Punta to Stanley and then South
Punta to Stanley and then South
Last time we left it the James Clark Ross was alongside the berth at Puerto Montades, to the North of Punta Arenas and some of the new scientific crew had just arrived. The ship had to be off berth by the evening of the 8th Jan and headed south, along the coast, so as to lay at anchor just to the east of the city itself. The ship would be there just until lunchtime of the next day. By then half of the crew would have changed over and all bar two of the new scientific staff would have arrived. Old and New scientific staff and those of the crew to fly back to the UK were thus able to make only a whistle-stop tour of the city itself before heading their various ways.
And so it was, at midday on the 8th Jan, that the ship left South America, not to return until heading back towards the northern hemisphere in 3 months time. Before the ship could leave, the new scientific team that had not previously worked on the JCR were required to have a full ships safety brief. Once completed, the ship went on her way back to Stanley in the Falkland Islands.
At 8am on 11th Jan the James Clark Ross arrived at FIPASS for the 3rd time this season and, with the crew changeover, also hitting the mid-point of her season in the southern hemisphere. As well as being a routine mid-season changeover, this was also to be a historic day for the James Clark Ross, as well as for BAS. Having banned the word last from use on the ship and on the web page over recent months, this was to be the LAST day that Chris Elliott would serve as Captain on the James Clark Ross, after a total of 38 years working on BAS ships. After this short 3 and a half month run on the James Clark Ross, her captaincy was passed over from Captain Elliott to Captain Burgan for the last ever time at 5pm on 11th January 2006.
For those that were paying off the ship this was the final couple of days in the southern hemisphere, and for those heading on the next 6 week cruise it would be the last chance of a spot of warm summer weather prior to heading all the way down to about 75 degrees south. The weather in the Falklands willingly obliged, giving those with the free time a chance to see some of the summer wildlife or just relax with either a spot of golf, fishing or hill walking.
After 48 hours of perfect weather in the Falklands it was time to set sail again for colder climes, with the newly joined ships compliment, and the long-serving doctor. The ship left FIPASS at 10:39 on 13th January to anchor in Port William, where emergency and lifeboat drills were carried out. The JCR departed from Port William at 14:00 for the weeklong passage to Pine Island Bay where the science work would start in earnest.
Finishing on the Science Plan with Rob Larter
JR141 Scientific Program
On this research cruise JCR is heading further south and west into the Pacific Ocean than she has ever been before, to Pine Island Bay (see map). The objectives are to investigate the history of the Antarctic Ice Sheet since the last ice age (about 20,000 years ago) and present day interactions between the ice sheet and the ocean.
Why Pine Island Bay?
Over the past few decades the part of the ice sheet around Pine Island Bay has been changing more rapidly than in any other part of Antarctica. Studies using data from satellites have shown that the ice is thinning and that grounding lines of the main glaciers (where the ice starts to float over the sea) in this area are retreating. As the base of a large part of the ice sheet around Pine Island Bay lies below sea level, this has raised concerns that continued thinning and retreat could lead to collapse of this sector of the ice sheet, and ultimately neighbouring sectors as well. If this happened the resulting rise in global sea level would be between 1 and 5 m, depending on the extent of the collapse.
At present it is not clear to what extent the changes in the ice sheet around Pine Island Bay are a continuation of the glacial recession that started at the end of the last ice age and to what extent they reflect more recent climatic changes. To answer this question we need to find out more about the history of this part of the ice sheet, to improve understanding of the processes responsible for the recent changes, and to combine our results with computer models of ice sheets.
Investigating ice sheet history
During the last ice age grounded ice extended onto 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.
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.
The vibrocorer being installed on the stern deck of JCR in Port Stanley before the start of the cruise. The vibrocorer is on loan from, and will be operated by engineers from, the British Geological Survey Marine Operations Group.(Photo by Rob Larter)
Studying interactions between the ice sheet and the ocean
Recent studies have shown that relatively warm water from the deep ocean is upwelling onto the continental shelf in Pine Island Bay. Circulation of this water beneath floating glacier tongues has been proposed as a likely explanation of the simultaneous thinning and grounding line retreat affecting several large glaciers in this region. We will study the flow of water onto the continental shelf and into and out of the cavities beneath floating glacier tongues by lowering instruments that measure the temperature and electrical conductivity of the water. These measurements can be used to calculate water salinity and flow patterns. The flow of ocean currents will also be measured directly using another sophisticated sonar device, the ‘acoustic doppler current profiler’. In a similar way to which the tone of a siren changes depending on whether it is approaching or going away from you, this instrument uses the shift in frequency of sound reflected from microscopic particles in the water to calculate the speed and direction in which water is flowing at different depths beneath the ship.