Field Update: Nov. 25, 2010

The oceanographers from NIWA (National Institute for Water and Atmosphere, in NZ) and WHOI (Woods Hole Oceanographic Institution, in the U.S.) got together and spent all day deploying the first of the inductive oceanographic moorings (Site #1) through the ice shelf into the water below. We will be deploying another mooring at the Site #2 location to the south, but this is the first one, and the team is harnessed up and ready to go. Craig Stewart (NIWA) and Will Ostrom (WHOI) have checked all of the rigging and determined that everything is correct. The mooring has a heavy weight on its lower end, to keep the tension on the cable and help it to hang straight down through the water column under the ice shelf, even if there are strong currents acting on the cable down there. They’ve cut a small hatch in the wood deck over the ice hole and have made a notch to allow the cable to go down through it, improving the safety of this operation. There are five Nortek Aquadops (acoustic doppler current profilers) and three SBE (Sea-Bird Electronics) MicroCAT (conductivity, temperature and pressure) recorders to be attached to the cable at specified locations below the ice shelf. These are attached with clamps and must be placed precisely to ensure that we bracket the water column from top to bottom to collect the data.

Craig adjusts his cap and heads for the winch to ease off the brake and lower the weight as Will guides it through the deck and down into the ice hole. The people’s harnesses are clipped to safety lines for protection around the hole, which is fairly large and potentially dangerous if one of them were to slip.

They measure the cable as it spools out and calculate the distance from the weight where they need to attach the first sensor, an Aquadop. They work together to fix the instrument in place and then lower it down into the ice.

Dick Limeburner works the winch and releases the brake to lower the cable or stop it, when Will and Craig call for it. They attach the first MicroCAT.

Then they attach a cone that will help the sensors align with the hole in the bottom of the ice shelf when it comes time to recover the mooring in a few months. The cone will help center the cable in case it gets caught on the edge of the ice on its way up, to avoid losing the sensors or damaging them.

During recovery operations, a load cell will also be used to identify changes in the hanging weight of the mooring. Changes in the load cell readings can indicate that one of the instruments might be catching on the edge of the hole in the ice shelf. We will be able to see changes in the load and slow or reverse the winch to prevent the loss or damage to any of the instruments.

The deployment pattern repeats, with another Aquadop and another MicroCAT being attached, then another cone, all going down the hole one after another. They measure the distance between the instruments and then spool out the cable to the next station, which is about 100 meters higher up from the last one to provide an equal spacing of instruments through the water column. Each of the instruments has been programmed to make measurements every 15 minutes for as long as they are deployed – in this case for two months. They record the data in the memory of the individual instruments, but also transmit their data up through the cable to a recorder at the surface of the ice. This is a strategy to reduce the risk of losing the data if we are ultimately unable to recover the sensors. Over the time they are deployed, the ice hole will re-freeze and become solid again around the cable through the ice shelf. We will have to re-melt the hole in order to recover the series of instruments, which has never been done, to our knowledge, through ice this thick.

But that is a chore for another day. Right now our focus is getting all of the instruments deployed and checking to see that they are both acquiring and transmitting data. There are still hours to go and the air temperature in the MECC is dropping because we need to have the door open to anchor the winch sufficiently to the sledge. Craig, Will, Dick and Saane work steadily, attaching each instrument in their turn, checking the bolts and ensuring that they are all ready for their long, cold soak in the ocean below the ice. As their hands get cold, the nuts and bolts get harder to turn and they concentrate more on every task to prevent losing something down the hole.

The process becomes routine and the team works together, communicating with each other to accomplish what needs to be done, at the correct time.

Saane documents the deployment with her camera and notes the depths in the logbook. This is the record of what was done during the deployment.

Then it’s on to the next instrument, and the work continues step by step.

The team members watch each other, the winch, the cable and the ropes, always ensuring safety as they continue to spool out the 800+ meters of cable that make up the mooring. Spirits are high – hard work can be fun too!

Each instrument and cone has been mapped out in advance based on the measurements of ice thickness, mean sea level, depth to the seafloor and other variables to plan out the mooring to achieve the best results.

The cold is becoming quite noticeable now and ECW gear is broken out – “Big Red” for the U.S. team and orange and black parkas for the Kiwis, along with gloves and hats in layer after layer – and the work continues.

The last pair of instruments are attached to the cable and then another 260+ meters of cable goes out to account for the thickness of the ice shelf above the final instruments – allowing measurements in the water below the ice.

The final step is to establish a means of anchoring the mooring at the surface, so that the load can be transferred to a tripod once the MECC is moved out of the way. The mooring cable will gradually freeze into the ice as the hole closes, but the termination will be supported by the tripod above the surface, which is connected to the data recorder that sits on top of the snow. The data is flowing up the cable to the data recorder which can be read at

The oceanography team gathers for a victory picture and the feeling of a job well done. The first oceanographic mooring is in place and they can sleep well knowing that all of the planning has been worth the effort. This is an example of the successful collaboration between U.S. and N.Z. teams participating in the Coulman High Project and the results show how important all of our efforts have been. We’re one team from two countries working together to accomplish more than either of us could do alone. The support from both Scott Base (Antarctica New Zealand) and McMurdo Station (Raytheon Polar Services Co.) has made this all possible, as has the funding from both the Foundation for Research, Science and Technology (NZ) and the National Science Foundation’s Office of Polar Programs (US). We’re going to learn a lot in the coming months about the environment below the ice shelf that will help us plan the future drilling.

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