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Jonathan Gula - One of the best experts on this subject based on the ideXlab platform.
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Interaction of the Gulf Stream with small scale topography: a focus on lee waves.
Scientific reports, 2020Co-Authors: Charly De Marez, Noé Lahaye, Jonathan GulaAbstract:The generation of lee waves in the Gulf Stream along the U.S. seaboard is investigated using high resolution realistic simulations. The model reproduces the surface signature of the waves, which compares favourably with observations from satellite sun glitter images in the region. In particular, a large number of internal waves are observed above the Charleston Bump. These waves match well with the linear theory describing topographically-generated internal waves, which can be used to estimate the associated vertical transport of momentum and energy extracted from the mean flow. Finally, small scale topographic features are shown to have a significant impact on the mean flow in this region of the Gulf Stream, and the specific role of lee waves in this context is outlined.
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the Gulf Stream north wall ageostrophic circulation and frontogenesis
Journal of Physical Oceanography, 2019Co-Authors: James C Mcwilliams, Jonathan Gula, Jeroen M MolemakerAbstract:AbstractEastward zonal jets are common in the ocean and atmosphere, for example, the Gulf Stream and jet Stream. They are characterized by atypically strong horizontal velocity, baroclinic vertical...
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Submesoscale Coherent Vortices in the Gulf Stream
Geophysical Research Letters, 2019Co-Authors: Jonathan Gula, Tanya M. Blacic, Robert E. ToddAbstract:Seismic images and glider sections of the Gulf Stream front along the U.S. eastern seaboard capture deep, lens-shaped submesoscale features. These features have radii of 5-20 km, thicknesses of 150-300 m, and are located at depths greater than 500 m. These are typical signatures of anticyclonic submesoscale coherent vortices. A submesoscale-resolving realistic simulation, which reproduces submesoscale coherent vortices with the same characteristics, is used to analyze their generation mechanism. Submesoscale coherent vortices are primarily generated where the Gulf Stream meets the Charleston Bump, a deep topographic feature, due to the frictional effects and intense mixing in the wake of the topography. These submesoscale coherent vortices can transport waters from the Charleston Bump's thick bottom mixed layer over long distances and spread them within the subtropical gyre. Their net effect on heat and salt distribution remains to be quantified. Plain Language Summary The interior of the ocean is populated by small-scale coherent vortices, which redistribute water properties on the scale of basins. These structures are very difficult to observe. They have no surface signature and small dimensions, on the order of 1-50 km, such that they are missed by satellites and sampled only by chance. Furthermore, climate-scale ocean models do not resolve these type of motions and do not take into account their impacts for the large-scale transport and distribution of heat, nutrients, and other materials. Understanding and parameterizing these phenomena within models is critical for a better prediction of climate. Here we present new observations of submesoscale coherent vortices from seismic images and glider sections in the region of the Gulf Stream. We use a numerical model at very high resolution to reproduce vortices with the same characteristics and to analyze their generation mechanism. These vortices are generated where the Gulf Stream interacts with a deep topographic feature called the Charleston Bump due to frictional effects and intense mixing in the wake of the topography. These vortices transport waters from the Charleston Bump's thick bottom mixed layer and act to spread them all around the subtropical gyre.
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submesoscale Streamers exchange water on the north wall of the Gulf Stream
Geophysical Research Letters, 2016Co-Authors: Jody M Klymak, Jonathan Gula, Leif N. Thomas, Miles A Sundermeyer, Eric A Dasaro, Kipp R Shearman, Craig M Lee, Ramsey R Harcourt, Andrey Y Shcherbina, Jeroen M MolemakerAbstract:The Gulf Stream is a major conduit of warm surface water from the tropics to the subpolar North Atlantic. Here we observe and simulate a submesoscale (<20 km) mechanism by which the Gulf Stream exchanges water with subpolar water to the north. Along isopycnals, the front has a sharp compensated temperature-salinity contrast, with distinct mixed water between the two water masses 2 and 4 km wide. This mixed water does not increase downStream despite substantial energy available for mixing. A series of Streamers detrain this water at the crest of meanders. Subpolar water replaces the mixed water and resharpens the front. The water mass exchange accounts for a northward flux of salt of 0.5–2.5 psu m2 s−1, (large-scale diffusivity O (100 m2 s−1)). This is similar to bulk-scale flux estimates of 1.2 psu m2 s−1 and supplies fresher water to the Gulf Stream required for the production of 18° subtropical mode water.
