The mountains encircling Marguerite Bay on three sides were clearly visible today (7 August) in the partly cloudy skies and bright sunshine, as we worked at the eastern end of Marguerite Bay. In spite of the cold, it was a great viewing day. We are currently (1856) steaming towards station #36 and are at -68° 01.406 S; -67° 55.165 W. The winds are moderate at 8 to 10 kts out of the west (269) and the air temperature is -19.1°C. The barometer is climbing and reads 984.8 mlb.
A nearly full moon was visible through a thin cloud layer as the Palmer approached station #40 in the wee hours of 6 August. The temperature was still falling towards -20°C when Frank Stewart, Jay Ardi, Wendy Kozlowski, and Erin Macri were transferred to a large ice floe to install an ice buoy and to make ice collections. This station also had a CTD and a phytoplankton tow and was completed in the early morning about daybreak. The steam towards station #39 became harder and harder with increased ice ridging and a very sticky snow. We reached a point where in backing and ramming, we were only making a ship length or two before we came to a stop and had to back up again. So we stopped short of the station location and did a phytoplankton tow, a CTD cast, and a series of Plummet net vertical casts to collect zooplankton. The use of the plummet net was as a partial replacement for the 1-m2 MOCNESS, which cannot be towed properly in this very heavy pack ice. Likewise, BIOMAPER-II was sidelined for the entire day because of the backing and ramming. In the evening, to get to station #38, we elected to backtrack to a position west of the Kirkwood Islands and then to head east toward the station #38.
John Klinck reports that on 6 August, the CTD group had a slow day only doing two casts, both inside Marguerite Bay along the 300 line. The ice prevented us from getting any closer than 8.5 mi from the second, innermost, station.
Station #40 (704 m) has a well mixed surface layer to about 80 m. There are a few prominent layers in the pycnocline. Water properties below about 300 m are nearly constant with only the barest hint of a temperature maximum or an O2 minimum, at the typical depth.
Almost station #39 (188 m) has a well-mixed surface layer to about 95 m. The station is too shallow to have a deep temperature maximum. The T-S plot shows that the upper pycnocline is either fresh for its temperature or warm for its salinity, compared to other stations on this shelf. Or, the upper part of the pycnocline here is less dense than elsewhere on the shelf.
We have caught up with the backlog of salinity samples and have had time to make a preliminary comparison among sensors. There is some scatter in the various measurements and station #25, at which the CTD ingested sediment as it neared the bottom, is not used for this calibration. There is a persistent difference of about 0.002 between the two salinity sensors on the CTD. Both CTD sensors are higher than the salinometer by about 0.01. There is no trend in these differences with either time or salinity. One niskin bottle (5) has a significantly higher variability (-0.05 to -0.1) than the others which may indicate leakage. Deep and shallow bottles have error rates of order 0.02 with a few outliers. This analysis will be repeated in about a week as more salinity samples are taken and run through the salinometer.
Kendra Daly reports that on 6 August at station #39, the Daly group completed several rate measurement experiments and completed plummet net hauls at six discrete depth intervals between the surface and 185 m. The plummet net is a downward fishing net that can be opened and closed at set depths using messengers and a double trip mechanism, which holds the active bridles of the net. This net was used because the ship could not reliably maintain a forward speed under the current 10/10 ice conditions. The working metal parts of the double trip mechanism froze almost every time it came back on deck because it was exposed to the -20°C air temperatures. The judicious application of a heat gun and rubbing alcohol in key locations kept the operation going. The net collected a few small copepods and larval krill between 0-25, 25-50, and 50-75 m. Numerous krill larvae, copepods and Thysanoessa macrura were collected between 75-100 m. Copepods, Thysanoessa, and chaetognaths were observed in the 100-150 m depth interval. The deepest tow between 150 and 185 m contained the highest abundance of zooplankton, including copepods, Thysanoessa, tomopterid worms, medusae, chaetognaths, and a siphonophore.
Ana Sirovic reports that on 6 August, she deployed 1 difar sonobuoy while we were still making way towards station #39. She was able to monitor it for 36 min (that is a range of a bit less than 4 nm) and heard no biological noise.
Chris Ribic and Erik Chapman report that on 6 August (JD-218), they
surveyed for 3 hours and 38 minutes between stations 40 and 39. Ice conditions
were pretty steady at 10/10ths concentration. Several small groups of two
or three Adélies were seen during the transect. Only a single Snow
Petrel was seen, probably because there is little open water in this portion
of the Bay. Since coming into Marguerite Bay, very few Snow Petrels have
been seen, even in open water areas where they had been seeing the birds
in other areas on the survey grid. This may be because we are moving further
from the ice edge and the looser ice is where the birds have more reliable
access to food. A summary of the counts is the following:
BIOMAPER-II/MOCNESS report (P. Wiebe, C. Ashjian, and S. Gallager):
As noted above, BIOMAPER-II was not deployed on 6 August, but not without trying. At the end of station #39, it was decided to steam back along the trackline to the previous station location and then find a new way with less ice to get to the next station. With the ice already broken along the route, towing conditions were good. The towed body was readied for deployment, but a problem with the hydraulics fluid in the reservoir for the BIOMAPER-II winch and handling system caused a substantial delay. Then, the power pack for the winch needed to be turned on and run for a while before using the equipment to allow the oil in the system to warm up. Finally, the towed body was taken of the garage and ready to be picked up, but the winch readouts on the main control box located out on the 0-1 stopped working. After a substantial period of trouble shooting the winch control system, first in the bitterly cold night air and then in the main lab, a blown fuse, largely hidden from view and not shown on any schematics, was discovered on a circuit board inside the control box. It was quickly replaced. With the winch control system was finally working again, we again got the fish out of the van and on the deck, and asked the bridge to slow down so we could launch it. But the bridge said to wait 5 minutes while the ship got through a rough spot. Minutes passed and finally it was clear that our old pathway was no more to be seen. We were cutting through new ice and snow, and the need to back and ram was quite clear. BIOMAPER-II went back into the van to await better towing conditions.
There was no 1-m2 MOCNESS tow on 6 August, although one was scheduled, because net towing was not possible under the pack ice conditions experienced in this area of Marguerite Bay.