Evolution of an Intrathermocline Lens over the Lofoten Basin

The Lofoten Basin of the Norwegian Sea is the main reservoir of heat in the Polar seas; it stands out as an area of high mesoscale activity and the existence of a quasi-permanent anticyclonic vortex. The observations of Argo floats over the period of 2005–2014 (17,600 profiles measured by 125 recorders) were used in the area of 55–80° N and 30–15° W, covering the Lofoten Basin. The Argo-based Model for Investigation of the Global Ocean (AMIGO) was used. The method makes it possible to obtain annual mean velocity fields and thermohaline characteristics up to a depth of 1500 m in 1° squares. One large-scale anticyclonic vortex covering the deepest part of the Lofoten area was observed in the depth column from 30 to 1500 m with velocity values increasing from 0–2 cm/s in the vortex center to 7–12 cm/s at its periphery. A local anticyclonic vortex (a lens of warm and saline waters) with a radius of about 35 km at depths of 250–700 m with an average long-term position of the center at 69.5° N and 3.5° E is also distinguished along the vertical distributions of thermohaline characteristics. In this contribution, we simulate the evolution of this lens, represented as an anticyclonic vortex patch located in the middle layer, within the framework of a three-layer quasi-geostrophic model using the Contour Dynamics Method. Calculations showed that the model can adequately reproduce the nature of the lens drift under the influences of various types of ocean currents and bottom topography. Comparison of the model results with the in situ observations of the vortex trajectories gives satisfactory results.