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1. Lagrangian coherence and source of water of Loop Current Frontal Eddies in the Gulf of Mexico. Progress in Oceanography.

   Hiron, L. (August 2022, Progress in Oceanography)

   Elsevier Publishing Company (Ed.)

   Loop Current Frontal Eddies (LCFEs) are known to intensify and assist in the Loop Current (LC) eddy shedding. In addition to interacting with the LC, these eddies also modify the circulation in the eastern Gulf of Mexico by attracting water and passive tracers such as chlorophyll, Mississippi freshwater, and pollutants to the LC-LCFE front. During the 2010 Deepwater Horizon oil spill, part of the oil was entrained not only in the LC-LCFE front but also inside an LCFE, where it remained for weeks. This study assesses the ability of the LCFEs to transport water and passive tracers without exchange with the exterior (i.e., Lagrangian coherence) using altimetry and a high-resolution model. The following open questions are answered: (1) How long can the LCFEs remain Lagrangian coherent at and below the surface? (2) What is the source of water for the formation of LCFEs? (3) Can the formation of Lagrangian coherent LCFEs attract shelf water? Strong frontal eddies leading to LC eddy shedding are investigated using a 1-km resolution model for the Gulf of Mexico and altimetry. The results show that LCFEs are composed of waters originating from the outer band of the LC front, the region north of the LC, and the western West Florida Shelf and Mississippi/Alabama/Florida shelf, and potentially drive cross-shelf exchange of particles, water properties, and nutrients. At depth (≈180 m), most LCFE water comes from the outer band of the LC front in the form of smaller frontal eddies. Once formed, LCFEs can transport water and passive tracers in their interior without exchange with the exterior for weeks: these eddies remained Lagrangian coherent for up to 25 days in the altimetry dataset and 18 days at the surface and 29 days at depth (≈180 m) in the simulation. LCFE can remain Lagrangian coherent up to a depth of ≈ 560 m. Additional analyses show that the LCFE involved in the Deepwater Horizon oil spill formed from water near the oil rig location, in agreement with previous studies. Temperature-salinity diagrams from a high-resolution model and aircraft expendable profilers show that LCFEs are composed of Gulf of Mexico water as opposed to LC water. Therefore, LCFE formation and propagation actively modify the surrounding circulation and affect the evolution of the flow and the transport of oil and other passive tracers in the Eastern Gulf of Mexico. 

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2. Eddy‐Induced Iron Transport Sustains the Biological Productivity in the Gulf of Alaska

   https://doi.org/10.1029/2025JC022996  

   Ito, T; Timmerman, A_H V; Bjouklund, A; Stanley, S I; Abe, Y; Reinhard, C T; Montoya, J (February 2026, Journal of Geophysical Research: Oceans)

   Abstract The surface waters of the subarctic northeastern Pacific Ocean contain high concentrations of macronutrients such as phosphate and nitrate, which can potentially drive photosynthesis and biological uptake of carbon dioxide. Regional biological productivity, however, is limited by a lack of necessary micronutrients such as iron. In the Gulf of Alaska, there is a strong biogeochemical gradient from highly productive and nitrogen‐limited coastal waters to the weakly productive and iron‐limited open ocean. It has been hypothesized that the cross‐shelf transport by ocean eddies transports the iron‐rich coastal waters to the offshore regions. An eddy‐permitting ocean biogeochemistry model is developed to simulate the role of mesoscale ocean eddies in shaping nutrient cycling and regional biological productivity. Model skills are first evaluated using in situ and satellite observations. Through a case study and sensitivity experiments, the physical and biogeochemical structures of the mesoscale eddies are examined, informing the mechanisms behind cross‐shelf transport of dissolved iron. Anticyclonic eddies generated along the continental shelves during the late winter contain an elevated level of dissolved iron just below the surface of the mixed layer. The biological productivity in the late spring and early summer in the offshore regions is supported by these anticyclonic eddies within about 300 km from the coastline. A sensitivity experiment is performed to purposefully suppress the mesoscale features, showing a reduction in the biological productivity accompanied by a reduction in eddy activity in this region. Resolving mesoscale eddies is crucial for correctly representing the biological productivity in this region. 

