Atlantic Water in the Nordic Seas: Locally eddy-permitting ocean simulation in a global setup

Abstract

Warm and salty Atlantic Water is transported by the Norwegian Atlantic Current through the Nordic Seas. A fraction of it enters the Arctic Ocean where it contributes significantly to its heat budget. Resolving the complex circulation structure in the Nordic Seas, in particular eddies, presents a numerical challenge in ocean models. Here, we present a hindcast experiment for the years 1969–2009 with a global configuration of the Finite Element Sea‐ice Ocean Model, employing a high‐resolution mesh in the Nordic Seas and Arctic Ocean (4.5 km). We show that substantial improvements can be achieved in the circulation structure, hydrography and eddy kinetic energy in the Nordic Seas compared with a coarse‐resolution reference run. A better represented Norwegian Atlantic Front Current (NwAFC) in the high‐resolution setup leads to a reduction of a strong negative temperature bias in the eastern Nordic Seas. The Atlantic Water inflow through the Iceland‐Faroe Ridge is found to be very sensitive to mesh resolution, and high resolution is required to adequately represent this inflow and the downstream NwAFC. With increased mesh resolution, the simulated ocean temperature is significantly improved at Barents Sea Opening (BSO), and the Atlantic Water volume transport in Fram Strait becomes much closer to observations in terms of both magnitude and variability. By using passive tracers, the origins of water masses at BSO and Fram Strait are identified. Our study also indicates that eddy‐resolving meshes are required to further improve the representation of dynamical processes in the region, in particular in Fram Strait.

A 4.5 km resolution Arctic Ocean simulation with the global multi-resolution model FESOM 1.4

“…The first baroclinic Rossby radius in the Fram Strait is very small (about 2 km in winter); thus, our high-resolution (4.5 km grid size) simulation cannot resolve mesoscale eddies. At this resolution, the simulated warm AW is confined to the strong boundary current and does not reach the central Fram Strait, presenting a cold bias in the center of the strait (Wekerle et al, 2017a). As in other high-resolution, but not eddy-resolving, models (e.g., Fieg et al, 2010), our simulated AW temperature in the boundary current is too high in the Fram Strait and north of Svalbard (Fig.…”

Eddy‐Resolving Simulation of the Atlantic Water Circulation in the Fram Strait With Focus on the Seasonal Cycle

“…The resolution of 4.5 km applied there was instrumental in improving the circulation and hydrography in the Nordic Seas, but still left a significant temperature bias in the central Fram Strait. Furthermore, the simulated levels of eddy kinetic energy in the Fram Strait by Wekerle et al () are too low compared to the observations. This indicates that a resolution approaching a kilometer scale is indeed necessary for simulating the AW recirculation and eddy dynamics, and calls for new studies clarifying the role of eddies in Fram Strait.…”

A 4.5 km resolution Arctic Ocean simulation with the global multi-resolution model FESOM1.4

“…The first baroclinic Rossby radius in Fram Strait is very small (about 2 km in winter), thus our high resolution (4.5 km grid size) simulation cannot resolve mesoscale eddies. At this resolution the simulated warm AW is confined to the strong boundary current and does not reach (Wekerle et al, 2017). As in other high resolution, but not eddy-resolving models (e.g., Fieg et al, 2010), our simulated AW temperature in the boundary current is too high at Fram…”