal cycle and including modeling insights from coastal operational oceanography, complement the description of frontal activity in the Bay of Biscay.

In the Gulf of Mexico (GoM) at least three near-surface water masses are affected by mesoscale processes that modulate the biogeochemical cycles. Prior studies have presented different classifications of water masses where the greater emphasis was on deep waters and not on the surface waters (σθ −3), as in this work. Here presents a new classification of water masses in the GoM, based on thermohaline properties and dissolved oxygen (DO) concentration using data from a total of five summer and winter cruises carried out primarily in the central GoM. The reclassification includes an adjustment to the spatial range of Caribbean Surface Water (CSW), which is detected only during the summer. This water mass extends from the surface to ≈ 90 m and features warm waters (27–32 °C), high salinities (up to ≈ 36.8), non-detectable nitrate concentration, and negative values of the apparent oxygen utilization (AOU) of ≈ −27 μmol kg−1. Below the CSW, the deeper Gulf Common Water (GCW) was also redefined and characterized by a subsurface DO maximum, with values ≈ 50 μmol kg−1 higher than that found in surface waters. In winter, a replacement of the CSW by the GCW affected the biogeochemical composition of surface water as observed from an increase in nitrate concentrations, positives values of AOU (≈ 90 μmol kg−1) and a decrease in surface temperatures (Nortes season. CARS2009 analysis supports the formation of the subsurface maximum of DO during the summer and disappears in winter. In this work also named surface water that is characterized by a low salt content (≈ 33.1) from 0 to 20 m as Freshwater Influenced Surface Water (FISW).

The dynamics of the Loop Current (LC) and the detached Loop Current eddies (LCEs) dominate the surface circulation of the Gulf of Mexico (GoM) and transport Caribbean Water (CW) into the gulf. In this work, 25 years (1993–2017) of daily satellite data are used to investigate the variability of these physical processes and their effect on chlorophyll a (Chl a) concentrations from 1998 to 2017, including temporal changes, mean differences, and regional concentration tendencies. The physical variables analyzed are absolute dynamic topography (ADT) and oceanic currents. From the ADT and oceanic current monthly climatologies, it is shown that there is an annual intrusion of CW with an inward incursion that starts in spring, peaks in the summer, reaches to 28∘ N and 90.45∘ W, and then retreats in winter to approximately 26.5 ∘ N and 88.3 ∘ W. Minimum surface Chl a concentrations (−3) are found during the summer–autumn period inside the region of maximum incursion of CW; the opposite is observed during the winter period when Chl a concentrations were at a maximum, e.g., > 0.14 mg m−3. The 3-year running averages of the ADT 40 cm isoline qualitatively reproduce the climatological pattern of 25 years showing that before 2002 CW was less intrusive. This suggests that from 2003 onward, larger volumes of oligotrophic waters from the Caribbean Sea have invaded the western GoM and reduced mean surface Chl a concentrations. A direct comparison between the 1998–2002 and 2009–2014 periods indicates that in the latter time interval, the Chl a concentration above waters deeper than 250 m has decreased significantly.

Wind conditions strongly affect migratory costs and shape flyways and detours for many birds, especially soaring birds. However, whether winds also influence individual variability in migratory choices is an unexplored question. Cory's shearwaters (Calonectris borealis) exhibit migratory flexibility, changing non-breeding destination across the Atlantic Ocean within and between years. Here, we investigated how wind dynamics affect the spatiotemporal migratory behaviour and whether they influence individual choices of non-breeding destination. We analysed 168 GLS tracks of migratory Cory's shearwaters over five years in relation to concurrent wind data. We found no evidence for an association of the use of specific paths or destinations with particular wind conditions. Our results suggest that shearwaters deliberately choose their non-breeding destination, even when the choice entails longer distances and higher energetic costs for displacement due to unfavourable wind conditions en route. Favourable winds trigger migration only when directed towards specific areas but not to others. Despite their dependence on wind for dynamic soaring, Cory's shearwaters show a high individuality in migratory behaviour that cannot be explained by individual birds encountering different meteorological conditions at departure or during migratory movements. Fundação para a Ciência e a Tecnologia (FCT); Marie Curie Intra-European Fellowship; Marie Curie COFUND/Beatriu de Pinós Programme; Instituto das Florestas e da Conservação da Natureza info:eu-repo/semantics/publishedVersion

International audience; Installation of an Ocean Thermal Energy Conversion pilot plant (OTEC) off the Caribbean coast of Martinique is expected to use approximately 100 000 m 3 h-1 of deep seawater for its functioning. This study examined the potential effects of the cold nutrient-rich deep seawater discharge on the phytoplankton community living in the surface warm oligotrophic waters before the installation of the pilot plant. Numerical simulations of deep seawater upwelled by the OTEC, showed that a 3.0 °C temperature change, considered as a critical threshold for temperature impact, was never reached during an annual cycle on the top 150 m of the water column on two considered sections centered on the OTEC. The thermal effect should be limited, less than 1 km 2 on the area exhibited a temperature difference of 0.3 °C (absolute value), producing a negligible thermic impact on the phytoplankton assemblage. The impact on phytoplankton of the resulting mixed deep and surface seawater was evaluated by in situ microcosm experiments. Two scenarios of water mix ratio (2 % and 10 % of deep water) were tested at two incubation depths (deep chlorophyll-a maximum: DCM and bottom of the euphotic layer: BEL). The larger impact was obtained at DCM for the highest deep seawater addition (10 %), with a development of diatoms and haptophytes, whereas 2 % addition induced only a limited change of the phytoplankton community (relatively higher Prochlorococcus sp. abundance, but without significant shift of the assemblage). This study suggested that the OTEC plant would significantly modify the phytoplankton assemblage with a shift from pico-phytoplankton toward micro-phytoplankton only in the case of a discharge affecting the DCM and would be restricted to a local scale. Since the lower impact on the phytoplankton assemblage was obtained at BEL, this depth can be recommended for the discharge of the deep seawater to exploit the OTEC plant

