Report of Activities on the RVIB N.B.
Palmer Cruise 02-04
The deep water work at offshore
station 13, which was begun in the evening of 2 September, continued into the
early morning hours of 3 September. The CTD, back from a cast to 2934 m, was
brought on board about 0100. The ROV was
deployed between 0130 and 0300 to complete the work at the station. BIOMAPER-II
was deployed for the short 8 nm run to station 12 located on the edge of the
continental shelf. The ROV was again
deployed for a brief under-ice survey followed by a CTD cast. Both were
completed by 1000. A 1-m MOCNESS tow was attempted, but electrical problems
forced the tow to be rescheduled for the next station. BIOMAPER-II was towyoed between stations 12 and 11 and seabird and mammal
observations were made along the route.
As the Palmer approached station 11 around 1400 hours, a large group of Adélie
penguins was spotted. BIOMAPER-II was
quickly brought on deck and then the stalking began. The goal was to
temporarily capture some of the birds in order to deploy the remaining four
satellite tags and to diet-sample some of the birds. The ship moved up on the
birds, which were all together at one side of a moderate sized floe. The ship
stopped when they became a bit restless. The personnel carrier on the Palmer's bow was rigged and then the
first group of four penguin handlers went over onto a flow next to the ship
with an assortment of collecting nets and other gear. A second group of three
went immediately after. With seven handlers on the pack ice armed with nets and
long metal rods to check for ice thickness, they set off. Slowly making their way across several floes,
the handlers were spread out in a circle around the group of penguins that were
alarmed but not moving. Heidi Geitz, a lead scientist in the group made the first move on
the birds and they fled onto another floe where the other group of handlers was
waiting. Penguins are not smart about
getting away and they tend to run around in circles. A number were caught right off and then after
the remaining penguins stopped a short distance away, a second foray netted
more. In the end the handlers managed to
catch 9 birds out of fourteen that were on the floe when the hunt started. The
birds were brought back to the floe next to the ship and they were measured,
weighted, tagged, and diet-sampled over a two-hour period. It was a very
successful effort.
The work at station 11 also
included two CTD casts, a 1-m MOCNESS tow, a drift net collection for krill furcilia with the two 1-m ring nets, and a Tucker trawl.
This work was completed just before
The weather during the day
provided good working conditions. There
was a lovely sunrise in spite of the high clouds that covered the sky. The sun painted them an attractive orange
color and the seascape added to the scene with icebergs dotting the horizon.
The low clouds persisted during the day, but scattered breaks allowed a fair
amount of sunlight to come through. There was a light fog in the area that
reduced the visibility a bit. The air
temperature rose during the morning peaking about -3ºC at
CTD Group report (Eileen
Hofmann, Bob Beardsley, Baris Salihoglu,
Chris MacKay, Francisco (
Beginning in late evening of 2
September and extending into 3 September, a CTD/Rosette cast was done at
station 13, which is the outer-most station on survey transect 2. This was a deep cast to 2934 m and as a result
the FRRF and CMiPS instruments were removed.
Following this station, CTD/Rosette casts were done at stations 12 and 11 on
survey transect 2 as the survey sampling moved back onto the continental shelf.
Station 12 was in 899 m of water
at the shelf edge. As a result, the FRRF
sensor was not placed on the CTD/Rosette.
The CMiPS was re-installed on the CTD/Rosette
for this cast and the lowering speeds in the upper 200 m were set for optimum
sampling with this instrument. Station
11 was on the continental shelf in 467 m of water. At this station two casts were done. The first was to 300 m with lowering speeds
appropriate for CMiPS. The second was to within a few meters of the
bottom and the lowering speeds in the upper 100 m were optimum for the FRRF.
The vertical hydrographic
structure at station 13 showed what is expected for an oceanic station. The Winter Water layer was about 60 m deep
with a temperature of -1.81ºC to -1.80ºC.
Below this, temperature increased to a maximum of 1.72 at 275 m after
which it decreased in a monotonic manner to 0.38ºC at the bottom. The maximum salinity of 34.726 was at 680 m
and the bottom salinity was 34.70. These values indicated the presence of Upper
and Lower Circumpolar Deep Water. This station
was just on the inshore side of the southern boundary of the Antarctic Circumpolar
Current because the 1.8ºC isotherm was not crossed.
At the shelf edge station (number
12) the surface waters were at freezing (-1.80ºC to -1.81ºC) and the Winter
Water layer extended to about 75 m.
Below this, temperature increased to a maximum of 1.71ºC at 440 m, after
which it decreased to 1.19ºC at the bottom.
Salinity was at a maximum of 34.726 at 815 m. Thus, the water mass structure at this station
was similar to that observed at station 13.
The water column at station 13
showed temperatures in the upper 10 m to 15 m that were above freezing (-1.79ºC
to -1.78ºC). Temperatures below this were near freezing (-1.81ºC to -1.80ºC). The maximum temperature at this station of
1.58ºC was found at 350 m. The
corresponding salinity was 34.703. Below
this, temperature decreased to 1.41ºC at the bottom. Bottom salinity was 34.71. Again, this vertical structure indicated the
presence of both Upper and Lower Circumpolar Deep Water.
