Users Guide for LATEXtools

Users GuideThis guide presents the LATEXtools package of Matlab routines, designed for planning and performing oceanographic cruises with a Lagrangian sampling strategy

Impacts of meso-to submeso-scale features on the ocean circulation in the Coral Sea

International audienceAs part of the South Pacific subtropical gyre, the encounter of the South Equatorial Current (SEC)with the complex bottom topography and numerous islands of the southwest tropical Pacific resultsinto a series of zonal jets, flowing mainly westward off the tip of archipelagos. Moreover, themesoscale activity at basin scale is dominated by westward-propagating nonlinear eddies, with astrong impact on the ocean circulation, the mixing of water masses and tracers' distribution. Eddy-jet interactions are studied here with the data collected in September 2012 during theBIFURCATION cruise in the Coral Sea, under the auspices of SPICE (Southwest PacIfic OceanCirculation and Climate Experiment). We analyze and explain in situ data with the help of satellite-based remote sensing data (altimetry, SSS, SST, ocean color), and we estimate the mass transportbudget within the Coral Sea. We show that the mesoscale activity is a significant contributor to the0-600m transport estimates (5-10 Sv) and is essential for the interpretation of hydrologicalobservations. A specific mesoscale eddy is identified as responsible for the connection between theNorth Vanuatu Jet (NVJ) and the North Caledonian Jet (NCJ). By using a Lagrangian technique, weare able to confirm the long-term connection between the NVJ and the NCJ through mesoscaleactivity. At a smaller scale, our analysis shows that surface temperature and salinity gradients can beassociated with hydrodynamical submesoscale features depicted by Finite Size LyapunovExponents (FSLE). These structures can also be linked to the presence of diazotroph species, incontrast with the general oligotrophy of the area. This study offers interesting outlooks for the useof FSLE to study the distribution of biogeochemical elements

Study of (sub)mesoscale circulations and their influences on the spatial distribution of biogeochemical/biological elements with coupled physical and biogeochemical in situ and satellite observations

Les structures de (sous)mésoéchelle (tourbillons, filaments ou fronts) sont des composantes majeures de la circulation océanique et dirigent la distribution des éléments chimiques et biologiques dans l'océan. Cependant, encore peu d'observations attestent de cette influence. L'objectif de cette thèse est de regrouper divers jeux de données in situ, acquis aux échelles typiques de la (sous)mésoéchelle et de coupler ces informations à des observations satellites haute-résolution et des sorties de modèles numériques pour identifier et mieux comprendre l'influence de la circulation fine échelle sur la distribution spatiale des éléments. Dans un premier temps, une étude globale de la circulation océanique de surface dans le Pacifique Sud-Ouest permet de donner un aperçu de l'importance des circulations de chaque échelle (de la grande à la petite échelle) sur la distribution horizontale des éléments biogéochimiques dans cette région. Dans un second temps, l'influence de la mésoéchelle dans deux régions (mer de Corail et zone autour de 170°O et 19°S) mises en avant par la première étude pour leurs caractéristiques hydrodynamiques et biogéochimiques, est inspectée. Deux cas d'études montrent respectivement que les tourbillons océaniques, en particulier les anticyclones, sont responsables du transport et de l'échange de masses d'eau entre deux courants indépendants et que la circulation à mésoéchelle est une des sources de la formation d'un bloom phytoplanctonique. Enfin, deux autres études témoignent de l'influence des fronts et des vitesses verticales à sousmésoéchelle sur la distribution horizontale et vertical de matière et sur la structure des communautés phytoplanctoniques.Meso- and submesoscale features (eddies, filaments, fronts) are key components of the oceanic circulation and drive the distribution of chemical and biological elements in the ocean. However, very few in situ observations confirm this influence. The aim of this PhD thesis is to use various in situ datasets, achieved at (sub)mesoscale, coupled with high-resolution satellite observations and modelled outputs to identify and better understand the impact of fine scale circulations on the spatial distribution of biogeochemical matter. Firstly, a global study of the entire southwest Pacific surface circulation provides an overview of the significance of each scale (from large to submesoscale) circulations on the horizontal distribution of biogeochemical components in this region. Secondly, the influence of mesoscale activity is inspected in two regions (Coral Sea and the region around 170°W and 19°S) highlighted by the previous study for their hydrodynamical and biogeochemical characteristics. Two cases study show, respectively, that eddies, and in particular anticyclones, are able to transport water masses between two independant jets and that mesoscale trajectories of surface water masses are responsible for a phytoplanktonic bloom formation. Finally, two other studies highlight the influence of submesoscale fronts and vertical velocities on the horizontal and vertical distribution of biogeochemical matter and on the phytoplanktonic community structure

Routes of the Upper Branch of the Atlantic Meridional Overturning Circulation according to an Ocean State Estimate.

