Observed Variability of the North Atlantic Current in the Rockall Trough From 4 Years of Mooring Measurements

L Houpert,B Moat,D Rayner,S Jones,N Fraser,C Johnson,S Cunningham,N P Holliday

doi:10.1029/2020jc016403

Abstract

AbstractThe Rockall Trough is one of the main conduits for warm Atlantic Water to the Nordic Seas. Ocean heat anomalies, originating from the eastern subpolar gyre, are known to influence Arctic sea ice extent, marine ecosystems, and continental climate. Knowledge of the transport through this basin has previously been limited to estimates from hydrographic sections which cannot characterize the intra‐annual and multiannual variability. As part of the Overturning in the Subpolar North Atlantic Programme (OSNAP), a mooring array was deployed in the Rockall Trough in order to obtain the first continuous measurements of transport. Here, we define the methodology and the errors associated with estimating these transports. Results show a 4‐year mean northward transport of 6.6 Sv (1 Sv = 106 m3/s) by the North Atlantic Current (NAC) in the east and interior of the Rockall Trough (2014–2018). A mean transport of −2.0 Sv (southward) is observed in the west of the basin, which could be part of a recirculation around the Rockall Plateau. The 90‐day low‐pass‐filtered transport shows large subannual and interannual variability (−1.6 to 9.1 Sv), mostly resulting from changes in the midbasin geostrophic transport. Satellite altimetry reveals the periods of low and high transport are associated with significant changes in the Rockall Trough circulation. There is a detectable seasonal signal, with the greatest transport in spring and autumn.

Highlights

In 2014, the Overturning in the Subpolar North Atlantic Programme (OSNAP)established an array of more than fifty moorings across the subpolar North Atlantic, with the objective of continuously measuring the strength, structure and variability of the circulation
Altimetry-derived currents are representative of the large-scale flow associated with the North Atlantic Current (NAC) branches, the circulation schematic drawn in the Rockall Trough is mostly representing a period of high transport as defined in the manuscript by the high transport composite state
UK-OSNAP moorings are indicated by yellow stars and the Extend Ellet Line hydrographic stations used in this study are indicated by black crosses and labelled on (b)

Summary

Introduction

In 2014, the Overturning in the Subpolar North Atlantic Programme (OSNAP). Established an array of more than fifty moorings across the subpolar North Atlantic, with the objective of continuously measuring the strength, structure and variability of the circulation. The array is able to diagnose both the horizontal and overturning circulations and their associated fluxes of heat and fresh-water. The programme combines measurements of the temperature, salinity and directly measured currents, with salinity and temperature fields derived from purposefully deployed ocean gliders, Argo floats and hydrographic cruises, with satellite altimetry and mass balance constraints

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Discussion

Conclusion