Daily Updates from
our Teacher at Sea
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Daily Updates from our Teacher at Sea |
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September 14
Ice is not just ice...
| Navigating a ship safely in the Arctic Ocean requires
knowing what sorts of obstacles might get in your way, and how to avoid
them. Sea ice for instance!
Luckily we are in an ice breaker whose hull is designed to plow through most of the frozen obstacles in our path. Most of the time, that is. Often the ice is too thick for even this ship and we have to find other routes to take, like steering the ship through the cracks between ice patches. |
Crack between ice floes - from NOAA photo library |
View of ice during helo flight. |
Our helo flight of August
26 was for "ice reconaissance" in order to see what the safest pathway
for the ship would be through the ice.
The Ice Observer on the flight was responsible for reporting the different ice types back to the ship. |
| There are different shapes and sizes of ice.
These are some of the terms that are often used while assessing the ice
conditions.
Finger Rafting: the ice looks like someone
interlocking their fingers together and when pressure is added it will
thrust the "fingers" alternately over and under each other.
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Finger Rafting |
Grease Ice |
Grease Ice: the surface freezes so it forms a thin sheet of ice. It looks like a grease slick. |
| Pancake Ice: the ice begins to thicken in
areas to form small pancake shapes with raised rims around the outer edge.
This rim is formed when pieces strike against each other, or may be formed
by wave motion. As the small pancake ice comes together it forms
larger pancake ice.
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Large Pancake Ice |
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pancake ice merging together. |
Pack Ice |
Pressure Ridge Forming |
Pressure Ridges: formed when two ice flows collide together, similar to plate tectonics on land. The part that is forced downward is called an "ice keel". |
| Some floes of sea ice may remain for many
years while others will last only one year. These distinctions bring
about the names:
First Year Ice: Sea ice that is not more than one winter's growth. It can be anywhere from 30 cm - 120 cm thick. It can get up to 200 cm thick in the form of pressure ridges. Multi-year Ice: Sea ice
that has survived at least two summers' melt. It can measure up to
3 meters / 13 feet in thickness.
Facts: - Ice grows rapidly at first and then the growth rate slows. - As ice gets thicker and thicker, it is more difficult for heat to transfer through it. Yes, heat does transfer through ice. What temperature would a substance have to be for no heat to transfer through it? - Ice that is seen above water is just a small
part of the whole ice floe. If it's sea ice, then 5/6 of its mass
is under the water, if it's an iceberg then 8/9 of its mass is under water.
Icebergs are different from sea ice. They form from bits that break
off of land-locked glaciers and are made of fresh water. You will
find some, but not many icebergs in the Arctic. Sea ice however,
is salty, yet with only 1/3 as much salt as the sea water from which it
formed.
- Ice sometimes appears blue in color. This
happens when ice forms from seawater, the salt seeps out into the water
and sinks as brine, leaving freshwater-ice behind.
- As ice ages, its salinity level goes down. - The Arctic receives as much precipitation as the driest area of Washington State. - Arctic snowfall average is about 5 - 10 inches a year. - Older ice is better to melt and drink if you are shipwrecked and thirsty. - Multi-year ice is less common in Antarctica than in the Arctic.
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NOAA Guide to Sea Ice - http://response.restoration.noaa.gov/oilaids/seaice/seaice.html
