22 Dec - The week on ES
Date: Sunday 21st December 2003.
Position @ 1200 Local, (GMT -3): 72°49 South 20°33 West.
Next destination: Halley
ETA: PM Monday 22nd December 2003.
Distance to go: 400 Nautical Miles.
Distance sailed from South Georgia: 2057 Nautical Miles.
Current weather: Overcast, Good Visibility.
Sea State: Calm, 6/10ths ice coverage. Small-medium floes of medium thickness.
Wind: Variable Knots.
Barometric pressure: 997.3 mb.
Air temperature: -1.1°C.
Sea temperature: 0-1.5°C.
Click to see position map.
This Week on ES
It's been a week of frantic activity on the Shackleton. We've been having daily training sessions preparing us for Halley, 3 hourly XBT launches, medical mayhem and a couple of social events too, to make sure that everyone is tired out by the end of the day.
Training has been on cargo handling, vehicles, relief operations, emergency contingency plans and first aid.
First aid was supplemented by a voluntary session on insertion of intravenous cannulae. By the look on her face, Rhian doesn't seem to be enjoying herself but everyone was smiling again by the end of the session.
On Saturday night we all had a chance to let our hair down and relax after the stresses of learning all week. The event was a horse racing night and despite the kidnapping of Nigel Colgan, the nights big winner, the Shack managed to maintain it's reputation as a generous vessel by raising over £1000 for leukaemia research. Thankfully Nigel was recovered later in the evening with no more damage than a scratch on his favourite spanner and an empty wallet because the 'ransom' money all went to charity.
This morning the Fids were all raised gently from their slumbers by the dulcet tones of the Shack's resident choir singing Christmas carols. Some were more receptive to this than others but all were serenaded in order to encourage everyone to attend for the weekly tidy up of the whole ship. Below is a photo taken before singing commenced. The post-carol picture was censored due to multiple rotten vegetable strikes to the singers.
As we get closer to the continent and out of the polynya, there have been sightings of some Emperor Penguins, Leopard Seals and Crabeater Seals. No pictures yet because they've been too far away! We also had our first sighting of the continental ice sheet this morning. We're really getting there and although we're guaranteed a white Christmas this year, I think most of us are too excited thinking about getting to Halley to think about cards and Christmas. I'm sure that later on in the season when things slow down a bit and we need something to cheer us up, we'll use Christmas as a good excuse. Better late than never!!
Probing a polynya with XBTs
We are currently sailing through a vast expanse of calm, open water. The last thing one might expect this close to Antarctica. Open water, as far as the eye can see in every direction. Perfect sailing conditions. This is a polynya: a large expanse of water surrounded by ice. (The name comes from polyi-, meaning open or hollow in Russian. To hear how it is pronounced, click here.) After days of rocky seas followed by ice crunching, the flat waters are a peculiar but welcome relief. No-one really knows why the polynya is here but its regular occurrence in this area was one of the factors in determining the location of Halley Research Station i.e. ease of access by ship.
The polynya is, however, not just a convenient oceanographic feature,- it is a major driving force behind ocean circulation around Antarctica and beyond. In areas where sea ice is present, the upper layer of the ocean is essentially capped, preventing the transfer of heat, moisture and gases between the ocean and atmosphere. In the open water of a polynya, approximately one hundred times more heat can be transferred between the atmosphere and ocean than if there is sea ice present. During 1974-76, a huge polynya measuring 350 x 1000 km (approximately the same area as France) formed for three consecutive years. This gave an enormous atmospheric kick to ocean circulations, the effects of which are still being observed decades later in the central Atlantic. We now think that such events may occur every few decades.
There are a few theories about why polynyas form and their role in the ocean circulation system, but more data is needed before these can be conclusive. To this end, expendable bathythermographs (XBTs), are launched every year from the RRS Ernest Shackleton as she passes through the polynya. German researchers usually monitor a section along the Greenwich Meridian on their way to Neumayer Station and we monitor the area further west. There is in addition, a US-led effort to take a ship into a polynya during the winter if another large event occurs.
XBTs are precision weights containing a thermistor-type thermometer and miles of copper wire. When the probe hits water, a connection is made, the wire unravels and the computer starts recording temperature data until either the wire snaps or the maximum monitoring depth of the probe (up to 1800m) is reached. The top 500m are of most interest as it is here that the temperature varies quite rapidly. The data is returned to Cambridge for oceanographic analysis and also transmitted immediately to the Met Office for use in forecasting and climate models.
The video clip shows the recent sea ice conditions around Antarctica as seen from satellite images.Antarctica is the brown, open water is the light blue. The other colours show the percentage of the sea surface that is covered with ice. The arrow at the bottom left points to where the polynya (light blue) develops as the clip progresses.Click to see movie clip (715K).
The photo shows Graham, the new Halley chippie, deploying an XBT. The XBT is the bomb shaped object just falling out the end of the launcher.
Frank, Vanesssa, Kevin, Katie, Ben, Simon, Craig, Rhian and Sue have also been helping & so thanks to all of them as well as the Shackleton crew for slowing the ship down every three hours. Thanks also to Ian Renfrew for his XBT report and the chief scientist on this project, Keith Nicholls.
By Rhian "who pinched all my hair?" Salmon.
Forthcoming Events: Arrival at Halley. This could be next week or next month dependent upon the ice and weather conditions.
Contributors this week: Rhian for a jargon free account of XBTs and polynyas.
Diary 11 should be available around the 28th December.
This will be my last web diary from the Shackleton because I'm disembarking at Halley. I hope you've enjoyed reading my words about the trip so far. It's possible that I'll write some of the Halley web diaries over the next year. I hand the ES diary over to Sue Dowling. To see me launching an XBT, click here. Have a very merry Christmas and a happy New Year.