The origins of the upper branch of the Atlantic meridional overturning circulation (AMOC) are traced with backward-in-time Lagrangian trajectories, quantifying the partition of volume transport between different routes of entry from the Indo-Pacific into the Atlantic. Particles are advected by the velocity field from a recent release of "Estimating the Circulation and Climate of the Ocean" (ECCOv4). This global time-variable velocity field is a dynamically consistent interpolation of over 1 billion oceanographic observations collected between 1992 and 2015. Of the 13.6 Sverdrups (1 Sv = 106 m3/s) flowing northward across 6°S, 15% enters the Atlantic from Drake Passage, 35% enters from the straits between Asia and Australia (Indonesian Throughflow), and 49% comes from the region south of Australia (Tasman Leakage). Because of blending in the Agulhas region, water mass properties in the South Atlantic are not a good indicator of origin

Observed surface thermohaline variability at mesoscale to submesoscale in the Coral Sea, southwest Pacific Ocean.

International audienceSeveral theoretical and numerical studies have recently pointed out thecrucial role of small oceanic structures, with typical scales of 50 km orless, on the ocean eddies (100-300 km), which are associated with themost important part of the total ocean kinetic energy. Indeed, the oceanicflow is driven by nonlinear scale interactions that transfer energy upscale(to the large-scale circulation up to 1,000 km) or downscale (typically lessthan 1m). Knowledge about all these scales is required to explain thedispersion and diffusion of tracers such as sea surface salinity (SSS). Italso echoes the importance of knowing such scales for the calibration andvalidation of the ongoing Aquarius and SMOS satellite missions. In thepresent study, the small-scale features in SSS are examined using in situobservations collected from a thermosalinograph (TSG) during theBifurcation cruise (Sept. 2012) operated in the southwest Pacific Oceanunder the auspices of the SPICE project. The TSG data are replaced in thecontext of the mesoscale eddies and submesoscale ocean dynamics usinga front detection approach based on a Lagrangian technique thatdetermines the Finite-Size Lyapunov Exponents (FSLE). Several examplesof interactions between mesoscale eddies and submesoscale or frontalstructures in SSS will be considered to characterize the stirring and thedispersion of Lagrangian coherent structures. Estimates of the satelliteproducts, as well as considering the biogeochemistry of the surface oceanin the region, will be also presented and discussed

A Lagrangian Estimate of the Mediterranean Outflow's Origin

International audienceThe origin of the Mediterranean Outflow is investigated by deploying six millions virtual Lagrangian parcels at the Strait of Gibraltar, and tracing them backward in time using velocity estimates from an eddy-permitting reanalysis. The Lagrangian parcels are followed until they intercept one of three sections. The hypothesis is that each section is associated with distinct water masses: the Gulf of Lions, related to Western Mediterranean Deep Water and Western Intermediate Water, carries 86% of the Outflow's transport; the Northern Tyrrhenian, related to Tyrrhenian Deep and Intermediate Waters, carries 1% of the transport; the Strait of Sicily, related to Levantine Intermediate Waters, carries 13% of the transport. The median transit times from the sections to the Strait of Gibraltar range from 5 years (Gulf of Lions) to 8 years (Strait of Sicily)

The fate of a southwest Pacific bloom: gauging the impact of submesoscale vs. mesoscale circulation on biological gradients in the subtropics

