3.6.1. Flow Regime

The flow below 180 m was strong (mean 18 cm s<sup>−</sup>1, max 60 cm s−1) with a semidiurnal tidal component (Figures 4 and 9, Table 3). The monthly mean flow speed (Umean) varied between 12 and 25 cm s<sup>−</sup>1. Low mean flow speeds (Umean < 15 cm s<sup>−</sup>1) were measured in June and July, and high mean flow speeds (Umean > 20 cm s−1) were measured in March and in late autumn in between October and December. During the remaining months, Umean varied between 16 and 18 cm s−1. At depths above 180 m (recorded with MLM), flow speeds varied more. From May to August, Umean was < 15 cm s−<sup>1</sup> in between 115 and 180 m depth. Umean reached maxima at 90 m and at <50 mm depth with 27 and >45 cm s<sup>−</sup>1, respectively (Figure 9A).

The maximum monthly flow speeds (Umax) below 180 m depth varied between 30 and 70 cm s−1. Umax was <45 cm s−<sup>1</sup> in May and June and ~60 cm s−<sup>1</sup> between October and December. During the other months, Umax varied between 50 and 55 cm s<sup>−</sup>1. Between 125 and 180 m water depth, Umax was <50 cm s<sup>−</sup>1. At depths of <117 m, Umax was >100 cm s−<sup>1</sup> except in August, with peak speeds (>200 cm s<sup>−</sup>1) measured around 60 and 100 m depths (Figure 9B).

**Figure 9.** Monthly water column values for (**A**) mean flow speed, (**B**) maximum flow speed, (**C**) percentage of southward flow (90–270◦), and (**D**) direction of most energetic fluctuations at SLM (depths 180–210 m) and MLM (depths 50–190 m) lander positions. The thick black line marks the mean of the recorded period. The dashed horizontal lines represent the definition for surface waters (<80 m) and the depths of the living CWCs at Nakken (>190 m). The values were calculated from a 1 h running median to avoid outliers.

The current direction was determined by the orientation of the fjord and was dominantly southward (between 90◦ and 270◦) beneath 180 m, varying in between 80 and 180 m, and southward (May and June) or northward (July and August) near the surface (Figure 9C, Table 3). In July and December, the flow direction was dominantly northward (Figure 9C). The direction of the most energetic flow, um, was dominantly southward across the water column (150◦–163◦, at depths >180–208 m and 160◦–170◦ at depths <180 m). The northward flow was measured at ~150 m depth in May and depths <100 m in August (Figure 9D).

The flow regime at NK bank reef was mostly subcritical, but it supported hydraulic jumps with flow velocities >Umean. These are observed as rapid changes in hydrographic parameters. For example, in the winter months, temperature, salinity, and turbidity fluctuated within 12 h ΔΘ = 0.4 ◦C, ΔSA = 0.15 g kg<sup>−</sup>1, and Δturbidity >0.2 NTU. Following the categorization of Juva et al. (2020) [22], the flow state is thus partially subcritical (PBsc).