International audience; We evidence and study the differences in turbulence statistics in ocean dynamics carried by wind forcing at the air-sea interface. Surface currents at the air-sea interaction are of crucial importance because they transport heat from low to high latitudes. At first order, oceanic currents are generated by the balance of the Coriolis and pressure gradient forces (geostrophic current) and the balance of the Coriolis and the frictional forces dominated by wind stress (Ekman current) in the surface ocean layers. The study was conducted by computing statistical moments on the shapes of spectra computed within the framework of microcanonical multi-fractal formalism. Remotely sensed daily datasets derived from one year of altimetry and wind data were used in this study, allowing for the computation of two kinds of vector fields: geostrophy with and geostrophy without wind stress forcing. We explore the statistical properties of singularity spectra computed from velocity norms and vorticity data, notably in relation with kurtosis information to underline the differences in the turbulent regimes associated with both kinds of velocity fields.

An accurate quantification of the role of the ocean as source/sink of greenhouse gases (GHGs) requires to access the high-resolution of the GHG air–sea flux at the interface. In this paper we present a novel method to reconstruct maps of surface ocean partial pressure of CO2 ( pCO2) and air–sea CO2 fluxes at super resolution (4 km, i.e., 1/32° at these latitudes) using sea surface temperature (SST) and ocean color (OC) data at this resolution, and CarbonTracker CO2 fluxes data at low resolution (110 km). Inference of super-resolution pCO2 and air–sea CO2 fluxes is performed using novel nonlinear signal processing methodologies that prove efficient in the context of oceanography. The theoretical background comes from the microcanonical multifractal formalism which unlocks the geometrical determination of cascading properties of physical intensive variables. As a consequence, a multi-resolution analysis performed on the signal of the so-called singularity exponents allows for the correct and near optimal cross-scale inference of GHG fluxes, as the inference suits the geometric realization of the cascade. We apply such a methodology to the study offshore of the Benguela area. The inferred representation of oceanic partial pressure of CO2 improves and enhances the description provided by CarbonTracker, capturing the small-scale variability. We examine different combinations of ocean color and sea surface temperature products in order to increase the number of valid points and the quality of the inferred pCO2 field. The methodology is validated using in situ measurements by means of statistical errors. We find that mean absolute and relative errors in the inferred values of pCO2 with respect to in situ measurements are smaller than for CarbonTracker.

Physical processes forced by alongshore winds and currents are known to strongly influence the biogeochemistry of coastal waters. Combining in situ observations (moored platforms, hydrographic surveys) and satellite data (sea surface wind and sea surface height), we investigate the transient occurrence of wind-driven upwelling/downwelling and current-driven upwelling events off southeast Australia. Remote-sensed indices are developed and calibrated with multiannual time series of in situ temperature and current measurements at two shelf locations. Based on archives up to 10 years long, climatological analyses of these indices reveal various latitudinal regimes with respect to seasonality, magnitude, duration of events, and their driving mechanisms (wind or current). Generally, downwelling-favorable winds prevail in this region; however, we demonstrate that up to 10 wind-driven upwelling days per month occur during spring/summer at 28-33.5 degrees S and up to 5 days in summer further south. Current-driven upwelling upstream of the East Australian Current separation zone (approximate to 32 degrees S) occurs twice as often as downstream. Using independent in situ data sets, we show that the response of the coastal ocean is consistent with our climatology of shelf processes: upwelling leads to a large range of temperatures and elevated nutrient concentrations on the shelf, maximized in the wind-driven case, while downwelling results in destratified nutrient-poor waters. The combination of these sporadic wind- and current-driven processes may drive an important part of the high-frequency variability of coastal temperature and nutrient content. Our results suggest that localized nutrient enrichment events of variable magnitude are favored at specific latitudes and seasons, potentially impacting coastal ecosystems. Key Points Multisensor analysis of shelf processes combining in situ and satellite data Spatio-temporal variability of transient wind and current-driven up/downwelling Cold/nutrient-rich water intrusions favoured at specific locations/seasons

The small-scale features in sea surface temperature and salinity fields (SST and SSS) of the Coral Sea are examined using high horizontal spatial and short-term temporal in situ measurements. These features are extracted from thermosalinographs (TSGs) gathered onboard commercial and research vessels and at one long-term fixed station. The analyses are performed along the vessel tracks and the structures of small-scale features are extracted by high-pass spatial filtering the original TSG data. For SSS, it is shown that the features at the scale of mesoscale eddies (approximate to 100 km) vary from about -1.1 to +0.6 psu in the Coral Sea region. Processes sustaining such range include rainfall events, stirring by mesoscale eddies, and the latitudinal displacement of the sharp front associated with the edge of the Western Pacific Warm Pool at the seasonal time scales. The TSG data have revealed the presence of a sharp front (0.4-0.6 psu) between the subtropical and equatorial waters instead of a smooth gradient in the standard SSS climatologies. Within the context of recent remotely sensed observations of salinity, this could represent an important limitation for the validation and calibration of satellite products. In addition to these spatial considerations, temporal variations at one long-term station near Vanuatu show that the coupled air-sea responses to intraseasonal tropical variability, such as the Madden-Julian Oscillation, may have a signature in both SST and SSS fields. However, this response is found to be complex and not necessarily in phase. In the Coral Sea region, our results suggest that MJO-induced variability on SST and SSS exhibit little coherency at the seasonal time scales.

