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

1 May 2002

A primary mission on the Southern Ocean GLOBEC survey cruises is to map the distribution of krill in the fall and winter periods as part of the effort to increase our understanding of how these animals survive during the ice covered winter period when water column primary production comes to a halt. One aspect of this is the identification of krill hot spots, places where the krill occur in super abundance in dense patches or layers. During the first cruise in austral fall of last year, the broad-scale survey encountered two areas within the grid area that were designated krill hot spots. One was in Laubeuf Fjord in the northern end of Marguerite Bay and the other was in the shoal areas off the northwest coast of Alexander Island. This year, while the areas in Laubeuf Fjord sampled by the Palmer had krill present, they were not in the numbers that would make the area a hot spot. On 1 May, we surveyed the first portion of the other region, that around stations 60 and 61. Last year at this time, station 61 was clogged with icebergs and it was thought that the icebergs were grounded and would be there for a long time (weeks to months at the least). We thought of the place as a graveyard for the icebergs. However, when we came back to the location after completing the grid, the place was cleared out and only a few icebergs were left. But the name, the graveyard stuck and this time around, the location has lived up to its name. Scattered throughout the station area were many icebergs, although they were not packed in as tightly as they were the last year. This was also a place where we came across numerous seals, some whales, and lots of sea birds. This time it was the same, at least so far for the seals and seabirds. The high frequency acoustics revealed a very strong scattering layer between 170 and 260 m that was very krill-like. On small flat topped chunks of ice were seals laying in sleep and a number were sighted in the water. So this krill hot spot appeared to be alive and well for a second year.

A particularly large group of icebergs were grounded right next to our station 61. The Palmer moved gingerly through them to get to the station location. Crabeater seals were at the base of one of the icebergs and others were so close together that only narrow passages existed between them. Each had a unique blue/white coloration and scores of caves and cracks. A swell was running in the area and as it came up against the behemoths, huge surges were created and breaking waves that sometimes crested their tops some 50 to 100 feet above the sea surface.

The weather on 1 May remained pretty benign, but overcast with dark clouds above. Only on the horizon was there the light of the sun peaking through to the north. The clouds again shrouded the mountains of Alexander Island only exposing their flanks and the tremendous ice piedmont leading down to waters edge. During the day, snow fell on and off and the visibility varied accordingly. The wind speed stayed between 15 and 25 kts out of the east throughout the day and the barometer stayed high (990.4 mlb at 1345). Air temperature continued to vary in a narrow ranges (-1 to -2ºC).

Work was completed at station 59, 60, 61 and 62, including 4 CTDs, and APOP cast and MOCNESS tow at station 62. Seabirds and marine mammals were surveyed during daylight periods when the visibility permitted and BIOMAPER-II was deployed on the transits between stations. Two sonobuoys were again deployed.

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

The CTD group did four casts on 1 May. Water column mixed layer conditions varied radically from a thin freezing layer, to a winter-like thick freezing layer to a moderately thick layer above freezing. Surface salinity increased with distance offshore. The deep temperature also varied, being warmer, in general with distance offshore, but the differing bottom depths made comparisons difficult.

Station 59 (cast 63, 380 m). The mixed layer was uniform to 20 m (-1.8ºC, 33.15 psu, 0.2 ug/l chlorophyll) and there was nearly uniform temperature through the pycnocline, with energetic temperature and salinity reversals. Deep temperature was uniform (1.0ºC) with no temperature maximum.

Station 60 (cast 64, 313 m). The mixed layer was uniform to 90 m (-1.8ºC, 33.3 psu, 0.05 ug/l chlorophyll). There was sm all-scale temperature and salinity variability to 200 m, and slightly increasing temperature and salinity near the bottom (0.6ºC).

Station 61 (cast 65, 167 m). The mixed layer was uniform to 55 m (-1.6ºC, 33.4 psu, 0.07 ug/l chlorophyll). Strong, small l-scale variability occurred to 100 m. There was an increase in temperature and salinity within 20 m of the bottom.

Station 62 (cast 66, 400 m). The mixed layer was uniform to 65 m (-1.5ºC, 33.4 psu, 0.1 ug/l chlorophyll). Small-scale variability occurred to 300 m and there was evidence of 20 m thick layers. The deep temperature (1.3ºC) had no temperature maximum.

Microstructure Profiler (CMiPS) report (Chris Mackay)

The microstructure instrument, CMiPS has continued to collect data on most CTD casts during the cruise. When working in ice great care must be taken to ensure that the delicate thermistors aren't damaged by small pieces of floating ice. The ship uses the stern thruster and propellers to clear an opening in the ice for the CTD and CMiPS to be lowered through. At station 59, early on 1 May, the ice immediately refilled the opening requiring the CTD to be deployed and recovered quite quickly. On the positive side, the ship motion is minimal when in the ice allowing the instrument to be lowered at a smooth and constant speed. This makes the data easier to interpret and it has been possible to start looking at some small scale structure measured by the instrument at these recent stations.

