As indicated in the preface to the report on the Palmer's 11 August activities, earlier in the day (13 August), we were underway to assist the Gould under cold, but clear and sunny conditions. After leaving the Gould about 1600 and steaming for about 3 hours towards our next station (#52), we again received a call from the Gould seeking assistance because of their inability to move through the ice pack they were encountering. We are currently returning to their location where the Palmer will provide additional assistance getting them to a place where ice pack conditions should permit the Gould to move independently. Weather conditions have changed dramatically in the last few hours. Currently (2114), the barometer has dropped down into the basement again at 946.5 mlb. The air temperature is up some to -11.8°C and the wind is out of the southeast (122) at 30 kts. A heavy snow fall is blowing horizontally across the deck making the visibility close to zero. Our position is -68° 02.575S; -70° 06.569W and we are some 9 nm from the Gould.
The 12th of August was the first day that we had seen the sun and had any blue sky to speak of since we left Marguerite Bay. The barometer hit bottom early in morning at about 946 mlb and by 0800 was rising. It seemed that we were in the eye of the low pressure system that was passing over us and that was why, for a while, the skies were clear overhead. Temperature, which for the past several days had been around freezing fell down into the - 5 to -7°C range. There were strong gusty winds in the 25 to 35 kt range for a good portion of the day. Off and on throughout the day, clouds would move in and create white-out snow conditions. Work was completed at two stations, #49 and 50, and nearly completed at station #51. At station #49, in addition to a CTD cast, an ice buoy was deployed along with the collection of ice cores. At station #50, an ROV under-ice survey, an ice dive, CTD cast, and a 1-m2 MOCNESS tow were done. The MOCNESS tow was not successful as described below. Jose Torres and his group did a dive in bright sunshine just 50 meters or so from the ship. The ice pack, however, was particularly heavy and tended to close up the open water area that was created by the ship. By the time the dive was completed, their return was blocked by quite a number of big chunks of ice. The Captain had to maneuver the ship back and forth several times before he could get close enough to the zodiac to put the personnel basket over the side to pick people up. In the process, the ship shoved ice cakes under the zodiac beaching it. The personnel transfer was quickly made and as was the zodiac recovery. At station #51, a Tucker trawl to collect live animals, a CTD cast, and an ice collection were made. The trawl catch was a particularly nice one. Many adult krill were caught and Kendra Daly and Jose Torres had the experimental animals that they had long been looking for. Later in the night, a 1-m2 MOCNESS was attempted, but it proved too windy and the ice too thick to permit it.
John Klinck reports that on 12 August, the CTD group did two stations in the mid-shelf region of line 260.
Station #49 (486 m) has a deep mixed layer to 90 m with no structure. The next 50 m shows several distinct temperature reversals, with matching oxygen structure. The rest of the water column indicates active layers with layers up to 20 m thick. A weak oxygen max occurs at 300 m, with a temperature maximum at about the same level.
Station #50 (302 m) has a mixed layer to 65 m with no structure. A smooth pycnocline covers the next 100 m. Near bottom (lowest 100 m) gradients become rather weak with no indication of layering. The lowest O2 and highest temperature (1.5° C) are at the bottom.
Kendra Daly reports that the Daly/Torres group has completed several Tucker Trawls in the past couple of days. A Tucker Trawl to about 500 m at station #46 collected a number of larval and adult krill, other euphausiids, e.g., Euphausia crystallorophias, E. triacantha, and Thysanoessa macrucra, two myctophids, many copepods (Calanoides acutus, Calanus propinquus, Metridia guerlachei, and Paraeuchaeta antarctica), ctenophores, and chaetognaths. Another Tucker Trawl at station #48 to about 500 m collected only a few larval and adult krill, Thysanoessa, copepods, ctenophores, and one medusea. A Tucker Trawl at station #51 collected a large number of larval and adult krill. The ship's Simrad acoustic system indicated that the net probably sampled an aggregation between 80 and 100 m. A number of rate measurement experiments are currently being processed using animals from the station #51 catch.
An under-ice dive survey at station #50 indicated that there were few larval krill at this station and only 2 small ctenophores were observed. A large medusae was collected that contained numerous larval krill.
Ari Friedlaender reports that on 12 August, incidental marine mammal observations began in the morning at 0900 (67° 51.57S, 72° 30.57W) and lasted until reaching station 50 at 0940. Blowing snow and fog limited visibility to less than 500 meters. However, once we reached station, the fog and snow blew through and conditions became excellent. Ice cover was 10/10 of vast, snow covered floes with substantial ridging (0.5 meter height). There were only sparse small cracks and pools. No cetacean sightings were made.
Ari's report for 8 August got lost in the email ether and just showed up. On that day he reported that observations were made briefly from 0900-0920 as we steamed back towards station #34. Sighting conditions were poor. Snow fog limited visibility to 0.5 nm at best, and ice cover was 9/10 with snow covered first year ice and large leads/pools covered in new sheets of nilas and cemented pancakes. Incidental observations were made from the bridge and the stern as we traced and retraced our course while doing MOCNESS and other trawls. Effort began again at 1455 on the way back to station #34, where BIOMAPER-II was put in the water, and then we moved on towards station #33. No sightings were made during the day.
Ana Sirovic reports that on 12 August, she deployed 2 difar sonobuoys, both in transit to station #51. The first buoy was monitored for 43 minutes. Again seal upsweeps were heard, 4 calls over an 11-min period. We were within range of the second buoy for longer (mostly due to the heavy ice and the need for some B&R) and it was monitored for 2 h 24 min. This buoy, however, only brought about the recordings of the familiar engine and ice noise. The range on both buoys was less than 6 nm.
Chris Ribic and Erik Chapman report that on 12 August, they had no luck
surveying because we were on station during daylight hours. They did 1.5
hours of night vision work last night on the way to station #49 and saw
3 Snow Petrels near open water during that time.
BIOMAPER-II/MOCNESS report (P. Wiebe, C. Ashjian, and S. Gallager):
BIOMAPER-II was towyoed between stations #48, 49, and 50. About 5 nm from station #50, the wire hung up on a piece of ice. Unfortunately, the fish was again pulled to the surface and had hit the undersurface of the ice before the ship was stopped. Fortunately, the power stayed on and none of the sensor systems failed. It took more than 30 minutes to get to the place where the wire was hung up on some monster cakes of ice. The ship had to pull forward a bit, then back up pushing the ice out of the way, followed by gunning the engines and using the propellers to create a jet of water to blow the ice out of the way. It took ten or more of these maneuvers to finally get the wire to break free of the ice and come to the open ice free water area just aft of the stern. Then we hauled up the 150 m of wire that was out. When the fish neared the surface, it was clear that it had been damaged because it was not flying properly. And indeed, portions of the tail were wrecked. The VPR camera frame was also bent more, but only to the extent that Scott needed to do another calibration. A new tail was fabricated out of plywood in the ship's shop in time to deploy the towed body at the next opportunity.
The MOCNESS tow #12 at station #50 proved unsuccessful as noted above. The launch went smoothly and net was just below the surface when a large ice cake slide in from the side and ran into the mouth of the net system, lifted it up and then twisted it over onto its back. Somehow the ice moved out from under the net frame and the net slide back into the water and sank down next to the stern. The net was checked out hanging down off the
stern and it appeared undamaged. The tow was completed, but in the encounter with the ice cake, the net bar slides had been bent inward just enough to cause the net bars to hang up before reaching the bottom of the frame and no quantitative samples were collected.