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

9 September 2002

 

The mountains of Adelaide Island were hidden from view by low clouds that stayed the day as we worked along the near shore areas at stations 9, 8, and part of 5 on 9 September. Just after midnight BIOMAPER-II was deployed at the end of station 17 for the transit to station 9. Upon arriving about 0800, a pair of CTD casts was completed and then a 1-m MOCNESS tow was done with the ship headed towards station 8. To save some time, the short steam to station 8 was done without BIOMAPER-II in the water. Station 8 was located within a few miles of the ice cliffs of the Fuchs Ice Piedmont, which extended several hundred feet above the ocean surface. There were collapsed pieces of the ice shelf incipient icebergs - at the shelf edge and the station location was amidst several large icebergs. The station area had a remarkable amount of ice-free open water. Only a pair of CTDs was done at this station in the early afternoon. Although an under-ice SCUBA dive was scheduled for this station, winds around 30 kts and the lack of suitable pack ice caused it to be cancelled. BIOMAPER-II was deployed for the 24 nm run to station 5, the last station of the survey. During the daylight periods of the transit between stations, seabird and marine mammal surveys were conducted.

 

Work at station 5 got started with an hour-long drift net tow around 2200 following the retrieval of BIOMAPER-II. After that the ship was repositioned for the combined work of ice collecting and the under-ice survey with the ROV. Almost immediately after the ROV was deployed and was out on its long tether, the drift of the ship and the pack ice in the steady 20+ kt winds caused the ship and ice to overrun the ROV and tether. They ended up under the ship with the tether stuck near the ship's rudder and the ROV stuck in large chunks of ice up forward about where the transducers for the new Simrad multibeam system is located. A serious attempt to free the vehicle could not be attempted until after the ice collecting team came back on board. Once they were back on board, Captain Joe used the forward thruster to create the currents needed to free the ROV and move it back to the stern area where it was recovered around 0130 on 10 September.

 

The weather on the last full day of work on the SO GLOBEC survey grid was not particularly pleasant. Winds were out of the northeast all day with speeds varying from 15 to 30 kts. The air temperature rose from a morning low of -7C to an evening high of -2C. Barometric pressure began a slow decline during the day starting at 1012 mb and ending up at 1006 mb around midnight. Snow began falling around 0600 and all but the heated main decks were again white and slippery. At mid-day, there was just a raw wind and a moderate fog that significantly reduced the visibility. This condition persisted into the night.

 

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

Late on the evening of 8 September and into the early morning hours of 9 September we did two CTD/Rosette casts at station 17, which is the inner-most sampling location on survey transect 3. The first cast was for microstructure sampling with CMiPS to 350 m; the second extended to near the bottom at 506 m, and included sampling with FRRF in the upper 100 m. Following completion of station 17, we moved north to the inner part of survey transect 2 and occupied stations 9 and 8. Two CTD/Rosette casts were done at each of these stations, similar to those done at station 17. At station 8, eight Niskin bottles were closed at the bottom of the cast to provide replicate samples for nutrient analysis.

 

Station 8 is the shallowest station in the SO GLOBEC survey grid, being in about 70 m of water. This station provides a data point on the landward side of the narrow coastal current that flows south-southwest along the coast of Adelaide Island. It also provides a site that is potentially too shallow to be affected by Circumpolar Deep Water and as a result represents inner shelf water that has not been modified by mixing with oceanic waters.

 

The vertical thermohaline distributions measured at station 17 show a well-mixed Winter Water layer that extends to about 75 m and is characterized by a temperature of -1.82C and salinity of 33.98. Below the Winter Water layer, temperature and salinity increase and have values that are representative of Upper and Lower Circumpolar Deep Water. The maximum temperature of 1.52C was encountered at 318 m.

 

The upper water column thermohaline properties at station 9 were similar to those observed at station 17. However, at depth only the modified form of Upper Circumpolar Deep Water was present. The temperature maximum of 1.42 C was found at the bottom with a corresponding salinity of 34.69. The hydrographic observations made at stations 17 and 9 provide further evidence of an intrusion of Circumpolar Deep Water moving onto the west Antarctic Peninsula continental shelf and also of an older intrusion that may have become stranded on the shelf.

 

The vertical temperature and salinity distributions observed at station 8 were a sharp contrast to those observed at all of the other stations occupied on the survey grid. Water column temperatures ranged from -1.78C at the surface to -1.52C at the bottom (68 m). Salinity ranged from 34.05 at the surface to 34.12 at the bottom. This station was at the inshore edge of the large polynya off Adelaide Island and the above freezing temperatures and higher salinity at this site are consistent with what was observed at other sampling locations within the polynya.

 

Seabirds (Chris Ribic and Erik Chapman)

Seabirds and Crabeater seals were surveyed for over five hours on 9 September as the ship traveled between stations 17, 9, 8, and 5. The survey took us less than 10 miles from Adelaide Island at station 8 and represented our final survey within the SO GLOBEC study grid. Ice concentration varied between 6 and 9/10ths coverage and the primary ice type also varied between new gray and large floes of first-year ice. Blowing snow limited visibility, but we were able to see within the 300 m of the ship and so we were able to collect data within our survey strip continuously.

