OSNAP 2014 R/V Knorr Leg 2 Cruise report – RAFOS Float Program A total of 120 subsurface acoustically tracked RAFOS floats are being released during 2014, 2015 and 2016 OSNAP cruises to directly observe the pathways of Overflow Waters (OW) throughout the subpolar North Atlantic. An array of 10 260-Hz sound sources will be used to track the floats until all the moored arrays are recovered in 2018. Figure 1 shows the approximate positions and pong times for all 10 sound sources. In addition, six short-mission RAFOS floats and one profiling SOLO float with acoustic receiver are being released in 2014 to confirm and monitor sound source performance.

Deployments for 2014 are as follows:

• KN221-01: 10 RAFOS floats in the Charlie-Gibbs Fracture Zone (CGFZ); sound sources #8, 9 and 10; 2 monitoring RAFOS floats.

• KN221-02: 10 RAFOS floats on the eastern flank of the Reykjanes Ridge; sound sources #5, 6 and 7; 2 monitoring RAFOS floats in the Iceland Basin and 1 monitoring float in the Irminger Basin; 1 profiling SOLO float with acoustic receiver in the Irminger Basin.

• KN221-03: 19 RAFOS floats in the Overflow Water over the east Greenland slope; sound sources #1, 3 and 4; 1 monitoring RAFOS float in the Labrador Sea.

• R/V Thalassa: sound source #2 (Johannes Karstenson, chief scientist; replacement cruise for R/V Merien).

Tables 1 and 2 below give the deployment information for float and sound source deployments on KN221-02. RAFOS floats released on the eastern flank of the Reykjanes Ridge were ballasted for 1800, 2000 and 2200 m. The general deployment strategy was to release them 100-200 m above the sea floor

Figure 1. Sound source mooring positions and pong times (once daily) for ten sound sources deployed as part of the OSNAP program.

of the ridge flank to target the thin Iceland-Scotland Overflow Water (ISOW) layer flowing southwestward there. Figure 2 shows the CTD temperature, salinity, and density sections with the float deployment sites superimposed.

Figure 2. RAFOS float deployment locations and depths plotted on CTD salinity, temperature, and density. The two floats at ~1000 m were the monitoring floats deployed in the Iceland Basin. Not shown are the monitoring RAFOS and SOLO deployed in the Irminger Basin. Most of the RAFOS floats were released using the “holey tube” made out of PVC with a piston and starch ring that would dissolve and release the float when submerged off the fantail. On one occasion (3rd monitoring RAFOS float s/n 1177), it was raining and the starch ring dissolved prematurely, and the float slipped into the water from above before the tube was submerged. On another occasion, the starch ring would not release and the float was removed from the tube and launched by hand.

Table 1. RAFOS and SOLO float deployment information.

Instrument Deployment Deployment Latitude Longitude RAFOS Water Depth

Ballast/Target Depth Iridium

Station S/N Date Time GMT (N) (W) Windows Meters Meters ID

26 1046 21-Jul-2014 17:18 57 58.13 23 9.23 14 3001 1000 300034010115350

32 1222 22-Jul-2014 17:37 57 57.71 27 0.56 12 2674 1000 300234060400580

n/a 1310 23-Jul-2014 23:09 58 37.21 29 58.96 730 1950 1800 300234061826920

41 1311 23-Jul-2014 20:42 58 37.5 29 56.02 730 2023 1800 300234061822910

n/a 1312 23-Jul-2014 21:24 58 34.26 29 48.04 730 2015 1800 300234061820930

40 1313 23-Jul-2014 15:39 58 29.41 29 32.07 730 2520 2000 300234061820920

n/a 1314 23-Jul-2014 12:30 58 20.65 29 7.05 730 2280 2000 300234061820910

n/a 1316 23-Jul-2014 18:00 58 31.75 29 35.25 730 2150 2000 300234061820890

n/a 1325 22-Jul-2014 22:54 57 59.56 28 2.39 730 2396 2200 300234061823900

33 1326 22-Jul-2014 22:27 57 58.86 27 55.57 730 2400 2200 300234061828890

n/a 1329 23-Jul-2014 04:20 58 4.92 28 24.21 730 2350 2200 300234061825830

36 1330 23-Jul-2014 05:00 58 8.52 28 32.5 180 2300 2200 300234061823850

n/a 1177 26-Jul-2014 19:30 59 12.78 37 28.66 290 3018 1000 300234010350940

n/a SOLO958 26-Jul-2014 19:21 59 12.64 39 28.61 n/a 3018 1000 300034012176600

Sound source moorings were deployed under the direction of Mark Graham of the RSMAS/U. of Miami, using NIOZ’s double barreled capstan winch. Moorings were adjusted at each site to fit the mooring to the bathymetry, and maintain the sound source height between 1150 and 1200 meters. At Site #5 (sound source s/n 85), one 50-m shot of 3/16th wirerope was removed. At Site #6 (sound source s/n 86) a 10 m ¼ wirerope was replaced with a 50-m shot of identical diameter wire. At Site # 7 (sound source s/n 87) the 50-m and 41-m 3/16th wirerope were removed. A last minute change in cruise plans brought the Knorr quite close to the site for sound source #4, which was to be deployed on Leg 3. This gave us the opportunity to deploy this sound source off the OSNAP line, which would provide better tracking of floats when initially deployed on the line. This plan was scrapped however when the NIOZ winch suffered mechanical problems that would only allow for take-up and not pay-out. Table 2. Sound source deployment information.

Instrument Pong Deployment Deployment Latitude Longitude Site Water Depth

Ballast/Target Depth

CTD Station S/N Time Date Time GMT (N) (W) Number Meters Meters

n/a SS85 00:45 9-Jul-2014 10:24 59 2.328 34 14.172 5 2565 1200

n/a SS86 00:05 14-Jul-2014 18:18 58 1.260 27 49.014 6 2344 1200

n/a SS87 00:15 15-Jul-2014 10:24 58 0.502 22 59.411 7 2991 1200 Sound source moorings were trilaterated by Adam Houk RSMAS/U. of Miami to give exact position of acoustic release, and therefore anchor. Resultant plots of trilaterated positions are shown in Figures 3 through 5.

Figure 3. Trilateration of sound source #85 at site #5. We released this mooring asking the bridge for a 0.15 mile fallback.

Figure 4. Trilateration of sound source #86 at site #6. We released this mooring asking the bridge for a 0.20 mile fallback.

Figure 5. Trilateration of sound source #87 at site #7. We released this mooring asking the bridge for a 0.20 mile fallback. In this case, target was input into the program as ‘anchor over’; actual target was 59.00N and 23.00W, closer to actual position than 504 meters shown in plot.