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

1 September 2002

The N.B. Palmer and the L.M. Gould arrived at station 4 about midnight on 30 August/1 September and work aboard the Palmer began almost immediately. Dual deployment of the two 1-m ring nets off the stern of the Palmer in the upper 10 m of the water column has proven to be a very effective means of collecting krill furcilia for experimental purposes and this was done for about an hour. The ROV was deployed for about two hours for an under-ice survey, but the condition of the ice floes prevented the deployment of the ice collectors. A pair of CTD casts was done in close proximity to the Gould, which was also doing a CTD cast. These casts will be used for inter-calibration of the CTD data from the two vessels. A 1-m MOCNESS tow completed the work by 0830 at station 4. The Gould, meanwhile, was able to move around the area on its own and once BIOMAPER-II was deployed for the towyo to station 3, the Palmer steamed towards the offshore region of the survey grid, leaving the Gould behind.

The work at station 3 in the mid-afternoon consisted only of a pair of CTD casts. BIOMAPER-II was left in the water and collected time-series data while the CTD casts were being done and was then towyoed during the transit to station 3. Work at this station, which was situated on the edge of the continental shelf in water approximately 800 m deep, began with ice collection on a small floe next the starboard side of the ship. The presence of a long period swell with a ~1.5 m wave height and the lack of consolidation of the floes in the area made it necessary to deploy a Zodiac onto the floe for the ice collectors touse as a work platform. A single CTD cast was made to the sea floor because CMiPS was being serviced and the water column was too deep for the FRRF. An attempt was made to make a 10-m MOCNESS tow to 1000 m, but in the process of deployment, that electrical signal cable running between the cable termination and the MOCNESS underwater unit was snagged and broken. The tow was scrubbed because of the lateness of the hour and the time required for the repair. Instead, BIOMAPER-II was deployed and towyoed to station 1 approximately 12 miles away.

The weather on 1 September was quite workable. The air temperature varied between -0.9ºC in the morning to -5ºC in the evening. Barometric pressure dropped down from around 980 to 969.5 mb around noon and then started a slow rise reaching 980 mb by midnight. Winds backed around from northerly to southeasterly and then southerly during the course of the day. Winds out of the southeast have been a novelty on this cruise. The wind speed was under 15 kts in the morning, increasing to 15 to 20 kt in the afternoon, and was in the 25 to 30 kt range in the evening. A high cloud layer was present during the day, but visibility was good. For much of the day, “water sky” could be seen to the northwest and north indicating that a lot of open water was not far away.

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

Today was a busy day for the CTD group. We completed CTD casts at stations 4, 3, and 2 as we moved offshore along survey transect 1. At stations 4 and 3, two CTD casts were done. The first was to 300 m for CMiPS sampling; the second included FRRF sampling in the upper 100 m and extended to within a few meters of the bottom, which was at about 340 m and 350 m, respectively. Station 2 was at the shelf edge in 830 m of water. No FRRF sampling was done at this station, so only a single cast was made to near the bottom. The lowering speeds in the upper 200 m were appropriate for sampling with CMiPS.

At station 4, surface waters were just at freezing (-1.809ºC) and the well-mixed Winter Water layer extended to 60 m. Below this, temperature increased to a maximum of 1.58ºC at 285 m, after which it again decreased to 1.42ºC at the bottom. The salinity at the temperature maximum was 34.70 and that at the bottom was 34.72.

At station 3, the surface waters were above freezing at -1.78ºC. The well-mixed Winter Water layer was the shallowest observed so far on the survey, extending over the upper 50 m to 55 m of the water column. As observed at station 4, temperature increased to a maximum of 1.58ºC at 255 m with a corresponding salinity of 34.70. Below this depth, temperature decreased to 1.53ºC at the bottom. Bottom salinity was 34.71. Water of 1.5ºC was found from 217 m to the bottom, which results in a layer of warm water that is almost 125 m thick. This may be related to the warmer surface waters at this location. The data acquired from CMiPS at this station, as well as at other locations, should help in understanding how these water masses mix.

