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

14 September 2002

On 14 September, the N.B. Palmer steamed along a trackline that took it through the northern end of the Gerlache Strait, the southern end of the Bransfield Strait, and finally through the Boyd Strait and out onto the continental shelf headed for the southern tip of South America. According to the “Geographic Names of the Antarctic”, both the Bransfield Strait and the Boyd Strait were named in the 1820s after masters in the Royal Navy by British expeditions under James Weddell. The Gerlache Strait was explored by a Belgian expedition in 1898 and named after the leader of that expedition.

In the morning of 14 September, the CTD work came to a premature end when the CTD/rosette system touched the bottom during a cast at station 6 in the Bransfield Strait. Normally, on casts to the bottom an acoustic alarm system is activated when the unit is within a few meters of the bottom, but for some unknown reason the alarm did not sound and the system sat on the bottom before it was realized that the pressure readings had stopped changing. There was no damage to the CTD unit, but the wire within a few meters of the cable termination had unraveled because of the release of tension. To continue using the CTD would have required re-terminating - a lengthy process. In addition, CMiPS was showing signs of needing to be serviced, which was also a lengthy process. The decision was made to complete the last stations using Expendable CTDs. Beyond the stations specifically designed to look at the confluence of water masses in the inland passage region, XBTs or XCTDs were taken at 10 nm intervals along the transit route and will continue to be dropped until reaching the 200-mile limit of Argentina.

September 14 was also a day of rather frenetic activity as the various scientific groups disassembled the scientific equipment and packed it away in the limited time before reaching the end of the protected waters of the inland passage. During the evening, the process of tying everything down was completed and the Palmer was ready for whatever rough weather and high seas might be in store during the transit across the Drake Passage.

Weather on 14 September was good for working, although it is quite cloudy and snow was still falling lightly in the morning. Air temperature began the day around -2ºC and gradually rose to around 0ºC. Barometric pressure again varied within narrow limits decreasing slowly from 1012 to 1006 mb over the course of the day. Winds dropped from the previous evening's high of 30 knots to 15 knots or less for most of the day and came from nearly every point on the compass during one time of day or another. While still in the Bransfield Strait, the waters were largely pack ice free and only small icebergs, bergy bits, and other ice chunks were present. As we came out into the Boyd Strait, we came into more pack ice, but it was in patches with lots of open water in between. The pack ice was loose and unconsolidated made up of many small pancakes and larger floes. There were many seals (fur seals and Crabeaters) and some Adélie penguins on the floes. In the afternoon, there were patches of fog with low visibility and times when it appeared that the sun was about to break out, but then didn't. Seas remained moderate with a swell running that gave the Palmer a motion not experienced often in the past few weeks.

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

In the early morning of 14 September, we completed CTD/CMiPS casts at two additional stations on the transect along the axis of the Gerlache Strait. At the second of these stations, the CTD/Rosette hit the bottom resulting in damage to the hydro wire that required re-terminating the connections. Because this was nearly the last of the planned CTD casts on this cruise, the decision was made to finish the transect using XCTDs. Therefore, the last two stations were completed in this manner.

Following completion of the Gerlache Strait transect, we dropped six XBTs at 10 nm intervals along a transect that extended from Croker Passage, at the northern end of the Strait, northward across Bransfield Strait. This transect ended at Boyd Strait, which is between Smith and Snow Islands and provides a deep connection between Bransfield Strait and Drake Passage.

Once through Boyd Strait, we entered Drake Passage and began a third transect that extends across the Passage to the Argentine 200-mile limit. We are dropping XCTDs at 10 nm intervals along this transect with the objective of characterizing variability in the Polar Front. This will provide the eighth such section across Drake Passage as a result of the U.S. SO GLOBEC cruises.

The CTD/CMiPS casts from Gerlache Strait showed considerable small-scale variability at places where Circumpolar Deep Water, Bransfield Strait water, and possibly Weddell Sea water come together. Also, this section showed the expected inflow of Circumpolar Deep Water into Gerlache Strait around Brabant Island. This data set should help constrain estimates of the exchange of Bransfield Strait water and Circumpolar Deep Water, originating on the west Antarctic Peninsula continental shelf, through the Gerlache Strait.

