We are currently (1258 on 4 August) at station #26 in the middle of the continental shelf on transect line 5. This is a major station with under ice diving and a 1-m2 MOCNESS tow in addition to the phytoplankton ring net tow and CTD to the bottom, which is about 340 m below the sea ice surface. An ROV was also scheduled, but electronic problems with the ROV communication system have not yet been resolved. Skies are cloudy, but visibility is good. Our position is -67° 20.037S; -71° 12.698W. The air temperature is -0.1°C and the wind is out of the northwest (335) at 15 to 18 kts. The barometer has not changed much over the past 24 hours and is now reading 973.0 mlb.
August 3 was another two-station day. Station #23 was another deep station (water depth 3647) and the CTD to the bottom and 1-m MOCNESS tow to 1000 m took 3 to 4 hours each. In addition, there was again a long steam to get back onto the continental shelf and station #24 while towyoing BIOMAPER-II and doing bird and mammal surveys. Just before arriving at station #24, Jose Torres did a 10-m2 MOCNESS trawl tow to 1000 m, which also took about 4 hours and ended about 1945. Then, we steamed the 8 miles back to the station #24 location to begin the ring net and CTD cast before putting BIOMAPER-II back into the water for the run to station #25.
John Klinck reports that on 3 August, the CTD group did two casts on the offshore end of line 340 and plotted another section of nutrient observations.
Station #23 (3583 m) is one of the deepest stations yet. The mixed layer was rather deep (120 m) with uniform conditions throughout. The temperature maximum and O2 minimum layer is at around 300 m. Below these obvious and common features are the LCDW layer at around 1500 m and the continual increase in O2 and decrease in temperature to the bottom. No interesting features were seen over the deep part of the cast.
Station #24 (503 m) is on the outer shelf with a uniform surface layer to 80 m. The temperature maximum and O2 minimum layer is around 300 m, but there is considerable indication of layering in the pycnocline with some layers approaching 20 m thick and causing temperature reversals.
Nutrients were plotted for the 420 line. The nutrients have much the same character as the previous sections. However, silicate is lower at station #16 centered on 200 m and the silicate to nitrate ratio is lower about 2.6 (reduced from 2.75) at this point too. There is a nitrate maximum in a layer between 100 and 300 m as well as a phosphate maximum in the pycnocline.
Ari Friedlaender reports that on 3 August, whales appeared in the morning before the steam to station #24. At 0950, while doing a 1-m2 MOCNESS tow at station #23, three minke whales were seen off the stern of the ship. They passed the ship to port and were seen twice more before leaving. Full observation effort began at 1025 as we steamed to station #24. Skies were foggy, with visibility limited to 0.5 nautical miles. Ice conditions were made of small floes, cakes, and bits of brash. Total coverage was 9/10 with sporadic leads. As the transit continued, the floes became more consolidated and cemented into larger floes. The survey effort ended at 1515 (66° 54.258S, 72° 38.081W), with no subsequent cetacean sightings. The only sightings made were of three Adelie penguins.
Ana Sirovic reports that on 3 August, she deployed 1 sonobuoy and monitored it for 1 h 20 min., but heard no biological sounds. She is still getting very poor range on the directional antenna and plans to work with Jeff Otten on fixing it on 4 August.
Chris Ribic and Erik Chapman report that on 3 August (JD-215), they
surveyed for 4 hours and 38 minutes between stations #23 and 24. Ice conditions
varied between 8 and 10 tenths concentration. They saw few birds overall
today, but began to see more Snow Petrels as we approached station #24.
They saw just one Adélie penguin in today's survey. One surprising
sighting was a single Black Browed Albatross sitting on the ice. The bird
was probably displaced during a storm from open water to the north where
Black Browed Albatross typically range. The bird was probably unable to
fly out of the pack in today's extremely low winds.
|Southern Giant Petrel||2|
|Black Browed Albatross||1|
They surveyed for one hour last night from the bridge and saw 1 Snow Petrel and 7 Adélie penguins.
BIOMAPER-II/MOCNESS report (P. Wiebe, C. Ashjian, and S. Gallager):
BIOMAPER-II was successfully towyoed during transits between stations #23, 24, and 25 on 3 August. Intermittent noise on the video signal coming from the high resolution VPR camera (In legacy lingo "Camera 4") degraded the quality of the images, but otherwise the sensor systems on the towed body were running OK. There were no towing wire hangups on ice cakes along the transits between stations. But the level wind problem surfaced again, and again the problem was traced to a short in a terminal box mounted on the base of the winch. With another cleaning and drying of the terminal strips, the winch was again put back into service and the towyoing continued.
During the run between stations #23 and 24, some very interesting acoustic structure was observed at the base of the mixed layer that looked like Langmuir circulation cells, but in reverse i.e. most intense near the base of the mixed layer. But of course, Langmuir cells are wind driven and this area is covered with ice, so it must be some kind of thermohaline circulation caused by the freezing of sea water and the resulting increased salinity causes the water to sink. When BIOMAPER-II went through a zone where these "cells" were present. The VPR images contained fairly large numbers of krill furcilia.
At the shelf break and onto the shelf in water depths of around 400 meters, a strong acoustic layer was observed along the trackline extending from the bottom up to between 60 and 100 meters above the bottom. Sometimes the backscattering from the layer was fairly uniform throughout and other times the layer was split with significantly higher backscattering in the half of the layer closest to the bottom. Unfortunately, the layering is deeper than BIOMAPER-II can dive to in part because of the restrictions we have imposed on the depth of towyoing due to the towing wire/ice hangup problem, but also because the VPR camera housing are not rated to go much below 300 m depth. This layer was observed on earlier sections and in the outer half of the shelf region. Krill overwintering has been hypothesized to take place near the seafloor on the continental shelf as well as in and just under the pack ice. So sampling this portion of the water column has become an important issue now that the acoustic system is providing solid evidence that some kind of build up of biomass is occurring there.