Subregional characterization of mesoscale eddies across the Brazil-Malvinas Confluence

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. This article is protected by copyright. All rights reserved.

[1]  J. Molines,et al.  Stochastic variability of oceanic flows above topography anomalies , 2011, 1103.4445.

[2]  Reto Knutti,et al.  Southern Ocean eddy phenomenology , 2015 .

[3]  L. Fu.  Pattern and velocity of propagation of the global ocean eddy variability , 2009 .

[4]  N. R. McDonald,et al.  A Simple Model for Sheddies: Ocean Eddies Formed from Shed Vorticity , 2016 .

[5]  R. Matano,et al.  A two-way nested simulation of the oceanic circulation in the Southwestern Atlantic , 2014 .

[6]  A. Piola,et al.  Multiple jets in the Malvinas Current , 2013 .

[7]  Dudley B. Chelton,et al.  Randomness, Symmetry, and Scaling of Mesoscale Eddy Life Cycles , 2014 .

[8]  S. Garzoli,et al.  The South Atlantic and the Atlantic Meridional Overturning Circulation , 2011 .

[9]  J. McWilliams,et al.  Submesoscale Instability and Generation of Mesoscale Anticyclones near a Separation of the California Undercurrent , 2015 .

[10]  V. Menezes,et al.  Double‐celled subtropical gyre in the South Atlantic Ocean: Means, trends, and interannual changes , 2011 .

[11]  The role of vorticity fluxes in the dynamics of the Zapiola Anticyclone , 2008 .

[12]  J. McWilliams,et al.  A New Sea Surface Height–Based Code for Oceanic Mesoscale Eddy Tracking , 2014 .

[13]  Huijie Xue,et al.  Dynamical processes within an anticyclonic eddy revealed from Argo floats , 2015 .

[14]  D. Stevens,et al.  Circulation and water mass modification in the Brazil-Malvinas Confluence , 2010 .

[15]  C. Wunsch,et al.  Ocean Circulation Kinetic Energy: Reservoirs, Sources, and Sinks , 2009 .

[16]  M. Meredith,et al.  On the structure, paths, and fluxes associated with Agulhas rings , 1999 .

[17]  P. Abreu,et al.  Multiannual trends in fronts and distribution of nutrients and chlorophyll in the southwestern Atlantic (30–62°S) , 2000 .

[18]  Joaquín Tintoré,et al.  Circulation in the Alboran Sea as Determined by Quasi-Synoptic Hydrographic Observations. Part I: Three-Dimensional Structure of the Two Anticyclonic Gyres , 1996 .

[19]  A. Orsi,et al.  On the meridional extent and fronts of the Antarctic Circumpolar Current , 1995 .

[20]  Michael J. Behrenfeld,et al.  Regional variations in the influence of mesoscale eddies on near‐surface chlorophyll , 2014 .

[21]  K. Speer,et al.  Response of the Antarctic Circumpolar Current to atmospheric variability , 2008 .

[22]  D. Chelton,et al.  The Influence of Nonlinear Mesoscale Eddies on Near-Surface Oceanic Chlorophyll , 2011, Science.

[23]  Gilles Larnicol,et al.  Combining Argo and remote-sensing data to estimate the ocean three-dimensional temperature fields—a first approach based on simulated observations , 2004 .

[24]  D. Chelton,et al.  Seasonal variability in the southwestern Atlantic , 1993 .

[25]  D. Chelton,et al.  Satellite observations of chlorophyll, phytoplankton biomass, and Ekman pumping in nonlinear mesoscale eddies , 2013 .

[26]  J. McWilliams,et al.  Topographic generation of submesoscale centrifugal instability and energy dissipation , 2016, Nature Communications.

[27]  Joaquín Tintoré,et al.  Mesoscale subduction at the Almeria-Oran front: Part 1: Ageostrophic flow , 2001 .

[28]  Matthew H. England,et al.  On the water masses and mean circulation of the South Atlantic Ocean , 1999 .

[29]  Thomas M. Smith,et al.  Daily High-Resolution-Blended Analyses for Sea Surface Temperature , 2007 .

[30]  P. L. Traon,et al.  High Resolution 3-D temperature and salinity fields derived from in situ and satellite observations , 2012 .

[31]  R. Morrow,et al.  A new estimate of the global 3D geostrophic ocean circulation based on satellite data and in-situ measurements , 2012 .

[32]  R. Preisendorfer,et al.  Principal Component Analysis in Meteorology and Oceanography , 1988 .

