PVL Ltd. - PRODUCT NEWS
Highly reliable flow switch helps BAS record the ebb and flow of the Antarctic Ocean
If you thought it was cold this winter, try drilling through 1,000m of ice at
temperatures of -20°C. 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
difference rates of melt below the Antarctic ice shelves to assess the effects of climate
The team is funded by the National Environment Council and chronicles the
changes in ice shelves and the effect the melting water has on the oceans and the
environment. Relatively warm water fl ooding 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. Ice melting sounds so
simple, but we dont know much about the effect it has, explained Dr Keith
Mackinson of the British Antarctic Societys Polar Oceans team.
By predicting the response of the ice shelves to the changing ocean conditions, it will be
possible to forecast Antarctics 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 in ice shelves, both ones that are melting slowly and ones that are melting
rapidly. Then they make numerical models to map the boundaries of the shelf, the
turbulence speed 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 fi rst time, a view of the boundary layer below the ice shelf to compare and
contrast a slowly melting shelf with a rapid one to understand the physics of one of
the worlds most unknown environments.
At the northern George V ice shelf, the shelf is 500m deep, but when the team
moved south to the Larsen C ice shelf, the drilling depth doubled to 1,000m. Drilling
engineer, Paul Anker had to upgrade the drilling and accompanying water heating
equipment to be capable of drilling a 300 400mm hole through a fl oating ice shelf
that was twice as deep as the previous terrain.
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 fl ow 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 Antarctic, the
cold conditions means that a hole starts to refreeze as soon drilling begins, so three
heaters are used, all fi tted with a MR1K fl ow, one inch brass fl ow switch, supplied
by PVL Limited.
The melted water is pumped into a tank and heated up to a temperature of 90°C
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.
The MR1K flow switch operates between 6 to 60litre/minute; although the BAS in
Antarctic operated it at 45litre/minute. The flow switch switches off the oil supply from
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 to 20 hours,
allowing observations to be made and recorded.
The team work in the Antarctics summer months, so have 24hour daylight
and work in temperatures typically from -20 to 0°C. The flow switches operate for a
small number of days at each drill hole 2011/12 field season Larsen C and George VI ice shelves, 3 sites, 5 holes, and 2000 m ice drilled to protect the heaters, but they are used repeatedly during the teams length of stay on the ice shelf.
However, in the winter, it gets REALLY cold, and the team leave Antarctic, 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, after the temperatures at Antarctic have plummeted
to -50°C in the winter months.
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, says Dr Mackinson. 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", he admits.
For more information, contact...
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Fax : +44(0) 1892 663690
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Website : www.pvl.co.uk
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