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

24 April 2002

 

On April 24, the broad-scale survey was conducted along the inner and central area of Marguerite Bay. The weather remained very good for working, although in the hours before first light, a light snow fell. By dawn, there were high overcast skies with clouds that just cut off the tops of the mountains surrounding the Bay. During most of the day, visibility was very good with skies remaining cloudy to partly cloudy with occasional patches of blue sky. It started to snow again in the evening leaving a white coating on the non-heated decks.

 

Winds were generally light to moderate - around 10 to 12 kts out of the east in the morning and 15 to 18 kts out of the north in the afternoon. The barometric pressure was 983.7 mlb in mid-afternoon, up from 974.5 mlb around 0200. The air temperature ranged from -2.1C to 0.9C, and in the afternoon, the sea surface temperature was near the freezing mark at -1.693C and the salinity was 33.977 psu. On the trackline between stations, the ship steamed through a mixture of b rash ice, large pancakes, and larger slabs of much thicker year-old ice. Much of the new ice had a golden greenish brown color indicating lots of algae and microzooplankton were present in it in contrast to the year old slabs that were a purer white. During the steam from station 40 to 41, the pack ice ended and station 41, at the entrance to Marguerite Bay, was in open water.

 

During this day, work was completed at stations 38, 39, 40 and started at station 41. Three CTDs were made, a MOCNESS tow was made at station 40, an APOP cast was made at station 41, and an ice collection was made at station 40. Seabird and mammal surveys were conducted along the transits between stations during daylight, and BIOMAPER-II was towyoed between stations 38, 39, 40 and 41. 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 three casts today in the center of Marguerite Bay ranging from 200 to 600 m. The surface layers were thick near the coast and becoming thinner, with more vertical structure, with distance away from the coast. Surface temperatures were near freezing and surface salinity was near 33. Double diffusive layering had become weak. Deep temperatures were below 1.3C meaning that there was little influence of oceanic water.

 

Station 38 (cast 42, 188 m). There was a uniform surface layer to 45 m. Surface chlorophyll was 0.4 μg/l. There were thick layers (10-15 m) in pycnocline. No double diffusive variability was evident. There was a steady increase of temperature and salinity to the bottom.

 

Station 39 (cast 43, 405 m). The surface layer went to 50 m with density increasing with depth, but the temperature was about -1.8C. The surface chlorophyll was 0.6 μg/l declining to 0.3 at the bottom of the mixed layer. The Winter Water (WW) layer (30 m thick) was centered at 90 m. and the pycnocline extended from 100 to 250 m with little small scale structure. There was no deep temperature maximum. The bottom temp was 1.2C.

 

Station 40 (cast 44, 635 m). There was a thin (15 m), cold (-1.7C) surface layer and increasing temperature and salinity to the top of the pycnocline at 120 m. The surface chlorophyll was 0.5 μg/l declining to 0.15 at 30 m and on down to detection limits at the top of the pycnocline. A few thin layers (2-4 m) occurred in the pycnocline. The deep temperature was 1.3C, but there was no temperature maximum.

 

Marine Mammal report (Debra Glasgow)

The marine mammal survey began on 24 April at 0835 on the transit to station 40 in overcast conditions and in 9/10 young discoloured brown ice. Three Adlie penguins were seen at 0850, which proved to be the most exciting event for the d ay as no cetaceans were sighted. Few birds were recorded for the day, however. While stopped at station 40, Erik Chapman sighted a crabeater seal hauling out on the ice and I recorded 2 seals three nautical miles away but could not identify them at that distance. These were the only sightings of the day.

 

Marine Mammal passive listening report (Ana Sirovic)

A total of 11 sonobuoys were deployed during the six day period 19 to 24 April, all omnidirectional. April 19 and 20 were spent surveying the outer shelf and shelf break. They were busy days with multiple whale sightings and sonobuoys were deployed after the sightings. Blue whale calls were heard on all 4 sonobuoys deployed and humpback calls (most likely a song) were recorded on 3 of the buoys. I also heard an interesting non-biological noise on one of the buoys: a fairly loud earthquake. This occurred at 2234 on April 20. Unfortunately, I did not have a directional sonobuoy out at this time, so I could not determine the location of the earthquake.

 

April 21 was a stormy day with decks closed for most of the day during which just 1 sonobuoy was deployed. Again blue whale calls were recorded, but there were also low-frequency (20-50 Hz) up-sweeps that were most likely of biological origin. Unfortunately, I don't know what animal could have made that noise.

 

April 22-24 were spent near to or inside Marguerite Bay. On 6 sonobuoys deployed during this period, lots of cracking ice was heard, but no biological noise. Together with no whale sightings and low bird abundance, this is an interesting (and unexpected) finding.

 

Sea Birds (Erik Chapman and Matthew Becker)

Seabirds were surveyed between stations 39 and 41 on 24 April for almost 4 hours in excellent observing conditions. We were well within Marguerite Bay, but headed west toward the open ocean on survey line 6. Ice conditions were similar throughout, with 9/10 to 10/10 coverage. About 8/10ths of the ice coverage was new pancake ice about 30 cm thick that had been heavily flooded with seawater and was stained root-beer brown with diatoms. The remaining 1/10th ice coverage was 3 m floes of one year old ice. Six to 12 unidentified penguins were reported by Mate John Higdon and Julian Ashford at about 0300 this morning in the same area. No penguins were sighted during the day survey, though they would have been foraging and would be more difficult to see than when they are hauled out on the ice at night. Other birds were in very low densities in the beginning of the survey, but the numbers picked up significantly toward the end of the survey period as the edge of the ice was approached. During that time, we were probably within 1 to 2 nm from the ice edge and groups of Southern Fulmars and larger numbers of Snow Petrels began to be observed. We also saw a single group of 16 Antarctic Petrels in this area. The ice edge is believed to be a productive foraging area for Snow Petrels. Presumably, the Southern Fulmars, a species typically associated with open water, were associated with the open water nearby.

