The large-scale circulation in the upper layers of ocean in the Faroes ecoregion is dominated by branches of the North Atlantic Current that flow south and north of the islands towards the Norwegian Sea. A large part of the Atlantic water crosses the Iceland–Faroe Ridge, where it meets colder and less saline water masses of Arctic origin. This results in the formation of the highly productive Iceland–Faroe front (see figure 9). Norwegian Sea Deep Water flows southward through the Faroe–Shetland Channel and Faroe Bank Channel (sill depth is 840 m) and continues southward as North Atlantic Deep.
The Atlantic water flowing through the ecoregion is mainly a mixture of waters from the North Atlantic current and waters from the North Atlantic Subpolar Gyre (a cyclonic gyre over the Labrador and Irminger seas, sometimes extending into the northeastern Atlantic). As a result, the temperature and salinity of the upper Atlantic water in the ecoregion varies on multi‑annual time scales, steered by the strength of the Subpolar Gyre.
In general, a strong Subpolar Gyre results in colder and fresher conditions in the ecoregion. The Subpolar Gyre waters are also rich in nutrients, and silicate dynamics on the Faroe Shelf have been linked to the dynamics of the Subpolar Gyre, where a strong gyre transports silicate into the region. This has a further effect on the dynamics of primary production on the Faroe Shelf.
On the Faroe Shelf, the clockwise residual circulation partly isolates the shelf water which, therefore, is somewhat colder and fresher than the surrounding Atlantic water. The long-term trends on the shelf, however, tend to follow the trends in the Atlantic water.
Figure 9: a: large-scale upper layer circulation in and around
the Faroes ecoregion (arrows). Thick dashed grey line indicates the Iceland–Faroe
Front, while the dashed blue line indicates the Faroe Shelf Front. The Faroes ecoregion
is shown with a thin black solid line, while the outline of the map shown in
panel b is also indicated with a thin solid black line. The colours indicate
average sea surface temperature (SST) based on remotely sensed monthly SST maps
in the period 2003–2020 (NASA Goddard Space Flight Center, Ocean Ecology
Laboratory, Ocean Biology Processing Group) with 200 m, 500 m, and 2 000 m
depth contours shown in grey. b: topography
of the Faroe Shelf. The shelf front region is indicated by blue lines; primary
production phenological ecoregions are indicated by coloured areas. The
abbreviations are as follows: Central Shelf (CS), Western Region (WR), Outer
Shelf (OS) and Eastern Banks (EB). ‘N04’ and ‘St. S’ indicate stations referred
to in the text. 100 m, 200 m, 300 m, and 500 m depth
contours are shown in grey.