Report of Activities on the RVIB N.B. Palmer Cruise 0202

28 April 2002

Each of the Southern Ocean GLOBEC survey cruises has quickly established a rhythm for the work at a station and for the underway data collection. Everyone becomes choreographed and knows the sequence of jobs that need to be done once the ship reaches a station or sets out for the next one. The work goes on around the clock and the elements of station work vary only within fairly narrow limits usually by adding extras to the planned activities or dropping an activity that comes at an inopportune time. The beat goes on, only broken by the unexpected - bad weather, rugged ice pack, and instrument failure are the principal causes - until the survey grid is completed. Fortunately, the Raytheon technical support staff and the scientific personnel are able to quickly repair or replace failing instruments, and mostly it is the weather or the ice pack that breaks the rhythm and the pace. The work, while repetitious, has its rewards in the pictures of hydrographic structure, currents, and biological spatial distributions that are unfolding. It is the painting of an ecological picture that contains the expected and the unexpected, and the wondering of what will appear next that moves the work forward. And it takes the dedicated efforts of everyone on board to make it happen.

We passed the mid-point of the station work on the grid a couple of days ago and completion of the grid now seems much closer. During 28 April, we were working along the inner portion of survey line 7 that took us over the very deep (>1500 m in some places) trough that cuts across the opening of Marguerite Bay and leads into George VI sound in the southern portion of the Bay. During the day, the weather was foggy, snowy, and dreary. Very low clouds have been with us now for a couple of days, although occasionally at night they have thinned to let the moonlight through. Winds were around 14 to 18 kts out of the northeast (038-042) and the barometer rose slowly during the day (988.9 mlb at 1630). Air temperature was again right around the freezing mark (-0.5ºC). By evening the decks had a white coating again of fairly wet snow. During the late evening, the weather worsened some; the winds picked up to 25 to 30 and more snow began falling. What was unexpected was the fact that the sea water was so cold (around -1.7ºC) that the snow did not melt when coming down on to the sea surface, but instead floated and flakes were aggregated making white patches, which were then were swirled in the currents set up by the ships wake and also by the wind-induced surface currents and circulation cells.

Work was completed at stations 51, 52, 53, 54 including 4 CTDs, and a deep MOCNESS tow and an APOP cast at station 54. Seabird and marine mammal observations were made during daylight when the visibility was adequate. BIOMAPE R-II was deployed partway to station 52, after undergoing additional servicing, and towyoed between stations 52 and 53, but it was on deck for more work between 53 and 54. Two sonobuoys were again deployed along the trackline.

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

The CTD group did four casts today along the 260 line from the middle of the shelf to the entrance of Marguerite Bay. One station (54) was in Marguerite Trough. The mixed layer continued to cool and deepen, with temperatures nearing the freezing point (-1.84ºC). Surface salinity declined toward the coast, as we have seen on other lines. The deep water was cool indicating long residence times on the shelf.

Station 51 (cast 55, 743 m). There was a uniform mixed layer to 50 m. (-1.4ºC, 33.5 psu, 0.1 μg/l chlorophyll). Vigorous layering was evident with thicknesses up to 10 m. The deep temperature was about 1.35ºC with no temperature maximum.

Station 52 (cast 56, 1421 m). There was a uniform mixed layer to 30 m. (-1.7ºC, 33.3 psu, 0.1 μg/l chlorophyll). A relic mixed layer occurred from 30 to 50 m (-1.1ºC, 33.7psu). Vigorous layering was evident with thicknesses up to 10 m. The deep temperature was about 1.4ºC with no temperature maximum.

Station 53 (cast 57, 778 m). There was a uniform mixed layer to 30 m (-1.8ºC, 33.3 psu, 0.1 μg/l chlorophyll) and weak small-scale variability in the pycnocline. The deep temperature was uniform (1.3ºC) over about 400 m with no temperature maximum.

Station 54 (cast 58, 1170 m). A uniform mixed layer went to 30 m. (-1.8ºC, 33.1 psu, 0.1 μg/l chlorophyll). There was energetic layering evident with thicknesses 3 to 20 m. Two Deep temperature maxima occurred (450 m and 1100m) both about 1.3ºC.

Marine Mammal report (Debra Glasgow)

April 28 was yet another day of fog, snow, and poor and variable visibility, unfortunately. Three small blows were seen at approximately 1435 by John Higdon and Wendy Kozlowski, while the Palmer was stopped at Station 53. There was a thick fog at the time and the blows were seen at the edge of visibility—less than 300 meters. The whales blew several times at 030º to port, but had disappeared by the time I arrived on the bridge a few minutes later. Eight fur seals were recorded for the day. To date, there have been 21 sightings of cetaceans, with a total of 49 animals.

A summary of the total cetacean sightings to 28 April 2002 is the following:

Species	Number of Animals
Minke	2
Like minke	1
Like blue	1
Like sei	3
Humpback	19
Like humpback	9
Commersons dolphin	1
Unidentified dolphin	4
Unidentified large whale	1
Unidentified small cetacean	2
Unidentified large baleen whale	3
Unidentified whale	3
Total animals	49

Sea Birds (Erik Chapman and Matthew Becker)

Seabird survey time on 28 April was limited as a result of dense morning fog patches, followed later in the day by blowing snow (which continued into the evening, precluding night observations as well). No surface 1-m ring net tow was taken, but morphometric measurements were taken in the evening on an Antarctic petrel, which had landed on the back deck.

