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

5 September 2002


The broad-scale survey of the northern sector of the Southern Ocean GLOBEC survey grid has been proceeding very well in large part because the weather has been favorable and the pack ice has been much less formidable than in the southern and central sectors.  Light winds out of the southwest for the most part and clear days have been of great benefit to the work on deck.   For much of the northern region covered thus far, there have been large recently frozen-over leads and thinner pack ice in general.


Upon completion of station 16 just before midnight on 4/5 September, BIOMAPER-II was towyoed from station 16 to station 15.  A pair of CTD casts was done at Station 15 between 0700 and 0800 with BIOMAPER-II remaining in the water to make time-series acoustic observations during the casts. The towyo to station 14 took place in late morning and the Palmer arrived at the station about noon.  First up was an under ice SCUBA dive, but this took longer to get underway because of the recurrent problem of getting the Zodiac's outboard motor to run. More outboard motor problems at the end of a successful diving operation made it necessary for the Palmer to move to the location of the Zodiac to get the divers back on board.  During the dive, the CTD was repeatedly profiled to obtain microstructure profiles of the upper 300 m of the water column. After the divers were back on board, a final CTD cast was made to the sea floor.


In the late afternoon, BIOMAPER-II was again deployed for the run off the continental shelf to station 23, the seaward station on the SO GLOBEC survey line 4. Work at station 23 began at 2200 with the deployment of the pair of 1-m ring nets for an hour-long drift tow to catch larval krill. The day ended with the start of an ROV under-ice survey just before midnight.


September 5 was another mostly very clear day. In the early morning, there were nearby icebergs with sea smoke rising from the open water regions in their wakes. Thin high cloud bands were overhead and a high cloud layer shrouded the tops of Adelaide Island some 60 nm in the distance. During mid-day, skies were clear.  High clouds moved in over the area during the late afternoon.  From under the clouds, we could still see the mountains of Adelaide Island with their mantle of white. A light snow developed in the evening, but did not persist. For a second day, winds were quite light with speeds less than 10 kts for essentially the entire day.  The winds were from the southwest until mid-afternoon and then shifted to the east.  Air temperature was between -16 and -17.5ºC until about noon and then rose rapidly to -10ºC. Barometric pressure rose over the course of the day from 1004 to 1009 mb.


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

In early morning of 5 September, we arrived at station 15, which is at the outer end of survey transect 3 in about 535 m of water.  Two casts were made at this station.  The first was to 350 m for sampling with CMiPS.  The second extended over the entire water column.  No FRRF sampling was done at this station.


After completion of station 15, we steamed to station 14, which is the outer-most sampling site on survey line 3.  This station is at the shelf edge in about 877 m of water. The first scheduled activity at station 15 was an ice dive by the Torres group.  Once again we used the time during the dive to do a series of shallow casts with CMiPS to measure microstructure variability.  We were able to complete 4 casts to 375 m while the ice dive was ongoing, with each cast taking about 20 minutes.  This now gives three sites at which a time series of microstructure in the upper 350 to 375 m of the water column was acquired with CMiPS.  These measurements are likely to be some of the more unique data acquired during the SO GLOBEC cruises.  Following the CMiPS casts, we did an additional CTD/Rosette deployment that extended to within a few meters of the bottom.  No FRRF sampling was done at this station.


The thermohaline structure at station 14 showed a well-mixed Winter Water layer (at -1.82ºC to -1.83ºC) that extended to 65 m.  Salinity in the Winter Water layer was relatively constant at 33.89.  Below the well mixed layer, temperature increased as Upper Circumpolar Deep Water was encountered, and reached a maximum of 1.67ºC at about 280 m with a corresponding salinity of 34.70.  Below this, temperature decreased to 1.15ºC at the bottom.  The corresponding bottom salinity was 34.72.  This indicates the presence of Lower Circumpolar Deep Water at this location and supports the suggestion that there is an intrusion of oceanic water moving onto the west Antarctic Peninsula shelf in this portion of the survey grid.