The Eastern Boundary Upwelling Systems (EBUS) contribute to one fifth of the global catches in the ocean. Often associated with Oxygen Minimum Zones (OMZs), EBUS represent key regions for the oceanic nitrogen (N) cycle. Important bioavailable N loss due to denitrification and anammox processes as well as greenhouse gas emissions (e.g, N2O) occur also in these EBUS. However, their dynamics are currently crudely represented in global models. In the climate change context, improving our capability to properly represent these areas is crucial due to anticipated changes in the winds, productivity, and oxygen content. We developed a biogeochemical model (BioEBUS) taking into account the main processes linked with EBUS and associated OMZs. We implemented this model in a 3-D realistic coupled physical/biogeochemical configuration in the Namibian upwelling system (northern Benguela) using the high-resolution hydrodynamic ROMS model. We present here a validation using in situ and satellite data as well as diagnostic metrics and sensitivity analyses of key parameters and N2O parameterizations. The impact of parameter values on the OMZ off Namibia, on N loss, and on N2O concentrations and emissions is detailed. The model realistically reproduces the vertical distribution and seasonal cycle of observed oxygen, nitrate, and chlorophyll a concentrations, and the rates of microbial processes (e.g, NH4+ and NO2− oxidation, NO3− reduction, and anammox) as well. Based on our sensitivity analyses, biogeochemical parameter values associated with organic matter decomposition, vertical sinking, and nitrification play a key role for the low-oxygen water content, N loss, and N2O concentrations in the OMZ. Moreover, the explicit parameterization of both steps of nitrification, ammonium oxidation to nitrate with nitrite as an explicit intermediate, is necessary to improve the representation of microbial activity linked with the OMZ. The simulated minimum oxygen concentrations are driven by the poleward meridional advection of oxygen-depleted waters offshore of a 300 m isobath and by the biogeochemical activity inshore of this isobath, highlighting a spatial shift of dominant processes maintaining the minimum oxygen concentrations off Namibia. In the OMZ off Namibia, the magnitude of N2O outgassing and of N loss is comparable. Anammox contributes to about 20% of total N loss, an estimate lower than currently assumed (up to 50%) for the global ocean.

Surface currents in oceanic environments are of crucial importance because they transport momentum, heat, salt, and tracers over large distances that regulate both the local and large-scale climate conditions, and because they contribute to the Lagrangian displacement of floating material, ranging from living resources to marine pollution. In recent decades, the understanding of surface currents has benefited from the opportunity of observing sea level and wind stress via satellite-derived measurements. Combining these parameters into geostrophic and wind-driven components provides an estimate of surface currents with a quarter-degree horizontal resolution at a global scale and at a daily time scale. In the present study, improvements are made on the consideration of the time dependence of the main parameters implied in the determination of the Ekman wind-driven component, and on the treatment of the equatorial singularity. The resulting Geostrophic and Ekman Current Observatory (GEKCO) estimates were validated with independent observations from both Lagrangian and Eulerian perspectives. The statistics of comparison were significant over the globe for the 2000–2008 period. The only exception was the estimation of meridional current along the equator, which requires further developments of the dynamic model and, probably, more accurate measurements. Applications using our GEKCO surface current estimates in cross-disciplinary approaches from physical oceanography to marine ecology are presented and discussed.

SummaryMarine turtles are renowned long-distance navigators, able to reach remote targets in the oceanic environment; yet the sensory cues and navigational mechanisms they employ remain unclear [1–3]. Recent arena experiments indicated an involvement of magnetic cues in juvenile turtles' homing ability after simulated displacements [4, 5], but the actual role of geomagnetic information in guiding turtles navigating in their natural environment has remained beyond the reach of experimental investigations. In the present experiment, twenty satellite-tracked green turtles (Chelonia mydas) were transported to four open-sea release sites 100-120 km from their nesting beach on Mayotte island in the Mozambique Channel; 13 of them had magnets attached to their head [6] either during the outward journey or during the homing trip. All but one turtle safely returned to Mayotte to complete their egg-laying cycle, albeit with indirect routes, and showed a general inability to take into account the deflecting action of ocean currents as estimated through remote-sensing oceanographic measurements [7]. Magnetically treated turtles displayed a significant lengthening of their homing paths with respect to controls, either when treated during transportation or when treated during homing. These findings represent the first field evidence for the involvement of geomagnetic cues in sea-turtle navigation.

Dissolved oxygen in sea water affects marine habitats and biogeochemical cycles. Oceanic zones with oxygen deficits represent 7% of the volume and 8% of the area of the oceans, and are thought to be expanding. One of the most pronounced lies in the region off Peru, where mesoscale activity in the form of fronts and eddies is strong. Here, we study the dynamics of the Peruvian oxygen minimum zone in a Lagrangian framework, using a coupled physical-biogeochemical numerical model and finite-size Lyapunov exponent fields, to evaluate the role of mesoscale activity. We find that, at depths between 380 and 600 m, mesoscale structures have two distinct roles. First, their mean positions and paths delimit and maintain the oxygen minimum zone boundaries. Second, their high-frequency fluctuations inject oxygen across the oxygen minimum zone boundaries and eddy fluxes are one order of magnitude higher than mean oxygen fluxes. We conclude that these eddy fluxes contribute to the ventilation of the Peruvian oxygen minimum zone., J.H.B., C.L. and E.H.-G. acknowledge support from FEDER and MINECO (Spain) through projects ESCOLA (CTM2012-39025-C02-01) and INTENSE@COSYP (FIS2012-30634). J.H.B. acknowledges financial support of the Portuguese FCT (Foundation for Science and Technology) and Fundo Social Europeu (FSE/QREN/POPH) through the predoctoral grant SFRH/BD/63840/2009. I.M. would like to acknowledge the EUR-OCEANS Consortium for support through a Flagship post-doctoral fellowship on deoxygenation in the oceans.

