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Ody A, Thibaut T, Berline L, Changeux T, André JM, Chevalier C, Blanfuné A, Blanchot J, Ruitton S, Stiger-Pouvreau V, Connan S, Grelet J, Aurelle D, Guéné M, Bataille H, Bachelier C, Guillemain D, Schmidt N, Fauvelle V, Guasco S, Ménard F. From In Situ to satellite observations of pelagic Sargassum distribution and aggregation in the Tropical North Atlantic Ocean. PLoS One 2019; 14:e0222584. [PMID: 31527915 PMCID: PMC6748567 DOI: 10.1371/journal.pone.0222584] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2018] [Accepted: 09/03/2019] [Indexed: 11/18/2022] Open
Abstract
The present study reports on observations carried out in the Tropical North Atlantic in summer and autumn 2017, documenting Sargassum aggregations using both ship-deck observations and satellite sensor observations at three resolutions (MSI-10 m, OLCI-300 m, VIIRS-750 m and MODIS-1 km). Both datasets reported that in summer, Sargassum aggregations were mainly observed off Brazil and near the Caribbean Islands, while they accumulated near the African coast in autumn. Based on in situ observations, we propose a five-class typology allowing standardisation of the description of in situ Sargassum raft shapes and sizes. The most commonly observed Sargassum raft type was windrows, but large rafts composed of a quasi-circular patch hundreds of meters wide were also observed. Satellite imagery showed that these rafts formed larger Sargassum aggregations over a wide range of scales, with smaller aggregations (of tens of m2 area) nested within larger ones (of hundreds of km2). Match-ups between different satellite sensors and in situ observations were limited for this dataset, mainly because of high cloud cover during the periods of observation. Nevertheless, comparisons between the two datasets showed that satellite sensors successfully detected Sargassum abundance and aggregation patterns consistent with in situ observations. MODIS and VIIRS sensors were better suited to describing the Sargassum aggregation distribution and dynamics at Atlantic scale, while the new sensors, OLCI and MSI, proved their ability to detect Sargassum aggregations and to describe their (sub-) mesoscale nested structure. The high variability in raft shape, size, thickness, depth and biomass density observed in situ means that caution is called for when using satellite maps of Sargassum distribution and biomass estimation. Improvements would require additional in situ and airborne observations or very high-resolution satellite imagery.
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Affiliation(s)
- Anouck Ody
- Aix-Marseille Univ., Université de Toulon, CNRS, IRD, MIO UM 110, Marseille, France
| | - Thierry Thibaut
- Aix-Marseille Univ., Université de Toulon, CNRS, IRD, MIO UM 110, Marseille, France
| | - Léo Berline
- Aix-Marseille Univ., Université de Toulon, CNRS, IRD, MIO UM 110, Marseille, France
| | - Thomas Changeux
- Aix-Marseille Univ., Université de Toulon, CNRS, IRD, MIO UM 110, Marseille, France
| | - Jean-Michel André
- Aix-Marseille Univ., Université de Toulon, CNRS, IRD, MIO UM 110, Marseille, France
| | - Cristèle Chevalier
- Aix-Marseille Univ., Université de Toulon, CNRS, IRD, MIO UM 110, Marseille, France
| | - Aurélie Blanfuné
- Aix-Marseille Univ., Université de Toulon, CNRS, IRD, MIO UM 110, Marseille, France
| | - Jean Blanchot
- Aix-Marseille Univ., Université de Toulon, CNRS, IRD, MIO UM 110, Marseille, France
| | - Sandrine Ruitton
- Aix-Marseille Univ., Université de Toulon, CNRS, IRD, MIO UM 110, Marseille, France
| | - Valérie Stiger-Pouvreau
- Université de Bretagne Occidentale (UBO), Institut Universitaire Européen de la Mer (IUEM), LEMAR UMR 6539, Technopôle Brest-Iroise, Plouzané, France
| | - Solène Connan
- Université de Bretagne Occidentale (UBO), Institut Universitaire Européen de la Mer (IUEM), LEMAR UMR 6539, Technopôle Brest-Iroise, Plouzané, France
| | - Jacques Grelet
- IRD DR-OUEST, US191 IMAGO, Technopole de Brest-Iroise—Site de la Pointe du Diable, Plouzané, France
| | - Didier Aurelle
- Aix-Marseille Univ., Université de Toulon, CNRS, IRD, MIO UM 110, Marseille, France
| | - Mathilde Guéné
- Université des Antilles, UMR BOREA, Campus de Fouillole, BP 592, Pointe-à-Pitre, Guadeloupe, France
| | | | - Céline Bachelier
- IRD DR-OUEST, US191 IMAGO, Technopole de Brest-Iroise—Site de la Pointe du Diable, Plouzané, France
| | - Dorian Guillemain
- Aix Marseille Univ, CNRS, IRD, IRSTEA, OSU PYTHEAS, Marseille, France
| | - Natascha Schmidt
- Aix-Marseille Univ., Université de Toulon, CNRS, IRD, MIO UM 110, Marseille, France
| | - Vincent Fauvelle
- Aix-Marseille Univ., Université de Toulon, CNRS, IRD, MIO UM 110, Marseille, France
| | - Sophie Guasco
- Aix-Marseille Univ., Université de Toulon, CNRS, IRD, MIO UM 110, Marseille, France
