This is mid-winter on the Western Antarctic Peninsula and the pack ice is still in the development phase. As a result, as we head into the southern portion of the survey grid, we are encountering increasingly tough ice conditions to work in. The extreme cold is also making working conditions quite difficult as noted below. Still we are moving from station to station and are able to do much of what was intended. We have just completed work at station #63 and are now steaming for station #73. Our current position on 18 August at 0046 is -68° 20.433S; -73° 23.170W. The air temperature is - 20.6°C and the wind is out of the east northeast (073) at about 29 kts. The barometer at 954.7 mlb is falling again. The clear skies for much of the day have given way to clouds and a light snow is falling.
On 16 August, we completed work at stations #54, 59, and 60, which were located along the southern and outer margin of Marguerite Bay. The jump in station numbers (#54 to 59) reflects the fact that we dropped stations #55 to 58, which were located in the southern end of Marguerite Bay, an area known as King George VI sound. The ice pack conditions made it too difficult and time consuming to attempt to get there. At station #54, a CTD, a phytoplankton ring net tow, and an ice collection was done. BIOMAPER-II was deployed for a portion of the transit to station #59. This transit was interesting because it started in the very deep water (greater than 1000 meters) associated with canyon system that comes across the continental shelf and into Marguerite Bay. In steaming south to station #59, the steep canyon walls rose up abruptly to a shoal depth of about 140 m and the dipped down again into another trough with depths of 400+ m before rising to shallower depths near the coast. The cold air temperatures on this day limited some of our activities at station #59. Thus the dive that was scheduled for the Torres group was nixed because it was just too cold- below -25°C. This was unfortunate because we had been running through a number of good sized leads which would have made diving an easy thing to do. At station #59, a CTD, ring net tow, and a ROV under ice survey took place. Several long leads allowed BIOMAPER-II to again be deployed for a portion of the transit to station #60. After the usual CTD and ring net, a Live Tucker Trawl was scheduled, but had to be dropped because of impossible towing conditions. A series of Plummet net vertical tows were done instead. Even that last resort method of collecting zooplankton is marginal under the extreme cold. The net freezes almost immediately once above the sea surface and the sample must be quickly removed to prevent it from freezing too.
John Klinck reports on two stations that the CTD group did on 16 August on the south side of the entrance to Marguerite Bay. Station #54 (1142 m) is in the Marguerite Trough, which explains its great depth for a coastal station. The mixed layer extends to about 50 m with no structure. The region between 50 and 100 m has increasing temperature and salinity which joins with the pycnocline between 100 and 200 m. There is only slight indication of layering in the pycnocline. A broad O2 minimum is centered on 350 m and the temperature maximum is a bump at 450 m. An O2 maximum and a temperature minimum are evident between 850 and 950 m; the significance of this structure is not clear. It might be LCDW, but that would require a deep (1000 m) connection to the ocean. Alternatively, it could be deep mixing or the intrusion of denser (colder, saltier) water from the shallower shelf or in Marguerite Bay. This may be the evidence of some small amount of dense water being formed on the shelf.
Station #59 (400 m) has a mixed layer to 60 m with strong layering (10-20 m thick) throughout the pycnocline. Temperature is rising and O2 is falling below 250 m, so the temperature maximum and O2 minimum occur at the bottom.
Jason Hyatt reports that the study site experienced some extremely cold temperatures on 15 and 16 August, with a maximum temperature of -20°C and an average of -23.8°C. The northerly winds have not yet kicked in to bring down some warmer air. As of 1200Z on 16 August, a low is approaching, but the leading edge is weak, so we 'may' get some weak northerlies. The trailing edge, on the other hand, has tightly packed isobars, which cause the easterlies and southerlies and more cold air. The 17 August morning INMARSAT link will bring the next isobar image, and show how the approaching low manifests itself.
