We return to the ocean the next day with better weather
The crew flies over our proposed site, descends to 300 feet and then climbs back to 2500 feet to check the wind speed and direction. While we turn around to return to the drop site, the cargo deck crew prepares the ALAMO float.
We scientists are seated along the sides (with our seatbelts fastened) and the loadmasters don harnesses and tether themselves to anchor points on the cargo deck. It’s time to open the cargo door!
When the navigator tells the loadmaster that we are at the proper location, they launch the ALAMO, its parachute deploys, and it drifts out of sight quickly, before we can see if it landed in the water.
Everyone wants to know that the ALAMO landed safely in the water, so Major Hicks circles back several times while we search the surface of the ocean for the orange parachute. We never saw any sign of it.
When we land, Kirsty comes on board with a smile on her face and says that the ALAMO float has already sent us an email to say that it has successfully made its first measurements!
In addition to mapping the properties of the Ross Ice Shelf with the IcePod, we measuring the ocean properties just north of the ice shelf. We will do this with ALAMO floats (Air Launched Autonomous MicroOberserver). ALAMO floats measure three critical properties of the ocean: temperature, salinity, and pressure. They do this while slowly sinking to the bottom of the ocean and then rising back to the surface. When they are at the surface, they place a phone call via Iridium satellites and literally email their data back to us.
ALAMO floats are a fairly new technology which has been used mostly in warm subtropical waters to date. A major complication in polar waters is the possible presence of sea ice. The ALAMO floats have a sea-ice-avoidance algorithm that detects whether there is likely to be sea ice as they rise upward, and to not surface if sea ice is likely to be present. The sensors and communications electronics are on top of the float, and we don’t want it to get damaged by running into sea ice from below.
The floats are deployed from the air, which makes it possible to go places that ships can’t go. A perfect example of such a location is the waters just north of the Ross Ice Shelf. In this region, the sea ice melts out near the ice shelf in late November while there is still lots of ice to the north, keeping ships away. An icebreaker, the Nathaniel B. Palmer, is the first ship scheduled to visit this region in late January. By deploying the ALAMO floats by airplane, we can make ocean measurements 6-8 weeks sooner than we could make them from a ship. These springtime measurements will contribute to our understand of the seasonal cycle of the sea ice in this region.
Our first challenge is that we need to be able to see where we are deploying the floats. In particular, we need a day without low clouds, which are quite common in this area. Our second challenge is that we need to be sure that we are dropping the floats into water and not onto sea ice. Satellite images help us in our planning, but in the end we just have to fly out there and look firsthand.
We finally get the word that we will get an airplane dedicated to flying the ROSETTA mission!
The LC 130 have a SABIR (Special Airborne Mission Installation and Response) arm, which allows attachment of specialized instrumentation packages like the IcePod.
The IcePod is controlled by electronic equipment that is installed in a custom-build rack that fits perfectly against the curved inside wall of the airplane.
So what does the IcePod do? It provides a top-to-bottom view of the ice shelf. First, it has visible and infrared cameras that take images of the surface of the ice shelf. It has a scanning LIDAR, which shines a laser beam on the surface of the ice shelf and measures the time it takes for the laser light to reflect back, which allows us to measure the height of features on the surface of the shelf. It has a shallow ice radar, which emits a powerful radio signal that penetrates into the ice, and it listens for the reflections, which tell us about different layers of snow and ice in the upper part of the ice shelf. There is also a deep ice radar, which is at a different radio frequency, and penetrates to the bottom of the ice shelf, telling us where the bottom of the ice shelf is in contact with seawater. Finally, there is a navigation system to tell us very precisely where we are so that we can make accurate maps of the ice shelf.
The Observation Tube (usually called the Ob Tube) is a gateway to another world. It is a vertical metal pipe, or tunnel, through the sea ice leading to a small (one person at a time!) glass observation platform about 10-15 feet below sea level.
The Ob Tube is located just a couple hundred meters offshore of town, but, because it is on sea ice, safety procedures must be followed to visit it. The rules require that one travel with a buddy, perform a safety sign-out at the firehouse, and carry a VHF radio. After dinner one night a small group of us went to check it out.
I went last. We had to tell each person when their 10 minutes was up. Everybody wanted to stay in the tube for longer, partly because it was much warmer underwater (just below freezing) than on the windswept surface of the ice. Mostly, though, they want to remain because it is really fascinating.
It was late evening, but the sunlight shone through the ice with a pretty greenish light.
Besides looking at the sea ice, I enjoyed looking at some large but delicate ice crystals that formed on the outside of the tube, and a large school of small fish that stayed just a little too far away to see very well. The most interesting thing, though, was hearing the pinging sound made by seals as they swam nearby. I did not see a seal underwater, but some people have.
Sea ice gets compressed against the shore near the southern tip of Pram Point sea ice is forced into the shoreline and crumples and breaks in features known as pressure ridges.
I took an interesting guided tour of this area. (Secretary of State John Kerry toured it a couple days after I did and pictures from his tour appeared in the New York Times and Washington Post.)
To a certain extent Ice can flow and bend but if it is stressed beyond a certain point it breaks.
The dramatic ice features are certainly very interesting, but there is more to the story. Weddell seals swim from the Ross Sea under the sea ice to find the gaps and holes around the pressure ridges. They haul themselves out on the ice, which provides them safe refuge from their predators (leopard seals and orcas) that swim in more open waters.
The relative safety of the sea ice makes this a good place to raise seal pups, and we came across several on our tour.
Weddell seals live further south than any other mammal (except for the few people who live at the South Pole) and Scott Base is the southernmost point in their range.