Report of Activities on the RVIB N.B.
Palmer Cruise 02-04
The N.B. Palmer and the L.M.
Gould were finally able to rendezvous during the morning of 31 August in
the vicinity of station 22. The high winds and white-out conditions that had delayed
the meeting of the vessels had abated some by the late evening of 30
August. While there was still some snow
falling, the winds were down in the 20 kt range and a
transfer of personnel and equipment was possible prior to beginning the third
convoy. This transfer took place by zodiac boat in a large lead about 0930 and
was completed by 1100. Three people from
the Gould came over to the Palmer along with their gear and personal
effects for the duration of the survey of the northern sector of the Southern
Ocean GLOBEC grid. Two, Heidi Geitz and Bret Pickeral, are part
of Bill Fraser's penguin group. They
came to the Palmer in order to
enhance their opportunities to deploy the remaining five satellite tags on Adélie
penguins encountered during the survey.
The Gould's process stations
do not afford as much opportunity. An
extra personnel basket to be deployed from the Palmer's bow for use by the penguin group was also transferred
temporarily, since the Gould had two
of them. The other person to make the transfer was Chris Fritsen,
who works on sea ice microbiota. He wanted more access to the variety of pack
ice types that are likely to be encountered during the survey of sector three.
The convoy got underway for the
~50 nm steam north toward station 4, the intended location for the third
process site. Along the trackline at approximately 10
nm intervals, XBT's were dropped to vertical temperature
profiles. About an hour and a half into the journey a group of Adélie penguins
was sighted swimming in a lead. One
hauled out onto the pack ice, while the others disappeared. A Zodiac was launched from the Palmer with a group of the seabird
specialists and within 45 minutes the penguin had been netted and tagged. It was a good start for the work in the
northern sector. While the Zodiac was
out, the pair of ring nets was deployed off the stern in the upper 5 to 10 m in
hopes of collecting more krill furcilia for
experimental work, but time was short and few were caught.
The transit to station 4 went
remarkably well primarily because the pack ice was somewhat thinner and there
was more open water around the floes. More importantly, the floes themselves
were broken up into smaller pieces that were easy to move through. As we got close to station 4, a long period
swell running from the north under the pack ice became evident. Along with the
high winds of 30 August, the swell was also playing havoc with the pack ice. In
an evening radio communication with the Gould,
it was clear that they had not seen pack ice that was suitable for staging a
third process station. The storm on the
30th had broken up all of the big floes and loosened up all of the pack ice to such
an extent that it would be hard to put people on the ice and take cores for an
extended period of time as required for a time-series station. Unfortunately, better conditions did not
appear to be anywhere close, so the convoy continued on to station 4. We
arrived there about
During the evening of 31 August,
there was a scientific investigator's meeting to discuss the station work for
grid sector three. There was consensus
that after station 4, the work would proceed out to station 1 and then back
south along the continental shelf to station 23. The most inshore stations
would be approached after that and work at them would be done to the extent
possible.
The remnants of the 30 August
storm were present through the late night period of 30/31 August. After that
winds dropped below 30 kts by 0600, but a light snow
persisted. The air temperature, which reached a high of +0.6ºC stayed around 0ºC
until mid-afternoon when a wind shift from northeasterly to westerly took place. Then the temperature dropped over several hours
down to about -5ºC. The wind shift and
temperature change corresponded with a shift in the barometric pressure from
falling to a minimum of 974 mb to rising slowly. By
the end of the day, winds were in the
CTD Group report (Eileen
Hofmann, Bob Beardsley, Baris Salihoglu,
Chris MacKay, Francisco (
In the early morning of 31 August
the weather conditions cleared sufficiently for the Palmer to resume the transit to meet the Gould and move it to the next process site. Soon after getting underway, the CTD group
began an XBT survey which continued throughout the day and ended in late
evening when the site selected for the next process station was reached. A total of ten XBTs
were dropped along the transit at about 10 nm intervals. Of these, seven were T-7 probes with a
nominal depth of 760 m; the remaining three were T-4 probes which have a
nominal depth of 460 m.
Because of the sea ice, the wire
for three of the XBTs broke before the probe
encountered the bottom or reached its maximum depth. The data from these casts provided
measurements of the upper water column; however, the casts were repeated to
obtain a full temperature profile. The remaining seven XBTs
returned temperature data from the full depth of the probe or until the bottom
was reached.
The start of the XBT survey was
near station 13 on survey transect 2 from which it extended in a
north-northeast direction towards survey station 4 in the mid-portion of
transect one. As a result, the XBT survey
cut across the portion of the northern part of the survey grid where previous
SO GLOBEC cruises have observed onshore bottom intrusions of Circumpolar Deep
Water.
Temperature profiles from the
first
The surface temperatures along
the XBT survey were above the freezing point, with the warmest temperature of
-1.72ºC occurring at the north end of the transect. The depth of the well-mixed Winter Water
layer along the transect was about 60 m. This is the warmest surface water and
shallowest Winter Water layer encountered during the survey. These upper water
column characteristics may result from mixing of the surface waters with the
warmer water at depth. This process also
likely contributes to the reduced sea ice cover and extensive areas of open water
that have been encountered during this transit.
