CNRS Laboratory of Ocean Physics

Brest, France

CNRS Laboratory of Ocean Physics

Brest, France
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Prothin S.,Institute Superieure Of Laeronautique Et Of Lespace Isae Toulouse | Djeridi H.,CNRS Laboratory of Ocean Physics | Billard J.-Y.,CNRS Naval Academy Research Institute
Journal of Fluids and Structures | Year: 2014

In this paper, the influence of a single tip vortex on boundary layer detachment is studied. This study offers a preliminary approach in order to better understand the interaction between a propeller hub vortex and the rudder installed in its wake. This configuration belongs to the field of marine propulsion and encompasses such specific problem as cavitation inception, modification of propulsive performances and induced vibrations. To better understand the complex mechanisms due to propeller-rudder interactions it was decided to emphasize configurations where the hub vortex is generated by an elliptical 3-D foil and is located upstream of a 2-D NACA0015 foil at high incidences for a Reynolds number of 5×105. The physical mechanisms were studied using Time Resolved Stereoscopic Particle Image Velocimetry (TR-SPIV) techniques. Particular attention was paid to the detachment at 25° incidence and a detailed cartography of the mean and turbulent properties of the wake is presented. Proper Orthogonal Decomposition (POD) analysis was applied in order to highlight the unsteady nature of the flow using phase averaging based on the first POD coefficients to characterize the turbulent and coherent process in the near wake of the rudder. © 2013 Elsevier Ltd.

Jaramillo J.L.,University of Burgundy | Jaramillo J.L.,CNRS Laboratory of Ocean Physics
Journal of Physics A: Mathematical and Theoretical | Year: 2016

We revisit the discussion of the energetics of quasi-geostrophic flows from a geometric perspective based on the introduction of an effective metric, built in terms of the flow stratification and the Coriolis parameter. In particular, an appropriate notion of normal modes is defined through a spectral geometry problem in the ocean basin (a compact manifold with boundary) for the associated Laplace-Beltrami scalar operator. This spectral problem can be used to systematically encode non-local aspects of stratification and topography. As examples of applications we revisit the isotropy assumption in geostrophic turbulence, identify (a patch of) the hyperbolic space H3 as the leading-order term in the effective geometry for the deep mesoscale ocean and, finally, discuss some diagnostic tools based on a simple statistical mechanics toy-model to be used in numerical simulations and/or observations of quasigeostrophic flows. © 2016 IOP Publishing Ltd.

Vazquez-Rodriguez M.,CSIC - Institute of Marine Research | Perez F.F.,CSIC - Institute of Marine Research | Velo A.,CSIC - Institute of Marine Research | Rios A.F.,CSIC - Institute of Marine Research | Mercier H.,CNRS Laboratory of Ocean Physics
Biogeosciences | Year: 2012

The lack of observational pH data has made it difficult to assess recent rates of ocean acidification, particularly in the high latitudes. Here we present a time series that spans over 27 yr (1981-2008) of high-quality carbon system measurements in the North Atlantic, which comprises fourteen cruises and covers the important water mass formation areas of the Irminger and Iceland Basins. We provide direct quantification of acidification rates in upper and intermediate North Atlantic waters. The highest rates were associated with surface waters and with Labrador Sea Water (LSW). The Subarctic Intermediate and Subpolar Mode Waters (SAIW and SPMW) showed acidification rates of 0.0019 ± 0.0001 and 0.0012 ± 0.0002 yr-1, respectively. The deep convection activity in the North Atlantic Subpolar Gyre injects surface waters loaded with anthropogenic CO2 into lower layers, provoking the remarkable acidification rate observed for LSW in the Iceland Basin (0.0016 ± 0.0002 yr1). An extrapolation of the observed linear acidification trends suggests that the pH of LSW could drop 0.45 units with respect to pre-industrial levels by the time atmospheric CO2 concentrations reach ∼775 ppm. Under circulation conditions and evolution of CO2 emission rates similar to those of the last three decades, by the time atmospheric CO2 reaches 550 ppm, an aragonite undersaturation state could be reached in the cLSW of the Iceland Basin, earlier than surface SPMW. © 2013 Author(s).

