Meeting Abstracts
The Lofoten Basin Eddy
Thomas Rossby, Henrik Søiland
University of Rhode Island
(Abstract received 05/21/2012 for session A)
ABSTRACT
Embedded in the pool of warm North Atlantic Water that fills the Lofoten Basin sits a small yet intense anticyclonic eddy. Despite its small size it appears to be positioned over the deepest spot of the basin at about 70°N, 3°E. The hydrographic data base suggests that the is a permanent feature of the Lofoten Basin.
A shipboard survey of the eddy in the summer of 2010 using an ADCP and CTD casts revealed a core of adiabatic water from below a shallow seasonal mixed layer to >1000 m with a very well-defined axi-symmetric velocity structure with a relative vorticity in excess of -0.9 (f = local Coriolis parameter) and highest velocities (0.7-0.8 m/s) at about 18 km radius (at 6-700 m depth). By combining the ADCP velocity with the hydrographic data, it is clear that the eddy spans the entire water column – from the surface to the bottom. The permanence of the eddy in terms its ability to trap fluid was documented by a set of RAFOS floats that remained in it for up to 300 days. A float at 900 m depth near the center exhibited an orbital period of 26.0 hours, only 2% longer than the pendulum day, for over 50 days.
There is good evidence that the eddy is maintained by a supply of anticyclonic eddies shed from the Norwegian Atlantic Current where it flows over the very steep escarpment of the Lofoten Islands. But it is not yet clear how these actually merge with or maintain the eddy. Which means that despite its permanence, we have little knowledge of its energetics: how it is pumped up on the one hand, and loss of potential energy through convective heat loss in winter and frictional losses on the other. There is much to be learned here.