Journal article Open Access

Structure and transport of the North Atlantic Current in the eastern subpolar gyre from sustained glider observations

Houpert, Loic; Inall, Mark; Dumont, Estelle; Gary, Stefan; Johnson, Clare; Porter, Marie; Johns, Bill; Cunningham, Stuart

Repeat glider sections obtained during 2014‐2016, as part of the Overturning in the Subpolar North Atlantic Program (OSNAP), are used to quantify the circulation and transport of North Atlantic Current (NAC) branches over the Rockall Plateau. Using sixteen gliders 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 < 27.55kg.m−3) estimated by Sarafanov et al. [2012] 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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