Report of Activities on the RVIB N.B.
Palmer Cruise 02-04
The search for a suitable site
for the Gould's second process
station continued into a second day.
Although we were not able to reach station 41 because of the tough pack
ice conditions, the nearby site that we had reached looked good from a
scientific perspective. It was not, however,
thought to be a safe place to base the Gould
given the pack ice's considerable drift over the past week and the potential
for the open leads in the area to close tight under unfavorable wind
conditions. During the late night period of 18/19 August, the Palmer and the Gould convoyed back to a location near grid station 42. There the Palmer started station work while
waiting for sufficient daylight to make an assessment about the feasibility of
that location as a process station. This
location was also deemed unsuitable and station 28 was targeted as a third
possibility. After the work was completed at station 42, the Palmer and Gould set out for station 28.
Heavy ice conditions blocked the approach to station 28 and in the
evening we ended up situated near station 27 instead. The site was also found wanting as a base for
the Gould. During the course of the late afternoon and
evening, discussions ensued between the Palmer
and the Gould about other locations
to assess. Near
August 19 was the coldest day yet on the cruise. There was a nice start to the day. In the morning around 0700, the winds were out of the northwest about 15 to 20 kts and the air temperature was -5ºC. The ROV was just coming on deck after its under-ice survey, the ice collectors had completed their sampling, and the CTD was about to be deployed. Within 15 minutes, the wind had changed direction to southwest and sped up to between 25 and 30 kts. The temperature fell rapidly. By 1200, the wind was up to 40 kts and the temperature had dropped to -18.3ºC. With the high winds, the wind chill on the deck was below -50ºC. During the late morning and afternoon under these brutal conditions, a 1-m and a 10-m MOCNESS tow and Tucker trawl were completed. Late in the afternoon after the trawl came on board, BIOMAPER-II was deployed for about two hours. The towed body was recovered when white-out conditions (blowing snow) forced both ships to stop for a time. Visibility was so poor that the Captain and mates on the Gould could not see to follow in the Palmer's keel water. The wind remained fierce (25 to 38 kts out of the southwest) into the night and the air temperature dropped down to -23.4ºC.
Coinciding with the wind shift
and temperature change was a similar change in the barometric pressure. It had
been dropping during the previous day and that continued until the wind shift
around 0700 where the pressure bottomed out at 966 mb.
For the rest of the day, the pressure rose and reached 987 mb
around
CTD Group report (Baris Salihoglu, Eileen Hofmann,
Bob Beardsley, Chris MacKay, Francisco (
Throughout the late hours of 17
August and during 18 August, we did an XBT survey during the north-eastward
transit to escort the Gould to the second
process site. The XBT transect started at the shelf break around survey station
74 and ended on the shelf west of survey station 41.
During the north-eastward
transit, usable temperature data were obtained from 11 XBT probes, either T-7
or T-4 depending on the depth, spaced at about 10 nm intervals. Additional
probes were dropped, but interference from the extensive sea ice cover caused
the wire to break prior to reaching the bottom or the maximum depth of the XBT.
Towards the middle of the transit
(between 67° 33.6'S 73° 17.9'W and 67° 30.6'S
72° 28.3'W) we started
experiencing very low ice coverage at the water surface and surface water
temperatures above freezing (~-1.82). This also helped the ship to speed up in
the open water.
After plotting the vertical
temperature distribution along the transit, it was observed that the
(relatively) warm surface waters coincided with an intrusion of warm (1.6-1.75°C)
Upper Circumpolar Deep Water around 400 m. This water mass is characterized
with temperatures above 1.6°C and it is generally located between 400 to 600 m
deep. As we got further on-shelf we started observing surface water
temperatures that are close to the freezing point of sea-water (-1.83°C to
-1.85°C) and this coincided with the high ice coverage.
During the April-May 2002
MOCNESS/ADCP/OPC Report (Phil Alatalo, Ryan Dorland, Peter Wiebe, Dicky
Allison, Scott Gallager, Gareth Lawson)
Diverse assemblages of organisms
continue to characterize the catch from MOCNESS nets at nearly all depths. Tow
#6 was a cold mid-morning deployment on Aug. 19th,
BIOMAPER II group report
(Gareth Lawson, Peter Wiebe, Scott Gallager, Phil Alatalo Dicky Allison, Alec
Scott)
The BIOMAPER II was deployed in
the early evening of August 18 for a two hour towyo
between stations 42 and 27. This was by far our most exciting (and
nerve-wracking) deployment to date as the wind was blowing at 40 knots, making
it difficult to keep the tow-body in position on deck, and bringing the
temperature with wind chill down to a bracing -51ºC! Scattering was low throughout
most of the water column, other than a weak layer coincident with the pycnocline at 90-110 m. Images that we captured with the
VPR suggest that this layer was composed of copepods. We also observed one
single denser patch of backscatter at 150 m, of unknown composition. At
present, only our 120 and 200 kHz transducers are operational. Since lower
frequencies are able to penetrate farther through water and our lowest
frequency transducers (43 kHz) are not working, we are currently limited to
looking 300 m from the tow-body. The body is generally towed between the
surface and 100 to 200 m, which means that we can make observations no deeper
than 500 m. On this particular occasion, we sent the tow-body down to only 100 m,
and with the bottom at 450 m, we were unable to determine whether the deep
layer observed close to the bottom two days ago was also present in this area.
Current Position and
Conditions
The convoy to station 43 ended
around
Cheers, Peter