The vertical temperature distribution derived from the XBT section northward through the Bransfield Strait shows clearly the inflow of Circumpolar Deep Water via Boyd Strait. This water mass is apparent far into the Bransfield Strait. The surface temperatures along the XBT transect were well above freezing. This is a marked difference from the freezing surface temperatures observed during the transit through this area at the start of the cruise.

Marine Mammal report (Chico Viddi)

The SO GLOBEC grid has been completed and we are leaving beautiful Antarctica behind as we head back to Chile. During the few days before and after the grid ended, not a single cetacean was seen. The hours of marine mammal observation that have been logged now total 311.3 and the “effective effort” hours total 144.6. During this past week (9 to 15 September), 31.2 observation hours were logged, of which 12.56 corresponded to “effective effort”. Between 9 and 11 September, little effective effort was achieved since the viewing conditions were not the best. There were very dense fog patches and snow, and therefore visibility was very poor (14.3 hours of observation, but only 2.5 effort hours during the period). No marine mammals were seen on 9 September and only 9 crabeater seals were counted on the 10th. No survey was performed on 11 September since the entire day was spent at the time-series station and fog was too dense to even do incidental observations. After three gray, foggy, and cloudy days, the sunshine returned on 12 September with clear blue skies and great visibility. No cetaceans were seen, but 18 pinnipeds were observed: 2 Crabeater seals (Lobodon carcinophagus), 1 leopard seal (Hydrurga leptonix) and 15 Antarctic fur seals (Arctocephalus gazella). Antarctic fur seals had not been seen since we were steaming south towards the SO GLOBEC grid, about 40 days ago in the area of Gerlache Strait. The marine mammal survey on 12 September ended at 1048, when we arrived at Palmer Station.

On 13 September, 5.1 observation hours were achieved after leaving Palmer Station at noon. The day was great. Initially it was windless with only high clouds and open water in the Bismark Strait with some great icebergs and patches of brash ice. Conditions for marine mammal surveying were excellent until 1548, when clouds, mist, and fog covered the mountains and the horizon. Although almost 4 hours of “effective effort” were achieved, only 4 fur seals were seen. Unfortunately, one of the fur seals sighted on an ice floe had debris around its neck (probably a piece of net). Pollution in Antarctica, mainly due to fishing debris, has produced much attention and environmental concern. The sight of fur seals affected by debris is not an uncommon occurrence. Sadly, it has been reported several times. September 14 was characterized by many dense fog patches, which affected the marine mammal survey considerably. Only 2.9 "effective effort" hours were logged out of 8.4 observation hours. In spite of marginal viewing conditions, the 14th was by far the best day for pinniped estimates of abundance and diversity. An outstanding number of 407 pinnipeds were counted including 19 leopard seals, 31 Crabeater seals and 288 Antarctic fur seals. Unidentified pinnipeds numbered 79, since visibility was often bad. Only dark dots could be seen on the ice, but they were clear enough to know they were seals.

With less than 5 days steaming from Punta Arenas, we are now moving through the Drake Passage. Marine mammal observations will be made until our arrival in port.

Current Position and Conditions

The N.B. Palmer is now well into the Drake Passage and most of the packing that can be done at sea has been completed. It is a time for cruise report writing and for reflecting back upon a cruise that required perseverance and patience, but has ended quite successfully. We are currently about 115 miles away from the Argentine 200-mile limit and some 540 nm from Punta Arenas, Chile. Our current position at 1107 on 15 September is -60º 37.102′S; -63º 07.724′W. It is moderately foggy with the sun breaking through on occasion. The air temperature is -0.2ºC and the barometric pressure is 1008.0 mb. Winds are 13 to 15 kts out of the north-northeast (021). For the most part we are steaming in open water.

We plan to arrive in Punta Arenas, Chile in two to three days after steaming through Estrecho de la Maire and along the eastern Argentine seaboard to the Straits of Magellan. At the eastern entrance of the straits, we will pick up a pilot and then steam the remaining distance to Punta Arenas west along the straits.

This will be the last report of the daily reports for NBP02-04. Many thanks to all the investigators who contributed to these reports. Thanks also the Officers and crew of the N.B. Palmer for their excellent support in carrying out the navigation and ship handling aspects of the cruise. We very much appreciate the excellent logistical support provided by MPC Chris Shepherd and the Raytheon Technical Support Group.

Cheers, Peter