| | - Frédéric Ménard
- Aix-Marseille Univ., Université de Toulon, CNRS, IRD, MIO UM 110, Marseille, France
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Abstract
Floating oil, plastics, and marine organisms are continually redistributed by ocean surface currents. Prediction of their resulting distribution on the surface is a fundamental, long-standing, and practically important problem. The dominant paradigm is dispersion within the dynamical context of a nondivergent flow: objects initially close together will on average spread apart but the area of surface patches of material does not change. Although this paradigm is likely valid at mesoscales, larger than 100 km in horizontal scale, recent theoretical studies of submesoscales (less than ∼10 km) predict strong surface convergences and downwelling associated with horizontal density fronts and cyclonic vortices. Here we show that such structures can dramatically concentrate floating material. More than half of an array of ∼200 surface drifters covering ∼20 × 20 km2 converged into a 60 × 60 m region within a week, a factor of more than 105 decrease in area, before slowly dispersing. As predicted, the convergence occurred at density fronts and with cyclonic vorticity. A zipperlike structure may play an important role. Cyclonic vorticity and vertical velocity reached 0.001 s-1 and 0.01 ms-1, respectively, which is much larger than usually inferred. This suggests a paradigm in which nearby objects form submesoscale clusters, and these clusters then spread apart. Together, these effects set both the overall extent and the finescale texture of a patch of floating material. Material concentrated at submesoscale convergences can create unique communities of organisms, amplify impacts of toxic material, and create opportunities to more efficiently recover such material.
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Observed and simulated submesoscale vertical pump of an anticyclonic eddy in the South China Sea. Sci Rep 2017; 7:44011. [PMID: 28276467 PMCID: PMC5343664 DOI: 10.1038/srep44011] [Citation(s) in RCA: 45] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2016] [Accepted: 02/02/2017] [Indexed: 11/16/2022] Open
Abstract
Oceanic mesoscale eddies with typical sizes of 30–200 km contain more than half of the kinetic energy of the ocean. With an average lifespan of several months, they are major contributors to the transport of heat, nutrients, plankton, dissolved oxygen and carbon in the ocean. Mesoscale eddies have been observed and studied over the past 50 years, nonetheless our understanding of the details of their structure remains incomplete due to lack of systematic high-resolution measurements. To bridge this gap, a survey of a mesoscale anticyclone was conducted in early 2014 in the South China Sea capturing its structure at submesoscale resolution. By modeling an anticyclone of comparable size and position at three horizontal resolutions the authors verify the resolution requirements for capturing the observed variability in dynamical quantities, and quantify the role of ageostrophic motions on the vertical transport associated with the anticyclone. Results indicate that different submesoscale processes contribute to the vertical transport depending on depth and distance from the eddy center, with frontogenesis playing a key role. Vertical transport by anticyclones cannot be reliably estimated by coarse-resolution or even mesoscale-resolving models, with important implications for global estimates of the eddy-driven vertical pumping of biophysical and chemical tracers.
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Lumpkin R, Özgökmen T, Centurioni L. Advances in the Application of Surface Drifters. ANNUAL REVIEW OF MARINE SCIENCE 2017; 9:59-81. [PMID: 27575739 DOI: 10.1146/annurev-marine-010816-060641] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Surface drifting buoys, or drifters, are used in oceanographic and climate research, oil spill tracking, weather forecasting, search and rescue operations, calibration and validation of velocities from high-frequency radar and from altimeters, iceberg tracking, and support of offshore drilling operations. In this review, we present a brief history of drifters, from the message in a bottle to the latest satellite-tracked, multisensor drifters. We discuss the different types of drifters currently used for research and operations as well as drifter designs in development. We conclude with a discussion of the various properties that can be observed with drifters, with heavy emphasis on a critical process that cannot adequately be observed by any other instrument: dispersion in the upper ocean, driven by turbulence at scales from waves through the submesoscale to the large-scale geostrophic eddies.
