The Southern Ocean GLOBEC broad-scale survey work aboard the R/V
N.B. Palmer is now well into its second week. Since the last report, work
has been completed at stations 23 to 67 in spite of rather extreme working
conditions. The work has included thirty-nine CTD profiles, twenty-four
XBTs, fifteen XCTDs, eight 1-m2 MOCNESS tows, 6 surface ring
net tows, 29 sonabuoy and 4 satellite tracked drogue deployments, bird
and mammal surveys on most of the transits between stations, and BIOMAPER
II towyo's between a majority of the stations. Seabeam bathymetry data,
ADCP data, surface temperature, salinity, and fluorescence data, and meteorological
data continue to be collected around the clock.
The weather has been a major factor impeding our progress to some extent and limiting the deployment of instruments at some stations. We have had a number of days with sustained wind in the 40 to 50 knot range with gusts even higher. On these occasions, seas of 5 m or more curtailed the deployment of the CTD or MOCNESS and even made difficult the use of XBTs or XCTDs. The towed body, BIOMAPER-II, has had to ride out several of the stormy periods in the water because the rapid onset of the high winds and seas made it impossible to recover it. The motion compensation system used in the towing of BIOMAPER-II, however, has worked reasonably well under the extreme conditions and data were collected during the gales.
The sampling to date has resulted in the development of a high quality data set on the physics and biology of the survey area. There is a strong intrusion of Upper Circumpolar Deep Water (UDCW) on the west Antarctic Peninsula continental shelf that aligns along the axis of the canyon that extends from the shelf break into Marguerite Bay. A large meander in the Southern ACC boundary was found to be associated with a large bathymetric feature just off the shelf edge west of Marguerite Bay. This may trigger a second on-shelf intrusion of UCDW in the southern part of the survey region. The nutrient distributions suggest a downwelling associated with the anticyclonic portion of the meander in the southern ACC boundary and upwelling in the cyclonic portion of the meander. These distributions match the patterns seen in the hydrography and in the ADCP current distributions. The satellite-tracked drifters are providing an interesting picture of the surface currents in this region. One has provided evidence for a tidal or inertial current near Station 26. A number of drifters were driven into Marguerite Bay by the strong winds experienced over the past week. There is evidence in the hydrography, ADCP, and satellite drifters data for a coastal current flow into Marguerite Bay from the north and out to the southwest along the western edge of Alexander Island.
Bird surveys have documented the presence and abundance patterns of a number of sea birds. Among the species encountered thus far are: Antarctic Petrel (Thalassoica antarctica), Cape Petrel (Daption capense), Southern Fulmar (Fulmarus glacialoides), Blue Petrel (Halobaena caerulea), Southern Giant Petrel (Macronectes giganteus), Snow Petrel (Pagrodoma nivea), Kelp Gull (Larus dominicanus), Broad-billed Prion (Pachyptila vittata), Sooty Shearwater (Puffinus grifeus), and the Gray-Headed (Diomedea chrysostoma) or Black Browed Albatross (Diomedea melanophris). So far, however, no penguins have been sighted. Similarly, the mammal surveys have documented the presence and distribution patterns of the minke, orca, humpback, finback, and possibly a blue whale. In addition, there have been substantial numbers of crabeater seals, and somewhat fewer Weddell, Antarctic, and leopard seals. Sonabuoys have been used to listen to the mammal calls and sounds, and they have been recorded for post-cruise analyses.
Along track towyoing with BIOMAPER-II has provided a comprehensive view of the volume backscattering at 4 frequencies (43, 120, 200, and 420 kHz) after some serious electronic problems with the sonar were solved. The pattern of volume backscattering suggests that the water column is largely dominated by moderate size zooplankton and krill; larger fish-like targets are relatively rare. The continental shelf areas have significantly higher backscattering than do the offshore areas surveyed. Patches of krill occur sporadically on the shelf and in Marguerite Bay. Particularly intense patches of krill have been observed near shore off Alexander Island on the southern part of the survey and in these regions seals and sea birds have been particularly abundant. The concurrent VPR data provide the supporting evidence for the interpretation of the acoustic data as do the samples collected by MOCNESS.
In spite of the serious electronic problems with some of the equipment and the too frequent gale force winds and seas, completion of the survey portion of the cruise is in sight. The technical support we are receiving from the Raytheon technical support group and the ship's officers and crew continues to be excellent. To read the daily reports, which provide more detail about our work to date, go to the U.S. GLOBEC Web site (www.usglobec.org) and click on the SO GLOBEC icon to get to the SO GLOBEC Web site.
Kindest regards,
Peter Wiebe, Chief Scientist