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

23 April 2002

April 23 was another very beautiful day in Northern reaches of Marguerite Bay. The sun rose around 0830 with clear skies overhead and glassy seas (no wind). There was bright sun and essentially no clouds all day, except over the mountains of Adelaide Island where there were some clouds as a backdrop to the peaks. The rugged mountains surrounding Marguerite Bay, blanketed with snow, were dazzling with the brightness of the sun reflecting off the white surfaces. The winds remained low all day (generally less than 15 kts out of the east) and the seas calm. Icebergs were frequently encountered along the trackline. Part way between stations 35 and 36, we encountered patches of newly formed pancake, ice fragments, and bergy bits slowly oscillating in a moderate swell. The amount of sea ice that we encountered increased throughout day as we worked our way towards the central region of Bay. Towards dusk, a band of high clouds moved in from the north accompanied by a falling barometer, which dipped down to 973.6 mlb around midnight. Air temperatures ranged from -2.2 to 1.3ºC during the day and sea surface temperatures were all below freezing. Surface salinities (less than 33 psu) were the freshest yet seen on the cruise.

About 0830 on 23 April, the N.B. Palmer rendezvoused with the L.M. Gould mid-way between stations 35 and 36 in Laubeuf Fjord. The Gould deployed a zodiac to come over to the Palmer under ideal conditions and there was a two way transfer of equipment and science supplies. Live animals collected by Kendra Daly and Jose Torres on the Gould were brought over to the Palmer for use in experimental work by Dezhang Chu. Within an hour, the transit to Station 36 was resumed.

During this day, work started on 22 April at station 34 was completed, as were the scheduled activities at stations 35, 36, and 37. Four CTD’s were made, one each at station 35 and 36, and two at station 37 (shallow with FRRF and deep without FRRF). A relatively deep MOCNESS tow was made at station 34, an APOP cast was made at station 36, and an ice collection was made at station 37. To do the latter, the ship’s starboard crane was used together with a personnel carrier to position the collectors just above the sea ice surface enabling them to do the collecting. Sea bird and mammal surveys were conducted along the transits between stations and BIOMAPER-II was towyoed between stations 35 and 36, and 37 and 38. It was out the water for transit between 36 and 37 for additional maintenance. Two sonobuoys were deployed along the survey trackline to record marine mammal calls.

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

The CTD group did four casts today at three stations in the northern part of Marguerite Bay. At all three stations the surface layer had either multiple layers (relic mixed layers) or continuous change of property to the pycnocline. The surface chlorophyll was lower than at earlier stations. No station had a deep temperature maximum. The deep water temperatures indicated no recent intrusions of oceanic water.

Station 35 (cast 38, 658 m). The surface mixed layer went to 10 m with an older surface layer to 50 m. Surface chlorophyll was 0.2 μg/l, but decreased across the surface layer. A weak Winter Water (WW) layer existed between 80 and 100 m. There were layers (3-10 m thick) in pycnocline and there was a uniform deep temperature of 1.3ºC.

Station 36 (cast 39, 287 m). There was a uniform surface layer to 15 m. The rest of the surface layer (to 70 m depth) had 20 m thick layers of alternately warm and cold water (+-0.3ºC). Surface chlorophyll was 0.2 μg/l. Small scale variability was lacking in the pycnocline, but there were two layered intrusions (20 m thick). Temperature and salinity increased to the bottom with no temperature maximum.

Station 37 (cast 40, 41 517 m). The first cast was to 100 m for the FRRF and no bottles were closed. The surface layer extended to 25 m with temperature and salinity that increased with depth. A warm layer (20 m thick, -0.8 ºC) was centered at 40 m. The surface layer graded smoothly into the pycnocline where some small scale variability was present. Surface chlorophyll was 0.15 μg/l. Temperature increased continuously being about 1.3ºC at the bottom.

Marine Mammal report (Debra Glasgow)

The 23rd of April was a day of excellent visibility and spectacular scenery, but despite the marine mammal survey starting at 0827 and finally ending at 1636, no cetaceans were sighted. There were very few birds today and only 4 fur seals, 1 crabeater seal, and 2 unidentified seals that looked very much like Ross seals, but were too far away to positively identify. All the seals recorded were on small ice floes. Ice conditions were variable, but from 1428, we entered an area of large streaks of frazil/grease ice that developed into young pancake ice around 1444 at -68 02.60ºS, -67 57.87ºW, which continued until we stopped at station 37 after sunset. Some pancake ice was collected when we stopped at approximately 1636, at 68.10.81ºS, 68.13. 75ºW, which proved to be about 4 cm thick.