The thermohaline structure at station 15 was similar to that observed at station 14, consisting of a well-mixed Winter Water layer overlying warmer Circumpolar Deep Water.  The primary difference in the two locations was warmer temperatures at station 14, i.e., a temperature maximum of 1.80ºC and 1.16ºC at 876 m.  The salinity of the deeper waters was also somewhat higher, being 34.72 from 415 m to the bottom. This temperature and salinity structure indicates that station 14 is just at the southern boundary of the Antarctic Circumpolar Current (ACC).  Thus, this observation, combined with those from other shelf edge stations, shows that the ACC is located along the shelf edge over most of the area covered in the survey grid.


The CTD/CMiPS casts at station 14 were done under ideal weather conditions, excellent visibility with a high cloud bank so that we could see the sun on Adelaide Island, and -10ºC to -5ºC air temperatures with very weak winds.  The Palmer was stopped in a small lead, surrounded by icebergs.  On the transit to this station, we noticed sea smoke rising in the open water around many icebergs.  This suggests that these micro-environments, although perhaps small in area, could be contributing significantly to the local heat flux by cooling the surface waters. Due to the 2-m swell from offshore, many of the icebergs appeared to be bobbing, which would also enhance melting and mixing around the iceberg. The spatial density of icebergs has increased during the last cross-shelf transect, and particularly so along the transit to this station.


Using the Main 1 and Port radars on the Palmer bridge, we measured the distance and size of the large iceberg nearest the ship at the time of the third CTD/CMiPS downcast; the berg was 1.3 nm from the ship, and roughly 240-280 m in diameter. It appeared to have an aspect ratio of 1/5, so with a height above water of roughly 50 m, it could extend as deep as 50 x 9 = 450 m.  We then counted the number of icebergs clearly distinguished on the radar image within the 3-nm radius.  The total was 1 within 1.3 nm, and 49 within 3 nm.  This gives a roughly calculated concentration of 1 iceberg/2 km2.  It's unclear what influence being this close to a relatively large iceberg and in a region of icebergs has on the water structure measured at this station because there was no obvious change in upper water column properties, such as salinity, observed in the CTD measurements.  This is clearly an area for research.


Seabirds (Chris Ribic and Erik Chapman)

On the morning of 5 September, seabird and Crabeater seal surveys were conducted for almost three hours as the ship approached station 14, the furthest offshore station on the third survey line from the northern edge of the study area.  After station work was completed at station 14, the ship began to move south-west toward station 23, along the shelf-break.  Surveys were conducted for an additional 2 hours on this track before the daylight was lost.  Both surveys were located well offshore, near the shelf-break and relatively close to the ice-edge west of the ship.   Daylight was more than 10 hours and surveys were not cut off until 1800 hours.  Ice conditions varied between 8 and 10/10ths coverage and ice-type was consistently 6 m diameter cake floes throughout the day.  A steady swell of about 2 feet ran through the pack throughout the day.  As we have seen throughout the cruise, there were dozens of large icebergs off the shelf-break.


There was a strong presence of top predators during today's survey indicated the presence of important biological processes here.  Adélie Penguins were more abundant in today's survey than on any other day on the SO GLOBEC cruises.  Two hundred and ten birds were observed in groups of between 4 and 35 birds in just under 5 hours of surveying.  Most of the birds were recorded in the last two hours of the day as the ship began to move southwest from station 14 along the shelf-break.  BIOMAPER-II recorded bands of krill swarms in the upper 100 m of the water column beneath the ice in a concurrent bio-acoustic survey.  Six Emperor Penguins and 9 Crabeater Seals were also observed in the same area.


Snow Petrels were also relatively abundant in today's surveys as they have been throughout the cruise offshore, in open water near the ice-edge.  Just a single Antarctic Petrel was observed, however.  This was quite different from previous offshore surveys where this species has been as abundant as Snow Petrels over open water.  


