Report of Activities on the RVIB N.B. Palmer Cruise 02-04
Station work at offshore station 63 was completed just at on 23/24 August and the transit to station 62, about 12 nm away, commenced with BIOMAPER-II in tow. The pack ice along the outer continental shelf in the central sector of the Southern Ocean GLOBEC grid has proven to be very tough to move through. While there were some leads aligned in the direction we wished to travel, much of the time the Palmer had to move across small floes interspersed with ridges made from floes that had been jammed together during earlier wind events. The ridges formed substantial barriers and consequently it took about 5 hours to go the distance, averaging about 2 kts. The towed body had to be retrieved an hour before arriving on station 62 because the backing and ramming had become incessant.
The start of work at station 62 was delayed briefly by a surprise fire drill. By a little after 0900, a party of ice collectors was on a floe and the ROV was surveying the underside of the floe. The station site was apparently home for a substantial number of Crabeater seals that showed up in the open water behind the stern. They treated those working on deck to a real show by romping about in the water and on the surrounding floes. The CTD at station 62, on the edge of the continental shelf, went to more than 1000 m and was completed about 1300. Rather than take additional time at station to take a series of net tows, it was decided to wait until late in the afternoon to do the tows so that seabird and mammal observations could be made in the afternoon sunlight while transiting to station 48.
For a number of days, we have been looking for a way to move to the stations closer to shore without having to ram our way through the pack ice. Satellite images of the ice surface during the past several days have shown lead areas of substantial size that appeared to provide access inshore. Shortly after we left station 62, we finally managed to enter one of those lead systems. The leads meandering path led to the east almost directly to station 48. Instead of continuing on to station 61 on survey line 8, we used the lead system to steam towards station 48 located on survey line 7. Once in the lead, BIOMAPER-II was deployed for along-track towyoing. During the early part of the steam, large numbers of Crabeater seals seen were hauled out on the sides of the lead in groups of 5 to 10 individuals.
Late in the afternoon, BIOMAPER-II was retrieved and a series of tows was undertaken. First in was a Tucker trawl for live animal collection, followed by the 1-m MOCNESS, and then the 10-m MOCNESS. The 1-m MOCNESS tow collections were fine, but telemetry problems plagued the tow and no OPC data were collected. In addition, the flow meter failed to work for most of the time. At the end of the towing, BIOMAPER-II was again deployed for the final portion of the transit to station 48.
The weather on 24 August reflected the changeable nature of the Antarctic. In the morning the high thin clouds of the night before were present out on the perimeter of the area and overhead skies were clear. It was a very nice sunny start to the day. Although the air temperature was around -24.6ºC, winds were light (~ 6 kts) out of the northwest and working conditions were OK. By late afternoon, it had clouded over and a fog enveloped the area cutting the visibility down considerably. The temperature had risen to -14.8ºC and the winds were only slightly higher out of the north. It was snowing by evening, first as flurries and then harder. This was accompanied by a rise in the temperature to -8.0ºC around 2100. Around , the winds picked up to 20 to 25 kts out of the southwest and the snow was driven horizontally across the decks. The temperature began to fall after the change in wind direction and was -11.4ºC by . The changes were reflected in a modest drop in barometric pressure from 996.7 mb in the morning to 990.5 around .
CTD Group report (Eileen Hofmann,
Bob Beardsley, Baris Salihoglu,
Chris MacKay, Francisco (
One CTD cast was completed on 24 August at survey station 62, which is along the outer part of survey transect 8. This was the last of the closely spaced stations designed to provide higher spatial resolution in this portion of the survey grid. Station 62 is in 1091 m of water and the CTD cast extended to near the bottom, ending at 1085 m. The cast included the CMiPS sensor, but not the FRRF sensor, which can only be deployed to 500 m.
