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

9 May 2002

The N.B. Palmer made its last foray out to the edge of the Western Antarctic continental shelf off of Charcot Island during 9 May before turning back to shore on the final survey line (#13). Although the massive icebergs were left behind, the sea ice was with us all the way out the shelf break, but for the most part it was new ice and did not hamper the work on station or the towyoing of BIOMAPER-II. The exception was the use of the 1-m nets, which could only be towed vertically for surface zooplankton because the ice conditions prevented an oblique tow.

The weather continued to be unbelievably clear and cloud free, with moderate winds. Working conditions were very good, except for the cutting cold air. The barometric pressure peaked in the late night of 8/9 May around 999 mlb and then decreased slowly during the day reaching 992 mlb near midnight. Winds stayed mostly in the 14 to 18 kt range and air temperatures ranged from -11 to -15ºC.

On May 9, work was completed at broad-scale survey stations 88, 89, and 90. CTD casts were made at each of these stations. A 1-m Reeve net tow was done at station 88 and 1-m ring net was towed for surface zooplankton at station 90. Both nets were towed vertically because ice conditions prevented an oblique tow. The ROV was successfully deployed at station 88 for an under ice survey for krill. BIOMAPER-II was in for transits between the all of the stations. Seabird and marine mammal surveys took place during the daylight period and 2 sonobuoys were deployed during the transit to stations 89 and 90.

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

On 9 May, the CTD group did three stations, two at the outer edge of the shelf and one in mid-shelf. All stations were shallow (400 m). One outer shelf station (89) showed oceanic influence, while the other two had cold deep temperatures. All three surface layers had multiple layers indicating different depths of mixing in recent days.

Station 88 (cast 92, 430 m). Surface conditions were uniform to 30 m (-1.84ºC, 33.5 psu, 0.06 ug/l chlorophyll). A deeper uniform layer extended to about 80 m and below, the pycnocline extended to 200 m with several large layers (10-15 m thick). The deep temperature was nearly uniform (1.2ºC).

Station 89 (cast 93, 423 m). Surface conditions were uniform to 60 m (-1.82ºC, 33.85 psu, 0.2 ug/l chlorophyll). Thick temperature layers occurred below the mixed layer to 320 m. The temperature (1.8ºC) was at 225 m and a cold uniform temperature layer occurred at the bottom (15 m thick).

Station 90 (cast 94, 405 m). Surface conditions were uniform to 30 m (-1.88ºC, 33.8 psu, 0.07 ug/l chlorophyll). A second uniform surface layer extended to 70 m. Small-scale temperature and salinity variability occurred throughout the pycnocline to 250 m. The deep temperature was nearly uniform (1.3ºC).

Marine Mammal report (Debra Glasgow)

The marine mammal survey began on 9 May at 0930 surrounded by a vast plain of young grey ice dotted with a few icebergs and small pools covered in nilas. An occasional pressure ridge or crack created some texture to the blank page of ice before us. The sun rose at about 1020, contributing little warmth to the ambient air temperature of minus 11.9ºC, in fact, it got colder as the day wore on. There was a mainly clear sky and excellent visibility. At 0950, the first of 16 fur seals for the day were recorded. A male and a female were lying on a pressure ridge in the ice near a large pool of water coated with nilas. As the ship bore down on them, we came to within 50 meters of the seals and the female galloped (as only fur seals can down here) across the ice and slid into the pool, the male was a bit more relaxed and merely took a few paces away and lay back down. This was the first of three male/female pairs for the day and all the fur seals seen were on ice. Five crabeater seals were also recorded, but were swimming as a tight group in the water in a small pool in the ice near the ship at 1435. Last night, while stopped at station 87 at approximately 2120, Jenny White and Julian Ashford saw a “like minke” whale in the lights outside the CTD door of the Baltic room, while the CTD was going down. The whale surfaced twice, traveling towards the stern of the ship about 50-80 meters away at the outer edge of a pool in the ice. They saw both body, falcate dorsal fin and 2 blows. I kept a watch of the pool area and the surrounding ice that was visible in the lights for over half an hour, but apart from seeing an unidentified seal swimming past the CTD cable, no further whales were sighted. When we moved on Ana Sirovic deployed a sonobuoy and some odontocete sound was later recorded (WOS#38, 69 15.575ºS; 75 38.431ºW).

At approximately 0946, while I was identifying some seals on the port side, Capt. Joe Borkowski saw one blow in a pool abeam to starboard. He described the blow as low and bushy, but despite several watchers on the bridge, unfortunately the whale did not reappear. This whale has been recorded as a “like minke” (WOS#39, 68 52.62ºS; 76 49.37ºW).

At 1509, two minke whales were observed to blow and surface at the edge of a pool within the ice to starboard, swimming in a narrow channel of open water between the edge of the ice and the nilas coating the pool. On a bearing 300º and 1.2 nautical miles away, they swam parallel with the ship for 2-3 surfacings and then turned towards the ship, swimming under the nilas before disappearing. Digital photos were taken of the ice habitat (WOS#40 68 53.32ºS; 77 12.53ºW).

The survey ended at 1638 in poor light after yet another colorful sunset at 1547. Ice conditions were - 9/10, 60% consolidated pancake 10-20 cm thick - sometimes thicker, 20% young grey ice, 20% open pools mostly coated with nilas, and a few icebergs. Ice was variable, but similar for most of the day.

