3.2.2. Bottom Water Hydrography

The annual bottom temperature at Nakken bank reef ranged from 7.4 to 8.3 ◦C, with a mean temperature of 7.8 ◦C. This included two distinct phases: cool temperatures (<7.8 ◦C) observed from May to mid-November and warm temperatures (>7.8 ◦C) measured from

late November to April (Figure 3), indicating heat dissipation from the surface during autumn and water column mixing in spring. March was the warmest month. September and October were the coolest months (Figures 3 and 4). Bottom water salinity varied between 35.00 and 35.34 g kg−<sup>1</sup> with the lowest salinities (<35.2 g kg<sup>−</sup>1) observed in autumn and winter, and the highest salinities observed in late spring, indicating the water source variability between North Atlantic water (SA > 35 g kg−1)-dominated and Norwegian coastal water-dominated waters. The salinities measured by MLM were ~0.05 g kg−<sup>1</sup> higher than those measured by SLM (Figure 3) during the time both landers were at the sea bed, whereas measured temperatures were similar. Relatively high sigma-theta (density) values of >27.35 kg m−<sup>3</sup> were measured from May until October (Figure 3). Bottom water oxygen values varied from 6.58 to 6.68 mL L−1, with the highest values in October and lowest values in January (Figure 4) following temperature variations. Turbidity values reached up to 1.5 NTU between July and August. Turbidity values dropped in October to around 0.15 NTU. They remained low (<0.15 NTU) with few turbid events (>0.2 NTU) until the end of the deployment (Figure 4).

**Figure 3.** Bottom water Θ, SA-values at Nakken bank reef. Months are color coded. The larger circles (SLM) and squares (MLM) mark the monthly median values, and stars show the cruise CTD cast median values for 205–215 m depth.

**Figure 4.** Nakken bottom water (~210 m) characteristics for (**A**) temperature, (**B**) oxygen, (**C**) turbidity, (**D**) daily mean horizontal flow velocity (up northward and down southward flow) at Nakken, and (**E**) daily maximum wind speed from Utsira coastal station based on data from MET Norway. The prevailing wind directions are marked with green (northerly from NW (315◦) to NE (45◦)) and yellow (southerly from SE (135◦) to SW (225◦)). The thicker line (in three first rows) shows the 1-d running mean.
