Questions

Now for the questions. These are from the 8th grade class:

1. Are glaciers/icebergs predominantly fresh water or saltwater? In our
book "Troubling a Star", by Madeline L'Engle, the main character refers to blue, green, and fire-like ice. We were wondering if this was figurative language or literal. If there really is colored ice what is the cause?

        The ice that forms on the sea is primarily fresh water, though some salt may get trapped in pockets if the ice forms quickly. When the ice forms, the pure water crystallizes out and leaves the salt behind. In fact, during winter when lots of sea ice forms, it causes an increase in the salinity of the seawater below the ice. That increased salinity further influences ocean currents as the cold, saline water sinks more readily.

        As far as colors, yes there are blues and blue-greens that you see in the ice. These colors are caused by how the light is absorbed and reflected asit passes through the ice. New ice has lots of air bubbles in it, so it appears clear. Old, compacted ice, however, such as ice from the bottom of glaciers or ice shelves, has little air left in it and appears blue or blue-green (see photo). Sometimes these colors are quite striking.

2. We understand the ice flows are fast moving ice. Do they actually
flow into the ocean? Since the water is 29'F does the ice remain frozen?

        Glaciers slowly flow downward toward the sea and actually flow into the ocean in many places around Antarctica. They remain frozen because the water is so close to freezing anyway. The edges of the glaciers may break off (also called calving), especially in the warmer part of the summer, causing many of the large ice bergs you see floating in the southern ocean. Large bergs may take many years to break up and finally melt in the cold waters.

3. How do scientist detect crevices? We know that satellite imagery
would allow for detection, but has this technology been developed and used consistently? We understand that sled dogs, which are no longer allowed in Antarctica, used to be quite good at detecting them. Is this true?

        There really is not a good way to detect crevasses on glaciers except by direct observation. Satellite images might help, but the nearly constant cloud cover over Antarctica precludes their use most of the time, so they are not very practical when you need information right away. When lots of snow is on the ground, either drifted snow or new snow, it is nearly impossible to detect crevasses. However, the snow forms bridges over them that are usually safe to cross. Late in the summer, when the snow is melting and still covering the crevasses, is the most dangerous time to be out on a glacier. You might make out slight depressions in the snow that give them away. Otherwise, you move slowly and probe ahead with an ice axe.

        Dogs somehow have been better at detecting the presence of crevasses than humans. No one knows how they do this, but perhaps they can see the slight depressions in the snow better than us. When coming up to them, they act nervous and will stop before crossing them. Despite this, many dog teams fell into crevasses in early exploration. When walking across a glacier, one must never cross alone, and always stay roped to another person so that if the forward person falls through, the other person can stop the fall and pull you out. Numerous people have died or disappeared into crevasses in the early days of Antarctic exploration, but that rarely happens today because of strict safety regulations.

4. Please define differences between glaciers and icebergs. How are
glaciers formed: salt and fresh? When saltwater freezes does the freezing affect the salt dispersion? Does an iceberg taste salty when you lick it? Are icebergs frozen solid or are there gaps of air? Why does an iceberg float? Are icebergs slippery or is there snow for traction?

        Glaciers are formed by snowfall that builds up over time, as long as
snowfall exceeds snowmelt each year. So, it has to be in a consistently
cold region for a glacier to form, such as high in the mountains or in high latitudes or polar regions. The ice is constantly forming and flowing downward, too slow to be visible, but leaving clear signs of its movements such as rock debris scoured from the edges of valleys or lots of crevasses where the glacier breaks apart when moving over steep terrain. As mentioned above, the ice bergs are simply the glaciers calving off into the sea. These bergs may have weird shapes sculpted by the waves and occur in a variety of sizes. They are not be confused with the tabular ice bergs that break off from ice shelves. These shelves form on the sea, are flat and layered from annual snowfalls, such as the one in the attached photo, and may be over a hundred feet thick. So, as you observe ice bergs down here, you can tell if they originated from a glacier or an ice shelf by their shape.

        The ice is fresh water, it floats because ice is less dense than water
and contains air bubbles. Sometimes, we take a small piece of ice from thesea and use it for iced tea or other drinks--it's the best water in the
world!

5. How much pack ice forms in a year? How much melts each year? Are the two rates balanced? If not what is the difference. Our impression is that the pack ice is receding, but at what rate?

         The amount of pack ice that forms each year is highly variable. In
especially cold winters, enough ice forms on the sea around Antarctica to essentially double the size of the continent. In warmer years it is much less. Usually, most of the ice will break up in the summer, but there are many regions with permanent ice shelves and fast ice (ice attached to land). Some of these shelves, however, have started to break up for the first time in recorded history, probably due to global warming. The average winter temperature in the Antarctic Peninsula has increased by 4-5 C over the past 20 years and this is impacting the amount of sea ice thatnow forms each winter.

        It is not possible to give a rate of decline for pack ice throughout all
of Antarctica because in some areas it is receding faster than others. In
addition, we still have the occasional cold year that increases the pack
ice again. However, with the breakup of some of the permanent ice shelves, there definitely is a decline taking place, especially in the Antarctic Peninsula.

These were all really good questions again. I could answer them more
fully if I could show you some photos as examples. I will try to do this
when I visit your school after I return to Wilmington next month.
Thank you for your questions and I'll look forward to hearing from you again.

Questions, Comments
email David Hughes, djh6183@uncwil.edu
Last updated February 21, 2000