Report of Activities
on the RVIB N.B. Palmer Cruise 02-02
Changeable weather is the hallmark of the Western Antarctic
Continental Shelf and 27 April was no exception as the Palmer worked on outer
portion of broad-scale survey line 7. The high winds of the day before had
disappeared, but the large swell remained for most of the day. In the very
early morning before sunrise, there was a clear spell and the full moon
illuminated the scene. Throughout the morning, the winds were light (6 to 10 kts) out of the south, but a dense low fog developed
cutting the visibility to short distances. Except for the swell, the surface of
the sea had only light chop. By
April 27th was also the first of the Big Screen Movie nights
on the Palmer, presented by Amy Kukulya and Romeo Lariviere. The helicopter hanger was converted into a
theater with a big white bed sheet screen on the helo-door
during the day by an elite group of movie enthusiasts. At 2000 sharp, a DVD
version of “Swordfish” played to an
enthralled audience bolstered by galley gorp and popcorn.
Work at station 47 was finished in the early morning hours
of 27 April with an APOP cast and work was completed work at 48, 49 and 50.
Three CTDs and a number of XBT casts were made. The XBTs were used to explore the extent of a deep warm water
zone indicative on an intrusion of water from offshore. A 1-m ring net tow was done at station 48; a
MOCNESS and a 1-m Reeve net tow were done at station 50. Seabird and marine mammal observations were
made during daylight when the visibility was adequate. BIOMAPER-II was towyoed between stations 47 to 49 and was under repair for
the transits between station 49 to 50. Two sonobuoys were
deployed along the trackline.
CTD Group report (John Klinck, Tim Boyer, Chris Mackay,
Julian Ashford, Andres Sepulveda, Kristin Cobb)
Today the CTD group did 3 CTD casts and 14 XBT casts (3
failures and 2 repeats) along the outer part of the 260 line. The XBT's, some launched April 28, but reported here for
convenience, were done on the transit between stations 50 and 51.
These casts are quite varied having different mixed layer
depths and properties. While all three have visible temperature and salinity
variability in the pycnocline, Station 48 had the
most energetic temperature structure seen so far on the cruise with layer thicknesses
that range from 50 to 3 m. The deep warm temperature indicates some exchange
with the Antarctic Circumpolar Current (ACC), which is not surprising for this
station near the shelf break. Station 49 is rather like the other mid-shelf
stations on this cruise with no deep warm water. Finally, Station 50 in the middle of the
shelf has clear indication of an oceanic water intrusion about 100 m thick.
XBT casts were made at Station 50 after the net tow (about 3
nm north of the station) and then every 5 km along the course to Station 50.
The two closest XBTs indicated water warmer than 1.6ºC,
but the remainder had no indication of Circumpolar Deep Water. It seems that
the warm water was not coming from along shelf where the earlier intrusion was
detected.
Station 48 (cast 52, 427 m). There
was a uniform mixed layer to 70 m (-0.7ºC, 33.8) with chlorophyll measuring 0.6
μg/l. A clear
Winter Water (WW) layer was centered on 85 m.
The temperature profile was very ragged having 3 step changes (0.4ºC) in
temperature over about 10 m separating 30 to 50 m thick layers. Smaller-scale
structure was layers 5-10 m thick and energetic smaller-scale variability.
There was a deep temperature maximum (1.6ºC) below 300 m.
Station 49 (cast 53, 484 m). The
mixed layer was uniform to 70 m (-1.2ºC, 33.6) with chlorophyll measuring 0.3 μg/l. A WW layer
was centered on 90 m. There was energetic small-scale structure from 100 to 300
m, with a thickness of about 5 m. There
was a deep temperature maximum (1.4ºC) at 300 m.
Station 50 (cast 54, 392 m). The
mixed layer extended to 50 m with uniform properties (-1.1ºC, 33.6, 0.35 μg/l.) A WW
layer was centered on 60 m. Energetic small-scale structure occurred from 80 to
250 m, with a thicknesses of about 5 m. There was a deep temperature maximum (1.7ºC)
at 230 m. Several thick (30 - 40 m)
isothermal layers were evident below 220 m.
Nutrients Status Report (Rob Masserini)
Yulia Serebrennikova
and I have been kept out of trouble, mainly due to the CTD marathon inside of
Marine Mammal report (Debra Glasgow)
April 27 was a difficult day for observations of marine
mammals as thick fog persisted throughout the day. Visibility in the morning was
worse at <300 meters and only an Incidental watch was kept from 0904 to
lunchtime at 1130. Conditions improved
somewhat in the afternoon, but visibility remained variable between <300
meters to <3 nautical miles. An On Effort watch was kept for most of the afternoon,
however. Twelve fur seals and 1 unidentified seal were recorded. At the end of
the day at 1659 as the light was fading, 4 humpback whales appeared out of the
fog ahead of the ship at 118 about 0.1 n miles away. They ignored the ship, passing
to starboard within 100 meters, and continued socializing, turning on their
backs and waving pectoral fins, spyhopping, turning
side on to each other and occasionally vocalizing above the water as they breathed.
Some video footage was taken of this interaction though conditions were poor
with heavy fog and a confused, beam on swell. On the tape is a clear ID shot of
one of their flukes and an obscured shot of another. They disappeared back into
the fog moments after the video was taken, still interacting with each other.
Sea Birds (Erik Chapman and Matthew Becker)
The seabird survey effort started on 27 April with a 1-m
ring net tow at station 48 before the sun rose.
