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© The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Meunier, T., Pérez-Brunius, P., & Bower, A. Reconstructing the three-dimensional structure of loop current rings from satellite altimetry and in situ data using the gravest empirical modes method. Remote Sensing, 14(17), (2022): 4174, https://doi.org/10.3390/rs14174174., The three-dimensional structure of Gulf of Mexico’s warm-core rings, detaching from the Loop Current, is investigated using satellite altimetry and a large set of ARGO float profiles. Reconstruction of the Loop Current rings (LCRs) vertical structure from sea surface height observations is made possible by the use of the gravest empirical modes method (GEM). The GEMs are transfer functions that associate a value of temperature and salinity for each variable pair {dynamic height; pressure}, and are computed by estimating an empirical relationship between dynamic height and the vertical thermohaline structure of the ocean. Between 1993 and 2021, 40 LCRs were detected in the altimetry and their three-dimensional thermohaline structure was reconstructed, as well as a number of dynamically relevant variables (geostrophic and cyclogeostrophic velocity, relative vorticity, potential vorticity, available potential energy and kinetic energy density, etc.). The structure of a typical LCR was computed by fitting an analytical stream function to the LCRs dynamic height signature and reconstructing its vertical structure with the GEM. The total heat and salt contents and energy of each LCR were computed and their cumulative effect on the Gulf of Mexico’s heat, salt and energy balance is discussed. We show that LCRs have a dramatic impact on these balances and estimate that residual surface heat fluxes of −13 W m−2 are necessary to compensate their heat input, while the fresh water outflow of the Mississippi river approximately compensates for their salt excess input. An average energy dissipation of O [10−10–10−9] W kg−1 would be necessary to balance their energy input., This work is part of the LC-floats project, funded by the US National Academy of Sciences through the Understanding Gulf Ocean Systems grant 2000010488.

Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 126(10),(2021): e2021JC017375.,https://doi.org/10.1029/2021JC017375., The Deep Water Horizon oil spill dramatically impacted the Gulf of Mexico from the seafloor to the surface. While dispersion of contaminants at the surface has been extensively studied, little is known about deep water dispersion properties. This study describes the results of the Deep Water Dispersion Experiment (DWDE), which consisted of the release of surface drifters and acoustically tracked RAFOS floats drifting at 300 and 1,500 dbar in the Gulf of Mexico. We show that surface diffusivity is elevated and decreases with depth: on average, diffusivity at 1,500 dbar is 5 times smaller than at the surface, suggesting that the dispersion of contaminants at depth is a significantly slower process than at the surface. This study also examines the turbulent regimes driving the dispersion, although conflicting evidences and large uncertainties do not allow definitive conclusions. At all depths, while the growth of dispersion and kurtosis with time supports the possibility of an exponential regime at very short time scales, indicating that early dispersion is nonlocal, finite size Lyapunov exponents support the hypothesis of local dispersion, suggesting that eddies of size comparable to the initial separation (6 km), may dominate the early dispersion. At longer time scales, the quadratic growth of dispersion is indicative of a ballistic regime, where a mean shear flow would be the dominating process. Examination of the along- and across-bathymetry components of float velocities supports the idea that boundary currents could be the source for this shear dispersion., This research has been funded by the Mexican National Council for Science and Technology - Mexican Ministry of Energy - Hydrocarbon Fund, project 201441. This is a contribution of the Gulf of Mexico Research Consortium (CIGoM)., 2022-03-18

This is the final data report for all acoustically-tracked subsurface RAFOS floats deployed for the “Deep Water Dispersion Experiment: RAFOS Float Study in Support of Analysis of Possible Consequences of Large Scale Oil-Spills under Various Scenarios” (DWDE). This study is part of the larger program “Deep and Shallow Particle Dispersion and Biological Connectivity over the Continental Slope in the Western Gulf of Mexico”, of the Gulf of Mexico Research Consortium (CIGoM). The objective of the DWDE project was to measure and evaluate the ocean circulation at various depths in order to estimate the rates and pathways by which a passive tracer (e.g. pollutant, nutrients, etc.) would spread. The experiment consisted of the deployment 93 RAFOS floats and five sound source moorings (needed for tracking the floats underwater) over the course of five cruises, between June 2016 and January 2019, in the Perdido region of the Gulf of Mexico. The floats were deployed nearly simultaneously at stacked depths of 300 and 1500 dbar, in sets of 2-4 instruments per station, for calculating dispersion statistics. Mission lengths for the floats were set to ~12 to 18 months. Included in this report are cruise summaries, statistics and notes on sound source and float performance, sound source drift calculations, description of the RAFOS float data processing steps, and figures., Funding was provided by the Mexican National Council for Science and Technology - Mexican Ministry of Energy - Hydrocarbon Fund, project 201441. This work was completed through a contract by the Center for Scientific Research and Higher Education at Ensenada (CICESE) under Grant No. 188355 to the Woods Hole Oceanographic Institution.

