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

2 September 2002


The Antarctic Circumpolar Current (ACC), which runs clockwise around the Antarctic Continent, is one of the oceans great current systems. In the region off the Western Antarctic Peninsula where the Southern Ocean GLOBEC survey grid is located, the current often flows right up against the edge of the continental shelf.  Such was the case on 2 September.  The two stations where work was carried out were in the core of the ACC. Work at grid station 1, which was farthest offshore, was in 3217 m of water.  BIOMAPER-II was towyoed from station 2 to station 1 arriving about 0230. An attempt was made to deploy the ROV, but high winds, an ocean swell, and pack ice with large open water areas made it impossible to position the ship so that the ROV could effectively survey the under surface of a floe. Two CTD casts were completed, the first with the FRRF to 100 m followed by a deep CTD cast to the sea floor. This latter cast was a “cup” run as described below. A tradition has developed to use a very deep CTD cast to send styrofoam cups that have been highly decorated with colored pens to the sea floor. The high pressure compresses the cups and they return much smaller and sometimes in weird shapes creating a memento of the cruise of sorts. A second attempt at deploying the ROV took place after the CTD casts, but conditions had not improved sufficiently to permit it.


BIOMAPER-II was again deployed for the 26 nm transit between stations 1 and 13. Just before the launch, a group of Adélie penguins was spotted on a floe near the ship and the deployment was delayed while the penguin group mobilized to go after them. But the penguins had other ideas and they disappeared into the water before much in the way of preparations was done.  During the transit, another group of penguins was spotted, but they were on a floe that was judged too difficult to approach and the transit proceeded after only a short interruption.


Prior to arrival at station 13, BIOMAPER-II was retrieved so that the 10-m MOCNESS could be deployed for a 1000 m tow that would take us up to the station location.  The trawl went into the water around 1500 and was hauled on deck with all 6 nets closed about 2000.  At station 13, work was started around 2100 with the pair of 1-m ring nets deployed for an hour off the stern. This was another “drift net” tow in the upper 10 m with the main propellers turning just enough to force water to flow gently past the nets. Another good catch of krill furcilia was obtained using this strategy. A CTD cast to 2944 m was started a few minutes before midnight.


The near gale winds (28-33 kts) out of the southwest that began in the evening of 1 September continued for much of the 2nd and for a time became gale force (> 35 kts). They dropped down to 14-16 kts in the evening. The barometric pressure rose sharply from 875 mb to 1000 before leveling off around midnight. Air temperature remained between -4 and -7ºC all day.  Although the day started out cloudy, it turned into a brilliant bright day with the sun highlighting the white of the pack ice and icebergs against a dark blue cloudy sky off in the distance. Skies were very clear overhead. A long period swell continued to propagate through the area. Large bergy bits surrounded by pack ice undulated with a weird rocking motion that was some slower harmonic period of the swell.  


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

In the early morning of 2 September, we arrived at station 1, which is at the outer end of survey transect 1.  This is one of the deepest stations included in the survey grid with a bottom depth of 3235 m. As such, station 1 provides a deep water endpoint for the hydrography, as well as for many of the other measurements made on the cruise.  It also provides a data point that is on the offshore side of the southern boundary of the Antarctic Circumpolar Current which represents oceanic conditions.


Station 1 also provided an opportunity to attach a large bag of decorated styrofoam cups to the CTD/Rosette and send these to the depths of the ocean.  The considerable pressure exerted by a 3225 m water column crushed the styrofoam cups to about the size of a shot glass.  This is an impressive illustration of the effect of pressure and it results in unusual and unique souvenirs for family and friends.


At station 1, one cast was made to 100 m for FRRF sampling.  After this cast, the CTD/Rosette was returned to the ship, the FRRF removed, and the CTD/Rosette re-deployed for a second cast that went to within a few meters of the bottom.


The vertical temperature profile from station 1 shows the structure expected of a deep water oceanic station.  The Winter Water layer was above freezing at -1.63ºC and extended to about 40 m.  The above freezing temperature, the shallowness of this layer, and the reduced ice cover around station 1 may indicate that this area has been exposed to more mixing than the shelf waters.


