Today, 6 August, is the coldest day of the cruise thus far. The relatively warm weather (temperatures around freezing) was swept away last night with a vengeance and during the day temperatures have remained below -17°C. We are currently completing work at a location near station 39 and are at -68° 35.305S; -68° 19.758W - 1633 local time). The winds have shifted and are now out of the southeast (126) at 7 to 10 kts, and the air temperature is -18.6°C. The barometer is still low at 967.1 mlb.
The work plan on 5 August was altered so that we could provide ice-breaking assistance to the R/V L.M. Gould as it steamed to their next work site, which was at broad-scale station #42 located in the outer margin of Marguerite Bay. The Gould set out towards station #42 from a point near Avian Island off the southern tip of Adelaide Island, while we were still working at station #28 in the early morning. In fact, they did not need our assistance breaking ice to get to the location and they arrived about an hour ahead of us. After we pulled BIOMAPER-II out of the water upon our arrival, the Palmer made a series of circles around the Gould to break the ice open in order to more easily approach to the Gould to make an equipment transfer. The equipment included a pair of ice buoys that Chris Fritsen and Bob Elder wanted us to deploy at stations #40 and 49. In a very skillfully orchestrated maneuver, Captain Joe brought the bow of the Palmer up to the stern of the Gould and then the crane on the main deck forward of the bridge on the Palmer was used to pick up a cargo net full of the equipment and haul it up to the bow of the Palmer. The return of the cargo net included a package of samples for the Gould. In addition to the equipment, a couple of cases of peanut butter were also passed from the Gould to the Palmer because there was a dire shortage on the Palmer of this essential food stuff from the vegetarians' view point.
The operation was completed by 1000 and we immediately started a phytoplankton tow and a CTD at this station location. Following the CTD, the 10-m2 MOCNESS was deployed and in spite of the ice, the tow was successfully completed. We then set off towards station #41, while towyoing BIOMAPER-II. (As a result of the diversion, we have elected to steam this portion of the survey grid in reverse order until we returned to the location where the survey was diverted). But it got much tougher to go through the ice pack, which was crisscrossed with ridges, and backing and ramming became frequent. As a result, we pulled the towed body from the water some 4 or 5 miles from station #41 to wait for better towing conditions. The CTD and phytoplankton tow was quickly completed at station #41 and we continued on towards station #40 in increasingly restraining sea ice conditions without BIOMAPER-II being deployed.
August 5th was a day for weather contrasts. A deep low pressure system passed over the Marguerite Bay with winds throughout the day in the 30 kt range. For a good portion of the day, the air temperature remained about freezing (0°C), accompanied by snow and sleet. In the early evening, a front passed and the air temperature dropped precipitously to below -13°C. During the night the temperature dipped to -20°C, with wind chills well below -30°C. Fortunately, the winds dropped, as well.
John Klinck reports that on 5 August, the CTD group did three casts on the north side of and near the center of the entrance to Marguerite Bay. These stations had typical character for the mid-shelf, except for the mixed layer. All three stations have clear stratification in the mixed layer which may be due to the warm air temperatures, leading to decreased convection and gradual restratification.
Station #28 (369 m) is on the inner end of the 340 line at the entrance of Marguerite Bay. The mixed layer is about 70 m deep with clear density structure due to both temperature and salinity structure. Very clear, thick layering is ongoing in the pycnocline with temperature reversals in a layer around 120 m. The deep structure is like many other stations with a temperature maximum about 300 m and a weak O2 minimum around 250 m.
Station #42 (765 m) is on the 300 line in the center of the entrance to Marguerite Bay. The upper ocean is linearly stratified down to about 120 m making it difficult to determine what is the mixed layer. Weak, thin layering is seen in the pycnocline and below. The O2 minimum and temperature maximum are in their traditional places, 250 and 300 m, respectively.
Station #41 (670 m) looks like station #42.
