Jan 11 - Seabed Survey
Date: 11th January 2004
Noon Position: Noon position lat 53 30.5 S long 38 21.1 W
Distance Travelled since Immingham: 20814 Nautical Miles
Air temperature: 4.6°
Sea temperature: 3.9°C
The JCR this Week.
This week has been governed by the elements once again, be they either ice, wind or water. At the moment we are riding out a storm (hove to) at the northern end of South Georgia. Being hove to is when the vessel is steaming very slowly, just using enough speed and choosing a course to make conditions comfortable onboard i.e. not moving very far. Hopefully the weather will soon abate and we'll be able to carry on with the survey once more.
| Mega-berg off South Georgia.
Click to enlarge.
| Riding out the waves.
Click to enlarge.
The two pictures above show the things that have most effected this week's work. The left hand one shows the side view of a mega-berg, one of several that are presently in this area, and the right hand one shows the bows plowing through yet more rough seas. The one image that isn't shown is the fog and mist that has also hung around us for most of the week. The mega-bergs are probably from the Larsen ice shelf which started to break up some years ago. They have travelled northwards from the Weddell sea to their present positions, some of them might now be aground as the sea bed shallows around South Georgia. Whether grounded or not they are all now shedding hundreds, if not thousands, of smaller bergs. These combined with the foggy conditions have made it a testing week for all on the bridge, as they try to go in the required direction only to be faced with the hundreds of bergs in our path.
The picture below shows the bridge's navigation screen whilst trying to conduct part of the acoustic survey. We were supposed to follow the green lines that form the grid, unfortunately every red dot shown is an ice berg plotted from the radar screens. We started at the (left-hand) side of the chart and have so far only plotted bergs there on this picture, but you can see that the bottom end of the first line is just red with bergs. This caused the line to be curtailed somewhat. The red shaded areas at the bottom and at the left hand side are the mega-bergs nearest to us, to give you a sense of scale each of the north-south green lines are forty miles long.
Unfortunately this is effecting the present survey and causing changes in the scientific priorities, so that we can make the best use of our time here. So far lines have had to be shortened and changed as the ship twists and turns to avoid the bergs. The aim of the survey is to look at the life populating this particular area of ocean and in particular krill which makes up the majority of the food supply for the whales, seals and birds of the area. This survey is conducted three times whilst the ship is down here, nominally in October, January and March, we'll talk some more about it next week.
The weather deteriorated once more early Saturday morning provoking the decision to break off and seek shelter in Rosita harbour on the northern side of the island. This allowed a calibration of the survey echo sounders to take place whilst in sheltered waters. Though having made calm waters the bridge navigation screen did cause a few smiles. It demonstrated one of the joys of Antarctic navigation, it occurs when the charts are not as quite as up to date as one might think. The satellite GPS position for the ship is much more accurate now and so it can place the ship in some unlikely locations when superimposed on older charts. The image below shows the ship on top of a 300 foot cliff, we can assure you we weren't there! If you're having trouble spotting the ship we're the blue mark on the grey area in the centre at the bottom of the screen, grey is the land!
We'll just have to see what the next week brings us. It hasn't been all bad, we did have one good afternoon which brought everyone one out to admire the shapes of the icebergs. Below is Nathan's picture of the week, just to prove all those pictures are his own!
Science Bit In The Middle.
Our thanks to Peter Morris, (BAS Geological Sciences) for his explanation of our recent seabed survey off South Georgia.
The rocks below the Scotia Sea form a small oceanic plate, which over the course of many millions of years has been jostled between the much larger South American plate to the North and the Antarctic plate to the south. The island of South Georgia itself is the highest part of a small block of continental rock, broken away from South America and currently trapped on the northern margin of the Scotia plate. Very slow movements are still taking place along this margin and one of the effects of this is a series of earthquakes. During the present cruise we have been carrying out swath surveys around the southern and western edges of the South Georgia block to try and gain a better idea of the structure of its boundaries (which is poorly known in this area) and to see whether there are any obvious traces of recent earthquake activity (such as fresh fault scarps). This information will help us better understand the nature of the movements, which are currently taking place.
We spent four days carrying out a regional survey of the southern edge of the block and a further day along the western edge. A whole series of linear features and fault blocks have been defined for the first time. At one or two locations we appear to have imaged areas of seafloor where large piles of debris lie scattered around, possibly dislodged from the shelf margin by earthquake activity.
Doctor Emma has had to confine her jollying to the science control centre recently and is presently helping out on the midnight to noon shift. Her duties include monitoring the acoustics screens, otherwise know as "Krill TV". You can see from the shot below that she is finding it all very interesting! (Don't worry the real worker is hiding behind the chair. We'll try to catch her working for our next edition...
Tune in next week for the next episode of "Places to find Doctors asleep!"
(I'm sure Emma will reap her revenge on us when she's taken over the diary and we have departed. Ed.)
Thank You's for the week.
Thanks to all the photographers who allowed me to trawl through their pictures and particularly to Jon Watkins who seems to have provided the majority of this week's shots.
A final thought until next week...
Well we wait for the storm to subside and then hopefully we can finish the science program. Then it'll be a dash to King Edward Point and Bird Island to pick-up the last of our passengers and then next Sunday will see us Falklands bound once more.
Next week will be the last for this crew, so we'll aim to make it a bumper picture issue to remind our families and friends what we all look like!
In conclusion, our final picture this week was taken last night at dusk in Rosita Harbour.