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

18 April 2002

 

Work down on the Western Antarctic Continental shelf in the fall and winter often seems like an endless collection of cloudy dreary days with little sunlight, but every once in a while a day comes along that is really quite special. April 18 was one of those days. The first view of Adelaide Island happened in the early morning as the sun was rising. Finally the clouds lifted enough so that the full majesty of the snow covered peaks and the Fuchs ice Piedmont could be seen. We were steaming on survey line three towards the island and as we approached station 16, the mountains loomed larger and become more spectacular. The scene was a contrast in shades of gray in the clouds high above and the dark blue/black of the ocean surface, and the brilliant white of the snow covering almost all of the land surface of the island. Later in the afternoon, while at station 17, the sun shone on the craggy mountains highlighting the snow against the dark clouds high above and the sea surface had a glassy slowly undulating texture in the very light winds that prevailed.

 

There are two principal sets of mountain peaks on Adelaide Island. One is on the southern end of the island and the other is more northerly about mid-way along its length. Separating them is a valley. The Fuchs ice Piedmont starts with an ice cliff 30 to 40 meters tall at waters edge along the length of the island, and rises to more than 600 m to fill in the valley and ring the mountains with a thick sheet of ice. Crevasses cut coarse lines parallel with the ice cliffs. A mixture of colors ranging from white to a azure blue paint the face of the cliffs and the azure blue is in scalloped out in places where it appears the cliff that has given way and formed an iceberg. The evening sunset was also memorable. As one of the science party commented at dinner, we really needed a day like this.

 

The work was completed during 18 April at stations 15, 16, and 17, and included 3 CTDs, 2 MOCNESS tows, and a 1-m Reeve net tow. Along track work, however, only consisted of bird and mammal surveying because it was discovered, when BIOMAPER-II was brought on board at the start of station 15, that there was a broken strand of the outer armor on the towing cable. This necessitated the cutting of the cable behind the break and re-termination of the end of the cable. This process took about 12 hours and no acoustics or video data were collected between stations 15 to 17 and part of the way to station 18.

 

As noted above, the weather on 18 April was close to ideal. During the early morning hours, the wind was out of the northeast at 15 to 20 kts, the air temperature was 0.3C (above freezing), and the barometric pressure was 982.1 mlb, up a bit from the last few days. By mid-afternoon, the wind speed was close to zero, the sea surface was glassy, and a good portion of the sky was cloud-free.

 

CTD Group report (John Klinck, Tim Boyer, Chris Mackay, Julian Ashford, Andres Sepulveda, Kristin Cobb)

The CTD group did 3 casts today. All three were similar to coastal stations not affected by oceanic intrusions. Energetic layering, with thicknesses ranging from 1 m to above 10 m, was seen throughout the pycnocline (middle third of the cast). The only unusual feature was the two-layered surface layer (cold over warm) over the weak winter water layer. The deep temperature maximum was below 1.5C, so this water has been on the shelf for a while.

 

Station 15 (Cast 18, 545 m) had considerable temperature structure in the upper 100 m with a uniform mixed layer (-0.8C) to 30 m, a warmer layer (-0.5C, 30 m thick) and a cold layer the same temperature as the surface layer. The pycnocline was inhabited with several 10 m thick layers and numerous 1-2 m layers. The deep temperature maximum (1.5C) was at 300 m.

 

Station 16 (Cast 19, 515 m) had much the same structure as the previous cast, except the surface layer was only 20 m thick and the warmer surface layer was 50 m thick. Surface temperature was below -1.0C. Energetic layering occurred throughout the cast, but was strongest in the pycnocline. The deep temperature maximum (1.4C) was at 300 m.

 

Station 17 (Cast 20, 434 m) had a surface layer with gradually increasing density to about 75 m. There was small scale structure in temperature and salinity through the upper 200 m of the cast. The deep temperature maximum (1.4C) was around 300 m.