This station was just over the continental shelf near the shelf break
and lots of phytoplankton was present, but no zooplankton visible to the naked
eye. A fog settled in overnight and
limited our visibility during transit between stations 48 and 50. Most of the day, visibility was about 200 m
or less from the ship, too short a distance to collect data within the transect. We did
manage to collect data when the fog lifted for 30 min before we reached station
49 and for a little over 4 hours on our way to station 50 before darkness fell. There were few birds observed during the
survey, mainly open water species including Blue Petrels, Southern Fulmars,
A summary of the species and number of individuals of birds
and seals observed during 4 hours, 10 minutes of daytime surveys between consecutive
stations 48 to 50 is the following:
|
Species (common name) |
Species (scientific name) |
Number observed |
|
|
Daption capense |
11 |
|
Southern Fulmar |
Fulmarus glacialoides |
5 |
|
Antarctic Petrel |
Thalassoica |
6 |
|
|
Oceanites oceanicus
|
1 |
|
Blue Petrel |
Halobaena caeulea |
8 |
|
Southern Giant Petrel |
Macronectes gfiganteus |
2 |
|
Grey-headed Albatross |
Diomedea chrysostoma |
1 |
|
Antarctic Fur Seal |
Arctocephalus gazella |
7 |
Material Properties of Zooplankton Report (Dezang Chu, Peter Wiebe)
On April 27, at station 47 (67 14.712ºS; 74 31.74ºW), an
APOP cast was made using juvenile krill (E.
superba) with mean length and standard deviation of 35 and 5 mm,
respectively. All animals were alive after the APOP cast even though a few
animals were not as healthy as others before the cast. The experimental chamber
was lowered and raised at a speed of 10 m/minutes and stopped at every 20
meters for a few minutes of data acquisition. The cast lasted about 1 and a
half hour and did not seem to have much impact on the krill survival. The
measured sound speed contrasts varied basically between 1.01 and 1.03 with no
clear depth dependence. No obvious
difference in the measured sound speed contrasts between the down cast and up
cast was observed. The mean and standard
deviation of the sound speed contrast for both the down and casts were 1.020
and 0.007, respectively. The density measurement was conducted on the same
animals following the APOP cast. The measured density contrast was 1.027. The measured
mean values of sound speed contrast is between those for the adults (mean
length of 52 mm) and the smaller or younger juveniles (mean length of 27 mm) obtained
from the previous casts (see daily reports of April 17 and 19 of this cruise),
suggesting the mean values of density contrast did not show clear and
consistent dependence on life stages despite the fact that the density contrast
of the youngest juveniles did have the smallest value (see daily report April
19th).
In the evening at station 50 (67 50.807ºS, 72 25.978ºW), a
Reeve net tow was made. Although not many krill were caught as hoped (only a
few juveniles), more than 100 1.5-cm
long live amphipods (Parathemisto),
thousands of 2-3 mm long copepods (Calanus), and a few adult mysids (Arctomysis) were
caught. We are planning to make material
properties measurements on Parathemisto and Calanus in the next few days.
Zooplankton (MOCNESS/BIOMAPER-II) report (Carin Ashjian, Peter Wiebe)
Our thirteenth MOCNESS tow was conducted mid-shelf along
transect line 7 at station 50 in ~ 400 m of water. The tow was conducted to 360 m. The tow was successful except that the strobe
was not firing when the net was recovered. Krill furcilia
were observed in many nets at this station, over the depth range of 250-75
m. Larger krill were observed from 360-150
m and then again from 75-100 m. Copepods
were observed at all depths (0-360 m). Ostracods were seen in the deepest net (360-250 m).
Amphipods were seen from 75-50 m and then again in the surface net (25-0
m). Diatoms were abundant in the 25-50 m
interval.
BIOMAPER-II was deployed after the completion of deep water
station 47 in the wee hours on 27 April and towyoed
to station 48 on the edge of the continental shelf. and
then onto station 49. It was sidelined
for the transit between stations 49 to 51 while repair work on the echosounder was performed.
Since the large swell caused the damage to the towing cable that forced
a re-termination at station 29, the echosounder has
had a problem with intermittent introduction of noise on the lower 3
frequencies. At first, it was thought
that the noise source might be associated with the ship operating in shallow
water, but then it appeared while working in deeper water. The noise source, which might be the result
of a component failure in the echosounder, has proved
to be difficult to track down. After
several days of trouble shooting, we do not seem closer to finding the source
of noise problem, although several other problems have been identified and
fixed. The data on some frequencies is
not of high quality, but the spatial patterns are still evident even with the
presence of the unwanted noise. An
additional problem developed on 27 April.
The up-looking 120 kHz transducer abruptly stopped pinging during the
transit between station 48 and 49, and then after some time again began to work,
although intermittently. Peter Martin has had his hands full trying to keep the
acoustic system functioning in BIOMAPER-II.
Volume backscattering in the offshore waters between
stations 47 and 48 was very light throughout the water column, except near the surface
on the 1 MHz echograms, which continued to show high backscattering where the
VPR showed lots of diatoms and radiolarians in the water column. There was also not much backscattering near
the surface, except for some thin layers as the Palmer steamed from station 48 to 49. Along this transit, the
bottom shoaled to around 390 m and there was a bottom scattering layer
extending up above the bottom about 60 m.
There was a mid-water layer just above it, which was also about 60 m
thick. This mid-water layer showed up on
the 43 echogram in spite of the noise, but not the bottom layer. There was a second mid-water layer higher up
in the water column (200 m below the surface) that was much patchier. There
were occasional small krill-like patches in the upper mid-depth scattering
layer. High backscattering continued to occur on the 1 MHz echograms in the
diatom rich near the surface waters.
Cheers, Peter