Report of Activities on the RVIB N.B.
Palmer Cruise 02-04
August 27 was a day in which only
a modicum of progress was made in the transit from station 40 to one of the
stations on the Southern Ocean GLOBEC survey line 5. The original intent was to move to station
28, but there was essentially no progress in heading north from station 40 for
about 12 hrs. The pack ice was too tightly compressed. The Palmer
then headed to the west over a similar trackline to
that made coming into the station area and, with time for work in the central
grid sector running out, the decision was made to head for station 26
approximately 68 nm away. Advancement in
that direction in the ridge-ridden pack ice was also very slow and during the
day as a whole, the net distance traveled by the Palmer was 8.7 nm or 0.4 nm/hr.
In the evening, the Palmer stopped for about 3 hours to make
some of the measurements that had been scheduled for station 40 twenty-four
hours earlier. These included ice collection and an ROV under-ice survey, and vertical
net tows with the 1-m diameter Reeve net (for live animal collection) and a 1-m
ring net (for a quantitative collection). As we got underway, two XBTs were taken to get a temperature profile at the location. The frequent need to back and ram to make
forward progress prevented the deployment of BIOMAPER-II and no along-track
data were collected with the towed body on 27 August.
The early morning of 27 August
was heavily clouded and snow was still in the air. The clouds thinned around mid-day and the sun
was barely visible as a faint yellow ball. The clouds were still present late
into the night. The air temperature was relatively mild, ranging from -3ºC to -6.5ºC
during the day and the barometric pressure varied between 996 and 993 mb. The winds varied
between 15 and 25 kts all day, but they shifted from
northwest to west-southwest around
CTD Group report (Eileen
Hofmann, Bob Beardsley, Baris Salihoglu,
Chris MacKay, Francisco (
During the late hours of 26
August, while we were trying to reach survey station 28, a sudden change in
wind direction closed the leads that the ship was following. This resulted in considerable delay in our
plans to reach station 28, and the whole day of 27 August was spent trying to
get to station 28. As a result, no CTD casts were made during this time. This
gave us the time to analyze data from the stations that have been occupied and
to construct maps showing horizontal distributions of water properties.
The distribution of the
temperature maximum below 200 m showed the southern boundary of the Antarctic
Circumpolar Current (ACC), distinguished by the 1.6ºC isotherm flowing along
the outer boundary of the continental shelf. Temperatures greater than 1.5ºC
below 200 m correspond to Upper Circumpolar Deep Water (UCDW) and this was also present along the outer continental shelf.
A plume of UCDW intruded about 50
km onto the shelf towards
The vertical temperature section
for transect 6 which extends from off-shelf into the Marguerite Trough showed
modified UCDW (1.4ºC) present in the Trough with no apparent connection with
the warm water masses at the outer edge of the shelf. There are two possible explanations
for the existence of modified UCDW in the Trough. First, either the UCDW that
sits along the shelf edge moved across the shelf earlier this season or,
second, it is intruding through Marguerite Trough as also observed during the
NBP02-02 cruise. As we occupy more stations towards the north of the study region,
we will better be able to understand whether a similar intrusion into the
Marguerite Trough still exists or not.
Another water mass that was
observed off-shore of the shelf break at depths of 800 to 1000 is Lower
Circumpolar Deep Water (LCDW), which is distinguished by a salinity maximum of
34.72 at temperatures around 1.5ºC.
The surface horizontal salinity
distributions showed an increase of 0.3 relative to the NBP02-02 cruise. The
reason for the large increase in salinity is ice formation and brine rejection.
The dynamic topography which is
the vertical integral of the density anomaly, is a traditional method used in
determining the circulation. Although on the west Antarctic Peninsula
continental shelf the dynamic topography is weak because the density variation
is weak and the shelf is shallow (~500 m), the dynamic topography distribution
showed a clear pattern of an anti-cyclonic gyre toward the edge of the shelf.
The gyre was attached to the ACC, which flows to the northeast along the outer edge
of the continental shelf. Southwest of
this cyclonic gyre, part of another cyclonic gyre was observed which might have
formed by the meandering of the ACC.
Krill Physiology and Fish
Ecology (Jose Torres, Tom Bailey, Joe Donnelly, Melanie Parker)
The fish ecology/krill physiology
team has a number of missions. Each deals with the ecology or physiology of our
target organism, the Antarctic krill, or other important species in the
Antarctic marine ecosystem. Our ecological interests are concerned with where
the larger sizes of krill are located within our study area, as well as the
fish that eat them. Of course, we also want to know how many there are and at what
depth they reside at. In our last report
we described our main sampling tool, the MOC 10 net, and a little bit of what
we found. In this report we will tell you about our “physiology” mission. In later reports we'll tell you more about
what we've been finding in our nets and what we have seen on our under ice
dives in search of krill larvae.
For those of you who are
wondering what the biological term “physiology” means, it is the study of how
the different systems in animals work, both individually and in concert, to
form a working whole animal. For example,
we might be interested in how the digestive system works in krill, and how much
food they would need to grow and be healthy.
Much of what a medical doctor does is applied physiology, only on humans
instead of krill!
Our main focus on this cruise is
to look at the overwintering strategies of krill,
especially, the way krill use energy. It
is not only Antarctic krill that have to deal with lean times in the winter
months. Many marine and terrestrial
species also have to face food shortages. So, when we want to find out what the
krill are doing, we can first look to see how other species cope with the
problem. This may give us hints as to what the krill are doing.
