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

15 May 2002

The final day of post survey grid sampling took place in Crystal Sound, which lies just north of Adelaide and Laird Islands. The scenery in Crystal Sound was spectacular. Tall mountains on the northern end of Adelaide and on Laird Island and then beyond on the Antarctic Peninsula proper ring the southern and eastern end of the sound. Lower mountains of Lavoisier and a series of smaller islands lay to the north. First light happened around 0800 and that was when we could begin to see the outlines of the mountains and the red hues coloring the few clouds on the horizon where the sun would make its appearance. The weather was great all day with bright sun and clouds only on horizon, and winds mostly less than 10 kts out of the southwest. Right towards dusk, clouds began to move in from the north and as night closed in, the clouds began to obscure the mountains. The steaming for Palmer Station began about 1800 with the barometer beginning to fall from a high around 1007 mlb in the early morning and the winds picking up. In the late evening, the barometer had dropped to 1003.5 and the winds were around 30 kts out of the southwest. The air temperature warmed during the day from a morning low of -7ºC to an evening high of -1.8ºC.

The work on 15 May consisted of doing a Reeve net tow just after midnight to catch live krill for use in an APOP cast, which was done shortly after. This was followed by a MOCNESS tow and a CTD in the vicinity of the krill patch. A nearby location with pack ice was chosen for the last ROV under ice survey. After that the sea bird observers began a search from the bridge for a site in which to use the zodiac to go and find penguins returning from feeding to their haul out locations in order to do “diet sampling”. A decision was made for the Palmer to steam over to a set of small set of islands, the Barcroft Islands, that were known for being the site of a penguin colony. (These islands and several others south of Lavoisier Island are named after noted scientists who have conducted cold climate or ice research.) The “penguin seekers” left in the Zodiac shortly before noon. The Palmer then moved a mile or two so that a sonobuoy could be deployed to listen for marine mammal sounds while the ship lay doing the calibration work with BIOMAPER-II and APOP back at the position where the Zodiac was dropped off. (The reason for deploying the sonobuoy at a distance is because of the noise generated by the ship totally obscures most biological sounds.) The afternoon was spent doing the BIOMAPER-II and the APOP acoustic calibrations in succession. About 1600, the bird observers returned from a very successful trip (14 penguins sampled). And after the APOP calibration was finished about 1800, the N.B. Palmer got underway for Palmer Station.

Although, there is still some more work to be accomplished on the steam back to Punta Arenas, Chile, the work in Crystal Sound marked the end of the data collection for many in the scientific party.

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

The CTD group did one cast on 15 May in Crystal Sound. This station was close to the location where krill were found so that the effect of krill on ammonia could be determined (or discounted). This station had a deep surface mixed layer and cold, even colder then the inner shelf, sub-pycnocline temperatures.

Station 99 aka CS1 (cast 107, 360 m). The surface layer extended to 90 m (-1.3ºC, 33.5 psu, 0.007 ug/l chlorophyll), but there was a 10 m thick cold, but not freezing, layer at the surface. A thin pycnocline extended from 100 to 150 m. Deep temperature gradually increased all the way to the bottom. The temperature maximum was at the bottom, 1.1ºC.

Marine Mammal report (Debra Glasgow)

The marine mammal survey started on 15 May at 0905 as the Palmer steamed through Matha Strait to find penguins for the bird researchers who were hoping to get diet samples. We eventually stopped at some small rocks/islands near a penguin colony on the Barcroft Islands. Last night, a giant krill patch was encountered about 30 km's long and time was spent doing various work in the area, but unfortunately by daylight we had left that area. Two humpbacks were sighted by Richard Wisner and others as they dove off the bow in predawn semi-darkness at approximately 0810. They could see the underside of the flukes (which were white) as the whales dove. These whales were also seen off the stern by others. Unfortunately I heard about it too late to sight the whales. During the night, several seals were also seen passing on ice floes in the lights of the ship. At 0905, the first of the day's 2 crabeater seals was recorded on an ice floe before the sun rise at approximately 0930. One fur seal was also recorded on a nearby floe. The Palmer traveled through many icebergs and patches of brash and abundant growlers. Air temperature -6.9º, wind < 10 knots from 210º, Beaufort sea state 3 or less once we came in to the lee of land. I was hoping to spend some time today taking ID photographs of any whales we encountered from a zodiac, but there were no cetaceans seen before we stopped to drop off the penguin researchers and to do APOP and BIOMAPER-II calibrations. Also there were zodiac engine problems. Although we were stopped, I continued to keep an Incidental watch hoping that the zodiac would be fixed in time for any passing cetaceans. Ana Sirovic deployed a sonobuoy while we were still on transit at 0927 and heard some humpback sound. She also deployed a directional sonobuoy at 1157, two nautical miles away from where we were stopped for the calibrations at 66 28.76ºS; 67 02.47ºW - no sound was heard, however. We stayed at this position from approximately 1230 until after dark. It was a beautiful, calm, but cool, sunny day.