While our understanding of the early oceanic developmental stage of sea turtles has improved markedly over recent decades, the spatial context for this life history stage remains unknown for Indian Ocean loggerhead turtle populations. To address this gap in our knowledge, 18 juvenile loggerheads were satellite tracked from Reunion Island (21.2A degrees S, 55.3A degrees E) between 2007 and 2011. Nine turtles swam north toward Oman (20.5A degrees N, 58.8A degrees E), where one of the world's largest rookeries of loggerheads is located. Three individuals traveled south toward South Africa and Madagascar, countries that also host loggerhead nesting grounds. Fourteen of the transmitters relayed diving profiles. A dichotomy between diurnal and nocturnal diving behavior was observed with a larger number of shorter dives occurring during the day. Diving behavior also differed according to movement behavior as individuals spent more time in subsurface waters (between 10 and 20 m) during transit phases. The study provides an understanding of the oceanic movement behavior of juvenile loggerheads in the Indian Ocean that suggests the existence of an atypical trans-equatorial developmental cycle for the species at the ocean basin scale in the Indian Ocean. These results address a significant gap in the understanding of loggerhead oceanic movements and may help with the conservation of the species.

A water mass analysis of the Coral Sea thermocline waters provides a description of their distribution, pathways and mixture based on recent oceanographic cruises in this region of strong western boundary currents. The Optimum Multiparameter method is used to determine the relative contribution of core water masses based on their measured temperature, salinity and dissolved oxygen. The thermocline waters, carried by the broad South Equatorial Current (SEC), are essentially composed of four core water masses of different origins. Coming from the south, the South Pacific Tropical Water South (SPTWS, delta = 25.3 kg m−3) and the Western South Pacific Central Water (WSPCW, σ = 26.3 kg m−3) enter the Coral Sea by the channel between the island of New Caledonia and the Vanuatu archipelago. Coming from the north, the South Pacific Tropical Water North (SPTWN, σ = 24.5 kg m−3) and the Pacific Equatorial Water (PEW, σ = 26.3 kg m−3) flow north of Vanuatu. The upper thermocline water that exits the Coral Sea equatorward, is mainly composed of SPTWN carried by the New Guinea Coastal Undercurrent. In contrast, upper thermocline waters exiting the Coral Sea poleward, in the East Australian Current, is dominated by SPTWS. The relative contributions are different in the lower thermocline where WSPCW dominates both western boundary currents. This refined description is consistent with the dynamics of the main currents, with a very strong depth dependence in the partitioning of incoming SEC waters.

International audience; Transmission of information across the scales of a complex signal has some interesting potential, notably in the derivation of sub-pixel information, cross-scale inference and data fusion. It follows the structure of complex signals themselves, when they are considered as acquisitions of complex systems. In this work we contemplate the problem of cross-scale information inference through the determination of appropriate multiscale decomposition. Our goal is to derive a generic methodology that can be applied to propagate information across the scales in a wide variety of complex signals. Consequently, we first focus on the determination of appropriate multiscale characteristics, and we show that singularity exponents computed in microcanonical formulations are much better candidates for the characterization of transitions in complex signals: they outperform the classical "linear filtering" approach of the state-of-the-art edge detectors (for the case of 2D signals). This is a fundamental topic as edges are usually considered as important multiscale features in an image. The comparison is done within the formalism of reconstructible systems. Critical exponents, naturally associated to phase transitions and used in complex systems methods in the framework of criticality are key notions in Statistical Physics that can lead to the complete determination of the geometrical cascade properties in complex signals. We study optimal multiresolution analysis associated to critical exponents through the concept of "optimal wavelet". We demonstrate the usefulness of multiresolution analysis associated to critical exponents in two decisive examples: the reconstruction of perturbated optical phase in Adaptive Optics (AO) and the generation of high resolution ocean dynamics from low resolution altimetry data.

ISI Document Delivery No.: BDG99 Times Cited: 0 Cited Reference Count: 18 Cited References: Bandstra L., 2005, GLOBAL BIOGEOCHEMICA, V19 Butz A, 2009, APPL OPTICS, V48, P3322, DOI 10.1364/AO.48.003322 Butz A, 2011, GEOPHYS RES LETT, V38, DOI 10.1029/2011GL047888 Eriksson K., 1996, COMPUTATIONAL DIFFER Garcon V., 2011, PHYS BIOGEOCHE UNPUB, VXXX Hasekamp OP, 2008, J GEOPHYS RES-ATMOS, V113, DOI 10.1029/2008JD010379 Montes I, 2010, J GEOPHYS RES-OCEANS, V115, DOI 10.1029/2009JC005710 Muzy J.F., 1995, MULTIFRACTALES TURBU Paulmier A, 2008, CONT SHELF RES, V28, P2746, DOI 10.1016/j.csr.2008.09.012 Penven P, 2001, GEOPHYS RES LETT, V28, P1055, DOI 10.1029/2000GL011760 Penven P., 2000, THESIS U BRETAGNE OC Pottier C, 2008, REMOTE SENS ENVIRON, V112, P4242, DOI 10.1016/j.rse.2008.07.010 Veitch J, 2009, PROG OCEANOGR, V83, P296, DOI 10.1016/j.pocean.2009.07.008 Vihharev J., 2012, P IEEE IGARSS 2012 I Wagner T., 2012, OPTIMAL CON IN PRESS Waldron HN, 2009, OCEAN SCI, V5, P711 Yahia H., 2008, J PHYS A, V41 Yahia H, 2010, PATTERN RECOGN, V43, P3591, DOI 10.1016/j.patcog.2010.04.011 Garbe, C. S. Butz, A. Dadou, I. Dewitte, B. Garcon, V. Illig, S. Paulmier, A. Sudre, J. Yahia, H. IGARSS Proceedings Paper IEEE International Geoscience and Remote Sensing Symposium (IGARSS) JUL 22-27, 2012 Munich, GERMANY IEEE, IEEE Geosci & Remote Sensing Soc (GRSS), DLR, ESA 345 E 47TH ST, NEW YORK, NY 10017 USA; The EBUS (Eastern Boundary Upwelling Systems) and OMZs (Oxygen Minimum Zone) contribute very significantly to the gas exchange between the ocean and the atmosphere, notably with respect to the greenhouse gases (hereafter GHG). From in-situ ocean measurements, the uncertainty of the net global ocean-atmosphere CO2 fluxes is between 20 and 30%, and could be much higher in the EBUS-OMZ. Off Peru, very few in-situ data are available presently, which justifies alternative approaches for assessing these fluxes. In this contribution we introduce

