Report of Activities on the RVIB N.B. Palmer Cruise 02-02
10 May 2002
Some 27 days after starting the broad-scale sampling on the
Southern Ocean GLOBEC survey grid, the last two stations were reached and
sampled on 10 May. At on the
10th, the N.B. Palmer had traveled
2544 nm (5596 km) since leaving
The transit along survey line 13 to stations 91 and 92 was entirely in the pack ice, although it was fairly new and not difficult ice to work in. And it was another day of clear, cloud free skies and moderate winds. The barometric pressure, which decreased to a low of 992 mlb around of 8/9 May began slowly rising during the day and reached a high of the day around of 1000.7 mlb. Winds were out of the south and below 20 kts most of the day. They dropped to around 5 kts late at night. Air temperatures remained quite cold, ranging between -15.5ºC to -12.6ºC.
On May 10, the work completed at broad-scale survey stations
91 and 92, included 2 CTD casts, one at each of the stations. A MOCNESS tow was taken at station 92 along
with an ROV under ice survey and an ice collection. BIOMAPER-II was in for transits between the
stations. Seabird and marine mammal surveys took place during the daylight
period and 1 sonobuoy was deployed during the long
transit between stations 92 and 51 on the way back to
Following the completion of the sampling, the Palmer set a course to the northeast following a set of way points designed to provide new SeaBeam bathymetry data along a path that approximated the zone in which the highest krill layers and patches were found. It also was across areas where deep uncharted canyons (> 1000 m) were believed to exit.
With the grid completed, a number of tasks that needed to be
done before reaching port came into focus.
During the past 24 hours, a chart of the survey region and points north
as far as Palmer station was up in the main lab for individuals in the scientific
party to express their ideas about where and what they wished to do with the
remaining ship time. These ideas were
consolidated into concrete geographical positions and activities, and a draft
of the plan was presented at the science meeting held in the 03 lounge. Most of
the scientific party and Captain Joe and Chief Engineer J. Pierce were able to
make the meeting because at this hour most individuals on the different watches
were up. The stated desires for post-grid work involved a number of locations
CTD Group report (John Klinck, Tim Boyer, Chris Mackay, Julian Ashford, Andres Sepulveda, Kristin Cobb)
The CTD group did two stations on 10 May on the middle and inner part of the 020 line (survey line 13) at the southern end of the grid. The mid-shelf station (91) had continuously increasing, but weak, stratification to 300 m, while the inner station showed a very deep, freezing surface layer over a clear pycnocline. Energetic layers were seen in the pycnocline at both stations. The deep water was very cold indicating no oceanic influence.
Station 91 (cast 95, 406 m). The surface layer was composed of two 15 m thick layers, which sat above a very weak pycnocline down to 200 m. The pycnocline had numerous temperature layers with thicknesses ranging from to 20 m. Considerable salinity variability was also evident. There was a deep temperature maximum (1.4ºC) at 300 m.
Station 92 (cast 96, 418 m). There was a uniform surface layer to 85 m (-1.72ºC, 33.4 psu, 0.05 ug/l chlorlophyll). Three warm temperature layers (10-15 m thick) occurred between 100 and 150 m. The bottom temperature was 1.1ºC with no temperature maximum.
Microstructure Profiler (CMiPS) report (Chris Mackay)
May 10 marked the end of the CTD grid. CMiPS has been installed on the CTD for most of these stations and has worked well, in the background, not interfering with the work or schedule of the CTD. Analysis of various samples of data have indicated it's ability to detect and measure double diffusion, which was a major objective. In addition, data from CMiPS have been used on a few occasions to confirm a feature in the water column detected by the CTD. Over the last week, CMiPS was found to be detecting a 15 Hz vibration with its pressure sensor. One possible source has been identified as the wake from a stainless steel rod in the frame around the SeaBird pressure case. This rod has now been modified with tape to change its wake and confirm whether it is an influence. Additionally, CMiPS has been rotated 180º in its mounting bracket to position the pressure port away from this noise source. During operations on the grid CMiPS has generated nearly 1.5 gigabytes of data which will take some time to process after the cruise.
Marine Mammal report (Debra Glasgow)
May 10, a crisp, clear morning at -12ºC, found us stopped in the ice at the last station (92) of the grid for CTD and Sea Rover work under the ice, and a MOCNESS tow. An incidental survey began while the MOCNESS was being towed at 2 knots just after lunch at 1319, which changed to On Effort survey when the Palmer began the transit north east to the first way point off the grid. Eighteen crabeater seals were counted lying on floes in groups of 2 to 6 near small open pools throughout the day. The ice consisted mostly of young grey ice and nilas bound by many icebergs mixed with some medium size first year floes and brash with rafted pancake. You could see the ice forming around us when we were stopped on station and it grew progressively thicker as the day wore on. The wind chill stayed around minus 30 degrees all day limiting outside movement as winter was gaining a good grip in this region. The sun disappeared below the horizon at 1535 and the survey ended in poor light 41 minutes later at 1616. There have been 40 total cetacean sightings for the voyage to date, consisting of 86 animals.