Sea Birds (Erik Chapman and Matthew Becker)

Seabirds were surveyed for 5 hours on 23 April in the north-east corner of Marguerite Bay in ideal conditions. Yesterday’s survey was completed after making the turn into Marguerite Bay along the southern end of Adelaide Island where a dramatic decrease in numbers of birds was observed. Today the ship moved past large tabular ice bergs during the transit from station 35 to 36 and passed through a few small bands of brash ice. During the transit toward the center of Marguerite Bay and station 37, young ice appeared, which gradually changed to slightly older and more substantial ice further south. About 7/10ths concentration grease ice was first observed, which then changed to small pancake, slightly larger pancake ice (about the size of a dinner plate) and finally pancake ice that had rafted, frozen into a solid sheet, and then broken into smaller pieces. Despite seeing 9 seabird species in the survey, very few individuals were observed and Snow Petrels were the most abundant. This was somewhat surprising, since we have typically seen a much greater density of Snow Petrels in habitat with 5 to 7 tenths concentration ice. This was also surprising given the presence of zooplankton in the top 100 m according to SIMRAD readouts and a large number of larval krill in a surface tow that we did at station 37. So, there appeared to be food in the area relatively close to the surface, but there was not a lot of activity by predators in general (birds, seals or whales) here. The flying birds that we are seeing not only require food in the water column, but they also need prey very close to the surface. For these predators, it may be that zooplankton weren't made available to them at the surface by physical processes. Perhaps the stabilizing effect of young ice and low winds did not create the type of turbulence in the surface layers that would bring the food to the surface. Or perhaps there is a more productive foraging area somewhere else. Regardless, it will be interesting to learn more about the biological and physical characteristics of this area from other research groups aboard the ship.

The days work was complete with a ½ hour night survey using night vision goggles from the bridge. The presence of ice of any kind, even grease ice, greatly increases the effectiveness of surveying with the goggles and we could see beyond 300 m from the ship quite clearly. During the survey, 6 Snow Petrels were observed flying over about 9/10ths pancake ice coverage.

A summary of the species and number of individuals of birds and seals observed during 5 hours, 7 minutes of daytime surveys between consecutive stations 35, 36, and 37 is the following:

Species (common name)	Species (scientific name)	Number observed
Cape Petrel (“Pintado Petrel”)	Daption capense	3
Southern Fulmar	Fulmarus glacialoides	1
Antarctic Petrel	Thalassoica antarctica	8
Wilsons Storm Petrel	Oceanites oceanicus	1
Unidentified Skua		2
Snow Petrel	Pagodroma nivea	17
Southern Giant Petrel	Macronectes giganteus	3
Kelp Gull	Larus dominicanus	4

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

The work of measuring the material properties of Antarctic krill and other zooplankton has been slowed by the fact that attempts to collect live animals with the Reeve Net have been not very successful. So taking advantage of the fact that there was to be a rendezvous with the Gould, Kendra Daly, who is on the Gould, was asked if her group could spare some of their live krill without interfering with her experiments. She generously provided a large number of living individuals of several different species when the two ships met at station 36 around 0900, including a few hundred euphausiids (E. superba and E. crystallorophias), mysids (Arctomysis), and a number of different kinds of amphipods, as well as different sizes of fish (Pleuragramma).

Almost all of krill, mysids, and amphipods were alive and happy when the transfer from the Gould to the N.B. Palmer was completed. Unfortunately, only a few fish of size between 60 and 70 mm (Pleuragramma antarticum) were alive when we received them and they all died except for one before we could start the measurements. We did two sets of material property measurements on them. The first one set was conducted about an hour and a half after we had received them, and the second set was done in the evening.

The sound speed and density contrasts from the first set measurements on the fish were 1.01714 and 1.02611. Smaller than those of krill! The sound speed contrast of the second set of measurements was similar to that from the first, 1.01347, while the density contrast was significantly smaller than that from the first set, 1.0071. However, the density measurement in the first set was measured by displacement volume and weight. This method is subject to larger error than the dual-density method (which is more accurate, but more time consuming) that was used in the second set of measurements.

