We are currently (1535 on 2 August) at station #22 (-66° 36.444 S; -72° 11.131W), which is the outermost station on transect line 4. It is off the continental shelf in water some 3376 meters deep. A CTD to the sea floor is underway and a Tucker trawl to collect live animals is up next. The weather is mostly cloudy with an air temperature of -4.8°C. The winds are moderate at 12-16 kts out of the north-northeast (020).
We began 1 August at the inner most station on transect line 4 just off the southwestern tip of Adelaide Island. In the early morning, it was cloudy with a light snow falling. Winds were light, 5-8 kts, out of the Northwest, and air temperature down around -10°C. Work at this station included a phytoplankton net tow and a CTD cast. During the steam to station #19, the sun came out for a brief time giving us a terrific view of the snow covered peaks of Adelaide Island. Work at station 19 began midday and consisted of a CTD cast to 600 m, a live Tucker trawl tow, and a 10-m2 MOCNESS tow. For most of the transits between stations we were plowing through the omnipresent pack ice, but fortunately it was possible to do the net towing at station #19 in a large lead. By this time, it had clouded over again and for most of the afternoon and evening there was a light snow falling. In the evening at station 20, the only work scheduled was a CTD to 500 m. Bird and mammal surveys took place during the morning daylight period during the transit between stations #18 and 19, but noticeably absent was the towyoing of BIOMAPER-II, which was still under repair.
John Klinck reports that, on 1 August, the CTD group did three stations starting at the coastal end of the 380 line. Vertical sections of nutrients have been plotted for lines 500 and 460; a description is provided below. The salinometers seemed to be reacting to temperature fluctuations in the salinometer closet. Recent changes in the heating and air conditioning caused problems with temperature control. Reversing these changes seems to have stabilized the situation. All will be well if another calibration tomorrow morning yields consistent results. Then, we need to plow through the salinity backlog- a toilsome task.
Station #18 (480 m) at the onshore end of the 380 line is relentlessly typical with a mixed layer to about 80 m. There is some density variation in the bottom half of the mixed layer. Temperature, salinity and density increase continuously to the bottom of the cast. There is a very weak temperature maximum and O2 maximum (note max not min) at about 420 m. Some layering is evident in the pycnocline between 80 and 200 m.
Station #19 (404 m) is a near repeat of the previous station, except that the mixed layer is a little deeper (100 m) and there is no structure in the mixed layer. There is a weak temperature maximum at 300 m and a broad O2 minimum from 220 to 340 m. Thin layers are evident from 120 m to 250 m or so.
Concentrations of macronutrients nitrate, nitrite, silicate, phosphate and ammonium were measured by Rob Masserini and Yulia Serebrennikova from Kent Fanning's group. These values for the first two lines were plotted in vertical sections. A short description of these plots follows.
Along the 500 line, surface silicates are fairly uniform at 65 to 70 mM with a sharp change across the pycnocline. Deeper values increase linearly with depth from 95 to about 110 mM. The largest subpycnocline values occur at the shelf break. Surface phosphate is 2.0 to 2.1 mM; subpycnocline values are rather uniform at 2.4 mM. Mixed layer nitrate is 28 to 29. Nitrate increases quickly across the pycnocline leading to uniform 34 to 35 mM below the pycnocline. Ammonia is 0.5 to 0.6 mM in the mixed layer. Concentrations are less than 0.05 below the pycnocline. Across this section, all nutrient isopleths are basically horizontal with some spreading or lifting at the coast, due, presumably, to additional mixing there.
Along the 460 line, mixed layer silicate is 65 to 70 mM. In and below the pycnocline, silicate increases with depth and from offshore to onshore having largest values of 110 mM. There is a local high of silicate at the shelf break which is clear in the mixed layer and within the pycnocline. Near surface phosphate is 2.0 mM. There is a near linear increase to 2.4 mM at about 150 m. Phosphate is maximum between 150 and 200 m and shows a weak decline with depth. The interior phosphate maximum is not observed at the coast. Nitrate offshore of the shelf break is uniform with depth from 100 to 1000 m at 36 mM. The offshore surface values are 31 to 33 mM. Over the shelf, the mixed layer concentration is 28 to 29 mM. There is a broad nitrate maximum between 150 and 300 m of 34 mM. Ammonium in the mixed layer is highest offshore (0.9 mM) decreasing monotonically to about 0.1 mM at the coast. There is little measured ammonium below the pycnocline. A small maximum at the bottom (0.1 mM) occurs in the center of the section.
Overall, these two sections are rather different. The 500 line is regular in the vertical and the nutrients generally follow the density structure or have different uniform values above and below the pycnocline. The 460 line has a variety of horizontal structure both above and below the pycnocline. The high nitrates offshore seem to be associated with the ACC. This is collaborated by the 1.8°C temperatures at the offshore end of the section.
Ari Friedlaender reports that on 1 August observations were made in transit from station #18 to 19 heading offshore, perpendicular to Adelaide Island. Conditions were good with light winds, mostly cloudy skies, and over 1-mile visibility. Ice conditions were primarily vast floes of consolidated smaller floes and cakes with new snow covering them. There were also pressure ridges forming where floes were colliding and being forced together. While ice coverage was rather complete, there were long, thin leads (several km's long, 100 meters wide) at regular intervals throughout the transit. A total of 15 crabeater seals were sighted, as were 2 Weddell seals, and 3 other seals that could not be identified. Three groups of 9-12 Adelie penguins were seen as was a larger group of 40 birds. When we reached station 19 and began a Tucker trawl, 2 Emperor penguins were sighted behind the ship. The only cetacean sighting was a brief glimpse of a minke whale that surfaced off the starboard beam of the ship as we reached station #19.
Ana Sirovic deployed two difar sonobuoys on 1 August. One was deployed while in transit between stations 18 and 19, which was monitored it for one hour. The other one was deployed after Jenny White sighted a minke whale as we were on station #19. The buoy gave out signal for a bit over 2 and a half hours. No whale calls were heard on either of the buoys.
Chris Ribic and Erik Chapman reported that on 1 August (JD-213), they
surveyed for 3 hours and 55 minutes between stations18 and 19. Ice conditions
were between 8 and 10 tenths. During most of the survey, the ship traveled
through ice interrupted by leads that appeared to be created by the motion
of wind driven ice bergs in the area. Associated with these leads were
Adélie penguins, Emperor penguins, and Snow Petrels. Crabeater seals
were also observed both hauled out on the ice and in the water. The Adélies
were observed in three groups of between 9 and 20 birds off the 300m transect
line. Also seen were 16 adult Southern Giant Petrels in 10/10ths ice eating
a seal carcass.
|Southern Giant Petrel||14|
They surveyed for two hours last night from the bridge and saw 5 Snow Petrels associated with leads in the ice.
BIOMAPER-II/MOCNESS report (P. Wiebe, C. Ashjian, and S. Gallager):
BIOMAPER-II remained in the deck van and repairs to the towed body continued. The major initiative on this day was to resurrect the VPR mounting framework and the VPR cameras and strobe light, and to finish rigging the tail assembly.
No 1-m2 MOCNESS tow was done on 1 August.