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

27 August 2002


August 27 was a day in which only a modicum of progress was made in the transit from station 40 to one of the stations on the Southern Ocean GLOBEC survey line 5.  The original intent was to move to station 28, but there was essentially no progress in heading north from station 40 for about 12 hrs. The pack ice was too tightly compressed.  The Palmer then headed to the west over a similar trackline to that made coming into the station area and, with time for work in the central grid sector running out, the decision was made to head for station 26 approximately 68 nm away.  Advancement in that direction in the ridge-ridden pack ice was also very slow and during the day as a whole, the net distance traveled by the Palmer was 8.7 nm or 0.4 nm/hr. 


In the evening, the Palmer stopped for about 3 hours to make some of the measurements that had been scheduled for station 40 twenty-four hours earlier. These included ice collection and an ROV under-ice survey, and vertical net tows with the 1-m diameter Reeve net (for live animal collection) and a 1-m ring net (for a quantitative collection). As we got underway, two XBTs were taken to get a temperature profile at the location.  The frequent need to back and ram to make forward progress prevented the deployment of BIOMAPER-II and no along-track data were collected with the towed body on 27 August.


The early morning of 27 August was heavily clouded and snow was still in the air.  The clouds thinned around mid-day and the sun was barely visible as a faint yellow ball. The clouds were still present late into the night. The air temperature was relatively mild, ranging from -3ºC to -6.5ºC during the day and the barometric pressure varied between 996 and 993 mb.  The winds varied between 15 and 25 kts all day, but they shifted from northwest to west-southwest around noon. This wind shift helped relax the pressure on the pack ice and made it possible for the Palmer to move through it with less difficulty, although it remained a challenge.


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

During the late hours of 26 August, while we were trying to reach survey station 28, a sudden change in wind direction closed the leads that the ship was following.  This resulted in considerable delay in our plans to reach station 28, and the whole day of 27 August was spent trying to get to station 28. As a result, no CTD casts were made during this time. This gave us the time to analyze data from the stations that have been occupied and to construct maps showing horizontal distributions of water properties.


The distribution of the temperature maximum below 200 m showed the southern boundary of the Antarctic Circumpolar Current (ACC), distinguished by the 1.6ºC isotherm flowing along the outer boundary of the continental shelf. Temperatures greater than 1.5ºC below 200 m correspond to Upper Circumpolar Deep Water (UCDW) and this was also present along the outer continental shelf.


A plume of UCDW intruded about 50 km onto the shelf towards Marguerite Bay in the central study region. During the NBP02-02 cruise, a weak intrusion of warmer waters (1.5ºC) was observed at the same region, but the time resolution of data from the cruise was not sufficient to determine if this water was intruding from the ocean or if it originated in the northeast part of the study region and was moved into the central region by the prevailing circulation.


The vertical temperature section for transect 6 which extends from off-shelf into the Marguerite Trough showed modified UCDW (1.4ºC) present in the Trough with no apparent connection with the warm water masses at the outer edge of the shelf. There are two possible explanations for the existence of modified UCDW in the Trough. First, either the UCDW that sits along the shelf edge moved across the shelf earlier this season or, second, it is intruding through Marguerite Trough as also observed during the NBP02-02 cruise. As we occupy more stations towards the north of the study region, we will better be able to understand whether a similar intrusion into the Marguerite Trough still exists or not.


Another water mass that was observed off-shore of the shelf break at depths of 800 to 1000 is Lower Circumpolar Deep Water (LCDW), which is distinguished by a salinity maximum of 34.72 at temperatures around 1.5ºC.


The surface horizontal salinity distributions showed an increase of 0.3 relative to the NBP02-02 cruise. The reason for the large increase in salinity is ice formation and brine rejection.


The dynamic topography which is the vertical integral of the density anomaly, is a traditional method used in determining the circulation. Although on the west Antarctic Peninsula continental shelf the dynamic topography is weak because the density variation is weak and the shelf is shallow (~500 m), the dynamic topography distribution showed a clear pattern of an anti-cyclonic gyre toward the edge of the shelf. The gyre was attached to the ACC, which flows to the northeast along the outer edge of the continental shelf.  Southwest of this cyclonic gyre, part of another cyclonic gyre was observed which might have formed by the meandering of the ACC.


Krill Physiology and Fish Ecology (Jose Torres, Tom Bailey, Joe Donnelly, Melanie Parker)

The fish ecology/krill physiology team has a number of missions. Each deals with the ecology or physiology of our target organism, the Antarctic krill, or other important species in the Antarctic marine ecosystem. Our ecological interests are concerned with where the larger sizes of krill are located within our study area, as well as the fish that eat them. Of course, we also want to know how many there are and at what depth they reside at.  In our last report we described our main sampling tool, the MOC 10 net, and a little bit of what we found. In this report we will tell you about our “physiology” mission.  In later reports we'll tell you more about what we've been finding in our nets and what we have seen on our under ice dives in search of krill larvae.


For those of you who are wondering what the biological term “physiology” means, it is the study of how the different systems in animals work, both individually and in concert, to form a working whole animal.  For example, we might be interested in how the digestive system works in krill, and how much food they would need to grow and be healthy.  Much of what a medical doctor does is applied physiology, only on humans instead of krill!


Our main focus on this cruise is to look at the overwintering strategies of krill, especially, the way krill use energy.  It is not only Antarctic krill that have to deal with lean times in the winter months.  Many marine and terrestrial species also have to face food shortages. So, when we want to find out what the krill are doing, we can first look to see how other species cope with the problem. This may give us hints as to what the krill are doing.


