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

25 April 2002

 

There are thirteen survey lines on the Southern Ocean GLOBEC broad-scale survey grid. Lines 4 to 7 are the longest, running from the deep offshore waters of the Antarctic circumpolar current to the inner portions of Marguerite Bay. Each line is about 160 nm (300 km) and it takes about 3 days to complete a lines station and along track work. On April 25, we were mid-way along survey line 6 headed off shore.

 

The fine working weather experienced over the past few days became a memory as weather turned to a much less benign state. In the early hours of 25 April, the winds picked up substantially and by early morning were blowing 30 to 35 kts. The barometer dipped down into the mid- 970 mlb region, before climbing again to around 980 by mid-morning. Although, the skies in late morning were partly cloudy, with areas of blue sky, by afternoon the clouds thickened and the barometer began to drop again. Winds most of the day were in the 20 to 25 kt range . During the late afternoon, the barometer began an accelerated drop from about 976 and reached 966 mlb around 2300. As the low pressure area moved in, winds again picked up into the 30 kt range, the seas became quite rough, and remained so throughout the night. A driving snow accompanied the high winds. Air temperature varied little throughout the day remaining between -1.0 to -1.7C.

 

During the 25th of April, work was finished at station 41 and completed at 42, 43, and 44. Four CTDs were made, a MOCNESS tow was made at station 43, a 1-m Reeve Net live tow, and a 1-m ring net surface zooplankton tow were taken at Station 44. Seabird and mammal surveys were conducted along the transits between stations during daylight, and BIOMAPER-II was towyoed between stations 43 and 44 missing the transits between stations 41, 42, and 43, while chasing an elusive sonar ground fault. 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 at four stations along a line going offshore from the entrance of Marguerite Bay to the middle of the shelf. All stations had uniform mixed layers from 50 to 70 m deep. Only the mid shelf station had a remnant Winter Water (WW) layer. Deep water temperatures were 1.3 to 1.4C. Weak to moderate small-scale variability was seen in the pycnocline.

 

Station 41 (cast 45, 749 m). There was a uniform surface layer to 70 m (-1.2C, 33.45). The surface chlorophyll was 0.2 μg/l. A weak layering (3 m) occurred in the pycnocline and the deep temperature (1.3C) was uniform with no clear temperature maximum.

 

Station 42 (cast 46, 871 m). The uniform surface layer went down to 60 m (-1.5C, 33.4). The surface chlorophyll was 0.15 μg/l. There was moderate layering (3 m) in the pycnocline and the deep temperature (1.4C) was uniform with no clear temperature maximum.

 

Station 43 (cast 47, 413 m). The uniform surface layer went down to 50 m (-1.2C, 33.4). The surface chlorophyll was 0.2 μg/l. Moderate layering (3 m) occurred in the pycnocline and there was a weak temperature (1.3C) at 350 m.

 

Station 44 (cast 48, 395 m). The uniform surface layer went down to 45 m (-1.3C, 33.4). The surface chlorophyll was 0.2 μg/l. A weak WW layer was centered on 100 m and there was moderate layering (3-10 m) in the pycnocline. There was a weak temperature maximum (1.4C) at 350 m.

 

Marine Mammal report (Debra Glasgow)

On 25 April at 1038 (- 67 50.53S; 71 07.31W), one humpback appeared and came over to the ship as the Palmer was at station 43 doing a CTD cast. The whale came within 5 meters of the ship staying mainly near the stern and beside the CTD door. It lolled around on its back after investigating the CTD, diving right beside it, and then lay upside down waving its pectoral fins - not slapping them. It blew repeatedly right next to the ship, sometimes making vocal sounds when it breathed. Obviously it was curious and in no hurry, and it stayed with us until 1110 when it finally moved away from the ship and disappeared. Identification photos were taken by Ana Sirovic and Deb Glasgow.

