First Direct Estimates of Volume and Water Mass Transports Across the Reykjanes Ridge

Petit, Tillys; Mercier, Herlé; Thierry, Virginie

doi:10.1029/2018jc013999

Cited by 27 publications

(51 citation statements)

References 48 publications

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“…At 1000-m depth, Argo floats reveal a continuous current following the Eastern RR flank until reaching the CGFZ, with some of the flow crossing the ridge North of 57.3 • N and some crossing at the Bight Fracture Zone (56-57 • N). This is coherent with the results from Petit et al (2018), which observed that water at this depth (their layer 3) was more likely to cross the ridge North of 56 • N. This southwestward flow is present in our simulations, with too intense velocity amplitudes in NATL, but realistic amplitudes at higher resolution in POLGYR. In both cases, we clearly see the flow crossing the ridge north of 56 • N.…”

Section: Mean Circulationsupporting

confidence: 91%

Barotropic vorticity balance of the North Atlantic subpolar gyre in an eddy-resolving model

Corre¹,

Gula²,

Tréguier³

2019

Preprint

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Abstract. The circulation in the North Atlantic Subpolar gyre is complex and strongly influenced by the topography. The gyre dynamics is traditionally understood as the result of a topographic Sverdrup balance, which corresponds to a first order balance between the planetary vorticity advection, the bottom pressure torque and the wind stress curl. However, this dynamics has been studied mostly with non-eddy-resolving models and a crude representation of the bottom topography. Here we revisit the barotropic vorticity balance of the North Atlantic Subpolar gyre using a high resolution simulation (≈ 2-km) with topography-following vertical coordinates to better represent the mesoscale turbulence and flow-topography interactions. Our findings highlight that, locally, there is a first order balance between the bottom pressure torque and the nonlinear terms, albeit with a high degree of cancellation between each other. However, balances integrated over different regions of the gyre – shelf, slope and interior – still highlight the important role played by nonlinearities and the bottom drag curls. In particular the topographic Sverdrup balance cannot describe the dynamics in the interior of the gyre. The main sources of cyclonic vorticity are the nonlinear terms due to eddies generated along eastern boundary currents and the time-mean nonlinear terms from the Northwest Corner. Our results suggest that a good representation of the mesoscale activity along with a good positioning of the Northwest corner are two important conditions for a better representation of the circulation in the North Atlantic Subpolar Gyre.

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Section: Mean Circulationsupporting

confidence: 91%

Barotropic vorticity balance of the North Atlantic subpolar gyre in an eddy-resolving model

Corre¹,

Gula²,

Tréguier³

2019

Preprint

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“…Intermediate Water (IW) is a low‐oxygenated water mass observed in the upper 1,000 m of the water column and originating from the eastern subpolar gyre (Harvey & Arhan, ; van Aken & de Boer, ). It was observed during the RREX2015 cruise along the Reykjanes Ridge between 27.52 σ 0 and 27.71 σ 0 (Petit et al, ). At this density range, IW differs from the other water masses by having an oxygen concentration lower than 272 μmol/kg (Petit et al, ).…”

Section: Resultsmentioning

confidence: 99%

“…It was observed during the RREX2015 cruise along the Reykjanes Ridge between 27.52 σ 0 and 27.71 σ 0 (Petit et al, ). At this density range, IW differs from the other water masses by having an oxygen concentration lower than 272 μmol/kg (Petit et al, ). IW was sampled at the CGFZ by the deep floats launched during RREX2015 and RREX2017 (Figures and ).…”

Section: Resultsmentioning

confidence: 99%

“…Within the North Atlantic subpolar gyre, ISOW flows southward east of the Reykjanes Ridge in the Iceland Basin (e.g., Daniault et al, 2016;Fleischmann et al, 2001;McCartney, 1992;Zou et al, 2017; Figure 1). Most of the southward ISOW flow ultimately reaches the Irminger Sea through the Charlie-Gibbs Fracture Zone (CGFZ) near 52°N (Bower & Furey, 2017;Kanzow & Zenk, 2014;McCartney, 1992;Saunders, 1994) and the Bight Fracture Zone near 57°N (Lankhorst & Zenk, 2006;Petit et al, 2018;Xu et al, 2010; Figure 1). Along its southward pathway, ISOW interacts with North East Atlantic Deep Water (NEADW), an old water mass flowing northward in the eastern North Atlantic.…”

