Report of Activities on the RVIB N.B. Palmer Cruise 02-04
The sixth of August found us
working for a second day in
The early evening was spent
steaming to a rendezvous point where an exchange of equipment and supplies took
place between the Palmer and the Gould. The pack ice limited the drift of
the vessels and made it possible to position the ships with the bow of the Palmer within a few meters of the stern
of the Gould. The exchange was made
using the bow crane on the Palmer to
move cargo nets with the gear between the Palmer's
bow and the Gould's stern deck. The transfers took about an hour, after which
the Palmer steamed south to a
location north of
In the morning before sunrise (0730), the skies were cloudy and the air temperature was -5.2ºC. The barometric pressure (1017.4 mb) was down a bit from the last day or two and the wind was out of the south (177) at about 5 kts. The sea surface temperature was -1.795ºC and salinity was 33.845 psu. The morning turned beautiful with the sun breaking through the overcast skies so that there was a hazy cloudiness filtering the sunlight. In the mid-afternoon, there was a low thin foggy mist to the atmosphere and the sun, shining through, was a yellow ball with blurred edges. What little wind there had been in the morning died and it was calm throughout the afternoon and evening. During the transfer with the Gould, a very fine misty snow fell lightly and the air temperature was around -7ºC.
CTD Group report (Eileen Hofmann,
Bob Beardsley, Baris Salihoglu,
In the late evening of 5 August,
we began a CTD section along a transect that extended across Matha Strait, the opening into Crystal Sound between
Adelaide Island to the south and Watkins Island to the north. The purpose of the transect
is to look at water inflow into
The transect consisted of 3 stations at 5 nm intervals. The depth at the center station was about 570 m, which puts it in the area of the deep trough. CTD casts were made to the bottom at all stations. The transect was completed in the morning of 6 August.
Temperature increased with depth
at all stations, with the warmest bottom temperature (about 1.2ºC) occurring at
the central station. The vertical oxygen profile showed an oxygen minimum at
about 200 to 300 m. Salinity increased
to 34.71 at depth. These properties are characteristic
of modified CDW, which forms from mixing of CDW with the overlying Antarctic
Surface Water. Thus, it appears that CDW
extends across the west
At all stations, the Winter Water layer was 80 m to 100 m thick. Surface temperatures were slightly above freezing at about 1.75ºC. It may be that upwelling/mixing of the deeper warmer water contributes to the surface waters remaining above freezing.
During the first CTD cast, problems with the data acquisition software were encountered. Large spikes appeared in the data at random intervals. On the second cast the spiking in the data became so bad that it was not possible to observe the profiles produced by the CTD sensors on the computer screen. After checking numerous potential problems, it was determined that the computer used for data acquisition was bad. This computer was swapped out for another and this seemed to fix the problem.
However, the fix was short-lived. On the next cast, the spiking returned. Examination of the processed data files showed that these had been corrupted by the large spikes in the data, but the data collected on tape were good. This provided further evidence that the problem was with the acquisition computer and/or software. After considerable effort on the part of the ship's ETs and ITs, it was determined that the ship's computer system had become infected by a virus and that this was causing the software/computer problems. This has now been fixed and we have recovered the CTD cast files from the back-up tapes.
We thank Fred Stuart, Todd Johnson, and Paul Huckins for their help and effort in fixing the problems with the CTD computer system.
Sea Birds (Chris Ribic and Erik Chapman)
On the afternoon of 6 August, the
ship headed toward the
These samples were taken about 1
mile from where 14 diet samples were taken in the
ROV report (Scott Gallager, Phil Alatalo)
The objective of the ROV studies is to observe and quantify the distribution, abundance, behavior and size distribution of larval krill in association with the underside ice surface and sea surface hydrography. A Benthos SeaRover ROV was equipped with a variety of physical and biological sensors including a stereo camera system with a field of view of 1 m3, a synchronized strobe, a CTD, an Imagenix 881a 630 kHz-1 Mhz sector scanning sonar, an uplooking DVL Navigator 1200kHz ADCP, and the standard forward looking pan and tilt color camera.
The ROV is deployed off the stern with 200 m of tether paid out with a 50 lb. clump weight at a depth of 20 m. The ROV first descends to 20 m and travels at least 10 m away from the ship. The ROV then ascends to about 5 m depth or until the underside of the ice is observed in the pan and tilt camera. A trackline is established extending radially away from the ship out to a distance of approximately 100 m. As the ROV travels the trackline at a speed of about 2-10 cm/s, the stereo camera is used to image the under-ice surface and associated organisms such as larval krill and their Ctenophore predators. Precise positioning and sizing of targets within the 1 m3 is established through post-processing using a stereogrammetry algorithm. The forward speed of the ROV is established with data from the ADCP and used in conjunction with the image volume to calculate volume sampled per unit time. For example, at a forward speed of 10 cm/s, a new 1 m3 field will be imaged every 10 s. The ADCP also provides distance to the under-ice surface and backscatter intensity. The sector scanning sonar is used to evaluate distance from the ice and for locating krill swarms. The CTD provides backup data on ROV depth and documentation of hydrography. In addition to larval distribution, swimming behavior is also quantified. Stereogrammetry is used to measure swimming speeds and direction to obtain a vector for each individual every 1/30 s. To correct for background motion, the instantaneous vector for all particles in the field of view are ensemble- averaged and subtracted from each organism at 1/30 s intervals. Thus the swimming speed, direction and body posture, angle of attack, etc. is quantified as a function of body size and developmental stage.
Today's deployment (6 August) was
the first ROV observations for this cruise. We deployed in
Current position and conditions
Our work was completed in