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submesoscale dynamics of a Gulf Stream frontal eddy in the south atlantic bight
Journal of Physical Oceanography, 2016Co-Authors: Jonathan Gula, Jeroen M Molemaker, James C McwilliamsAbstract:AbstractFrontal eddies are commonly observed and understood as the product of an instability of the Gulf Stream along the southeastern U.S. seaboard. Here, the authors study the dynamics of a simulated Gulf Stream frontal eddy in the South Atlantic Bight, including its structure, propagation, and emergent submesoscale interior and neighboring substructure, at very high resolution (dx = 150 m). A rich submesoscale structure is revealed inside the frontal eddy. Meander-induced frontogenesis sharpens the gradients and forms very sharp fronts between the eddy and the adjacent Gulf Stream. The strong straining increases the velocity shear and suppresses the development of barotropic instability on the upStream face of the meander trough. Barotropic instability of the sheared flow develops from small-amplitude perturbations when the straining weakens at the trough. Small-scale meandering perturbations evolve into rolled-up submesoscale vortices that are advected back into the interior of the frontal eddy. The d...
James C Mcwilliams - One of the best experts on this subject based on the ideXlab platform.
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the Gulf Stream north wall ageostrophic circulation and frontogenesis
Journal of Physical Oceanography, 2019Co-Authors: James C Mcwilliams, Jonathan Gula, Jeroen M MolemakerAbstract:AbstractEastward zonal jets are common in the ocean and atmosphere, for example, the Gulf Stream and jet Stream. They are characterized by atypically strong horizontal velocity, baroclinic vertical...
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submesoscale dynamics of a Gulf Stream frontal eddy in the south atlantic bight
Journal of Physical Oceanography, 2016Co-Authors: Jonathan Gula, Jeroen M Molemaker, James C McwilliamsAbstract:AbstractFrontal eddies are commonly observed and understood as the product of an instability of the Gulf Stream along the southeastern U.S. seaboard. Here, the authors study the dynamics of a simulated Gulf Stream frontal eddy in the South Atlantic Bight, including its structure, propagation, and emergent submesoscale interior and neighboring substructure, at very high resolution (dx = 150 m). A rich submesoscale structure is revealed inside the frontal eddy. Meander-induced frontogenesis sharpens the gradients and forms very sharp fronts between the eddy and the adjacent Gulf Stream. The strong straining increases the velocity shear and suppresses the development of barotropic instability on the upStream face of the meander trough. Barotropic instability of the sheared flow develops from small-amplitude perturbations when the straining weakens at the trough. Small-scale meandering perturbations evolve into rolled-up submesoscale vortices that are advected back into the interior of the frontal eddy. The d...
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topographic vorticity generation submesoscale instability and vortex street formation in the Gulf Stream
Geophysical Research Letters, 2015Co-Authors: Jonathan Gula, M J Molemaker, James C McwilliamsAbstract:Meanders and eddies are routinely observed in the Gulf Stream along the South Atlantic Bight. We analyze here the instability processes that lead to the formation of submesoscale eddies on the cyclonic side of the Gulf Stream at the exit of the Florida Straits using very high resolution realistic simulations. The positive relative vorticity and potential vorticity on the cyclonic side of the Gulf Stream are strongly intensified in the Straits due to topographic drag along the continental slope. The bottom drag amplifies the cyclonic shear by generating large positive vertical vorticity values within the sloped turbulent bottom boundary layer. DownStream from the Straits the current becomes unstable to horizontal shear instability, rolls up, and forms a street of submesoscale vortices. The vortices expand as they propagate northward along the shelf, where they can generate large vertical displacements and enhance cross-shelf exchanges.
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Gulf Stream dynamics along the southeastern u s seaboard
Journal of Physical Oceanography, 2015Co-Authors: Jonathan Gula, Jeroen M Molemaker, James C McwilliamsAbstract:AbstractThe Gulf Stream strongly interacts with the topography along the southeastern U.S. seaboard, between the Straits of Florida and Cape Hatteras. The dynamics of the Gulf Stream in this region is investigated with a set of realistic, very high-resolution simulations using the Regional Ocean Modeling System (ROMS). The mean path is strongly influenced by the topography and in particular the Charleston Bump. There are significant local pressure anomalies and topographic form stresses exerted by the bump that retard the mean flow and steer the mean current pathway seaward. The topography provides, through bottom pressure torque, the positive input of barotropic vorticity necessary to balance the meridional transport of fluid and close the gyre-scale vorticity balance. The effect of the topography on the development of meanders and eddies is studied by computing energy budgets of the eddies and the mean flow. The baroclinic instability is stabilized by the slope everywhere except past the bump. The flow ...