[33]  Larry W. O'Neill,et al.  Satellite Observations of Mesoscale Eddy-Induced Ekman Pumping , 2015 .

[34]  Milton Kampel,et al.  Multi-sensor satellite and in situ measurements of a warm core ocean eddy south of the Brazil–Malvinas Confluence region , 2006 .

[35]  A. Gordon,et al.  Agulhas Eddies: A Synoptic View Using Geosat ERM Data , 1995 .

[36]  A. Piola,et al.  Altimeter‐derived seasonal circulation on the southwest Atlantic shelf: 27°–43°S , 2015, Journal of geophysical research. Oceans.

[37]  E. Mason,et al.  Impact of vertical and horizontal advection on nutrient distribution in the southeast Pacific , 2015 .

[38]  A. Pascual,et al.  Net primary production in the Gulf Stream sustained by quasi‐geostrophic vertical exchanges , 2015 .

[39]  Fabrice Hernandez,et al.  Can We Merge GEOSAT Follow-On with TOPEX/Poseidon and ERS-2 for an Improved Description of the Ocean Circulation? , 2003 .

[40]  S. Garzoli.  Geostrophic velocity and transport variability in the Brazil-Malvinas Confluence , 1993 .

[41]  Adrian P. Martin,et al.  The spatial variability of vertical velocity in an Iceland basin eddy dipole , 2013 .

[42]  Oceanic time variability near a large scale topographic circulation , 2009 .

[43]  A. Czaja,et al.  The observed signature of mesoscale eddies in sea surface temperature and the associated heat transport , 2012 .

[44]  C. Provost,et al.  Brazil Malvinas Frontal System as seen from 9 years of advanced very high resolution radiometer data , 2004 .

[45]  Ananda Pascual,et al.  Improved description of the ocean mesoscale variability by combining four satellite altimeters , 2006 .

[46]  A. Gordon.  Brazil-Malvinas Confluence ― 1984 , 1989 .

[47]  Guilherme P. Castelão,et al.  The signature of mesoscale eddies on the air‐sea turbulent heat fluxes in the South Atlantic Ocean , 2015 .

[48]  Stefan Rahmstorf,et al.  On the driving processes of the Atlantic meridional overturning circulation , 2007 .

[49]  Interaction of Mesoscale Variability with Large-Scale Waves in the Argentine Basin , 2007 .

[50]  B. Qiu,et al.  Oceanic mass transport by mesoscale eddies , 2014, Science.

[51]  L. Stramma,et al.  Upper-level circulation in the South Atlantic Ocean , 1991 .

[52]  D. Chelton,et al.  Global observations of nonlinear mesoscale eddies , 2011 .

[53]  J. Azevedo,et al.  Eddy Surface properties and propagation at Southern Hemisphere western boundary current systems , 2015 .

[54]  D. McGillicuddy,et al.  Mechanisms of Physical-Biological-Biogeochemical Interaction at the Oceanic Mesoscale. , 2016, Annual review of marine science.

[55]  M. A. R. K. J. O H N C O S T E L L O,et al.  Surface Area and the Seabed Area, Volume, Depth, Slope, and Topographic Variation for the World’s Seas, Oceans, and Countries , 2010 .

[56]  James C. McWilliams,et al.  Global heat and salt transports by eddy movement , 2014, Nature Communications.

[57]  Charles Troupin,et al.  Implications of refined altimetry on estimates of mesoscale activity and eddy‐driven offshore transport in the Eastern Boundary Upwelling Systems , 2014 .

[58]  Bruno Buongiorno Nardelli,et al.  Vortex waves and vertical motion in a mesoscale cyclonic eddy , 2013 .

[59]  B. Hoskins,et al.  A new look at the ?-equation , 1978 .

[60]  Reto Knutti,et al.  Imprint of Southern Ocean eddies on winds, clouds and rainfall , 2013 .

[61]  Alexis Chaigneau,et al.  Mesoscale eddies off Peru in altimeter records: Identification algorithms and eddy spatio-temporal patterns , 2008 .

[62]  Robert B. Scott,et al.  Effects of stencil width on surface ocean geostrophic velocity and vorticity estimation from gridded satellite altimeter data , 2012 .

[63]  J. McWilliams,et al.  A Formal Theory for Vortex Rossby Waves and Vortex Evolution , 2003 .

[64]  Gilles Reverdin,et al.  Global high-resolution mapping of ocean circulation from TOPEX/Poseidon and ERS-1 and -2 , 2000 .

[65]  Youichi Tanimoto,et al.  SST-Induced Surface Wind Variations over the Brazil-Malvinas Confluence : Satellite and In Situ Observations , 2005 .

