The R/V N.B. Palmer has left the Western Antarctic Peninsula continental shelf research site of the Southern Ocean GLOBEC program and has begun the trek back to Punta Arenas, Chile. We are now in the Drake Passage at -62 50.277°S; -68 49.990°W (2 June - 1533 local) with near gale winds of 28 to 34 kts out of the east (090). Although the last of the station work was completed yesterday, XBTs will be taken at a number of locations as we cross the polar front and sonabuoys will continue to be deployed to listen for marine mammal calls and sounds. Our expected arrival time in Punta Arenas is 6 June. In the interim, the scientific party will be packing gear either for storage in Chile awaiting the next cruise which begins in mid-July or for shipment to the U.S. Leaders of the research parties will also be writing up sections for the cruise report. This will be the last daily report for this cruise.
June 1 was the final day for collecting data in the research site on this broad-scale survey cruise. A BIOMAPER-II towyo section along transect line two was completed about 1430 and then two deep CTD stations were completed at locations beyond the continental shelf that were extensions of the lines of stations on survey transects one and two. The CTD came back aboard after the final cast about 2230 and shortly after the steaming began for Punta Arenas, Chile. The weather during the day was ideal for surveying birds and mammals. Skies had a high cloud overcast and visibility was very good. Winds remained under 10 kts for most of the day and out of the east southeast. Thus, the seas were calm and free of sea ice.
Eileen Hofmann reports that 1 June was the final day of stations for the CTD group. The day started with closely spaced (3 nm) XBT drops along survey transect two as the BIOMAPER-II was towed offshore. This section was occupied early in the survey and the XBT data provided a means for assessing the changes that have taken place in the intervening time. A preliminary look at the XBT data shows that the bottom intrusion of Circumpolar Deep Water that was observed at the start of the survey is still present. However, the intensity of the intrusion seems to have increased. The 1.5 C isotherm is further onto the shelf and the 1.8°C isotherm is now at the outer end of the survey transect. This suggests that the southern boundary of the ACC has moved closer to the shelf edge.
Following the completion of survey transect two, one deep (2800 m) CTD cast was done about 10 nm further offshore on this transect. This allowed us to determine the location of the southern boundary of the ACC and the southern ACC front. After completion of this cast we next steamed to a location about 20 nm offshore of the end of survey transect 1 and did another deep (3100 m) CTD cast. This cast served two purposes. First, it allowed the location of the southern ACC front and boundary to be determined, which was not possible from the stations occupied on this transect earlier in the cruise. Second, it allowed cruise participants to send decorated styraform cups to a depth of more than 3000 meters on the CTD. The CTD and accompanying large bag of crushed styraform cups were successfully recovered. As always, the cups illustrate the effect of the pressure associated with 3000 m of water.
The successful completion of the CTD survey work and acquisition of a high quality data set are due to the efforts of the hydrographic group, Bob Beardsley, Sue Beardsley, Mark Christmas, Susan Howard, Rosario Sanay, Baris Salihoglu, and Aparana Sreenivasan. Thanks also go to Howard Rutherford and Rebecca Conroy for their efforts in collecting and ensuring a quality nutrient data set. Finally, many thanks go to Raytheon MTs, Matt Burke, and Dave Green, and ETs Jeff Otten and Jan Szelag. Their efforts and cheerful willingness to help made the cruise enjoyable as well as productive.
