The weather this morning (29 July) was clear and cold. There has been very little wind most of the day - around 5 kts or less.out of the southeast - but the air coming off the ice shelf is really frigid around -14°C. A sea smoke (caused by evaporation of seawater as a result of the big difference in temperature between the warmer surface sea water at 1.85°C and the air) reduced the horizontal visibility especially when we were in areas with a lot of open water as we were in the morning. Our current position at ~1700 (29 July) is -66° 27.83S; -68° 04.64W. Winds are fairly light at 10 to 12 kts out of the southwest (235) and the air temperature is -9.4°C.
Yesterday on transect #1, we finished the work at station #4,which was started the day before, and at stations #5, 6, and on transect #2, we completed work at station #7. Between stations, we towyo'd BIOMAPER-II and surveyed birds and mammals. The station work included net tows for phytoplankton and zooplankton, the CTD casts, sea ice collection (at station #4), an ROV deployment (at station #4), and an under ice dive (at station #5). The success of the divers in collecting krill from small patches under the ice for experimental purposes, made it unnecessary to take a Tucker trawl for live animal collection later in the day. The day was not without its mishaps. At station #4, the 1-m2 MOCNESS was damaged as a result of the wire hanging up on the ice it was being towed. A report of this occurrence is given below.
John Klinck reports that the CTD group completed three more stations today to finish the northernmost line (500 line) to Adelaide Island and to start the 460 line by doing the innermost station.
Station #5 (724 m) has the character of a deep mid-shelf station with a mixed layer to about 90 m with freezing temperatures (-1.82° ) and very uniform properties. There is some stratification in the lowest 15 m of this surface layer. The permanent pycnocline (100 to 200 m) shows strong layers (about 5 m thick) with some temperature reversals. A weak temperature maximum and O2 minimum occur at about 300 m. There is a second temperature maximum at about 400 m with a slightly higher salinity, perhaps indicating two separate intrusions of oceanic water coming from two different depths. The T-S diagram from station 4 shows a similar double peaked temperature maximum.
Station #6 (288 m) is a few kilometers from the coast. The mixed layer is thinner here (about 55 m) with very weak structure and an abrupt jump in properties at the bottom. The pycnocline is thicker (up to 150 m). There is no deep temperature or O2 maximum because the water is too shallow.
Station #7 (120 m) is the inner station on the next line south (460 line). There is a mixed layer to 40 m with a sharp transition to warmer water below. The surface layer is clearly stratified. Surface O2 (top 15 m) is low, although this may be due to insufficient adjustment of the O2 sensor at the beginning of the cast. The water properties change abruptly at the base of the mixed layer, but there are no deep minima or maxima. However, even this shallow water maintains a two-layer character with modified oceanic water below a clear mixed layer.
Along this section, the isopleths of water property are largely horizontal inshore of the shelf break while they descend sharply offshore of the shelf break. Over the inner 50 km of this section, the mixed layer has a lower salinity (below 33.85) indicating the influence of the coastal current or continuing glacial melt along the coast. There does not seem to be any distinct water properties in the deep section on the inner side of the shelf.
Ari Friedlaender reported that on 28 July sighting effort for marine mammals began at 0915 en route to station #5. Skies were clear, save a few high, scattered clouds. Ice coverage was variable throughout the day, ranging from 6-9/10ths. As we moved closer to the coast, leads became larger and more frequent. Offshore, the leads appeared to be covered by new grey ice. The remaining ice was mostly new ice and consolidated cakes less than 20 meters in diameter with old snow and low ridging. The leads varied in size from 10's of meters to several kilometers in diameter. As well, a healthy number of small and medium sized icebergs freckled our view. Sighting effort ended upon reaching station 5 at 1300. No cetaceans and only a single juvenile emperor penguin were sighted. Incidental effort resumed from 1520-1620 leaving station #5, until light diminished. No cetaceans were sighted during this time either, however, a single crabeater seal was sighted in a small lead.
Ana Sirovic deployed three sonobouys, all of them while in transit between different stations. No biological sounds were heard on any of the bouys, but reception was very bad and the ranges very short. She is hoping, by some miracle, she will start hearing whales soon!
