24 February, 1999
February 24, 1999
Greetings from Sulzberger Bay! Today was a lot of fun. Although we only conducted multibeam surveys during my 12 hour shift, the scenery outside was great! We saw lots of ice today . . . and penguins! I saw both Adelie and Emperor Penguins, and I also saw one seal (I'm not sure which species). This afternoon we had a surprise -- it was an emergency drill! Every week we have an emergency drill, similar to how schools are required to have fire drills once a month. Where do you suppose we have to go for an emergency drill? What should we take with us?
There were so many icebergs in the water today that sometimes we had to actually change the direction of the ship. Let's take some time to look at yesterday's question: "What's the difference between icebergs and sea ice?" Icebergs are produced where the ice sheet meets the ocean -- at grounded ice cliffs, glaciers, or ice shelves. When pieces of the ice calve off into the ocean, icebergs are formed. Large tabular icebergs are calved from the ice shelves and are usually 200 to 300 meters (650 to 1000 ft) thick! Usually about 4/5 of an average iceberg is submerged, and only about 1/5 can be seen above the water. Icebergs occur in many shapes and sizes, and an average iceberg has a life expectancy of about 4 years until it moves into warmer water and melts. When icebergs are only a few meters across, they are called growlers. Icebergs that are tens of meters across are called bergy bits. Giant icebergs that break off the ice shelf can be over a hundred kilometers across! One such iceberg broke of the Amery Ice Shelf in 1963. It was 110 by 75 kilometers (68 by 47 miles) and was followed by satellite for almost 12 years before it broke up into pieces that were too small to track. As this giant iceberg was carried around by the ocean currents, it actually collided with other ice shelves and created even more large icebergs!
Sea ice is the name given to all the ice that freezes from the sea water. It can grow to a thickness of many feet. During the winter, the amount of ice around the continent grows substantially. Antarctic sea ice cover varies from a minimum of four million square kilometers in February to a maximum of 20 million square kilometers in September. As you can see, sea ice formation doesn't just happen all at once. As it gets colder in the Antarctic autumn, some of the open water develops needle-shaped crystals forming a slush. This is sometimes called frazil ice. If a film forms across the surface, it is called grease ice. Grease ice gives the water a matte appearance -- we were able to see some yesterday when the water was especially calm. As the water continues to freeze into pieces, it can form pancake ice. Typically, pancake ice is made of pieces that are less than 7 meters across. It is called pancake ice because the edges are rounded as the waves jostle the pieces against one another. As the ice continues to grow and thicken, the pancakes get bigger and bigger. In addition to the freezing of sea water, snow is added to the top of the ice to help increase it's size. If the pieces become larger than about 7 meters across, they are called cake ice. Eventually the ice forms one solid, floating layer which can reach a thickness of several meters. As I write this journal, I can look out the porthole and see pancake ice beginning to form. We are approaching autumn in Antarctica, and the sea is already beginning to freeze.
The Nathaniel B. Palmer is built to break sea ice up to 1 meter thick at 3 knots. If we are breaking ice, the ship actually runs up on the ice and the weight of the ship breaks it into smaller pieces. In order to break heavy ice, the ship rams back and forth. There is also a way to make the ship roll from side to side if necessary. We haven't had to break any heavy sea ice since I've been aboard. Today, we have been traveling through pack ice. Pack ice is made up of various sizes of ice pieces that are floating with the currents. Most of the pack ice that we are seeing was part of the solid layer of sea ice that covered this area last winter. Since it is now late summer, the pack has broken up and is moving with the winds and the currents. When the pieces of ice are spread apart with water between them it is called loose or open pack. Close pack is when the pieces of ice are pretty close together and you can't see much water at all. Today, we have been in a lot of loose pack ice. When we go through close pack ice, it sounds almost like a carwash inside the ship. The closer the pack, the louder it gets! I can just imagine the sound when they do have to ram back and forth!
Sometime during the expedition, we will be entering an area where there is no satellite coverage. As a result, we will not be able to upload/download email and I will note able to send out the journals and pictures. I will continue writing them each day, and they will be mailed out as satellite coverage allows. Please be patient . . . we're not exactly sure when this will happen. I just wanted to let you know that it was a possiblity. I hope that you are having a great week. I know that I am!
Latitude: 76 degrees 30 minutes South
Longitude: 155 degrees 01 minute West
Temperature: -7 degrees C
Barometer: 984.6 mb
Wind Speed: 12.9 knot
Wind Direction: 98 degrees (from the east)
Sunrise Today: 02:18
Sunset Today: 20:44
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