06 May 2001 - A week at the Dentists ?
RRS James Clark Ross Diary
Noon Position : 15°53' North, 46°52' West, Still approximately 750 miles from Barbados, not far from last weeks position.
Distance travelled since Grimsby: 32,322 nautical miles
Air temperature @ noon: 26.3 degrees Celsius
Sea temperature @ noon: 25.3 degrees Celsius
A week at the dentists?
Well if not quite the dentists, but we have been experiencing an awful lot of drilling this week. To be more precise ever since the previous update, and that was last Sunday, all our time this week has been dedicated to deploying the BGS "Bridge" drill to the seabed and back as many times as possible. The sites to drill were chosen by the science party using data supplied from the TOBI data described last week . They were those having the least sediment and therefore the greatest chance of providing the rock samples that will help describe the area geologically.
The BGS 'Bridge' Drill - What is it?
This is an amazing piece of equipment developed by the British Geological Survey (BGS) in Edinburgh for drilling seabed rock samples up to 77 cm long. This may not seem very surprising to people who know this field of activities and BGS themselves have a drill that will take samples up to 5 metres long. What makes the drill we are using special, however is that it operates deeper and BGS have developed a method to mark the core as it is taken. The core is marked with a scribe line during the cutting process and its orientation measured by compasses mounted on the rig. This is especially important for the geologists, who would like to know the orientation of the cores for a number of reasons e.g. to measure the direction of the magnetic field in the sample, and to measure the orientation of crystals and fractures in the rocks.British Geological Survey
Above you can see the tripod frame of the drill emerging from its last deployment to the sea bed which was in excess of 2000 metres below us.
The scientists are choosing the drill sites based on targets identified on the TOBI images, but trying to hit those targets by dangling the drill on 2000 metres of wire is not easy: factors such as submarine currents and uncertainties in the ship's satellite positioning mean that the drill can be placed with an accuracy of tens of metres rather than metres. So to give us a better chance of gaining the best samples we can, the drill has a camera onboard to take photographs of the area it has landed on. Below are two of the images from the last week, taken from the seabed a long way below us. In the one on the left you canmake out one of the drill's legs and if you look carefully enough some of the sediment drifting by that was disturbed on landing. Please click on the images to enlarge.
Now the cable may be a way of getting nice pictures of where the drill has landed, but it does have other uses. It supplies the 1500 volt supply to the drill unit to drive all the various components and also allows the drill to be monitored and controlled from the ship. Below is a photograph of the display seen onboard, showing the penetration of the drill into the sea bed along with the condition and operation of the other equipment. This includes the compass readings, amount of flushing water to the drill bit and the power and speed of the drill bit itself along with other useful information to guide the operator. The operators insist it is not a games console and any similarity to a flight simulator is purely accidental. The picture on the right shows Dave Wallis and Chris MacLeod at the chart table planning the next drill site.
So what does this wonderful tool give us? Well some of our recent results are shown below. We've included a pencil in the first one to try and give it some scale, but the cores are 35 mm in diameter. Some of the sites this week have been sediment in disguise with a thin crust over the top of it, giving the appearance of solid rock but when you drill through this layer it is just sediment underneath - which is not what we are after. The colours and textures exhibited in the rocks are quite varied and they're very pretty, and the geologists onboard are getting very excited about the samples.
So who are the BGS Team?
It has been a busy week onboard for birthdays, with four in this last week. They started on Wednesday with a joint celebrationas Norman Thomas, our Electrical Officer, reached his Fiftieth and shared it with James Baker, one of our Able Seaman who reached the grand old age of 34. James and Norman are pictured here with an artistic creation in the shape of a cake courtesy of the galley. We hope Norman will remember his Fiftieth for more than the 0400 in the morning call out to help fix things - sorry Norman...
In wishing them well we mustn't forgot our other birthday people in the shape of Tracy MacAskill on Thursday and Jim Fox on Saturday. After a hectic week our resident card maker was looking forward to a quiet time, but it is not to be, with still three birthdays before UK and one next week.
The next week will see our science programme continue as we have approximately ten more days of work before we start to make progress more speedily Northwards. We only wonder if we can steam more than 42 miles in the coming week as that is all we did last week!