 

Marine Mammal report (Debra Glasgow)

The marine mammal survey began well at 0815 on 18 April while transiting to Station 16. It was overcast, but visibility was good and the Beaufort sea state 4. The snow covered peaks of Adelaide Island were visible ahead of us. Observations of fur seals started from 1026 and they continued to be sighted throughout the day. Thirty three were counted in all, most were resting in small groups of 2-6 on the surface with flippers extended.

 

Matt Becker sighted a like minke whale 300 meters away at 1158 porpoising to port with the characteristic v-shaped bow wave, heading away from the ship at -66 57.30S; -69 32.33W. At 1322, three sei whales were sighted at -67 00.69S; -69 21.51W, 3 nautical miles to port at 270. The animals milled at the surface, their tall upright columnar blows seen repeatedly. The same type of 'blows' were seen again in the same area at 1619, this time 7 nautical miles away, and directly ahead of the ship as we headed back the way we had come while towing the MOCNESS nets. This was our best day of survey yet, as the sea calmed right down to Beaufort sea state 2 late in the afternoon and the days survey ended at 1718 with a beautiful sunset. The sun went down at approximately 1700.

 

Marine Mammal passive listening report (Ana Sirovic)

During the period from April 14-18, a total of 9 sonobuoys were deployed. Seven of them were omnidirectional and 2 were directional (Difar - fixing and ranging) sonobuoys. Blue whale calls were heard on 7 of the sonobuoys. Most of the calls were rather faint and distant, with a couple of exceptions. An omni deployed on April 16 showed some blue whale calls, and after Deb Glasgow reported having seen something that could have been a blue whale ~350 m from the ship, a Difar buoy was deployed as well. The calls heard on that buoy were rather loud and it was able to provide bearings on the calling whale. The first set of bearings showed that the animal was swimming in the north-northeasterly direction, which coincided with the swimming direction observed by Deb. Bearings determined approximately 20 min later showed an animal swimming in the southwesterly direction. It is hard to tell if this was the same animal that changed its swimming direction or if it was a different animal. Unfortunately, BIOMAPER-II was at depth at the time and it was not possible to get off the transect and attempt to locate the calling animal.

 

Another set of loud blue whale calls was heard on an omni deployed on April 18. This deployment occurred at night, while transiting between stations 17 and 18, and no visual confirmations were possible. But calling patterns implied the presence of at least 2-3 calling animals. Calling continued for over an hour, at which point the signal from the sonobuoy got too weak and monitoring the animals became impossible.

 

Sea Birds (Erik Chapman and Matthew Becker)

On April 18, we surveyed in excellent conditions for 4 and a half hours between stations 15 and 17. This transit took us close to land, finishing about 10 nautical miles from the southern end of Adelaide Island. Winds were calm and for the first time this cruise, there were just a few ship following birds during the transit. Overall, bird densities were low; Cape Petrel and Southern Fulmar were the most common species. Two Snow Petrels and the first Antarctic Tern of the cruise were seen as the Palmer left station 16. Blue Petrels and prions were absent from the survey and only a single Antarctic Petrel was observed. Some surface seizing feeding by Cape Petrels was seen today, but less than during previous surveys further off the shelf. A summary of the observations is the following:

 

Species (common name)

Species (scientific name)

Number observed

Cape Petrel (Pintado Petrel)

Daption capense

17

Southern Fulmar

Fulmarus glacialoides

14

Antarctic Petrel

Thalassoica antarctica

1

Blue Petrel

Halobaena caerulea

0

Unidentified Prion

 

0

Grey-headed Albatross

Diomedea chrysostoma

1

Wilsons Storm-petrel

Oceanites oceanicus

4

Unidentified Skua

 

0

Southern Giant Petrel

Macronectes giganteus

2

Antarctic Fur Seal

Arctocephalus gazella

16

 

Material Properties of Zooplankton Report (Dezang Chu, Peter Wiebe)

At station 17, a 1-m Reeve net tow was made to about 350 m. Although there was a persistent scattering layer between 290-350 m from the echogram of the Simrad EK500 echo sounder, only a handful of juvenile krill were caught. There were not sufficient individuals to do either a shipboard laboratory experiment or an over-the-side APOP profile experiment.