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submesoscale cold filaments in the Gulf Stream
Journal of Physical Oceanography, 2014Co-Authors: Jonathan Gula, Jeroen M Molemaker, James C McwilliamsAbstract:AbstractA set of realistic, very high-resolution simulations is made for the Gulf Stream region using the oceanic model Regional Oceanic Modeling System (ROMS) to study the life cycle of the intense submesoscale cold filaments that form on the subtropical gyre, interior wall of the Gulf Stream. The surface buoyancy gradients and ageostrophic secondary circulations intensify in response to the mesoscale strain field as predicted by the theory of filamentogenesis. It can be understood in terms of a dual frontogenetic process, along the lines understood for a single front. There is, however, a stronger secondary circulation due to the amplification at the center of a cold filament. Filament dynamics in the presence of a mixed layer are not adequately described by the classical thermal wind balance. The effect of vertical mixing of momentum due to turbulence in the surface layer is of the same order of magnitude as the pressure gradient and Coriolis force and contributes equally to a so-called turbulent therm...
Robert E. Todd - One of the best experts on this subject based on the ideXlab platform.
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Submesoscale Coherent Vortices in the Gulf Stream
Geophysical Research Letters, 2019Co-Authors: Jonathan Gula, Tanya M. Blacic, Robert E. ToddAbstract:Seismic images and glider sections of the Gulf Stream front along the U.S. eastern seaboard capture deep, lens-shaped submesoscale features. These features have radii of 5-20 km, thicknesses of 150-300 m, and are located at depths greater than 500 m. These are typical signatures of anticyclonic submesoscale coherent vortices. A submesoscale-resolving realistic simulation, which reproduces submesoscale coherent vortices with the same characteristics, is used to analyze their generation mechanism. Submesoscale coherent vortices are primarily generated where the Gulf Stream meets the Charleston Bump, a deep topographic feature, due to the frictional effects and intense mixing in the wake of the topography. These submesoscale coherent vortices can transport waters from the Charleston Bump's thick bottom mixed layer over long distances and spread them within the subtropical gyre. Their net effect on heat and salt distribution remains to be quantified. Plain Language Summary The interior of the ocean is populated by small-scale coherent vortices, which redistribute water properties on the scale of basins. These structures are very difficult to observe. They have no surface signature and small dimensions, on the order of 1-50 km, such that they are missed by satellites and sampled only by chance. Furthermore, climate-scale ocean models do not resolve these type of motions and do not take into account their impacts for the large-scale transport and distribution of heat, nutrients, and other materials. Understanding and parameterizing these phenomena within models is critical for a better prediction of climate. Here we present new observations of submesoscale coherent vortices from seismic images and glider sections in the region of the Gulf Stream. We use a numerical model at very high resolution to reproduce vortices with the same characteristics and to analyze their generation mechanism. These vortices are generated where the Gulf Stream interacts with a deep topographic feature called the Charleston Bump due to frictional effects and intense mixing in the wake of the topography. These vortices transport waters from the Charleston Bump's thick bottom mixed layer and act to spread them all around the subtropical gyre.
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high frequency internal waves and thick bottom mixed layers observed by gliders in the Gulf Stream
Geophysical Research Letters, 2017Co-Authors: Robert E. ToddAbstract:Autonomous underwater gliders are conducting high-resolution surveys within the Gulf Stream along the U.S. East Coast. Glider surveys reveal two mechanisms by which energy is extracted from the Gulf Stream as it flows over the Blake Plateau, a portion of the outer continental shelf between Florida and North Carolina where bottom depths are less than 1000 m. Internal waves with vertical velocities exceeding 0.1 m s−1 and frequencies just below the local buoyancy frequency are routinely found over the Blake Plateau, particularly near the Charleston Bump, a prominent topographic feature. These waves are likely internal lee waves generated by the subinertial Gulf Stream flow over the irregular bathymetry of the outer continental shelf. Bottom mixed layers with O(100) m thickness are also frequently encountered; these thick bottom mixed layers likely form in the lee of topography due to enhanced turbulence generated by O(1) m s−1 near-bottom flows.
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direct interaction between the Gulf Stream and the shelfbreak south of new england
Scientific Reports, 2012Co-Authors: Glen Gawarkiewicz, Robert E. Todd, Albert J Plueddemann, Magdalena Andres, James P ManningAbstract:Sea surface temperature imagery, satellite altimetry and a surface drifter track reveal an unusual tilt in the Gulf Stream path that brought the Gulf Stream to 39.9°N near the Middle Atlantic Bight shelfbreak—200 km north of its mean position—in October 2011, while a large meander brought Gulf Stream water within 12 km of the shelfbreak in December 2011. Near-bottom temperature measurements from lobster traps on the outer continental shelf south of New England show distinct warming events (temperature increases exceeding 6°C) in November and December 2011. Moored profiler measurements over the continental slope show high salinities and temperatures, suggesting that the warm water on the continental shelf originated in the Gulf Stream. The combination of unusual water properties over the shelf and slope in late fall and the subsequent mild winter may affect seasonal stratification and habitat selection for marine life over the continental shelf in 2012.