The temperature profile showed a well mixed layer, which was at the freezing point, extending from the surface to about 100 m. Below this, temperature increased to a maximum of 1.70ºC at 315 m, after which it decreased monotonically to 0.98ºC at 1085 m. The salinity profile showed values of 34.04 to 34.09 in the upper 100 m. Below this salinity increaseed to a maximum value of 34.727 at 625 m and then decreaseed to 34.718 at the bottom of the cast. Dissolved oxygen showed a minimum concentration between 310 m and 315 m.
The hydrographic properties from
station 62 showed Upper and Lower Circumpolar Deep Water to be present at the
shelf slope in the southern portion of the survey grid. This provides a deep reservoir of warm,
salty, and low oxygen water that can then move onto the west
The stations completed to date
are being used to develop horizontal distributions of properties such as the
depth of the temperature maximum below 200 m, which can be used to trace the
on-shelf movement of Upper Circumpolar Deep Water. The construction of these maps has been
problematic because of the small number of stations occupied along the
across-shelf transects due to the extensive sea ice cover. However, one
observation that has emerged from the distribution plots is that the southern
boundary of the Antarctic Circumpolar Current is located along the outer edge
of the west
CMiPS Report (Bob Beardsley, Chris Mackay)
This is the first report on CMiPS with more explanation to come in later reports. CMiPS stands for CTD-Microstructure Profiling System, which is a self-contained instrument designed to measure temperature and conductivity rapidly using very small, rapid-response thermistors and a two-electrode conductivity sensor. Our CMiPS is mounted on the CTD rosette frame with its sensors oriented facing down and located near the bottom of the frame, so that the flow to the CMiPS sensors is as uninterrupted as possible. CMiPS samples two temperatures, one conductivity, and a high-resolution pressure transducer at 512 Hz, recording the raw data on a hard drive in the instrument. This rapid sample rate plus the fast-response design of the sensors allows CMiPS to measure temperature and conductivity on very small vertical scales, e.g., if the instrument is dropping at 40 m/min, then the vertical distance between two samples is 0.1 cm. Analysis of the fluctuations of temperature and conductivity on these short scales (called 'microstructure') provides evidence if turbulent mixing is occurring somewhere in the water column and how homogeneous different layers are.
CMiPS was used for the first time on NBP02-02, so it is still a new instrument. On this cruise, CMiPS has been collecting good temperature data on most of the CTD casts. However, a series of problems have plagued it. Chris has been a wizard tracking down the various problems, making improvements to the instrument, increasing its sensitivity, changing probes, cleaning them, etc. On CTD cast 39, the CMiPS data looked very noisy and off-scale; characteristic of water inside the head. So Chris drained out the oil, found a broken rubber diaphragm which separates the olive oil in the head from the sea water outside. Chris then rebuilt the head, put in a new diaphragm, and replaced a thermistor that was clearly bad. After a thorough cleaning to make sure there was no olive oil on the sensors, CMiPS was put back on the CTD in time for our most recent CTD cast 41.
The CMiPS data from cast 41 looks perfect, i.e., perfectly good! All signals look very clean, and the two temperature time series agree very well to better than 0.0001ºC.
Note: As far as we know, this is the first time microstructure has been measured successfully with an instrument attached to the CTD! All other microstructure instruments are free-fall instruments, designed to drop without any contamination by the motion of the ship on the tether. What is making our NBP02-04 measurements so exciting is a) CMiPS is a great instrument and b) the ship motion in the ice is almost zero, so the actual downward speed of CMiPS through the water is almost constant (40 m/min), with very little if any variation due to ship motion. Both conditions are needed for a CTD-attached instrument to get great data, and we can thank Mother Nature for the ice, the NBP for getting us here, and Chris and the CMiPS support team at home (Rolf Lueck, Laurie Padman, and others) for CMiPS.