Section: Introductionmentioning

confidence: 99%

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ISOW Spreading and Mixing as Revealed by Deep‐Argo Floats Launched in the Charlie‐Gibbs Fracture Zone

et al. 2019

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To improve our understanding of deep circulation, we deployed five Deep‐Argo floats (0–4,000 m) in the Charlie‐Gibbs Fracture Zone (CGFZ), which channels the flow of Iceland‐Scotland Overflow Water (ISOW), a dense water mass of the North Atlantic Ocean. The floats were programed to drift at 2,750 dbar in the ISOW layer. The floats mainly moved westward in the CGFZ, although some of them followed different routes for few cycles depending on northward intrusions of the North Atlantic Current over the CGFZ. One float revealed a direct route for ISOW from CGFZ to the Deep Western Boundary Current at Flemish Cap. In the CGFZ, oxygen data acquired by the floats revealed that the ISOW layer, characterized by salinity higher than 34.94 and density greater than 27.8 kg/m, was mainly composed of the highly oxygenated ISOW and the less oxygenated North East Atlantic Deep Water (NEADW), a complex water mass from the East Atlantic. In the ISOW layer, the relative contribution of ISOW was generally larger in the northern valley than in the southern valley of CGFZ. Northward intrusions of the North Atlantic Current above the CGFZ increased the relative contribution of NEADW in the northern valley and favors mixing between ISOW and NEADW. The ISOW‐NEADW signal flowing westward from the CGFZ toward the Deep Western Boundary Current was progressively diluted by Labrador Sea Water and Denmark Strait Overflow Water. Oxygen measurements from Deep‐Argo floats are essential for a better understanding and characterization of the mixing and spreading of deep water masses.

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“…Our compilation of microstructure data (Figure a) includes field campaigns described and analyzed by Waterhouse et al () as well as data from eight additional projects: INDOMIX (Bouruet‐Aubertot et al, ); OUTPACE (Bouruet‐Aubertot et al, ); three cruises over the Izu‐Ogasawara ridge, hereafter referred to as IZU (Hibiya et al, ); DoMORE (Thurnherr et al, ); RidgeMix (Vic et al, ); OVIDE (Ferron et al, ); RREX (Petit et al, ); and PROVOLO (Fer et al, ). The compilation encompasses a total of 19 campaigns cumulating 1,171 microstructure profiles.…”

Section: Comparison To Microstructure and Finestructure Observationsmentioning

confidence: 99%

A Parameterization of Local and Remote Tidal Mixing

Lavergne

Vic

Madec

et al. 2020

J Adv Model Earth Syst

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Vertical mixing is often regarded as the Achilles' heel of ocean models. In particular, few models include a comprehensive and energy-constrained parameterization of mixing by internal ocean tides. Here, we present an energy-conserving mixing scheme which accounts for the local breaking of high-mode internal tides and the distant dissipation of low-mode internal tides. The scheme relies on four static two-dimensional maps of internal tide dissipation, constructed using mode-by-mode Lagrangian tracking of energy beams from sources to sinks. Each map is associated with a distinct dissipative process and a corresponding vertical structure. Applied to an observational climatology of stratification, the scheme produces a global three-dimensional map of dissipation which compares well with available microstructure observations and with upper-ocean finestructure mixing estimates. This relative agreement, both in magnitude and spatial structure across ocean basins, suggests that internal tides underpin most of observed dissipation in the ocean interior at the global scale. The proposed parameterization is therefore expected to improve understanding, mapping, and modeling of ocean mixing.Plain Language Summary When tidal ocean currents flow over bumpy seafloor, they generate internal tidal waves. Internal waves are the subsurface analog of surface waves that break on beaches. Like surface waves, internal tidal waves often become unstable and break into turbulence. This turbulence is a primary cause of mixing between stacked ocean layers-a key process regulating ocean currents and biology and a key ingredient of computer models of the global ocean. In this article, a three-dimensional global map of mixing induced by internal tidal waves is presented. This map incorporates a large variety of energy pathways from the generation of tidal waves to turbulence, accounting for the conservation of energy. The map is compared to available observations of turbulence across the globe and found to reproduce with good fidelity the main patterns identified in observations. This relatively good agreement suggests that internal tidal waves are the main source of turbulence in the subsurface ocean and implies that the map may serve a range of applications. In particular, the three-dimensional map provides an efficient and realistic means to represent mixing by internal tidal waves in global ocean models.

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First Direct Estimates of Volume and Water Mass Transports Across the Reykjanes Ridge

Cited by 27 publications

References 48 publications

Barotropic vorticity balance of the North Atlantic subpolar gyre in an eddy-resolving model

Barotropic vorticity balance of the North Atlantic subpolar gyre in an eddy-resolving model

ISOW Spreading and Mixing as Revealed by Deep‐Argo Floats Launched in the Charlie‐Gibbs Fracture Zone

A Parameterization of Local and Remote Tidal Mixing

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