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| Di Lorenzo, E.; Schneider, N.; Cobb, K. M.; Franks, P. J. S.; Chhak, K.; Miller, A. J.; Mcwilliams, J. C.; Bograd, S. J.; Arango, H.; Curchitser, E.; Powell, T. M.; Riviere, Pascal. |
| Decadal fluctuations in salinity, nutrients, chlorophyll, a variety of zooplankton taxa, and fish stocks in the Northeast Pacific are often poorly correlated with the most widely-used index of large- scale climate variability in the region - the Pacific Decadal Oscillation (PDO). We define a new pattern of climate change, the North Pacific Gyre Oscillation (NPGO) and show that its variability is significantly correlated with previously unexplained fluctuations of salinity, nutrients and chlorophyll. Fluctuations in the NPGO are driven by regional and basin-scale variations in wind-driven upwelling and horizontal advection - the fundamental processes controlling salinity and nutrient concentrations. Nutrient fluctuations drive concomitant changes in... |
| Tipo: Text |
Palavras-chave: North Pacific Ocean climate; Salinity and nutrient variability; Upwelling and ecosystems. |
| Ano: 2008 |
URL: https://archimer.ifremer.fr/doc/00483/59492/62351.pdf |
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| Riviere, Pascal; Klein, Patrice. |
| Following some recent linear and nonlinear studies the authors examine, using numerical simulations of a classical two-layer model, the effect of an asymmetric friction on the nonlinear equilibrium of moderately unstable baroclinic systems, The results show that the presence of an asymmetric friction leads to a significant wave scale selection: ''long'' waves (in terms of their zonal wavelengths) emerge with a traditional asymmetric friction (with the upper layer less viscous than the lower layer), while only ''short'' waves dominate with a nontraditional asymmetric friction (with the lower layer less viscous than the upper layer). The role of the nonlinear interactions and. more precisely, the effects of an asymmetric friction on the wave-mean flow and... |
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| Ano: 1997 |
URL: http://archimer.ifremer.fr/doc/00336/44705/44915.pdf |
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| Chenillat, Fanny; Riviere, Pascal; Capet, Xavier; Di Lorenzo, E.; Blanke, Bruno. |
| On interannual and longer time scales, dynamical and biogeochemical fluctuations in the North Pacific are dominated by two modes of variability, namely the Pacific Decadal Oscillation and the North Pacific Gyre Oscillation (NPGO). In this study the regional expression of the NPGO in the California Current System (CCS) is detailed. The statistical relationship between the NPGO index and nearshore wind variability (mostly upwelling favorable) along the U. S. West coast is strongest in the wintertime (December to March) off Central California. Most importantly, NPGO fluctuations are associated with a seasonal shift of 1-2 months in the onset of the upwelling season. Regional numerical simulations show that an early (late) onset of upwelling during the... |
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| Ano: 2012 |
URL: http://archimer.ifremer.fr/doc/00063/17396/15062.pdf |
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| Franks, Peter J. S.; Di Lorenzo, Emanuele; Goebel, Nicole L.; Chenillat, Fanny; Riviere, Pascal; Edward, Christopher A.; Miller, Arthur J.. |
| Understanding the effects of climate change on planktonic ecosystems requires the synthesis of large, diverse data sets of variables that often interact in nonlinear ways. One fruitful approach to this synthesis is the use of numerical models. Here, we describe how models have been used to gain understanding of the physical-biological couplings leading to decadal changes in the southern California Current ecosystem. Moving from basin scales to local scales, we show how atmospheric, physical oceanographic, and biological dynamics interact to create long-term fluctuations in the dynamics of the California Current ecosystem. |
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| Ano: 2013 |
URL: http://archimer.ifremer.fr/doc/00156/26735/24829.pdf |
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| Perruche, Coralie; Riviere, Pascal; Pondaven, Philippe; Carton, Xavier. |
| This paper aims at studying analytically the functioning of a very simple ecosystem model with two phytoplankton species. First, using the dynamical system theory, we determine its nonlinear equilibria, their stability and characteristic timescales with a focus on phytoplankton competition. Particular attention is paid to the model sensitivity to parameter change. Then, the influence of vertical mixing and sinking of detritus on the vertically-distributed ecosystem model is investigated. The analytical results reveal a high diversity of ecosystem structures with fixed points and limit cycles that are mainly sensitive to variations of light intensity and total amount of nitrogen matter. The sensitivity to other parameters such as remineralisation, growth... |
| Tipo: Text |
Palavras-chave: Water mixing; Dynamical system; Phytoplankton; Competition; Ecosystem; Modelling. |
| Ano: 2010 |
URL: http://archimer.ifremer.fr/doc/2009/publication-7334.pdf |
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| Levy, Marina; Ferrari, Raffaele; Franks, Peter J. S.; Martin, Adrian P.; Riviere, Pascal. |
| A common dynamical paradigm is that turbulence in the upper ocean is dominated by three classes of motion: mesoscale geostrophic eddies, internal waves and microscale three-dimensional turbulence. Close to the ocean surface, however, a fourth class of turbulent motion is important: submesoscale frontal dynamics. These have a horizontal scale of O(1-10) km, a vertical scale of O(100) m, and a time scale of O(1) day. Here we review the physical-chemical- biological dynamics of submesoscale features, and discuss strategies for sampling them. Submesoscale fronts arise dynamically through nonlinear instabilities of the mesoscale currents. They are ephemeral, lasting only a few days after they are formed. Strong submesoscale vertical velocities can drive... |
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| Ano: 2012 |
URL: https://archimer.ifremer.fr/doc/00483/59486/62356.pdf |
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| Siegelman, Lia; Roquet, Fabien; Mensah, Vigan; Riviere, Pascal; Pauthenet, Etienne; Picard, Baptiste; Guinet, Christophe. |
| Most available CTD Satellite Relay Data Logger (CTD-SRDL) profiles are heavily compressed before satellite transmission. High-resolution profiles recorded at the sampling frequency of 0.5 Hz are, however, available upon physical retrieval of the logger. Between 2014 and 2018, several loggers deployed on elephant seals in the Southern Ocean have been set in continuous recording mode, capturing both the ascent and descent for over 60 profiles per day during several months, opening new horizons for the physical oceanography community. Taking advantage of a new dataset made of seven such loggers, a postprocessing procedure is proposed and validated to improve the quality of all CTD-SRDL data: that is, both high-resolution profiles and compressed low-resolution... |
| Tipo: Text |
Palavras-chave: Algorithms; Data processing; In situ oceanic observations. |
| Ano: 2019 |
URL: https://archimer.ifremer.fr/doc/00494/60567/64043.pdf |
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| Chenillat, Fanny; Riviere, Pascal; Capet, Xavier; Franks, Peter J. S.; Blanke, Bruno. |
| 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... |
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| Ano: 2013 |
URL: http://archimer.ifremer.fr/doc/00146/25706/24010.pdf |
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