 

A summary of the species and number of individuals of birds and seals observed during 3 hours, 47 minutes of daytime surveys between consecutive stations 39 to 41 is the following:

 

Species (common name)

Species (scientific name)

Number observed

Southern Fulmar

Fulmarus glacialoides

13

Antarctic Petrel

Thalassoica antarctica

16

Snow Petrel

Pagodroma nivea

36

Southern Giant Petrel

Macronectes giganteus

1

Kelp Gull

Larus dominicanus

2

 

 

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

On 24 April en route from station 39 (68 41.238S, 67 59.760W) to station 40 (68 28.890S, 68 47.940W), the measurements of sound speed contrast on 7 big red amphipods (tentatively Eusirus) were repeated. Three animals out of seven were dead at the start of the experiment (in the previous day, there was one dead animal). This time there were no visible bubbles attached to the exoskeleton during the measurements. The sound speed contrast was 1.0383 as compared to the value of 1.096 obtained in the previous day. This result may be due to the presence of the mixture of alive and dead individuals or because of unseen bubbles in the first experiment. More experiments are needed to resolve this issue. The density contrast was 1.051, heavier than krill we had measured so far on this cruise.

 

At station 41 (68 16.320S, 69 35.280W), an APOP cast was done in the same way as the previous casts. At the end of the cast, we found out that one of the broadband transducers (receiver) was not firmly mounted onto the chamber. This might be a reason why a larger mean sound speed contrast (1.0365) was obtained compared to the values obtained earlier (all less than 1.03). There was again no apparent depth dependence. Another interesting phenomenon was that the difference between down cast and up cast was larger than before, 1.0326 for the down cast and 1.0404 for the up cast. However, their corresponding standard deviations were small, 0.0036 and 0.0037, respectively, indicating they were self-consistent. Further examination of the data and more experiments are needed to look into this problem.

 

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

Our tenth MOCNESS tow was conducted on April 24 at station 40 in a deep basin (~650 m) in the center region of Marguerite Bay. The tow was conducted to 580 m because of uncertainties regarding the course of the ship and the presence of loose pack ice. The ship was able to move fairly freely through the ice as the tow was conducted and most ice was pushed well away from the wire by the ship. In a few instances, ice came close to the wire, but at no time was there real concern that the ice would be caught under the wire. Krill were observed from 100-580 m. The deepest intervals also contained pieces of siphonophores and copepods (200-350 m) and amphipods (350-580 m). Amphipods again were observed from 150 -200 m. Jellyfish were caught in the 150-200, 75-100 m, and 25-50 m intervals. Ctenophores (3) were captured in the 100-150 m interval. Fish were captured in the 50-100 m range. Copepods were seen from 0-100 m. The surface depth contained copepods, 1 adult fish, and 10 larval fish.

 

VPR Report

The video plankton recorder on BIOMAPER has performed excellently through much of the cruise. The plankton composition differs markedly from that observed in this region during fall 2001. Much of the shelf contained numerous algal mats throughout the water column which apparently originated from blooms of diatoms in the surface waters. Also observed on the shelf were abundant radiolarians, some polychaete worms, some small copepods. Very few krill of any size have been seen. The plankton composition near Adelaide Island in the coastal current differed from that on the shelf, with fewer diatoms and algal mats. Most of the very few krill observed so far were seen at this location. The plankton inside of Marguerite Bay has been characterized by small copepods. Although patches of krill likely were present, we have not been able to sample them with the VPR to date. Marine snow also is abundant in Marguerite Bay.

 

The VPR system suffered two temporary breakdowns in the past 1.5 days. The first was caused by the strobe lens becoming loose and rotating 90 degrees within the strobe housing so that insufficient light was focused on the imaged volume. The second breakdown was caused by one of the cameras apparently losing alignment due likely to vibration. Both situations were competently rectified by Phil Alatalo and the other VPR technicians. The VPR system is now running well.

 

BIOMAPER-II functioned well during the transits between stations 38 to 40. A ground fault in the sonar system appeared just before the towed body was brought onto the deck at the start of station 40 work. Although a leaky connector on the up-looking 200 kHz transducer seemed to be the cause, during the transit from station 40 to 41, the fault return and more recent attempts to locate the cause have failed. This ground fault may be related to a pattern of increased noise seen recently on the 43 and 120 kHz frequencies and to a lesser extent on the 200 and 420 frequencies.

 

Once again, the scattering layers showed a diel migration pattern. Intense acoustics scattering was located just below surface during the night and just before first light in 120 kHz echograms and in 200 and 420 kHz echograms albeit with less intensity. By 0800, these three frequencies all showed distinct migration of the backscattering downward. A clear area developed at the surface as the sunrise took place. As the light of day brightened, the top portion of the scattering layer got deeper. By mid-morning, the clear zone was about 50 meters deep marking the top of the intense backscattering layer, which extended down to about 100 m. Below 100 m, lighter scattering extended into the depths. After sunset, the higher levels of backscattering were again at the surface.

 

During the transit out from station 39, which was closest to shore, to the more offshore station 41, the backscattering on the 120 to 420 kHz echograms became markedly reduced and reinforcing the notion that backscattering levels in Marguerite Bay are substantially higher than in the more offshore waters of the continental shelf. Just before arriving at station 41 around 2200, a krill-like patch was observed just below the surface that was small, but quite intense. None similar to this were observed in Marguerite Bay, but they have been observed sporadically on the shelf.

 

Cheers, Peter