Report of Activities on the RVIB N.B. Palmer Cruise 02-04
11-12 September 2002
The convoy with the L.M. Gould ended on 11 September when we reached the location chosen for the time-series station north of the northern tip of Renaud Island (-65º 11′S; -65º 35′W) and about 100 nm north of the northern most survey line on the SO GLOBEC station grid. The Gould remained in the area long enough to make some ice collections before heading off toward Palmer Station. The station was located very close to a small iceberg surrounded by pack ice. Water depths ranged from 530 to 735 m. At this station, a series of five sets of CTD casts were done within a 24-hour period. Simultaneous with the CTD casts was the acquisition of acoustic data with BIOMAPER-II, the ADCP, and the Simrad EK 500 echosounders. Both pairs of the BIOMAPER-II 120 and 200 kHz transducers were facing downward and the towed body was held at 10 m depth. In periods between the CTD casts, there were two ROV deployments and two 1-m MOCNESS tows, one each during the day and during the night. An under-ice dive was done in early afternoon. While the divers were away from the ship, BIOMAPER-II was deployed for calibration using standard target tungston carbide balls. In the late evening after the second MOCNESS tow, the pair of 1-m ring nets was deployed in the upper 10 m off the stern to collect furcilia for experimental work. The time series began at 0500 on 11 September and ended at 0400 on 12 September.
Steaming to the north resumed
with the next stop being Palmer Station, located on
The hike up the glacier along a flagged route was especially nice given the long period spent at sea. The low sun angle and variable cloudiness gave rise to a complex lighting that made the views from the top especially rewarding. The route led past a Weddell seal that had just given birth to a pup in an isolated place at the head of a small ice covered inlet. During the evening, personnel from both the Gould and the Palmer attended a barbecue at the very kind invitation of the station manager. It was a terrific spread and a great evening to share the cruise experiences with the station personnel and between personnel from the different vessels.
September 11 was a gray day with
low clouds and no sunshine. The winds were
light (<10 kts out of the west-northwest) and the
air was relatively warm (-1 to +0.4ºC). There was a mist in the air throughout the
day, but when the ice collectors were out on the ice, they stripped down to
shirt sleeves because of the relative warmth.
The visibility was low in the fog and mist. The barometric pressure rose
from 1010 mb in the early morning to 1017 mb in the evening and then plateaued. The high pressure continued into 12 September
with a peak of 1018 mb reached about 0900.
Temperature on the 12th continued to be remarkably mild reaching a high of +4ºC
while the N.B. Palmer was anchored in
CTD Group report (Eileen
Hofmann, Bob Beardsley, Baris Salihoglu,
Chris MacKay, Francisco (
September 11 was a busy day for
the hydrography group. We began work at the time-series station off
One objective of the science plan for September 11 was for the CTD group to sample close to an iceberg while the other groups characterized the biological distributions in the vicinity of icebergs. The first block of CTD/Rosette casts was made roughly 1 nm from an iceberg at about 0643 with the ship at -65º 11.04′S; -65º 33.86′W. Two other icebergs were within 1.5 nm and a total of 11 within 2.5 nm. To keep on the science plan schedule, just two casts were made to 400 m and no water samples were collected. These casts showed considerable structure in the upper 200 m, but the ice conditions there were no good for an ROV under-ice survey and ice sampling, the next two sets of measurements scheduled. Therefore, the decision was made to make a 1-m MOCNESS tow back along the ship's course towards the SW where thicker ice had been observed. Near the end of this tow, the ship again passed a small iceberg. When the tow was completed, the ship steamed back to this iceberg and set up for the ROV and ice sampling. The L.M. Gould was just completing ice sampling at a site near this iceberg, and reported that the conditions were good for ice sampling, since the ice had some flooding with interesting biology.
After the Palmer finished its morning ROV and ice sampling, the ship moved closer to this iceberg to start the second block of CTD/Rosette casts. The remaining blocks of casts were made at different sites close to this iceberg. Visual and radar measurements of this iceberg show it to be roughly oval in plan view, approximately 140 m long by 105 m wide, with an average height above sea level of 10 m. Assuming a constant plan form in the vertical, this iceberg should have extended down to roughly 90 m. For each block of casts, the Palmer was docked in the ice close to the iceberg, with radar ranges to the leading side of the iceberg varying from 0.159 nm (290 m) to 0.234 nm (430 m). These positions were located on different sides of the iceberg. While this iceberg was small, the waters around it were teaming with life. Dense scattering layers were observed, large samples of krill were collected, and seals and Emperor penguins were observed off the stern.
