Evan Mason

Baylor University

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Ananda Pascual

Mediterranean Institute for Advanced Studies

Simón Ruíz

Mediterranean Institute for Advanced Studies

Josep Lluís Pelegrí

Consejo Superior de Investigaciones Científicas

Pablo Sangrà

Universidad de Las Palmas de Gran Canaria

Joaquı́n Tintoré

Mediterranean Institute for Advanced Studies

Baptiste Mourre

Balearic Islands Coastal Observing and Forecasting System

Bàrbara Barceló‐Llull

Mediterranean Institute for Advanced Studies

Antonio Sánchez‐Román

Universidad de Murcia

Arthur Capet

Université Libre de Bruxelles

Charles Troupin

University of Liège

Cooperative Institutions

Centre National de la Recherche Scientifique

227

Institut de Recherche pour le Développement

168

Consejo Superior de Investigaciones Científicas

Laboratoire d’Études en Géophysique et Océanographie Spatiales

Université Grenoble Alpes

National Research Council

Université Toulouse III - Paul Sabatier

Institut des Géosciences de l'Environnement

Institut polytechnique de Grenoble

Université de Toulouse

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Do Sardinella aurita spawning seasons match local retention patterns in the Senegalese–Mauritanian upwelling region?

Fisheries Oceanography (2015)

Baye Cheikh Mbaye Timothée Brochier Vincent Échevin Alban Lazar Marina Lévy

Abstract Sardinella aurit a is the most abundant small pelagic fish in the Senegalese–Mauritanian region. The success of its reproduction crucially depends on the local circulation as this determines whether larvae reach coastal nursery areas favorable to their survival or are dispersed into the open ocean. As a first step towards evaluating sardinella vulnerability to climate‐driven hydrodynamical changes, this study aims at underpinning how transport pathways drive optimal spatial and seasonal patterns for sardinella reproduction. We have used two estimates of the Senegalese–Mauritanian coastal seasonal circulation simulated by two hydrodynamical model configurations that differ in their forcing and topography. Nursery areas are determined by evaluating coastal retention with a Lagrangian individual‐based model that accounts for processes such as diel vertical migration and mortality as a result of lethal temperature exposure. Our results suggest that the shelf zones located at the Arguin Bank (19.5°N–21°N) and south of Senegal (12°N–14.75°N) are highly retentive. We find maximum retention rates in July–August and November–December over the Arguin Bank; from February–July and November–December over the southern Senegalese shelf; and lower retention rates over the central region (14.75°N–19.5°N) that are locally maximum in June–July when the upwelling weakens. These retention areas and their seasonality are in agreement with previously reported spawning patterns, suggesting that the Sardinella aurita spawning strategy may result from a trade‐off between retention patterns associated with the seasonal circulation and food availability. Exposure to lethal temperatures, although not well studied, could be a further limiting factor for spawning. The Lagrangian analysis reveals important connectivity between sub‐regions within and south of the system and hence underlines the importance for joint management of the S ardinella aurita stock.

Sardinella

Diel vertical migration

Ichthyoplankton

10.1111/fog.12094

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Citations (41)

EddyNet: A Deep Neural Network For Pixel-Wise Classification of Oceanic Eddies

IGARSS 2022 - 2022 IEEE International Geoscience and Remote Sensing Symposium (2018)

Redouane Lguensat Miao Sun Ronan Fablet Pierre Tandeo Evan Mason

This work presents EddyNet, a deep learning based architecture for automated eddy detection and classification from Sea Surface Height (SSH) maps provided by the Copernicus Marine and Environment Monitoring Service (CMEMS). EddyNet consists of a convolutional encoder-decoder followed by a pixel-wise classification layer. The output is a map with the same size of the input where pixels have the following labels {`0': Non eddy, `1': anticyclonic eddy, `2': cyclonic eddy}. Keras Python code, the training datasets and EddyNet weights files are open-source and freely available on https://github.com/redouanelg/EddyNet.