At the shelf edge (station 2), surface waters were colder than observed at the two previous shelf stations. The temperature in the upper 70 m was at the freezing point (-1.81ºC to -1.83ºC). Below this, temperature increased to 1.74ºC at 276 m and then decreased to 1.17ºC at the bottom. The corresponding salinity values were 34.67 and 34.72, respectively.

The thermohaline structure observed at these three stations shows Upper and Lower Circumpolar Deep Water at the shelf edge and on the continental shelf. The presence of Lower Circumpolar Deep Water at station 2 is revealing because it suggests a relatively strong intrusion of oceanic water onto the west Antarctic Peninsula continental shelf. The stations along survey transect 2, which will be done next, will allow us to better determine the on shelf extent of the intrusion.

Sea Ice Observations (Chris Fritsen, Jenny Boc, Frank Stewart, Sue Beardsley, Bob Beardsley, and Chico Viddi)

This is a preliminary analysis of the ice observations taken over the past 24-plus hours starting on 31 August. During the transit from station 4 to station 1, we experienced a north to northwest swell running through the ice pack. Hourly observations of the ice conditions using standardized ASPeCT protocols documented the gradient in ice conditions associated with the transit from deep ice conditions to those nearer the ice edge and those imposed by the swell. Specifically, there was a change in the pack from that being dominated by 7 to 9 tenths coverage of first year ice floes measuring 20 to 100 meters in diameter and 50 to 70 centimeters in thickness near station 4 to small (5 to 10 meter in diameter) first year ice floes measuring 30 to 50 cm in thickness at station 1. Brash and Shuga appeared in the pack as we passed station 3 and continued to be present at 2 to 4 tenths coverage as we neared station 1. The floes also became more rounded (indicative of prolonged exposure to swell) compared to those inshore which had the rectangular shape, which is indicative of recent swell-induced deformation. Preliminary analysis also showed that weighted average thickness for the undeformed ice floes changed from 50 cm to 25 cm over the 60 nm distance. Such observations when coupled with the Sea Surface Microwave Imager (SSMI) information should allow better constraints on an ice budget for the region.

Seabirds (Chris Ribic and Erik Chapman)

The seabird and Crabeater seal survey was conducted for almost six-and-a-half hours on 1 September as the ship moved offshore between stations 4 and 2 on the northern-most line of the study grid. Ice conditions were mainly 6 m diameter first-year cake ice separated by small cracks of open water. A 0.5 m swell continued to run through the ice, and the ship passed by several large ice-bergs, each associated with small areas of open water.

The seabird species assemblage was similar to that observed yesterday. We continued to record relatively large numbers of Antarctic and Snow Petrels milling over leads. A single Kelp Gull followed the ship for much of the morning, periodically leaving the ship to fly over water immediately adjacent to nearby icebergs. Two Southern Fulmars were recorded flying directionally offshore, toward the ice edge. Five Southern Giant Petrels were recorded in the survey, more than have been observed on any previous day.

Twenty-four Adélie Penguins were observed in several small groups. The Adélies appeared to be concentrated in a large area covered by thin, gray, slushy ice that covered an old lead. They were less common in the larger, snow-covered cake floes that covered most of the survey area. However, two Emperor Penguins, including a juvenile, were observed in the cake ice.

A summary of the birds and marine mammals observed on 1 September (YD 244) during 6 hours, 26 minutes of survey time as the ship traveled between stations 4, 3, and 2 is the following:

Species (common name)	Species (scientific name)	Number observed
Snow Petrel	Pagodroma nivea	23
Antarctic Petrel	Thalassoica antarctica	35
Southern Fulmar	Fulmarus glacialoides	2
Kelp Gull	Laru dominicanus	1
Southern Giant Petrel	Macronectes giganteus	5
Adélie Penguin	Pygoscelis adelii	24
Emperor Penguin	Aptenodytes forsteri	2

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

Tow #10 for the 1 m² net took place at Station 4 at 0700 on 4 September. Towing conditions at the station were conducive for another successful tow in water 351 m deep. Biomass of the nets matched the acoustic scattering seen on the Simrad echo-sounder: peaks at 300-325 m and again between 75 and 25 m. Taxonomic composition of these layers showed copepods in the deep layer and krill dominating the upper water column. Abundant radiolarians were found at all depths.

