Report of Activities on the RVIB N.B. Palmer Cruise 02-04
The pack ice in the southern sector of the SO GLOBEC grid is proving to be a tough obstacle to overcome. In the evening of 12 August, we finished up work at station 77 around 2230 and headed for station 80 some 26 miles away. At 0730 on 13 August, we were still about 12 miles away and it was clear that we could not spend additional time trying to get there. A mile long lead was in the area and that is where the work intended for station 80 was done. The work in the lead included a CTD cast, a BIOMAPER-II time-series profile, and two Tucker trawls to collect live animals for experimental purposes. About , the Palmer headed northwest toward station 81. We arrived at the station around 1615 after getting a break in the ice pack and making good time toward the end of the run. The station was done in another lead only 0.5 miles from the intended station location. After the CTD, there was a Tucker trawl taken to get additional live animals to work with and, unlike the one taken earlier in the day, the catch was a good one. This was followed by a meter net tow in the upper 50 m. Around 1900, we again started steaming - this time for station 82 on the edge of the continental shelf.
A false fire alarm sounded about 2245 that turned into an unplanned drill. Everyone in the science party got to the level 3 assembly point very quickly. Apparently, the alarm was triggered by a smoke detector in the hydro lab where the nutrient auto-analyzer was located, but there was no smoke or fire.
In the wee hours of 13/14 August, a decision point was reached. The struggle to steam and work on survey lines 11 and 12 gave rise to the likelihood that as much or more survey time would be required to get to stations 83, 84, and 85 as was required to get to the earlier stations. This would jeopardize the possibility that we could cover the ten stations on survey lines 9 and 10 in the time remaining to work in the southern sector. Although some of those stations may also be unapproachable, the decision was made to drop the work on line 13 and instead head along the continental shelf toward stations 75 and 74 once the work was completed at station 82. This would enable us to focus our effort during the next 4 or 5 days on lines 9 and 10.
August 14 was cloudy with snow off and on throughout the day. The morning started out cold (-9.6șC at 0038), but warmed during the day and into the evening to -2.0șC by 2030. The barometer fell from around 995 mb in the morning to 984.8 mb at night. The winds were almost a repeat of the cycle on the previous day. They were light (~6 kts) out of the north around 0700, but changed to westerly by 1100 and picked up to around 20 kts and remained that way for most of the rest of the day. Around , winds increased substantially and the air temperature dropped to -10șC, a portent of more extreme weather on 14 August.
CTD Group report (Eileen
Hofmann, Baris Salihoglu,
Bob Beardsley, Chris MacKay, Francisco (
During the past 24 hours, the CTD group was able to complete casts at four stations, three along survey transect 12 and the outer station (number 75) at the seaward end of transect 11. The stations along transect 12 consisted of one near station 80 and stations 81 and 82. Station 80 was determined to be unreachable because of sea ice, so the decision was made to stop and do a station where possible. The CTD casts included the FRRF and CMiPS sensors.
At station 75, a strong surface was encountered. The bridge crew reported that they were steaming into a 1.2 knot current while trying to reach the station and once on station had to counter this flow to remain at the sampling site. While doing the CTD cast, the effect of the current was obvious as it moved sea ice by the ship.
The completion of the four stations on 13 August provided sufficient data to construct vertical across-shelf property sections for transects 12 and 11. The vertical temperature section from transect 12 (more southern) shows water above 1.0șC covering the shelf below 250 m, with maximum temperatures of 1.3șC to 1.35șC at mid-shelf. The corresponding salinity distribution confirms that this is Upper Circumpolar Deep Water. This distribution is in sharp contrast to the temperature distribution observed during NBP02-02, which showed 1.3șC water only at the outer shelf edge.
The vertical temperature section along transect 11 shows the southern boundary of the Antarctic Circumpolar Current at the outer end of the transect (station 75), which accounts for the strong current encountered while steaming to this station and while on station. The apparent southerly set of this current may indicate that this is part of a meander in the southern Antarctic Circumpolar Current Front. Upper Circumpolar Deep Water extends onshore from station 75 for about 25 km. Inshore of this, the bottom waters of the shelf are composed of modified Circumpolar Deep Water.
Surface waters along both transects were well mixed to about 100 m and were just at freezing (-1.83șC). The isotherms along transect 12 sloped downward from inshore to offshore. The -1.5șC isotherm deepened from 100 m at the inshore edge to 150 m at the outer edge of the transect. This may reflect the extent to which waters in this region have been exposed to atmospheric mixing and cooling.
Marine Mammal report (
Day 13 and 14 (Monday, 12 and
Not everyday is Sunday. After our great day on Sunday, 11 August, no whales have been observed the past two days. Observation hours totaled 13.95 during the two day period (12 and 13 August), but only 3.12 hours of effective effort were achieved. There were 10.83 hours of incidental observation which corresponded to observation made during stations or during bad weather or viewing conditions. The cumulative effective effort observation hours of marine mammals to date now total 36.7 (excluding incidental hours). Weather conditions were not optimal for cetacean surveying. It was foggy and windy (14-20 knots), and it snowed most of the day, which affected viewing conditions considerably. Ice coverage varied from 8/10 to 10/10 with first year ice. The only marine mammal seen during these two days was the crabeater seal (Lobodon carcinophagus). Seals were seen during stations and between stations. On Monday, not many seals were seen (five seals in two different sightings), but on Tuesday crabeater seals were common most of the day: a total of 30 seals in 7 different sightings. They were most often seen along the edge of long and narrow ice breaks.
ROV report (Scott Gallager, Phil Alatalo)
The ROV was deployed for an under-ice survey on 12 August at Station 77 in the vicinity of open leads, grease ice, and thin ice floes. At 1824, the ship positioned itself in a lead with thick ice on either side. The ice collection team went over onto the ice followed by the ROV deployment in the lead. The Simrad and ADCP acoustic systems showed strong scattering at 300, 150, and 100 m, but not near the surface. The under-ice surface was smooth in the region of a floe, and jagged under ridges. Some second-year ice was observed with dark layers intermixed with light ice layers, particularly on edges 50 cm thick or greater. Unfortunately, very few furcilia were in the water column. Only the occasional larva swam by with no aggregations of organisms in the many pockets created by the ice ridges. Fish larvae were abundant swimming within the deeper pockets and ice shelves. A few ctenophores, with tentacles extended, floated by the cameras view. The habitat afforded by the many nooks and crannies screamed krill country, but the krill were nowhere to be found. The ROV was taken out of the water at 1951.
Current Position and Conditions
We are currently steaming for station 73, having recently completed work at station 74. Our position at 0045 is -68ș 19.131′S; -75ș 23.676′W. The winds have subsided from the gale force winds that blew most of the day and are now 8-12 kts out southwest (247). The air temperature is -19.2șC (Brrrrrr!) and the barometric pressure is 994.3 mb. Skies are partly cloudy and the first quarter moon is partially veiled, but clearly visible.