Structure and Formation of Anticyclonic Eddies in the Iceland Basin

Zhao, Jianrong; Bower, Amy S.; Yang, Jiayan; Lin, Xiaopei; Zhou, Chun

doi:10.1029/2018jc013886

Cited by 22 publications

(30 citation statements)

References 76 publications

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“…Another anticyclonic eddy presenting a structure similar to the UK Plankton Reactivity in the Marine Environment eddy was surveyed in June 1998 by Read and Pollard (). Zhao, Bower, Yang, Lin, and Zhou () used high‐resolution observations to document the structure of an anticyclonic eddy found during the June–November 2015 period in the Iceland Basin (58–59°N, 23–21°W). They also found similar anticyclonic eddies in high‐resolution numerical model simulations, which they used to explore eddy formation.…”

Section: Discussionmentioning

confidence: 99%

Structure and Transport of the North Atlantic Current in the Eastern Subpolar Gyre From Sustained Glider Observations

et al. 2018

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Repeat glider sections obtained during 2014–2016, as part of the Overturning in the Subpolar North Atlantic Program, are used to quantify the circulation and transport of North Atlantic Current (NAC) branches over the Rockall Plateau. Using 16 glider sections collected along 58°N and between 21°W and 15°W, absolute geostrophic velocities are calculated, and subsequently the horizontal and vertical structure of the transport are characterized. The annual mean northward transport (± standard deviation) is 5.1 ± 3.2 Sv over the Rockall Plateau. During summer (May to October), the mean northward transport is stronger and reaches 6.7 ± 2.6 Sv. This accounts for 43% of the total NAC transport of upper‐ocean waters (σO<27.55 kg/m3) estimated by Sarafanov et al. (2012, https://doi.org/10.1029/2011JC007572) along 59.5°N, between the Reykjanes Ridge and Scotland. Two quasi‐permanent northward flowing branches of the NAC are identified: (i) the Hatton Bank Jet (6.3 ± 2.1 Sv) over the eastern flank of the Iceland Basin (20.5°W to 18.5°W) and (ii) the Rockall Bank Jet (1.5 ± 0.7 Sv) over the eastern flank of the Hatton‐Rockall Basin (16°W to 15°W). Transport associated with the Rockall Bank Jet is mostly depth independent during summer, while 30% of the Hatton Bank Jet transport is due to vertical geostrophic shear. Uncertainties are estimated for each individual glider section using a Monte Carlo approach, and mean uncertainties of the absolute transport are less than 0.5 Sv. Although comparisons with altimetry‐based estimates indicate similar large‐scale circulation patterns, altimetry data do not resolve small mesoscale current bands in the Hatton‐Rockall Basin which are strongly needed for the right transport estimates.

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Section: Discussionmentioning

confidence: 99%

Structure and Transport of the North Atlantic Current in the Eastern Subpolar Gyre From Sustained Glider Observations

et al. 2018

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“…Gray lines represent isopycnals (σ θ ) and gray boxes denote the core water properties of different water masses found in the Iceland Basin (top). Acronyms and water mass property references are as follows: Subpolar Mode Water (SPMW; Brambilla & Talley, 2008); Labrador Sea Water (LSW; Fogelqvist et al, 2003;van Aken & de Boer, 1995;Zhao et al, 2018); Icelandic Slope Water (ISW; Read, 2000;van Aken & de Boer, 1995); Iceland Scotland Overflow Water (ISOW; Fogelqvist et al, 2003;van Aken & de Boer, 1995).…”

Section: Errc Water Mass Structure and Along-stream Changesmentioning

confidence: 99%

Transport and Evolution of the East Reykjanes Ridge Current

2020

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This study of the first continuous multiyear observations of the East Reykjanes Ridge Current (ERRC) reveals a highly variable, mostly barotropic southwestward flow with a mean transport of 10-13 Sv. The ERRC effectively acts as a western boundary current in the Iceland Basin on the eastern flank of the Reykjanes Ridge. As part of the Overturning in the Subpolar North Atlantic Program (OSNAP), continuous measurements of the ERRC have been maintained for the first time using acoustic Doppler current profilers, current meters, and dynamic height moorings at six mooring sites near 58°N since 2014. Together with satellite altimetry and Argo profile and drift data, the mean transport, synoptic variability, water mass properties, and upstream and downstream pathways of the ERRC are examined. Results show that the ERRC forms in the northeastern Iceland Basin at the convergence of surface waters from the North Atlantic Current and deeper Icelandic Slope Water formed along the Iceland-Faroe Ridge. The ERRC becomes denser as it cools and freshens along the northern and western topography of the Basin before retroflecting over the Reykjanes Ridge near 59°N into the Irminger Current. Analysis of the flow-weighted density changes along the ERRC's path reveals that it is responsible for about one third of the net potential density change of waters circulating around the rim of the subpolar gyre. Plain Language Summary The East Reykjanes Ridge Current (ERRC) is an important but poorly studied flow in the Iceland Basin of the northern North Atlantic Ocean. This study investigates the ERRC using underwater floats, satellites, and 4 years of continuous mooring data to determine the current's pathways, water properties, and the strength of its transport. From its formation to the south of Iceland near 62°N, 18°W, the ERRC travels westward along the Icelandic slope before turning to the southwest as it follows the eastern flank of a shallow portion of the Mid-Atlantic Ridge, known as the Reykjanes Ridge. As the Reykjanes Ridge deepens, the ERRC eventually reaches its termination as it crosses westward over the ridge into the next basin. Results of this study show that the ERRC is approximately 900 km in length and has an average transport of 10-13 Sv (1 Sv = 1,000,000 m 3 /s). Significant water densification occurs along the ERRC's path, which makes it an important component in the broader picture of the Earth's climate system.