Sea Birds (Chris Ribic and Erik Chapman)
Seabird and Crabeater seal surveys were conducted for over four hours on 24 August as the ship traveled between stations 62 and 48. Ice conditions were /10ths concentration of vast floe and new gray ice. The ship traveled the length of a lead greater than 30 miles long. Crabeater Seals were abundant along the edge of the lead and were hauled out despite low temperatures approaching 20ºC. The seals were clumped in distribution along the lead and it will be interesting to note whether BIOMAPER II data observed krill swarms where seals were abundant.
A single Emperor Penguin and
three Adélie Penguins were observed along the lead as well. We may begin to see more Adélie Penguins as
we move further north in the study grid, closer to
A summary of the birds and marine mammals observed on 24 August (YD 236) during 4 hours, 15 minutes of survey time as the ship traveled between stations 62 and 48 is the following:
Species (common name)
Species (scientific name)
Marine Mammal report (Chico Viddi)
The survey of marine mammals has now logged 76.7 hours of effective effort (out of 168.5 observation hours). Twenty-nine sightings have been achieved up to date. The last three days have been amazing. There have been wonderful sunrises, sunsets, and a full moon during these sunny, moderately windy, and cold days. They make this continent and its ocean covered by ice appear as another wonderful planet. While at stations and steaming through thick ice (mainly first year ice) as well as in the narrow open water areas, many seals and cetacean sightings have been made. On Thursday 22 August, air and wind chill temperatures reached low values once again (-25.5 and 47.8ºC, respectively). Ice coverage was mostly 10/10ths and it was very thick with very small cracks. No cetacean was seen during daylight hours, but once we arrived at station 46, 18 Crabeater seals (Lobodon carcinophagus) were hauled out on the ice. They stayed there with very little apparent awareness of what was happening with this “big red-yellow visitor” (the Palmer). An outstanding sighting was made by Kathleen Gavahan at 1945 (-67º 62.53′S; -74º 62.07′W) while on the bridge. She saw two minke whales come to the surface to breathe in a very small crack in the ice right next to the ship. Since the vessel's lights were focused on that specific area, a large portion of the animal was visible through the water.
On Wednesday 23 August, no effective effort was made because most of the day was spent at station 64. Nevertheless, a few seals were seen and three cetacean sightings were made. At 0923, while the ice collectors were on the ice, First Mate Mike Watson and Sue and Bob Beardsley saw a whale surfacing in a small lead of open water at less than 500 m from the stern, in a wide area of thin ice (young grey ice). Two minke whales were observed at 1521 (-67º 30.50′S; -75º 03.83′W, 15º to starboard and 0.2 nm from the bow) while the Tucker trawl was being towed in the same area. Almost 30 minutes later (at 1549, -67º 30.64′S; -75º 02.40′W, 12º to port and 0.7 nm from the vessel), three whales were seen surfacing and circling. Whales in both sightings approached the vessel to within 100 m, allowing many on the Palmer to see and take pictures of them. The last three whales stayed quite close to the ship for at least five minutes and were seen swimming right behind our stern.
August 24 (Saturday) was probably the best day again for seal counting. The total count of Crabeater seals was 116 for the period of observations. Most of them were seen from 1300 to 1400 when a total of 51 seals were seen. Seals were observed mainly on ice, and only 12 seals were counted in the water. The first seals seen were while still at station 62 and during ROV operations. Three or four seals were swimming very close to the stern and more interestingly, around the ROV, as if they were somehow attracted by it. Some underwater footage of the seals was captured by the ROV (and Scott Gallager) as the seals got close to the vehicle. These seals stayed for a long time swimming close to the stern and sometimes hauling out on the ice. They did not seem to be afraid and it was possible for many in the science party to enjoy seeing these playful seals. During the CTD cast, the seals (being the same ones or not) appeared again to be attracted by the piece of equipment. Two seals hauled out on ice after swimming for a while close to the ship and seemed to be relaxing, rolling over, and taking a rest after the romping about. While this was happening, 9 Crabeater seals hauled out on the ice on the edge of the wake left the vessel 0.4 nm away. Once we left station 62 (at 1255), a group of seals was observed at 1313 (-67º 49.90′S; -74º 09.31′W) and again at 1626 (-67º 49.81′S; -73º 29.60′W). Twenty minutes later the observation period ended because of dense fog.
