Properties and dynamics of mesoscale eddies in Fram Strait from a comparison between two high-resolution ocean–sea ice models

Abstract

Abstract. Fram Strait, the deepest gateway to the Arctic Ocean, is strongly influenced by eddy dynamics. Here we analyse the output from two eddy-resolving models (ROMS – Regional Ocean Modeling System; FESOM – Finite-Element Sea-ice Ocean Model) with around 1 km mesh resolution in Fram Strait, with a focus on their representation of eddy properties and dynamics. A comparison with mooring observations shows that both models reasonably simulate hydrography and eddy kinetic energy. Despite differences in model formulation, they show relatively similar eddy properties. The eddies have a mean radius of 4.9 and 5.6 km in ROMS and FESOM, respectively, with slightly more cyclones (ROMS: 54 %, FESOM: 55 %) than anticyclones. The mean lifetime of detected eddies is relatively short in both simulations (ROMS: 10 d, FESOM: 11 d), and the mean travel distance is 35 km in both models. More anticyclones are trapped in deep depressions or move toward deep locations. The two models show comparable spatial patterns of baroclinic and barotropic instability. ROMS has relatively stronger eddy intensity and baroclinic instability, possibly due to its smaller grid size, while FESOM has stronger eddy kinetic energy in the West Spitsbergen Current. Overall, the relatively good agreement between the two models strengthens our confidence in their ability to realistically represent the Fram Strait ocean dynamics and also highlights the need for very high mesh resolution.

Seasonal and Mesoscale Variability of the Two Atlantic Water Recirculation Pathways in Fram Strait

“…We have confirmed the presence of two recirculation pathways at 78 inate in the WSC and are advected by the mean flow of the recirculation branch, or that they originate in the recirculation branch itself, provided it is subject to similar instabilities. We may also observe self-propagating eddies with a westward propagation speed, as suggested by previous studies (Wekerle et al, 2020;Bashmachnikov et al, 2020).…”

“…(Hattermann et al, 2016). Consistently, in two eddy resolving models, Wekerle et al (2020) found the main generation region…”

“…Consistently, in two eddy resolving models, Wekerle et al. (2020) found the main generation region of eddies that follow the southern recirculation pathway to be the central Fram Strait and not the WSC. However, they find barotropic and baroclinic instability to be much more efficient (accounting for larger mean to eddy energy transfers) in the WSC than in central Fram Strait.…”

“…Similar to the southern recirculation we can only speculate whether the AW eddies we observe at 0 • EW are generated by the WSC and advected by the mean flow or topographically steered, or generated by recirculating flow outside the WSC. The proximity to the WSC of R4 (compared to R2) makes at least some eddies originating from the WSC seem likely and, in two models, Wekerle et al (2020) found that most eddies following the path of the northern recirculation originated in the WSC, specifically anticyclones. If the northern recirculation exists as a mean flow that circulates around the Molloy Hole, a pertinent question is how eddies are able to detach from this mean flow and join the EGC at R4.…”

Submesoscale physicochemical dynamics directly shape bacterioplankton community structure in space and time

“…These growth-rate estimates do not take into account potential losses due to grazing by zooplankton or viral lysis, and thus represent rather the lower time limit. Based on this we hypothesize that, at the time of sampling, the age of the observed filament was already at least 10 d. Although temporal dynamics are not resolved by our sampling strategy, the approximated lifetime matches recent estimates of mesoscale eddies lifetime in Fram Strait based on high-resolution ocean-sea ice models (Wekerle et al 2020). The boundaries of these mesoscale eddies may harbor submesoscale filaments such as the one studied here.…”