Tuesday, January 15, 2013

Drilling through the PIG

The PIG is the Pine Island Glacier in Antarctica. It is a huge glacier that drains into the ocean. The last part of it actually floats on the ocean and is melted from below by relatively warm ocean water. It is this melting that makes PIG such an important contributor to sea level rise from ice loss.

We spent most of December and parts of January drilling several holes through about 500 m of ice and then putting instruments into the ocean below. The instruments measure temperature and salinity of the ocean water underneath and the rate of melt at the bottom of the ice sheet.

It is a great relief to successfully complete this season after last year was essentially a total bust. We had fantastic support from NSF and the logistics people, which made this possible.

Our camp was put in with a Twin Otter on loan from the British Antarctic Survey. The Twin Otter is the workhorse of Antarctica. Once on the ground we moved all our equipment and camp with snow machines.

The camp consisted of two larger tents, one a kitchen, and one a galley for up to 14 people. We slept in the smaller mountaineering tents.

The hot water drilling operation works by pumping water out of a pool, heating it up to about 70 deg Celsius and pumping it down a hole. The water is then recovered and pumped back into the pool.

The heaters are essentially the same that are used to produce high pressure hot water at car washes. The pump is in the back left and is configured to pump a constant 20 gal/minute at high pressure.

The hot water is routed into the borehole via a capstan winch. We drilled at a speed of between 65 and 95 meters per hour. The drilling speed decreases with depth, because the water at the drill tip gets colder as the hose descends into the borehole.
The orange hose behind the winch is used to pump water back out of the hole for recirculation.

Once the hole is finished a variety of science takes place. We used a borehole camera to image the hole, we dropped a sediment corer to the bottom of the ocean to find a record of past glacier advance and retreat, and then installed instruments to measure salinity, temperature, and water fluxes in the ocean below the shelf. In this picture Jim and Tim from the Naval Postgraduate School in Monterey lower a flux package instrument with a string of thermistors to measure ice temperatures in the bottom part of the ice shelf.

Hot water drilling offers great benefits, such as a warm hose for naps, hot water for showers, hot tubs, and laundry.

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