Chris Ribic and Erik Chapman report that on 1 June, they surveyed for
four hours in transit between stations 9 and 10. This survey covered the
outer portion of the continental shelf just north of Marguerite Bay and
ended at the shelf break. Although we did not travel through ice, the Snow
Petrel was the most common bird observed during the transect with Antarctic
Petrels also relatively common. The following table summarizes today's
|Species||Number (JD 152) 4 hours|
|Antarctic Petrel (Thalassoica antarctica)||15|
|Cape Petrel (Daption capense)||2|
|Southern Fulmar (Fulmarus glacialoides)||1|
|Blue Petrel (Halobaena caerulea)||0|
|Southern Giant Petrel (Macronectes giganteus)||1|
|Snow Petrel (Pagrodoma nivea)||34|
Ari Friedlander reports that on 1 June, his watch began at 1000 (local time) as we were steaming up the final transect line towards the CTD station. Conditions were optimal; cloudy skies, light wind and swells, and good visibility. The watch was kept until 1400 local time as we approached the last station. No whales and only 2 fur seals were seen. Catherine Berchock has summarized her last three days of sonabuoy deployments: On May 30th around 0630 (local), the 2nd mate, Marty Galster, spotted two groups of humpbacks from the bridge and in response, a difar sonabuoy was deployed by 0640. Humpbacks were heard, but the ship noise was very loud. The whales appeared to be off the port quarter according to the fix. An omni buoy was put in to record the full range of humpback calls, but this buoy had a lot of interference on it. On the way towards the Kirkwood Islands to fix the AWS, another difar was deployed 1030. Very loud calls from Humpbacks were heard. At 1118, Ari Friedlander called down to report a minke sighting and in responsee another difar was put in, but only humpbacks were heard. The final buoy of the day was deployed at 5 nm from the Kirkwood Islands, so listening could take place while waiting for the AWS team to finish. Humpbacks were still heard. After the work on the AWS was finished - we turned around and followed out same track back to the previous station location. In doing so, we passed by two buoys that had not scuttled yet, and an additional two hours of recordings were made from them. This was one of the best days for loud humpback vocalizations. Five buoys were deployed for a total of approximately 12 hours of recordings.
Due to King Neptune's visit on May 31st, few recordings were made. Two buoys were deployed, one at 1030 and the other (because a minke whale was spotted) at 1154. No vocalizations appear to have been heard, but that needs to be verified. A total of two hours were recorded.
Four difar sonobuoys were deployed on June 1st. The first was at 20 nm from the end of the BIOMAPER-II line and the second was at ~ 8 nm from the end of the line. Humpbacks were heard on both of these buoys in the general direction of behind and slightly off of our trackline. A third difar was deployed at ~7 nm from the first deep CTD station. After we left the CTD station, another difar was deployed and was able to get a good fix to the calling whale's location, which was ~ 5nm from our position at 1412 at an angle of 20 degrees from the port stern. A total of ten hours of recordings were made.
Thus far today, June 2nd, only one sonobuoy was deployed - an omnidirectional
at ~ 1300. No marine mammal sounds were heard during the hour of recording.
A few more buoys will be deployed tonight and tomorrow morning before we
cross the 200 mile limit, just to see what may be out here in the Drake
BIOMAPER-II/MOCNESS report (P. Wiebe, C. Ashjian, S. Gallager and
On 1 June, BIOMAPER-II continued to be towyoed between 0 and 250 m along the second broad-scale survey transect line as the ship headed to the outer margin of the continental shelf. The acoustic structure of the upper 70 m or so corresponded to the mixed layer and was relatively featureless except for near surface patches of high volume backscattering, which were hundreds of meters to a kilometer or two across and 10 to 20 m in vertical thickness. These occurred sporadically along the transect and were present until crossing the ACC front near the shelf break, and were probably composed of krill juvenile stages. The acoustic structure of the mixed layer zone was very different from the quasi-horizontal acoustic strata that were visible within the pcynocline, which extended from 70 m to about 200 m. Below the pcynocline for much of the transect, there was a layer of moderate backscattering intensity and the video provided images mostly of copepods and pteropods.
The specific scientific aims of this oceanographic expedition have been met and we have gathered a large number of sample collections and several massive data sets. These need to be analyzed and studied over the next year or two to begin to develop a coherent picture of the overwintering pattern of distribution and abundance of the krill, their prey, and their predators, and how the biology of the region is coupled to the physics of flow, hydrography, and sea ice. It is also important to note, that this is the first of four broad-scale cruises that will take place over a twenty-four month period. So this study has just begun and the true scientific understanding of our efforts will not be known for some time.
The success we have enjoyed on this expedition is due in large part to the very excellent technical assistance we have received from all nine members of the Raytheon Marine Technical support group. They have responded in a very positive and experienced way to the technical problems as they arose, and they provided a steady professional hand on the day to day operations. Likewise, the Ship's officers and crew provided excellent ship handling enabling us to safely work through high winds and seas, through sea ice and around icebergs, and in shallow uncharted topography. The friendly atmosphere that was set by Captain Mike Watson was evident throughout the ship. It made this expedition a pleasure to be on.