During the afternoon communications with the L.M. Gould on 21 August, it became clear that the Gould's ability to move around in the area off Adelaide Island was severely limited. In order for the vessel to arrive at Palmer Station as scheduled on 26 August, the Palmer has been requested to provide them with assistance in moving through the pack ice toward their destination. A contingency plan was established some time ago that if such a request was forth coming, we would break off our planned survey work at the end of the 21st of August and head back towards the Gould, which is about 200 nm to the northeast of us. This plan is now being put into effect and we are steaming to meet up with them somewhere in the vicinity of station #19, where we last left them, by mid-day on the 24th, and then we will convoy up towards Palmer Station. Our current position at 1214 on 22 August is -68° 36.116S; -75° 36.358W. Winds are out of the southwest (240) at 15 to 20 kts, the air temperature is -16.0° C, and the barometer is fairly steady at 954.7 mlb. Skies are partly cloudy.
High winds (above 30 kts) and blowing snow (from recent snowfalls) prevailed for most of 20 August. Only in the late afternoon did the winds diminish before again picking up in the evening. We completed work at stations #77, 78, and 83. Station #77 had a relatively light work schedule with a CTD and a phytoplankton net tow done around 0300. BIOMAPER-II was deployed for about an hour in an area between stations #77 and 78 where ice conditions permitted towing. In the late morning at station #78, an ROV deployment was done in addition to a CTD cast and a phytoplankton tow. There was an attempt to create a open track in the ice along which to do a 1-m2 MOCNESS tow by steaming back along the track coming into the station. Sharply increasing winds into the 40 to 50 kt range around noon, however, made it impossible to deploy the net, so the attempt was abandoned and we went on to station #83. Ice collection was added to the list of tasks (CTD + phytoplankton net tow) for this last station of the day. Once again, MOCNESS net towing was thwarted by pack ice under a lot of pressure; the ship's wake closed very quickly after our passage making it impossible to set up a run that did not require backing and ramming. In the late evening about 4 nm from station #83, on the way towards station #84, we stopped at a small open water pond and did some Plummet net casts, since no other zooplankton or mid-water fish sampling was possible.
John Klinck reports on 20 August, the CTD group did four stations today (actually three during the local twenty-four hour period). Three of these stations were on the inner to middle shelf on the 140 line. The fourth station was in the mid-shelf on the 100 line.
Station #76 (250 m) had a curious mixed layer with temperature inversions throughout its depth, which extended to about 80 m. Most curious was a thin layer at the surface (10 m) with salinity reduced by 0.08 compared to water at 30 m depth. The temperature between 10 and 30 m was above freezing by about 0.05° C. The rest of the mixed layer has some vertical structure punctuated by temperature reversals. Uniform layers (10 m thick) are evident throughout the cast. An abrupt pycnocline occurs at 150 m. Temperature and salinity increase while O2 decreases with depth below the pycnocline.
Station #77 (176 m) has a uniform mixed layer to about 80 m. The deeper water is cool and fresh, so there is a truncated pycnocline at about 100-120 m. Temperature and salinity increase throughout the rest of the water column.
Station #78 (523 m) has a uniform mixed layer to about 70 m. The upper pycnocline has a strong temperature reversal (0.3° C) which is associated with weaker oxygen and salinity excursions. A relatively smooth pycnocline down to 250 m transitions to nearly uniform conditions below about 300 m.
Station #83 (408 m) has a mixed layer to 90 m with nearly constant conditions. Properties change abruptly at the base of the mixed layer. A relatively smooth pycnocline extends to 300 m below which water properties are uniform.
Frank Stewart has summarized information about the collection of two ice biology cores at station #83. Sea ice biology cores 28 and 29 were collected at grid station #83 (68° 59.48 S 74.55.32 W) in the early evening of 20 August (JD 232). Station #83 is the 11th ice station sampled and the southernmost thus far. Sea ice at the site was consolidated into vast floes topped with ~15-20cm of light, dry snow. Pressure ridges and snow-covered ice blocks were present on less than 10% of the sea ice surface; the sampling site was level. Core 28 was taken approximately 15 m from the ship. The site was topped with 18 cm of snow and had a positive freeboard of 10 cm (water line 10 cm below ice surface). The core broke into four sections during extraction: 0-16 cm depth, 17-48 cm, 49-74 cm, and 75-121 cm. The top of the core (0-16 cm) was well-consolidated, hard white ice. The two middle sections were of gray ice that became progressively softer (slushy) with increasing depth. The lower section of the core (75-121 cm) was slushy and appeared unconsolidated due to a distinct network of brine channels that began at the top of the segment and extended downward before giving way to a layer of hard, clear ice (few gas bubbles) at 10 cm up from the base of the core. The four sections were placed into separate containers for processing aboard ship. A brine sample was scooped from the core hole after drilling. The thickness of the ice (measured with thickness tape) at core 28 was 142 cm. An internal slush layer or void that went undetected during drilling might account for the discrepancy between ice thickness and the combined length of the core sections.