The temporal evolution of a surface chlorophyll a bloom sampled in the western tropical South Pacific during the 2015 Oligotrophy to UlTra-oligotrophy PACific Experiment (OUTPACE) cruise is examined. This region is usually characterized by largely oligotrophic conditions, i.e. low concentrations of inorganic nutrients at the surface and deep chlorophyll a maxima. Therefore, the presence of a surface bloom represents a significant perturbation from the mean ecological state. Combining in situ and remote sensing datasets, we characterize both the bloom's biogeochemical properties and the physical circulation responsible for structuring it. Biogeochemical observations of the bloom document the bloom itself, a subsequent decrease of surface chlorophyll a, significantly reduced surface phosphate concentrations relative to subtropical gyre water farther east, and a physical decoupling of chlorophyll a from a deep nitracline. All these characteristics are consistent with nitrogen fixation occurring within the bloom. The physical data suggest surface mesoscale circulation is the primary mechanism driving the bloom's advection, whereas balanced motions expected at submesoscales provide little contribution to observed flow. Together, the data provide a narrative where subtropical gyre water can produce significant chlorophyll a concentrations at the surface that is stirred, deformed, and transported great distances by the mesoscale circulation. In this case, for the time period considered, the transport is in an easterly direction, contrary to both the large-scale and mean mesoscale flow. As a result, future studies concerning surface production in the region need to take into account the role complex mesoscale structures play in redistributing subtropical gyre water

Characterization of the mesoscale circulation during the OUTPACE cruise (Southwest Pacific)

International audienceThe circulation within the Southwest Pacific Ocean is today well established from a climatological point of view. The northern branch of the anticyclonic South Pacific gyre creates the South Equatorial current, a major westward current controlling the circulation in the Southwest Pacific. The complex topography as well as the barotropic instabilites cause intense mesoscale activity that is well observed with satellites but strongly undersampled with in situ observations. The ocean dynamics at mesoscale can have an important impact on the ecosystem of this oligotrophic region, and in particular on the development of species involved in the biological carbon pump. We use the in situ dataset of the OUTPACE cruise (ADCP, TSG, SVP data) coupled with specifically designed high resolution (1 / 8°) regional altimetric products produced by CLS (with support from CNES) to characterize the overall mesoscale conditions during the cruise. A preliminary comparison show that the higher resolution product summing Absolute Geostrophic currents and Ekman currents is in good agreement with in situ data. Lagrangian numerical experiments performed with this altimetric product allow us to identify the general surface circulation but also the regional origins and fates of water masses sampled during the cruise and in particular at local scale during the 3 Long-Duration stations. Our results show contrasting mesoscale regimes where simple recirculation in the gyre gives way to more complex, yet still generally westward flowing, currents

From large to submesoscale circulation during the OUTPACE cruise (Southwest Pacific)

International audienceThe circulation within the Southwest Pacific Ocean is today well established from a climatological point of view. The northern branch of the anticyclonic South Pacific gyre creates the South Equatorial current, a major westward current controlling the circulation in the Southwest Pacific. The complex topography as well as the barotropic instabilites cause intense mesoscale activity that is well observed with satellites but strongly undersampled with in situ observations. The ocean dynamics at mesoscale can have an important impact on the ecosystem of this oligotrophic region, and in particular on the development of species involved in the biological carbon pump. We use the in situ dataset of the OUTPACE cruise (ADCP, TSG, SVP data) to validate satellite data (altimetry, Sea Surface Temperature, Chlorophyll-a concentration) that allow to characterize the overall conditions during the cruise. In particular we used specifically designed high resolution (1/8) regional altimetric product (summing Absolute Geostrophic currents and Ekman currents) produced by CLS (with support from CNES) to study the circulation at different scale : large, mesoscale and submesoscale. Lagrangian numerical experiments performed with this altimetric product allow us to identify the general surface circulation. Mesoscale activity is examined through structure identification to determine its influence on the water masses encountered during the cruise. Finally the computation of Finite Size Lyapunov Exponents (FSLE), a Lagrangian diagnostic that identify frontal areas, allow to quantify the impact of these structure on the surface distribution of biogeochemistry quantities (temperature, salinity, chlorophyll..). Our results show that despite the strong mesoscale activity in this area, the meso- and submesoscale structures had a small, but non-negligable, influence on the water masses sampled during the cruise. Meso- and submesoscale participate in the surface distribution of tracers such as SST, SSS or chlorophyll-a but also of some micro-organismes such as bacteria or Prochlocorococcus