Below the Winter Water layer, the temperature increased to a maximum of 2.13ºC at the core of the Upper Circumpolar Deep Water.  Further below, temperature decreased and salinity increased to 34.72 at 600 m which corresponds to Lower Circumpolar Deep Water.  The temperature at the bottom of the CTD cast was 0.41ºC with a salinity of 34.70.  Thus, no other deep water masses, such as South Pacific Deep Water or Weddell Sea Deep Water, were present along this portion of the west Antarctic Peninsula continental shelf.


Seabirds (Chris Ribic and Erik Chapman)

Over five hours of observations were made as the ship moved along and offshore of the shelf-break between stations 1 and 13.  According to the most recent satellite ice image, we were near the ice-edge on 2 September and ice concentrations dipped to 5/10ths coverage of the ocean's surface for part of the day.  A one meter swell ran through the pack, and 2 to 6 m diameter cake floes were the dominant ice-type.  Toward the end of the day, the cake ice became more compact and we were once again moving through 10/10ths ice coverage.


Antarctic and Snow Petrels dominated the seabird species assemblage once again today.  Many of these birds were milling over the open water before being attracted to the ship.  Snow and Antarctic Petrels were recorded feeding on several occasions, dipping their bills into the water's surface or into slushy ice, presumably picking out some type of zooplankton.   Southern Giant Petrels were also recorded in the survey.   In general, flying birds became less abundant as the ship moved into more concentrated ice near station 13 in the afternoon.


Penguin tracks from groups and individuals of birds were observed on many of the small floes, particularly in areas near open water.  The tracks appeared to be fresh, and certainly were made after the storm we experienced two days ago.  Judging from the size of the tracks, they appeared made by Adélie Penguins; however, we recorded just 6 Adélies during the survey.  Perhaps these birds had moved through this area, tracking or looking for krill swarms under the ice sometime during the previous day or so.  Crabeater Seals were recorded on floes in one small area in the survey for the first time in several days.  To this point, Crabeaters have been uncommon in the northern portion of the grid.


A summary of the birds and marine mammals observed on 2 September (YD 245) during 5 hours, 18 minutes of survey time as the ship traveled between stations 1 and 13 is the following:


Species (common name)

Species (scientific name)

Number observed          

Snow Petrel            

Pagodroma nivea                        


Antarctic Petrel       

Thalassoica antarctica                 


Southern Giant Petrel  

Macronectes giganteus                  


Adélie Penguin     

Pygoscelis adelii                  


Crabeater Seal         

Lobodon carcinophagus  




Microplankton report (Phil Alatalo, Gustavo Thompson, and Scott Gallager)

Microplankton observed from the CTD samples continued to show little change geographically as we moved from the central sector of the survey grid to the northern sector. Stations 41 and 26, west of Marguerite Bay on the middle of the shelf, contained few flagellates at the surface with slightly higher concentrations of smaller particles at depth. Mid-shelf stations in the northern area (stations 4 and 3) had very low particle concentrations at the surface and little appreciable swimming motion at any depth..  A nice ciliate was observed at 100 m at the shelf break (station 2), but otherwise all depths were very low in particle abundance.  Off-shelf Station 1 was interesting in that Mesodinium, a small ciliate with distinctive swimming behavior, was present in the surface water, as well as an unidentified ciliate bearing a tail (Tontonia ?).  Mesodinium was present in nearly all samples earlier in April and May.  Some diatom chains were seen in water taken from 3211 m.  Otherwise, very few particles were recorded.  Station 1 was our northern-most oceanic station.


Motion analysis conducted on these samples showed few depths with greater than 10 particles/ml. Particle speed was generally low, 0.01-0.02 ml/sec. NGDR (net to gross displacement ratios; see report on 20 August for additional explanation) showed little discernable pattern, though was occasionally lower at surface and upper halocline depths.  Particle diameters were small, ranging from 15 to 26 μm.