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

The first science event on May 15 was a Reeve net tow that was designed to catch enough live krill for an APOP cast. A large krill patch was spotted by the BIOMAPER-II around 2010 on May 14 as it was towyoed from station 6 into the Crystal Sound. The patch was found along the Martha Strait (see Zooplankton (MOCNESS/BIOMAPER-II) report on May 14). The net tow was successful and caught more than 200 live krill (E. superba), including juveniles, sub-adults, and adults. The mean size was about 27 mm and standard deviation was 7 mm. An APOP cast was conducted right after the animals were collected. One of the objectives of this cast was to see whether there were any differences in sound speed and density contrasts between freshly caught krill and those that had been kept for a number days in the aquarium on board the ship. The procedures of the APOP cast were identical to the previous casts. The mean sound speed contrast was 1.030, a little bit higher than we expected for this size group, but still within a reasonable range of the sound speed contrast obtained during this cruise. The standard deviation was 0.004, no difference from the previous measurements on E. superba. The density contrast of these animals was 1.017, quite consistent with our previous measurements. In addition, a mild depth-dependence and noticeable differences between down cast and up cast were observed. However, the pattern was similar to that what we measured from the APOP calibration casts conducted on May 12 and May 15 described in the following paragraph. Most importantly, there were no statistically significant differences in measured sound speed and density contrasts between the freshly caught animals and those kept alive in aquariums for a few days.

In the afternoon, to confirm the calibration results obtained on May 12 (see cruise daily report on May 12), we conducted another APOP calibration cast in the Crystal Sound (66 28.834ºS; 67 02.405ºW). The water depth was about 400 m, enough for a 205 m APOP cast. The results resembled those obtained from the first calibration. The mean arrival time difference between the primary and the reference chambers was 45.5 ns, a little bit smaller than what we obtained from the first calibration (47.6 ns). The minimum and maximum differences were 9.7 ns and 96.6 ns, respectively. The shape of the measured variations in sound speed contrast as a function of depth was also similar to that from the previous calibration, indicating a consistent bias that can possibly be eliminated in our further data analysis.

It turned out that the APOP calibration cast was the last science event of the day. Right after the APOP cast, the ship started to steam to the Palmer Station and thus this was a marker of the conclusion of the science activities on the survey grid.

Sea Birds (Erik Chapman and Matthew Becker)

Sea bird observations were made during 5 hours of daylight on 14 May as the Palmer traveled toward the northern shore of Adelaide near consecutive station 8. The ship moved from open water, through grease ice, and into 9/10ths coverage pancake ice during the survey. Bird abundance was low with perhaps a slight increase in numbers as the ship moved from open water into the ice. Snow Petrels dominated the species assemblage and no species typically associated with open water, such as Cape Petrels and Southern Fulmars were observed today.

A summary of the species and number of individuals of birds within the 300 m transect during 4 hours and 59 minutes of daytime surveys near station 8 is the following:

Species (common name)	Species (scientific name)	Number observed
Snow Petrel	Pagodroma nivea	34
Antarctic Petrel	Thalassoica Antarctica	1
Kelp Gull	Laru dominicanus	2
Southern Giant Petrel	Macronectes giganteus	2

On 15 May, BIOMAPER-II and MOCNESS tows in Matha Strait indicated large patches of krill within 10 to 20 nautical miles of Barcroft Island (66 25ºS, 6710ºW), just south of Watkins Island in Crystal Sound. In the summer, there is a colony of 1600 breeding pairs in this area. We speculated that if penguins were foraging here, they would choose to haul out on nearby islands they were familiar with, rather than nearby floes.

