The work along transect line #2 has almost been completed. We are currently working at station #12 in the deep water (depth around 2970 m) off the continental shelf and will be heading for station #13 and the start of transect line #3 soon. Our current position at ~1241 (30 July) is -65° 59.169S; -71° 10.644W. Winds much stronger than yesterday with wind speeds around 30 kts out of the northeast (045) and the air temperature is -4.5°C. This air temperature is noticeably warmer than the -14°C of yesterday. This may not sound warmer, but the difference between -4.5°C and -14°C is very noticeable.
The weather on 29 July remained clear and cold for the entire day. The winds stayed light, but changed direction from southeast to northeast during evening. The sea smoke and the resulting relatively low horizontal visibility stayed with us until we were far out onto the shelf in 10/10 pack ice and little open water. Work was completed at stations #8, 9, and 10, and was started at station #11. BIOMAPER-II was towyo'd for most of the transits between stations and during the daylight, bird and mammal observations were made.
Early in the morning (~0400) on the 29th, the RVIB N.B. Palmer rendezvoused with the RV L.M Gould. The Gould had been working in a region near our station #1 and the ship was in the process of moving to a new location at the southern end of Adelaide Island. The purpose of the rendezvous was to swap some equipment and supplies between the vessels. The swap with the Gould went well. In spite of fairly solid pack ice, the Palmer did some side thrusting to make a small "pond" of open water and then the Gould came into open water pointed in an opposite direction and launched a zodiac, which came across the pond. The transfer of equipment was made with the Palmer's crane. In the transfer was a barrel of hydraulic fluid for the Palmer and medical supplies and some other items needed on the Gould. Included were some of the excess live krill that Kendra Daly had on the Palmer that went to Rodger Harvey on the Gould, in support of his experimental work.
John Klinck reports that the CTD group completed 4 stations today (8-11) which crossed the shelf along the 460 line. Only the offshore station remains to be done on this line (see tomorrow's report).
Station #8 (338 m) has much the same character that we saw in the middle shelf on the 500 line. There is a mixed layer to 100 m with no vertical structure and a sharp transitions to the pycnocline. Below the pycnocline (below 150 m) temperature and salinity increase while the oxygen decreases. There is a very weak oxygen minimum just above the bottom; temperature is maximum at the bottom.
Station #9 (508 m) has a mixed layer to about 100 m, but there is a clear vertical gradient in salinity producing some stratification throughout the layer. There seems to be a weak secondary mixed layer in the upper 30m. The pycnocline occupies about 100 m (from 100 to 200 m). There is a deep O2 minimum and temperature maximum at about 300m. There seems to be a cool mixed layer at the bottom with a thickness of about 50 m. Layering structure is evident in the temperature from 100 m to the bottom.
Station #10 (462 m) has a shallower mixed layer (70 m) with no vertical structure and a very abrupt transition at the bottom. The pycnocline covers about 100 m and the deep O2 minimum occurs at about 240 m, well above that at station #9. The temperature maximum, on the other hand, occurs at 300 m as at station #9. There is very clear layering with thicknesses up to 20 m and strong temperature reversals. A weak temperature minimum occurs about 40 m above the bottom.
Station #11 (980 m) is at the shelf break on the 460 line. The mixed layer extends to 80 m with no vertical structure. The pycnocline covers more than 120 m with clear temperature reversals in layers of 10 or so m thick. At 255 m, there is a strong interface where temperature increases by almost 0.4°C to 1.9°C and salinity jumps by 0.02. O2 drops a bit at the same place. This appears to be unmixed Upper Circumpolar Deep Water (UCDW) at the shelf break. Below 750 m, temperature decreases at a more rapid rate. The Antarctic Circumpolar Current (ACC) is clearly at the shelf break along this line.
Ari Friedlaender reported that an incidental watch for marine mammals ran from 0900-0930 before reaching station #9. Early on, visibility was obscured by patches of fog. Ice cover was 9/10ths of new grey ice and nilas covering leads, and small floes which were cemented with smaller cakes and brash. New snow covered much of the pack ice. Full observations commenced at 1220 as we departed station #9. Similar ice conditions prevailed, with most of the visible leads covered in new ice. At 1250, a single minke whale was sighted in a thin (10 meter diameter) lead surrounding freshly iced over larger leads. The whale seemed to surface through grease ice. In the same area as the whale, 4 seals were seen in another lead, as were 2 Adélie and 1 emperor penguin. At 1500, a single weddell seal was sighted on the ice, and soon thereafter, another minke was sighted in a series of leads that extended for several kilometers across the ship's track. Also in the vicinity were 3 emperor penguins. The minke whale surfaced twice in the lead, in a motion that was very arched, suggesting either very tight breathing space, or that the animal was preparing for a dive. After the second sighting, the whale was not seen again. Observations ended at 1600 as we approached station #10 and light was diminishing.