[66]  D. Chelton,et al.  Eddy properties in the Western Mediterranean Sea from satellite altimetry and a numerical simulation , 2016 .

[67]  John Abraham,et al.  A review of global ocean temperature observations: Implications for ocean heat content estimates and climate change , 2013, Reviews of Geophysics.

[68]  Yoshimine Ikeda,et al.  Geostrophic transport in the Brazil current region north of 20°S , 1990 .

[69]  D. Marshall,et al.  Significant sink of ocean-eddy energy near western boundaries , 2010 .

[70]  D. Chelton,et al.  Global observations of large oceanic eddies , 2007 .

[71]  A. Pascual,et al.  A Quasigeostrophic Analysis of a Meander in the Palamós Canyon: Vertical Velocity, Geopotential Tendency, and a Relocation Technique , 2004 .

[72]  Dudley B. Chelton,et al.  A Global Climatology of Surface Wind and Wind Stress Fields from Eight Years of QuikSCAT Scatterometer Data , 2008 .

[73]  S. Garzoli,et al.  Interannual to decadal changes in the western South Atlantic's surface circulation , 2011 .

[74]  J. Font,et al.  Identification of Marine Eddies from Altimetric Maps , 2003 .

[75]  M. Maltrud,et al.  Eddy-driven sediment transport in the Argentine Basin: Is the height of the Zapiola Rise hydrodynamically controlled? , 2015 .

[76]  Yannice Faugère,et al.  DUACS DT 2014 : the new multi-mission altimeter data set reprocessed over 20 years , 2016 .

[77]  A. Piola,et al.  The influence of the Brazil and Malvinas Currents on the Southwestern Atlantic Shelf circulation , 2010 .

[78]  C. Provost,et al.  Malvinas Current variability from Argo floats and satellite altimetry , 2016 .

[79]  L. Beal,et al.  Western Boundary Currents , 2013 .

[80]  Yannice Faugère,et al.  DUACS DT2014: the new multi-mission altimeter data set reprocessed over 20years , 2016 .

[81]  Björn C. Backeberg,et al.  Eddy properties in the Mozambique Channel: A comparison between observations and two numerical ocean circulation models , 2014 .

[82]  K. Speer,et al.  Eddy heat diffusion and Subantarctic Mode Water formation , 2008 .

[83]  Yi Chao,et al.  The salinity signature of the cross-shelf exchanges in the Southwestern Atlantic Ocean: Numerical simulations , 2014, Journal of geophysical research. Oceans.

[84]  Wei Zhao,et al.  Observed 3D Structure, Generation, and Dissipation of Oceanic Mesoscale Eddies in the South China Sea , 2016, Scientific Reports.

[85]  W. Dewar,et al.  Topographic inviscid dissipation of balanced flow , 2010 .

[86]  C. Provost,et al.  On eddy polarity distribution in the southwestern Atlantic , 2012 .

[87]  Tommy D. Dickey,et al.  A Vector Geometry–Based Eddy Detection Algorithm and Its Application to a High-Resolution Numerical Model Product and High-Frequency Radar Surface Velocities in the Southern California Bight , 2010 .

[88]  James C. McWilliams,et al.  The Canary Eddy Corridor: A major pathway for long-lived eddies in the subtropical North Atlantic , 2009 .

[89]  P. M. Saunders,et al.  Bottom Currents Derived from a Shipborne ADCP on WOCE Cruise A11 in the South Atlantic , 1995 .

[90]  G. Johnson,et al.  Global ocean surface velocities from drifters: Mean, variance, El Niño–Southern Oscillation response, and seasonal cycle , 2013 .

[91]  R. Pollard,et al.  Vorticity and vertical circulation at an ocean front , 1992 .

[92]  Y. Chao,et al.  The salinity signature of the cross-shelf exchanges in the Southwestern Atlantic Ocean: Satellite observations , 2014, Journal of geophysical research. Oceans.

[93]  S. Speich,et al.  Routes of Agulhas rings in the southeastern Cape Basin , 2010 .

[94]  S. Garzoli,et al.  Transports, frontal motions and eddies at the Brazil-Malvinas currents confluence , 1989 .

[95]  Walter H. F. Smith,et al.  Global Sea Floor Topography from Satellite Altimetry and Ship Depth Soundings , 1997 .

[96]  Oscar Pizarro,et al.  Vertical structure of mesoscale eddies in the eastern South Pacific Ocean: A composite analysis from altimetry and Argo profiling floats , 2011 .