The deep ocean (in this case 2363 m) requires long station times in order to sample to the sea floor for the CTD or even to 1000 m in the case of the net tows. So today (10 August) we have been working for much of the day at station #46, at the end of the line on Transect 46. We have finishing up work at station #46 (1842) and are just now getting underway and headed for a long steam to station #47. The weather today has been snowy for most of the day, but not much has accumulated. The winds have been in the 20 knot range until recently and now the winds are 32 to 37 kts out of the west (298) with gusts in the 40 knot range. The air temperature at -0.1°C is mild compared to the deep freeze values of 3 or 4 days ago. The barometer is down a bit at 970.1 mlb. Our position is -67° 05.68S; -73° 23.855W. The pack ice is much thinner out here just off the edge of the continental shelf and the ship has been moving more easily through it, no need for backing and ramming. Still towing is problematical with the tow cable always in constant danger of being snagged by a large chunk of ice as the pieces pushed aside by the passage of the ship fill in the wake.
On 9 August, we worked in windy snowy conditions at the final station (#29) in the coastal current region south of Adelaide Island and then at two mid-shelf stations, #43 and 44 to the west of Marguerite Bay. We arrived at station #43 about 1200 and started the work with an under ice dive by the Jose Torres group. The Ice Dive went well, in spite of the 30+ kt winds that were blowing. After the divers returned to the ship around 1400, Ari Friedlaender and Rebecca Pirzl went out for a short cross-bow tutorial in the zodiac before it was brought back on board. This was followed by a CTD, 1-m2 MOCNESS tow, and an under ice survey using the ROV. BIOMAPER-II was towyoed a portion of the distance from station #29 to 43, but suffered another electronic failure that could be traced to the ice collision of the previous day.
John Klinck reports that on 9 August, the CTD group did 4 stations: 2 on the shallow fringe south of Adelaide island, one at the end of line 308 and one on the 300 line. All of the shallow stations display a pycnocline of some sort between 100 and 150 m, so mixing is not sufficient to puncture the stratification even when the bottom is at the pycnocline. The surface mixed layer thickness and the evidence of lateral intrusions in the pycnocline vary considerably from station to station, even a few 10's of km apart. This may be due to small temporal or spatial scales for these processes.
Station #31 (156 m) has a mixed layer with uniform properties to 100 m and a clear pycnocline in the lower 50 m of the water column.
Station #30 (169 m) has a mixed layer to 70 m with uniform properties. The base of the mixed layer is rather sharp and the pycnocline has less stratification than other stations. Clear and numerous steps with thicknesses of 10 to 15 m populate the pycnocline. The transmissivity of the water decreases below the mixed layer and decreases again within about 20 m of the bottom.
Station #29 (182 m) has a mixed layer to 70 m, but temperature and salinity increase linearly across the mixed layer. Just below the mixed layer is a layer about 40 m thick with higher temperature (+0.2°C) and salinity (+0.05) which is apparently a laterally intruding layer. The stratification below this layer to the bottom has a weak pynocline followed by increasing temperature and salinity to the bottom.
Station #43 (470 m) is on the middle shelf and displays a uniform mixed layer to 50 m with linear stratification to about 100 m where a weak pycnocline occurs. There is some variability in the traces, but there is no evidence of steppy layers. A weak O2 maximum is at 250 m while two weak temperature maxima are evident at 300 and 400 m. Deep temperature is 1.35°C or so, meaning that the subpycnoline water has been on the shelf for a while.
Kendra Daly reports that on 8 August at station #34 in the mouth of Laubeuf Fjord was relatively abundant in plankton. Our Tucker trawl collected some larvae and immature adult Euphausia superba, mysids, amphipods, numerous copepods, medusae and ctenophores. We used adult krill collected from the Tucker trawl, the 10 m MOCNESS, and the 1-m MOCNESS tows to estimate physiological and feeding rates. The dive collections at station #43 in the mid-shelf region of Marguerite Bay yielded few larval krill and ctenophores. Divers observed only small scattered aggregations of krill under the sea ice.
Ari Friedlaender reports that on 9 August, the whales sighting effort was made from 0930-1115 as we steamed to station #43. Ice coverage was 10/10, with vast snow covered floes and very few patches of newly iced over pools. Snow fog again limited visibility to less than 0.5 nm. The only sightings made were 4 crabeater and 1 unidentified seals all seen swimming in the small pools.
Ana Sirovic reports that on 9 August, she deployed one sonobuoy as we were approaching station #43. She was able to monitor it for 38 min for a range of 3.2 nm. This is a very short range and it is likely that it was a sonobuoy malfunction rather than an actual indicator of the reception range. No whales, seals, or other biological noise were heard.
Chris Ribic and Erik Chapman report that on 9 August (JD-221), they
surveyed for 1 hour and 50 minutes on the way to station 43. Visibility
was poor with heavy snows during the observation period. Only Snow Petrels
and Adélie Penguins were seen in mostly 10/10ths ice concentration.
A summary of the observations is the following:
They surveyed for an hour last night and saw 7 Snow Petrels during that time.
BIOMAPER-II/MOCNESS report (P. Wiebe, C. Ashjian, and S. Gallager):
BIOMAPER-II was deployed on 9 August some distance from station #29 after repairs to the towed body were completed following the collision the day before with a piece of ice flowing out from under the ship's hull. It was being towyoed between 30 m and about 200 m when the Environmental Sensing System (ESS) which provides information about the towed body depth, temperature, salinity, fluorescence, and GPS position failed at a depth of about 130 m. It was brought back on deck about 45 minutes before we reached station #43. The problem was traced at first to a modem card inside the ESS underwater unit, but it was intermittent and took some time before a component was found that when replaced eliminated the intermittency upon bench testing (Thanks to Jeff Otten). But when plugged into the BIOMAPER-II's data and communication system, it still would not work. A second problem was found in the electronics in the telemetry bottle, which also took some time to remedy. This was on a board designed to handle the SAIL communications for the ESS system. An IC had been damaged by another component that had come loose probably during the ice collision. This component was free to shift back and forth and probably repeatedly hit the IC finally knocking it loose and shorting it out. Thanks to Romeo Larivieri, another replacement IC was found in the ET shop and this board was made functional again. This work, however, took about 24 hours, so BIOMAPER-II did not make it back into the water again during the 9th of August.
The tenth 1-m2 MOCNESS tow was conducted in marginal ice conditions. The tow started well, but we were beset by floes of ice that became trapped under the wire at frequent intervals throughout the tow. We often had to stop the ship and even back down to free the wire. This resulted in the MOCNESS dropping back down through the water column on the up cast and re-sampling depth intervals. We even sampled 250 m with three different nets! However, despite these difficulties, this was a very successful tow. The samples were in great shape. The ship handling abilities of our colleagues on the bridge should be commended!
Copepods were abundant from 75-419 meters. One myctophid was caught in the 419-300 m interval, along with a very large chaetognath. Opaque, large, euphausiids were caught in the 110-419 m depth range in low abundance. Furcilia were observed from 95 m or so to the surface. A very large salp was caught in the 21-45 m depth interval. Smaller salps also were caught in the upper 45 meters. Ctenophores were captured only in the 46-71 m interval.