 

Six seals were recorded for the day, five fur seals and one crabeater that were observed by Peter Wiebe investigating the MOCNESS cable as we were towing at station 43. Although overcast, good visibility and a sea state of Beaufort 4-5 for most of the day allowed for over 7 hours of survey. No other cetaceans were sighted.

 

Sea Birds (Erik Chapman and Matthew Becker)

Two Snow Petrels were captured and measured on the deck late last night, but no regurgitated stomach contents were found near the birds. Yulia Serebrennikova, from the nutrient group, found some fish that had been regurgitated overnight on the 04 deck behind the bridge. Unfortunately, the sample did not contain otoliths that could be used for species identification and the bird had already flown away when the fish was found. It may have been left by an Antarctic Petrel, which feeds mainly on fish and had left similar regurgitated stomach contents on the deck during GLOBEC I. We also tried to survey last night, but were not able to due to heavy snowfall.

 

As the sun came up on 25 April, the seas were just beginning to die down after a weak low pressure system passed through early this morning with 30 to 35 knot winds. The skies cleared and the barometer began to rise quickly creating good conditions for surveying during the day. The transit was between stations 42 and 44, heading out of Marguerite Bay over the mid-shelf region. Moving away from the ice, open water birds, including Cape Petrels and Southern Fulmars, followed the ship most of the day. We shifted our observation station from the bird box to inside the bridge where we can keep better track of ship followers. Most of the birds encountered were ship followers and bird densities were quite low during the transit. Data from the water column in this area suggested that there was little biomass in the water that could be made available to birds by physical processes that would bring food to the surface. Low surface biomass was indicated by BIOMAPER-II data between stations 43 and 44, along with results from a Reeve net and 1-m ring net tow at station 44. The 1-m surface tow found low biomass at the surface that included diatoms, amphipods, and larval krill.

 

A summary of the species and number of individuals of birds and seals observed during 4 hours, 30 minutes of daytime surveys between consecutive stations 42 to 44 is the following:

 

Species (common name)

Species (scientific name)

Number observed

Cape Petrel (Pintado Petrel)

Daption capense

15

Southern Fulmar

Fulmarus glacialoides

8

Antarctic Petrel

Thalassoica antarctica

18

Wilsons Storm Petrel

Oceanites oceanicus

1

Southern Giant Petrel

Macronectes giganteus

2

Blue Petrel

Halobaena caeulea

6

Antarctic Fur Seal

Arctocephalus gazella

2

 

 

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

On April 25, shipboard measurements of plankton material properties were made on mysids (Arctomysis) that were collected by Kendra Daly on the Gould and transferred to the Palmer at the rendezvous on 23 April. The mean length of the animals (total of 14) used in the experiment was 50.4 mm and the standard deviation was 4.7 mm.

 

The sound speed measurements were repeated twice. There was no evidence of any visible bubbles attached to the exoskeleton of the animals during the measurements. The sound speed contrasts from three measurements were 1.080, 1.072, and 1.078, respectively, much larger than expected. The density measurement was conducted after the sound speed measurements. The density contrast was 1.041 (+- 0.008), possibly heavier than krill, but lighter than the amphipods we measured in the previous day. This density contrast is still within a reasonable and expected range. The high sound speed contrasts, however, were not expected and there is some suspicion that there might be some micro-bubbles that were not observed attached to the animal bodies.

 

The Reeve net was towed at station 44 (67 37.350S; 69 52.020W). Although a scattering layer was present at about 50 to 60 m depth, the volume backscattering strength was not as strong as that expected from a krill scattering layer. The catch in the net tow was disappointing in that no large krill were caught, only a few amphipods, a juvenile krill, copepods, and phytoplankton.

 

Water Sampling for Microzooplankton (Phil Alatalo)

Sampling and recording for microzooplankton has continued steadily, though analysis of casual observations has lagged behind due to more pressing equipment issues. The small ciliate Mesodinium has continued to be present in all surface samples taken along survey line 3, from the slope water of Station 13 in to Adelaide Island. Mesodinium and other protozoans were most numerous inshore. Small diatoms and the larger Corethron sp comprised a larger proportion of the assemblage, particularly in the deeper samples along the shelf in to shore. Comparable depths at Stations 13 and 14 showed very little activity and very few particles.