Station 13 was the first to show
structure in the fluorescence vertical profile from the fluorometer
mounted on the CTD. During the downcast,
a maxima in fluorescence was observed between 30 and
40 m. On the upcast,
three Niskin bottles were closed at this depth to
obtain water for analysis by the Daly group.
A second maxima in fluorescence was observed
near the bottom. Again the Daly group
took water from the Niskin bottles closed at this
depth for further analysis. These additional
water samples, when combined with the data from the standard depths used for
chlorophyll analysis, may provide insight into what is causing the observed
signal in fluorescence.
The vertical profiles from the
CTD casts made on 3 September suggested that there is an intrusion of
Circumpolar Deep Water in the northern part of the survey grid. The spatial distribution of this intrusion will
be refined as data are acquired from the remainder of survey transect 2 and
survey transect 3.
Seabirds (Chris Ribic and Erik Chapman)
Seabird and Crabeater seal
surveys were conducted for just over 3 hours on 3 September as the ship
traveled toward
The same species assemblage was
observed today as during previous days off the continental shelf, near the
ice-edge. Snow Petrel, Antarctic Petrel,
Southern Fulmar, and Kelp Gull were all recorded in the survey. Bird abundances were noticeably lower as we
moved further inshore and into the pack ice.
Adélie Penguins continued to be observed, however, and several groups of
birds were observed later in the day in the denser ice-cover and larger floes.
At about 1400, a group of 22 Adélies was observed about 800 m off the port side on a 30
m diameter floe. The decision was made
to attempt to catch birds in order to diet sample the birds and to attach the
final satellite transmitters brought down by Dr. William Fraser's group that is
studying Adélie Penguin foraging ecology.
After being lowered onto the sea-ice, we managed to capture 9 of the 22 Adélies, of which 5 were diet sampled and 4 were fixed with
satellite tags. Diet samples consisted
of 100% adult krill (Euphausia superba),
most of which were between 40 to 45 mm in length.
A summary of the birds and marine
mammals observed on 3 September (YD 246) during 3 hours, 3 minutes of survey
time as the ship traveled between stations 12 and 11 is the following:
|
Species (common name) |
Species (scientific name) |
Number observed |
|
Snow Petrel |
Pagodroma nivea |
8 |
|
Antarctic Petrel |
Thalassoica |
1 |
|
Southern Fulmar |
Fulmarus glacialoides |
1 |
|
Kelp Gull |
Larus dominicanus |
2 |
|
Adélie Penguin |
Pygoscelis adelii |
31 |
|
Crabeater Seal |
Lobodon carcinophagus |
1 |
Marine Mammal report (
As is usual in this white ice
covered region surrounding the Antarctic continent, during the past several
days we have experienced very different and variable weather conditions. The 30th of August was a stormy day with
heavy snow fall and strong winds (45 to 55 kts),
which would not let us see farther than the bow and made us heave to for the whole
day. In contrast, 2 September was a
sunny “warm”, light wind day where air temperatures reached 0.6ºC. Also during
the last few days, we have gone from inshore to offshore stations with ice floe
size and thickness varying considerably. This ranged from first year ice of about
90 to 120 cm thick and 10/10ths coverage to pancakes and young gray with
5/10ths coverage and wide leads of open water. The former significantly
affected the vessel track while the latter did not. Since 28 August, 32.9 marine mammal
observation hours were logged of which 18.6 corresponded to “effective effort”.
The survey was affected mainly by
weather conditions and interrupted during stations. No marine mammal survey was performed during
29 and 30 August, since weather conditions did not permit it and therefore no marine
mammals were seen. After the storm on 30 August, the afternoon of 31 August was
better both for navigation and surveying.
Only two Crabeater seals (Lobodon carcinophagus) were seen, at 1451 and at 1534. Both seals were hauled out on the ice. On 1
September, 9.4 hours of observation were logged, with 5.6 hours of “effective
effort”. Even though there were good
viewing conditions, no cetaceans were seen, but four seals were sighted in four
different occasions (at 0829, 1334, 1612 and 1728). Two of the sightings were
of Weddell seals (Leptonychotes weddellii)
and the other two were too far away for identification. One of the Weddell
seals observed (at 1334, -65º 59.65′S; -70º 43.96′W) was very close
to the ship (less than 50 m). It was a very massive animal, probably more than
3 meters long.
For almost a week we had to wait
to be delighted with the sight of whales again. On 2 September, two whales were
observed in two different sightings. One of them was made by Nancy Ford in
early morning (identification unclear) and the second whale, a minke whale (Balaenoptera acutorostrata),
was observed at 1628 (-65º 59.42′S; -71º 07.00′W), at 0.78 nm and
90º to starboard. It surfaced for a few minutes in a medium-sized lead of open
water (an ice berg wake that was 100 m long).
