Cross-slope flow in the Atlantic Inflow Current driven by the on-shelf deflection of a slope current

M Porter,A.C Dale,S Jones,B Siemering,M.E Inall

doi:10.1016/j.dsr.2018.09.002

Abstract

We identify a newly described current, the Atlantic Inflow Current (AIC), a persistent pathway of Atlantic Water from the European Slope onto the Malin Shelf. Using drifters and gliders we examine the vertical and horizontal structure of the AIC and use Lagrangian statistics to quantify lateral mixing along its path. We estimate this current to have a transport of approximately 0.2 Sv, advecting 2.8 TW of heat onto the shelf (referenced to 7 °C) and 2.4 kT/day of the limiting nutrient, nitrate. This nutrient-rich AIC joins the Irish Coastal Current, continuing into the Minch and the outer Hebridean Shelf before ultimately entering the North Sea. The biological consequences of the influx of water masses and nutrients onto the shelf can range from altering primary production, and subsequent food web dynamics, to recruitment of fish larvae from oceanic water. A better understanding of the current dynamics described here is crucial for the assessment of shelf sea primary production and its impacts on carbon draw-down as well as recruitment for commercially important fisheries.

Highlights

2 In common with continental shelf seas worldwide, the Malin Shelf, west of Scotland and 3 north of Ireland, is largely isolated from the deep ocean by a steep slope and the associated 4 slope current at the shelf edge (Burrows and Thorpe, 1999; Souza et al, 2001)
3 Results and analysis The repeat vessel mounted Acoustic Doppler Current Profiler (VM-ADCP) transects collected during JC88 in July and August 2013 show a poleward along-slope flow with speeds of between 0.1 ms-1 and 0.2 ms-1, between 200 m and 190 400 m below the surface, extending a distance of up to 10 km oceanward from the shelf break 191 over the slope (Jones 2016)
The two transects were occupied within three weeks of each other, with the downstream transect beginning before the drifter release, on 5 July 2013, and the upstream transect beginning after the drifter release, on 29 July 2013

Summary

Introduction

2 In common with continental shelf seas worldwide, the Malin Shelf, west of Scotland and 3 north of Ireland, is largely isolated from the deep ocean by a steep slope and the associated 4 slope current at the shelf edge (Burrows and Thorpe, 1999; Souza et al, 2001). Crossing this 5 boundary there is an estimated net on-shelf transport of 0.5 Sv (Huthnance et al, 2009). We aim to quantify the transport of the North Atlantic sub-polar gyre from the slope current waters onto the Malin shelf

Objectives

Results

Discussion

Conclusion