Report of Activities on the RVIB N.B. Palmer Cruise 02-04

10 August 2002

The third day (10 August) of the convoy transit by the N.B. Palmer and the L.M. Gould from Crystal Sound to the vicinity of Station 77 on the Southern Ocean GLOBEC grid mostly consisted of steaming. The marine mammal group on the Gould led by Dan Costa had decided to wait to tag and to make measurements on more seals until getting into the southern portion of the grid. This in spite of the fact that a substantial number of seals were present along the trackline. The penguin group led by Heidi Geisz on that vessel were only interested in sampling penguins hauled out on the ice pack in the afternoon after they had been feeding. So we made good progress during the early part of the morning in ice pack that was easy to move through. The fast steaming through the ice pack came to an end about 1000, when the Palmer encountered substantially thicker ice pack that was a jumble of broken and rafted chunks of ice half a meter to a meter thick. Backing and ramming was required to make it forward. This was to some extent expected since we crossed the line marked by the southern outer portion of Marguerite Bay and the northern tip of Alexander Island and entered the southern sector of the grid. Last year, we were in substantially thicker ice once we got south of this line and this year it seems to be the same.

Just after noon the Gould called to express concern about the speed at which we were moving toward Station 77 and to raise the possibility that they take up residency to the east of our position at that time (approximately at station 60). A review of the most recent ice images revealed that the open ocean and ice edge had moved considerably east relative to where it was when we left Punta Arena, Chile at the end of July and now included portions of the SO GLOBEC grid. This was quite unexpected. Also areas to the south appeared in the image to have better ice conditions from a steaming point of view than what the convoy was plowing through at the time. The ensuing discussion resulted in their dropping the idea of going east and instead they worked with us to get to the original destination by heading offshore to the northwest toward the open water. The plan then was to turn to the southwest and head down the outer line of stations (65, 74, 75) before heading to the southeast along survey line 10 to station 77. This added considerable distance and time to the transit, but made it possible to get to the desired location. This plan was executed.

During the night of 9/10 August, the air temperature dropped to -10ºC, warmed during the day to around -6.4ºC, and then dropped back down in the evening to -9.0ºC. Winds were light at about 7-8 kts out of the north (349) in the morning, shifted to about 8 kts out of the southwest (223) by mid-afternoon, and were stronger in the evening, 20-22 kts out of the southwest (233). This change was reflected in the barometric pressure that was at 979.9 mb in the morning, 977.8 mb in mid-afternoon, but 981.0 mb and rising in the evening. The skies were mostly cloudy during the day, but quite variable. In the morning, it was very cloudy with the sea ice merging seamlessly with the gray sky so that the horizon was not discernable. There were some snow flurries and light freezing rain and then it cleared and off in the distance there were patches of blue sky. On occasion the sun was like a spotlight shining on icebergs in the distance turning them to a brilliant white against a dark background. Beautiful!

CTD Group report (Eileen Hofmann, Baris Salihoglu, Bob Beardsley, Chris MacKay, Francisco (Chico) Viddi, Sue Beardsley)

While stopped for predator sampling on 9 August during the transit to the first process station, we were able to do one CTD/CMiPS cast at a location that is approximately between survey stations 20 and 21 (-67º 11.32′S; 70º 33.09′W). This station provided the first real test of CMiPS, which is used for microstructure sampling. The next CTD/CMiPS cast was done on 11 August after situating the Gould at the first process site. This station is approximately at the location of survey station 75. (The time between the two casts was occupied with XBT surveying as described in previous reports.) Depths at the two stations were about 500 m and 420 m, respectively. Both CTD/CMiPS casts were to within 8-10 m of the bottom.

The vertical property distributions from the two stations were quite similar in spite of the large spatial separation (about 180 km) between the two sites. Maximum temperature at the bottom of both casts was 1.3ºC with a salinity of 34.6. These values are indicative of modified Circumpolar Deep Water, which covers the west Antarctic Peninsula at depths below about 200 m to 250 m. The presence of this water indicates that no new intrusions of Circumpolar Deep Water are present at these sites. This is consistent with what has been observed on earlier SO GLOBEC cruise. The two CTD sites are in regions of the west Antarctic Peninsula shelf that are not typically affected by Circumpolar Deep Water intrusions.

At both stations, the surface waters were at the freezing point and the Winter Water layer covered the upper 80 m to 100 m of the water column. This hydrographic structure is typical for winter conditions on the west Antarctic Peninsula continental shelf.

