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Jan 25 - Crew Change

Date: 25th January 2004

Noon Position: lat 60 14.0' S, long 65 16.5' W (584 miles from Stanley)
Distance Travelled since Immingham: 22900 Nautical Miles
Air temperature: 5.6°C
Sea temperature: 3.2°C


The JCR this Week.

This week the JCR has undergone some major changes. We said farewell to Captain Paterson and his crew as they flew home for a well earned break and we welcomed Captain Burgan and his crew who will take us south once more.

We swapped our biosciences team for geoscientists under the guidance of principal scientist Rob Larter. With them came a huge amount of equipment for taking images of and samples from the sea bed.

The look of the ship has also changed, with the aft deck undergoing a radical transformation following the installation of one very large corer:
 

Photo by Carol Pudsey. Click to enlarge Photo by Carol Pudsey. Click to enlarge.

Before the installation.
Click to enlarge.

After.
Click to enlarge.

These changes have left the few of us remaining on board with mixed feelings. For Peter Morris it is a welcome relief from his solitary "swath watch", to have some colleagues to share the work. For Dave King, 2nd mate, its a warm welcome to old friends and his usual sailing crew. For myself it is a daunting prospect, taking over the writing of the diary from Simon (and trying very hard to remember all he taught me), as well as a certain sadness at saying good-bye to many good friends and neighbours. On the other hand this is a very happy time, with a new group of friends to get to know and to share time with and a whole new and probably very muddy world of geoscience to discover.

For the next three weeks we will be working in the Bellingshausen Sea, to the west of the Antarctic peninsula. Rob Larter has kindly written us an introduction to the science we will be doing there.


Science Bit In The Middle.

This weekend we are on our way to the Bellingshausen Sea, which is the southeastern corner of the Pacific Ocean. It lies to the west of the Antarctic Peninsula, the narrow strip of the Antarctic continent that points towards South America. The area that we are going to is marked on the map below by a rectangular box.

 Location map. Click to enlarge.

What will we be doing in the Bellingshausen Sea?

Our objective is to find out what changes have taken place in this area since the last ice age. 20,000 years ago, grounded ice extended to the edge of the continental shelf around most of Antarctica. We will use the ship's advanced sonar systems to image features on the sea floor that were formed at the base of the ice sheet and left behind as the ice retreated.

These systems are:

  • The EM120 multibeam echo sounder ('swath bathymetry system'), which reveals the detailed topography of the sea floor.
  • The TOPAS sub-bottom acoustic profiler, which provides vertical sections along the ship's track through glacial and post-glacial sediments.

 Swathbathymetry system. Click to enlarge.

An artist's impression of the fan-shaped array of echo sounder beams in the water beneath the ship. There are 191 individual beams, each directed at a different angle, allowing a swath that is four times as wide as the water is deep to be mapped from a single survey line.

On the basis of the sonar data we will select sites to collect sediment cores. Analysis of the cores will reveal a record of the changes that have taken place since the ice retreated. After the cruise, samples from the cores will be radiocarbon dated to find out when, and how quickly, the ice retreated.

 Corer. Click to enlarge

The gravity corer (yellow) during a trial deployment at Port Stanley before the start of the cruise.

Why are we doing this?

The Bellingshausen Sea is adjacent to the West Antarctic Ice Sheet, which some scientists have suggested is potentially unstable. Although the West Antarctic Ice Sheet is only a fraction of the size of the East Antarctic Ice Sheet, its complete collapse would raise sea level by about 6 m, which would have devastating consequences in many parts of the world. By improving knowledge of the history of the ice sheet we expect to obtain clues about its future stability.

Reconnaissance data suggest that when the West Antarctic Ice Sheet expanded to cover the continental shelf, one of the major pathways through which ice drained from it was in the Bellingshausen Sea. We interpret a 150 km-wide, 700m-deep trough near the edge of the continental shelf as having contained an enormous, fast-flowing glacier. Beyond the mouth of the trough, thick sediments have accumulated on the continental slope. Such sediment accumulations are known as 'trough mouth fans' and are characteristic of places where large glaciers reached the edge of the continental shelf.

 Profiles. Click to enlarge.

The flanks of the continental shelf trough as seen on sub-bottom acoustic profiles. The broad, dark band running along the profiles is the sea-floor reflection.

The volume of ice that must have drained through such a large glacier implies that the glacier must have been fed by a large ice drainage basin. The map below shows a tentative interpretation of the extent of this drainage basin, covering an area of more than 300,000 square km. This is equivalent to about 15% of the area of the modern West Antarctic Ice Sheet. By finding out how and when ice retreated in such a major drainage basin we expect to obtain clues that can be used to predict future changes in other sectors of the ice sheet.

 Drainage basin map. Click to enlarge.

Topographic map (500 m contour interval) showing the main ice drainage basins around the study area. Thick white lines mark boundaries of basins. Dashed lines show boundaries of Bellingshausen Sea trough. The dotted line marks the continental shelf edge.


Captain Burgan's crew.

To briefly introduce the new crew, here are a few photographs. There will be more formal introductions over the forthcoming weeks.

The Bridge Team. Click to enlarge. John Summers, Mark Thomas, Dave king, Kevin Holmes and Paul Clarke.
Colin Smith, Duncan anderson, Tom Elliott and Rich Turner. Officers in the bar. Click to enlarge.
The Saloon stewards. Click to enlarge. Nick Greenwood, Mick Weirs and Lee Jones.

A final thought...

Many thanks to all of Captain Elliott's and Captain Paterson's team for their hard work, friendship and the many adventures we shared. Many thanks in particular to Simon for his hard work on the diary. We wish them all a happy and relaxing leave and look forward to seeing them back in June.

 Cape Pembroke by Sarah Hardy. Click to enlarge.

Cape Pembroke Lighthouse. Proving the sun does shine in the Falkland Islands. A million thanks to Sarah Hardy to whom it was initially an adventure, then a challenge and finally an obsession to get this photograph. Click to enlarge.