Enduring Lagrangian coherence of a Loop Current ring assessed using independent observations

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.Comment: In press in nature.com/Scientific Report

Connectivity of the Pulley Ridge with remote locations as inferred from satellite- tracked drifter trajectories

Using historical (1994-2017) satellite‐tracked surface drifter trajectory data, we conduct a probabilistic Lagrangian circulation study which sheds light on the connectivity of Pulley Ridge with other locations in the Gulf of Mexico and adjacent areas. The analysis reveals that Pulley Ridge is connected with the North Atlantic, the Caribbean Sea, and most of the Gulf of Mexico. Preferred connecting pathways are identified and arrival times to potential reef sites computed. The study demonstrates the importance of Pulley Ridge as a source for neighboring regions like the Dry Tortugasa, the Florida Keys, Campeche Bank, and the east Florida coast as well as a self‐recruitment area for species with short competence time. The study further suggests that the reefs in the Caribbean Sea, the Dry Tortugas, the western Florida Keys, and the West Florida Shelf can act as sources for Pulley Ridge, indicating the importance of Pulley Ridge as a central refugium for species in the Gulf of Mexico

Assessment of numerical simulations of deep circulation and variability in the Gulf of Mexico using recent observations

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)

Connectivity of Pulley Ridge With Remote Locations as Inferred From Satellite‐Tracked Drifter Trajectories

Using historical (1994–2017) satellite‐tracked surface drifter trajectory data, we conduct a probabilistic Lagrangian circulation study which sheds light on the connectivity of Pulley Ridge with other locations in the Gulf of Mexico and adjacent areas. The analysis reveals that Pulley Ridge is connected with the North Atlantic, the Caribbean Sea, and most of the Gulf of Mexico. Preferred connecting pathways are identified and arrival times to potential reef sites computed. The study demonstrates the importance of Pulley Ridge as a source for neighboring regions like the Dry Tortugasa, the Florida Keys, Campeche Bank, and the east Florida coast as well as a self‐recruitment area for species with short competence time. The study further suggests that the reefs in the Caribbean Sea, the Dry Tortugas, the western Florida Keys, and the West Florida Shelf can act as sources for Pulley Ridge, indicating the importance of Pulley Ridge as a central refugium for species in the Gulf of Mexico.Key PointsHistorical drifter data reveal oceanographic connectivity pathways within the Gulf of MexicoThe uncovered pathways constitute a first-order constraint for any surface tracer (e.g., spilled oil, toxic algae bloom, buoyant egg masses)Drifter data suggest the importance of Pulley Ridge mesophotic reef as a refugium for the Gulf of Mexic

Lagrangian Geography of the Deep Gulf of Mexico

Abstract Using trajectories from acoustically tracked (RAFOS) floats in the Gulf of Mexico, we construct a geography of its Lagrangian circulation within the 1500–2500-m layer. This is done by building a Markov-chain representation of the Lagrangian dynamics. The geography is composed of weakly interacting provinces that constrain the connectivity at depth. The main geography includes two provinces of near-equal areas separated by a roughly meridional boundary. The residence time is about 4.5 (3.5) years in the western (eastern) province. The exchange between these provinces is effected through a slow cyclonic circulation, which is well constrained in the western basin by preservation of f/H, where f is the Coriolis parameter and H is depth. Secondary provinces of varied shapes covering smaller areas are identified with residence times ranging from about 0.4 to 1.2 years or so. Except for the main provinces, the deep Lagrangian geography does not resemble the surface Lagrangian geography recently inferred from satellite-tracked drifter trajectories. This implies disparate connectivity characteristics with potential implications for pollutant (e.g., oil) dispersal at the surface and at depth. Support for our results is provided by a Markov-chain analysis of satellite-tracked profiling (Argo) floats, which, while forming a smaller dataset and having seemingly different water-following characteristics than the RAFOS floats, replicate the main aspects of the Lagrangian geography. Our results find further validation in independent results from a chemical tracer release experiment

Variability of fish larvae assemblages relative to mesoscale features in the deep water region of the southern Gulf of Mexico

In the Gulf of Mexico (GoM), mesoscale features strongly influence hydrographic and circulation patterns, which can favor larval retention and/or transport. Most ichthyoplankton studies in the southern GoM (south of 25°N) have focused on the continental shelves and the Bay of Campeche (BoC), and little is known about larval fish assemblages in the oceanic region. We compared the structure of the assemblages among stations from contrasting mesoscale features in the deep water region (depths greater than 1000 m), hypothesizing that there is a higher similarity in assemblages from stations within the same feature. Ichthyoplankton samples were collected in the upper 200 m during two oceanographic cruises. Analyses of sea surface heights and temperature anomaly profiles allowed us to identify the stations corresponding to specific mesoscale features, including cyclonic and anticyclonic eddies, upwelling, river discharge waters transported offshore, and the Loop Current. Larval fish assemblages were not strictly differentiated among features, except for one assemblage identified within an anticyclonic eddy. Stations within the BoC could be discriminated from the northern oceanic region due to high larval fish abundances and to the occurrence of taxa that inhabit coastal and neritic habitats as adults, which are transported offshore due to local oceanographic processes.Fil: Echeverri García, Laura del Pilar. Consejo Nacional de Ciencia y Tecnología de México. Centro de Investigación Científica y de Educación Superior de Ensenada Baja California; MéxicoFil: Daudén Bengoa, Gonzalo. Consejo Nacional de Ciencia y Tecnología de México. Centro de Investigación Científica y de Educación Superior de Ensenada Baja California; MéxicoFil: Cano Compaire, Jesus. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Consejo Nacional de Ciencia y Tecnología de México. Centro de Investigación Científica y de Educación Superior de Ensenada Baja California; MéxicoFil: Jiménez Rosenberg, Sylvia P. A.. Centro Interdisciplinario de Ciencias Marinas; MéxicoFil: Pérez Brunius, Paula. Consejo Nacional de Ciencia y Tecnología de México. Centro de Investigación Científica y de Educación Superior de Ensenada Baja California; MéxicoFil: Ferreira Bartrina, Vicente. Consejo Nacional de Ciencia y Tecnología de México. Centro de Investigación Científica y de Educación Superior de Ensenada Baja California; MéxicoFil: Herzka, Sharon Z.. Consejo Nacional de Ciencia y Tecnología de México. Centro de Investigación Científica y de Educación Superior de Ensenada Baja California; Méxic

Gulf of Mexico (GoM) Bottom Sediments and Depositional Processes: A Baseline for Future Oil Spills

The deposition/accumulation of oil on the seafloor is heavily influenced by sediment/texture/composition and sedimentary processes/accumulation rates. The objective of this chapter is to provide a baseline of Gulf of Mexico sediment types and transport/depositional processes to help guide managers where oiled sediments may be expected to be deposited and potentially accumulate on the seafloor in the event of a future oil spill. Based solely on sediments/processes/accumulation rates, regions most vulnerable to oil deposition/accumulation include the deep eastern basin, followed by the western/southwestern basin, and north and west continental margins. The least vulnerable regions include the northwest Cuban shelf and the carbonate-dominated west Florida shelf and Campeche Bank. This is intended to be used as a general, “first cut” tool and does not consider local variations in sediments/processes