Sea Birds (Erik Chapman and Matthew Becker)

The ship traveled through concentrated ice coverage today between stations 88 and 90. Bird surveys were conducted for almost 4 hours during the transit during beautiful, sunny conditions. Recently frozen leads, covered with new gray ice and some patches of open water were separated by about 0.5 nautical miles of 10/10th new white or consolidated pancake ice. A surface tow at station 90 indicated no diatoms, a few adult Euphausia superba, and copepods, comprised of a large number of Metridia spp.

Bird observations reflected the ice habitat encountered during the survey. Low numbers of Snow Petrels and 2 Antarctic Petrels were recorded during the transit and the birds were mainly associated with open water leads. Once again, no Adélie Penguins were observed.

A summary of the species and number of individuals of birds and seals within the 300 m transect during 3 hours, 44 minutes of daytime surveys between consecutive stations 88 and 90 is the following:

Species (common name)	Species (scientific name)	Number observed
Snow Petrel	Pagodroma nivea	28
Antarctic Petrel	Thalassoica Antarctica	2

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

Note that the report that should have been presented here was mistakenly incorporated into the report for 8 May. Please see that report for a description of the Reeve Net tow results. There were no experimental activities with this project on 8 May, only data processing.

Water Sampling for Microzooplankton (Phil Alatalo)

Survey line 10 started with station 76 in thick ice near Lazarev Bay. Not surprisingly, ice cover seemed to have a dampening effect on the microplankton. Diatoms continued to decline in surface waters, particle abundance was lower at the surface in areas of established ice, ciliate protozoans were much smaller in size, and overall motility of dinoflagellates and microzooplankton was diminished. Surface water at station 76 exhibited these conditions, yet still contained one observed Mesodinium ciliate. At 100 m and again at 175 m, particle abundance was greatly enhanced. In the pancake ice of stations 77 and 78, Mesodinium and a few diatoms appeared in the surface samples. Here diatoms were found throughout the water column, as they presumably had only recently been covered with wind-reducing ice cover. Station 80, near the shelf break, had a noticeably more diverse assemblage of diatoms, ciliates, and Mesodiniuim at the surface.

Nearby statition 81 on the 11th survey line, displayed the same diatom diversity and abundance as station 80, but Mesodinium was not observed. Surface chlorophyll values reflected the presence of diatoms (0.3 ug Chlorphyll/l). Heading landward, heavy pancake ice was already present by station 82, which was devoid of diatoms at all depths sampled. Mesodinium, because it can swim and photosynthesize, continued to be present all the way into station 84, but only at the surface. Very small, dense particles became increasingly prevalent at all depths along the shelf stations 82, 83, and 84. More diatoms were present throughout the water column, but tended to be small pennate or chain diatoms, less apt to sink in the water column. The larger Corethron sp. And Chaetoceras sp. diatoms were found either at the surface in deep offshore stations, or having sunk to deeper depths along the shelf and near shore. General motility of microplankton at all stations had decreased considerably.

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

The 21st MOCNESS tow of the cruise was conducted at the shelf break south of Charcot Island on 9 May. The tow was done at mid-day in ~420 m of water and fished down to 390 m. The junction box for the strobe light system was frozen prior to deployment of the net and hence the strobe system was not used. Remarkably the net response functioned throughout the tow, suggesting some conflict between the strobe system and the net response.

Quite low abundances were observed in most of the nets, especially at depth. The deepest layer (390-300) had very few animals, mostly copepods with 1 krill larva. Copepods were found at all depths. Metridia made a lovely showing (blue bioluminescence) starting at 150 m up to 25 m, with greatest abundances in the 75-100 m depth range. The upper portion of the water column (75-25 m) contained diatoms as well, however, not in overwhelming abundance. Chaetognaths were observed from 300-100 m and a few amphipods from 150-75 m. Large ctenophores (3 total) were collected from 75-25 m. Krill were not abundant in any of the nets.

The BIOMAPER-II survey of zooplankton and micronekton continued on 9 May along the tracklines between stations 87, 88, 89, 90, and 91. This trackline took us to the edge of the shelf on survey line 12 to station 89 arriving about noon, and then south west along the shelf edge to station 90 during the afternoon. During the late evening, the transit on survey line 13 from station 90 to 91 began. As has been the case for about half the cruise, at each station, the towed body was brought on deck while the station work was done to reduce the chance of damage either to the wire or BIOMAPER-II while working in the pack ice.

In the mid-shelf region between stations 87 and 88, volume backscattering was in general relatively low with occasional intense patches of scatterers in the near surface region, which extended from below the ship's wake turbulence layer to between 50 and 70 m. During the morning run between stations 88 and 89, a dense krill patch was seen at 80 m both acoustically and by video shortly after the run started and others were seen sporadically along the trackline, but the background scattering remained light. Thin scattering layers were seen intermittently in the pycnocline and there was a bottom layer about 140 thick of moderate backscattering in water around 400 m deep. The mid-water depth zone had very low scattering. One problem with having very calm surface waters as experienced in towing through the ice pack is that the possibility of cross-talk between the upper and lower transducers is more likely. On this run, the bottom return from the lower 120 kHz transducer sometimes appeared on the upper 120 kHz echogram and corrupting the upper's data. Under normal non-sea ice conditions, this does not often happen.

The run along the shelf break to station 90 in the afternoon provided backscattering records very similar to those from the morning run. From time to time more intense small patches occurred near the surface. The deep scattering layer at the bottom was pretty skimpy along this stretch. Headed back towards shore after leaving station 90, more thin layers appeared in the pycnocline and the mixed layer had more scattering along with some more intense patches. Just before midnight, very strong scattering patches, presumably of krill, appeared about 5 nm from station 91. A couple were in the form of columns 70 meters tall and a few hundred meters across During this transit, the bottom layer was present, but relatively weak.

Cheers, Peter