If you thought it was cold this winter, try drilling through 1000m of ice at temperatures of -20degC. These are the conditions that the British Antarctic Survey (BAS) team worked in when drilling through ice shelves to get a “window into the ocean”. The project is the first time that climate modellers will be able to see the different rates of melt below the floating Antarctic ice shelves to assess the effects of climate change.
The team is funded by the Natural Environment Research Council and chronicles the changes in ice shelves and the effect the melt water has on the oceans and the environment. Relatively warm water flooding the continental shelf in parts of the Antarctic is causing high melt rates at the base of the ice shelves. This could be due to changes in ocean condition; researchers need to know what is reducing the restraining effect of the shelves.
Climate modellers use data such as how warm and how salty the water is and how quickly it melts the ice, to predict the rate of climate change. Dr Keith Makinson of the British Antarctic Survey’s Polar Oceans team explains: “Ice melting sounds so simple, but we don’t know much about the effect it has.” By predicting the response of the ice shelves to the changing ocean conditions, it will be possible to better forecast Antarctic’s contribution to sea level change and how it will be affected by climate change.
To observe the conditions and effects, the team use a hot-water drill to make access holes through ice shelves, both ones that are melting slowly and ones that are melting rapidly. Then they make numerical models of the ice shelf and ocean that include turbulence and the transfer of heat towards the ice.
Although the measuring instruments are connected to a data logger which will store the data for over a year, a subset of data from altimeter and temperature sensors is also transferred from the research base on the ice to the United Kingdom via a satellite link for immediate use. The data will provide, for the first time, a view of the boundary layer below the ice shelf to compare and contrast a slowly melting shelf with a rapidly melting one, in order to understand the physics of one of the world’s least known environments.
On Larsen C and George VI ice shelves the ice is almost 400m deep, but when the team move south to Ronne Ice Shelf, the drilling depth will increase to 1000m. Drilling engineer Paul Anker is upgrading the drill and accompanying water heating equipment to be capable of drilling a 300–400mm hole through the floating ice shelf that is over twice the depth of previous drilling work.
Once drilled, precise instruments are suspended below the ice shelf for 12 months. Millimetre measurements will detect turbulence eddies, allowing researchers to monitor the speed of the flow of the ice shelf boundary as well as its temperature and the rate of melt.
One of the challenges to the data collection process is that in Antarctica, the cold conditions means that a hole starts to refreeze as soon as drilling begins, so three heaters are used, all fitted with a MR1K flow, one inch brass flow switch, supplied by PVL Limited.
The melt water is pumped into a tank and heated up to a temperature of 90degC, and pumped through a hose which is lowered slowly – at a rate of 80mm/minute – drilling down into the shelf to melt the ice, to form the access hole to the ocean beneath.
PVL’s MR1K flow switch operates between 6–60L/minute, and BAS operated it at 45L/minute in Antarctica. The flow switch switches off the oil burner for the heater if the flow of water to them is interrupted at any time and for any reason, to protect the heater from damage. The access hole is open for 12–20h, allowing observations to be made and recorded.
The team work in the Antarctic’s summer months, so have 24h daylight and work in temperatures typically from -20 to 0degC. The flow switches operate for a small number of days at each drill hole to protect the heaters, but they are used repeatedly during the team’s length of stay on the ice shelf.
However, in the winter, it gets really cold, and the team leave Antarctica, but leave the equipment behind. Cables and wires are left in the ice, together with the flow switches, which will be collected again the following summer. The flow switches are expected to operate again when they are recovered from their ice storage several months later, where the Antarctic winter temperatures can plummet to -50degC.
Dr Makinson says: “We have never had any problems with the flow switches used, although we take spares in case our mis-use of them causes them not to work. We have pushed the specifications of the flow switches, especially in terms of storage temperatures, but have never had a failure – unless we have abused the switch and it is frozen solid.”
To find out more about flow switches from PVL, please visit the website at www.pvl.co.uk.