Core 29 was taken 12 m from core 28 on a transect parallel to the starboard side of the ship. The core hole was topped with 23 cm of snow and had a positive freeboard of 6 cm. Again, the core broke into four sections during extraction: 0-24 cm depth, 25-68 cm, 79-136 cm, and 137-155 cm. The bulk of the core was of hard, gray ice with sections of softer ice at the top of the first middle section (25-68 cm) and at the very bottom of the core (137-155 cm). Air bubbles in the ice were visible and distinct along the length of the core. Sections were separated for processing. A 10 cm void/slush layer began at 68 cm; brine/slush in this void was sampled prior to extracting the lower sections of the core. An ice thickness measurement of 156 cm corresponded well with the combined length of the core sections. Samples were brought on board and ice core sections were diluted with 0.2 mm-filtered seawater at a ratio of 2:1 sea water:core meltwater; the brine samples were not diluted. All samples were left to melt in the dark at 4-7°C. Bacterial production rates at 0°C in the presence and absence of protist grazers will be measured, via the uptake of tritiated thymidine, for specific samples. All core-section and brine samples will be sub-sampled for later determination of algal and bacterial biomass. If sample volume is adequate, fractions of the sub-samples will be consolidated, filtered, and preserved for electrophoretic and PCR-based analysis of the taxonomic composition of the ice bacterial community. In at least one of the core-section or brine sub-samples, production by the autotrophic component of the ice community will be measured by the uptake of carbon-14 over a range of light levels (photosynthesis vs. irradiance curve courtesy of W. Kozlowski). Particular attention will be paid to characterizing the microbial community in the bottom section of core 28 that was infiltrated with brine channels (to an extent not yet seen in ice collected this cruise) and in the brine/slush sample extracted from above the void in core 29. The availability of liquid water in these sections suggests the possibility of high levels of microbial activity and biomass.
Kerry Claffey reports on an ice station at broad-scale survey station #74 and the installation of a complex buoy on 18 August. The site was characterized as vast floes, relatively flat topography, and a narrow lead off the starboard bow of the Palmer. There was lots of snow, with snow depths ranging between 25 and 40 cm, but mostly 35-35 cm deep. The buoy contained the following instruments:
1) A 130 cm thermistor string. This string reaches from 15 cm above
the snow surface, 35 cm through the snow, 65 cm through the ice, and 20
cm into the water below the ice. There are temperature measuring thermistors
every 5 cm along the string.
2) An air temperature probe, installed 120 cm above the ice.
3) a snow depth gauge - This gauge will measure any increase or decrease in snow depth from the current 37 cm of snow on top of the ice.
4) A barometer.
5) An underwater depth gauge - This gauge is mounted 195 cm below the bottom of the ice looking up at the ice bottom and will indicate if the bottom of the ice sheet sees any growth.
6) An underwater temperature probe, installed 200 cm below the ice surface.
This buoy will send data back to the Cold Region Laboratory through the ARGOS satellite system.
The installation of the system involved drilling a 10" diameter hole for Buoy electronics tube and then placing the buoy electronics into it. Two flights of the 10 inch auger to drill were needed for the underwater depth gauge. This hole was located 1.5 to 2 m away from buoy electronics. While attempting to place the underwater depth gauge mount into hole, the stand broke. While the MT's came up with a solution for putting this stand back together, The snow depth gauge and air temperature gauge were installed just forward of the underwater depth gauge hole. (Kerry says he only fell into the 10" underwater depth gauge hole three times while installing the snow depth gauge.) The MT's connected the broken underwater depth gauge pipe stand back together using friction tape and two PVC half collars clamped together with hose clamps. The underwater depth gauge was then successfully installed. The thermistor string was install last through 34 cm of snow and 64 cm of ice. A check of the buoy instrumentation showed the water temperature probe was already reading -1.8° and the air temperature probe showed that the temperature had dropped to -12°C during the installation process.