Marine Mammal report (Debra Glasgow)

The marine mammal survey started at 0950 on 1 May during the transit to station 61 in overcast conditions. Pastel colors from the sunrise reflected on the snow on the mountains behind us. The Palmer passed through an extensive area of very small ice floes, growlers, bergy bits, and grounded icebergs surrounded in shuga and grease ice. Crabeater seals rested on many of the floes and a few swam in the water/shug a around the growlers. A total of 38 were counted for the day, most of whom were seen in the morning between Stations 60 and 61. A male fur seal was also sighted on a small floe in this area and a further 9 seals at least could be seen on floes in the distance too far away to positively identify. At 0946, a leopard seal was recorded <300 meters to port on an ice floe by the bird observers and another at 1158 was in the water and appeared to have something in its mouth. Visibility deteriorated as we left Station 62 due to fog and snow, limiting sight ability. It remained variable between <300 meters and <3 nautical miles. At 1545, the visibility suddenly cleared and the horizon could be seen until survey ended in poor light at 1640. No cetaceans were sighted.

Sea Birds (Erik Chapman and Matthew Becker)

Previous at-sea survey work in the Antarctic has shown that seabird species assemblages are structured by ice-habitat, with species like Cape Petrels, Blue Petrels, Southern Fulmars, and Chinstrap Penguins found in open water conditions, while others such as Snow Petrels, and Adélie Penguins are typically found within the pack. Antarctic Petrels have been found to be associated with the marginal ice zone, within the pack and in open water close to the ice edge. So far during the SO GLOBEC cruises, we have found our observations to be consistent with the idea that bird species composition varies significantly with the availability of ice habitat. The 1 May results from the survey that took us from 7 to 10/10ths ice coverage to open water repeated this pattern.

Ice coverage today was approximately 90% shuga ice, with the remainder comprised of broken-up floes from last year's pack measuring around 1 to 2 m in diameter. A morning surface tow at station 60 revealed little in the way of available surface prey for flying birds, and there were no diatoms in the sample. However, BIOMAPER-II data from this transect, which took us near the north shore of Alexander Island in the southern end of Marguerite Bay, indicated what are believed to be swarms of krill deep in a deep scattering layer. There were also a large number of Crabeater Seals in this area, presumably feeding on the krill-like layers that BIOMAPER-II was observing. Several Leopard Seals and Antarctic Fur Seals were also observed.

Although there were some penguin tracks in floes before the sun came up this morning, no Adélie Penguins were seen in the area. This may indicate that the krill were too deep for Adélies to efficiently forage for, or that Adélies were feeding in larger numbers in another area where krill are more abundant and available to them within 100 m of the surface. During the summer, Adélies typically dive 30 to 50 m when feeding on krill. Although Adélies were shown to be diving over 200 m during Bill Fraser's satellite tagging effort last winter, this is likely not as energetically efficient as foraging nearer to the surface. Because penguins comprise a very significant portion of the Antarctic predator community (numbering in the hundreds of thousands on the Peninsula alone), and Marguerite Bay hosts over 40,000 breeding Adélies during the summer months, why these birds (and many of the other Peninsula sub-populations) are apparently not utilizing the bay to the extent we would expect if krill were relatively abundant there is a key question. Alternative explanations for these results that warrant further investigation include: 1) Adélies are focusing their winter foraging activity in areas with high krill abundance and availability in Marguerite Bay, but not within the grid. 2) Adélies are dispersed and feeding on patchy krill resources in low densities over a large area in and around Marguerite Bay. 3) Adélies are focusing their winter foraging activity in areas with high krill abundance and availability outside Marguerite Bay.

While Adélie Penguins were not observed during today's survey, there were a relatively high number of Snow Petrels working the ice edge and around leads in the dense ice pack between stations 60 and 61. As we left station 61, the shuga and small floes gave way to frazil and grease ice covering 5 to 7/10ths of the ocean surface. Ice concentration continued to decrease until we once again found ourselves in open water by mid-afternoon. At this point, Southern Fulmars, Cape Petrels, Antarctic Petrels, a few Wilson's Storm Petrels and a Grey-headed Albatross w ere observed and Snow Petrels quickly disappeared from the survey. In addition to the availability of invertebrate prey near the water surface around the ice edge, we observed six species (Southern Fulmars, Cape Petrels, Giant Petrels, Wilson's Storm Petrels, Antarctic Petrels, and Snow Petrels) of birds scavenging off a Leopard Seal kill in the early afternoon. No identification was able to be made on the kill, as we likely came upon it late and no positive visual on the prey was made. Nevertheless, the observations made led us to strongly suspect a seal kill. In addition, the typical behavior indicative of a penguin kill (i.e., seal slapping the penguin carcass on the water's surface) was not observed. Bird species were seen feeding, presumably on bits of flesh, on the surface around the seal.