 

Bird abundances were low today and Snow Petrels were the most abundant species. Snow Petrels were milling over leads, as were Antarctic Petrels. A single Southern Fulmar, a species that was relatively abundant north of the study grid, was observed today as we approached the northern edge of the survey area. After seeing a large number of Crabeater Seals yesterday, we recorded just 4 in today's transect. In general, Crabeater Seals have been abundant along the southern shore of Adelaide and throughout the southern sector of the grid, off Alexander Island.

 

A summary of the birds and marine mammals observed on 8 September (YD 252) during 51 minutes of survey time as the ship moved between stations 17 and 9, 2 hours between stations 9 and 8, and 2 hours 6 minutes as the ship traveled between stations 8 and 5 is the following:

 

Species (common name)

Species (scientific name)

Number observed

Snow Petrel

Pagodroma nivea

25

Southern Fulmar

Flumarus glacialoides

1

Southern Giant Petrel

Macronectes giganteus

1

Antarctic Petrel

Thalassoica antarctica

8

Crabeater Seal

Lobodon carcinophagus

4

 

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

Tow #15 for the 1-m2 MOCNESS system occurred on 8 September at station 19, located in the Johnston Passage, southwest of Adelaide Island. The tow was conducted in open water with variable depth (500-700 m) just after midnight. Distinct separation of copepods from krill was evident here. Very few copepods were found above 200 m and few euphausiids were collected below 350 m. The 38 kHz Simrad layer at 350-400 m, therefore was likely due to large calanoid copepods. Variable scattering from the ADCP and Simrad between 50-125 m was attributed to krill. High krill counts were recorded in all nets between 200 and 25 m.

 

Oblique net 0 caught lots of Euphausia superba, copepods, salps, and chaetognaths. From this net, twenty-one krill were individually frozen in vials and placed in -80C for DNA analysis. In the deepest net (525-350 m), large calanoid copepods were most abundant and included some ovigerous Paraeuchaeta females. Several large amphipods, siphonophores, and ostracods added to the biomass. At 350-200 m, large copepods constituted the main component of net 2, but many smaller copepods were present as well. Otherwise, taxonomic composition was similar to net 1, except that krill juveniles (Thysanoeesa macrura) were present. T. macrura, pteropods, and siphonophores were dominant between 200-150 m. Between 150 m and the surface E. superba joined T. macrura as the main taxonomic component of these shallower nets. Very few copepods were present above 200 m. Large chaetognaths were found above 75 m and limacinid pteropods were present at all depths. Biomass between 25-0 m was minimal.

 

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

Our first towyo of September 9 was between stations 17 and 9. A shallow scattering layer was present between the surface and 100 m. VPR observations indicated that the layer consisted primarily of copepods, diatoms, and krill. We also observed infrequent ostracods, foraminifera, amphipods, ctenophores (possibly Beroe), and medusae. As was observed at a similar time in the early morning yesterday, the acoustic layer frequently intensified into dense and large (500 to 875 m long) patches centered at 50 m. BIOMAPER-II repeatedly intersected these patches, and large krill were observed with the VPR, except on one occasion when VPR observations within the patch were only of pteropods. At 0550, these dense patches began to appear deeper in the water column, and by 0740 were found at 225 m. During this time period, diffuse scattering persisted near the pycnocline, at 70 m. A deep scattering layer was present below 250 m, at which depths large individual targets were also evident. Half-way to station 9, the bottom shoaled up past 250 m, reaching a minimum of 175 m. At these shallower bottom depths, the deep layer became much less intense, although we still observed large targets 25 to 60 m from the bottom.

 

In order to save on time, the BIOMAPER-II was kept out of the water during the transit from station 9 to station 8, and so our second towyo of the day was between stations 8 and 5. There was some evidence of a shallow scattering layer in the mixed layer, particularly as we neared station 5. In the 25 to 90 m depth range, the VPR captured images of krill, copepods (including Oithona and Calanus), diatoms, pteropods, radiolarians, and ctenophores. Large acoustic patches were not evident, but we did observe a number of small patches (40 to 120 m long) of dense backscatter at shallow depths (30 to 50 m). On those occasions that the towbody passed through these patches, krill and large copepods were seen on the VPR. Diffuse scattering and large individual targets were again present deeper than 275 m. A 1-m2 MOCNESS tow at station 5 captured one salp, many copepods, and krill (Euphausia crystallorophias) between 200 and 350 m; the krill likely contributed substantially to the scattering observed in this depth range.

 

Current Position and Conditions

With the work of the SO GLOBEC survey grid completed, the Palmer is now steaming to a site west of Renaud Island where a time-series station will take place to look at the pattern of spatial change in the turbulence structure of the water column in relationship to the vertical distribution of the species living in the water column. The L.M. Gould is following in our wake. Our current position at 2250 on 10 September is -65 30.152′S; -66 51.579′W. The air temperature is -0.6C and the barometric pressure is 1009.5 mb. Winds are around 5 kts out of the west (279). Skies are cloudy and snow has been falling lightly for the past several hours. The pack ice is becoming thinner as we head northeast along the Western Antarctic continental shelf.

 

Cheers, Peter