A high biomass was obtained from net 0, which consisted mainly of copepods, euphausiids, chaetognaths, ctenophores, and salps. The high biomass of the deep net (325-300 m) was composed of chaetognaths, ostracods, amphipods, and a siphonophore in addition to copepods. Biomass dropped off dramatically between 300 and 200, with chaetognaths and smaller copepods replacing the large Paraeuchaeta sp. found in net 1. Between 200 and 100 m, a low biomass, high diversity composition prevailed: siphonophores, pteropods, ostracods, amphipods, and tomopterid worms. Thysanoessa (all stages) and occasionally E. superba krill increased in number, peaking between 75 and 25 m. Of note was the low number of copepods above 100 m. Pteropods, siphonophores, and a large (6 cm) ctenophore made up the remainder of the shallow depth samples.

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

After a two-day hiatus from towing the BIOMAPER II while we assisted the Gould in reaching its next position, on September 1 we recommenced our broad-scale survey with a long towyo between stations 4 and 2 along the northernmost of our survey transects. Scattering was extremely low throughout most of the water column. A very diffuse shallow scattering layer was present centered at 25 m and between 75 and 125 m we observed occasional enhancements in scattering levels. At station 3, we kept the BIOMAPER II in the water while a CTD was conducted. Further processing of the acoustic data we collected while stationary should allow us to track individual animals that moved through our sound beams. This should then allow us to make inferences about the behavior of these animals.

As has been the case in many of our previous tows, VPR observations suggested that the plankton community in the upper 100 m of the water column was diverse and composed of diatoms, copepods (including calanoids), larvaceans, medusae, and radiolarians. Of these, diatoms were among the most abundant, particularly shallower than 50 m. We also made numerous observations of small krill, mostly associated with the weak layers that were evident acoustically. Individual images were also positively identified as a ctenophore, a pteropod, and a salp. At 1730, our VPR image-capturing was rudely interrupted when the strobe lens came loose. We thus had to finish the last two hours of the towyo without the benefit of any VPR data. Thankfully, repairing the lens was a simple task once the BIOMAPER II was back on board.

For the entire duration of the towyo, there was a strong scattering layer associated with the bottom (325 m), extending 40 to 55 m above the bottom. Soon after the start of the transect, a particularly intense region of scattering developed right next to the bottom within this overall layer. Just before sunset (1645), this intense region migrated from its position next to the bottom to the top of the layer, 55 m above bottom.

As we've described in previous reports, during much of this cruise we have been beset by problems with the BIOMAPER II not flying perfectly level, and the associated problem of our up-looking transducers occasionally receiving echoes reflected from the tow cable. While we were in transit with the Gould, we took advantage of the time on our hands to address these issues. Stian Alesandrini, one of our very capable marine technicians, flattened out a bend that had developed in the towbail that attaches the tow cable to the BIOMAPER II. We believe that this bend might have been the root of our problems. Thus far, straightening the bend appears to have done a great deal towards keeping the towbody flying level and keeping the tow cable out of the line of sight of the transducers.

Current Position and Conditions

Offshore stations take considerable time to complete because of the very deep water depths (~3000 m) and the time it takes to deploy the CTD to the sea floor or the net systems to 1000 m. Thus, we are now at the second station of the day (13), having just started to work. Our current position at 2133 on 2 September is -66º 01.660′S; -71º 10.325′W. The air temperature is -5.1ºC and the barometric pressure is 1002.1 mb and leveling off. Winds are moderate at around 13 kts out of the west-southwest (240). Skies are partly cloudy and visibility is good. The pack ice is made up of small floes that are easy to work in. A low-amplitude long-period swell is running through the region.

Cheers, Peter