Jose Torres reports that on 5 August, his group completed a 0-500 m MOC-10 tow in the axis of the canyon that runs from the shelf break through the mouth of Marguerite Bay and into George VI sound. Although our trawl wire had several close encounters with ice floes, we had a very successful tow. When driving through ice as thick as we are seeing now, any successful trawl is the result of serious teamwork. Our Marine Techs and science party are on constant watch on the back deck ready to stop the boat if the wire gets hooked up. Our captain and mates back down on the wire if need be, and our winch operator stands ready to take cable up or pay it out quickly. Everyone breathes a little easier when the net is safely on deck.
Our mid-canyon catch showed differences in faunal composition from the oceanic community we recently sampled west of the shelf break at station #24. We picked up several individuals of the neritic euphausiid, Euphausia crystallorophias, and Thysanoessa macrura was less obvious as a numerical dominant. The fish fauna remained similar: Electrona antarctica, Protomyctophum bolini, and Bathylagus antarcticus were captured in our 200-500 m net. Cyclothone were not caught at this station, and the large coronate scyphomedusae Periphylla were absent as well. We expected to see a few individuals of the Antarctic silverfish, Pleuragramma antarcticum, but they were conspicuously absent.
Ari Friedlaender reports that on 5 August the ship began steaming after rendezvous with the L.M. Gould and finishing station #42 at 1405. Marine mammal observations then commenced and continued until 1605 when diminishing light and sighting conditions forced us to stop. Visibility was poor throughout the transit with fog and blowing snow keeping visibility between 0.5 and 0.3 nautical miles. Ice became 10/10 coverage, with vast snow covered floes with recent ridging, and newly frozen over leads. The snow cover seemed to be wet and heavy, as the recent temperatures have been hovering around freezing. While no cetaceans were sighted, there was activity. Seven Adelie penguins, 5 unidentified seals, and 13 crabeater seals were counted. Most of the animals were hauled out among the newly formed ridges, near small leads.
Ana Sirovic reports that on 5 August, she deployed one difar buoy as we were steaming to station #41 and received its signal for only 23 min. She assumes that it got crushed by the ice as we were moving through heavy pack. No whales were heard during this deployment.
Chris Ribic and Erik Chapman report that on 5 August (JD217), they surveyed
for 2 hours and 10 minutes between stations #42 and 41. Ice conditions
were pretty steady at 10/10ths concentration. Few birds were seen overall
in the heavy ice and most notably, no Snow Petrels were observed. They
saw 12 Southern Giant Petrels today, including a group of 9 birds grouped
on the ice around what may have been an Adélie penguin carcass.
It is interesting to note that Southern Giant Petrels have been seen in
the dense ice. So far, two groups of Southern Giant Petrels have been observed
feeding on a carcass far from open water. It could be that the petrels
are looking for penguins and or seals that are "trapped" on the ice when
the lead they were diving through closed up during heavy winds.
|Southern Giant Petrel||12|
They surveyed for 1 hour and 30 minutes last night from the bridge and
saw 1 Snow Petrel.
BIOMAPER-II/MOCNESS report (P. Wiebe, C. Ashjian, and S. Gallager):
BIOMAPER-II was towyoed between stations #28 and 42 and then again between #42 and 41. The increasingly heavy pack ice and the need to back and ram to make forward progress towards the next station (#40), resulted in very poor quality data and the possibility of damage to the towed body. In fact, during the latter towyo and while it was below 30 m depth, something collided with the frame. It probably happened while the ship was backing and ramming with all four engines running. Apparently the frame took a hit of ice when the fish came up to 30 m - the top of the towyos under these conditions. We surmise that a big chunk of ice got thrust down that far and hit the camera frame. One camera was knocked 180° out of alignment and when we tried to turn it around by hand, it could not be budged. Some very large force was required to rotate the camera. The camera frame itself had some welds broken, which were repaired. Fortunately, the cameras were not damaged and with re-calibration, the system has been ready to again be deployed when towing conditions improve.
During the towyo's to station #28 and away from it, a number krill patches were observed both acoustically and optically with the VPR in the upper 40 to 50 meters. Krill patches were also evident just before the towed body was recovered near station #41. This was in spite of the significantly increased noise levels coming into downlooking 120 and 43 echograms from increased pitch on the propellers and increased power being applied to get us through the ice pack.
There were no 1-m2 MOCNESS tows taken on 5 August.