On the long‐term stability of the Lofoten Basin Eddy

Abstract

In recent years, several studies have identified an area of intense anticyclonic activity about 500 km straight west of the Lofoten Islands at 70°N in the northern Norwegian Sea. Now recognized as the coherent Lofoten Basin Eddy (LBE), it is maintained by a supply of anticyclonic eddies that break away from the Norwegian Atlantic Current. Here we show from ship‐based surveys of its velocity field that it is quite stable with a central core in solid body rotation ∼1000 m deep, ∼8 km radius, and a relative vorticity close to its theoretical limit –f. The surveys also show the LBE typically has a >60 km radius with maximum swirl velocities at 17–20 km radius. From the velocity field, we estimate the dynamic height amplitude at the surface to be about ∼0.21 ± 0.03 dyn. m. Second, altimetry from the last 20 years shows the extremum in sea surface height relative to the surrounding waters to be about the same, 0.2 dyn. m. Third, a float trapped in the LBE for many months reveals a clear cyclonic wandering of the eddy over the deepest parts of the basin. Last, three hydrographic sections from the 1960s show the dynamic height signal to be virtually the same then as it is now. From these observations, we conclude that the LBE is a permanent feature of the Nordic Seas and plays a central role in maintaining the pool of warm water in the western Lofoten Basin.

Arctic Ocean surface geostrophic circulation 2003–2014

“…There is a persistent patch of high EKE sitting in the Lofoten Basin (see Fig. 1 for the location of bathymetric features) near (3 • E, 70 • N), the socalled Lofoten Basin Eddy (Søiland et al, 2016). Away from the shelf break, the EKE is generally higher in the eastern basins of the Greenland and Norwegian seas compared to the western basins, separated by the mid-basin ridge system (Bulczak et al, 2015).…”

The Lofoten Basin eddy: Three years of evolution as observed by Seagliders

“…Using shipborne measurements of currents, Søiland et al . [] described a solid‐body rotation of 7–8 km of the core with vorticity of – . In agreement with this, Figure c shows a solid‐body rotation extending to about 5 km from the center.…”

“…We call this anticyclonic eddy the Lofoten Basin Eddy (LBE). Since then, several studies addressed the mesoscale activity in the basin using observations of hydrography [ Ivanov and Korablev , ; Rossby et al ., ; Raj et al ., ], numerical models [ Köhl , ; Volkov et al ., ], satellite altimetry [ Raj et al ., ; Søiland et al ., ], and surface drifters and subsurface floats [ Rossby et al ., ; Voet et al ., ; Andersson et al ., ; Koszalka et al ., ; Søiland and Rossby , ]. Lagrangian studies described the pathways, eddy kinetic energy, lateral mixing rates in the basin, as well as position and radius of LBE.…”

“…Hydrographic and ocean current observations have been limited to cruises of opportunity and short duration surveys. The present consensus is that LBE is maintained by merging of anticyclonic eddies which drift westward after being shed off the eastern branch of the NwAC [ Köhl , ; Raj et al ., ; Volkov et al ., ; Raj et al ., ; Søiland et al ., ]. The geometry of the basin attracts the anticyclones to the bottom depression and enables dynamical stability for the vortex.…”

The Northeast Greenland Shelf as a Potential Habitat for the Northeast Arctic Cod

“…Eddy shedding brings AW off the upper shelf slope and into the Lofoten Basin (Rossby et al, 2009;Søiland et al, 2016) where it either recirculates or flows along the Mohn Ridge toward the Jan Mayen area (Isachsen and Nøst, 2012). Farther north the AW bifurcates at the entrance to the Barents Sea with one branch flowing to the northwest of Svalbard and the other entering the Barents Sea.…”