Ana Sirovic deployed three difar sonobuoys and listened for a total of 8 hours. No biological noise was heard. The first buoy was deployed 4.7 nm before station #9 and was within range for 5 hours. The second buoy was deployed after a visual sighting of 1 minke whale. It failed soon after deployment and another buoy was deployed shortly. The second deployment occurred 3 nm before station #10, so we stayed within range for some time and she listened to this buoy for 3 hours before losing signal.
Chris Ribic and Erik Chapman reported that on 29 July (JD-210), they
surveyed, for 4 hours and 39 minutes in heavy first year pack ice between
consecutive stations #8 and 10. Ice varied between 7 and 10/10ths
coverage and consisted of cakes, large floes and new gray ice. The ice
was the heaviest we've seen and the only open water was found in well defined
leads or in small areas where some water was between floes. Again, we saw
a low number of Snow Petrels, mainly over the open water. In addition,
we saw 4 Emperor Penguins and 2 Adélie penguins, all associated
with ice directly adjacent to a lead.
They surveyed for an hour at night from the bridge and saw a single
BIOMAPER-II/MOCNESS report (P. Wiebe, C. Ashjian, and S. Gallager):
BIOMAPER-II was towyo'd partially between stations #7 and 8 and then between stations #8 to 11. Station #7 is in shallow water (~125 m), very close to the Fuchs Ice Piedmont which has an ice wall about 30 meters tall where it meets the ocean. The station area was clogged with ice and icebergs. While the CTD cast was being done, the echosounder in BIOMAPER-II, which was "parked" at about 20 meters below the surface, stopped transmitting. Attempts to get it running while still in the water failed and so the towed body was brought on board for another round of fixing. Within a short period, we found a broken wire in the mecca connectors leading to the sea water grounds. The sea water switch works by having two exposed electrical leads, one in the bottom of the interior of the towed body and one taped up near the video cameras above the top of the fish. In order for the echosounder to transmit, both leads have to be in sea water so that the circuit is completed using seawater as the conductor. If the fish breaks through the sea surface and the top lead is in air, the echosounder cannot transmit, thus protecting the transducers, which could be damaged by transmitting in air. If a lead has a broken wire, however, the connection in seawater won't happen. Apparently one of the wires developed the break while we were on station and disabled the transmitter. It took more than an hour to replace the bad wiring and get the system back to operational. We put BIOMAPER-II back into the water only a mile or so before station #8. It has worked properly for the rest of the transits between stations on transect #2.
The backscattering continues to be very low throughout the water column. Only occasionally do we see a layer of substantially higher backscattering in the upper hundred meters. One of those times, we were on our way between station #8 and 9 when a strong scattering layer appeared centered about 60 meters. The towed body went down through the layer and many adolescent (furcilia) krill adolescents 5 to 8 mm appeared on the video camera images verifying that the acoustic patch structure was made up largely of krill.
A 1-m2 MOCNESS tow (#3) was done at station #11. This was only possible
through the efforts of the Raytheon marine technicians who worked over
the past 36 hours to repair the frame, fabricate new front fenders to replace
the ones damaged beyond repair, check out all the electronics and sensors,
and re-wire the cable termination (See previous report for an explanation
of how the system was damaged). A couple of hours before the scheduled
time for deployment a substantial group of investigators gathered in the
wet lab to finish outfitting the MOCNESS Strobes Light system (lots of
re-wiring and testing), put the nets back on the net bars, and install
the Optical Plankton Counter. Then, the system was moved out of the wet
lab and into the position of launch and recovery on the aft deck forward
of the MOCNESS-10. The tow was conducted to 600 m with a bottom depth of
900 m at the start of the tow and 500 m or so by the end of the tow. This
was a more oceanic type of tow. Many chaetognaths were observed at depth
(200-600 m), with large copepods and a few Euphausia suberba and
Thyanoessa. A large myctophid was captured in the 200-150 m depth
range along with krill. Salps, ctenophores, ostracods, and polychaetes
were seen from 100-150 m. Small fishes were seen in the 50-75 m range along
with naked pteropods, chaetognaths, and polychaetes. E. superba
larvae were observed at all depths in the upper 100 m. Pteropds, amphipods,
and chaetognaths were seen in the upper 75 m. Abundances overall were low.