The depth of the Winter Water layer varied over the casts from a minimum of about 30 m to a maximum of almost 70 m. The shallowest Winter Water layer observed during the cruise, 30 m, was seen during the second set of CTD/Rosette casts The vertical temperature and salinity distributions from the second set of casts showed a gradual increase with depth rather than a homogeneous distribution that changes abruptly at the bottom of the Winter Water layer, as is typically observed. The different structure of the Winter Water layer at this site is suggestive of mixing of the upper water column with the deeper waters. Also, considerable small-scale variability in temperature and salinity, consistent with mixing, was observed in the Winter Water layer.
Below the Winter Water layer, temperature increased to a maximum of 1.43 between 550 and 630 m and remained at this temperature to the bottom. The salinity of the deeper waters was 34.69. These properties are characteristic of Upper Circumpolar Deep Water that has been modified by mixing with the overlying Winter Water and the Antarctic Surface Water that is present in the summer and fall.
Microplankton report (Phil Alatalo, Gustavo Thompson, and Scott Gallager)
With the exception of under-ice
and slush-ice sampling at dive sites and ice stations, the microplankton
observed during the period September
has been typical of the winter assemblage seen thus far. The following stations
have most recently been sampled in the northern sector of the survey grid:
stations 13, 12, 11, 10, 16, 15, 14, 23, 22, 21, 20, 19, 18, 17, 9, 8, 5, and
MOCNESS Report (Phil Alatalo, Peter Wiebe, Ryan Dorland, Dicky Allison, Scott Gallager, Gareth Lawson)
MOCNESS tow #18 occurred at dawn
on 11 September at a special station west of
The oblique net 0 contained mostly E. superba, copepods, and chaetognaths, with several siphonophores present. Individual specimens of krill were frozen for A. Bucklin and a bulk sample of krill was frozen for D. Costa. While copepods and chaetognaths were most abundant between 500 and 350 m, a diverse assemblage of ostracods, siphonophores, tomopterid worms, and radiolarians were observed. Net catches were sparse between 350 and 50 m. T. macrura were present between 200 and 75 m, with furcilia stages dominant between 100 and 75 m. Limacina sp. pteropods were particularly abundant between 150 and 75 m. Net 7 caught very high numbers of E. superba and a few amphipods. The surface net (25 and 0 m) contained very little zooplankton.
The second MOCNESS tow at the Renaud Island Station and the last one for the cruise took place in the evening of Sept. 11th. Results of tow 19 were similar to the morning tow except that a thick layer of krill at the surface resulted in extremely high surface biomass. While a full complement of other taxa was present at depth, in general biomass below the surface depths was low. Euphausiids dominated biomass and abundance at nearly every depth. Copepods were never abundant. While fishing net 4 (150-100 m) ice caught the towing wire, causing the instrument to drop to 202 m. Otherwise, the MOCNESS and OPC systems were successful.
Much biomass was obtained from
net 0. Euphausiids,
primarily E. superba, were dominant.
One large ctenophore was given to K. Scolardi and
several krill were frozen from this net for A. Bucklin's genetic analysis of
Antarctic zooplankton. Euphausiids were also frozen
for D. Costa and D. Chu for biochemical study and
acoustical study back in the
BIOMAPER-II group report (Gareth Lawson, Peter Wiebe, Scott Gallager, Phil Alatalo, Dicky Allison, Alec Scott)
On September 11, we deployed the
BIOMAPER-II six times, as part of the 24-hour time-series study done off
The other deployments made at the station were done in conjunction with repeated CTD casts. This allowed us to compare our acoustic measurements of the water column to CTD microstructure profiles, while simultaneously making observations of organisms as they passed under our transducers. Since the BIOMAPER-II was kept stationary at a depth of 10 m for the duration of each deployment, we did not attempt to capture any images with the VPR. The deployments were one to two hours long, and were performed at 0520, 1210, 1710, 2245, and 0230 (i.e., in the morning of September 12). Each time, noise from the bow thrusters being used to keep the ship in position for the CTD prevented us from making observations deeper than 150 or 200 m. Nonetheless, there was a strong indication of enhanced scattering in a thin band associated with the pycnocline.
During the first deployment, very little biological scattering was observed. By the second run, a backscattering layer had developed centered at 50 to 60 m. In the third deployment, a weak layer of backscatter was present very close to the towbody, but it wasn't until the fourth run that we saw any very strong signal. On this deployment, a very dense layer developed quite suddenly, extending from the depth of the BIOMAPER-II downwards by 5 to 23 m. For much of the time that this layer was evident acoustically, people working the CTD in the Baltic Room were able to actually see the krill swarm at the surface. During the fifth run, a somewhat weaker layer was evident between 14 and 30 m. On all deployments, the layers that we observed were highly variable in density and position in the water column.
While we were moored in
Current Position and Conditions
The trek back to