Crabeater seals were not the only marine mammals seen on 24 August. A leopard seal (Hydrurga leptonix) was observed at about 1310 (-67º 50.05′S; -74º 08.31′W) by Chris Ribic and Erik Chapman. It was very close to a group of Crabeater seals. They were all on ice, so there probably was not much chance for the leopard seal to hunt the Crabeater seals. We also had three cetacean sightings. The first one was made at 0918 (-67º 48.77′S; -74º 11.34′W) while still at station 62. Two minke whales were observed surfacing to breathe in a very small crack about 700 m from the ship. A Crabeater seal was right on the edge of the crack where the whales were seen. The second sighting was made at 1355 (-67º 49.31′S; -73º 59.91′W), at 0.8 nm, 18º to starboard. It was seen surfacing on the same spot three times before diving for about 5 minutes after which it was seen less than 150 m from the bow. A few minutes later the whale was seen more than 300 m behind the vessel.
Finally, a peculiar and interesting observation was made at 1541 (-67º 48.02′S; -73º 38.70′W). Several splashes were seen ahead of the vessel. As we got closer to these splashes, we still could not identify the animal. It was unlikely to be a baleen whale given the velocity of the movement, but it was big enough to resemble a small whale. Since a number of seals were observed during the day and within the area, it would not be unlikely that the observation corresponded to Orca hunting behavior (going after a seal or a penguin). Unfortunately, we could not be sure about the animal identification and the sighting will remain as “unidentified cetacean”.
BIOMAPER II group report (Gareth Lawson, Peter Wiebe, Scott Gallager, Phil Alatalo, Dicky Allison, Alec Scott)
Early in the morning of August 24, BIOMAPER II was deployed in the water for a towyo between stations 63 and 62. The shallow scattering layer that has been present for the past many days was still evident, associated with the top of the pycnocline at 60 m. At times this layer was quite dense, reaching backscattering levels as high as -70 dB, rather than its usual -75 to -80 dB. Observations made with the VPR suggest that this layer was composed of copepods (including Calanus), diatoms, radiolarians, chaetognaths, and tomopterid worms. A number of small (perhaps juvenile) krill images were captured at the end of the transect, while the towbody was in a particularly dense portion of the surface layer. It is important to note that when we use the term krill, we are referring to all kinds of euphausiids. In addition to our target species, Euphausia superba, there are at least four other euphausiid species known to co-exist in this region, Thysanoessa spp. being the most common. The latter species have a bi-lobed eye which is easy to discern in the VPR images from this and the last three cruises, provided that the eye is clearly evident in the captured image.
There was also some very limited suggestion of enhanced backscatter at some points along the transect near 300 m, but nothing nearly as strong as the distinct patches and layers we observed on earlier towyos at this depth. VPR images indicated that below 200 m, a diverse species assemblage was present, including medusae, radiolarians, worms, and copepods. We also observed one adult krill at 160 m depth. The entire tow was in deep water, so we didn’t observe the bottom and therefore could not determine whether a bottom layer was present.
Later in the day, between 1430 and 1730, we had a second towyo from station 62 to 48. Interestingly, on this occasion the shallow scattering layer present between 60 and 120 m depth was far more diffuse than on previous tows. VPR observations in this depth range again indicated the presence of copepods, diatoms, larvaceans, and radiolarians. A number of very dense (up to -50 dB) krill-like patches were present between 250 and 300 m, but we didn’t manage to make any observations with the VPR within these aggregations. A reasonably dense layer was also present from the bottom (400 m) to 60 m above-bottom. This layer was beyond the maximum depth attainable by the BIOMAPER II, so we couldn’t determine its composition with the VPR; hopefully, future MOCNESS net tows will reveal what’s hiding down there.