Ari Friedlaender reports that on 16 August, marine mammal observations began at 0925 as we steamed towards station #59. Skies were partly cloudy, visibility was very good and ice coverage was nearly 10/10 with some long leads (500 meters wide by several kms long) that were mostly covered in new gray white ice. The areas that were not covered were easily recognizable at any distance by the sea smoke rising up. This made spotting whale blows in open water difficult as they would have blended in extremely well. The ship traveled in these leads for some time during our transit to station, which ended at 1410. No cetaceans were sighted, although numerous penguins (see bird observations) and 24 crabeater seals were seen. One of the seal sightings was of at least 12 animals swimming through a lead together.
Ana Sirovic reports that in the morning of 16 August, 18 minutes after we left station #53, she started hearing crabeater seal calls on the buoy that was deployed while she was on the ice with the ice coring party. The calls (grunts) continued for over one and a half hours, at which point the signal from the buoy was lost. Even as the signal strength was getting very weak, the calls were still very clear. The calls were approximately 3 seconds long. Average beginning and ending frequencies were 25 and 45 Hz, respectively, with a maximum frequency 69 Hz. Multiple harmonics were present for most calls, sometimes up to as high as 800 Hz. There were at least 2 animals calling: one close to the sonobuoy and the other somewhat farther away. This is obvious because there are several overlapping calls of different strengths on the recording. The sonobuoy hydrophone has pressure sensors that enable detection of the direction that the noise is coming from, after the signal has been processed with the appropriate software. Usually, this kind of analysis can give further insight into the minimum number of animals that are calling. Unfortunately she hasn't been able to get meaningful data from this recording, probably because the animal(s) was too close to the buoy, so the only way to estimate the number calling animals are the overlaps. The buoy that was deployed in the afternoon of the 16th, on the way to station #59, provided no biological noise. She was able to listen to it for 2 hours 40 minutes and got a range of 7.4 nm.
Chris Ribic and Erik Chapman report that on 16 August (JD-228), they
had a good amount of time surveying between stations. They surveyed for
4 hours and 40 minutes between stations #54 and 59. There was backing and
ramming throughout much of the transect and the Palmer covered about
13 or 14 miles during the survey. This survey took us through vast floes
of thick ice and several long leads that were covered with new gray ice
and a small amount of open water. Snow Petrels were seen over the leads
and some Adélie Penguins were seen feeding in open water or hauled
out on the ice. More Emperor Penguins were seen than on any other survey
period hauled out near or feeding in the leads. Before sunrise, they surveyed
for 30 minutes as the Palmer approached station #54 and 34 Snow
Petrels were seen, most of which were flying directionally by the ship.
A summary of their observations is the following:
BIOMAPER-II/MOCNESS report (P. Wiebe, C. Ashjian, and S. Gallager):
After leaving station #54, the Palmer encountered several strong ice ridges which required backing and ramming to get through them. But after that, we entered a wide lead that took us in the direction of station #59, so BIOMAPER-II was deployed. With the towed body in the water, krill patches were immediately seen at around 200 m and in lowering it on the first towyo, it went through a small patch near the surface and got some good VPR images of them. This was a very good run because the ice on the lead was very thin and the ship could make a fairly constant speed with only a couple of engines running. Fortunate too, was the fact that the topography in this area was pretty deep and there were not any surprises. But at the end of the lead and before reaching station #59, Captain Joe turned the Palmer to the south cutting across some ice ridges. The ship ground to a halt and it was clear that the towyoing for this transit had come to an end.
BIOMAPER-II went back in shortly after leaving station #59 because there were open leads running along the coastline in this area allowing the towing to proceed smoothly. Just before 1700, the ship left the large lead that we had been towing along and entered an area of brash ice surrounding a field of icebergs. The Palmer passed by one huge iceberg so close that it looked like you could reach out from the bridge wing and touch it. The highest part of the ship did not come close to matching the height of this big baby. About 2030, we had to again end the towyoing before reaching the station because backing and ramming had become necessary as a result of the very thick ridges and lack of open water. Just before bringing the towed body on deck, strong scattering layers were seen in association with the highly variable bottom topography, which may have been dominated by krill.
No 1-m2 MOCNESS tows were done on 16 August.