30-31 May 2001
N.B. Palmer

This is the last day of the data acquisition phase of the Southern Ocean GLOBEC broad-scale survey of the Western Peninsula and Marguerite Bay region of the Antarctic ecosystem. We are now doing a BIOMAPER-II towyo section along transect line two of the original survey because technical problems early in the cruise caused us to miss getting data with the towed body along this line. Our current position is -66 13.98°S; -70 23.19°W. The wind is less than 10 kts out of the south southeast (165) and the air temperature is -5.0°C.

On 30 May, we started a series of short transects to define the coastal current off the southwestern portion of Adaliade Island using CTDs at point locations and BIOMAPER-II towyos along the trackline. The weather was a bit better than the previous day with the winds light, < 10 kts and no snow. High broken clouds allowed much better visibility. It remained well below freezing - around - 4.0°C. BIOMAPER-II was in the water and we were just finishing the CTD at Station 94 when a fax was received around 0900 that had the code to do the software fix for the ailing AWS wind speed logging. The survey was discontinued and with the gear on board, we steamed for the Kirkwood Islands to repair the AWS. By 1230, we had arrived at the Kirkwoods. In spite of less than optimal conditions, a Zodiac with a party of six made its way through the choppy seas to the island.

They had some difficulty finding a landing spot because the surf was up much more than 5 days ago when the installation took place. Eventually, a spot was found where they could get ashore. Around 1415, as the light of the day was fading, the group finished the job and were picked up by the Zodiac, which had been waiting just offshore. While the island party were doing the AWS repair, a test of the track point system was being conducted on board the Palmer to see whether a repair of the cable was successful. Jan Zelag had discovered at least one of the wires was broken in the base of one of the cable terminations and may have been the reason for the poor performance of the track point system to date. A final test was done when the Zodiac returned to the side of the Palmer. A transducer was put at 3 m over the side of the inflatable and it then drifted out away from the side of the ship while track point system tried to follow them. This was done successfully.

By 1600, the ship was back underway for the place where work had been stopped in the morning. BIOMAPER-II was deployed when the break off point was reached about 1930 and towyos were recommenced along the trackline to station 95 where the next CTD was done. The last of the coastal current CTD stations (#99) in the section was completed about 1000 on the 31st after BIOMAPER-II was brought on board.

We then steamed northeast to the location of mooring A1 (-67 01.134°S; -69 01.217°W) in calm seas and light winds (about 10 kts out of south southwest - 215 degrees) and with an air temperature (-5.0°C) that was fostering the development of sea ice. Large patches of sea ice occurred along the trackline. Early in the transit, the coastline of Adalaide Island was visible with the cloud line nearly down to the water in some places and peaks showing in others. The sun, low in the sky, was out and casting shadows on the mountains and on the sea ice chunks as they flowed by. The bright rays created a rainbow where snow showers were coming down between us and Adailade Island.

During the Seabeam survey of the bathymetry around mooring A1 in the early afternoon, the skies cleared over the mountains of Adalaide Island and a magnificent view appeared. The tall white snow cloaked mountains with almost no rock showing merged at their base with the Fuchs Ice Piedmont. This tremendous ice sheet is 610 meters or so high at the top and 30+ meters tall where the ice shelf meets the ocean. Many crevasses were evident along the margin of the shelf and it became evident why there were so many icebergs present in the local waters. From our work site, the ice shelf edge was about 9 nm away and the mountain peaks were about 20 nm. During the period of the survey (1300 to 1430), the sun, which had shown so brightly at the beginning, was setting by the time we left the site and deep shadows developed on the mountain sides that disappeared a short time later leaving only the peak tops lite for a few minutes before they too faded into dusk.

Following the Seabeam survey, we steamed to the near shore end of broad-scale survey transect #2. But instead of stopping at Survey Station #6, the ship was moved in towards the ice shelf edge to where the water was about 100 m deep to define the inner edge of the coastal current in this area. This depth occurred about 1.5 miles from the ice cliffs. There a CTD profile was made around 1700 and then the ROV was deployed to look for krill under the sea ice, which was 10/10 in the area. BIOMAPER-II was put back into the water after the station work was completed and the towyos along survey transect line #2 were started about 2200 on the 31st. Along the trackline, XBTs were dropped at 10 nm intervals.

