During every long cruise, there is need for a break, a time to put down the tools of science and enjoy the environment in which the work is being done. Today was the opportunity for such a break for many on the Palmer. At station #74, where we are now (18 August), the installation of an intermediate ice buoy is taking place on a large ice floe and requires about 6 hours to complete. This was enough time to put out the gangplank and to let the ship's scientists, officers, and crew walk out onto the ice pack and see the Palmer from a unique vantage point. Once the sightseeing was done, a game of football was organized and played with great zeal. During the initial period of the stay at the floe, the skies cleared briefly and visibility improved substantially, but currently at 1833, the clouds have returned and it is snowing; visibility is low. The winds are now up around 30 kts out of the northwest (337) and the air temperature is -7.6°C. The barometer is low at 957.3 mlb. Our position is -68° 49.715S; -72° 56.332W.
Early in the morning on 17 August, it was very cold, windy (wind chills around -50°C), and gloomy, but by noon, it had turned into a beautiful day with clear skies and great visibility. The mountains of Alexander Island were still visible way off in the distance to our east, but only one very large rectangular shaped iceberg was in view. The rest was a vast expanse of sea ice, a mixture of large out-of-round floes ringed with ridges. Occasionally there were thin ice areas that were likely to have been open water ponds some days ago. It was still quite cold- below -20°C, but the wind had dropped and being on deck was not such a problem. Work on this day was completed at stations #61, 62, and 63, which were located off the northwestern tip of Alexander Island from near the coastline to mid-shelf. The tasks at station #61 were done quickly late at night and consisted only of a CTD and phytoplankton ring net tow. During the transit to station #62, BIOMAPER-II was deployed for about an hour during a period when ice conditions permitted towyoing. A Tucker trawl was scheduled for station #62 along with a CTD, and ring net tow, but the pack ice conditions did not allow it. Instead, the Plummet net was used to make vertical zooplankton collections. On the way to station #63, we came into pack ice conditions that again permitted BIOMAPER-II towyoing. The station work at #63 was more extensive and included an ROV under ice survey, a CTD cast, a phytoplankton ring net tow, and a 1-m2 MOCNESS tow. The 1-m2 MOCNESS tow was done while the Palmer retraced the path taken to steam to station #62, since towing across unbroken ice was not possible. A 10-m2 MOCNESS was also scheduled, but the ice conditions were just marginal enough to cause it to be cancelled. Snow started falling as we finished the MOCNESS tow and the winds were starting to pick up.
John Klinck reports on 17 August the CTD group did four stations today, although counting can be problematic depending on ones use of local or UCT days. In any case, these four stations are on the middle to inner part of the shelf along the 220 line, which end on the northern tip of Alexander Island. Station #62 has one of the strangest features I have seen, but it appears in several properties and also on the upcast.
Station #60 (291 m) has a mixed layer with no structure to about 80 m. There is a thin pycnocline to about 100 m below which temperature and salinity gradually increase. Some layering is seen below the bottom of the mixed layer. There are no internal O2 minima or temperature maxima as the water column is too shallow.
Station #61 (206 m) has a mixed layer to about 50 m. The rest of the water column has increase of temperature and salinity with depth with numerous sudden jumps in both. There are no internal O2 minima or temperature maxima as the water column is too shallow.
Station #62 (460 m) has a mixed layer to about 50 m. The pycnocline extends from 50 to 250 m with only small variability. However, at 150 m, there is a sudden decrease in temperature (by 0.6°C), and an increase on O2 (by 0.5 ml-1), and salinity (by 0.1). It looks like a 30 m thick layer of water (colder, fresher, more oxygen) is sliding through the pycnocline at this station. The source of this water (-0.8°C, 34.22, 5.8 ml-1) might be possible to pinpoint one we get observations from stations surrounding this one.
