scholarly journals Enhanced mixing across the gyre boundary at the Gulf Stream front

2020 ◽  
Vol 117 (30) ◽  
pp. 17607-17614
Author(s):  
Jacob O. Wenegrat ◽  
Leif N. Thomas ◽  
Miles A. Sundermeyer ◽  
John R. Taylor ◽  
Eric A. D’Asaro ◽  
...  
Keyword(s):  
North Atlantic ◽  
Gulf Stream ◽  
Subtropical Gyre ◽  
Freshwater Flux ◽  
Mode Water ◽  
Horizontal Structure ◽  
The North ◽  
Shear Dispersion ◽  
General Importance ◽  
The North Atlantic

The Gulf Stream front separates the North Atlantic subtropical and subpolar ocean gyres, water masses with distinct physical and biogeochemical properties. Exchange across the front is believed to be necessary to balance the freshwater budget of the subtropical gyre and to support the biological productivity of the region; however, the physical mechanisms responsible have been the subject of long-standing debate. Here, the evolution of a passive dye released within the north wall of the Gulf Stream provides direct observational evidence of enhanced mixing across the Gulf Stream front. Numerical simulations indicate that the observed rapid cross-frontal mixing occurs via shear dispersion, generated by frontal instabilities and episodic vertical mixing. This provides unique direct evidence for the role of submesoscale fronts in generating lateral mixing, a mechanism which has been hypothesized to be of general importance for setting the horizontal structure of the ocean mixed layer. Along the Gulf Stream front in the North Atlantic, these observations further suggest that shear dispersion at sharp fronts may provide a source of freshwater flux large enough to explain much of the freshwater deficit in the subtropical-mode water budget and a flux of nutrients comparable to other mechanisms believed to control primary productivity in the subtropical gyre.

The spiralling North Atlantic Subtropical Gyre

2020 ◽  
Author(s):  
Kristofer Döös ◽  
Sara Berglund ◽  
Trevor Mcdougall ◽  
Sjoerd Groeskamp
Keyword(s):  
North Atlantic ◽  
Gulf Stream ◽  
Subtropical Gyre ◽  
The South ◽  
Spiral Flow ◽  
The North ◽  
Saline Waters ◽  
Downward Spiral ◽  
Meridional Overturning ◽  
The North Atlantic

<p>The North Atlantic Subtropical Gyre is shown to have a downward spiral flow beneath the mixed layer, where the water slowly gets denser, colder and fresher as it spins around the gyre. This path is traced with Lagrangian trajectories as they enter the Gyre in the Gulf Stream from the south until they exit through the North Atlantic Drift. The preliminary results indicate that these warm, saline waters from the south gradually becomes fresher, colder and denser due to mixing with waters originating from the North Atlantic. There are indications that there is also a diapycnal mixing, in the eastern part of the gyre due to mixing with the saline Mediterranean Waters, which would then be crucial for the Atlantic Meridional Overturning. The mixing in the rest of the gyre is dominated by isopycnic mixing, which transforms gradually the water into colder and fresher water as it spins down the gyre into the abyssal ocean before heading north.</p>

scholarly journals Modeling the Exposure of the Macaronesia Islands (NE Atlantic) to Marine Plastic Pollution

2021 ◽  
Vol 8 ◽  
Author(s):  
Cláudio Cardoso ◽  
Rui M. A. Caldeira
Keyword(s):  
Canary Islands ◽  
North Atlantic ◽  
Gulf Stream ◽  
Oceanic Islands ◽  
Subtropical Gyre ◽  
Plastic Pollution ◽  
Cabo Verde ◽  
The North ◽  
African Coast ◽  
The North Atlantic