Joubert W.R.,South African Council for Scientific and Industrial Research | Joubert W.R.,University of Cape Town | Thomalla S.J.,South African Council for Scientific and Industrial Research | Thomalla S.J.,University of Cape Town | And 6 more authors.
Biogeosciences | Year: 2011

As part of the Bonus-GoodHope (BGH) campaign, 15N-labelled nitrate, ammonium and urea uptake measurements were made along the BGH transect from Cape Town to ∼60°S in late austral summer, 2008. Our results are categorised according to distinct hydrographic regions defined by oceanic fronts and open ocean zones. High regenerated nitrate uptake rate in the oligotrophic Subtropical Zone (STZ) resulted in low f-ratios (f = 0.2) with nitrogen uptake being dominated by ρurea, which contributed up to 70 % of total nitrogen uptake. Size fractionated chlorophyll data showed that the greatest contribution (>50 %) of picophytoplankton (<2 μm) were found in the STZ, consistent with a community based on regenerated production. The Subantarctic Zone (SAZ) showed the greatest total integrated nitrogen uptake (10.3 mmol m -2 d -1), mainly due to enhanced nutrient supply within an anticyclonic eddy observed in this region. A decrease in the contribution of smaller size classes to the phytoplankton community was observed with increasing latitude, concurrent with a decrease in the contribution of regenerated production. Higher f-ratios observed in the SAZ (f = 0.49), Polar Frontal Zone (f= 0.41) and Antarctic Zone (f = 0.45) relative to the STZ (f = 0.24), indicate a higher contribution of NO3-uptake relative to total nitrogen and potentially higher export production. High ambient regenerated nutrient concentrations are indicative of active regeneration processes throughout the transect and ascribed to late summer season sampling. Higher depth integrated uptake rates also correspond with higher surface iron concentrations. No clear correlation was observed between carbon export estimates derived from new production and 234Th flux. In addition, export derived from 15N estimates were 2-20 times greater than those based on 234Th flux. Variability in the magnitude of export is likely due to intrinsically different methods, compounded by differences in integration time scales for the two proxies of carbon export. © Author(s) 2011.

Marchesiello P.,Laboratoire dEtudes en Geophysique et Oceanographie Spatiale LEGOS | Capet X.,CNRS Laboratory of Ocean Physics | Menkes C.,British Petroleum | Kennan S.C.,National Science Foundation
Ocean Modelling | Year: 2011

Submesoscale dynamics in tropical instability waves (TIWs) of the Pacific ocean are analyzed from nested numerical simulations of increasing resolution (36km, 12km, and 4km). It is shown that numerical convergence, as determined by an invariance of the kinetic energy (KE) spectrum with resolution, can be obtained for grid spacing around 10km. This finding contrasts with mid-latitude simulations of submesoscale processes that do not converge even for grid spacing less than 1km. The difference is associated with the larger Rossby radius of deformation at low latitudes due to the weaker Coriolis parameter. For the same reason, the mixed layer Rossby radius is larger as well, resulting in submesoscale mixed layer eddies (MLEs) with scales of 50-200km. Similar to MLEs at mid-latitudes, those eddies that form at TIW fronts restratify the mixed layer by releasing available potential energy. They lead to an additional source of KE at submesoscale that is larger in the finer resolution simulations. At wavelengths smaller than the mesoscale peak of KE injection, a forward cascade of KE is evident in the simulations where three dynamical ranges are observed: a quasi-inertial range of slope k-2, a pre-dissipation range and a far-dissipation range. Numerical dissipation is evaluated and significant dissipation is found to occur in a pre-dissipation range, i.e., for wavenumbers well below the range where the KE spectrum tails off exponentially. © 2011 Elsevier Ltd.

Echevin V.,CNRS LAPLACE Lab | Albert A.,CNRS LAPLACE Lab | Levy M.,CNRS LAPLACE Lab | Graco M.,Instituto del MAR del PEru IMARPE | And 3 more authors.
Continental Shelf Research | Year: 2014

The impact of intraseasonal coastal-trapped waves on the nearshore Peru ecosystem is investigated using observations and a regional eddy-resolving physical-ecosystem coupled model. Model results show that intraseasonal variability over the period 2000-2006 represents about one fourth of the total surface chlorophyll variance and one third of the carbon export variance on the Peruvian shelf. Evidence is presented that subsurface nutrient and chlorophyll intraseasonal variability are mainly forced by the coastally trapped waves triggered by intraseasonal equatorial Kelvin waves reaching the South American coast, and propagate poleward along the Peru shore at a speed close to that of high order coastal trapped waves modes. The currents associated with the coastal waves induce an input of nutrients that triggers a subsequent phytoplankton bloom and carbon export. The impact of the local wind-forced intraseasonal variability on the ecosystem is of a similar order of magnitude to that remotely forced in the northern part of the Peru shelf on [50-90] day time scales and dominates over the entire shelf on [20-30] day time scales. © 2013 Elsevier Ltd.

Chenillat F.,Institut Universitaire de France | Chenillat F.,CNRS Laboratory of Ocean Physics | Riviere P.,Institut Universitaire de France | Capet X.,University Pierre and Marie Curie | And 2 more authors.
PLoS ONE | Year: 2013

The variability of the California Current System (CCS) is primarily driven by variability in regional wind forcing. In particular, the timing of the spring transition, i.e., the onset of upwelling-favorable winds, varies considerably in the CCS with changes in the North Pacific Gyre Oscillation. Using a coupled physical-biogeochemical model, this study examines the sensitivity of the ecosystem functioning in the CCS to a lead or lag in the spring transition. An early spring transition results in an increased vertical nutrient flux at the coast, with the largest ecosystem consequences, both in relative amplitude and persistence, hundreds of kilometers offshore and at the highest trophic level of the modeled food web. A budget analysis reveals that the propagation of the perturbation offshore and up the food web is driven by remineralization and grazing/predation involving both large and small plankton species. © 2013 Chenillat et al.