Matthew J Hornbach - One of the best experts on this subject based on the ideXlab platform.
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recent changes to the Gulf Stream causing widespread gas hydrate destabilization
AGU Fall Meeting Abstracts, 2012Co-Authors: Benjamin J Phrampus, Matthew J HornbachAbstract:The Gulf Stream is an ocean current that modulates climate in the Northern Hemisphere by transporting warm waters from the Gulf of Mexico into the North Atlantic and Arctic oceans. A changing Gulf Stream has the potential to thaw and convert hundreds of gigatonnes of frozen methane hydrate trapped below the sea floor into methane gas, increasing the risk of slope failure and methane release. How the Gulf Stream changes with time and what effect these changes have on methane hydrate stability is unclear. Here, using seismic data combined with thermal models, we show that recent changes in intermediate-depth ocean temperature associated with the Gulf Stream are rapidly destabilizing methane hydrate along a broad swathe of the North American margin. The area of active hydrate destabilization covers at least 10,000 square kilometres of the United States eastern margin, and occurs in a region prone to kilometre-scale slope failures. Previous hypothetical studies postulated that an increase of five degrees Celsius in intermediate-depth ocean temperatures could release enough methane to explain extreme global warming events like the Palaeocene-Eocene thermal maximum (PETM) and trigger widespread ocean acidification. Our analysis suggests that changes in Gulf Stream flow or temperature within the past 5,000 years or so are warming the western North Atlantic margin by up to eight degrees Celsius and are now triggering the destabilization of 2.5 gigatonnes of methane hydrate (about 0.2 per cent of that required to cause the PETM). This destabilization extends along hundreds of kilometres of the margin and may continue for centuries. It is unlikely that the western North Atlantic margin is the only area experiencing changing ocean currents; our estimate of 2.5 gigatonnes of destabilizing methane hydrate may therefore represent only a fraction of the methane hydrate currently destabilizing globally. The transport from ocean to atmosphere of any methane released--and thus its impact on climate--remains uncertain.
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recent changes to the Gulf Stream causing widespread gas hydrate destabilization
Nature, 2012Co-Authors: Benjamin J Phrampus, Matthew J HornbachAbstract:Seismic data and modelling are used to reveal clathrate destabilization along the eastern margin of the United States; the destabilization is probably linked to warming, or a slight shift, in the Gulf Stream. Clathrates store enormous amounts of methane, much of it in shallow ocean shelf environments. It has been proposed that sudden methane release from clathrates could cause abrupt climate changes, and this has been invoked to explain past warming events such as the Paleocene–Eocene thermal maximum. Clathrate destabilization in the modern climate is possible, especially in cases of pronounced ocean warming. Here, Benjamin Phrampus and Matthew Hornbach use seismic data and modelling to reveal clathrate destabilization along the United States Eastern margin. The destabilization is thought to be linked to warming of the Gulf Stream, or to a slight shift in its position. The climatic impact of the methane released by clathrate destabilization remains uncertain, however, because it is not clear how much of the methane would actually enter the atmosphere. The Gulf Stream is an ocean current that modulates climate in the Northern Hemisphere by transporting warm waters from the Gulf of Mexico into the North Atlantic and Arctic oceans1,2. A changing Gulf Stream has the potential to thaw and convert hundreds of gigatonnes of frozen methane hydrate trapped below the sea floor into methane gas, increasing the risk of slope failure and methane release3,4,5,6,7,8,9. How the Gulf Stream changes with time and what effect these changes have on methane hydrate stability is unclear. Here, using seismic data combined with thermal models, we show that recent changes in intermediate-depth ocean temperature associated with the Gulf Stream are rapidly destabilizing methane hydrate along a broad swathe of the North American margin. The area of active hydrate destabilization covers at least 10,000 square kilometres of the United States eastern margin, and occurs in a region prone to kilometre-scale slope failures. Previous hypothetical studies3,5 postulated that an increase of five degrees Celsius in intermediate-depth ocean temperatures could release enough methane to explain extreme global warming events like the Palaeocene–Eocene thermal maximum (PETM) and trigger widespread ocean acidification7. Our analysis suggests that changes in Gulf Stream flow or temperature within the past 5,000 years or so are warming the western North Atlantic margin by up to eight degrees Celsius and are now triggering the destabilization of 2.5 gigatonnes of methane hydrate (about 0.2 per cent of that required to cause the PETM). This destabilization extends along hundreds of kilometres of the margin and may continue for centuries. It is unlikely that the western North Atlantic margin is the only area experiencing changing ocean currents10,11,12; our estimate of 2.5 gigatonnes of destabilizing methane hydrate may therefore represent only a fraction of the methane hydrate currently destabilizing globally. The transport from ocean to atmosphere of any methane released—and thus its impact on climate—remains uncertain.