Author Posting. © American Meteorological Society, 2020. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 50(4), (2020): 1045-1064, doi:10.1175/JPO-D-19-0137.1., Three simulations of the circulation in the Gulf of Mexico (the “Gulf”) using different numerical general circulation models are compared with results of recent large-scale observational campaigns conducted throughout the deep (>1500 m) Gulf. Analyses of these observations have provided new understanding of large-scale mean circulation features and variability throughout the deep Gulf. Important features include cyclonic flow along the continental slope, deep cyclonic circulation in the western Gulf, a counterrotating pair of cells under the Loop Current region, and a cyclonic cell to the south of this pair. These dominant circulation features are represented in each of the ocean model simulations, although with some obvious differences. A striking difference between all the models and the observations is that the simulated deep eddy kinetic energy under the Loop Current region is generally less than one-half of that computed from observations. A multidecadal integration of one of these numerical simulations is used to evaluate the uncertainty of estimates of velocity statistics in the deep Gulf computed from limited-length (4 years) observational or model records. This analysis shows that the main deep circulation features identified from the observational studies appear to be robust and are not substantially impacted by variability on time scales longer than the observational records. Differences in strengths and structures of the circulation features are identified, however, and quantified through standard error analysis of the statistical estimates using the model solutions., This work was supported by the Gulf Research Program of the National Academy of Sciences under Awards 2000006422 and 2000009966. The content is solely the responsibility of the authors and does not necessarily represent the official views of the Gulf Research Program or the National Academy of Sciences. The authors acknowledge the GLORYS project for providing the ocean reanalysis data used in the ROMS simulation. GLORYS is jointly conducted by MERCATOR OCEAN, CORIOLIS, and CNRS/INSU. Installation, recovery, data acquisition, and processing of the CANEK group current-meter moorings were possible because of CICESE-PetróleosMexicanos Grant PEP-CICESE 428229851 and the dedicated work of the crew of the B/O Justo Sierra and scientists of the CANEK group. The authors thank Dr. Aljaz Maslo, CICESE, for assistance with analysis of model data. The Bureau of Ocean Energy Management (BOEM), U.S. Dept. of the Interior, provided funding for the Lagrangian Study of the Deep Circulation in the Gulf of Mexico and the Observations and Dynamics of the Loop Current study. HYCOM simulation data are available from the HYCOM data server (https://www.hycom.org/data/goml0pt04/expt-02pt2), MITgcm data are available from the ECCO data server (http://ecco.ucsd.edu/gom_results2.html), and the ROMS simulation data are available from GRIIDC (NA.x837.000:0001).

Author Posting. © American Meteorological Society, 2019. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 49(6), (2019):1463-1483, doi: 10.1175/JPO-D-18-0213.1., A set of float trajectories, deployed at 1500- and 2500-m depths throughout the deep Gulf of Mexico from 2011 to 2015, are analyzed for mesoscale processes under the Loop Current (LC). In the eastern basin, December 2012–June 2014 had >40 floats per month, which was of sufficient density to allow capturing detailed flow patterns of deep eddies and topographic Rossby waves (TRWs), while two LC eddies formed and separated. A northward advance of the LC front compresses the lower water column and generates an anticyclone. For an extended LC, baroclinic instability eddies (of both signs) develop under the southward-propagating large-scale meanders of the upper-layer jet, resulting in a transfer of eddy kinetic energy (EKE) to the lower layer. The increase in lower-layer EKE occurs only over a few months during meander activity and LC eddy detachment events, a relatively short interval compared with the LC intrusion cycle. Deep EKE of these eddies is dispersed to the west and northwest through radiating TRWs, of which examples were found to the west of the LC. Because of this radiation of EKE, the lower layer of the eastern basin becomes relatively quiescent, particularly in the northeastern basin, when the LC is retracted and a LC eddy has departed. A mean west-to-east, anticyclone–cyclone dipole flow under a mean LC was directly comparable to similar results from a previous moored LC array and also showed connections to an anticlockwise boundary current in the southeastern basin., The authors were supported by the Department of the Interior, Bureau of Ocean Energy Management (BOEM), Contract M08PC20043 to Leidos, Inc., Raleigh, NC. The authors also wish to acknowledge the enthusiastic support of Dr. Alexis Lugo-Fernández, the BOEM Contracting Officer’s Technical Representative, during the study into the Deep Circulation of the Gulf of Mexico, using Lagrangian Methods. Thanks go to the captains and crews of the R/V Pelican and B/O Justo Sierra, J. Malbrough (LUMCON), J. Singer (Leidos), J. Valdes (WHOI), B. Guest (WHOI), and the CANEK group (CICESE)., 2020-05-29