Arzel O.,CNRS Laboratory of Ocean Physics | England M.H.,University of New South Wales
Climate Dynamics | Year: 2013

The influence of changes in surface wind-stress on the properties (amplitude and period) and domain of existence of thermohaline millennial oscillations is studied by means of a coupled model of intermediate complexity set up in an idealized spherical sector geometry of the Atlantic basin. Using the atmospheric CO2 concentration as the control parameter, bifurcation diagrams of the model are built to show that the influence of wind-stress changes on glacial abrupt variability is threefold. First, millennial-scale oscillations are significantly amplified through wind-feedback-induced changes in both northern sea ice export and oceanic heat transport. Changes in surface wind-stress more than double the amplitude of the strong warming events that punctuate glacial abrupt variability obtained under prescribed winds in the model. Second, the average duration of both stadials and interstadials is significantly lengthened and the temporal structure of observed variability is better captured under interactive winds. Third, the generation of millennial-scale oscillations is shown to occur for significantly colder climates when wind-stress feedback is enabled. This behaviour results from the strengthening of the negative temperature-advection feedback associated with stronger northward oceanic heat transport under interactive winds. © 2012 Springer-Verlag.

Griffies S.M.,National Oceanic and Atmospheric Administration | Treguier A.M.,CNRS Laboratory of Ocean Physics
International Geophysics | Year: 2013

This chapter focuses on numerical models used to understand and predict large-scale circulation, such as the circulation comprising basin and global scales. It is organized according to two themes. The first addresses physical and numerical topics forming a foundation for ocean models. We focus here on the science of ocean models, in which we ask questions about fundamental processes and develop the mathematical equations for ocean thermo-hydrodynamics. We also touch upon various methods used to represent the continuum ocean fluid with a discrete computer model, raising such topics as the finite volume formulation of the ocean equations; the choice for vertical coordinate; the complementary issues related to horizontal gridding; and the pervasive questions of subgrid scale parameterizations. The second theme of this chapter concerns the applications of ocean models, in particular how to design an experiment and how to analyze results. This material forms the basis for ocean modelling, with the aim being to mechanistically describe, interpret, understand, and predict emergent features of the simulated, and ultimately the observed, ocean. © 2013 Elsevier Ltd.

Gonzalez-Davila M.,University of Las Palmas de Gran Canaria | Santana-Casiano J.M.,University of Las Palmas de Gran Canaria | Fine R.A.,University of Miami | Happell J.,University of Miami | And 2 more authors.
Biogeosciences | Year: 2011

Carbonate system variables were measured in the South Atlantic sector of the Southern Ocean along a transect from South Africa to the southern limit of the Antarctic Circumpolar Current (ACC) from February to March 2008. Eddies detached from the retroflection of the Agulhas Current increased the gradients observed along the fronts. Minima in the fugacity of CO2, fCO 2, and maxima in pH on either side of the frontal zone were observed, noting that within the frontal zone fCO2 reached maximum values and pH was at a minimum. Vertical distributions of water masses were described by their carbonate system properties and their relationship to CFC concentrations. Upper Circumpolar Deep Water (UCDW) and Lower Circumpolar Deep Water (LCDW) offered pHT,25 values of 7.56 and 7.61, respectively. The UCDW also had higher concentrations of CFC-12 (>0.2 pmol kg-1) as compared to deeper waters, revealing that UCDW was mixed with recently ventilated waters. Calcite and aragonite saturation states (Ω) were also affected by the presence of these two water masses with high carbonate concentrations. The aragonite saturation horizon was observed at 1000 m in the subtropical area and north of the Subantarctic Front. At the position of the Polar Front, and under the influence of UCDW and LCDW, the aragonite saturation horizon deepened from 800 m to 1500 m at 50.37° S, and reached 700 m south of 57.5° S. High latitudes proved to be the most sensitive areas to predicted anthropogenic carbon increase. Buffer coefficients related to changes in [CO2], [H+] and Ω with changes in dissolved inorganic carbon (CT) and total alkalinity (AT) offered minima values in the Antarctic Intermediate Water and UCDW layers. These coefficients suggest that a small increase in CT will sharply decrease the status of pH and carbonate saturation. Here we present data that suggest that south of 55° S, surface water will be under-saturated with respect to aragonite within the next few decades. © 2011 Author(s).

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