Glen Gawarkiewicz - One of the best experts on this subject based on the ideXlab platform.
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Gulf Stream ring water intrusion on the mid atlantic bight continental shelf break affects microbially driven carbon cycling
Frontiers in Marine Science, 2019Co-Authors: Adrienne Hoarfrost, John M Bane, Glen Gawarkiewicz, John Paul Balmonte, Sherif Ghobrial, Kai Ziervogel, Carol ArnostiAbstract:Warm core, anticyclonic rings that spin off from the Gulf Stream circulate through the region directly offshore of the Mid-Atlantic Bight. If a warm core ring reaches the continental shelf break, its warm, highly saline water may subduct under cooler, fresher continental shelf surface water, resulting in subsurface waters at the shelf break and over the upper continental slope with high temperatures and salinities and distinct physical and chemical properties characteristic of Gulf Stream water. Such intruding water may also have microbial communities with distinct functional capacities, which may in turn affect the rate and nature of carbon cycling in this coastal/shelf environment. However, the functional capabilities of microbial communities within ring intrusion waters relative to surrounding continental shelf waters are largely unexplored. We investigated microbial community capacity to initiate organic matter remineralization by measuring hydrolysis of a suite of polysaccharide, peptide, and glucose substrates along a transect oriented across the Mid-Atlantic Bight shelf, shelf break, and upper slope. At the outermost sampling site, warm and salty water derived from a Gulf Stream warm core ring was present in the lower portion of the water column. This water exhibited hydrolytic capacities distinct from other sampling sites, and exhibited lower heterotrophic bacterial productivity overall. Warm core rings adjacent to the Mid-Atlantic Bight shelf have increased in frequency and duration in recent years. As the influence of warm core rings on the continental shelf and slope increases in the future, the rate and nature of organic matter remineralization on the continental shelf may also shift.
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dynamics of the direct intrusion of Gulf Stream ring water onto the mid atlantic bight shelf
Geophysical Research Letters, 2015Co-Authors: Weifeng Zhang, Glen GawarkiewiczAbstract:Onshore intrusions of offshore waters onto the Mid-Atlantic Bight shelf can greatly affect shelf circulation, biogeochemistry, and fisheries. Previous studies have concentrated on onshore intrusions of slope water. Here we present a direct intrusion of Gulf Stream warm-core ring water onto the shelf representing a previously unknown exchange process at the shelfbreak. Impingement of warm-core rings at the shelfbreak generates along-isobath intrusions that grow like Pinocchio's nose, extending hundreds of kilometers to the southwest. By combining satellite and Ocean Observatory Initiative Pioneer Array data and idealized numerical simulations, we discover that the intrusion results from topographically induced vorticity variation of the ring water, rather than from entrainment of the shelfbreak frontal jet. This intrusion of the Gulf Stream ring water has important biogeochemical implications and could facilitate migration of marine species across the shelfbreak barrier and transport low-nutrient surface Gulf Stream ring water to the otherwise productive shelfbreak region.
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direct interaction between the Gulf Stream and the shelfbreak south of new england
Scientific Reports, 2012Co-Authors: Glen Gawarkiewicz, Robert E. Todd, Albert J Plueddemann, Magdalena Andres, James P ManningAbstract:Sea surface temperature imagery, satellite altimetry and a surface drifter track reveal an unusual tilt in the Gulf Stream path that brought the Gulf Stream to 39.9°N near the Middle Atlantic Bight shelfbreak—200 km north of its mean position—in October 2011, while a large meander brought Gulf Stream water within 12 km of the shelfbreak in December 2011. Near-bottom temperature measurements from lobster traps on the outer continental shelf south of New England show distinct warming events (temperature increases exceeding 6°C) in November and December 2011. Moored profiler measurements over the continental slope show high salinities and temperatures, suggesting that the warm water on the continental shelf originated in the Gulf Stream. The combination of unusual water properties over the shelf and slope in late fall and the subsequent mild winter may affect seasonal stratification and habitat selection for marine life over the continental shelf in 2012.