In contrast, water collected directly under the ice by divers from Station 26 contained high concentrations of particles, including diatoms, dinoflagellates, ciliates, and several veliger larvae.  These elongate, shelled molluscan larvae resemble gymnosomatous pteropod larvae and are being held in hopes of achieving metamorphosis into a more identifiable stage of development.  This diverse and abundant assemblage of organisms in close association with the under surface of the ice, is thought to be a result of concentrated phyto- and micro-plankton in sea ice.


A sample of brine taken from a seepage bore hole at station 12 revealed a remarkable concentration of Mesodinium sp. on order 200 per milliliter. Single cells were highly autofluorescent suggesting the captive chloroplasts were photosynthesizing. As noted above, this fast swimming ciliate has been abundant in surface waters during the fall months, disappearing from the water column in the winter. Mesodinium sp. overwintering in brine channels may be a significant contributor to rapid resurgence of both primary and secondary production in the spring as the ice melts and releases its captive community of microplankton. 


BIOMAPER II group report (Gareth Lawson, Peter Wiebe, Scott Gallager, Phil Alatalo, Dicky Allison, Alec Scott)

On September 2, we conducted two towyos with BIOMAPER-II, the first of which was during the two hour transit between stations 2 and 1. For much of the towyo there was little scattering evident in the water column other than two very dense, krill-like patches at 25 and 50 m. Occasional enhancements in background scattering also were evident at 150 m. Toward the end of the tow, a strong shallow scattering layer developed between 40 and 70 m. All along in this depth range the VPR had been capturing images of diatoms and some few krill, but once we encountered this layer, many more of these organisms were observed. Early in the towyo, we also saw two thecosomatous pteropods: small planktonic gastropods whose hard shells reflect a great deal of sound for their small size.


Our environmental data suggest that the quite sudden appearance of the shallow layer may be associated with our crossing over a front, with distinct hydrographic features and mixed layer depths on either side of the frontal feature. Scattering increased below 300 m, but this was well beyond the range of the VPR and so we don't know anything about the species composition in this portion of the column.


Later in the morning, we had the BIOMAPER-II back in the water for our second towyo of the day, this time transiting from station 1 to station 13. A dense shallow scattering layer was present between 25 and 60 m, in close association with the strong pycnocline. We also observed a deeper and more diffuse scattering layer centered at 100 m and extending to 150 m. This latter layer was much more evident at 200 kHz than at 120 kHz, while the shallow layer was stronger at 120 kHz. Smaller organisms reflect sound stronger at higher frequencies than at lower frequencies, suggesting that the shallow layer was composed of larger organisms than the deeper one. The VPR repeatedly sampled the shallow layer, which appears to have consisted of a diverse species assemblage that included radiolarians, copepods, krill, ctenophores, and many diatoms. Near the end of the tow, a number of denser patches were evident within the overall shallow layer. The BIOMAPER II intercepted one of these patches, and we observed a number of krill with the VPR.


Environmental data collected on this tow indicated that the location of the pycnocline varied along-transect between 40 and 60 m. Moreover, both acoustic layers showed wave-like oscillations in depth, suggesting the possible presence of an internal wave. Similar to how surface waves develop at the air-sea surface boundary due to the difference in density between these two media, internal waves are waves that develop across density gradients within the ocean's interior. This transect skirted alongside the continental shelf of the Antarctic Peninsula, and internal waves often form at and propagate away from continental shelf breaks.


Current Position and Conditions

The work in the northern sector of the Southern Ocean GLOBEC survey grid is moving along at a much faster pace that in previous sectors primarily because the pack ice is easily traversed. We are current steaming between station 11 and 10 in the in the middle of the continental shelf off Adelaide Island. Our current position at 0031 on 4 September is -66º 16.911′S; -70º 16.41′W.  The air temperature is -13.4ºC and the barometric pressure is 1001.0 mb and holding steady.  Winds are light at around 10-12 kts out of the south-southwest (210). Skies are partly cloudy and a light snow fell earlier in the evening. Venus, however, shone brightly on the horizon about an hour ago; visibility is good.  The pack ice is much more consolidated and is made up of larger flows than offshore, but still easy to move through.


Cheers, Peter