Ocean flows are routinely inferred from low-resolution satellite altimetry measurements of sea surface height assuming a geostrophic balance. Recent nonlinear dynamical systems techniques have revealed that surface currents derived from altimetry can support mesoscale eddies with material boundaries that do not filament for many months, thereby representing effective transport mechanisms. However, the long-range Lagrangian coherence assessed for mesoscale eddy boundaries detected from altimetry is constrained by the impossibility of current altimeters to resolve ageostrophic submesoscale motions. These may act to prevent Lagrangian coherence from manifesting in the rigorous form described by the nonlinear dynamical systems theories. Here we use a combination of satellite ocean color and surface drifter trajectory data, rarely available simultaneously over an extended period of time, to provide observational evidence for the enduring Lagrangian coherence of a Loop Current ring detected from altimetry. We also seek indications of this behavior in the flow produced by a data-assimilative system which demonstrated ability to reproduce observed relative dispersion statistics down into the marginally submesoscale range. However, the simulated flow, total surface and subsurface or subsampled emulating altimetry, is not found to support the long-lasting Lagrangian coherence that characterizes the observed ring. This highlights the importance of the Lagrangian metrics produced by the nonlinear dynamical systems tools employed here in assessing model performance

The flow of subtropical waters carried into the northern North Atlantic Ocean by the North Atlantic Current– subpolar front system (NAC–SPF) is an important component of the meridional overturning circulation. These waters become colder and denser as they flow through the subpolar region, both by mixing with the colder subpolar waters and by atmospheric cooling. The relative roles of these two processes remain to be quantified, and the mechanisms driving lateral mixing need to be better understood. To address those questions, a new methodology is developed to estimate the mean absolute transports of mass and heat for the top 1000 dbar in the region of the NAC–SPF for the time period 1993–2000. The transports are obtained by combining historical hydrography with isopycnal RAFOS float data from the area. The mean absolute transport potential field shows an NAC–SPF “pipe,” defined by two bounding transport potential contours. This pipe transports 10.0 ± 3.5 Sv (Sv ≡ 106 m3 s−1) (top 1000 dbar) from the subtropics into the eastern subpolar North Atlantic. In contrast to earlier studies, the northward-flowing NAC follows a distinct meandering path, with no evidence of permanent branches peeling off the current before reaching the “Northwest Corner.” As the current enters the Northwest Corner, it loses its tight structure and maybe splits into two or more branches, which together constitute the eastward flow along the SPF. The eastward flow between the Northwest Corner and the Mid-Atlantic Ridge is not as tightly defined because of the meandering and/or eddy shedding of the branches constituing the SPF. As the flow approaches the Mid-Atlantic Ridge, it converges to cross above the Charlie–Gibbs and Faraday Fracture Zones. The mean absolute temperature transport (top 1000 dbar) by the 10-Sv pipe was estimated across 10 transects crossing the NAC–SPF. Because the mean mass flux is constant in the pipe, variations in the mean temperature transports result from lateral exchan

To obtain a description of the hydrographic state of the North Atlantic Current-subpolar front (NAC-SPF) system, historical hydrographic data from the subpolar North Atlantic are projected into a baroclinic stream-function space, resulting in three-dimensional Gravest Empirical Mode (GEM) fields for temperature and specific volume anomaly, parameterized by pressure, dynamic height, and day of the year. From the specific volume anomaly GEM, the corresponding potential vorticity field is calculated. These fields are constructed for 12 subregions, chosen to follow the mean path of the NAC-SPF system. Analysis of the seasonal potential vorticity cycle of the GEM fields shows that the main mechanism for the formation of Subpolar Mode Water is winter convection. The GEM fields are also used to obtain the approximate location of formation sites for the different Subpolar Mode Water classes. The evolution of the mean fields for the waters is studied along baroclinic streamlines of the NAC-SPF system. This shows that cross-frontal mixing, between the cold and fresh subpolar waters and the salty and warm waters coming north from the subtropics via the Gulf Stream, is the dominant mechanism for the light-to-dense transformation process of the NAC-SPF waters that enter the western subpolar region. On the other hand, a combination of atmospheric cooling, vertical mixing during wintertime convection, and entrainment of the saltier waters found on the northeastern subtropical gyre is the main factor transforming the NAC-SPF waters that enter the eastern subpolar gyre. This suggests that an influx along the eastern margin of salty water from the European Basin plays a significant role in the transformation of the NAC-SPF waters that continue their way toward the Nordic seas. © 2004 American Meteorological Society.