Seabirds (Chris Ribic and Erik Chapman)
On August 31, a seabird and
Crabeater seal survey was conducted while the N.B. Palmer traveled toward station 4 in convoy with the L.M. Gould from the starting point near
station 22. This survey 40 to 60 miles offshore
brought us to the northern-most section of the grid where ice conditions were
dramatically different from those farther south. Ice concentration varied between 6 and
9/10ths coverage of vast floes and small floes separated by areas of open
water. Sea-ice thickness varied considerably,
from 40 cm to more than 1 m. As noted
above, XBT data in this area has indicated the presence of warm water
associated with the Antarctic Circumpolar Current, which may be responsible for
maintaining the considerable open water and thin ice here. Through much of the day, a swell of 1.5 to 2
m ran through the pack as a reminder of the storm we've experienced over the
last two days and perhaps an indication of our relatively close proximity to
the ice edge. The seabird species assemblage here differed dramatically from
those in areas of the grid farther inside the pack ice. We saw more species and birds on 31 August
that on any previous day of the survey and we saw species that are typically
found in open water and species that are typically associated with
sea-ice. The open water species observed
included the Southern Fulmar and Blue Petrel.
We also saw a single adult Kelp Gull, a species that typically remains
close to land that may have moved farther offshore toward the ice-edge as the
pack ice continued to be compacted inshore.
A single Southern Giant Petrel was also recorded in today's survey. Satellite telemetry of Southern Giant Petrels
on the
A group of at least 30 Adélies was recorded porpoising
through a large lead. One individual
from this group hauled out on a floe and we were able to assist birders from
Dr. Bill Fraser's group fix this bird with a satellite tag that will record
dive-depth and location for this bird over the next several weeks. An Emperor Penguin was also observed in a separate
lead. No seals were observed in today's
survey.
A summary of the birds and marine
mammals observed on 31 August (YD 243) during 4 hours, 21 minutes of survey
time as the ship traveled near station 4 from near station 22 is the following:
|
Species (common name) |
Species (scientific name) |
Number observed |
|
Snow Petrel |
Pagodroma nivea
|
54 |
|
Antarctic Petrel |
Thalassoica |
30 |
|
Southern Fulmar |
Fulmarus glacialoides |
4 |
|
Blue Petrel |
Haobaena caerulea |
1 |
|
Kelp Gull |
Laru dominicanus |
1 |
|
Southern Giant Petrel |
Macronectes giganteus |
4 |
|
Adélie Penguin |
Pygoscelis adelii |
30 |
|
Emperor Penguin |
Aptenodytes forsteri |
1 |
Krill distribution, physiology,
and predation (Kendra Daly, Kerri Scolardi, Emily Yam
and Jason Zimmerman)
We deployed the Tucker Trawl
three times, towing it repeatedly between the surface and about 30 m in
depth. Although this sampling strategy yielded
about 20 larval Euphausia superba per
tow, small ice chunks caught in the towed net damaged many of the animals. We decided instead to deploy the Reeve Net
and the Ring Net in tandem (the Reeve Net attached to the cable about 3 m below
the Ring Net) at about 10 and 7 m, respectively, below the stern. Using this
method we collected a couple of hundred E.
superba and E. crystallorophias
larvae in excellent condition. The
larvae were furciliae stage
Based on net collections and
diver and ROV observations to date, larval krill appear to be distributed very
differently from our last winter GLOBEC cruise.
In contrast to the high densities of larvae concentrated under sea ice
last year, this year larvae are scare and may be primarily in the upper water
column. Instead of feeding on sea ice
biota, which is present on the undersurface of sea ice thus year, they may be
feeding on aggregates in the surface layer.
The chitinous outer exoskeleton of krill is
relatively transparent, so we can see food in their stomachs if they have been
feeding recently. Most of the larvae collected
had small amounts of material in their guts and intestines, in contrast to
larger krill, which seldom had material in their stomachs.
We are currently measuring growth
and molting rates on the larval krill.
We completed experiments to measure ingestion and egestion
rates of larvae using surface seawater as a food source. The furcilia produced
numerous fecal pellets (egested unassimilated material after feeding) over the
time period of the experiment, indicating active feeding. Although chlorophyll concentrations are
relatively low (0.02 g L-1) throughout the water column, sticky
aggregates of detrital material and microplankton are present in near surface waters. These aggregates are composed of varying
material. Many are radiolarians with a
silica “lattice” outer framework, remaining from a fall bloom, some are larvacean houses, other aggregates
are long setae from a fall bloom of chain diatoms. Unidentifiable small detrital
particles adhere to these aggregates, as well as veliger
larvae, small larval worms, and small copepods.
Another ubiquitous component appears to be glacial flour. The small,
often colorful, crystalline fragments range in size from a few tens of microns
to hundreds of microns in size. We have observed
these particles in samples from the water column and ice and in the guts and
fecal pellets of krill on all four GLOBEC cruises. Although these particles have no nutritional
value, they may add additional weight to the fecal pellets thereby increasing
their sinking rates into deep water.
We also are continuing to observe
diet in ctenophores and to measure their digestion rates. In addition we are measuring ctenophore respiration
and excretion rates in collaboration with Jose Torres.
Current Position and
Conditions
Work in the northern sector of
the Southern Ocean GLOBEC survey grid is proceeding apace. During the first day
of the survey, work at three stations was completed. We are now at Station 1 located off the continental
shelf in 3000 meters of water and work here will be completed shortly. Our current position at 0741 on 2 September
is -65º 37.291′S; -70º 36.241′W.
The air temperature is -7.1ºC and the barometric pressure is 988.5 mb and rising. Winds
are back up into the 30 kt range (30-35 kts) out of the southwest (217). The pack ice is mixed with
considerable open water and the Palmer
is gently moving in response to a long period swell moving through the area. High clouds cover the entire region, but
visibility is good.
Cheers, Peter