25 May 2001
N.B. Palmer

The high winds and seas experienced during the middle portion of the survey grid caused the cancellation of several MOCNESS tows. The missing tows left a significant gap in our sampling of the zooplankton in Western Peninsula Shelf region area under study. To remedy this, late yesterday and early today (26 May), we returned to those sites and made the tows. We are currently in the midst of a bathymetric survey of the area in the vicinity of the B-line moorings. We are currently at -68 20.495°S; -69 01.690°W (1300 local). The wind is out of the south (070) at 15 to 18 kts and the air temperature is -4.0°C.

The work on 25 May began with a XBT/CTD section from the northern part of Alexander Island across to the Kirkwood Islands to better define the origins of the coastal current, which flows along the coast to the southwest of Marguerite Bay. This section was finished in the area where the first of two Automated Weather Stations were to be installed. We arrived at the Kirkwoods about 0930 and in the dim first light, we started looking at the various islands and their prospects as the installation site through the binoculars. There was only one big piece of rock and it was mostly ice and snow covered. We very slowly made our way into a position about ½ a mile or so away from the biggest island after we ascertained that the other smaller pieces of exposed rock were almost certainly covered with water during periods of high winds and waves. While we were making the observations from the bridge and coming up with a decision about the AWS prospects, the Marine Techs were loading up the AWS equipment into the Zodiac to be ready if given the GO. The weather was cooperative with winds in the 10 to 15 kt range out of the south (170) and good visibility (high broken clouds most of the day). It was cold, however, with the temperature around -3.0°C. Around 1000 the decision was made to launch the Zodiac and make the trip over to the largest island. A party of six made the trip to the island with Bob Beardsley in the lead and after some difficulty, they found an acceptable landing site and made it onto land. Some five to six hours later, they returned having successfully moved the equipment to the top of the island and done the installation. Weather information from this site will soon be available from a Web site at the University of Minnesota, which provides real-time information from all the AWS sites under their jurisdiction. The second Zodiac was also launched to scout the area around the islands looking for whales and to launch a sonabuoy away from the Palmer, but no whales were seen.

Once the Zodiac parties were back on board, we set sail for Survey Station 37, arriving about 2230. A MOCNESS was tow was completed there just after midnight with winds in the 25 to 30 knot range coming from the southwest.

Eileen Hofmann reports that after completing the fine-scale patch survey, the next small-scale study was a series of CTD and XBT casts across the coastal current that flows out of the southern part of Marguerite Bay to the west-southwest around Alexander Island. This study consisted of two CTD casts and closely spaced (3 nautical mile) XBT drops. The section extended eastward towards the Kirkland Islands and covered the deep canyon that runs across the center of Marguerite Bay.

The temperature cross-section constructed from these data shows the coastal current, which appears to be about 10-15 km wide. The temperature below 300 m shows that the water filling the deep trench is derived from Circumpolar Deep Water, which is found off the continental shelf. The deep trench acts as a conduit to allow this water to flow onto the shelf. The temperature isotherms show 1.4° C water hugging the eastern side of the trench at about 600 m to 700 m. This is consistent with what is expected from geostrophically balanced flow. The depth of the warmer water suggests that the deep water in the trench may be derived from Lower Circumpolar Deep Water. Confirmation of this will require further study and comparisons. The isotherm pattern also suggests that the warmer water is forced out of the trench and floods the adjacent shelf regions. This may provide a mechanism for periodic flushing of the shallower shelf regions with the warmer Circumpolar Deep Water. The frequency of this flushing is likely related to the meander frequency and intensity of the southern boundary of the ACC.

Following completion of the CTD and XBT section, we steamed for the Kirkland Islands for deployment of the first Automatic Weather Station (AWS). While waiting for the AWS deployment we began the task of compiling information about the CTD, XBT, and XCTD casts for inclusion in the cruise report.

Chris Ribic and Erik Chapman reported that on 25 May, several Snow Petrels landed on the ship early in the morning as we traveled through an area with lots of brash and icebergs. We managed to catch one Snow Petrel at 0100 (local time) and to diet sample the bird. The bird did not regurgitate any fresh stomach contents, only the thick oil that petrels produce in their stomachs. In the evening, two Antarctic Petrels landed on the ship and diet samples from both revealed that they had eaten mainly fish. They were able to collect otoliths ("fish ear bones") from one sample that should indicate the species and size-class of the fish in its stomach. Also observed during the daylight period were a large group of Antarctic Petrels flying high above the group of islands where the AWS was deployed. There were between eighty and ninety birds in the group and the birds were seen throughout most of the day. Kelp Gulls (mostly immature), Southern Giant Petrels (immatures), Snow Petrels, Blue Eyed Shags and a Southern Fulmar were also observed. In addition, four Adélie Penguins and feeding Antarctic Petrels were also seen by the party installing the AWS.