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3. Frontal Subduction of the Mid-Atlantic Bight Shelf Water at the Onshore Edge of a Warm-Core Ring

   https://doi.org/10.1029/2018JC013794  

   Zhang, Weifeng G.; Partida, Jacob (October 2018, Journal of Geophysical Research: Oceans)

   This work studies the subduction of the shelf water along the onshore edge of a warm-core ring (WCR) that impinges on the edge of the Mid-Atlantic Bight continental shelf. The dynamical analysis is based on observations by satellites and from the Ocean Observatories Initiative Pioneer Array observatory as well as idealized numerical model simulations. They together show that frontogenesis-induced submesoscale frontal subduction with order-one Rossby and Froude numbers occurs on the onshore edge of the ring. The subduction flow results from the onshore migration of the WCR that intensifies the density front on the interface of the ring and shelf waters. The subduction is a part of the cross-front secondary circulation trying to relax the intensifying density front. The dramatically different physical and biogeochemical properties of the ring and shelf waters provide a great opportunity to visualize the subduction phenomenon. Entrained by the ring-edge current, the subducted shelf water is subsequently transported offshore below a surface layer of ring water and alongside of the surface-visible shelf-water streamer. It explains the historical observations of isolated subsurface packets of shelf water along the ring periphery in the slope sea. Model-based estimate suggests that this type of subduction-associated subsurface cross-shelfbreak transport of the shelf water could be substantial relative to other major forms of shelfbreak water exchange. This study also proposes that outward spreading of the ring-edge front by the frontal subduction may facilitate entrainment of the shelf water by the ring-edge current and enhances the shelf-water streamer transport at the shelf edge. 

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4. Sargassum Enrichment in Mesoscale Eddies of the Great Atlantic Sargassum Belt

   Zhang, Yingjun; Barnes, Brian B; McGillicuddy, Dennis J; Hu, Chuanmin (March 2025, Geophysical research letters)

   Pelagic Sargassum has increased dramatically in the past decade, primarily in the annually recurrent Great Atlantic Sargassum Belt (GASB) that extends from the coast of West Africa to the Gulf of Mexico. Using satellite observations of Sargassum density and mesoscale eddies from 2011 to 2023, we investigate whether more Sargassum can be found in mesoscale eddies. Cyclonic eddies were found to contain 6%–47% more Sargassum (relative to eddy-free waters) across all selected regions within the GASB, with the highest Sargassum density in their inner cores (<0.5 eddy radius). Impacts of anticyclonic eddies were weaker and varied between regions. In addition, Sargassum enrichment tended to be higher in eddies with greater size or amplitude, such as the North Brazil Current rings and those in the Caribbean Sea. These findings may inform Sargassum mitigation strategies, for example, through physical removal in targeted locations. 

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5. (2014) Coastal Pioneer New England Shelf Mobile Assets (CP05MOAS)

   https://doi.org/10.58046/ooi-cp05moas  

   NSF_Ocean_Observatories_Initiative (January 2014, US NSF Ocean Observatories Initiative)

   Two kinds of Mobile Assets survey the area in and around the array of moorings at the Coastal Pioneer Array – Coastal Gliders and Coastal Autonomous Underwater Vehicles (AUVs).\n\nAn array of 6 Coastal Gliders (Teledyne-Webb Slocum Gliders) sample large, mesoscale features through a broad region (130 x 185 km) of the outer continental shelf between the shelf break and the Gulf Stream. The role of these gliders in monitoring this broader area is to resolve rings, eddies and meanders from the Gulf Stream as they impinge on the shelf break front. These Teledyne-Webb Slocum Gliders fly through the water column along saw-tooth paths, penetrating the sea surface and diving down to a maximum depth of 1000 meters.\n\nAn array of two Coastal AUVs (REMUS-600 AUVs) travel along transects across the shelf-break frontal system extending beyond the mooring array, covering an area approximately 80 x 100 km in size centered on the array of moorings. The primary role of the AUVs is to resolve cross- and along-front “eddy fluxes” due to frontal instabilities, wind forcing, and mesoscale variability. These AUVs travel along saw-toothed transects, penetrating the sea surface and diving down to a maximum depth of 600 meters. 

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