The constant increase of marine plastic pollution poses an unprecedented risk to oceanic islands, which become increasingly exposed to a hazard of which they have very little control. Located in the Northeast Atlantic Ocean, the Macaronesia is comprised by the Azores, Madeira, Canary Islands, and Cabo Verde. Although past studies suggest that most plastic items collected on these islands are from offshore regions, their actual sources remain unclear to present date. As such, we focus on the characterization of the potential sources and pathways of plastic particles reaching the Macaronesia archipelagos. This is achieved by combining modeled datasets for ocean currents, winds and waves with a Lagrangian tool used to track virtual particles released around the archipelagos for a 10-year period, making a distinction between surface and submerged particles. Global drifter trajectories are also assessed, selecting those that intercept the archipelagos. Our results demonstrate that the North Atlantic subtropical gyre is the most conspicuous feature in particles and drifter trajectories. The Gulf Stream acts as the main pathway for all archipelagos at a regional scale, though with less significance to Cabo Verde. Surface particles are connected to regional sources in a shorter timescale than mixed particles, mainly because of the wind. Intercepting high-windage particle trajectories are dominant at the center of the North Atlantic subtropical gyre, demonstrating that particles originating from the North Atlantic “garbage patch” are most likely to intercept the archipelagos if considerably exposed to the wind. Regarding the connectivity to sources, all archipelagos are significantly exposed to areas of intensive fishing activity, mainly those located in the Gulf Stream (Azores), in international waters off the Portuguese coast (Madeira and Canary Islands) and along the Northwestern African coast (Cabo Verde). The east coasts of Central and North America are the main sources of land-based particles reaching the Azores, Madeira, and Canary Islands, whereas the Northwestern African coast is the main source for land-based particles reaching Cabo Verde. Our results demonstrate how vulnerable the Macaronesian archipelagos are to marine plastic pollution, highlighting the urgency for international cooperation to mitigate the exposure of oceanic islands to marine plastic pollution.

Air–Sea Fluxes over the Gulf Stream Region: Atmospheric Controls and Trends

2010 ◽  
Vol 23 (10) ◽  
pp. 2651-2670 ◽  
Author(s):  
Jeffrey Shaman ◽  
R. M. Samelson ◽  
Eric Skyllingstad
Keyword(s):  
Heat Flux ◽  
Latent Heat ◽  
North Atlantic ◽  
Gulf Stream ◽  
Heat Fluxes ◽  
High Flux ◽  
Mode Water ◽  
The North ◽  
Storm Frequency ◽  
The North Atlantic

Abstract The intraseasonal variability of turbulent surface heat fluxes over the Gulf Stream extension and subtropical mode water regions of the North Atlantic, and long-term trends in these fluxes, are explored using NCEP–NCAR reanalysis. Wintertime sensible and latent heat fluxes from these surface waters are characterized by episodic high flux events due to cold air outbreaks from North America. Up to 60% of the November–March (NDJFM) total sensible heat flux and 45% of latent heat flux occurs on these high flux days. On average 41% (34%) of the total NDJFM sensible (latent) heat flux takes place during just 17% (20%) of the days. Over the last 60 years, seasonal NDJFM sensible and latent heat fluxes over the Climate Variability and Predictability (CLIVAR) Mode Water Dynamic Experiment (CLIMODE) region have increased owing to an increased number of high flux event days. The increased storm frequency has altered average wintertime temperature conditions in the region, producing colder surface air conditions over the North American eastern seaboard and Labrador Sea and warmer temperatures over the Sargasso Sea. These temperature changes have increased low-level vertical wind shear and baroclinicity along the North Atlantic storm track over the last 60 years and may further favor the trend of increasing storm frequency over the Gulf Stream extension and adjacent region.

scholarly journals Simulated Response to Recent Freshwater Flux Change over the Gulf Stream and Its Extension: Coupled Ocean–Atmosphere Adjustment and Atlantic–Pacific Teleconnection

2011 ◽  
Vol 24 (15) ◽  
pp. 3971-3988 ◽  
Author(s):  
Liping Zhang ◽  
Lixin Wu ◽  
Jiaxu Zhang
Keyword(s):  
North Atlantic ◽  
Gulf Stream ◽  
Tropical Pacific ◽  
Late Winter ◽  
Freshwater Flux ◽  
The North ◽  
Flux Change ◽  
Ocean Atmosphere ◽  
The North Atlantic ◽  
The Tropical Pacific