The N.B. Palmer approached the island complex in mid-morning, and we left by Zodiac at 1145 for Barcroft Island. After just 15 minutes of searching, we began seeing birds hauling out on small rock islands in the area. Groups of Adélies continued to be observed, porpoising in the water and resting on ice or land, throughout the day and we estimated there to be several hundred penguins in the immediate vicinity. We began capturing, sampling, and releasing penguins within 30 minutes of leaving the N.B. Palmer and did not stop until we lost daylight at around 1500.

Fourteen Adélie Penguins were diet sampled from 5 distinct groups of birds. The penguins were taken from small islands, small ice-bergs, and sea-ice. All birds sampled had fresh stomach contents that were easily identifiable, indicating that they had just returned from foraging. Body weights from the 8 male and 6 female penguins averaged 4800 grams. These relatively heavy weights are indicators of excellent body condition. Perhaps these birds are preparing for a period of limited prey availability in the winter, and eventually the demands of summer breeding effort next spring. Diet samples included approximately 75% Euphausia superba in both larval and adult age-classes. Adult krill appeared to mostly be 43 to 48 mm long. About 20% of the samples were amphipods, comprised of three species. The remaining 5% of the stomach contents were fish.

ROV Under-Ice Investigations (Andrew Girard, Amy Kukulya, Gaelin Rosenwaks, Philip Alatalo)

Another significant ROV deployment occurred at the Crystal Sound station early on May 15, 2002. Information from the previous BIOMAPER II cast, the SIMRAD, and the MOCNESS tow showed krill were present from about 200 m to 100 m in dense layers. ROV 8 was deployed at 0715 in an area composed of what little ice was available. Older floes were interspersed between pancake and brash ice. Subsurface ice was densely contoured, indicating older ice, though no ice-algae was observed. Though all ice surfaces were knobby and eroded, the bergs tended to have large projecting blocks whereas pancake ice was more smooth and uniform. No krill furcilia were observed. Separation of larval, juvenile, and adult forms is nothing new, yet it is unusual that given the mixture of ice types and age as well as dense layers of adults at depth, more furcilia were not found. Based on this one observation, it appears that krill furcilia are not found in the same habitat as juveniles and adults, at least not this early in the winter season. A small berg bearing down upon the ship persuaded us to retrieve the Sea Rover after less than an hour at 0800.

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

MOCNESS tow #24 was conducted in Matha Strait between the shelf and Crystal Sound. The tow was conducted starting at about 0400. Prior to launching the MOCNESS, a patch of elevated backscatter was identified on the SIMRAD echosounder in the hopes of sampling a krill patch. The net was towed through elevated backscatter and sampled the patch. Unfortunately, all of the net bars hung up part way down the rods because of entanglement with the net skirts. This resulted in the first net fishing for the entire tow and the subsequent 8 nets sampling with only ~1/2 of the net mouth volume.

The first net, which fished for the entire tow with at least part of the mouth open, captured a substantial quantity of krill. The deepest discrete net (200-175) captured a very small quantity of furcilia and copepods. Krill were abundant from 175-75 m, with greatest abundances at 125-100 m. Copepods were collected at depth (175-125 m), from 75-50 m, and in the surface net (25-0) where Metridia were collected. Amphipods were collected from 125-75 m. Diatoms and algal matter were present in the upper 75 m. A few furcilia also were observed from 50-25 m.

Although the transducers on BIOMAPER-II have been calibrated by the manufacturer of the acoustic system (HTI), it is important to do a field calibration as well to determine the extent to which environmental conditions have caused deviations from the factory calibration. To do the calibration, the upper looking transducers were taken out of their top frame mounts and bolted into a calibration rig that Terry Hammar (WHOI) had made up to bolt onto one side of the towed body so that both sets of transducers were side by side facing downward. A series of 3 standard targets (calibration balls of 31.8 mm, 21.2 mm, and ping pong ball) were suspended underneath the transducers at 5, 6, and 7 m. A number of runs with different sets of the transducers were done with the calibration balls hanging directly under them. In spite of the very low winds, the very narrow beam widths (3 degrees for all, but the 43 kHz, which was 6 degrees) together with moderate current made it difficult to get the balls aligned with the axis of the transducers. After three hours, a satisfactory set of measurements were obtained.

Cheers, Peter