A summary of the birds and marine mammals observed on 5 September (YD 248) during 2 hours  46 minutes of survey time as the ship moved between stations 15 and 14 and 2 hours of survey time as the ship traveled between 14 and 23 is the following:


Species (common name)

Species (scientific name)

Number observed          

Snow Petrel            

Pagodroma nivea                


Antarctic Petrel       

Thalassoica antarctica         


Emperor Penguin        

Aptenodytes forsteri           


Adélie Penguin         

Pygoscelis adelii               


Crabeater Seal         

Lobodon carcinophagus           




Marine Mammal report (Chico Viddi)

The 4th and 5th of September were two wonderful days, with blue skies and bright and beautiful sunrises and sunsets. Pinks and reds returned to the horizon. During these two days there was surprisingly little wind considering what we have been experiencing. If it were not for the air temperature (which reached -17.0ºC on 5 September), one could imagine that we were not in Antarctica and not in winter.   Observations during these past two days totaled 17.4 hours (8.6 on 4 September and 8.8 on the 5th); 10 hours corresponded to “effective effort”.


Even though viewing conditions were excellent on 4 September and we steamed through wide areas of open waters, not a single marine mammal was seen in the 5.6 hours of effective effort.  Observations were stopped at 1357 when we reached station 16.


On 5 September, 4.4 effective hours were achieved (interrupted from 1150 to 1614 while at station 14). Eighteen crabeater seals were observed, all of them seen after 1600. Two Minke whales were sighted at 1208 (-66º 24.51′S; -71º 22.46′W). They were seen 0.2 nm from the bow in the open water (less than 50 m wide) left by the vessel as it came onto station 14 and just before the divers left the ship.


There was a considerable difference between the water column acoustic patch structures registered on 4 and 5 September. There were few patches observed on the 4th during the transects, while on the 5th, there were many moderate to dense patches registered, mainly during the afternoon. This increase in patch presence is likely associated with the marine mammal presence (as well as the many penguin groups seen in the area). 


ROV report (Scott Gallager, Phil Alatalo, Alec Scott)

ROV deployment 21 was performed at Station 23 (-66º 35.955′; -72º 06.535′) on 5 September in the presence of small re-frozen floes among pancake ice and freshly formed brash. Four 60 m transects were performed out from the starboard side of the ship. In general, very small numbers of krill furcilia were found at this offshore station. The big surprise was the observation of juvenile and adult krill in fairly large numbers ranging from directly under the ice to a depth of 60 m. This was the first time older individuals have been seen under the ice in any great number. About 20 to 30 individuals were present in the field of view if the main ROV camera at any one time, translating into a concentration of greater than 100 per cubic meter. 


MOCNESS Report (Phil Alatalo, Peter Wiebe, Dicky Allison, Ryan Dorland, Scott Gallager, Gareth Lawson)

Our twelfth 1-m2 MOCNESS tow occurred well into the shelf at Station 16, late Sept. 4.  Despite the recent drop in temperature (-16.5ºC) and its initial effect on some of the sensors, the tow produced good quantities of zooplankton at each depth.  Copepods, krill, and chaetognaths comprised the bulk of the samples. While amphipods and fish have become more regular in their occurrence, limacinid (shelled) pteropods were found in each net.


Net 0 provided a diverse mixture of zooplankton for genetic studies by Ann Bucklin and a ctenophore for Kerri Scolardi's thesis work.  Copepods and chaetognaths were most numerous.  One midwater fish, Gymnoscopelus braueri, contributed significantly to the biomass of this net.


The deepest net interval (480-350 m) caught mostly large calanoid copepods. Chaetognaths, in a variety of size ranges, provided the next highest biomass here.  Large amphipods were caught and a large ctenophore was recorded for K. Scolardi.  The next deep net (350-200 m) also held a variety of zooplankton taxa.  Translucent copepods (Calanus acutus, C. propinquus, Metridia sp., Onceae sp., etc.) made up the bulk of biomass, together with Thysanoessa sp.and Euphausia tricantha krill. Radiolarians, chaetognaths, ostracods, pteropods, and polychaete worms were observed.  Biomass and copepod abundance dropped between 200 and150 m. Euphausiids, pteropods, and radiolarians were more abundant while a large ctenophore contributed to Net 3 biomass. Between 150 and 75 m, biomass dropped somewhat, with mostly Thysanoessa and other krill dominating the catches.  Between 75-50 m, a layer of C. propinquus increased the biomass dramatically.  Salps, krill, a ctenophore, radiolarians, and gymnosome pteropods made up the remainder of this depth interval.  The top 50 m was similar in composition. Chaetognaths and large calanoid copepods (Paraeuchaeta sp., C. propinquus) dominated the abundance. Several large ctenophores were removed for K. Scolardi.  Fish larvae, more limacinid pteropods, E. tricantha, Thysanoessa sp.,and amphipods were all present in the surface water at Sta. 16.