Abstract Recent observation has shown that the dominant mode of the net freshwater flux variations over the North Atlantic Ocean is the significant trend of freshwater loss over the Gulf Stream region and its extension. In this paper, the coupled ocean–atmosphere response to this freshwater flux change is investigated based on a series of the Fast Ocean–Atmosphere Model coupled-model experiments. The model demonstrates that the freshwater loss over the Gulf Stream and its extension region directly forces an anomalous cyclonic gyre and triggers a SST dipole with cooling in the western subtropical and warming in the eastern subpolar North Atlantic. The freshwater loss also forces a significant response in the atmosphere with a negative NAO-like response in early winter and a basin-scale ridge resembling the eastern Atlantic mode (EAM) in late winter. The salinification also strengthens the Atlantic meridional overturning circulation and thus the poleward heat transport, leading to tropical cooling. The freshwater loss over the Gulf Stream and its extension also leads to an El Niño–like warming in the tropical Pacific and cooling in the North Pacific, similar to the responses in previous water-hosing experiments with an input of freshwater in the subpolar North Atlantic. The tropical Pacific responses subsequently strengthen the Northern Hemispheric atmospheric anomalies in early winter, but reverse them in late winter through an emanation of Rossby wave trains. Overall, the tropical Pacific air–sea coupling plays a damping role, while local air–sea coupling tends to enhance the ocean and atmospheric responses over the North Atlantic.

scholarly journals Western Boundary Currents and Frontal Air–Sea Interaction: Gulf Stream and Kuroshio Extension

2010 ◽  
Vol 23 (21) ◽  
pp. 5644-5667 ◽  
Author(s):  
Kathryn A. Kelly ◽  
R. Justin Small ◽  
R. M. Samelson ◽  
Bo Qiu ◽  
Terrence M. Joyce ◽  
...  
Keyword(s):  
North Atlantic ◽  
North Pacific ◽  
Gulf Stream ◽  
Kuroshio Extension ◽  
Western Boundary ◽  
Mode Water ◽  
The North ◽  
The North Atlantic ◽  
Current Systems ◽  
The North Pacific

Abstract In the Northern Hemisphere midlatitude western boundary current (WBC) systems there is a complex interaction between dynamics and thermodynamics and between atmosphere and ocean. Their potential contribution to the climate system motivated major parallel field programs in both the North Pacific [Kuroshio Extension System Study (KESS)] and the North Atlantic [Climate Variability and Predictability (CLIVAR) Mode Water Dynamics Experiment (CLIMODE)], and preliminary observations and analyses from these programs highlight that complexity. The Gulf Stream (GS) in the North Atlantic and the Kuroshio Extension (KE) in the North Pacific have broad similarities, as subtropical gyre WBCs, but they also have significant differences, which affect the regional air–sea exchange processes and their larger-scale interactions. The 15-yr satellite altimeter data record, which provides a rich source of information, is combined here with the longer historical record from in situ data to describe and compare the current systems. While many important similarities have been noted on the dynamic and thermodynamic aspects of the time-varying GS and KE, some not-so-subtle differences exist in current variability, mode water properties, and recirculation gyre structure. This paper provides a comprehensive comparison of these two current systems from both dynamical and thermodynamical perspectives with the goal of developing and evaluating hypotheses about the physics underlying the observed differences, and exploring the WBC’s potential to influence midlatitude sea–air interaction. Differences between the GS and KE systems offer opportunities to compare the dominant processes and thereby to advance understanding of their role in the climate system.

scholarly journals Modal composition of the central water in the North Atlantic subtropical gyre

2009 ◽  
Vol 6 (3) ◽  
pp. 2487-2506 ◽  
Author(s):  
A. Cianca ◽  
R. Santana ◽  
J. P. Marrero ◽  
M. J. Rueda ◽  
O. Llinás
Keyword(s):  
Time Series ◽  
North Atlantic ◽  
World Ocean ◽  
Average Density ◽  
Subtropical Gyre ◽  
Mode Water ◽  
Data Set ◽  
Modal Composition ◽  
The North ◽  
The North Atlantic