Python

Contextual image classification

10.1109/igarss.2018.8518411

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Citations (153)

Subregional characterization of mesoscale eddies across the B razil‐ M alvinas C onfluence

Journal of Geophysical Research Oceans (2017)

Evan Mason Ananda Pascual Peter Gaube Simón Ruíz Josep Lluís Pelegrí

Abstract Horizontal and vertical motions associated with coherent mesoscale structures, including eddies and meanders, are responsible for significant global transports of many properties, including heat and mass. Mesoscale vertical fluxes also influence upper ocean biological productivity by mediating the supply of nutrients into the euphotic layer, with potential impacts on the global carbon cycle. The Brazil‐Malvinas Confluence (BMC) is a western boundary current region in the South Atlantic with intense mesoscale activity. This region has an active role in the genesis and transformation of water masses and thus is a critical component of the Atlantic meridional overturning circulation. The collision between the Malvinas and Brazil Currents over the Patagonian shelf/slope creates an energetic front that translates offshore to form a vigorous eddy field. Recent improvements in gridded altimetric sea level anomaly fields allow us to track BMC mesoscale eddies with high spatial and temporal resolutions using an automated eddy tracker. We characterize the eddies across fourteen 5° × 5° subregions. Eddy‐centric composites of tracers and geostrophic currents diagnosed from a global reanalysis of surface and in situ data reveal substantial subregional heterogeneity. The in situ data are also used to compute the evolving quasi‐geostrophic vertical velocity ( QG ‐ ω ) associated with each instantaneous eddy instance. The QG ‐ ω eddy composites have the expected dipole patterns of alternating upwelling/downwelling, however, the magnitude and sign of azimuthally averaged vertical velocity varies among subregions. Maximum eddy values are found near fronts and sharp topographic gradients. In comparison with regional eddy composites, subregional composites provide refined information about mesoscale eddy heterogeneity.

Eddy

Downwelling

Boundary current

10.1002/2016jc012611

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Citations (61)

Assessment of High‐Resolution Regional Ocean Prediction Systems Using Multi‐Platform Observations

Baptiste Mourre Eva Aguiar Mélanie Juza Jaime Hernández-Lasheras Emma Reyes

Source

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Citations (2)

Copernicus (CMEMS) operational model intercomparison in the western Mediterranean Sea: Insights from an eddy tracker

Evan Mason Simón Ruíz Romain Bourdallé‐Badie Guillaume Reffray Marcos García Sotillo

Abstract. Rapid evolution of operational ocean models is driven by advances in numerics and sophisticated data assimilation schemes, computational power, and storage capacity. The Copernicus Marine Service (CMEMS) is a major provider of operational products that are made available through an online catalogue. The service includes global and regional forecasts in near-real-time and reanalysis modes. Here we apply an eddy tracker to daily SSH fields from three such reanalysis products from the CMEMS catalogue, with the objective to evaluate their performance in terms of their eddy properties and three-dimensional composite structures over the period 2013 through 2016. The products are (i) the Global Analysis Forecast, (ii) the Mediterranean Analysis Forecast, and (iii) the Iberia-Biscay-Ireland Analysis Forecast. The common domain between these reanalyses is the western Mediterranean Sea (WMED) between the Strait of Gibraltar and Sardinia. This is a complex region with strong density gradients, especially in the Alboran Sea in the west where Atlantic and Mediterranean waters compete. Surface eddy property maps over the WMED of eddy radii, amplitudes and nonlinearity are consistent between the models, as well as with gridded altimetric data that serve as a reference. Mean 3D eddy composites are shown only for three subregions in the Alboran Sea. These are mostly consistent between the models, with minor differences being attributed to details of the respective model configurations. This information can be informative for the ongoing development of these CMEMS operational modeling systems.

