Today (5 August), we finished work at station #28 and then accompanied the R/V L.M. Gould to broad-scale station #42 in case they had trouble getting to the desired location because of the pack ice. They plan to work in the area for a number of days. We are currently (2010) steaming between station #41 and 40 as we run a portion of the survey grid in reverse. The anticipated storm arrived today and made for poor working conditions. Our position is -68° 17.941S; -69° 25.491W. The air temperature is -0.9°C and the wind is out of the north (357) at 30+ kts. The barometer is still dropping and is now reading 951.6 mlb.
The work on August 4 was along the middle portion of the continental shelf on transect #5. In the early morning the air temperature was much warmer than we have experienced recently - around +1.0°C and the wind was out of the northwest at about 30 kts. Skies were cloudy with some mixed precipitation earlier in the morning, but later in the day the snow on the decks rapidly melted and water was cascading off the upper superstructure and down onto the helo deck and main deck creating small water falls. In the evening (2030), the winds were lighter - 14 to 18 kts out of the north (004), but the snow returned in spite of an air temperature around 0.2°C. The weather map showed a large low pressure system headed our way and already the barometer was dropping with a reading of 962.7, down from 973.0 mlb at 1300.
Work was completed at stations #25, 26, and 27. The CTD at station #25 came close enough to the bottom (~341 m) that some sediment was apparently kicked up and got into the pumping system used with the conductivity and temperature probes (there are two sets of each kind of probe on this CTD). Conductivity values on one of the two probes was very noisy on the up portion of the cast and the values were bad. Flushing the system during the transit to station #26 and then during the soak period at the station apparently fixed the problem. In addition to a phytoplankton tow and a CTD at #25, ice collections were made by Frank Stewart and Erin Macri. The personnel basket and the crane were used to put them over onto the ice next to the ship. Station #26 was an extended station with under ice diving by the Torres group, and a 1-m2 MOCNESS tow in addition to the CTD and phytoplankton tow. Although scheduled, the ROV work again had to be cancelled because the electronic problems have not yet been resolved. Station #27 was a short station with only a CTD cast and a phytoplankton net tow.
During the transit between stations, BIOMAPER-II was towyoed, until an ice ridge was encountered near station #27 (more about that below), and there was some daylight available in the afternoon transit for bird and mammal observations.
John Klinck reports that on 4 August, the CTD group did three stations from the center of the shelf along the 340 line to the opening of Marguerite Bay. There is no indication of recent intrusions of oceanic water at these stations, in spite of their being along the canyon. Given the relatively low temperature of the subpycnocline water, this water has been on the shelf for a while.
A poster on the ship presenting results from a geological program in this area identifies the "canyon" running from the shelf break south to Marguerite Bay as the "Marguerite Trough".
Station #25 (420 m) is a typical midshelf station with a mixed layer to about 60 m and a gradual transition to the pycnocline over about 10 m. The permanent pycnocline extends to about 150 m. There is a weak temperature maximum about 50 m above the bottom at 350 m. A small drop in O2 occurs in a layer at the bottom about 20 m thick.
Station #26 (485 m) has a similar structure to station #25, except the mixed layer is only about 50 m thick. The deep O2 has two clear minima at 200 and 450 m. The water below 200 m is almost isothermal.
Station #27 (768 m) has a mixed layer to 50 m with a steppy structure in temperature and salinity down to about 130 m. A distinct O2 minimum occurs at 240 m and the temperature maximum is at about 350 m. Deeper conditions have steadily increasing salinity and decreasing temperature.
Jose Torres has summarized the work his group has been doing for the period 27 July to 4 August. Thus far the Torres group has completed 3 tows at consecutive stations #12, 19, and 24 with the 10-m2 MOCNESS (MOC-10). In conjunction with the Daly group, and with considerable help by Christian MacDonald, visual observations and live animal collections underneath the pack ice using SCUBA were completed at consecutive stations #5, 9, 15, and 26. Live animal collections were made with a 1.5-m2 Tucker trawl in collaboration with the Daly group at stations #1, 13, 19, and 22. Live specimens collected during the dives and live net tows were the subject of 106 individual measurements of metabolism and excretion.
Preliminary results. Two of the three MOC 10 tows (12 and 24) took place off the shelf and sampled to 1000 m. One was a little east of midshelf (19) and sampled to 300 m. A typical oceanic fauna was encountered at the two off-shelf stations with the following rough species breakdown:
0-50: Themisto gaudichaudii, Thysanoessa macrura, cydippid
50-100: Thysanoessa macrura (>50 individuals- clear dominant), Sagitta
100-200: T. macrura ( >50 individuals-clear dominant), Cyclothone, Tomopterus
200-500: Electrona antarctica, Protomyctophum bolini, Notolepis coatsi, T. macrura (>50), Euphausia triacantha, Cyphocaris sp., Atolla sp.