Abstract. The modal composition of the Central Water in the North Atlantic subtropical gyre is not clearly defined, as there are some uncertainties related to mode identification, as well as modes which are not well documented. This study shows that eastern North Atlantic Central Water (eastern NACW) in the subtropical gyre is composed of three modes: The North Atlantic Subpolar Mode Water (NASPMW σt=27.1 to 27.3), the Madeira Mode Water (MMW σt=26.4 to 26.6), and the mode water with a σt near 27.0, which is currently not well documented. We confirmed this mode based on the similarities found between it and the mode waters already reported. The similarities were determined from comparative analyses of the temperature/salinity standard curves and the gradients of the potential density anomalies of two concurrent data sets from two subtropical time-series stations (Bermuda Atlantic Time-series Study, BATS, in the west, and European Station for Time-series in the Ocean Canary Islands, ESTOC, in the east). In order to establish the outcropping regions, the corresponding pycnostads were determined using another climatologic data set (World Ocean Database, WOD2005). In this case, the pycnostads were located based on the presence of standard deviation minima from the average density anomalies. Finally, we confirmed that the pycnostads corresponded to the temperature values related to the modes by overlaying the characteristic modal isotherm of each of the modes in the geographic distribution of the pycnostads. Sea surface temperature data (SST) from the Ocean Pathfinder Program (OPP) were used to estimate the isotherms. The results showed a clear correspondence between the modal isotherms and the pycnostads, for both the modes that have already been documented and the mode confirmed in this study.

Gulf Stream rings as a source of iron to the North Atlantic subtropical gyre

2018 ◽  
Vol 11 (8) ◽  
pp. 594-598 ◽  
Author(s):  
Tim M. Conway ◽  
Jaime B. Palter ◽  
Gregory F. de Souza
Keyword(s):  
North Atlantic ◽  
Gulf Stream ◽  
Subtropical Gyre ◽  
The North ◽  
The North Atlantic

scholarly journals The North Atlantic Eddy Heat Transport and Its Relation with the Vertical Tilting of the Gulf Stream Axis

2017 ◽  
Vol 47 (6) ◽  
pp. 1281-1289 ◽  
Author(s):  
A. M. Treguier ◽  
C. Lique ◽  
J. Deshayes ◽  
J. M. Molines
Keyword(s):  
Numerical Model ◽  
Heat Transport ◽  
North Atlantic ◽  
Gulf Stream ◽  
Mean Flow ◽  
The North ◽  
Spatial Shift ◽  
Eddy Heat Flux ◽  
Eddy Heat Transport ◽  
The North Atlantic

AbstractCorrelations between temperature and velocity fluctuations are a significant contribution to the North Atlantic meridional heat transport, especially at the northern boundary of the subtropical gyre. In satellite observations and in a numerical model at ⅞° resolution, a localized pattern of positive eddy heat flux is found northwest of the Gulf Stream, downstream of its separation at Cape Hatteras. It is confined to the upper 500 m. A simple kinematic model of a meandering jet can explain the surface eddy flux, taking into account a spatial shift between the maximum velocity of the jet and the maximum cross-jet temperature gradient. In the Gulf Stream such a spatial shift results from the nonlinear temperature profile and the vertical tilting of the velocity profile with depth. The numerical model suggests that the meandering of the Gulf Stream could account, at least in part, for the large eddy heat transport (of order 0.3 PW) near 36°N in the North Atlantic and for its compensation by the mean flow.

scholarly journals Forecasting the Gulf Stream Path using Buoyancy and Wind Forcing over the North Atlantic

2021 ◽  
Author(s):  
Adrienne Silver ◽  
Avijit Gangopadhyay ◽  
Glen Gawarkiewicz ◽  
Arnold Taylor ◽  
Alejandra Sanchez‐Franks
Keyword(s):  
North Atlantic ◽  
Gulf Stream ◽  
Wind Forcing ◽  
The North ◽  
The North Atlantic
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