Report of Activities on the RVIB N.B. Palmer Cruise 02-04
For the second day in a row, a
bright sun came up over
Around 1600, we arrived at the
first of seven scheduled CTD station locations in the
The morning sun gave way to increased cloudiness as we steamed along the inland passage. There were multiple cloud layers and along the route there were low cloud patches with intense flurry activity. The sun occasionally shone on the peaks of some of the mountains as we moved through the inland passage in the early afternoon, but the clouds thickened and a light snow began falling about 1700. The wind picked up about this time from less than 10 kts to around 25 kts and became predominately northeasterly. Air temperatures ranged from -4ºC to 0ºC throughout the day, while the barometric pressure made a slow decline from 1016 to 1012 mb.
CTD Group report (Eileen
Hofmann, Bob Beardsley, Baris Salihoglu,
Chris MacKay, Francisco (
About mid-day on 13 September we
departed Palmer Station for the last part of cruise that will take us back to
At each station CMiPS casts are done from the surface to 350 m. The number of casts is dependent on the observed temperature and salinity structure, but is usually two to three casts per station. Following the CMiPS casts, one additional cast is done which extends to within a few meters of the bottom. On this cast, water samples were taken at three depths for microzooplankton studies by Gallager and Thompson.
The stations occupied during 13
September showed the front at the southern end of the Strait between CDW and
At the start of our cruise,
almost seven weeks ago, we did an XBT transect along the axis of
ROV report (Scott Gallager, Phil Alatalo, Alec Scott)
ROV deployment 23 was performed at Station 17 (-66º 58.335′; -69º 29.787′) on 8 September. From the surface, the ice was 60/40 coverage with medium sized (10 to 100 m), broken first year floes, 50 cm thick, rafted into deep piles and interspersed with open water leads. After checking all systems the ROV was deployed at 2036 only to find that the port thruster was producing a current overload. When this happens, it means that water has entered the motor most likely through the lip seal of the main shaft. One of two things can occur: the thruster will continue to function, but eventually burn itself out because of the excess current draw, or the thruster motor controller board in the main body of the ROV will overload and burn out a power transistor. The procedure when this happens is to shut off the controller for the bad thruster inside the topside power pack, which we did. This left the ROV unable to follow a straight course and turn only in the direction of port. Knowing there would not be time to retrieve the ROV, repair the thruster and get back into the water at this station, we positioned the ROV facing aft and began a transect in a slow arc out away from the ship and then back in towards the starboard side about the position of the A frame. This worked well, so we repeated the operation with a longer tether lead and followed another arc shaped transect. The ice was rafted deeply so it was difficult to remain at one depth. However, even with these shortcomings, we were able to get two 100 m long transects. Unfortunately, the furcilia abundance was low with scattered animals below even the more rugged surfaces. The concentration was roughly 1 to 2 per cubic meter. A few ctenophores were noted but they were not in high abundance. The ROV was retrieved and the port thruster repaired by draining the oil-filled housing, rinsing with fresh oil, and refilling. This operation required about 45 minutes before we were back in action and ready for the next station.
ROV deployment 24 began at station 5 (-66º 24.316′; -68º 22.772′) on 9 September, the last station on the northern sector of the grid. Surface ice conditions were 40/60 coverage with flooded floes and open leads. The ROV was deployed at 2332 local time in a 25 kt northeast wind, 19ºC wind chill, and blowing snow. The deck crew was prepared with goggles and face covers to guard against the harsh conditions. All the tether was paid out as the ROV ran directly away from the starboard quarter and dove to 8 m where a good view of the under ice surface could be attained. The under ice surface was surprisingly rough given the smooth conditions observed from the surface. During the first transect, a few small swarms of 50 to 100 furcilia were noted embedded in the upper ice crevasses. The ROV turned 90º towards the bow of the ship and proceeded on a bearing of 30º. A strong current took the ROV to the north and eventually under the ships hull. This would not have been a problem with the exception that the tether had, in the meantime, wrapped around the starboard rudder and through the opening between the two main screws. The ROV tether had become lodged between the ships hull and a large block of ice up under the hull just forward of amidships. The ensuing one and a half hours were a bit tense as the ROV was jockeyed around to get a better look at the snag. Unfortunately, the scope between the snag and the ROV was short enough to prevent turning a full 180º.
First Mate Mike Watson, Ice Pilot Vladimir Repin, Second Mate Paul Jarkiewkz, and Third Mate Rachelle Pagalunan, all were observing the conditions and suggesting potential moves. In a final attempt to dislodge the ROV, Captain Joe began gently swinging the forward thruster back and forth towards the starboard side and aft. Within a few seconds, we could see water moving past the ROV. The ROV dove hard and suddenly we could feel some freedom in the tether. With the ROV at safe depth of 40 m, the deck crew began pulling the tether free from the rudder. Soon, and with a sigh of relief, the deck crew reported the ROV lights in sight and retrieval operations commenced.
On 11 September, the first (#25)
of two ROV deployments took place at the 24 hour time-series station just south
of Renaud Island (-65º 10.382′; -65º 37.560′)
during daylight hours. The purpose of this last set of deployments was to
determine if furcilia undergo diel
vertical migration. Some forms of plankton swim up into the water column at
night and down to depth during daylight hours. There are many potential reasons
for this behavior, but the most likely one appears to be avoidance of visual
predators during the day. Adult and juvenile krill have been observed to
migrate hundreds of meters a day, but vertical migration in their furcilia stage larvae has not been observed. The
The second ROV deployment (#26) was performed at the 24 h time-series station just south of Renaud Island (-65º 07.709′; -65º 30.728′) close to where ROV 25 took place, but during night time hours. Surface ice conditions were the same as in ROV 25 with loosely packed floes which were flooded and snow covered. The ROV was deployed at 0046 on 12 September in a flurry of adult krill swarming at the surface. This phenomenon had not been observed before on this cruise so it attracted a number of people to the sides of the vessel. The ROV observed many adults, juveniles, and stage 6 furcilia, but the furcilia were not swarming as seen earlier in the day. On average about 10 to 100 furcilia per cubic meter were observed. As a side note, divers observed very dense furcilia concentrations during the daylight hours. The conclusions based on this and all our observations of day vs. night time deployments is that there does not appear to be any diel vertical migration in response to time of day or daylight in young furcilia stages. In fact, more intense swarming behavior was observed during day time deployments than at night. One reason for this may be that larvae are attracted to light because sunlight is needed for algal growth and ice algae and microplankton are their major prey. Predator avoidance does not seem to play a major role in their behavior. The under ice surface may provide sufficient refugia from predation and serve as a critical nursery with an abundance of food where sunlight can penetrate as a source of energy for photosynthesis. Even if the ice algae at this time of the year are not actively photosynthesizing, they could be releasing organics that act as an attractant to the hungry furcilia.
Current Position and Conditions
The N.B. Palmer has left the inland passage
and is now proceeding across the continental shelf towards the