Tow 12 differed from the previous shelf station, in that krill were present primarily around 100 m and copepods were very numerous at both surface and depth. The OPC successfully collected particle size data in conjunction with the MOCNESS.  Special thanks to Kendra Daly, and Joe Donnelly for zooplankton identification.


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

In the morning of September 5, we had the BIOMAPER-II in the water for 11.5 hours as we transited first from station 16 to station 15, and then on to station 14. At station 15 the CTD group performed their casts, during which time we collected data with the towbody stationary. Throughout the tow, there was little evidence of any shallow scattering layer, although episodic enhancements in scattering were evident at the top of the pycnocline (75 m). We also observed 15 very dense (up to -52 dB), tall (15 to 45 m), but short in horizontal extent (50 to 150 m) patches of krill-like backscatter, all centered at approximately 20 to 25 m. From VPR observations, it seems that the plankton in the 25 to 90 m depth range consisted primarily of copepods, radiolarians, diatoms, and krill. Less commonly observed taxa included ostracods, ctenophores, medusae, and larvaceans. In addition to the observation of krill not associated with acoustic patches, on the three occasions when we passed through one of the fifteen dense patches, we obtained images of large krill with the VPR.


Between 300 and 350 m, a fairly dense scattering layer also was present. The speckled appearance of this layer suggested the presence of large individual targets. A 1-m2 MOCNESS trawl was performed immediately prior to this towyo, covering very similar ground. The 200 to 350 m net captured large amphipods, many copepods, and two varieties of krill (Thysanoessa spp. and Euphausia tricantha). These quite strong scatterers are likely responsible for the enhanced scattering in this depth range.


Later in the day, we conducted a second towyo, now between stations 14 and 23. Very strong vertical bands of alternating high and low backscatter were again present in the mixed layer, much more prevalent than in previous towyos. As was the case in earlier transects, these bands were not present for the entire length of the towyo. Where they were evident, however, they again were spaced at strikingly regular intervals, ranging from 190 to 270 m apart. The bands of high backscatter were centered at 20 m, ranging in height from 30 to 45 m and in length from 67 to 100 m. Salinity data collected concurrent with our acoustic observations may suggest an association between salinity and the presence of groups of band structures; more detailed analyses of these data will test this notion. BIOMAPER-II bisected seven of the bands of high backscatter, at which time large krill were observed. Two of these were positively identified to the genus Euphausia.  Copepods, diatoms, and diffuse krill (i.e., not in dense acoustic patches) were also seen with the VPR in the upper 85 m of the water column. As is noted elsewhere in today's report, 18 seals and a huge number of Adélie penguins were sighted at the same time as we were observing the band structures. This last point is particularly exciting as one of the overall goals of this cruise and the Southern Ocean GLOBEC program as a whole is to understand the links between trophic levels in the local ecosystem.


At times during the tow, scattering was enhanced between 100 and 150 m, but the VPR was not able to sample these depths.  Below 275 m, scattering also became more intense. Correspondingly, the 1-m2 MOCNESS tow conducted immediately after we finished our towyo caught copepods, krill (Thysanoessa), amphipods, and ostracods between 200 and 400 m. Towards the end of the tow, four large patches (as long as 800 m) were observed within this overall layer of intensified backscatter.


Current Position and Conditions

The N.B. Palmer is currently a station 21, a mid-shelf station where most of the science groups on board the N.B. Palmer are making collections. Our position at 0023 on 7 September is -67º 02.598′S; -70º 42.692′W.  The air temperature is -14.2ºC and the barometric pressure is 1014.9 mb and holding steady.  Winds are light at around 5 kts out of the south-southwest (209). Skies are clear and visibility is good.  The pack ice is composed of large floes and the Palmer had to back and ram the last few miles to reach the station location.



Cheers, Peter