It then made a long dive (a characteristic behavior of minke whales is
that often they arch the tail stock high above the surface when beginning a
long dive). Twenty-four crabeater seals were seen during the day, all of them
hauled out on the ice. Twenty-one of these seals were seen between 1600 and
1700. The whale and most of the seals observed during the day were seen within
the same area, a pattern repeated on other occasions on this cruise. This might
be a good indicator of areas rich in food resources such as krill, which is a
prey item shared by both Crabeater seals and Minke whales.
Almost 9 hours of observation
were made on 3 September, but only 3.2 hours of “effective effort” due to time
spent on station. One Minke whale was seen (by Kathleen Gavahan)
at 1640 while at station 11, during the CTD cast. Three crabeater seals and one Weddell seal
also were observed. The survey of marine mammals has now logged 110.3 hours of “effective
effort” out of 233.9 hours of observation (47.15% of “effectiveness”).
Thirty-four sightings have been achieved up to date, counting 56 whales in
total, almost all of them Minkes (Balaenoptera acutorostrata). As the days get longer,
more observation and effort hours are being achieved.
ROV report (Scott Gallager, Phil Alatalo, Alec
Scott)
On 3 September there were the first back-to- back ROV deployments of the cruise. One was done at offshore Station 13 (ROV18)
and the other at shelf break Station 12 (ROV19). At Station 13 (-65º 59.793′S;
-71º 03.421′W), the ice was characterized by small floes drifting with
the wind and separated by narrow open leads and brash. An ocean swell caused the
floes to remain separated rather than re-freezing into a consolidated mass. The
ROV was deployed at 0150 local time. There were small numbers of furcilia drifting throughout the area, but they tended to
be concentrated up in the open leads and brash, and along edges of the broken
floes. Concentrations were low, approximating 1 to 10 per cubic meter. Four or
five ctenophores and some amphipods were also present in the area.
The second deployment of the
morning was at station 12 (-66º 06.163′S; -70º 52.343′W). The ROV
was deployed at 0712 local time just as first light appeared on the horizon.
Ice conditions were very similar to those of Station 13 - small floes held
apart by ocean swell. There were many more furcilia
at this station, but unlike the previous location, the larvae were located at
depth beneath the deepest ice projections rather than in the open leads and
brash. Given the early morning conditions, it is possible that the larvae
migrated to deeper regions of the ice pack (10 m). However, we have not
documented vertical migration in krill larvae and we suspect that there is
little if any effect of time of day on their distribution. One striking feature
of this station was the varied size structure of the larval populations. Furcilia stages 4 through 6 and even some juveniles were
present synoptically. A Reeve net tow made immediately before this deployment,
however, provided evidence for juvenile euphausiids
of Thysanoessa
sp. rather than Euphausia superba. The
species of the larger krill observed by the ROV remains a question.
BIOMAPER II group report
(Gareth Lawson, Peter Wiebe, Scott Gallager, Phil Alatalo, Dicky Allison, Alec
Scott)
On September 3 we conducted two
relatively short BIOMAPER II towyos, first in the
early morning between stations 13 and 12, and later at mid-day between stations
12 and 11. During the first tow, a diffuse shallow scattering layer was present
between 20 and 75 m. With the VPR we observed krill, copepods (including Calanus),
radiolarians, one ostracod, one chaetognath,
and diatoms in this depth range. Deeper in the water column, generally between
225 and 300 m, there were a number of large patches of moderate scattering
intensity (-75 dB) that were as long as 2.5 km.
During the second towyo, we observed very little scattering. An extremely
diffuse shallow scattering layer was present between 25 and 75 m. Images
captured with the VPR suggest that this layer was composed of many diatoms, and
some krill. Just below the acoustic layer (75 to 85 m), the VPR also observed
numerous ctenophores. For much of the transect, the
shallow layer showed enhancements in backscatter at fairly regular intervals,
at times reaching levels as high as -60 dB. The regularity in the alternation
between these areas within the layer of high and low scattering suggests the
possible presence of vertical circulation cells: vertical current structures
that serve to concentrate planktonic organisms (and
hence backscatter) in distinct vertical bands.
When seawater freezes it leaves behind its dissolved salts, in a process
called brine ejection. This results in denser water at the sea surface than
deeper in the water column, leading to downwards movement of surface waters and
the formation of circular current cells.' Such a process could be at play in
this region.
Current Position and
Conditions
Work at station 16 is nearing
completion and we will soon be moving towards the outer continental shelf again
headed for station 15. Our current position at 2216 on 4 September is -66º
44.913′S; -70º 05.174′W. The
air temperature is -15.3ºC and the barometric pressure is 1004.2 mb and holding steady.
Winds are light at around 10-12 kts out of the
south-southwest (207), as they have been for more than 24 hours. Skies are
partly cloudy; visibility is good. The
pack ice is much more consolidated here in the middle of the continental shelf
and is made up of larger flows than offshore.
There are, however, some very large leads in the area making it fairly
easy to move between stations.
Cheers, Peter