International audience; Atmospheric turbulence perturbates to a great extent the optical path of incoming light from outer space thereby limiting the resolution power of capturing devices. One of the most common techniques used in astronomical imaging to compensate for this perturbation is Adaptive Optics (AO). In this paper we explore the potential of Microcanonical Multiscale Formalism (MMF) for the reconstruction of the perturbated wavefront, from the low-resolution acquisition of the turbulent phase by a Hartmann-Shack wavefront sensor used in AO. In fact, turbulent flows, although chaotic in nature, are characterised by scale hierarchy and develop cascade like structures where transfer of energy takes place from one scale to the other. We make use of MMF to infer properties along the scales of the complex signal consisting of optical phase perturbation and perform reconstruction using an appropriate wavelet decomposition associated to the cascading properties of the turbulent flow.

International audience; A high-resolution, full-depth, hydrographic section across Drake Passage with tracers and horizontal velocity measurements was repeated within three weeks in austral summer 2006. In-situ data (temperature, salinity, dissolved-oxygen and horizontal current velocities) are used to determine the location of the fronts and eddies of the Antarctic Circumpolar Current (ACC) inferred by Barré et al. (2011) from 7-day composite dynamic topography maps along the transect. Frontal displacements are about 40 km (2 stations) along the section. Considerable differences in properties between the two sections are observed throughout the whole water column with values as high as 0.2 °C in temperature, 0.01 in salinity, 0.03 kg m-3 in neutral density and 10 μmol kg-1 in dissolved-oxygen concentration found below a depth of 3000 m. Only part of the differences is attributable to frontal or eddy displacements along the section. The other part results from the spatial heterogeneity of water properties upstream the section and the funnelling of the flow due to the topographic constraints of the Shackleton Fracture Zone (SFZ). The considerable short-term differences in water properties in rather large-scale structures that cannot be accounted for by frontal motions along the section call for caution when interpreting differences in hydrographical properties obtained by oceanographic cruises that are years apart in terms of climatic signals.The two sections show efficient ventilation of Antarctic Intermediate Water (AAIW) by Winter Water (WW) in the Yaghan Basin, with an estimated eddy-enhanced subduction rate of over 170 m year-1. The SFZ constitutes a barrier, causing the two Southern ACC Fronts (SACCF) branches to separate by about 400 km and creating sheltered conditions in partial isolation from the ACC, while promoting an active recirculation region in the Ona Basin. This active recirculation, marked by cyclonic eddies carrying cold, fresh and oxygenated water from south of the Southern Boundary of the ACC, causes effective ventilation of the whole Circumpolar Deep Water (CDW) density range. The differences in small-scale structures between the two sections deserve further analyses.

