21 January, 1998

Hello Everyone!

We are on our way to Cape Adare.  It is at the northwestern corner of the 
Ross Sea (the bottom right-hand corner of Antarctica on most maps).  It 
is very beautiful.  The Transantarctic Mountains line the western edge of 
Ross Sea, so that part of the coast has beautiful mountains and glaciers 
coming right to the ocean.  There is a lot of sea ice here, and it is a 
little noisy moving through it with the ship. The sea ice is in  big 
plates, about 15 feet wide and two feet thick.  The plates are floating 
on the ocean surface.  The penguins and seals like to sit on these plates 
in the sun.  I have seen many Adelie Penguins today.  There have been 
some sightings of Orcas, but I have not been able to get on deck fast 
enough to see one!

We are using many types of equipment to find out what is on and under  
the sea floor, but there are two main types.  One type uses sound to 
"make pictures" of the sea floor and the other type actually gets samples 
of the sea floor.

The first way we get pictures of the sea floor and what is under it is by 
using instruments to send a sound wave  into the water.  Some of the 
instruments are towed behind the boat and some are attached to the boat.  
The instruments send out a sound, like a beep or a boom, every few 
seconds. The wave travels to the sea floor.  Some of the sound bounces 
off the sea floor and some of the sound goes into the sea floor and 
bounces off layers in the sea floor.  The sound waves bounce back to the 
surface.  The deeper the sea floor (or the layers under the sea floor) 
the longer it takes for the sound to travel to the layer and back to the 
surface.  At the surface there are  listening devices - kind of like 
electronic ears. These "ears"  "hear" the sound as it comes back to the 
surface and they send it to  the computers and printers on the ship.  The 
sound is translated into an image.  You may have been on a boat and seen 
instruments that follow the bottom, sometimes these are called "fish 
finders" or "bottom profilers" - they use sound to trace the bottom under 
the boat.

You can try making your own sound wave by using a slinky. Sit on the 
floor with a friend about two feet apart.  Have your friend hold one end 
of the slinky and you hold the other.  Have your friend make a wave in 
the slinky by pushing it or shaking it.  Did it travel fast?  Now move 
about six feet away from your friend and make another wave.  Did this 
take longer to reach you?  This is just like sound - the closer  the sea 
floor is, the faster the sound moves from the source to the ears.  The 
farther the sea floor is, the longer it takes for the sound to move from 
the source to the ears!

The pictures we get show the layers of sediment and rock below the sea 
floor.  This is a little like looking at the side of a cake that has been 
cut in half, only, instead of icing and cake, there is rock and mud.  We 
can sample the layers and trace the layers over the ocean floor.  Some of 
the layers were made by the glaciers.  These are the layers we want to 
find!

There is another type of picture of the sea floor we get and that is a 
picture of the surface.  it looks a little like a photograph or a map.  
We get this picture in the same way, using sound, but the sound waves are 
so high frequency, they do not go into the sea floor - all of them bounce 
off and back to the listening devices.  This instrument (called a 
side-scan sonar) lets us see features on the sea floor, like grooves 
carved into the sea floor by giant icebergs!

Tomorrow I will tell you all about how we get samples from the sea floor! 
 This is very messy - but it is the part I like the best!

Write me soon - I hope you are fine!

E. Shackleton Bear