 

Mesodinium was again present in all surface samples during survey line 4 except the offshore Station 22. It was most abundant in the mid-shelf stations 20 and 21. At Station 19 Mesodinium was found as deep as 50 m, right above the thermocline. Ciliates and diatoms were common throughout all depths and most stations, except the deeper water of the slope Station 22 where they were noticeably absent.

 

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

MOCNESS tow #11 was conducted at mid-day on the shelf off of the mouth of Marguerite Bay at station 43. The water depth under the ship at all times exceeded 420 m, yet the tow to 400 m collected some sand. Heavy winds and strange currents made the flight of the net very strange and it is hypothesized that these same factors advected the ship away from the track of the net so that the net was fishing in water shallower than that over which the ship was traveling (and measuring water depth). The tow was very successful and no damage was sustained due to the sand collection, except to the sample from net 0 which was compromised. The plankton composition at this location differed from any observed previously. No krill of any life stage were numerous anywhere in the water column. Copepods were present at all depths. Siphonophores and amphipods were present in the deepest depth interval (300-400 m). Chaetognaths and a salp were present at 200-300 m. Only copepods were obvious from 150 200 m. Very low biomass and abundance was present from 50-100 m. A few fish were observed in the 75-150 m range. The copepods appeared to be Metridia in the 50-75 m range. Phytoplankton was present in the upper 50 m. Salps and amphipods also were present in the upper 25 m.

 

The BIOMAPER-II was launched at station #43 following the MOCNESS tow. The VPR observed a very different plankton community at this location (mid-shelf, off of the mouth of Marguerite Bay) than was seen on the shelf further to the north. Very small copepods and marine snow were present. The marine snow was less abundant than had been seen in Marguerite Bay. Few diatoms or algal mats were observed, which contrasted markedly with the situation mid-shelf further to the north.

 

An elusive ground fault that shows up in the water and disappears on deck kept the towed body sidle lined on the transits between stations 41 and 43 on survey line 6, while the source was sought. High winds and seas in the early morning also prevented deploying the fish once the electrical system had been probed (without finding the source of the fault) and it was ready to go. BIOMAPER-II was towyoed from Station 43 to 45 during the afternoon and evening of 25 April.

 

Along this portion of the survey line, there was a well developed bottom scattering layer extending 115 m above the bottom (~400 m) and the layer had an intense zone 25 meters thick starting at about 65 m. There was a surface backscattering layer evident for much of the run, which was not particularly strong, and sometimes thin layers of backscattering appeared in the pycnocline just below it. Along the transect to station 45, the backscattering in the upper water column was particularly low, except on the 1MHz echograms, which from about 60 m to the surface had strong backscattering. The VPR images during this time showed diatoms and radiolarians to be abundant.

 

Near midnight about 5 nm from station 45, a very large and intense krill-like patch appeared on the 43, 120, and 200 kHz echograms close to the bottom. The top of the patch was about 260 m below the surface and the bottom was at 370 m, and it was about 60 meters above the bottom. Based on an estimate of the distance the ship traveled while the patch was in view on the echogram, it was approximately 2 kilometers in horizontal extent. A second patch occurred a few minutes later with about the same vertical dimensions and a horizontal extent of at least 1 kilometer. This is the first occurrence of such patches noted on this cruise. The size and intensity of the two patches were strongly reminiscent of the patches seen in the Laubeuf Fjord and in waters off northwest Alexander Island and Lazareth Bay during the fall cruise last year. These two locations were dubbed krill hot spots. It is interesting that a number of the sighting of humpback whales this year are out in this outer continental shelf area. Perhaps the presence of krill-like patches, such as the ones observed, are the reason.

 

Cheers, Peter