The 31st of May was also noteworthy because of a visit from King Neptune. Pollywogs, those who had never crossed the Antarctic Circle, were sought to attend his appearance, which included his entourage of experienced circle crossers. The induction process that ensued was interesting, some might say fun, and largely enjoyed by all who participated in it.

Eileen Hofmann reports that after returning from repair of the AWS on Kirkland Island on 30 May, the CTD group completed the section of stations across the coastal current along the southwestern end of Adelaide Island on the morning of the 31st. The hydrographic data from these stations now allow us to better describe the southwesterly flowing coastal current. The additional stations will also allow us to refine the survey grid prior to the next SO GLOBEC cruise so that the coastal current is well resolved in the resulting data sets.

ADCP-derived current distributions provided by Susan Howard show the southwesterly flowing coastal current along the coast of Adelaide Island. The current appears as a narrow coherent structure that turns into Marguerite Bay around the southwestern tip of Adelaide Island. Maximum surface velocities associated with the current are on the order of 20 cm/sec.

After finishing the CTD stations, we moved to the location of survey station 6 to deploy BIOMAPER. However, before doing this, we did one additional CTD cast as close inshore as we could get to the ice shelves that extend seaward from Adelaide Island. This station was located about 1.5 nm from the ice shelves in about 100 m of water. The vertical profile of temperature and salinity from this station showed a lens of fresher and colder water extending from the surface to about 15 m. This lens is likely due to meltwater from the nearby ice shelves. This station also allowed us to clearly determine the inshore edge of the coastal current. We are now undertaking an XBT survey as we move offshore to determine the extent of the fresh water lens.

Chris Ribic and Erik Chapman report that on 31 May they surveyed for 1 hour and 31 minutes as the Palmer transited to the A-1 mooring location. This area was along the outer edge of the coastal current along the western shore of Adelaide Island, outside and just to the north of Marguerite Bay. The ocean surface was between one and seven tenths covered with new pancake ice in the transect. They recorded 25 birds overall; 24 Snow Petrels (Pagrodoma nivea) and a single Antarctic Petrel (Thalassoica antarctica). The density of Snow Petrels appeared lower than in the coastal current on the north side of Alexander Island and along the western shore of Alexander Island.

BIOMAPER-II/MOCNESS report (P. Wiebe, C. Ashjian, S. Gallager and C. Davis):
During the early morning hours of 30 May, BIOMAPER-II continued to be towyoed along the transect designed to sample the coastal current along the southern end of Adalaide Island. The shallow water and extremely variable bottom topography made it difficult to towyo deeper than 50 to 75 meters. The echograms revealed strong concentrations of what appeared to be krill patches in hollows in the topography. Some attempt was made to get BIOMAPER-II down into one of the hollows to enable visual images of the animals being ensonified, but the topography was too unpredictable and it did not happen. At station 94 around 0800 on the 30th, the towed body was brought on board the Palmer for the steam to the AWS repair site. Upon return to the station location late in the afternoon, the towyoing resumed. Often along the towyo route, what looked like krill aggregations continued to occur down in the deeper hollows in the topography, but because we could not towyo down to them as a result of the highly irregular topography, we can only surmise their makeup. Around 0800 on the 31st, BIOMAPER-II was brought on board at the completion of the coastal current section to await deployment at the next towyo site.

BIOMAPER-II was back into the water about 2200 on the 31st, where the CTD and ROV were done about 2 miles shoreward of Station #6 on the second broad-scale survey transect line. The towyos along this line were not as difficult as when we were around the Marguerite Bay area. The topography was much smoother and the water column deeper. So once away from the shallow water near the ice shelf, towyos down to 250 m were possible without to much worry that the bottom was going to come up unexpectedly. The acoustic backscattering along the trackline was initially fairly intense at depth and there were near surface patches of intense scattering. On one occasion, the towed body went through one of the patches and on the video adolescent krill were very abundant indicating that most of the very discrete and intense patches in this region of the water column are composed largely of krill. This transect line will be completed by early afternoon on 1 June.

Cheers, Peter