Something I have learned during my time here in Antarctica is that sea ice takes glider piloting to a whole new level. It can be an unpredictable moving obstacle that can mean danger for a glider. So in order to have a better understanding of this obstacle I spent some time learning about the different categories of sea ice and learning how to read sea ice coverage maps. Tom Holden is the Special Support Coordinator at NIC the National Ice Center and each morning his team sends the LTER scientists a sea ice image for the Anvers Island area. We then use these images to monitor the area and decide whether or not it is safe to fly the gliders.
Typically, my image categorizes the Anvers Island area sea ice into four categories (see image Dec. 3rd). On the December 3rd image you can see an example of the sea ice being broken down into A, B, C and D. Level A ice is classified as 1-2/1oths, Level B is 3-4/10ths, Level C is 5-6/10ths and D is 7-9/10ths. The classification of sea ice is actually based on a percentage, so Level A ice in an area actually means the area is about 10-20% sea ice compared to that of Level D which means an area is about 70-90% sea ice. To go even more in depth Tom sent me the following description which explains how the age of the ice also plays a role in how they analyze the images and than categorize.
The A, B, C and D that you see on the charts, are used to designate attributes to each individual area. Each area you see is analyzed, based upon the ice type (classification) AND the concentration. Ice types are based upon thickness and age of the ice. The purpose for this, is generally, older ice, is harder and thicker. The reason it is harder, is that gravity pulls on the brine content and it drains its way through, leaving nearly pure frozen water behind. New, Young ice is easily broken and Multi-year and glacial is the hardest to break.
Unfortunately, even with all this information the bottom line is still the more sea ice in an area, the more tightly it will be packed together, making it more difficult for a glider to surface. Comparing the various types and actually seeing them in real time and seeing the consistency of the ice allowed me to determine that a glider should be able to surface in Level A ice without problems. However, level B, C and D are a different story and therefore we avoid those areas.
However, aside from the fact that sea ice can be a nuisance and prohibit us from taking zodiacs out or potentially cause a glider to not surface it serves many useful purposes. Various species in both the Antarctic and Arctic use sea ice as a means of hunting, breeding, feeding and even resting. Down here in Antarctica we have seen numerous leopard seals hauled out on large chunks of sea ice napping. The same also goes for the various avian species such as the Adelie penguin.