500-1000: Electrona antarctica, Bathylagus antarcticus, Cyclothone microdon, Gennadas sp., Gnathophausia sp., Pasiphaea scotiae, Periphylla sp., T. macrura
Of the two stations, #24 was clearly higher in biomass, particularly in the fish fauna. There was a large shift in relative biomass composition by the two euphausiids E. triacantha and T. macrura between the present cruise and the cruise on the L.M. Gould. E. triacantha was far more abundant in the fall.
The MOC-10 tow at station 19 revealed a very different faunal composition.
0-50: Euphausia crystallorophias, Themisto gaudichaudii, Eusirus sp. larval fish unk sp.
50-100: Euphausia crystallorophias, hydromedusae
100-150: Euphausia crystallorophias, Themisto
150-200: Euphausia crystallorophias, Thysanoessa macrura, fish larvae unk sp
200-300: Euphausia superba, T. macrura
Dives have been very successful for collecting krill furcilia, with visual observations suggesting that concentrations were highest at stations #5 and 26. The composition of our Tucker trawl tows mirrored that of the MOC-10 sampling and the SCUBA observations.
Kendra Daly reported that on 4 August, the Daly group participated in the dive event at station #26. Despite winds gusting over 20 kts, a strong current, and a cranky outboard engine, the dive was highly successful. Large aggregations of larval krill were observed under a rafted ice floe. Several thousand larvae were collected, as well as several samples of sea ice biota from the under surface of the ice where larvae were feeding. Some rate measurement experiments were started at the dive site, and several more back on board the ship. Fewer ctenophores were observed compared to previous dive sites.
Ari Friedlaender reports that on 4 August, observations were made from 0900-0950 and from 1500-1620. Visibility was poor due to fog and blowing snow. Ice conditions were 9/10 large and vast floes, with new snow on them and newly frozen leads. Six Adélie penguins and 1 crabeater seal were sighted, no whales.
Ana Sirovic reports that on 4 August, she deployed one sonobuoy, as the 1-m2 MOCNESS tow was started at station #26. This deployment was used to troubleshoot the antenna problem. In the end, it was decided to take the preamplifier off the directional antenna. Various tests were tried once the preamp was off the science mast, but the uncertainty remains as to what the real antenna problem is. Ana did, however, get a very good range (12 nm) on the other antenna and was able to monitor the buoy for 4 hours. There was no biological noise to report.
BIOMAPER-II/MOCNESS report (P. Wiebe, C. Ashjian, and S. Gallager):
The BIOMAPER-II towyo on our way to station #26 was done without any towing wire hang-ups on ice, but at one point in a towyo leg, the ship's forward progress through the ice came to a stop because the ice was too thick. There was about 300 m of wire out when this happened and with the ship stopped, the fish sank quickly to that depth. After a bit of backing, the ship again put the power to the propellers and the mate, Dave Fahey "goosed" it. We came up to 5+ kts rather rapidly and the fish also came up rapidly. After that, we had no other problems in getting to station #26. The towyoing between stations #26 and 27 came to screeching halt when the ship ran into an ice ridge and could not get through it. The bridge called down to the BIOMAPER-II van and asked that the fish be pulled onto the deck so that they could get a run at the ridge and break through it. Since we were only 4 miles from station, we pulled the fish and then put it into the garage van so that Scott Gallager could continue the search for the elusive gremlins causing the noise on the high magnification video camera.
On 3 August, MOCNESS tow #7 to 1000 m was conducted off of the shelf break at station #23. The cod ends of the nets came up knotted together and the contents of the nets were damaged. Unfortunately, the animals appeared to be "liquified". During the tow, the wire caught on a piece of ice while the net was quite deep. The ship had to stop to free the wire, during which time the net fell in the water to over 1000 m. The net was fished up through the water column as the ship came back up to speed and then by hauling up the wire.
Only a few copepods were found below 800 m. A huge myctophid was observed in the 600-800 m range. Krill were seen from 400-100 m, mostly Thyssanoessa. Chaetognaths were observed from 100-400 m. The upper 50 m contained very little, mostly copepods.
On 4 August, MOCNESS tow #8 was conducted at station #26. Pteropods were observed throughout the water column. Ostracods and chaetognaths were seen from 200-382 m. The 100-200 m range contained siphonophores, chaetognaths, copepods, and Thyssanoessa. The 50-100 m range contained pteropods, copepods, Thysanoessa, ostracods, and a few ctenophores. A few Euphausia crystallophora were observed from 25-50 m, along with both naked and shelled pteropods. The upper 20 m contained very few animals, with only a few euphausiids, ostracods, and copepods.
All of the MOCNESS tows on this cruise have been marked by low abundances of krill of all life stages at all depths. This contrasts with the situation seen during the first GLOBEC cruise in April-May.