Chris Ribic and Erik Chapman reported that on 28 July (JD-209), they surveyed for 4 hours and 53 minutes in heavy first year pack ice between consecutive stations 4 and 6. Ice varied between 1 and 10/10ths coverage and consisted of cakes, large floes and new gray ice. We went through several large leads during the transects. Overall we saw a handful of Snow Petrels and a single Antarctic Petrel. We saw very few birds during the survey between stations #4 and 5. Ice conditions were similar to those off the shelf during this stretch of transect, yet we saw fewer birds. However, we began to pick up a few more Snow Petrels associated with leads between stations #5 and 6, as we approached an area with more open water near Adelaide Island.
A summary of the counts is the following:
They surveyed for an hour last night from the bridge and saw a single
BIOMAPER-II/MOCNESS report (P. Wiebe, C. Ashjian, and S. Gallager):
BIOMAPER-II was towyo'd between stations #4 to 6 and partially between stations #6 and 7. A series of small failures have been keeping the BIOMAPER-II group working long hours to keep the towed body operational. During the station activities at station #4, BIOMAPER-II's 43 kHz transducers were swapped because the down-looking transducer stopped working due to some as yet undetermined failure in the transducers electronic circuitry. Similarly, while BIOMAPER-II was on the deck during station #6, repairs were started on one of the two VPR cameras, which stopped working between station #5 and 6 because of water leaking into the camera case. This repair took some time and the towed body was not deployed again until we were well along the trackline to station #7.
The volume backscattering along these tracklines was mostly very low indicating a low standing stock of zooplankton in this area of the continental shelf off northwest Adelaide Island. There were several small patches of intense backscattering in the vicinity of stations #4 and 5 located between 40 and 60 meters below the surface, which were likely krill furcilia. Near the surface the VPR images were mostly of small copepods. Above some areas, there was a layer of diffuse scatterers extending up 25 to 50 meters above the bottom in water depths greater than 350 m. There was a discernable layer of scatterers with somewhat larger target strengths at depths of 200 to 300 m, but they were not very abundant.
The 1-m2 MOCNESS was deployed just after midnight at station #4 for a tow to ~300 m depth. Towing speed is normally between 1.5 and 2.5 kts and at this speed the open wake area behind the ship is a bit narrower than when BIOMAPER-II is being towed at 4 to 6 kts. As a result when the towing wire had assumed its inherent angle from the vertical at the towing speed (around 45° ), the wire was 25 or so meters behind the transom. At that distance, smaller bits of ice on the leading edge of the closing wake flowed into the path of the wire, hit it, and were then turned to one side or the other to pass on. But on two occasions during the tow, a much larger flat cake came drifting into the wire's path and the wire did not slip past it. It just started being dragged aft with the ice chunk as the ship steamed away from it. The first time this happened, the wire broke free on its own and came back into a normal towing position in the open water without any effect. Some time later, the wire again got hung up on a large piece of ice and this time the wire did not break free. As the wire was pulled aft at the surface, it caused the net to be pulled from several hundred meters below the surface right up to the surface and into the bottom of the offending ice cake. Jay Ardi was out on the deck quickly once the problem was known and took charge trying to get the wire freed. There was more than 500 m of wire out when the operation to get it freed started, more length than the water depth. After a series of very carefully orchestrated maneuvers of the ship and the winch, the wire did become free. When it did, however, with the ship slowed significantly, the wire and net sank to the sea floor, which was at ~350 meters. Jay then started a slow and measured sequence instructions to the winch operator and the mate on the bridge to bring the wire in and yet keep from dragging the net over the bottom. It was a very professional job that was done to get the net system back to the surface. It came to the surface and on board by about 0215. The frame was damaged, but all of the major parts were still attached to the frame. Several of the nets were partially full of ice that made then weigh a "ton", and there was a bucket of sediment in a net. The strobe light batteries took a heavy hit and one of the battery cases was flooded with sea water. The front fenders were destroyed- actually broken apart, the flow meter was knocked of its bracket, but saved by the safety line, the back fenders and plate with the optional sensors were bent down, but all the instruments were intact. The strobe light was OK. The net bar slides were bent some, but can be straightened, and the net response and net bar traps were intact. Amazingly none of the nets burst in spite of having a tremendous weight of ice in them. So all in all, we are lucky to have gotten the system back and in a condition that was repairable. And we are much more aware of the hazards of towing in the pack ice.