Sea Ice School
So, we've been traveling around in our Pisten Bully on a frozen ocean. In most places the ice is six feet or more thick and that is very safe. However, as we start to explore dive sites farther away from McMurdo Station, we may be traveling to places that no one has been yet this year. That means that the ice is untested and we must determine if it is safe to travel upon. To prepare us for our future travels on the sea ice, we need to go to Sea Ice School.
Some people dedicated their entire lives to studying ice. Many of these scientists can be found on other PolarTREC expeditions. I only received one day of Sea Ice School, so what I am sharing here is just an introduction.
Snow and ice in Antarctica get compressed, forming glaciers and ice shelves.
Types of Ice
Around McMurdo Station, there are three major locations with different types of ice. They are:
- Glaciers
- Ice Shelf
- Sea Ice
Glaciers
First, there are glaciers. Glaciers are created when ice and snow accumulate on land. Many times this ice and snow builds up on the sides of mountains. Over time, forces acting on the ice and snow compress it into more and more compact ice, forming a large ice mass. Air is also trapped in this ice. Over time, gravity pulls on this ice mass and it begins moving. As the ice moves, it can move around rocks and sediment. There are many glaciers around McMurdo Sound. As we travel around on the sea ice, we can see these glaciers moving towards the Sound.
In the foreground, you see sea ice. The straight wall of ice in the background is the Barne Glacier, flowing down into the sea ice.
There are lots of places to go for information on glaciers. I would start by clicking here.
To check out cool glacier projects from PolarTREC go to:
- Microorganisms in Antarctic Glacier Ice
- Dissolved Organic Matter in Antarctica
- Glacial History in Antarctica
- Flow Studies on an Antarctic Glacier
- Glacial Movement and Seismicity
Ice Shelf
An ice shelf is a thick, floating platform of ice that forms when a glacier or ice sheet flows down a coastline and onto the ocean surface. Ice shelves are only found in Antarctica, Canada, and Greenland. Close to McMurdo is the Ross Ice Shelf. The Ross Ice Shelf is Antarctica's largest ice shelf (about the same size as the country of France) and is several hundreds of meters thick. Some of the thicker places have been measured at 750 m thick. The ice shelf is advancing out into McMurdo Sound at a rate of 5-10 ft per day. Icebergs are parts of ice shelves that break off into the water. The largest recorded iceberg (Iceberg B-15) came from the Ross Ice Shelf in March 2000.
Icebergs, like these, break off of ice shelves and glaciers into the sea ice. These are frozen in place, surrounded by frozen ocean.
Sea Ice
For the most part, we won't be on glaciers or the Ross Ice Shelf. We'll be on sea ice. Sea ice is frozen ocean water. So, unlike glaciers and ice shelf, which are both freshwater, sea ice is frozen salt water. That changes a lot of things. When the air is cold enough, the ocean first forms a slushy mixture called Frazzle Ice. Eventually, frazzle ice thickens up to form clumps that look like lilypads or pancakes. This is called Pancake Ice. Finally, as it thickens up, this pancake ice becomes a solid sheet. As the ice continues to be cooled by the cold air, it freezes on the bottom, thickening up. Most of the sea ice around McMurdo is about six feet thick.
The problem with traveling on sea ice is cracks. Yikes!
Hazards
Because of the movement of a glacier and an ice shelf, large openings can occur in the ice as they move over uneven terrain. These openings can be quite deep and are called crevasses. Sea ice is floating on an ocean and has lot of forces acting on it. These forces cause cracks and buckles (called pressure ridges). If you drop something down a crevasse in a glacier, it goes thump at the bottom. If you drop something through a crack in the sea ice, it goes splash at the bottom.
Sea Ice School?
Sea ice school is training for all those traveling and working out on the frozen ocean, or sea ice. I learned a ton of information. Who knew that ice could be so fascinating? Probably the best part was the field experience - a whole day outside on the sea ice. I am so tired. You'll have to wait to tomorrow to see all the great photos from my day out on the sea ice!