It turns out that two main strategies exist to deal with food deprivation. One way is to store energy as fat for the leaner times ahead.  The storage strategy is practiced by animals as diverse as bears, caribou, penguins, seals, and many crustaceans.  Another way to deal with lower food supply is to reduce metabolism by entering a form of “hibernation”.  Hibernation, which can be thought of as a very deep sleep, reduces the need for energy.   Examples of this type of strategy include some reptiles, such as alligators and freshwater turtles, some amphibians, like toads, frogs, and salamanders, many insects that live in cold climates, and some crustaceans. Many species, such as the hibernating bears and the crustaceans, use a combination of fat storage and metabolic reduction to survive the winter. Still others do nothing different; they practice a “business as usual” strategy during the winter.


In the Antarctic, the most fascinating species are the krill and little crustaceans that enter a form of hibernation called diapause.  The little crustaceans are called copepods. They are about the size of a mosquito (no relation) and are important herbivores not only in the Antarctic, but throughout the world's oceans.  They can store up to 40% of their body weight as fat in anticipation of the winter months.  In fall, many of the copepods sink from the surface to depths greater than 400 meters and enter the dormant diapause state, which is an even deeper sleep than what the bears do.  They float there for months and when spring comes, rise again to the surface to begin feeding and reproducing.  We are not sure how they know when to wake up, but they are most likely cued by the increasing light of the Antarctic spring or late Antarctic winter. In fact, some of them are already beginning to wake up now!


We still are not sure what the star of our study, the Antarctic krill, does during the winter months.  That is an important part of why we are here.  From our study so far it looks as if many of the older krill, the largest ones, are now located deep in the bays and fjords of the Antarctic Peninsula instead of out on the continental shelf and open ocean where they are most common in the summer.  We have seen very few of the youngest stages of krill anywhere during our 2002 study. 


We are measuring metabolic rates of krill in our laboratory on the N.B. Palmer to see if larvae and adults do a “partial  hibernation” to help them get through the winter.  So far it looks as if krill drop their metabolism, or energy usage, by about 50% during the fall and winter months.  When we get home, we will be measuring their fat content to see if they have stored enough to survive the winter without eating.   


Seabirds (Chris Ribic and Erik Chapman)

The ship spent most of the day backing and ramming on 27 August, trying to move out of Marguerite Bay near station 40 and go to station 28.  We were not able to move very much through the thick ice, but we were able to observe from the bridge for over 7 hours.  Eight Antarctic Petrels were recorded for the first time in several days.  Previously, we've only seen Antarctic Petrels near the ice edge, and in general this species is typically found close to the interface between the pack ice and open water.  A single Southern Giant Petrel, a large petrel that feeds principally on carrion, was also observed today.  Snow Petrels were also seen in small numbers in the survey.  Five Adélie Penguins were observed hauled out along leads.  We rarely saw Adélies in the southern sector of the grid, but have consistently seen them in low numbers here in the central portion of the grid.


A summary of the birds and marine mammals observed on 27 August (YD 239) during 7 hours, 9 minutes of survey time as the ship traveled near station 40 is the following:


Species (common name)

Species (scientific name)

Number observed          

Snow Petrel                  

Pagodroma nivea                   


Adélie Penguin     

Pygoscelis adelii                  


Antarctic Petrel               

Thalassoica antarctica         


Southern Giant Petrel  

Macronectes giganteus          


Crabeater Seal         

Lobodon carcinophagus  




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

An ROV under-ice survey took place at Station 49 on 25 August. The ice was characterized by broken and re-frozen floes extensively rafted into many layers. The ROV went into the water for a short deployment at 1719 and was retrieved at 1812. A problem with the strobe light delayed the deployment 40 minutes as time was spent finding some electronic parts and a new bulb to replace one that apparently had blown out. We later discovered that the problem was not a blown bulb, but a temperature sensitive part in the power supply and control housing for the 3D VPR cameras and strobe. A few activated hand-warmers tossed into the housing provided the extra heat necessary to keep the power supplies above 20ºC for this deployment. We are working on building a ceramic heater to be installed in the electronics housing for future deployments. No furcilia were observed either on the relatively flat regions of the small floes or in the rough, complicated environment of the rafted and buckled ridge lines. A few small ctenophores were observed scattered throughout the area surveyed during the dive.


After a day of intensive backing and ramming the ship became free from the heavy grip of high pressure ice at Station 40. A few miles away from Station 40, on our way to Station 28, we stopped for an ice team and ROV deployment on 27 August at 67º 56.240′S; 70º 53.859′W. The air temperature was relatively warm at 6.2ºC, so the newly installed ceramic heater in the power supply electronics housing of the 3D camera system was not necessarily tested under extreme conditions. However, the strobe functioned normally so we are hoping the heater has solved our immediate temperature sensitive problem. The ice was characterized by large, flat floes of first year ice about 70 cm thick. A ridge line appeared about 500 m on the starboard side of the ship, but was too distant for the ROV to reach. The under ice surface was quite smooth and dimpled, but without rafting of any kind. A few cracks opened by ship activity showed the ice flow to be layered, but not extensively, with colored material. One corer used by the ice team was observed from below by the ROV. This observation was short lived as the corer was lost at it fell through the ice and down to the sea floor. Another bore hole was found after the ice team inserted a flag pole for the ROV to identify. One ctenophore and one seal were observed, but no larval krill.


Current Position and Conditions

This has been another day of backing and ramming through 10/10 pack ice heading for station 26.  We are currently about 16 nm from the station.  Our current position at 2200 on 28 August is -67º 20.722′S; -71º 40.807′W.  The air temperature is -7.8ºC and the barometric pressure is 1012.0 mb. Winds are <5 kts out of the west. It is cloudy, but visibility is good.


Cheers, Peter