Ice Cores: Kerry took two cores from near the radar reflector approximately
2 m toward the ship from the depth gauge (pinger) setup. Snow depth at
core site 34 cm. Core 74-1 was placed directly into core tube A from the
core barrel to be used later for salinity and O18 analysis.
Core 74-1 was 52 cm long, with breaks at 12 cm and 39 cm, 2 large brine
pockets appeared between 12 cm and 18 cm. Core 74-2 was cored next and
an immediate temperature profile of the core was taken:
The core length was 52 cm with breaks at 9 cm and 38 cm. This core was then placed in a core tube for later structure analysis.
Kerry Claffey summarizes information obtained while making ice collections at stations at #53 and 54 on 15 and 16 August respectively when the air temperatures ranged from -25 to -28°C under light winds (fortunately).
The ice at the station #53 site was characterized as vast floes, heavily ridged, most ridges and blocks <1 m high. Some upturned blocks were hidden by drifted snow. New snow, probably from the recent low pressure storm, was very light and powdery. Snow depths generally ranged from 20 to 35 cm.
A Transect line extending 45 feet, was sampled every 3 feet (that's what happens when you do not have a metric tape measure) extending from the Frank Stewart coring site away from the ship (the coring site was #45 on the transect line). The line ran perpendicular to the ship with 0 at the far end of the line. Statistics for the line are the following: average Ice depth 82 cm (maximum = 166 cm, minimum = 29 cm); average Snow depth was 28 cm (maximum = 42 cm, minimum = 12 cm); all had positive free board, which was generally 0-1 cm except when traversing some small blocks (maximum freeboard = 27 cm). The topography looked like small rolling hills, with blocks hidden by drifting snow. Highlights of the transect included an ice crust layer in the snow 28 cm below surface of the snow in the last 2 or 3 holes (snow depth = 34 to 42 cm). Three ice thickness holes were greater than 100 cm. One of these holes had a measurable under ice surface 60 cm thick and a full ice thickness of 143 cm probably caused by rafted blocks.
A Snow pit, made next to Frank Stewart's second coring site had fluffy
snow 26 cm deep and crystals of 1 to 2 mm grains. A thin (<0.5 cm) wind
crust was noted on very top of snow surface and the ice surface was well
frozen. The temperature profile was the following:
|Snow Pit Depth Temperature (°C)|
|Snow/ice interface temperature||-2.8°|
|10 cm temperature||-8.7°|
|20 cm temperature||-18.7°|
|25 cm temperature||-24.8° (25 cm temperaturejust under the snow crust)|
|Air temperature on thermistor||-25.1°|
Snow Densities were the following :
|26-28 cm||0.196 (surface) includes the wind crust layer|
Note: a slight variability in snow surface explains why the surface density sample is 2 cm higher than the temperature profile snow surface.
The ice at the station #54 site was characterized as vast floes, not so heavily ridged. The area of coring appeared flat. New snow, probably from the storm mentioned above, was very light and powdery. Snow depths generally ranged from 20 to 35 cm. Ice observations, done just before arriving at the station, were recorded as first year, 70 cm, vast floes, ridging 712, old snow, 30 cm depth. Two cores were taken and a snow pit was sampled. The statistics for these are the following:
Site 54 Claffey Core 1: Ice Hole = 51 cm; free board = +2 cm; snow depth
= 10 cm; core length = 40 cm; breaks at 3 and 21 cm; ice/snow interface
temperature = -5.1° C. The difference between
the core length and the core hole length indicates that we probably pushed
the bottom of the core under the ice and lost it. The top piece (3 cm)
of the core was very soft granular ice. The temperature profile (measured
from top of core) gave these readings:
|Depth||Temperature (° C)|
The bottom (39 cm), top (1 cm), and middle (16 cm) were the first three temperature measurements made, in that order. The 30 cm was the last temperature measurement made and we feel that the -6.1° reading was caused in part by the cold air penetrating into the ice core during the temperature taking process. As stated before 39 cm was probably not the real bottom of this core.
