March '97 Summary Cruise Narrative Science Party List Browse SeaSoar Sections

Local time is used throughout this narrative- GMT is five hours ahead.

2 MARCH, 1997
R/V Oceanus sailed from Woods Hole at 11:00 in moderate fog. As both weather and sea state were calm, we proceeded towards Ron Schlitz's moored array with the intent of redeploying the mooring while conditions remained favorable. Satellite imagery revealed a warm core ring to the southeast of the bank, but too far from the shelf to be of interest. A prominent intrusion of Scotian Shelf Water also extended along the southern flank of the bank, near the 100 m isobath. We chose to begin SeaSoar operations by surveying the intrusion while monitoring the progress of the ring in hopes that it would propagate northward.

3 MARCH, 1997
We arrived at 40° 52.02' N, 68° 30.61' W (mooring site 4) at 04:00. The mooring was successfully deployed in 53 m of water at 40° 52.04' N, 68° 30.63' W at 06:24. Following the deployment, we followed the mooring line offbank until we reached 80 m of water, where we deployed SeaSoar. We planned to tow outward along the mooring line and then proceed eastward following the 200 m isobath until we reached the Scotian Shelf Water intrusion. Our intent was to use the along-bank survey to identify interesting features extending in the cross-shelf direction. Shortly after deployment at 08:24, 40° 37.60' N, 68° 18.09' W, CTD failures indicated a short in the system. We recovered SeaSoar and traced the problem to a leak originating at a junction box cover screw. Repairs were completed and SeaSoar redeployed at 12:45. We then began an eastward transect along the southern edge of the bank between the 200 m and 300 m isobaths, looking for intrusions or other cross-bank features while enroute to the eastern survey site. At 21:15, 40° 41.91' N, 66° 49.62' W, SeaSoar ran down a high-flyer, shorting the CTD and precipitating a recovery. Closer inspection failed to reveal any apparent damage, and the vehicle was immediately redeployed. The South Flank survey line was displaced southward into deeper water to reduce the chances of more nighttime collisions with lobster gear.

4 MARCH, 1997
We arrived at the start of the eastern (intrusion) survey site a few hours before first light. Although we had originally intended to begin the survey by running towards the bank, concerns over visibility and further collisions with lobster gear motivated us to initially tow southeast into deeper water. The intrusion had a vertical extent of about 50 m and was marked by temperatures colder than 2° C and salinities fresher than 31.5 psu. It extended a few kilometers inshore of the shelfbreak front, near the 100 m isobath, and had a width of approximately 50 km. To map the cross-shelf extent of the intrusion, we ran off bank well past its southeastern edge. We then began a second line running northwest to approximately the 80 m isobath, separated by 10 km from the initial track. Building seas forced us to recover the SeaSoar at 12:30, shortly after beginning the second line. We remained hove to until 20:20 waiting for conditions to improve enough to resume work, at which time we redeployed SeaSoar and continued towing to the northwest.

5 MARCH, 1997
A CTD failure at 04:00 forced us to recover SeaSoar near 41° 28.71' N, 66° 30.86' W, the northwestern end of a survey leg. The problem was traced to the failure of a plastic connector, possibly due to increased brittleness brought on by prolonged oil immersion within the junction box assembly. We replaced the connector and redeployed SeaSoar at 08:30, resuming the sampling of the eastern radiator survey.

6 MARCH, 1997
Deteriorating weather and an approaching storm forced us to recover SeaSoar after completing the first pass of the eastern radiator survey. The vehicle was brought on board at 40° 57.71' N, 65° 53.87' W, 04:20, and we moved south to ride out the storm in deeper water. Considerable effort was spent securing equipment in anticipation of the upcoming storm. As we steamed south, SST increased to over 15° C and the ADCP revealed strong (over 1m/s) eastward currents. This was the northern edge of the warm-core ring observed earlier in satellite images. We remained hove to in 30-50 knot winds for the entire day. Winds increased and waves reached 6+ meters as the evening progressed.

7 MARCH, 1997
We spent the day hove to in deep water southeast of the eastern survey site under heavy weather. Winds subsided to 20 knots and wave height decreased through the day, but it remained too rough to SeaSoar. A fax arrived from Bill Williams relaying his suspicion that Jim Irish's Northeast Peak mooring had come adrift during the storm.

8 MARCH, 1997
Conditions calmed enough to deploy SeaSoar at around 06:00. We redeployed SeaSoar at the southwestern corner of the east survey site, but experienced electrical problems shortly after we began the initial transect. After recovering SeaSoar, we returned to the start of the survey pattern. The problem was traced to seawater penetration through a weakened, potted termination on the interior side of a high voltage junction box connector. We redeployed SeaSoar at 10:00 and began a second survey of the eastern site to observe how the Scotian Shelf water intrusion and the shelf break front had evolved in response to the storm. We found that the intrusion had shifted slightly offshore of the shelfbreak front and that intrusion waters had warmed and become more saline, presumably due to vigorous mechanical mixing with underlying slope waters during the storm.

9 MARCH, 1997
By 01:30, conditions had deteriorated severely, forcing us to recover SeaSoar under extremely rough conditions after completing only half of the second survey. Bill Williams confirmed that the Northeast Peak mooring was adrift and near the eastern survey site, though weather conditions prevented us from attempting a recovery. We remained hove to until 16:15, when rapidly settling seas allowed us to redeploy SeaSoar and complete the second half of the eastern survey. Forecasts indicated that we would have only a brief window of favorable weather before another storm materialized, so we planned to quickly complete the survey, search for the mooring and then make the transit to the southwestern mooring site during the period when conditions were too rough to SeaSoar. Conditions during this brief interlude were the best we experienced through the entire cruise.

10 MARCH, 1997
We recovered SeaSoar at 03:00 and began our search for the drifting mooring based on a 24-hour old ARGOS fix. After five hours of unsuccessful hunting, Dick Limeburner provided a more recent fix, which allowed us to quickly locate the buoy at 40° 44.01' N, 66° 15.39' W. The crew of the Oceanus executed a quick, flawless recovery and we were steaming for the southwestern mooring site by 11:30. Shortly after leaving the recovery site, winds picked up and seas roughened, slowing our westward progress.

11 MARCH, 1997
Seas settled enough to deploy SeaSoar at 05:30, allowing us to run a pair of transects bracketing the north-south component of Ron Schlitz's moored array. A waypoint which was incorrectly entered into the navigation computer created an eastward jog in the first survey line. Weather forecasts predicted yet another storm to arrive late in the afternoon. We recovered SeaSoar at 14:55 and secured the vehicle on deck, ending GLOBEC SeaSoar operations for the March cruise.

12 MARCH, 1997
R/V Oceanus returned to Woods Hole at 13:00.