Abstract
Abstract. Through the Faroese Channels – the collective name for a system of channels linking the Faroe–Shetland Channel, Wyville Thomson Basin, and Faroe Bank Channel – there is a deep flow of cold waters from Arctic regions that exit the system as overflow through the Faroe Bank Channel and across the Wyville Thomson Ridge. The upper layers, in contrast, are dominated by warm, saline water masses from the southwest, termed Atlantic water. In spite of intensive research over more than a century, there are still open questions on the passage of these waters through the system with conflicting views in recent literature. Of special note is the suggestion that there is a flow of Atlantic water from the Faroe–Shetland Channel through the Faroe Bank Channel, which circles the Faroes over the slope region in a clockwise direction. Here, we combine the observational evidence from ship-borne hydrography, moored current measurements, surface drifter tracks, and satellite altimetry to address these questions and propose a general scheme for the Atlantic water flow through this channel system. We find no evidence for a continuous flow of Atlantic water from the Faroe–Shetland Channel to the Faroe Bank Channel over the Faroese slope. Rather, the southwestward-flowing water over the Faroese slope of the Faroe–Shetland Channel is totally recirculated within the combined area of the Faroe–Shetland Channel and Wyville Thomson Basin, except possibly for a small release in the form of eddies. This does not exclude a possible westward flow over the southern tip of the Faroe Shelf, but even including that, we estimate that the average volume transport of a Circum-Faroe Current does not exceed 0.5 Sv (1 Sv = 106 m3 s−1). Also, there seems to be a persistent flow of Atlantic water from the western part of the Faroe Bank Channel into the Faroe–Shetland Channel that joins the Slope Current over the Scottish slope. These conclusions will affect potential impacts from offshore activities in the region and they imply that recently published observational estimates of the transport of warm water towards the Arctic obtained by different methods are incompatible.
Highlights
The Faroese Channels (Fig. 1) are the deepest passage across the submarine ridge system between Iceland and the Scottish continental shelf and among the key locations for exchange between the Nordic Seas and the rest of the world ocean
The results from the moored current measurements are used to give an overview of the Atlantic water large-scale circulation and to see in more detail how this water passes through the two ADCP sections: the Z-section and the Fsection (Fig. 2)
The ADCP measurements do not reach all the way to the surface, but they still reach well above the average depth of the deep boundary of the Atlantic water (Fig. 2b, c), which may be defined by the 5 ◦C isotherm (Berx et al, 2013)
Summary
The Faroese Channels (Fig. 1) are the deepest passage across the submarine ridge system between Iceland and the Scottish continental shelf and among the key locations for exchange between the Nordic Seas and the rest of the world ocean. There is a continuous flow of cold, dense water of Arctic origin flowing through the deep parts of this channel system (Fig. 1) that leaves the Norwegian Sea through the Faroe Bank Channel (Hansen and Østerhus, 2007) and as a weak overflow across the Wyville Thomson Ridge (Sherwin et al, 2008). The upper layers, in contrast, are dominated by warm and saline waters from the west, which we term the Atlantic inflow to the Nordic Seas (Hansen and Østerhus, 2000). The Atlantic inflow has a weak branch west of Iceland, but most of it enters the Norwegian Sea between Iceland and the European continent (Østerhus et al, 2005).
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