Copernicus

10.5194/os-2018-169

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Citations (3)

Mesoscale eddy variability in the Caribbean Sea

Ocean Dynamics (2022)

Margarita E. López-Álzate Juan‐Manuel Sayol Ismael Hernández‐Carrasco Andrés F. Osorio Evan Mason

Abstract The spatial distribution, and the monthly and seasonal variability of mesoscale eddy observations derived from the AVISO eddy atlas are assessed in the Caribbean Sea during 1993–2019. The average lifetime for the whole set of eddies is 62 ± 37 days, mean amplitude of 7 ± 4 cm for cyclonic and 7 ± 4 cm for anticyclonic and mean radius of 100 ± 31 km for cyclonic and 108 ± 32 km for anticyclonic. Cyclonic eddies are on average more nonlinear than anticyclonic ones. The spatio-temporal variability in the number of eddy observations is evaluated against the Mean Eddy Kinetic Energy (MEKE) derived from geostrophic currents as well as from seasonal winds. Spatial distribution of eddy observations is correlated with MEKE while the migration of the intertropical convergence zone explains the advection of eddies towards the southern part of the basin.

Anticyclone

Eddy

Intertropical Convergence Zone

10.1007/s10236-022-01525-9

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Citations (5)

Vorticity balance in the Northwestern African Upwelling

Charles Troupin Evan Mason Pablo Sangrà

Process studies of the drainage of the Canary Current by the Northwestern African Upwelling (NWAU) have shown that, in order to conserve potential vorticity, the southward flow along the upwelling system should be accompanied by a negative (anticyclonic) relative vorticity, which is provided by the upwelling jet circulation [Laiz et al., 2001]. Our hypothesis of upwelling-filament generation is related to the injection of positive relative vorticity: as the flow gains positive vorticity, it becomes unable to continue southward and detaches from the coast.

Anticyclone

Positive vorticity advection

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Generation of the Cape Ghir upwelling filament: A numerical study

Ocean Modelling (2011)

Charles Troupin Evan Mason Jean-Marie Beckers Pablo Sangrà

Forcing (mathematics)

10.1016/j.ocemod.2011.09.001

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Citations (25)

Geostrophic and ageostrophic circulation of a shallow anticyclonic eddy off Cape Bojador

Simón Ruíz Josep Lluís Pelegrí Mikhail Emelianov Ananda Pascual Evan Mason

A shallow mesoscale anticyclonic eddy, observed south of the Canary Islands with satellite altimetry, has been intensively studied with multiparametric sampling. Hydrographic data from a CTD installed on an undulating Nu-shuttle platform reveal the presence of a mesoscale anticyclonic eddy of ∼125 km diameter. The difference in sea level anomaly (SLA) between the interior and the edge of the eddy, as determined from altimetry, is ∼15 cm, which compares well with the maximum dynamic height differences as inferred using a very shallow reference level (130 m). Further, the associated surface geostrophic velocities, of about 35 cm s−1 in the northeast and southwest edges of the eddy, are in good agreement with direct velocity measurements from the ship. Deep rosette-CTD casts confirm that the structure is a shallow eddy extending no deeper than 250 m before the fusion with another anticyclone. The SLA-tendency (temporal rate of change of sea surface height) indicates a clear northwestward migration during the two first weeks of November 2008. Applying an eddy SSH-based tracker, the eddy's velocity propagation is estimated as 4 km d−1. Use of the QG-Omega equation diagnoses maximum downward/upward velocities of about ±2 m d−1. The instability of the Canary coastal jet appears to be the mechanism responsible for the generation of the shallow anticyclonic eddy.

Anticyclone

Sea-surface height

Geostrophic current

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Ichthyoplankton transport from the African coast to the Canary Islands

Journal of Marine Systems (2011)

Timothée Brochier Evan Mason Marta Moyano A. Berraho François Colas

Ichthyoplankton

Spawn (biology)

Engraulis

10.1016/j.jmarsys.2011.02.025

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Citations (60)