A summary of the species and number of individuals of birds and seals during 5 hours, 5 minutes of daytime surveys between consecutive stations 60 and 62 is the following:

Species (common name)	Species (scientific name)	Number observed
Cape Petrel (“Pintado Petrel”)	Daption capense	4
Southern Fulmar	Fulmarus glacialoides	8
Antarctic Petrel	Thalassoica antarctica	28
Wilsons Storm Petrel	Oceanites oceanicus	3
Blue Petrel	Halobaena caeulea	8
Southern Giant Petrel	Macronectes gfiganteus	7
Grey-headed Albatross	Diomedea chrysostoma	1
Snow Petrel	Pagodroma nivea	64
Kelp Gull	Larus dominicanus	1

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

On May 1, a combined shipboard and APOP cast measurement on adult krill (E. superba) was conducted duplicating what was d one on the previous day with E. crystallorophias. The krill used were collected again by Kendra Daly and transferred from the Gould on the second rendezvous between the two ships on 30 April 30. The mean length and standard deviation were 50 mm and 4 mm, respectively. The cast was made at station 62 (68 24.316ºS; 72 18.457ºW). The mean value of the sound speed contrast from the shipboard measurement was 1.039, while the mean value from the cast for the same animals was 1.044, with a standard deviation of 0.004. The difference was, again, not significant. This time the value obtained from the cast was slightly higher than that from the shipboard measurement, in contrast to an opposite scenario observed in the previous day (1.025 from the cast and 1.032 from the shipboard measurements). This observation suggested that there was no sign of any persistent bias between the APOP cast and shipboard measurements. Despite the fact that, for this species (E. superba), the sound speed contrast is the highest of all measurements made so far on the cruise, it is comparable to those values from the similar size groups of the same species (E. superba) reported on April 24 and 28 (1.037, and 1.040, respectively).

The difference of the mean sound speed contrasts between the down and up casts was about 0.002 (1.045 and 1.043, respectively) i.e., small and insignificant. The standard deviations for both down and up casts were the same (0.004), indicating that the measurements were consistent. In addition, this result also suggested that the smooth variation in sound speed contrast for up cast observed in the previous day was not due to the combination of the shipboard and the APOP cast measurements, in which the animals stayed in the animal compartment very long (more than two hours).

The density measurement was conducted very smoothly. All readings were consistent and repeatability was good. The measured density contrast of these adult krill was 1.036. Both the sound speed and density contrasts were the highest yet for this species (E. superba), indicating a positive correlation between the material properties and the life stages of the animals, a speculation we suggested before (see daily report on April 28).

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

On 1 May, the sixteenth MOCNESS tow was conducted at station 62, mid-shelf along line 8 of the survey grid. The tow was conducted to 400 m. Abundance was low in all the nets. Copepods were dominant at all depths from 25-400 m. A large, purple jellyfish was captured in the 350-400 m range. Ctenophores and ostracods were collected in the 200-350 m net. Krill furcilia were collected from 150-350 m. La rger krill were collected from 75-150 m and from 0-50 m. Amphipods were collected in the top net (0-25 m) and in the 50-75 m interval. Fish were collected in the upper 50 m.

VPR Report: Settings (f-stop, zoom etc.) for the low magnification camera were re-set following tow 31 to gain a greater depth of field and to better align the imaged volume with the strobe beam. This improved the images substantially. Unfortunately, we still are not seeing krill probably because of their relatively low numbers in the water column.

The high frequency acoustical, video, and environmental survey continued apace with BIOMAPER-II in the water along the transit lines between stations 59, 60, 61, and 62. While the ground fault problem has been solved and we have not seen any faults for the past couple of days, the problem of intermittent noise on the three lower frequencies (43, 120 and 200 kHz) and the problem with the up-looking 200 kHz transducer not functioning much of the time remain to be resolved. The data collection, however, continues in spite of these problems, and for the most part the data quality is OK to very good depending upon the frequency.

During the nighttime transit from stations 58 to 59 and then to 60 along the northern end of Alexander Island, strong patches of volume backscattering were noted at depths of 60 to 100 meters on the 4 lower frequencies. After leaving station 60, (the graveyard site), a strong scattering layer appeared starting about 170 m below the surface and extending down to about 260 m. The appearance of this layer was remarkably similar to the one that was present in the same location last year and was likely composed of krill. Further, the intensity of the scattering was the highest observed thus far on this cruise. The graveyard and points further southwest close to the western coastline of Alexander Island were previously an area dubbed a krill hot spot. It appears that this area is again a krill hot spot, especially since a substantial number of crabeater seals that feed on krill were present in the area. The bottom topography along the 13.5 nm transect line between n stations 60 to 61 was incredibly variable with the bottom rising rapidly to as shallow as 85 m from depths of 300 m or more and just as rapidly dropping down again. In the depressions between peaks in the bottom, the mid-water scattering layer intensified. The krill-like layer often was observed hugging the bottom when the bottom came up above 190 m and then as the bottom dropped off, the layer reformed across the depression, sometimes with intensification into discrete patches. Towards the end of the run to station 61, there was a definite thinning to the layer and its krill-like appearance was reduced. The upper 50 to 70 m of the water column along this line was almost devoid of scatterers.

During the 21 nm run from Station 61 to 62, scattering levels returned to those more typical of what has been observed on the earlier survey lines at locations in the middle of the continental shelf, a moderate intensity scattering layer at the bottom and in pycnocline below the mixed layer, and much less scattering at the surface or deeper mid-water depths.

Cheers, Peter