Station #63 (291 m) at the middle of the shelf on the 200 line has a uniform mixed layer to about 50 m with a 30 m gradient layer which matches the pycnocline at about 80 m. The gradual property change across the pycnocline (90 m to 250 m) has numerous small temperature reversals over layers of a few meters thickness. The bottom water properties are uniform, but no temperature maximum or O2 minimum occurs in the interior.
Kendra Daly reports that on 17 August, the Daly group was continuing to run rate measurement experiments for larval and juvenile Euphausia superba. Completed in the last few days were growth, ingestion, egestion, and assimilation efficiency experiments. Samples were also frozen for Rodger Harvey on the Gould to provide him with additional spatial coverage for his analyses of krill growth. In addition, the Daly group is collaborating with Scott Gallager, Phil Alatalo, Karen Fisher, and Gareth Lawson on experiments to measure feeding rates of larval and adult krill on microzooplankton.
Also completed on 17 August at station #62 were two plummet net series
in -23 to -29°C temperatures and 10/10 pack
ice. The heavy pack ice prevented us from towing a Tucker Trawl off the
stern of the ship to collect zooplankton. These temperatures and ice conditions
present a challenge for any outdoor operation to people and equipment,
especially since the wind chill temperatures were closer to -43°C.
The nets flash freeze as soon as they come on deck. All moving metal parts
freeze (i.e., winch, double trip mechanism on the net, net bars), ice forms
on the winch wire snagging the metal messengers (heavy round objects that
attach to and slide down the wire) released down the wire to open and close
the nets, the messengers themselves freeze shut, and fingers become immobile.
Trying to use a heat gun and turn small metal parts with big heavy mittens
on is a constant challenge. The success of these net hauls is due to the
excellent help from the Raytheon group, Jay Ardai, Christian McDonald,
and Jenny White, and the terrific teamwork by Mari Butler, Kerri Scolardi,
Emily Yam, Jose Torres, and Tom Bolmer. The net samples contained an assortment
of zooplankton, such as a few larval E. superba, the euphausiids,
macrura and E. crystallorophias, several different kinds of
copepods, Paraeuchaeta spp., Calanoides acutus, Calanus propinquus,
Metridia sp., ostrocods, amphipods, fish larvae, and chaetognaths.
*As a footnote: 15 August started off on the right note with a large gathering at Mari's Café (aka Mari Butler). The morning featured espresso, bagels, and the excellent blues musicians, Rob Masserini and Jose Torres.Ari Friedlaender reports that on 17 August observations began at 0840 as we traveled to station #62. Visibility was very poor due to fog. Ice was 10/10 coverage of vast floes with areas of ridging and few newly frozen leads. Before arriving at the station, and going off effort at 0945, three crabeater seals were seen. After leaving station #62 for 63 at 1145, viewing conditions improved dramatically, as the fog lifted and the skies were clear for the remainder of the afternoon. Ice conditions remained the same, however, with virtually no open water. Two more crabeater seals were seen during the transit, which ended at 1615 at station #63 (-68° 10.40S; -73° 00.50W).
Ana Sirovic reports that she deployed 2 sonobuoys, both while transiting to station #63. The first one was deployed 11.8 nm from the station. She listened to it for 52 min and heard no biological noise. The second buoy was deployed 5 nm before the station. That buoy was heard for a total of 4 h 2 min. Although it did not seem to be out of range, it stopped transmitting abruptly. On the second buoy calls from 2 seals were heard . The animals were at different bearings to the buoy (this time, there was no trouble getting good directionality for the calls) and they were making different types of noise: one was downsweeps from 920 to 310 Hz, about 3s in duration and the other was sets of 5-7 pulses with the top frequency of 390 Hz and the bottom frequency ranging between 220 and 350 Hz. The animals were consistent in the type of the noise they were making. The calls were made over the period of about 2 hours.