ISI Document Delivery No.: 841NR Times Cited: 2 Cited Reference Count: 40 Cited References: BENHAMOU S, 1994, ANIM BEHAV, V47, P1423, DOI 10.1006/anbe.1994.1189 Benhamou S, 2003, ANIM BEHAV, V65, P729, DOI 10.1006/anbe.2003.2092 Benhamou S, 2003, BEHAV PROCESS, V61, P95, DOI 10.1016/S0376-6357(02)00168-7 Benhamou S., 2010, ENCY BEHAV NEUROCIEN, V2, P497, DOI [10.10161B978-0-08-045396-5.00106-8, DOI 10.1016/B978-0-08-045396-5.00106-8] Benhamou S, 1996, ANIM BEHAV, V52, P201, DOI 10.1006/anbe.1996.0165 Benhamou S, 2003, J THEOR BIOL, V225, P235, DOI 10.1016/S0022-5193(03)00242-X BENHAMOU S, 1992, ANIM BEHAV, V43, P371, DOI 10.1016/S0003-3472(05)80097-1 Benhamou S, 2006, ECOLOGY, V87, P518, DOI 10.1890/05-0495 Benhamou S, 2004, J THEOR BIOL, V229, P209, DOI 10.1016/j.jtbi.2004.03.016 Bingman VP, 2005, ETHOL ECOL EVOL, V17, P295 Bonadonna F, 2005, P ROY SOC B-BIOL SCI, V272, P489, DOI 10.1098/rspb.2004.2984 Bourjea Jerome, 2007, Endangered Species Research, V3, P273, DOI 10.3354/esr00053 Bowen Brian W., 1996, P190 Codling EA, 2008, J R SOC INTERFACE, V5, P813, DOI 10.1098/rsif.2008.0014 Flemming JEM, 2006, ENVIRONMETRICS, V17, P351, DOI 10.1002/env.774 Girard C, 2006, MAR ECOL PROG SER, V322, P281, DOI 10.3354/meps322281 Hays GC, 2010, CONSERV BIOL, V24, P1636, DOI 10.1111/j.1523-1739.2010.01531.x Hays GC, 2001, J EXP BIOL, V204, P4093 Hays GC, 2003, P ROY SOC B-BIOL SCI, V270, pS5, DOI 10.1098/rsbl.2003.0022 Johnsen S, 2008, PHYS TODAY, V61, P29, DOI 10.1063/1.2897947 KENDALL DG, 1974, J ROY STAT SOC B MET, V36, P365 Lohmann KJ, 2008, J EXP MAR BIOL ECOL, V356, P83, DOI 10.1016/j.jembe.2007.12.017 Lohmann KJ, 2008, P NATL ACAD SCI USA, V105, P19096, DOI 10.1073/pnas.0801859105 Luschi P, 2007, CURR BIOL, V17, P126, DOI 10.1016/j.cub.2006.11.062 Luschi P, 2001, BEHAV ECOL SOCIOBIOL, V50, P528, DOI 10.1007/s002650100396 Mancho AM, 2006, COMPUT FLUIDS, V35, P416, DOI 10.1016/j.compfluid.2005.02.003 Maus S, 2007, GEOCHEM GEOPHY GEOSY, V8, DOI 10.1029/2007GC001643 MEYLAN AB, 1990, SCIENCE, V248, P724, DOI 10.1126/science.2333522 NORMAN JA, 1994, MOL ECOL, V3, P363, DOI 10.1111/j.1365-294X.1994.tb00076.x Papi F, 2000, J EXP BIOL, V203, P3435 Rio MH, 2011, J GEOPHYS RES-OCEANS, V116, DOI 10.1029/2010JC006505 Sudre J, 2008, OCEAN DYNAM, V58, P101, DOI 10.1007/s10236-008-0134-9 Thebault E, 2010, SPACE SCI REV, V155, P95, DOI 10.1007/s11214-010-9667-6 Thomas UN., 2008, GEOPHYS MONOGR SER, V177, P17, DOI [DOI 10.1029/177GM04, 10.1029/177GM04] Turiel A, 1998, PHYS REV LETT, V80, P1098, DOI 10.1103/PhysRevLett.80.1098 Turiel A, 2008, J PHYS A-MATH THEOR, V41, DOI 10.1088/1751-8113/41/1/015501 Wallraff HG, 2004, ANIM BEHAV, V67, P189, DOI 10.1016/j.anbehav.2003.06.007 Wiltschko R, 2006, BIOESSAYS, V28, P157, DOI 10.1002/bies.20363 Wyneken J., 2001, NMFSSEFSC470 NOAA Yahia H, 2010, PATTERN RECOGN, V43, P3591, DOI 10.1016/j.patcog.2010.04.011 Benhamou, Simon Sudre, Joel Bourjea, Jerome Ciccione, Stephane De Santis, Angelo Luschi, Paolo Agence nationale de la Recherche [ANR-07-BLAN-0220-01] The work was funded by Agence nationale de la Recherche http://www.agence-nationale-recherche.fr/, Programme ESTVOI (ANR-07-BLAN-0220-01). The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. 2 PUBLIC LIBRARY SCIENCE SAN FRANCISCO PLOS ONE; Background: Laboratory and field experiments have provided evidence that sea turtles use geomagnetic cues to navigate in the open sea. For instance, green turtles (Chelonia mydas) displaced 100 km away from their nesting site were impaired in returning home when carrying a strong magnet glued on the head. However, the actual role of geomagnetic cues remains unclear, since magnetically treated green turtles can perform large scale (> 2000 km) post-nesting migrations no differently from controls. Methodology/Principal Findings: In the present homing experiment, 24 green turtles were displaced 200 km away from their nesting site on an oceanic island, and tracked, for the first time in this type of experiment, with Global Positioning System (GPS), which is able to provide much more frequent and accurate locations than previously used tracking methods. Eight turtles were magnetically treated for 24-48 h on the nesting beach prior to displacement, and another eight turtles had a magnet glued on the head at the release site. The last eight turtles were used as controls. Detailed analyses of water masses-related (i.e., current-corrected) homing paths showed that magnetically treated turtles were able to navigate toward their nesting site as efficiently as controls, but those carrying magnets were significantly impaired once they arrived within 50 km of home. Conclusions/Significance: While green turtles do not seem to need geomagnetic cues to navigate far from the goal, these cues become necessary when turtles get closer to home. As the very last part of the homing trip (within a few kilometers of home) likely depends on non-magnetic cues, our results suggest that magnetic cues play a key role in sea turtle navigation at an intermediate scale by bridging the gap between large and small scale navigational processes, which both appear to depend on non-magnetic cues.

International audience; Adaptive Optics (AO) refers to (servo-control) methods used in astronomical imaging to compensate in real time for the loss of spatial resolution power of the instrument caused by the earth's upper atmosphere turbulence, which produces inhomogeneties of air refractive index and hence modifies in a chaotic manner the optical phase of incoming light from space. In this paper we present the first results of a radically new approach to phase reconstruction in AO based on non linear methods for the processing of complex signals having multiscale properties. We make use of the Microcanonical Multiscale Formalism (herein referred to as MMF) to infer properties along the scales of the complex signal made of the perturbated optical phase, and we perform the reconstruction of the phase using appropriate wavelet decomposition associated to the cascading properties of fully developped turbulence.

