Report of Activities on the RVIB N.B. Palmer Cruise 02-02
9 to
11 April 2002

 

This is the first report of the third broad-scale cruise of the U.S. Southern Ocean GLOBEC Program aboard the Research Vessel Ice Breaker Nathaniel B. Palmer. Two similar cruises took place last year (NBP01-03 and NBP01-04). The focus of this study is on the biology and physics of a region of the Antarctic shelf due south of tip of South America that extends from the northern tip of Adelaide Island to the southern portion of Alexander Island and includes Marguerite Bay. This cruise is a joint ship operation with the R/V L.M. Gould, which will be conducting process studies in the same geographic region.

 

We have two primary goals: to elucidate shelf physical circulation processes and their effect on sea ice formation and Antarctic krill (Euphausia superba) distribution and to examine the factors that govern krill survivorship and availability as food to higher trophic levels, including fish, seals, penguins, and whales. The work on this cruise will involve collecting data at a grid of 92 regularly spaced stations positioned nominally at 40 km intervals within the survey area. The station activities will involve the deployment of the CTD [to measure water column physical properties (temperature, salinity, and microstructure) and to collect water samples for nutrients, microzooplankton, phytoplankton], the towing of a variety of nets [to collect zooplankton, especially krill, and mid-water fish for studies of their distribution and abundance and for studies of their physiology and biochemistry], the deployment on an ROV [for under ice studies of krill distribution and behavior], and the collection of live zooplankton, especially krill, to study of material properties [sound speed contrast and density contrast]. The work on the cruise will also involve collection of data along the survey trackline between the stations. The along track activities will involve the towyoing of BIOMAPER-II between the surface and about 250 m [to collect multiple frequency (5) acoustic data from reverberation off water column animals, high resolution video data of individual zooplankton, and environmental data (temperature, salinity, fluorescence, etc.)] and the surveying of sea birds and marine mammals. Throughout the cruise a passive listening device (sonobuoy) will be deployed to listen to marine mammal calls and continuous measurements will be made of sea surface water properties, water currents (with ADCP), meteorological properties, and sea floor bathymetry (with SeaBeam). Attempts will be made to collect diet samples from the sea birds.

 

We left the port of Punta Arenas, Chile at 1100 hours on Tuesday, 9 April 2002 after an intensive week of cruise preparation, which went very smoothly thanks to the excellent preparations and assistance provided by the Raytheon Technical Support Group. There was a moderate wind and partly cloudy skies.

 

The course to the survey area (first station is at -65.6633S; -70.6580W) has taken us east from Punta Arenas through the straits of Magellan, then south along the eastern side of South America (Argentina), through the straits of Maire, then nearly straight south to the start of the grid. The distance from Punta Arenas to the work site is approximately 900 nm.

 

Shortly after leaving port, we stopped at a nearby dock to pick up the Cajun Cruncher, a small boat carried by the N.B. Palmer, which had undergone some repairs in Punta Arenas. After lunch, we had our first safety meeting with Chief Mate Richard Wishner presiding. This included dawning the survival suits and the exercise of getting the entire science party into a large life boat and strapped in. The safety meeting was followed by a science meeting led by MPC Alice Doyle and Chief Scientist Peter Wiebe. Then there was an on deck safety briefing and later a SeaBeam data ping editing class for those who had not previously done ping editing. Later in the afternoon, while steaming through the straits of Magellan, we slowed for a test deployment of BIOMAPER-II. This enabled those who will be handling the launch and recovery of the towed body to become familiar with the procedures in running the winch, slack tensioner, and overboarding sheave and docking mechanism together with the operation of the stern A-frame under good weather and sea conditions. It also provided an in-water test of all of the sensors systems while the system was being towed and fine tuning of the weight distribution in towed body to get it to tow horizontally. Around 1800 at the pilot drop-off point on the eastern end of the Straits of Magellan, three individuals (Sam Johnson of HTI, and Scott Gallager and Terry Hammar both from WHOI) who were assisting in the port setup of the hardware and software associated with BIOMAPER-II and the ROV, left the ship along with the pilot.

 

During 10 April, we steamed along the eastern side of the southern tip of South America reaching the straits of Maire in the late afternoon. Winds were in the 30 kt range during the morning, but the seas were moderate because we were in the lee of the land. As we approached Estrecho del la Maire, we could see high snow covered mountains in the distance. They were quickly obscured by a fast moving snow squall. The winds, out of the southwest, were fierce in the straits with speeds up in the high 40 to low 50 kt range and we were no longer in a lee. Fortunately, the current was running with the wind so that the seas were not as big as they might have been. Bucking the wind and current, however, resulted in the ships speed being slowed to about 5 kts as we made our way through the straits. During the night of 10th and the morning of the 11th of April, the winds remained in the high 40 to low 50's. There were gust up to and over 60 knots. Needless to say, it was not a comfortable night for anyone. The winds abated some in the late morning, but remained in mid-thirty knot range for the rest of the day and evening. As a result, the ship continued to make around 5 or 6 knots as we inched our way towards the 200 mile limit where our first work was to start.

 

About 0100 on 12 April, we crossed the 200 mile limit and began making science observations taking XBTs at 10 nm intervals, and recording SeaBeam bathymetry and along track sea surface and meteorological data. We are currently about 350 nm north of Station 1 (position at 0900 is -60 24.757S; -65 02.414W) and making about 10 knots. The skies are cloudy as they have been the past two days.

 

Cheers, Peter