Between the two sets of measurements on the fish, an APOP cast was made at noon. A mixture of adult and juvenile krill caught 8 days ago, with mean length of 43 mm and standard deviation of 8 mm), were used in the measurements. As in the previous casts, there was no evident depth dependence. The mean sound speed contrast of the down cast was 1.0195 (standard deviation of 0.0056), while the mean sound speed contrast of the up cast was 1.0249 (standard deviation of 0.0041). The overall mean sound speed was 1.0222 (standard deviation of 0.0055). As in the previous APOP casts, all animals were alive after the cast. The density contrast of the krill in the follow up density measurement was 1.0268, similar to the values we obtained in the previous measurements.

We also did measurements on 7 big red amphipods (tentatively Eusirus), mean length of 48 mm with about a 2 mm standard deviation. These creatures have a real hard exoskeleton to which visible bubbles kept attaching during the sound speed measurements (there were repeated efforts to remove the bubbles, but they kept reappearing for a while). The measurements were repeated several times until we believed the (visible) bubbles were gone. The resultant sound speed contrast was 1.096, a number that seemed too high for such animals. We didn’t do the density measurement since we wanted to repeat the sound speed measurement the next day and density measurement would kill them.

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

MOCNESS #9 was conducted in the deep basin of Laubeuf Fjord at station 34 just after midnight on 23 April. The water depth fluctuated between 700-850 m for the period of the tow and the net system fished down to 800 m. Again, the net response failed to function. Other than that, it was a very successful tow. The plankton community here differed markedly from those observed at other locations, being totally devoid of phytoplankton matter and characterized by large krill at all depths, numerous only at the surface, and several types of large amphipods. From 600-800 m copepods and several large, ovigerous euphausiids were observed. Krill, ctenophores, copepods, and some krill furcilia were observed from 50-600 m. The amphipods were white with orange eyes or very large and red in color (probably Eusirus). Copepods were very numerous from 75-100 m. From 25-50 m, a large ctenophore and both juvenile and larval (furcilia) krill were numerous. In the surface net, fishing from 0-25 m, large krill were abundant along with some amphipods and a single jelly that may have been a ctenophore. We caught also a high diversity of organisms in the water column net (0-1000 m), including a large myctophid fish. The catch from this net was preserved in alcohol.

The BIOMAPER-II survey effort continued in staccato fashion with towyoing between stations interspersed with transits where the towed body was being worked on in the deck van. The adjustments made to the VPR camera on 22 April were not sufficient and additional focus adjustments were needed to get optimal zooplankton images. These were done while work continued between stations 36 and 37. In addition, problems with the environmental sensing system over the last couple of days were resolved by re-wiring the SeaBird Pump to an auxiliary 12 volt supply and substituting the MOCNESS options underwater unit in place of the one that had failed in BIOMAPER-II so that fluorometry and transmissometry data could be collected.

The towyoing work in the northeastern portion of Marguerite Bay was a bit harrowing because of the incredibly variable topography. In this area, over distances of hundreds of meters to a kilometer or two, the bottom can go from 300 to 500 m to less than 100. Although, the Sea Beam bathymetry maps can now be used to anticipate changes in bottom depth, it is difficult to determine just how deep to let the towed body go (maximum depth 250 m) without danger of running into a portion of the bottom that had come up abruptly. On top of this, the afternoon and evening towyoing was done in sea ice, which comes with its own set of dangers. Sea ice thrust aside by the passage of the ship closes in the open wake region, but usually not until after the towing cable has past through the open water. However, there have been times when the ice springs into the wake between the ship and the wire, and if the ice slab is big enough, the wire stays with the ice while the ship pulls forward. Unless the ship is stopped quickly, the towed body can be pulled to the surface rather rapidly by the wire riding over the top of the ice slab, ultimately causing a collision with the ice. While this has not yet happened on this cruise, it did occur on the previous cruise last August with very negative consequences. Hence our wariness.

The acoustic backscattering in the northern portion of Marguerite Bay was much higher than observed on the continental shelf or further offshore. In addition, there was the first evidence for diel vertical migration by the zooplankton populations in the acoustic data sets on this cruise. During the night period on 23 April, the volume backscattering was highest right near the surface and this high backscattering extended down 50 to 100 m. This pattern was evident on the 120, 200, and 420 kHz echograms. By early morning, just after first light, highest backscattering was below about 50 m and a “clear” zone close to the surface had developed on the echograms. Later in the day, the scattering layer intensified at depth and there were discrete high intensity targets (fish?) present. After dark, the intense backscattering moved close to the surface in the zone that had been clear of scatterers during the day and the nighttime pattern was restored. Very little backscatter occurred on the 43 kHz echograms, except for noise from the ship.

Cheers, Peter