As regions of high primary production and being often associated to Oxygen Minimum Zones (OMZs), Eastern Boundary Upwelling Systems (EBUS) represent key regions for the oceanic nitrogen (N) cycle. Indeed, by exporting the Organic Matter (OM) and nutrients produced in the coastal region to the open ocean, EBUS can play an important role in sustaining primary production in subtropical gyres. Losses of fixed inorganic N, through denitrification and anammox processes and through nitrous oxide (N2O) emissions to the atmosphere, take place in oxygen depleted environments such as EBUS, and alleviate the role of these regions as a source of N. In the present study, we developed a 3-D coupled physical/biogeochemical (ROMS/BioBUS) model for investigating the full N budget in the Namibian sub-system of the Benguela Upwelling System (BUS). The different state variables of a climatological experiment have been compared to different data sets (satellite and in situ observations) and show that the model is able to represent this biogeochemical oceanic region. The N transfer is investigated in the Namibian upwelling system using this coupled model, especially in the Walvis Bay area between 22° S and 24° S where the OMZ is well developed (O2 < 0.5 ml O2 l−1). The upwelling process advects 24.2 × 1010 mol N yr−1 of nitrate enriched waters over the first 100 m over the slope and over the continental shelf. The meridional advection by the alongshore Benguela current brings also nutrient-rich waters with 21.1 × 1010 mol N yr−1. 10.5 × 1010 mol N yr−1 of OM are exported outside of the continental shelf (between 0 and 100-m depth). 32.4% and 18.1% of this OM are exported by advection in the form of Dissolved and Particulate Organic Matters (DOM and POM), respectively, however vertical sinking of POM represents the main contributor (49.5%) to OM export outside of the first 100-m depth of the water column on the continental shelf. The continental slope also represents a net N export (11.1 × 1010 mol N yr−1) between 0 and 100-m depth: advection processes export 14.4% of DOM and 1.8% of POM, and vertical sinking of POM contributes to 83.8%. Between 100 and 600-m depth, water column denitrification and anammox constitute a fixed inorganic N loss of 2.2 × 108 mol N yr−1 on the continental shelf and slope, which will not significantly influence the N transfer from the coast to the open ocean. At the bottom, an important quantity of OM is sequestrated in the upper sediments of the Walvis Bay area. 78.8% of POM vertical sinking at 100-m depth is sequestrated on the shelf sediment. Only 14% of POM vertical sinking reaches the sediment on the slope without being remineralized. From our estimation, the Walvis Bay area (0–100 m), can be a substantial N source (28.7 × 1010 mol N yr−1) for the eastern part of the South Atlantic Subtropical Gyre. Assuming the same area for the South Atlantic Subtropical Gyre as the North Atlantic Subtropical Gyre, this estimation is equivalent to 3.7 × 10−2 mol N m−2 yr−1 for the Walvis Bay area, and 0.38 mol N m−2 yr−1 by extrapolating for the entire Benguela upwelling system. This last estimation is of the same order as other possible N sources sustaining primary production in the subtropical gyres. The continental shelf off Walvis Bay area does not represent more than 1.2% of the world's major eastern boundary regions and 0.006% of the global ocean, its estimated N2O emission (2.9 × 108 mol N2O yr−1), using a parameterization based on oxygen consumption, contributes to 4% of the emissions in the eastern boundary regions, and represents 0.2% of global ocean N2O emission. Hence, even if the Walvis Bay area is a small domain, its N2O emissions have to be taken into account in the atmospheric N2O budget.

International audience; Short-term variations of deep water masses in Drake Passage revealed by a multiparametric analysis of the ANT-XXIII/3 bottle data J. Sudre, V. Garçon, C. Provost, N. Sennechael, O. Huhn, and M. Lacombe, doi:10.1016/j.dsr2.2011.01.005 A multiparametric analysis is applied on the ANT-XXIII/3 bottle data to determine the spreading and mixing of water masses across Drake Passage during January-February 2006, focusing our interest on the flow of the deep water masses. Mixing proportions are quantified along both the southward and northward journeys between the tip of South America and the Antarctic Peninsula. The method is sensitive enough to detect a marked variability in the flow pathways of the Circumpolar Deep Water, the Southeast Pacific Deep Water (SPDW) and the Weddell Sea Deep Water at the intersection of the Shackleton Fracture Zone (SFZ) and the West Scotia Ridge (WSR) between the southward and northward journeys. Indeed the presence of a sharp meander of the Southern branch of the Polar Front (PFS) together with the displacement of the northern branch of the Southern Antarctic Circumpolar Current Front (SACCFN) above the complex bathymetric structure of the WSR induced a strong perturbation in the deep flow field during the southward journey. The height of the SFZ crests clearly sets the lower limit of the SPDW in the Ona Basin. An enhanced δ3He signature is confined to the north of the Polar Front between 55.5°S and 56.5°S in the 1500-2200 m depth range. It clearly indicates the signature of the core of the Southeast Pacific Deep Slope Water. The entry pathway in the ACC of the SPDSW during ANT-XXIII/3 was farther to the south off the continental slope of South America, than it was during the WOCE A21 expedition in 1990, probably due to the sharp changes in the slope orientation at the extreme tip of the South America.

Motion analysis of complex signals is a particularly important and difficult topic, as classical Computer Vision and Image Processing methodologies, either based on some extended conservation hypothesis or regularity conditions, may show their inherent limitations. An important example of such signals are those coming from the remote sensing of the oceans. In those signals, the inherent complexities of the acquired phenomenon (a fluid in the regime of fully developed turbulence-FDT) are made even more fraught through the alterations coming from the acquisition process (sun glint, haze, missing data etc.). The importance of understanding and computing vector fields associated to motion in the oceans or in the atmosphere (e.g.: cloud motion) raises some fundamental questions and the need for derivating motion analysis and understanding algorithms that match the physical characteristics of the acquired signals. Among these questions, one of the most fundamental is to understand what classical methodologies (e.g.: such as the various implementations of the optical flow) are missing, and how their drawbacks can be mitigated. In this paper, we show that the fundamental problem of motion evaluation in complex and turbulent acquisitions can be tackled using new multiscale characterizations of transition fronts. The use of appropriate paradigms coming from Statistical Physics can be combined with some specific Signal Processing evaluation of the microcanonical cascade associated to turbulence. This leads to radically new methods for computing motion fields in these signals. These methods are first assessed on the results of a 3D oceanic circulation model, and then applied on real data.

International audience; The analysis of satellite-based ocean color data shows that low concentrations of surface chlorophyll-a (chl-a) found in the equatorial region of the Pacific Ocean varies in phase with the eastern edge of the warm pool. As is true for high sea surface temperatures, the existence and maintenance of these low concentrations are linked to the upper ocean stratification due to salinity. The present study also establishes the quasi permanence of a frontal zone in chlorophyll-a separating the regimes of the western region and the eastern-central cold tongue and, through the identification of this front in satellite-based ocean color data, it provides, for the first time, a reliable method for locating the eastern edge of the warm pool from surface observations only. Finally, the recognition of this front offers the opportunity to define a simple and robust index of the horizontal extension of the equatorial Pacific warm pool within the context of the ENSO variability.