Chris Ribic and Erik Chapman report that on 17 August (JD-229), they
surveyed for 5 hours and 38 minutes approaching station 61 and between
stations #61 and 62. The ice was mainly 10/10ths concentration and the
few leads that were encountered were mostly covered in gray white ice.
During the first hour of surveying, visibility was poor and the full 300
m survey transect was not always visible. It quickly cleared up though,
and soon visibility was to the horizon and some good survey work was done
under sunny skies. Not surprisingly, very few birds were seen in the dense
ice pack. They also surveyed for an hour and a half last night as the Palmer
stations #60 and 61. No birds were seen during the night surveys after
having seen good numbers of Snow Petrels during the two previous nights.
A summary of their observations is the following:
BIOMAPER-II/MOCNESS report (P. Wiebe, C. Ashjian, and S. Gallager):
BIOMAPER-II was deployed twice on 17 August, once on the transit between stations #61 and 62 and again between stations #62 and 63. The first run was relatively short because ice conditions were largely unfavorable for towyoing. The tow was over some rough topography and layers were observed that were likely dominated by krill. As usual, however, getting the towed body down into layers associated with the bottom is difficult given the current methods for doing towyos, so the VPR was never able to obtain images in the layers. The tow was ended when pack ice changed from relatively smooth medium thickness floes with some open leads into a ice rubble field. That is the term used for an area where ridges are piled upon ridges with few floes in between. At the time of recovery around 0800, the wind was in the 20 kt range and the wind chill was down below -50°C, so it did not take long for those on the deck to become cold. The recovery did not take long, although the hydraulics worked extremely slowly in the cold. Everything mechanical was slow motion. Once on deck the fish was hustled into the garage van and the deck lines coiled and put away along with the pole hooks, the pallet mover (Johnson Board), and dolly. In the afternoon, BIOMAPER-II was in the water between station #62 and 63 for most of the transit. It was a tough go, however, with some backing and ramming required while the fish was in the water. The ice was just thick enough for a need for four engines and the ship was pushing a lot of water. Along this line, the water column had low volume backscattering levels in the mixed layer. Relatively higher levels were seen as a layer near the bottom when the towed body reached the bottom of a towyo and the sea floor was in view. Few, if any krill patches were seen.
After several aborted attempts at earlier stations, a 1-m2
MOCNESS tow was finally completed in the evening at station #63. Ice conditions
were not conducive to doing a MOCNESS tow through unbroken ice, so the
steamed back down the trackline that it came to the station on for about
4 miles at 6 kts to break open the passage again. Then tow was done on
the reverse course. Getting the net into the water was a bit difficult
on the first attempt because ice chunks in the wake closed in too fast
and interfered with the deployment. The net was brought back on board,
examined, and then set up to do the launch again. The second time the launch
went smoothly. However, the stay on deck in the -20°C
temperatures caused the pressure and conductivity sensors to freeze up
and it took more than 15 minutes while the net was being lowered to maximum
sampling depth for them to warm up enough to start working. The tow also
went smoothly; no backing and ramming and no hang ups of the wire on ice
chunks. Although there was some concern that the tow might extend beyond
the path that had been cleared, there was no problem fishing the net in
the distance that was open. The very cold air temperature also made washing
the nets down very difficult. The sample buckets came in completely iced
up and the samples were nearly frozen. Ice crystals in the sample buckets
and in the ship's sea water supply, which was being used to work with the
samples, made it difficult to separate the zooplankton from the water-ice
mixture, but eventually it was done. The tow went to 240 meters. Copepods
and euphausiid larvae were caught throughout the water column, but the
copepods were most abundant at depth. Also in the deeper depths were pteropods.
At intermediate depths a small number of adult euphausiids, a combination
of Euphausia superba, Thysanoessa macrura and E. crystallorophias,
were caught. Copepods and euphausiid larvae in fewer numbers were caught
near the surface. Of course, there was the usual assortment of other taxonomic
groups represented in the samples including chaetognaths, amphipods, medusae,
and fish larvae.