It turns out that two main
strategies exist to deal with food deprivation. One way is to store energy as
fat for the leaner times ahead. The
storage strategy is practiced by animals as diverse as bears, caribou,
penguins, seals, and many crustaceans.
Another way to deal with lower food supply is to reduce metabolism by
entering a form of “hibernation”.
Hibernation, which can be thought of as a very deep sleep, reduces the
need for energy. Examples of this type
of strategy include some reptiles, such as alligators and freshwater turtles,
some amphibians, like toads, frogs, and salamanders, many insects that live in
cold climates, and some crustaceans. Many species, such as the hibernating
bears and the crustaceans, use a combination of fat storage and metabolic
reduction to survive the winter. Still others do nothing different; they
practice a “business as usual” strategy during the winter.
In the Antarctic, the most
fascinating species are the krill and little crustaceans that enter a form of
hibernation called diapause. The little crustaceans are called copepods.
They are about the size of a mosquito (no relation) and are important
herbivores not only in the Antarctic, but throughout the world's oceans. They can store up to 40% of their body weight
as fat in anticipation of the winter months.
In fall, many of the copepods sink from the surface to depths greater
than 400 meters and enter the dormant diapause state,
which is an even deeper sleep than what the bears do. They float there for months and when spring
comes, rise again to the surface to begin feeding and reproducing. We are not sure how they know when to wake
up, but they are most likely cued by the increasing light of the Antarctic
spring or late Antarctic winter. In fact, some of them are already beginning to
wake up now!
We still are not sure what the
star of our study, the Antarctic krill, does during the winter months. That is an important part of why we are here. From our study so far it looks as if many of
the older krill, the largest ones, are now located deep in the bays and fjords
of the
We are measuring metabolic rates of krill in our laboratory on the N.B. Palmer to see if larvae and adults do a “partial hibernation” to help them get through the winter. So far it looks as if krill drop their metabolism, or energy usage, by about 50% during the fall and winter months. When we get home, we will be measuring their fat content to see if they have stored enough to survive the winter without eating.
Seabirds (Chris Ribic and Erik Chapman)
The ship spent most of the day
backing and ramming on 27 August, trying to move out of
A summary of the birds and marine
mammals observed on 27 August (YD 239) during 7 hours, 9 minutes of survey time
as the ship traveled near station 40 is the following:
|
Species (common name) |
Species (scientific name) |
Number observed |
|
Snow Petrel |
Pagodroma nivea |
3 |
|
Adélie Penguin |
Pygoscelis adelii |
5 |
|
Antarctic Petrel |
Thalassoica |
8 |
|
Southern Giant Petrel |
Macronectes giganteus |
1 |
|
Crabeater Seal |
Lobodon carcinophagus |
8 |
ROV report (Scott Gallager, Phil Alatalo, Alec
Scott)
An ROV under-ice survey took
place at Station 49 on 25 August. The ice was characterized by broken and
re-frozen floes extensively rafted into many layers. The ROV went into the
water for a short deployment at 1719 and was retrieved at 1812. A problem with
the strobe light delayed the deployment 40 minutes as time was spent finding
some electronic parts and a new bulb to replace one that apparently had blown
out. We later discovered that the problem was not a blown bulb, but a
temperature sensitive part in the power supply and control housing for the 3D
VPR cameras and strobe. A few activated hand-warmers tossed into the housing provided
the extra heat necessary to keep the power supplies above 20ºC for this
deployment. We are working on building a ceramic heater to be installed in the
electronics housing for future deployments. No furcilia
were observed either on the relatively flat regions of the small floes or in
the rough, complicated environment of the rafted and buckled ridge lines. A few
small ctenophores were observed scattered throughout the area surveyed during
the dive.
After a day of intensive backing
and ramming the ship became free from the heavy grip of high pressure ice at
Station 40. A few miles away from Station 40, on our way to Station 28, we
stopped for an ice team and ROV deployment on 27 August at 67º 56.240′S; 70º
53.859′W. The air temperature was relatively warm at 6.2ºC, so the newly
installed ceramic heater in the power supply electronics housing of the 3D
camera system was not necessarily tested under extreme conditions. However, the
strobe functioned normally so we are hoping the heater has solved our immediate
temperature sensitive problem. The ice was characterized by large, flat floes
of first year ice about 70 cm thick. A ridge line appeared about 500 m on the
starboard side of the ship, but was too distant for the ROV to reach. The under
ice surface was quite smooth and dimpled, but without rafting of any kind. A
few cracks opened by ship activity showed the ice flow to be layered, but not
extensively, with colored material. One corer used by the ice team was observed
from below by the ROV. This observation was short lived as the corer was lost
at it fell through the ice and down to the sea floor. Another bore hole was
found after the ice team inserted a flag pole for the ROV to identify. One
ctenophore and one seal were observed, but no larval krill.
Current Position and
Conditions
This has been another day of
backing and ramming through 10/10 pack ice heading for station 26. We are currently about 16 nm from the
station. Our current position at 2200 on
28 August is -67º 20.722′S; -71º 40.807′W. The air temperature is -7.8ºC and the
barometric pressure is 1012.0 mb. Winds are <5 kts out of the west. It is cloudy, but visibility is good.
Cheers, Peter