23 January, 1998

Hello Everyone!

We are along Pennell Coast, near Cape Adare.  Did you find Cape Adare on 
a map, yet?

I got to play in the mud today!  Ian Howat and I got VERY dirty!  We have 
been taking lots of "cores" - long pipes that go into the sea floor and 
bring back samples of the layers under the sea floor.  In my last journal 
I asked if you could come up with reasons that we might want to collect 
cores from Ross Sea. 

When we open the core, we find layers of sediment (mud and sand and 
gravel and pebbles).  The bottom of the core has the oldest layers.  The 
top of the core has the youngest layers.  These layers tell us about the 
changes in the environment. The layers in the bottom tell us about what 
it was like a long time ago where the core was taken.  The top layers 
tell us about the environment today.

Each environment leaves different clues behind.  A beach leaves different 
clues than a glacier.  What kind of clues would you look for in a core to 
tell you that a beach used to be in the place you took the core?  Think 
about what you see at a beach.  Would you expect to find lots of tree 
roots and leaves?  Would you expect to find lots of sand?  A beach 
probably would leave behind sand as a clue that it used to be there!

When we look at the cores, we look for clues to the glaciers.  We want to 
tell a story about how the land in Antarctica looked during the last ice 
age. We look around Antarctica today to see what hints the glaciers today 
give us. 

In many places of the ocean floor around Antarctica we find three layers 
of sediment stacked on each other.  

The bottom layer is very hard.  It is muddy with sand and gravel and 
pebbles mixed in.  There are no fossils.  Where might this type of 
sediment be found in Antarctica?

The middle layer is muddy.  There are no big pebbles. There are a few 
fossils, mostly animals that live in the ocean.  There are no plant 
fossils.  Where might this layer be found in Antarctica?

The top layer is green and muddy.  It has fossil diatoms in it.  Diatoms 
are single-cell plants that live in the open ocean today.  They need 
sunshine to live because they are photosynthetic (they convert the sun's 
energy to food).  If we find diatoms in the sediment layers, what does 
that tell us about the environment when the diatoms lived?

If we look around Antarctica today, we find a layer like the bottom layer 
UNDER THE GLACIERS. No animals or plants can live under the glacier, so 
we do not find fossils from the animals.  We find a layer like the middle 
layer under the ICE SHELVES.  Ice shelves are big pieces of ice that 
FLOAT on the ocean and are attached to the land.  Ice shelves are too 
thick to allow light to reach the ocean, so no diatoms can live there.  
You can see the Ross Ice Shelf on your map of Antarctica - it is the size 
of Texas!  The top unit that we sample in the cores is the green unit 
that contains diatoms.  This unit is the most recent and tells us that 
the place we took the core has had the open ocean over it.  

The cores help us tell a story.  Where we see the hard bottom layer, we 
know that the glaciers once passed over.  If we map all the areas where 
we see the hard layer, we know how big the glaciers used to be!  If we 
map all the places we core the middle unit, we know all the places the 
ice shelf used to be!  Our work so far tells us that the glaciers and ice 
shelves in Ross Sea once were much larger than today!

Oops, I almost forgot to tell you what Ian and I did!  Once we cut the 
long pipe open, we exposed the sediment layers inside.  We took pictures 
of the layers and described what we saw.  We wrote down how big the 
sediment grains were and what color the layers were and if we saw any 
fossils (I found a big sponge!).  Once we were finished with that, we 
took many samples of the layers and placed each layer in a separate bag 
with a label.  We had to sample carefully and clean our sampling 
equipment between each sample.  Why is cleaning the sampling equipment so 
important?  Why do we so carefully layer each sample?  Why might we want 
photographs?

Tomorrow I'll tell you all about the different types of ice I am seeing!

I hope that you are well.  Write me when you can!

E. Shackleton Bear