 

During the day, there was an attempt to use the experimental chamber on shipboard to measure the density contrast of only two adult krill instead of the more than 10 krill used in the previous experiment. This was done to determine just how few individuals could be used and still get reliable information. These krill individuals were collected on the 15 April and were kept alive in a large tank in the aquarium room with running seawater. The measured density contrast, however, was erroneous (less than unity) due to the limited accuracy in weight and density measurements. So to conduct more experiments, additional live krill need to be collected.

 

Zooplankton (MOCNESS/BIOMAPER-II) report (Carin Ashjian, Peter Wiebe)

MOCNESS tow #4 was conducted on 18 April at approximately 0430 at mid-shelf on the third transect line of the survey. The bottom depth was approximately 500 m and the tow was conducted to 479 m. Some krill were observed below 350 m. Copepods were seen throughout the water column with the exception of the upper 25 m. Chaetognaths were seen below 250 m. Krill furcilia were observed from 75 to 150 m. Salps were observed at 250-350 m, 75-100 m, and 25-50 m. Algae was found in the 25-76 m depth range. Amphipods were abundant from 0-25 m along with some krill.

 

The second MOCNESS Tow (#5) taken on April 18 was done in the late afternoon at station 17, located near Adelaide Island in the cold, fresh coastal current. Copepods were found throughout the water column. Chaetognaths and large krill were found from 200-400 m. Phytoplankton and krill furcilia were found in the 50-150 m depth interval. Amphipods, krill furcilia, and copepods were found from 25-50 m. The upper 25 m contained copepods, fish larvae, and amphipods, but no furcilia. This was a successful tow, although the net response still did not function. The scenery of Adelaide Island was particularly refreshing.

 

BIOMAPER-II was collecting data during 18 April during the transit to Station 15, but as noted above, it was sidelined on the deck after a broken strand in the outer armor of the towing cable was found about 0330 while bringing the towed body on board the Palmer. Examination of the wire and over boarding sheave assembly revealed another problem. One of the newly installed rollers on the sheave was also damaged beyond repair. Once the decision to re-terminate the wire was made, it took about 12 hours to complete the work. Putting a termination on the end of an electro-optical towing cable is a complicated process. The cable termination itself is a heavy stainless block of steel that allows the towed body to be coupled to the end of the towing wire. It has been precision machined so that the cable end can be held fast and not give way under the high tensions and stresses that are imposed on it as BIOMAPER-II is towed, often in high seas. After disassembly of the previous assembly, the new cable end was threaded through the termination and the wire strands making up the cable armor were worked into a bird cage that was then pulled back into a tapered cylindrical opening on the outer end of the termination. The opening was then filled with a molten metal called Cerrobend that has a melting point of about 180F. Potting the opening with metal secures the end of the cable to the termination. The cable and termination combo can withstand pulls of more than 10,000 lbs. Then the inner cable core, which extends about 4 meters beyond the termination and has three electrical and three optical fibers, was equipped with connectors that can be plugged into the under water housings located inside the towed body. Making such water tight splices is also a time consuming process. Finally, a rubber boot had to be fashioned out of self vulcanizing rubber tape to prevent sharp bending of the cable where it enters the termination. The time and effort it takes to make up a new cable termination makes it desirable not to do this more than about once per cruise.

 

While the cable was being re-terminated, the roller on the sheave was replaced with a backup method of keeping the wire in place. BIOMAPER-II was put back in service about 2130 on 18 April halfway along the transit to station 18.

 

During the early morning transit to station 15, very strong near surface patches of backscattering were observed. These occurred sporadically and BIOMAPER-II did not pass through any of them so that the VPR could be used to identify their make up. Other wise, backscattering levels were relatively low throughout the water column. During the evening run to station 18, the backscattering levels were moderate to low and no patches of intense scattering showed up that might have been interpreted as krill swarms.

 

Cheers, Peter