Norwegian Atlantic Slope Current along the Lofoten Escarpment

Abstract

Abstract. Observations from moored instruments are analyzed to describe the Norwegian Atlantic Slope Current at the Lofoten Escarpment. The data set covers a 14-month period from June 2016 to September 2017, and resolves the core of the current from 200 to 650 m depth, between the 650 m and 1500 m isobaths. The along-slope current, vertically averaged between 200 and 600 m depth has an annual cycle amplitude of 0.1 m s−1 with strongest currents in winter, and a temporal average of 0.15 m s−1. Higher frequency variability is characterized by fluctuations that reach 0.8 m s−1, lasting for 1 to 2 weeks, and extend as deep as 600 m. In contrast to observations in Svinøy, the slope current is not barotropic and varies strongly with depth (a shear of 0.05 to 0.1 m s−1 per 100 m in all seasons). Within the limitations of the data, the average volume transport is estimated at 2.8 ± 1.8 Sv (1 Sv = 106 m3 s−1), with summer and winter averages of 2.3 and 4.0 Sv, respectively. The largest transport is associated with the high temperature classes (> 7 °C) in all seasons, with the largest values of both transport and temperature in winter. Calculations of the barotropic and baroclinic conversion rates using the moorings are supplemented by results from a high resolution numerical model. While the conversion from mean to eddy kinetic energy (e.g. barotropic instability) is likely negligible over the Lofoten Escarpment, the baroclinic conversion from mean potential energy into eddy kinetic energy (e.g. baroclinic instability), can be substantial with volume-averaged values of (1–2) × 10−4 W m−3.

Pathways and Water Mass Transformation Along and Across the Mohn‐Knipovich Ridge in the Nordic Seas

“…Although the wind stress curl in the Nordic Seas is predominantly positive, wind reversals can occasionally enhance exchange between the boundary and the interior of the Lofoten Basin and therefore enable crossovers between the slope and the front current. In addition to wind effects, the strong eddy variability near the Lofoten Islands provides a means for AW to enter the Lofoten Basin interior as well (Fer et al., 2020). The latter mechanism seems to be responsible for AW transport from the slope current to the interior at depth, whereas wind processes seem to steer the surface waters across the Vøring Plateau entering the Lofoten Basin from the south (Dugstad, Fer, et al., 2019).…”

Transport Barriers and the Retention of Calanus finmarchicus on the Lofoten Shelf in Early Spring

“…Based on the GLORYS 12v1 product, the energy conversion rates between mean flow and eddy fields were analyzed. The baroclinic conversion rate (BC) and the barotropic conversion rate (BT) were used to estimate the energy conversion between the mean potential energy (MPE) and the eddy potential energy (EPE), inferring the trend of baroclinic instability of currents, and the energy conversion between the MKE and the EKE inferring the trend of mean current barotropic instability (Fer et al., 2020; Li et al., 2020; von Appen et al., 2016). The energy conversion rates in both fields gave a solution to understand the transport barrier formation and disruption mechanisms.…”

Dynamical Controls of the Eastward Transport of Overwintering Calanus finmarchicus From the Lofoten Basin to the Continental Slope

“…The location of the particle release was chosen based on the highest EKE and the most baroclinically unstable part off the continental slope region (Isachsen, 2015; Trodahl & Isachsen, 2018). Due to the eddy activities caused by the baroclinic instability, this region has been shown to have the strongest shelf‐ocean water and plankton exchange (Dong et al., 2021; Fer et al., 2020). The average number of particles contained in each grid cell of size 0.1 × 0.2° over a 12‐year period average number of particles (ANP) was used as an indicator of particle origin.…”