Site 54 Claffy Core 2: Ice Hole = 50 cm; free board = +2cm; snow Depth
and ice/snow interface temperature: This core was taken at the same place
(same shovel hole) as Core 74-1. There were breaks at 15 cm, 33 cm, and
39 cm. The top of the core (first 3 to 5 cm) was very soft ice described
by Frank Stewart as re-frozen granular ice/snow. The temperature profile
(measured from top of core) gave these readings:
The bottom (50 cm), top (1 cm), and middle (25 cm) were the first three temperature measurements made, in that order, followed, in order, by 48 cm, 10 cm, 20 cm, 30 cm and 41 cm. Air temperature measured on the temperature probe was -22.4°C. Once again, the 41 cm temperature reading of -4.0° is suspect and probably caused by cold-air penetrating the ice core during the measurement process.
A snow pit made next to Frank Stewart's coring site had fluffy snow
that was 24 cm deep and crystals of 1 to 2 mm grains. A thin (<1 cm)
wind crust was noted on very top of snow surface. The ice surface was not
well frozen. Using hands, we were able to remove 2-3 cm of soft ice from
the bottom of the snow pit. (This is probably the soft ice noted at the
top of the cores.) After removing this ice, the snow pit flooded with 2
cm of liquid water. The snow pit was located far enough away from the core
holes and this layer of soft ice had not been removed from the core holes,
so that we do not think that the water was flooding from these holes. The
snow pit contained from 0-2 cm of soft ice/flooded slush, a 2-6 cm wicked
layer, and 6-24 cm of fluffy snow topped with wind crust <1cm.
|Snow Pit Depth||Temperature (°C)|
|Ice/Slush water interface (0 cm)||-2.2°C|
|6 cm||-2.7°C (top of wiked layer)|
|24 cm||-19.9°C (24cm temp. just underthe snow crust).|
|Air temp. on thermistor||-23.1°C|
Snow Densities were the following :
|22-24 cm||0.194 (surface) includes the wind crust layer|
Ari Friedlaender reported that on 19 August, marine mammal observations began at 0915 in 10/10 ice coverage of vast floes with heavy ridging and small irregular pools of open water. Skies were overcast and visibility was limited to 1 nm at best. Effort was paused from 1100-1200 while a MOCNESS trawl was attempted. Observations then ran until 1400 when we stopped for an ice dive (68° 50.06S, 72° 47.61W). No cetaceans were seen on this day, however, we counted 5 crabeater seals and 1 unidentified seal.
On 20 August, observations began as we left station #78. Conditions were poor with 10/10 ice coverage of thick, heavy floes, with scant few small cracks of open water. Winds were steady at near 40 knots and blowing snow limited visibility for sometime. the snow stopped blowing at 1330 and visibility improved slightly until observations ceased at 1530 (68° 59S, 74° 53W) en route to station #83. Twelve crabeater seals were seen in one lead, and no cetaceans were sighted.
Chris Ribic and Erik Chapman report that on 20 August (JD-232), they surveyed for 3 hours and 50 minutes between stations #78 and 83. Visibility improved in the afternoon as wind-driven snow that had limited our ability to see in the morning settled down to the surface of the ice. Only after the snow settled did we realize that it was actually a virtually cloudless day. We encountered mostly 10/10ths ice coverage with a few small leads. We saw few birds in the area with just 6 Snow Petrels and a single Antarctic Petrel. So far, we have seen few birds overall and very few penguins in particular south of Marguerite Bay. A summary of their daytime observations is the following:
Primary Ice: Mostly vast floes with 10/10ths concentration. Some open
water in cracks between floes.
BIOMAPER-II/MOCNESS report (P. Wiebe, C. Ashjian, and S. Gallager):
BIOMAPER-II was deployed for a short time during the transit between stations #77 and 78. As has been the case in the other mid-shelf portions of the survey area, a strong backscattering layer extended from the sea floor to about 100 m above the bottom. The variable bottom topography along this portion of the trackline and the always present danger that the ship might stop during the tow, limited the amount of wire that could be paid out to no more than the water depth. Thus, it was difficult to get BIOMAPER-II down into core of the layer. Attempts to get the VPR on the towed body into the top of the layer only resulted in collecting images of some copepods.
No 1-m2 MOCNESS tow was done on 20 August.