Report of Activities on the RVIB N.B. Palmer Cruise 02-04

15 August 2002

 

In the early morning hours of 15 August, the Palmer completed a six hour journey from station 74 on the continental shelf edge to station 73, some 19 miles closer to shore on survey line 10. A pair of CTD casts were quickly completed and then BIOMAPER-II was deployed for the steam to station 72. This was a remarkable development because electronic problems with the acoustic system in the towed body had caused it to be sidelined for much of the work period in the southern sector of the grid. Electrical problems again appeared during the deployment and after an hour of towyoing, BIOMAPER-II was recovered for additional repair, but not before it showed that a large krill swarm was present. It was again put back into the water in a long lead later in the morning and was towed for nearly two hours before running out of leads just after noon. The pack ice on the direct southeast trackline to station 72 was very hard to move through so the Palmer had spent the morning following leads that allowed us to move east, but not south. About noon, we had to bite the bullet and turn to the south in an attempt to reach station 72, but in a short time it became clear that towyoing BIOMAPER-II was not in the cards. On the southerly course, the Palmer had to back and ram almost continuously to make forward progress, so the towyoing was stopped.

 

After about 8 hours of steaming, station 72 was still some nine miles away and so a large lead was selected in which to do the station work around 1530 hrs. Three CTD casts were done followed by a Tucker trawl attempting to collect live krill furcilia for experimental work. So far this cruise, furcilia have been very rare in the net tow collections and in the under-ice surveys by diver and ROV. The lead proved long enough for both MOCNESS systems to be deployed, with ice collection and an ROV deployment taking place between the two tows. The station work was completed by 0200 on 16 August.

 

The weather started out nice in the morning of 15 August. It was a bit crisp (-12.8C), but the wind had died down and the skies, while partly cloudy, did not degrade the visibility. Another beautiful sunrise occurred because a section of sky clear of clouds just above the horizon allowed the sun to paint the overcast sky red and orange as it came up. Conditions deteriorated during the day, although not badly. The overcast thickened and lowered, and a light snow fell for a while. At 1553, the air temperature was -12.7C and the barometer was at 996.5 mb. It held steady during the day. The winds were light (~5 kts) out of the northeast (045) turning to the west as the day progressed, and the sea temperature was -1.802C. By 1930, the skies had cleared and the moon and Jupiter were bright overhead. The barometric pressure was 999.2 mb and gradually increasing. Around midnight, the air temperature had warmed to -7C and the barometric pressure was at 1002.1 mb.

 

CTD Group report (Baris Salihoglu, Eileen Hofmann, Bob Beardsley, Chris MacKay, Francisco (Chico) Viddi, Sue Beardsley)

Throughout the late hours of 13 August and during 14 and 15 August, we continued to move inshore along survey transect line 10. Three CTD casts were done at stations 74, 73, and 72 during this time. These casts also included the FRRF and CMiPS. At station 74, which was a deep station on the shelf break, a separate cast was made for the FRRF down to 100 m and then the FRRF was removed and the cast was repeated going down to the bottom.

 

Surface waters along transect 10 were well mixed to about 100 m and were just at seawater's freezing point (-1.83C). The isohalines sloped upward from inshore to offshore, but this could be counterintuitive. When compared with salinity distribution during NBP02-02, the salinity actually increased inshore because of ice formation (brine rejection), but this increase in salinity was not high enough to compensate for the reduction in salinity during summer (because of ice melt).

 

The vertical temperature section along transect 10 shows the southern boundary of the Antarctic Circumpolar Current (ACC) was located at the outer end of the transect (station 74). The Upper Circumpolar Deep Water (UCDW) passed over the sill which is located at the shelf break (about 200 km off the shore) and flowed onto the shelf. The water temperatures on the shelf changed between 1.3C and 1.4C below 400 meters. This indicates that the bottom waters of the shelf are composed of modified (mixed with cooler and fresher Antarctic Surface Water) UCDW. This is a big contrast with corresponding temperature distribution observed during NBP02-02, which showed 1.3C waters only at the outer shelf. In the approximately 10 weeks separating these observations the 1.3C isotherm located 220 km off the shoreline has moved at least 40 km farther into the shelf (because we could not get farther onto the shelf due to heavy ice cover we do not know the actual extent of 1.3C isotherm). This on-shelf movement of the deeper waters may be related to the presence of the southern boundary of the ACC along the shelf edge, which may produce dynamics that pump the deeper water onto the shelf.

 

Sea Birds (Chris Ribic and Erik Chapman)

On August 15, the ship backed and rammed through 9 to 10/10ths ice coverage as it headed between stations 73 and 72, toward Alexander Island to the south of Marguerite Bay. Surveys were conducted for 5 hours and 37 minutes in periodic snow squalls, but otherwise generally good observing conditions. Crabeater Seals were quite abundant near station 73 and unlike yesterday, they were mainly hauled out on ice adjacent to floes. Temperatures were warmer than yesterday and winds were very light, so the seals may have taken this opportunity to haul out and rest on the ice. Snow Petrels were not abundant, but represented the only birds in today's survey.

 

A summary of the birds and marine mammals observed on 15 August (YD 227) during 2 hours 37 minutes of survey time as the ship traveled between stations 73 and 72 is the following:

 

Species (common name)

Species (scientific name)

Number observed

Snow Petrel

Pagedroma nivea

6

Crabeater Seal

Lobodon carcinophagus

54

 

 

Marine Mammal report (Chico Viddi)

At 0830 on 15 August, viewing conditions were good for the cetacean survey. Eight hours of observations were made, of which 5.4 hours were effective observational effort. The sunrise was the only time when we could actually see a bit of sun. After that the day was cloudy and it snowed a good portion of the day. Floes of first year ice, about 70 to 100 cm thick made up the 7 to 10/10ths ice coverage. There were also variable sized leads of open water in the area covered by the ship as we steamed between stations 73 and 72. Crabeater seals (Lobodon carcinophagus) were numerous, totaling 68 seals. Almost every seal observed was seen during the morning: 55 seals were observed between 0900 (-68 30.35′S; -74 48.39′W) and 1000 (-68 31.95′S; -74 3514′W). Only two seals were seen in the water during this time. From 1000 to the end of the observation period, 13 seals were observed and only one seal was seen in the water. Three minke whales (Balaenoptera acutorostrata) were observed in two different sightings. The first one was made at 1001 (-68 31.97′S; -74 34.72′W), 6 to starboard and 0.63 nm from the vessel. Two whales were swimming in a narrow lead of open water (100 m wide). They were surfacing for several minutes on the same spot and they did not seem to react positively or negatively to the vessel's presence. Whales were as close as 50 m from starboard. The third whale (second sighting) was made at 1355 (-68 33.67′S; -74 08.83′W) 0.3 nm and at 9 to port. It was swimming north in a narrow lead of open water.

 

Current Position and Conditions

We are currently (17 August - 0959 hrs) at station 65 (-68 05.381′S; -74 43.101′W) working in 10/10 pack ice with the L.M. Gould about 3 miles away. Air temperature is -2.8C and the barometric pressure is 999.0 mb.. Winds were out of 313 (northwest) at 14 to 18 kts. It is cloudy and snowing lightly. This evening, the second convoy with the Gould to Sector two in the SO GLOBEC grid is planned.

 

Cheers, Peter