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

14 May 2002

 

On 14 May, the Palmer was again working for a good portion of the day in the survey grid area off to the northwest of Adelaide Island. It was another day of fine weather and good sea conditions. High atmospheric pressure dominated the region and the barometer recorded the highest readings yet on the cruise - 1012.4 mlb in the mid-afternoon. Winds were low to moderate13 to 15 kts in the morning and less than 10 kts in the afternoon and evening. The air temperature stayed between -7 and -8C. Some low broken clouds were over head during the day with patches of blue sky and to the east were the mountains of Adelaide Island and also the mountains on the Islands north of Adelaide Island sometimes brilliant in the rays of a low angled sun. During a good portion of the morning, there was no sea ice and the sea surface temperatures were around -1.4 to -1-1C when the ice was not present. As we came into the coastal current region near shore on survey line 2, the pack ice reappeared and the sea surface temperature dropped accordingly.

 

The activities on 14 May consisted of completing the last two CTDs along the transect down the axis of the Marguerite Trough started on 13 May, re-doing the towyo section with BIOMAPER-II from station 10 to station 8 on survey line 2, doing a new BIOMAPER-II run from station 6 into Crystal Sound looking for krill, and deploying a sonobuoy during the transit between stations 10 and 8. The first BIOMAPER-II towyo took place from early morning to early afternoon. During the transit, a series of XBT's were dropped in the vicinity of station 9, a place where water of anomalous temperature indicating offshore origin had previously been seen. The second towyo started in the early evening after steaming over to station 6 and lasted until mid-evening. During the second section, large patches of krill were surveyed in the vicinity of the Martha Strait leading into Crystal Sound. We had expected to see the krill concentrations there, thanks to the information that Meng Zhou, working aboard the L.M. Gould, had supplied during the previous 36 hours. When the Palmer reached the end of the section in Crystal Sound with no significant concentrations of krill present, the decision was made to steam back to the krill patch location. Work at the Crystal Sound station began there about midnight.

 

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

Today the CTD group did two CTD casts and 6 XBT drops. The two CTD casts completed the line of stations along Marguerite Trough. These stations showed a similar structure to that at the previous three, with some indication of offshore water in the bottom 100 m of the water column. However, the signal at these stations was rather weak. Rob Masserini and Yulia Serebrennikova reported that bottom silicate concentrations were 116 uM in the deeper (southern) parts of the trough confirming that this water was from similar depths in the Antarctic Circumpolar Current. There was an indication at station MT5, closest to the shelf edge, that this water was now spilling onto the shelf.

 

The 6 XBT (T-4 probes) were dropped in the transit from station 10 to 8 when we received a report from Peter Wiebe of 1.8C water at depth. XBT's were dropped at 30 minute intervals (approximately 2.5 nm separation) starting a couple of nm NW of station 9. The deep temperature maximum reached 1.55C, but no Upper Circumpolar Deep Water was detected. During the setup for these measurements, we noticed that there was no ice cover and the surface temperature was -1.1C, which was well above the typical -1.7C that we had been seeing. Once south of station 9, surface temperature returned to -1.7C and ice cover was again present.

 

Station 97 aka MT4 (cast 105, 598 m). The uniform surface layer extended to 70 m (-1.4C, 33.6 psu, 0.15 ug/l chlorophyll). A weak Winter Water layer was seen between 85 and 100 m. The pycnocline had some small-scale temperature and salinity variability. A thin temperature maximum layer (1.5C) was at 330 m. Below 500 m to the bottom was a layer of slightly higher oxygen and lower temperature.

 

Station 98 aka MT5 (cast 106, 606 m). The uniform surface layer extended to 55 m (-1.4C, 33.6 psu, 0.15 ug/l chlorophyll). The pycnocline extended to 200 m with some thin, but strong temperature layers. A thin (30 m) temperature maximum (1.5C) occurred at 275 m. Below 530 m to the bottom was a layer of slightly higher oxygen and lower temperature.

 

Phytoplankton Primary Production (Wendy Kozlowski, Kristy Aller)

Week four of sampling (4 May-10 May) for the primary production group brought to a close the water collection on the main sampling grid. Seven more simulated in situ (SIS) experiments were completed at stations 72, 75, 78, 82, 85, 88, and 91, showing continued low production (4.0 to 16.3 mgC/m2/d) in this Southern end of the grid. FRRF was deployed as part of the CTD rosette in nineteen more locations, including a second shallow cast at station 91. Unfortunately, the last four of these were not recorded due to an unknown instrument error (which seems to have since been resolved).

 

Chlorophylls continued to be sampled at twelve depths per CTD cast, and results show a trend matching production, with continued lower chlorophyll in the south than in the north. There appears to be an onshore offshore gradient as well on the six southernmost transects of the grid, with chlorophyll a levels ranging from as low as 8.9 mgC/m2 inshore to as high as 84.1 mgC/m2 (integrated to 100m). Particulate carbon samples were also preserved at eleven more stations during week four.

