Today (16 August), we have been working along the southern margin of Marguerite Bay and enjoying another day of massive icebergs, some open leads, and magnificent views of the mountains of Alexander Island. It has also been a day of extreme cold and harsh outdoor working conditions. Fortunately, most of the day the winds have been light and the wind chill per se has not been a very significant factor. Currently (2343), we are steaming to station #61, having just completed work at station #60. The air temperature is -27.2°C and the winds are coming out of the east (091) and are now stronger at 18 kts. Our position is -68° 44.713S; -71° 02.11W.
The 15th of August began as a beautiful pre-dawn morning with clear skies overhead and a dark bank of clouds off to the north and west. To the east were some high lenticular clouds lit up with the rays of the sun like beacons in the sky. To the south were the ghostly white cloaked mountains at the northern end of Alexander Island. And on the horizon in many directions were the varied shapes of icebergs breaking the flat plain of ice that continuously covers the sea surface in this area. Closer ahead were flat snow-covered floes, which ended in irregularly shaped ridges, areas where the floes have met and one has over-ridden the other. The ridges snake along, then divide into two or more parts and continue to wind their way across the ice pack surface. The day was extremely cold with temperatures hovering at or below -25°C. During the transits between stations, steam was rising out of the open water of our wake. The sea water temperature is about -1.84°C, but cold as that is, it was much, much warmer than the air and it was visibly giving up heat and moisture to the air. Looking out over the vast ice floes, there were other areas giving rise to plumes of steam - from freshly opened cracks or small leads. The ice is a dynamic entity, moving with the wind and the tides, opening cracks and leads and closing them.
The morning sunshine gave way to clouds about the time we ended the long transit from station #19, where we left the Gould setting up for an extended stay at that location, and arrived at station #52. At that station, we did a CTD and a phytoplankton ring net tow. Scheduled was a 1-m2 MOCNESS, but pack ice closed in on the wake to quickly to permit the tow to take place, even by following our previous trackline leading to the station. The steam to get from station #52 to 53 in pretty heavy ice pack was a struggle with the need to back and ram occurring frequently. As a result, BIOMAPER-II was sidelined during the transit. At station #53, in addition to a CTD, the ice collectors were out collecting cores and measuring the properties of the ice in a large floe. Upon the ice collectors returning to the Palmer, BIOMAPER-II was put into the water to get an acoustic and video profile at the station. While the towed body was deployed, a series of plummet net casts were done to try to catch what was in the layer. The plummet nets, which fished 0-40, 40-100 and 100-400+, did not catch a very much, although it was sufficient for Jose Torres to get some animals for his experimental work. The work at station #53 ended after midnight.
John Klinck reports that on 15 August, the CTD group did two stations on the southern side of the entrance to Marguerite Bay. The station closer to Marguerite Bay has the warmer deep temperature structure indicting more recent influence of oceanic waters.
Station #52 (507 m) has a mixed layer to about 65 m with no structure. A thick pycnocline extends from the base of the mixed layer to 200 m. Some weak layering is observed. Deep waters are almost uniform in character with no O2 minimum and only the slightest temperature maximum at around 380 m. The deep temperature is 1.3°C, indicating well adjusted, long resident shelf waters.
Station #53 (681 m) has a mixed layer to 50 m with increasing temperature and salinity with depth. Layering, with widths of 5 m, is evident from 60 m to below 300 m. A deep O2 minimum occurs at 350 m and a general temperature maximum extends from 350 to 420 m. The presence of a temperature maximum and slightly warmer deep temperatures says that this location has been influenced by oceanic water more recently than the adjacent station #52. The Marguerite Trough seems to be the conduit for this warmer deep water.
Jason Hyatt reports that 14 August (yesterday) was a day of weather extremes for the cruise. We experienced the winds of 55.24 knots at 0510 UTC, the lowest air temperature, -27.9°C at 1413 UTC, the lowest barometric pressure of 933.6 millibars at 0522, and besides the first day, July 24, we experienced the sunniest day, with shortwave solar insolation reaching 155 w m-2. Why, exactly did this happen? These were not separate lows and highs passing in a matter of days. Rather, the isobar images suggest the approach of a strong low with isobars tightly packed. This low stalled as it approached the mountains of the peninsula and sort of squirted through the passes, breaking up and reforming. It looks like these offspring passed over us in succession, with the low yesterday being the most extreme in a series of bizarre, difficult to predict, weather patterns. While, there do not appear to be any major lows coming around the bend, many of the lows we have experienced so far have not given much advance warning.
Jay Peterson reports that on 15 August an OPC/MOC1 tow was attempted at station #52, but ultimately canceled due to heavy ice cover.
Processing of the ADCP current data obtained at station #52 indicates that water is moving in a NNE direction at 0.08 m/s in the upper 80 m, with waters below this depth traveling to the West at a velocity of 0.14 m/s. ADCP backscatter during the CTD cast showed a scattering layer at ~190 m.
At station #53, heavy ice cover again prevented any attempt at collecting
OPC data. While on station, backscatter data from the ADCP indicated dense
scattering layers at 50 m and 190 m. Currents in the upper 170 m were westerly
with a maximum velocity of 0.22 m/s. Below 170 m the water was moving NW
at 0.2 m/s.
Jose Torres reports on diving underneath Antarctic ice:
During each yearly progression through the seasons about 16 million square kilometers of the Antarctic's Southern Ocean are covered and uncovered by pack ice. It is the world's most profound manifestation of seasonal change. As you might expect, several types of marine life use the pack ice in some way, either as a floor (seals and penguins), as a refuge from predation (larval krill), as a place of residence (ice algae), as a source of food (larval krill again) or place to hunt in (some fishes). To observe and collect the marine life that inhabits the under-ice environment (with the exception of seals and penguins, of course) SCUBA diving is a reliable and effective method.
