3.2.1. Water Column Hydrography

Waters in Langenuen consisted of seasonally forced surface waters down to ~100 m. The Norwegian coastal water (NCW) and the North Atlantic water (NAW, SA > 35 g kg<sup>−</sup>1) were present beneath the surface waters (Figure 2). The temperature at water depths above the CWC reefs (<80 m) ranged between 5.3 and 16.3 ◦C with the cool temperatures (<8 ◦C) recorded in winter (January 2017 and February 2016) and spring (April 2017 and May 2016) and the warm (>9 ◦C) temperatures observed in autumn (August 2017 and October 2016). Waters with temperatures >12 ◦C reached the depths of the uppermost corals (>80 m) at the three southernmost sites (HH, NK, and HN) in October 2016. The thermocline depth varied from 30 m in April 2017 to 100 m in October 2016. Beneath 80 m, the annual temperature range was between 7.5 and 12.2 ◦C, with a mean temperature of ~8 ◦C at CWCs living depths. Opposite to the surface waters, the cool bottom water temperatures (<7.8 ◦C, at depths >200 m) were measured in May 2016, August 2017, and October 2016, while the warm bottom temperatures (>8 ◦C, at depths >200 m) were recorded in January 2017, February 2016, and April 2017 (Figure 2, Table 3).

**Figure 2.** Depth profiles (y-axes) of hydrographic water properties at depths 50–250 m of the Langenuen Fjord: (first row) winter (February 2016 and January 2017), (second row) spring (April 2017 and May 2016), and (third row) autumn (August 2017 and October 2016), for (first column) temperature, (second column) salinity with 35 g kg−<sup>1</sup> marked, (third column) stratification, (fourth column) oxygen, (fifth column) fluorescence, and (sixth column) turbidity. The shaded area covers the range (min, max) of the variable for the station (HH—blue, NK—gray, HN—green, SN—orange, BV—purple) over the cruises and the solid (for year 2017 cruises) or the dashed (for year 2016 cruises) line shows the median value. The dashed horizontal lines represent the definition for CWC living depths (80–240 m).

**Table 3.** The range (min–max) of environmental conditions at the surface (10–80 m), at CWC walls at 80–220 m (sites HH and SN), and at CWC banks at 190–220 m (sites NK and BV) for winter (January 2017 and February 2016), spring (April 2017 and May 2016) and late summer and autumn (August 2017 and October 2016). Measured values include temperature, salinity, sigma-theta, buoyancy, oxygen, total alkalinity, dissolved organic carbon, nitrate, phosphate, silicate, stable isotopes, monthly mean speed, monthly maximum speed, southward direction, and monthly mean flow direction. Also shown are calculated values for in situ pHT (total scale), pCO2, and saturation states of aragonite and calcite. These parameters were calculated using CO2SYS [66]. For flow measurements, columns show periods of December 2016–February 2017, March 2017–April 2017 and May 2016, June 2016–August 2016/September 2016–November 2016. \* Flow data only from 180 to 200 m depth.



**Table 3.** *Cont.*

Above 80 m, salinity varied from <30 g kg−<sup>1</sup> at the surface (<20 m) to close to 35 g kg−<sup>1</sup> at depths ~80 m. The halocline depth varied from 20 to 60 m (not shown) except in February 2016, when the water column was well mixed (Figure 2). The 35 g kg−<sup>1</sup> isohaline depth (indicating North Atlantic water) varied from 220 m at the HH reef located south of the Langenuen in August 2017 to 75 m at the SN in April 2017. At the depths where CWCs occur, the salinity varied from <34.5 g kg−<sup>1</sup> at wall settings at depths 80–110 in February 2016 and in autumn to >35.3 g kg−<sup>1</sup> at depths >180 m in May 2016 and at depths >140 m in August 2017 (Figure 2, Table 3). In general, the northern sites were saltier than the southern sites indicating the NAW route from Korsfjord and fresh water output from Hardangerfjord. The surface layer (<80 m) was well stratified (N > 7 × <sup>10</sup><sup>3</sup> <sup>s</sup>−1) throughout the year. The strongest stratification occurred in May and August 2017 and in October 2016. Beneath 80 m, stratification varied from 0.2 to 20 × <sup>10</sup><sup>3</sup> <sup>s</sup>−<sup>1</sup> (Figure 2) without a clear seasonal or latitudinal signal. The waters at the CWC living depths were less dense at shallower wall reefs (HH, SN) than deeper bank and wall settings (NK, BV, HN) (Table 3). Sigma-theta values >27.35 kg m−<sup>3</sup> were measured at all sites in May 2016, August 2017, and October 2016 (Table 3). Across the water column and seasons, dissolved oxygen ranged from 4.96 to 7.11 mL L−1. In winter (January 2017 and February 2016), oxygen decreased with depth, and in April 2017, oxygen increased from 50 to 100 m and was well mixed beneath 100 m (Figure 2). At CWC living depths, oxygen ranged from 4.96 to 5.81 mL L−1. Fluorescence reached values >1 mg m−<sup>3</sup> in the uppermost 20 m in April 2017 and in October 2016 (not shown). Beneath 50 m, the fluorescence values were <0.05 mg m−<sup>3</sup> (Figure 2). In October 2016, turbidity reached values >1 NTU at the surface and at the bottom. The mean turbidity through the water column was ~0.2 NTU (Figure 2).