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“…The importance of mesoscale eddies on the large‐scale circulation, (e.g., Chelton et al, 2007; Zhao, Bower, Yang, & Lin, 2018; Zhao, Bower, Yang, Lin, & Zhou, 2018) and their role in the formation and redistribution of large‐scale thermohaline properties and tracers are well established (e.g., Bashmachnikov et al, 2018; Frenger et al, 2018; Testor et al, 2018; Treguier et al, 2012). Water masses trapped within eddies' cores can retain their thermohaline properties while being transported unobtrusively away from their place of origin (e.g., Flierl, 1981; Zhang et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

A Persistent Deep Anticyclonic Vortex in the Rockall Trough Sustained by Anticyclonic Vortices Shed From the Slope Current and Wintertime Convection

et al. 2020

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The presence of a persistent surface anticyclone centered at approximately 55°N, 12°W in the Rockall Trough, northeast North Atlantic, has been previously noted in satellite altimetry data. Here, we show that this surface anticyclone is the imprint of a deep, persistent, non-stationary anticyclonic vortex. Using wintertime 2007 and 2011 ship-board data, we describe the anticyclone's vertical structure for the first time and find that the anticyclone core is partly made of warm and salty Mediterranean Overflow Water. The anticyclone has a radius of~40 km, it stretches down to 2,000 m, with a velocity maximum around 500 m. To analyze the anticyclone's generating mechanism, we use a mesoscale-resolving (~2 km) simulation, which produces a realistic pattern of the Rockall Trough anticyclone. The simulation indicates that the anticyclone is locally formed and sustained by two types of processes: wintertime convection and merger with anticyclonic vortices shed from the slope current flowing poleward along the eastern Rockall Trough slope. Intense negative vorticity filaments are generated along the Rockall Trough southeastern slope, and they encapsulate Mediterranean Overflow Water as they detach and grow into anticyclonic vortices. These Mediterranean Overflow Water-rich vortices are advected into the trough, consequently merging with the Rockall Trough anticyclone and sustaining it. We suggest that the Rockall Trough anticyclone impacts regional intermediate water masses modifications, heat and salt budgets locally, and further afield into the neighboring subpolar northeast North Atlantic. Plain Language Summary Water masses of different origins converge in the Rockall Trough, a deep bathymetric depression in the northeast North Atlantic, and undergo transformations with direct implications for the inflow of warm water into the Nordic Seas. We use in situ observations to document, for the first time, the vertical structure of a subsurface anticyclone, which is a clockwise oceanic vortex in the trough. We show that the anticyclone has a radius of~40 km, extends down to 2,000 m, with a velocity maximum at 500 m depth. Its core is made of warm and salty Mediterranean water. We use outputs from a high-resolution (~2 km) realistic simulation to study the mechanisms driving the anticyclone. We show that the anticyclone is impacted predominantly by two different processes. One is the wintertime convection, which mixes waters from the surface down to 1,000 m inside the anticyclone. The other is the merger with smaller vortices that pinch off the slope current flowing northward along the Porcupine Bank, south of the Rockall Trough, and feed the anticyclone with water masses of Mediterranean origin. We showcase the potential impact of the anticyclone on the regional and nearby northeast North Atlantic heat and salt distributions.

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Structure and Formation of Anticyclonic Eddies in the Iceland Basin

Cited by 22 publications

References 76 publications

Structure and Transport of the North Atlantic Current in the Eastern Subpolar Gyre From Sustained Glider Observations

Structure and Transport of the North Atlantic Current in the Eastern Subpolar Gyre From Sustained Glider Observations

Transport and Evolution of the East Reykjanes Ridge Current

A Persistent Deep Anticyclonic Vortex in the Rockall Trough Sustained by Anticyclonic Vortices Shed From the Slope Current and Wintertime Convection

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