Diving beneath the pack ice requires a considerable amount of preparation and specialized equipment. First, to deal with the ice cold water, a dry suit is required. A dry suit is basically a tough rubber suit with a valve to inflate it and a valve to let the air out. It is made with feet attached, so that the only parts of your body that stick out are your head and your hands. Tight rubber seals at the neck and wrists prevent water from entering the suit. Because it is dry, you can wear heavy underwear underneath the suit to protect you from the cold. A tight rubber hood and protective gloves complete the Antarctic SCUBA diving outer garments. The suit attaches to your compressed air bottle via a pressure hose to allow you to inflate it.
Besides the cold, another big problem confronts the Antarctic diver: underneath the pack ice, the ocean is anywhere from 1,500 to 12,000 feet deep. You are essentially diving in the middle of the ocean, only with a roof over your head that prevents you from getting to the surface and safety. Tricky business. To dive safely, we use a tether system. Each diver is tethered to a "down line" that is in turn attached to a zodiac. The tethers are 100 feet long, which gives us room to maneuver, but we are only 100 feet from our dive boat, and safety, at any time.
Once underneath the ice, the vistas are glorious. Visibility during
the winter season is about 200 feet. Larval krill are very abundant in
some areas, forming small clouds underneath the ice. Jellyfish predators
also abound. Is it worth the effort to take a look? You bet. Keep in mind
that the area beneath the ice is an ecosystem 30% larger than the continental
USA, and that the only way to collect the animals that live there is to
go down and get them.
Ari Friedlaender reports that on 15 August, marine mammal observations began in the morning at 0840, en route to station #52. Conditions were fine; partly cloudy skies, good visibility, and 10/10 ice coverage of vast floes with low ridging. There were few open leads at this time. We arrived at station 52 at 1110, and ceased observations until leaving at 1320. Sighting conditions were similar to before, but ice conditions changed a bit. We entered a field of icebergs scattered in all directions as far as the eye could see. As well, the ice became more disturbed with more ridging, and meandering narrow leads. No cetaceans were sighted before ending observations at 1630 (68° 25.80S, 70° 41.09W). However, we did count nearly 50 crabeater seals. Forty of these were seen in one large group, which was traveling parallel with the ship in a narrow lead approximately 200-300 meters off the starboard beam. While still offshore of Alexander Island, several areas of sea smoke could be seen to our south, in the direction of the Island. Hopes are that this is a sign of looser ice or open leads near our track line to be surveyed tomorrow.
Ana Sirovic reports she deployed 2 buoys during the 13th and 14th of August. The first was deployed as the Palmer was steaming to meet the Gould on 13 August and it failed after 4 seconds of transmission. After meeting the Gould, it became impossible to deploy buoys because the Gould was following in the wake close behind us. She did try to deploy another buoy after minke sightings on 14 August, hoping that the Gould would evade it, but this buoy proved to be short-lived as well and it got stuck under the ice after 27 seconds.
On 15 August, Ana deployed 2 difar sonobuoys. The first one was deployed 8.5 nm from station #53. It was monitored for 1h 6 min and no biological noises were heard. The second buoy was deployed at station #53 into a crack (or rather a slushy opening) in the ice. There was a crabeater seal seen approximately 100 m from the deployment site. She was able to hear the buoy for over 7 hours (well into 16 August). The last part of the transmission was recorded and these tapes need to be studied, but a quick review showed very nice seal calls. Make sure to read tomorrow's issue of the daily report for the full update!
Chris Ribic and Erik Chapman report that on 15 August (JD-227), they had a good amount of time surveying between stations. They surveyed for 2 hours 46 minutes after the Palmer left the Gould at station #19 and approached station #52 and for 3 hours and 39 minutes between stations #52 and 53. The Palmer was backing and ramming through thick ice during most of the survey time, so although there was over 6 hours of surveying, not a lot of ground was covered during that time. Visibility was excellent, but not many birds were seen. They saw a few single Adélie Penguins and an Emperor Penguin between stations #52 and 53 and a few Snow Petrels flying high and directionally in the morning as the Palmer approached station #52. They also did an hour of night surveying just before sunrise and saw 34 Snow Petrels, most of which were also flying high and directionally as if heading to an area some distance away to feed. A summary of the observations is the following:
Primary Ice: Vast floes; 10/10ths coverage with 60 cm snow on top of
BIOMAPER-II/MOCNESS report (P. Wiebe, C. Ashjian, and S. Gallager):
The heavily ridged ice and thick floes in the area of stations #52 and 53 prevented BIOMAPER-II from being deployed on 15 August along the transect lines. There was too much backing and ramming. So instead, the towed body was deployed at the end of the regular station work to obtain a profile of the acoustic backscattering at that locations. This was in part done because the Simrad sounder was showing a pretty strong layer down around 100 m and another down about 350 m. But in setting up for the deployment of BIOMAPER-II and the plummet net casts, the ship back and rammed fairly intensively creating a large hole in the ice and apparently driving away the critters in the layer because when we turned on the BIOMAPER-II echosounder, the layer between 80 and 100 m was anemic and stayed that way for the duration of the Plummet net tows. The profile made at the end of the deployment went to about 200 m and no substantial concentrations of krill were encountered.
No 1-m2 MOCNESS tows were done on 15 August.