Sea Birds (Erik Chapman and Matthew Becker)
Survey time on 10 May was limited to just under an hour as the ship left the final station of the grid and headed north. Although we are finished with the survey grid, we will continue to collect survey data as the ship moves through the study area. Because much of the study area is now covered in ice, this will provide a unique opportunity to survey the same area immediately prior to, and following the onset of pack ice. Today's survey, however, was still in ice as the ship headed north from station 92. A MOCNESS tow and a survey from the ROV Sea Rover indicated adult krill at the surface at station 92.
Adélie Penguins were seen in this survey and were likely
feeding on the krill observed near the surface at station 92. We would like to be able to confirm or deny
this assumption by diet sampling Adélies in the ice. Unfortunately,
this may prove to be a difficult task considering the low abundance of Adélies in this area.
Even if we do see more Adélies, it will not be
easy to capture them as the birds seem to be using areas where ice is not
workable using zodiacs or on foot.
However, we will continue to look for opportunities to diet sample Adélies in ice in
A summary of the species and number of individuals of birds and seals within the 300 m transect during 56 minutes of daytime surveys between consecutive stations 92 and 51 is the following:
Species (common name)
Species (scientific name)
ROV Under-Ice Investigations (Andrew Girard, Amy Kukulya, Gaelin Rosenwaks, Philip Alatalo)
Having encountered ice on a more frequent basis towards the
end of the cruise, the Sea Rover ROV was deployed on a more frequent basis. Deployments
were made on the western side of
ROV 3 was deployed at station 76 outside
Great success was eventually achieved during ROV 4, although not immediately. An evening attempt on May 7th was abandoned due to ice and weather conditions. Thin new ice at station 84 was interspersed between long leads of open water. Wind speeds averaged 20 kts with gusts to 28 kt, causing the ship to free drift at about 1.5 kt. It was decided to postpone this investigation for more favorable conditions. By the next station, No. 85, wind had dropped and the ice was thicker, allowing the ship to "park" in the ice with the stern in ice-free water. ROV 4 deployment was shortly after sunrise at 1028. Most of the survey lines were conducted under the thinner ice bordering a small berg on the starboard side of the Palmer. Following the first survey, line, three floats were removed from the cable to assist in buoyancy control. During the remaining surveys, it became apparent that the starboard thruster was weak and nearly inoperative. The Rover's CTD ceased functioning as well. The ROV cameras captured images of single and small groups of krill furcilia congregating amongst contours formed under older ice; smooth, newly forming ice had far fewer furcilia. Excellent footage of swimming behavior was recorded, including distinct motion of pleopods, the swimming appendages of krill.
The Sea Rover ROV was picked up by the starboard aft crane at 1150. Onboard a thorough examination of the ROV provided some answers to the buoyancy and steering difficulties. Through Herculean efforts, Amy Kukulya and Andy Girard repaired, replaced, or rebuilt starboard and port thrusters, which had leaky O-rings and therefore had seawater in the hydraulic lines. A center ballast weight that had been lost was replaced, an up-looking orientation light was installed, and the CTD battery was serviced by Romeo LaRiviere.
ROV 5 deployed on the shelf at station 88 on May 9th at 0434 in cold (-11.5ºC) and windy (21-24 kt) conditions. Consolidated pancake ice constituted the surface ice conditions. On the first survey line, the ROV was returned to the ship for re-ballasting again. (Attaining proper trim is difficult due to the changing amount of tether cable that is paid out; minimizing the use of thrusters on the vehicle is important to avoid disturbing the layer of seawater under the ice.) However three nice survey lines to starboard were conducted, all approximately 35 m from the ship. The under-ice surface was a continuous sheet, though the ice edge curled downward making for a tricky entry from the ship's lead. Fine structure of the smooth surface appeared eroded: no crevices or sharp definition. Only a few krill furcilia were observed in this deployment. Retrieval occurred at 0555.
At the last grid station (92), the ROV conducted a dawn
survey at 1005. Temperatures were -11.5ºC,
but wind was light with sunny, clear skies.
The ice pack here at the tip of
Zooplankton (MOCNESS/BIOMAPER-II) report (Carin Ashjian, Peter Wiebe)
The 22nd MOCNESS tow was conducted on 10 May at station 92
just offshore of
The BIOMAPER-II run from station 90 to 91 started on 9 May and ended just after on 10 May. During that transit, a relatively weak bottom layer with a vertical thickness of about 100 m was present coming into station 91 and about an hour prior to arrival several large near surface krill-like patches occurred, as noted in the 9 May report. This kind of patchiness also was observed during the transit between station 91 and 92 in the upper 40 to 80 m of the water column. The deep bottom layer, which was strongest between 400 and 300 m, intensified significantly on the approach to station 91 and continued strong all the way to station 92. At the bottom of at least one towyo, BIOMAPER-II was in the top of the deep layer and the VPR collected images of large copepods supporting the idea that a dominant group of zooplankton living in that layer is overwintering copepods.