A Lagrangian study tracing water parcel origins in the Canary Upwelling System

Evan Mason,Josep L Pelegrí,Francois Colas

doi:10.3989/scimar.03608.18d

Abstract

The regional ocean circulation within the Canary Upwelling System between 31°N and 35°N is studied using numerical tools. Seasonal mean and near-instantaneous velocity fields from a previously-generated climatological Regional Ocean Modelling System (ROMS) solution of the Canary Basin are used to force a series of offline Lagrangian particle-tracking experiments. The primary objective is to identify the pathways through which water parcels arrive at the upwelling region north of Cape Ghir. Examining year-long pathways, the Azores Current contributes over 80% of particles annually, of which a large proportion arrive directly from offshore (from the northwest), while others travel along the shelf and slope from the Gulf of Cadiz. The remaining ~20% originate within the Gulf of Cadiz or come from the south, although the southern contribution is only significant in autumn and winter. When season-long pathways are considered, the alongshore contributions become increasingly important: northern contributions reach 40% in spring and summer, while southern values exceed 35% in winter. This study also shows that coastal upwelling changes both spatially and temporally. Upwelling becomes intensified near Cape Beddouza, with most upwelling occurring within ~40 km from shore although significant values may reach as far as 120 km offshore north of Cape Beddouza; at these locations the offshore integrated upwelling reaches as much as 4 times the offshore Ekman transport. In the Cape Beddouza area (32°N to 33°N), upwelling is negligible in February but intensifies in autumn, reaching as much as 3 times the offshore Ekman transport.

Highlights

The Canary Upwelling System (CUS) situated off northwest Africa and the western Iberian Peninsula (IP) is one of the four main eastern boundary upwellings which together occupy just 0.1% of the world ocean, yet account for 30% of the world’s fish catch (Durand et al 1998; Carr and Kearns 2003, Rykaczewski and Checkley 2008, Arístegui et al 2009)
In this paper we concentrate on the backwards runs, which provide information about the source regions of water parcels found within the release zone
We consider only trajectories from particles released within a target area between 31°N and 34°N. This region is chosen because it is considered important for cross-shore exchange with the open ocean (Laiz et al, 2001; Machín et al, 2006b), and is just north of the potential natural boundary constituted by the filament at Cape Ghir (30.6°N)

Summary

Introduction

The Canary Upwelling System (CUS) situated off northwest Africa and the western Iberian Peninsula (IP) is one of the four main eastern boundary upwellings which together occupy just 0.1% of the world ocean, yet account for 30% of the world’s fish catch (Durand et al 1998; Carr and Kearns 2003, Rykaczewski and Checkley 2008, Arístegui et al 2009). The CanUC is thought to originate in the region just south of the Gulf of Cadiz, where several studies have shown the existence of an inflow of North Atlantic Central Water (~1-2 Sv; NACW) from the open ocean to the coastal region (Stramma 1984, Lozier et al 1995, Machín et al 2006b). The conduit for this transfer is the zonal Azores Current (AzC), which transports about 3 Sv into the Gulf of Cadiz region (Peliz et al 2007, Lamas et al 2010). This deep flow experiences an annual reversal from equatorward to poleward flow that usually occurs around November (Fraile-Nuez et al 2010, Mason et al 2011)

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Results

Conclusion