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Affiliation(s)
- Rick Lumpkin
- Atlantic Oceanographic and Meteorological Laboratory, National Oceanic and Atmospheric Administration, Miami, Florida 33149;
| | - Tamay Özgökmen
- Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida 33149;
| | - Luca Centurioni
- Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California 92093;
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Potential Connectivity of Coldwater Black Coral Communities in the Northern Gulf of Mexico. PLoS One 2016; 11:e0156257. [PMID: 27218260 PMCID: PMC4878809 DOI: 10.1371/journal.pone.0156257] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2015] [Accepted: 05/11/2016] [Indexed: 11/19/2022] Open
Abstract
The black coral Leiopathes glaberrima is a foundation species of deep-sea benthic communities but little is known of the longevity of its larvae and the timing of spawning because it inhabits environments deeper than 50 m that are logistically challenging to observe. Here, the potential connectivity of L. glaberrima in the northern Gulf of Mexico was investigated using a genetic and a physical dispersal model. The genetic analysis focused on data collected at four sites distributed to the east and west of Mississippi Canyon, provided information integrated over many (~10,000) generations and revealed low but detectable realized connectivity. The physical dispersal model simulated the circulation in the northern Gulf at a 1km horizontal resolution with transport-tracking capabilities; virtual larvae were deployed 12 times over the course of 3 years and followed over intervals of 40 days. Connectivity between sites to the east and west of the canyon was hampered by the complex bathymetry, by differences in mean circulation to the east and west of the Mississippi Canyon, and by flow instabilities at scales of a few kilometers. Further, the interannual variability of the flow field surpassed seasonal changes. Together, these results suggest that a) dispersal among sites is limited, b) any recovery in the event of a large perturbation will depend on local larvae produced by surviving individuals, and c) a competency period longer than a month is required for the simulated potential connectivity to match the connectivity from multi-locus genetic data under the hypothesis that connectivity has not changed significantly over the past 10,000 generations.
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Beron-Vera FJ, Olascoaga MJ, Haller G, Farazmand M, Triñanes J, Wang Y. Dissipative inertial transport patterns near coherent Lagrangian eddies in the ocean. CHAOS (WOODBURY, N.Y.) 2015; 25:087412. [PMID: 26328583 DOI: 10.1063/1.4928693] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Recent developments in dynamical systems theory have revealed long-lived and coherent Lagrangian (i.e., material) eddies in incompressible, satellite-derived surface ocean velocity fields. Paradoxically, observed drifting buoys and floating matter tend to create dissipative-looking patterns near oceanic eddies, which appear to be inconsistent with the conservative fluid particle patterns created by coherent Lagrangian eddies. Here, we show that inclusion of inertial effects (i.e., those produced by the buoyancy and size finiteness of an object) in a rotating two-dimensional incompressible flow context resolves this paradox. Specifically, we obtain that anticyclonic coherent Lagrangian eddies attract (repel) negatively (positively) buoyant finite-size particles, while cyclonic coherent Lagrangian eddies attract (repel) positively (negatively) buoyant finite-size particles. We show how these results explain dissipative-looking satellite-tracked surface drifter and subsurface float trajectories, as well as satellite-derived Sargassum distributions.
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Affiliation(s)
- Francisco J Beron-Vera
- Department of Atmospheric Sciences, RSMAS, University of Miami, Miami, Florida 33149, USA
| | - María J Olascoaga
- Department of Ocean Sciences, RSMAS, University of Miami, Miami, Florida 33149, USA
| | - George Haller
- Institute for Mechanical Systems, ETH Zurich, Zurich, Switzerland
| | | | - Joaquín Triñanes
- Physical Oceanography Division, AOML, NOAA, Miami, Florida 33149, USA
| | - Yan Wang
- Department of Ocean Sciences, RSMAS, University of Miami, Miami, Florida 33149, USA
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Lovecchio S, Zonta F, Soldati A. Upscale energy transfer and flow topology in free-surface turbulence. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2015; 91:033010. [PMID: 25871205 DOI: 10.1103/physreve.91.033010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/20/2014] [Indexed: 06/04/2023]
Abstract
Free-surface turbulence, albeit constrained onto a two-dimensional space, exhibits features that barely resemble predictions of simplified two-dimensional modeling. We demonstrate that, in a three-dimensional open channel flow, surface turbulence is characterized by upscale energy transfer, which controls the long-term evolution of the larger scales. We are able to associate downscale and upscale energy transfer at the surface with the two-dimensional divergence of velocity. We finally demonstrate that surface compressibility confirms the strongly three-dimensional nature of surface turbulence.
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Affiliation(s)
- Salvatore Lovecchio
- Department of Electrical, Management and Mechanical Engineering, University of Udine, 33100, Udine, Italy
| | - Francesco Zonta
- Department of Electrical, Management and Mechanical Engineering, University of Udine, 33100, Udine, Italy
| | - Alfredo Soldati
- Department of Electrical, Management and Mechanical Engineering, University of Udine, 33100, Udine, Italy
- Department of Fluid Mechanics, CISM, 33100, Udine, Italy
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