 

Sea ice was sampled at five more locations during this week. Slush from between large pancakes (approximately 1m in diameter) was sampled using a bucket over the side of the ship as we departed station 78, and gray ice (5-7 cm thick) was sampled from the personnel basket at station 84. At stations 76, 85 and 92, full cores were taken from multi-year floes, and at station 92, two additional cores were collected, one for an integrated biology sample, and one split and melted undiluted for salinity and nutrients. A partial ice thickness transect was completed (ice thickness measured at two meter intervals for ten meters) at this ice station as well. Chlorophyll was measured, samples were collected for particulate carbon, and at least one production experiment was run per section from all cores and bucket ice samples, and nutrients and salinities were measured in those samples that were not diluted.

 

Marine Mammal report (Debra Glasgow)

Tuesday, 14 May dawned to find the Palmer in open water for a change with Beaufort sea state 3, the temperature at -7.7C, and around 10 knots of wind. A few icebergs dotted the skyline in the distance. The sun peeked above the horizon briefly at 0942 before disappearing behind cloud and the mountains of Adelaide Island slowly grew as the Palmer towed BIOMAPER-II between stations 10 and 8 towards them.

 

At 1020, two humpbacks surfaced 1.5 nautical miles ahead at 180, swimming 040 towards us. They were repeatedly diving raising their flukes, staying underwater for several minutes, then resurfacing to blow 2-3 times. At no time was any white seen on the flukes. They were swimming towards the ship, but passed abeam over 1 km away to starboard - too far for photos, especially as the light was very poor so early on such an overcast day. Ana Sirovic had deployed a sonobuoy not long before the sighting and some humpback sound was recorded. This was the only cetacean sighting for the day.

 

By 1158, we entered the ice edge into 8/10 pancake, grease, a few growlers, and shuga. It was not long after that fur seal sighting were made. A total of 19 fur seals were counted for the day, most on very small ice floes. Two crabeater seals were on an ice floe near the end of the day, and interestingly we again saw a small grouping of leopard seals - 6 in total, on separate floes between 1430 (66 41.06S; 68 57.22W ) and 1547 (66 36.55S; 68.40.13W). Other seals were visible in the distance using binoculars, but were too far away to identify. The marine mammal survey ended at 1549 in poor light not long after the Palmer began the transit through many icebergs towards Crystal Sound.

 

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

There were two towyo sections completed with BIOMAPER-II during 14 May. The first was along survey line 2 from station 10 to station 8. The reason for repeating this line was to look for evidence about the persistence of a striking diatom bloom that had been present in a large area of the outer shelf early in the cruise (e.g. see report for April 16), but was largely absent in the southern portion of the grid. In addition, it provided an opportunity to re-examine the presence of anomalously warm water in this region of the shelf where there had been a number of fish-like targets about 160 m below the surface that seemed to be more abundant than elsewhere along the survey line. On this towyo, the VPR data displayed the presence of diatoms in the mixed layer during the first portion of the run, but the impression was, not in the numbers seen earlier. Relatively high temperature water (~ 1.8C) was seen below 200 m, but only on one profile in the vicinity of station 10. There were a number of fish-like targets again present near station 9, starting at about 160 m and going down to about 300 m, as had been seen previously and essentially none were present on either end of the section. For most of the run, there was very light backscattering in the mixed layer and a zone of moderate backscattering starting at the top of the pycnocline that varied between being either diffuse or in the form of thin layers. In water that was about 470 m deep, there was a scattering layer 140 thick above the bottom with a more intense zone about 20 thick right at the bottom.

 

With information from Meng Zhou about the scattering layers he encountered while the L.M Gould was steaming north along the Western side of Adelaide Island and into Crystal Sound on the 12th and 13th of May on their way back to Palmer Station and then Punta Arenas, we decided to do a BIOMAPER-II transect from grid station 6 on survey line 1 into Crystal Sound where krill and their predators (penguins, seals, whales and seabirds) were reported to be in high numbers - a distance of about 22 nm. Low to moderate scattering levels were encountered during the first portion of this run, but on entering Matha Strait, which leads into Crystal Sound, very large concentrations of krill were encountered in layers and patches that equaled some of those we observed in the near shore waters off of the west coast of Alexander Island. Once through the straits and into the western portion of Crystal Sound, the backscattering diminished rapidly and the patch structures largely disappeared except for a fairly thin layer of krill that was in the upper mixed layer about 20 m thick and down about 30 meters below the surface. This layer also eventually disappeared and only surface layer patches occurred sporadically. On the transit to the final position in the Sound, where it had been anticipated that additional large krill concentrations might be found, volume backscattering was light to moderate and there were no krill present. Armed with this information, BIOMAPER-II was brought back on board and the Palmer steamed back to the position of the high krill concentrations to begin the station work in Crystal Sound.

 

 

Cheers, Peter