Sea Ice 101

Participated in a “Live event from IPY”, conference call from the ice. Which

included Kirk Beckendorf, TX, Grade and # students unknown

9.2 Sea Ice 101

9.2.1 Course Description: This is an upper level graduate and post doctoral level course (Mani and Scott being the only graduates and others being far more advanced), intended to give an idea of the various aspects of sea ice. In this course you will be given hands-on description of various kinds of ice and also have a chance to visit locations with different deformations. The lab section would be held in tandem with the lecture class. As part of the lab section, you would have a chance to play around on the ridges and drive the ski-doo. BE SURE TO DRESS WARM!!!

Instructor: Jackie Richter-Menge Co-Instructor: Bruce Elder

Class Hours: 8:30 am - 11:30 am, April 10th, 2007 Location: On the ice camp (within a 2 km radius)

Office Hours: Maybe at CRREL, Hanover, but only by appointment...

Textbook: Through word of mouth, so be sure to take notes since these things will not be repeated

9.2.2 Student’s Perspective by Mani Thomas Lecture 1:

The class covered the various formations that take place in the ice. The first thing that Jackie pointed out was the basic observational difference between first year and multi year ice. First year ice has a typical flat structure while multi year ice has significant undulations in them. Thus the air strip was built on first year ice while the camp in itself was located on multi year ice.

The first pit stop was at a lead that was due south west of the camp. A lead is an ice formation where a crack causes the ice to move apart. This lead was a significantly new one that had formed a couple of weeks ago. When observing leads, one thing that is typically observed is the presence of frost flowers. Frost flowers are structures that grow on frozen leads due to presence of superficial dents on the surface.

Lecture 2:

The next stop was at a multi year ice ridge. Ridges, unlike leads are formed due to ice hitting each other and creating a structure that is visible above the surface. Due to the properties of ice, the ratio of amount of ice that exists above the water to the ice that is below the water is about 1:4. This means that for every foot of ice that is visible above the surface, there is 4 feet of ice that is below the surface.

The crystals from multi year ice can be used for human consumption,

since the brine that is present in the water would have percolated into the water below, through the years of formation. When we observe the ice crystal, we can see a number of orifices within, where the brine percolated through.

When we look at the ridges present in multi year ice, they are found to occur in two forms. The first is the compression ridge, which is created ice floes collides in a head-on fashion. Compression ridges typically have no shape and exist in a “cauliflower” kind of structure. The second type of ridge is the shearing ridge, which is created when floes move in opposite directions, rubbing against each other. Due to the rubbing motion, shearing ridges typically have a lot of polygonal structure associated with them.

The multi year ice contains many interspersed leads and ridges. In many cases, leads drive right into a ridge dissipating their energy. This termination of a lead might create a brand new lead moving away from the ridge in a totally

different direction. Also observable in close proximity to a ridge is the presence of basin-like structures on the ice. The creation of a ridge typically causes ice to start piling on top of one another and this causes a cantilever kind of conditions pushing one of the sides of the ridge down creating the basins.

A very interesting phenomenon that can be observed in the structures present in the ice is the presence of brine stalactites (structures found hanging from the surface). These stalactites are created when the salt water trickles through the ice and freeze up when in contact with the -40F air.

Lecture 3:

From the location of the ridge, we proceeded to the region that was identified as the active zone for measurement purposes. This was the location where a significant amount of instrumentation was installed to obtain ground truth data regarding the ridge such as ridge height, water temperature and ridge keel shape.

Most of the measurements were collected by a combination of human divers and an Autonomous Underwater Vehicle (AUV). Prior to undertaking a dive, the human divers need to take a lot of precautionary steps. Typically, the

water under the ice is at -2F while the air is at -20F, so any water freezes up when it comes in contact with the air. To handle all these, the divers actually wear a suit (the red suit in the picture) that has an air insulation layer over and above the regular deep sea diving attire. This combination suit protects the divers from the severe cold temperature. I am not exactly sure how the buoyancy factor is tackled by the divers once they are inflated.

To handle the freezing up of water when in contact with the cold air, there is a "prep-hut" (the wooden box to the right) where the divers prepare themselves for the dive and thaw down after the dive.

The autonomous underwater vehicle is a robotic submarine manufactured by Gavia in Ireland. The device is composed of multiple segments with a

processor in each segment. Each segment performs the tack of capturing

specific data such as side SAR, visible imagery, GPS information. The vehicle is released into the water through the hole (shown in the figure below) and specific way points are provided. The device autonomously visits the various waypoints, collecting data and once everything is accomplished would return to the “homing”

location.

The first release for data collection went well but on its return journey it got stuck in a keel. To finally get it free, they had to release weights along the rope to which the AUV was tethered and pull it down from the keel. During this

extraction, the GPS sensor and the central control were slightly damaged. In some cases, the AUV could get stuck pretty tightly and that would require divers to get in to the water so as to shake it loose.

9.3 Participating in Field Work – A remote sensors view point