12 pages, 4 figures.-- Published by Copernicus Publications on behalf of the European Geosciences Union and the American Geophysical Union., Eastern Boundary Upwelling Systems (EBUS) are characterized by a high productivity of plankton associated with large commercial fisheries, thus playing key biological and socio-economical roles. Since they are populated by several physical oceanic structures such as filaments and eddies, which interact with the biological processes, it is a major challenge to study this sub- and mesoscale activity in connection with the chlorophyll distribution. The aim of this work is to make a comparative study of these four upwelling systems focussing on their surface stirring, using the Finite Size Lyapunov Exponents (FSLEs), and their biological activity, based on satellite data. First, the spatial distribution of horizontal mixing is analysed from time averages and from probability density functions of FSLEs, which allow us to divide each areas in two different subsystems. Then we studied the temporal variability of surface stirring focussing on the annual and seasonal cycle. We also proposed a ranking of the four EBUS based on the averaged mixing intensity. When investigating the links with chlorophyll concentration, the previous subsystems reveal distinct biological signatures. There is a global negative correlation between surface horizontal mixing and chlorophyll standing stocks over the four areas. To try to better understand this inverse relationship, we consider the vertical dimension by looking at the Ekman-transport and vertical velocities. We suggest the possibility of a changing response of the phytoplankton to sub/mesoscale turbulence, from a negative effect in the very productive coastal areas to a positive one in the open ocean. This study provides new insights for the understanding of the variable biological productivity in the ocean, which results from both dynamics of the marine ecosystem and of the 3-D turbulent medium., V. R. is supported by a PhD grant from Direction Générale de l’Armement. V. G. and J. S. acknowledge funding support from CNES and C. L. and E. H.-G. from PIF project OCEANTECH of the Spanish CSIC and FISICOS (FIS2007-60327) of MEC and FEDER.

6 pages, 4 figures, 1 table.-- PDF ArXiv pre-print: http://arxiv.org/abs/0904.1959, Meso- and submesoscales (fronts, eddies, filaments) in surface ocean flow have a crucial influence on marine ecosystems. Their dynamics partly control the foraging behaviour and the displacement of marine top predators (tuna, birds, turtles, and cetaceans). In this work we focus on the role of submesoscale structures in the Mozambique Channel on the distribution of a marine predator, the Great Frigatebird. Using a newly developed dynamical concept, namely the Finite-Size Lyapunov Exponent (FSLE), we have identified Lagrangian coherent structures (LCSs) present in the surface flow in the Channel over a 2-month observation period (August and September 2003). By comparing seabird satellite positions with LCSs locations, we demonstrate that frigatebirds track precisely these structures in the Mozambique Channel, providing the first evidence that a top predator is able to track these FSLE ridges to locate food patches. After comparing bird positions during long and short trips, and different parts of these trips, we propose several hypotheses to understand how frigatebirds can follow these LCSs. The birds might use visual and/or olfactory cues and/or atmospheric current changes over the structures to move along these biological corridors. The birds being often associated to tuna schools around foraging areas, a thorough comprehension of their foraging behaviour and movement during the breeding season is crucial not only to seabird ecology but also to an appropriate ecosystemic approach of fisheries in the channel., A Ph.D. fellowship for E.T.K was provided by the InstitutdeRecherche pour le Développement and the University Pierre and Marie Curie. Ph.D. financial support for V.R was provided by the Direction Ge´ne´ rale de l’Armement. The Laboratoire d’Etudes en Géophysique et Océanographie Spatiale contribution is supported by Centre National d’Etudes Spatiales funding. The Instituto de Física Interdisciplinar y Sistemas Complejos contribution is supported by Ministerio de Ciencia e Innovación and le Fonds Européen de Développement Régional through project FISICOS (FIS2007–60327), and by Consejo Superior de Investigaciones Cientificas through the Intramural Frontier Projects OCEANTECH. H.W.’s contribution was supported by the REMIGE project funded by Agence Nationale de la Recherche (ANR 2005 Biodiv-011).

A global 1/4° resolution product of surface currents has been developed by the Centre de Topographie des Oceans et de l’Hydrosphere. The surface current is calculated from a combination of Ekman currents derived from wind estimates from QuikSCAT satellite, geostrophic current anomalies derived from altimetry, and a mean geostrophic current derived from climatology. In the equatorial band, the currents are adjusted following the methodology proposed by Lagerloef et al. (J Geophys Res, 104(C10):22313–22326, 1999). These satellite-derived currents have been compared to different types of in situ current observations. A global validation is performed using Lagrangian surface drifting buoys and acoustic Doppler current profiler current observations along ship tracks. The comparison shows a very good agreement in the subtropical and mid-latitude bands. The correlation between the satellite-derived currents and the drifter currents in zonal mean bands is around 0.7 for most of the world oceans, both for the zonal and the meridional components. This correlation rises up to 0.8 in the regions of strong boundary currents. In the equatorial band, the correlation with the surface drifting buoys is reduced. A direct comparison with the TOGA/TAO moored current meter data at the equator shows that the low frequency currents are captured by the satellite current product, but there is a substantial high-frequency signal (

5 pages, 3 figures. We present a comparative study of the horizontal mixing properties, from satellite derived data of the surface velocity field, of the two eastern boundary Canary and Benguela upwelling systems, based on a Finite Size Lyapunov Exponents analysis. Each area can be subdivided into two subsystems attending to their mixing activity values. These coincide nicely with distinct biological signatures. When investigating links with chlorophyll as a proxy for biological activity in these two upwelling systems, results show that surface horizontal stirring and mixing vary inversely with chlorophyll standing stocks. Ekman-transport induced upwelling exhibits a positive correlation with chlorophyll. These two findings are complementary since spatial structure in plankton distributions results from both dynamics of the 3D turbulent medium and of the marine ecosystem. V.R. and C.L. were awarded a EUROCEANS Network of Excellence grant. V.R. is supported by a Ph.D. grant from DGA. V.G. acknowledges funding support from CNES, and C.L. and E.H-G. acknowledge funding support from PIF project OCEANTECH of the Spanish CSIC and FISICOS of MEC and FEDER.