Catherine Berchok has provided a summary of the sonabouy work for the past several days:

May 23rd:  An omnidirectional buoy was deployed at 0830 (local time), as we were stopped for the ROV in Lazarev Bay. The deployment was done because there were a few seals right around the boat. Nothing was heard except for the NB Palmer, the LM Gould and an 80 Hz continuous sound. The recording was stopped after 1.5 hours because of the 80 Hz sound making the buoy look defective. A difar sonabuoy was tossed in at 1100 as we left the ROV site for the ice edge in Lazarev Bay. The strange 80 Hz noise returned and since there was a lot of surface ice pack, it was suspected that ice crushing the buoys might be causing the noise. Recording was stopped after only one hour. At 1900, as we were stopped for the ROV again, The listening system was turned back on to try to pick up the signal from the difar buoy. In doing so, it was discovered that the 80 Hz noise was only appearing in radio receiver #2. Using a new receiver channel, an additional 5 minutes of 80 Hz-free recordings were made before the buoy scuttled itself. As a result not much was heard all day but the ship and ice noise.

May 24th: The bridge phoned Catherine around 0400 to say they had seen a group of four whales (possibly minke whales) swimming with the boat. Shortly after a difar sonobuoy was deployed and immediately there were loud humpback whale sounds. This was at 68 49.8°S; 71 58.9°W. At least three humpbacks were singing at the same time. A bearing fix put at least one whale off the stern and the other off the port side. A second difar was deployed at 0442 and it never transmitted. The third difar was deployed at 0500. A cross bearing fix between this and the first buoy gave a position for a calling whale to be off the port side of our track, closer to the first buoy. At 0651, a fourth difar was deployed and about 10 minutes later the bridge reported seeing a humpback whale go past the starboard bow of the ship. The bearing fixes, however, put some of them aft of the stern. One more difar was deployed around 0730. Between the bearing fixes and the time delays for arrivals on the last two buoys, it was clear that the ship had passed by the whales; no sounds seemed to be coming from ahead of it.

A science meeting on the bridge resulted in the decision to turn around and steam to the position where the humpback whales were last seen. At first light, a humpback was seen by Ari Friedlander and shortly after a Zodiac was deployed to work within the area where the whales occurred. The humpbacks were not fluking much at all, even when they were not being approached (only one was seen fluking during the outing). This indicated that they may not have been diving very deep. There was no evidence of surface feeding, nor were any feces observed. But given that they did not move out of the area during the observation period and were normally diving for 6-8 minutes, suggests they were possibly feeding.

After biopsying the cow of a cow/calf humpback pair, an omnidirectional buoy was deployed close to them. Bob Beardsley was manning the shipboard radio receivers and reported hearing faint humpback sounds from this buoy, more faint than the last two dfiars. This indicates that this particular congregation of whales was not those making the sounds. The final tally was seven humpbacks and six minkes. The tapes need to be reviewed to check for minke sounds. Return to the Palmer was about 1430 and the signals were still coming in from three of the buoys until two scuttled around 1500. Recording on the last one stopped at 2100.

May 25th: At the Kirkwood Islands for an AWS installation, one of the Zodiacs was used to scout for whales and to deploy a sonobuoy ~3 nm away from the Palmer at 68 19.7° S; 68 54.9° W. Aparna Sreenivasan was manning the controls this day and reported hearing faint humpback calls (which have been confirmed), and also some possible seal calls. The buoy was set to 90 feet, but appeared to have been either hitting on the bottom or that the surface wave motion was too great for the hydrophone. The recording lasted for ~ 2 hours.

BIOMAPER-II/MOCNESS report (P. Wiebe, C. Ashjian, S. Gallager and C. Davis):
There were no BIOMAPER-II deployments on 25 May.

A MOCNESS tow was made near midnight on 25 May at the location of survey Station 37. In spite of winds in the 25 to 30 kt range, the tow went to 375 m (water depth ~400 m) and sampled eight strata to the surface without difficulty. Krill larval forms were observed in greatest abundance between 100 and 50 m and they were also present in the 25 to 0 m sample. Below 100 m, salps and copepods were most noticeable.

Cheers, Peter