Today is Easter Sunday, April 4th and we are currently hard at work in the Palmer Deep area, just offshore Anvers Island and the U. S. Palmer Station. So far we have had a very successful cruise and all science staff are very impressed with the high degree of co-operation and planning in support of our endeavors.
We departed Punta Arenas on 28 March, as scheduled, and had calm seas for the crossing of the Drake Passage. Water samples were collected and filtered for organic particulate and carbon analyses by the Stanford University group. We occupied our first science way-point in the early hours of 1st of April in Crystal Sound but began collecting multi-beam data the day before, as we crossed the continental margin of the Antarctic Peninsula. We initiated a multi-beam and bathy 2000 survey of the Crystal Sound region and selected a core site in just over 1200 m of water.
The swath mapping is a powerful tool that greatly increases our ability to select strategic core sites. Kasten core #1 was successfully recovered and demonstrated a stratigraphy consistent with earlier paleoenvironmental records from Lallemand Fjord but within a higher productivity regime, overall. Over 300 discrete samples were collected from this core for paleomagnetic, diatom, geochemical, and physical properties measurements.
The swath-mapping program was continued into Lallemand Fjord toward the terminus of the Muller Ice Shelf. In the evening of the 1st of April we successfully retrieved all three of our sediment trap moorings which were deployed just over a year ago off the L. M. Gould. Nine of ten sediment traps were brought on-board and the sediment record they contain represents a valuable reference for sedimentation from a decaying ice shelf system.
The Muller Ice Shelf has calved a great deal over the summer as witnessed by the abundant tabular icebergs we found within the inner reaches of the fjord. The sediment sequence from all the traps contains a consistent seasonal signal marked by mid-core (presumably winter of í98) maxima in magnetic susceptibility. Detailed sedimentologic studies of these trap-cores will be done at Queen's University (Canada) in international co-operation with USAP-Hamilton College and Colgate University.
A biological dredge and CTD were collected in the near-ice shelf setting before completing the multi-beam imagery of the rest of Lallemand Fjord early on the 2nd of April. Strong winds with gusts in excess of 70 kt and large icebergs presented challenges to the bridge crew during the survey. These were overcome with great skill and enthusiasm that we now come to expect from Captain Joe's team. The heavy winds and rising seas prevented us from collecting a long core from Crystal Sound as we exited the Fjord and began our transit to Palmer Deep.
In route we found protection in the lee of Lavosier Island and coincidentally found a suitable site (via the Bathy2000) for a core in the northernmost stretch of Crystal Sound. Kasten core #2 was successfully recovered and demonstrated a largely biogenic (high productivity) paleoenvironmental signal.
Yet the magnetic susceptibilitly record contained a gradient identical to Kasten core #1, thus marking a regionally consistent change in paleoenvironment over the last few thousand years.
Brief downtime in the swath mapping was caused by the need to shut down the entire computer lab system during an electrical problem on the 00 deck. This difficult problem was quickly overcome under the supervision of Suzanne O'Hara thus allowing us to collect multi-beam imagery in-route to the Palmer Deep. We began the multi-beam survey of the Palmer Deep early on the 3rd of April and this was mostly completed by late in the afternoon of the same day. The swath map of the Palmer Deep was, to say the least, mesmerizing as it showed for the first time the complexity of the entire Palmer Deep deposystem. The main basin (basin III) is fed by a narrow channel that enters from the eastern slopes of the tiny Myriad Islands. It bends westward, and then U-turns sharply toward the east before opening up into the main flat of the basin; up against the steep (glacially prograded) slope of the eastern perimeter (the western end of the Bismark Strait). Basin I which is the main focus of post-cruise studies of ODP Leg 178 (Site 1098) is actually much larger than thought and constitutes an elongated trough that tapers toward the SW, it is clearly connected to the deeper Basin III but over a narrow sill. Magnetometer and pre-existing seismic data will be integrated with the swath map in order to discern the structural/tectonic and glacial history of the basin. Much remains to be learned from this remarkable data set.
The high-tech mooring assembled by the Stanford University team was deployed in the waning hours of daylight on the 3rd of April under the supervision of several curious Gentoo Penguins. The mooring (named Marjorie) consists of an ADCP current meter, two CTD units, three Aanderra current meters and two sediment traps. It is linked to the anchor with a double acoustic release and is scheduled for service next season during a cruise of the L. M. Gould. The mooring site was located in Basin I, near Site 1098 of ODP Leg 178. It should provide an important calibration tool for paleoenvironmental interpretations as well as a vital link with the on-going LTER study of the Palmer Region.
At present we are completing a biological grab survey and coring program in the Palmer Deep region. We have rescheduled our call to Palmer Station to the early morning of Monday, April 5th for the convenience of the Palmer Station staff and scientists.
After almost a week of work we are now forming into efficient teams, and there is excellent co-operation from ASA and ECO personnel. We are also grateful for the help provided in ping-editing by NSF and ASA participants. All are in good spirits in no small way because of the tasty products of Ernest and his staff of able assistants. We look forward to another four days of science on the good ship N. B. Palmer.
Eugene W. Domack
Professor of Geology