During the transit, the discrete dissolved oxygen samples taken from the Niskin bottles on the Rosette from the Crystal Sound survey and the two casts mentioned above were processed. The dissolved oxygen values obtained from the titrations were compared to the corresponding values measured by the oxygen sensor on the CTD. This comparison showed that values from the CTD-mounted oxygen sensor were consistently lower than the titrated values. Furthermore, it appeared that the offset between the two was larger for surface values than for deeper values. We will continue to take discrete oxygen samples to refine the calibration that will be needed to correct the CTD oxygen samples.

Phytoplankton Ecology / Primary Production (Kari Sines and Frank Stewart)

Primary production in the SO GLOBEC IV grid during NBP02-04 is being measured using two principle methods. First, net daily production is being estimated by carbon uptake during 24 hour “simulated in situ” (SIS) deck incubations. Water for these experiments is being collected once per day from the CTD rosette, at the station most prior to sunrise, at depths of zero to thirty meters. Secondly, water column profiles are being generated using a Fast Repetition Rate Fluorometer (FRRF) as part of the CTD package, at all stations where the depth is less than 500 meters. Chlorophyll measurements and particulate carbon sampling are also being completed for estimation of phytoplankton biomass.

During the first week of SO GLOBEC IV, the primary production group completed one SIS experiment at station 4 of the Crystal Sound grid. The FRRF has been deployed at four of the seven CTD stations, and chlorophyll and particulate carbon samples have been taken at two stations, Crystal Sound 4 and 7. In addition to the Crystal Sound transects, CTD sampling occurred at station Transit 1 where the FRRF was deployed and samples for phytoplankton biomass estimation were taken. Sampling for chlorophyll and particulate carbon in all these locations occurred at depths throughout the water column.

Sea Birds (Chris Ribic and Erik Chapman)

Sea Bird and seal observations were conducted on 10 August during almost 8 hours of survey time as the ship traveled toward station 77, across the southern edge of the mouth of Marguerite Bay. Ice conditions were consistently 9 to 10/10ths coverage with large heavily rafted 1.5 m one-year old floes. Few birds were observed in this area, though sightings included 7 Adélie Penguins and 4 Emperor Penguins. Eleven Snow Petrels and 4 Southern Giant Petrels were the only flying birds found in today's survey.

We are also collecting data on marine mammals observed during surveys and 42 Crabeater Seals were recorded in today's transect. These numbers agree with results from previous cruises that suggest Crabeater Seals are consistently found in relatively large numbers in the Southern portion of Marguerite Bay. Data from ADCP and SIMRAD instruments, which both use acoustics to give a relatively crude measure of the amount and distribution of zooplankton in the water column while the ship is underway, suggested a large amount of krill in the upper surface today. The apparent concentration of krill under the ice in this region could explain the high relative density of Crabeaters. It seems that Adélies tend to be in somewhat lighter ice conditions with more open water, which may explain the absence of penguins here despite the presence of krill.

A summary of the birds and marine mammals observed on 10 August (YD 222) during 7 hours, 45 minutes of survey time as the ship traveled south toward station 77 is the following:

Species (common name)	Species (scientific name)	Number observed
Snow Petrel	Pagodroma nivea	11
Adélie Penguin	Pygoscelis adeliae	7
Southern Giant Petrel	Macronectes giganteus	4
Emperor Penguin	Aptenodytes forsteri	4
Crabeater Seal	Lobodon carcinophagus	42

Marine Mammal report (Chico Viddi)

Effort began on 10 August at 0830 and finished at 1620. During this period there were only 2 “effort” hours, the rest were incidental hours. Effort was mainly interrupted due to weather conditions. The day had extremely variable weather, from partially cloudy (40%, when it was possible to see and admire Antarctica's blue sky, something we have not seen for a couple of days) to foggy snow. Ice coverage was 10/10 all day. To date, 30.7 observation effort hours have been achieved. The only species sighted today was the crabeater seal (Lobodon carcinophagus), although they were very numerous and were seen many times. More than 40 seals were seen in the different sightings. Most of them were seen from 1341 to 1402, between -68º 07.71′S; 73º 21.31′W and -68º 07.32′S; -73º 25.52′W, mainly concentrated along the edge of a long and narrow break of open water. A few more sightings were made at 1514 (-68º 03.73′S; 73º 37.93′W) where about 8 other seals were seen over an area of one square mile .

Current Position and Conditions

Finally we have reached the end point of the convoy and the Gould is situated at a location near grid station 77. The Palmer has begun the survey of the southern sector of the SO GLOBEC station grid. Our current position at 2355 on 10 August is -68º 08.672′S; -75º 25.442′W. The ice pack is variable with mostly 10/10 coverage, except along the outer continental shelf. The air temperature is -11.5ºC and the sea temperature is -1.851ºC. The barometer (982.6 mb) is rising slowly. Winds are out of the west (269) at about 10-15 kt. The skies are cloudy.

Cheers, Peter