Fulmars were the most frequently observed species, but the survey again indicated low numbers of individuals of all species--a constant trend since leaving Marguerite Bay for deep water surveys. During this time off the shelf, we have not recorded any sizable counts similar to those off Adelaide Island en route to Marguerite Bay, or the off shelf surveys on the first (furthest north) transect line. The return to ice-edge transects just outside the bay will hopefully provide an excellent opportunity for replication with surveys in the northern part of Marguerite Bay where high bird densities were observed. Should the same pattern in the southern portion of Marguerite Bay be seen, we will look to see if oceanographic data also indicate differences from offshore transects, or whether the differences in bird species assemblage appears to reflect changes in ice habitat alone.

A summary of the species and number of individuals of birds and seals observed during 3 hours, 2 minutes of daytime surveys between consecutive stations 51 to 54 is the following:

Species (common name)	Species (scientific name)	Number observed
Cape Petrel (“Pintado Petrel”)	Daption capense	4
Southern Fulmar	Fulmarus glacialoides	19
Antarctic Petrel	Thalassoica antarctica	9
Blue Petrel	Halobaena caeulea	9
Southern Giant Petrel	Macronectes gfiganteus	2
Snow Petrel	Pagodroma nivea	1
Antarctic Fur Seal	Arctocephalus gazella	4

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

On 28 April, shipboard measurements of the material properties were conducted on the amphipods (Parathemisto) that we caught with the Reeve net at station 50 on 27 April. These animals were quite uniform in size, with 20 mm in length and 2.9 mm in width. The standard deviations in length and width were 1.2 mm and 0.5 mm, respectively. We did shipboard measurements on these animals while heading to station 53 (68 29.328ºS; 70 37.800ºW). Shipboard measurements have been extremely difficult to make, since they have been made in a small tank without running water. As a result, the temperature changed during the experiment, which could have altered the experimental results. With the larger tank in the aquarium room that has running water, the APOP proved to be too bulky (including cable) to be operated properly. However, with creative and enormous efforts by Steve Tarrent, Jenny White, and Stian Alesandrini (MTs of Raytheon Technical Support on N.B. Palmer), shipboard measurements on Parathemisto were completed. About 150 animals were used in the experiment, the density contrast was 1.042, higher than expected, but not too bad. The sound speed contrast, however, was less than unity (0.984). To confirm the result, we repeated the measurement and the resultant sound speed contrast was 0.916. It seemed that there were micro bubbles trapped in the experimental chamber, since visible bubbles were not observed. To conduct the measurements on these animals correctly, different methods may be needed to remove any possible bubbles that were not inherently related to these animals.

Also on April 28, an APOP cast was made at station 54 (68 31.563ºS; 70 00.709ºW). This time adult krill (E. superba) were used with mean length of 53 and standard deviation of 5.5 mm, respectively, the largest krill group that has been measured so far in this cruise. The down cast and up cast didn’t have any difference that was statistically significant. The difference in their mean sound speed contrast is less than 0.002 (1.0388 and 1.0405, respectively). The overall mean value of the sound speed contrast for both down and up casts was 1.0397, and its standard deviation was 0.0082. The mean value is basically the highest value of all APOP casts and is consistent with the previous observation that the sound speed contrast of these krill may depend on their life stages, which are related to their size. Again, no apparent depth dependency was observed from this APOP cast. The density contrast, however, didn’t become larger as their size increases and the measured density contrast was 1.0255, in the same range as those reported earlier for krill (E. superba).

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

MOCNESS Tow #14 was conducted before midnight on 28 April at the southern mouth of Marguerite Bay in the deep trench that extends southwards into George VI Sound. The tow at station 56 sampled from the surface to 1000 m. This tow was remarkable in that it was the first to catch any abundance of krill, both larger (juvenile, adult) and furcilia. Copepods were abundant from 1000-100 m, but became relatively less numerous above 100 m. Many small purple medusae were observed in the 800-1000 m interval, along with a few krill. Chaetognaths and amphipods were observed from 400-800 m. Copepods were very numerous in the 200-400 m range along with large amphipods and a ctenophore. From 100-200 m, both a large pink amphipod and the white amphipods with orange eyes were present along with numerous small furcilia. The 50-100 m interval was dominated by "tons of teeming krill babies," as well as including several salps and white amphipods. Juvenile and adult krill dominated the 25-50 m depth interval, with some furcilia and copepods as well. These krill were E. superba. The surface net contained a large ctenophore, krill, and furcilia in lower abundance than sub 25 m depths.

Despite the abundance of furcilia in the MOCNESS, the VPR images taken during the BIOMAPER-II tow launch immediately following the MOCNESS did not observe furcilia, suggesting a patchy distribution for the krill. There were n o patches of acoustic backscatter observed using the BIOMAPER-II acoustics during this tow either.

Trouble-shooting the BIOMAPER-II acoustic system occurred during the early morning hours of 28 April and then once the wind and seas had calmed down, BIOMAPER-II was deployed while en route to station 52 before sunrise. The problem with the up-looking 200 kHz transducer continued and so at station 53, the towed body was brought back on deck for additional investigation and was not in the water for the transit to station 54.

On the way to station 52, just after sunrise, there was low volume backscattering in the surface layer and a band of moderate scatterers at 50 m. There was the typical higher scattering from bottom extending up almost 200 m, where the water depth was 420 m. Both layers were a persistent feature along the transect line. Between stations 52 and 53, minimal backscattering levels were present in the surface layer and below 100 m scattering increased to the bottom. There were no krill-like patches noted.

Cheers, Peter