Sunday 30 December 2007 à 17:38

Grazing the continent!

Par Sophie Mouge. Correspondent aboard the Aurora Australis

Captain Ian offers us a treat for the eyes by taking a short detour into Commonwealth Bay: everybody to the wheelhouse!


Yet another magnificent spectacle of Nature’s grandeur.

Icebergs.


We graze the imposing icebergs that come in every shape.

In the conference room, Stefan presents a slideshow of microscopic images of tissues of bony fish, both scientifically and aesthetically appealing. He uses the occasion to show us how Christmas is celebrated by creatures of the deep, as in this image of Antarctic organisms put together like a Christmas tree!

"Antarctic Christmas tree" naturally decorated with different organisms of benthic fauna.


A few hours later, there is a new spectacle: we travel along the Mertz glacier tongue. A “tongue” is produced as the glacier advances into the water. Internal movements enliven the Antarctic ice sheet. Every year, the continental ice flows a few centimeters toward the coast; the result is that some glaciers spill into the Southern Ocean.

Transition zone between the continent (at right in the photo) and the beginning of the table-shaped ice tongue (center of photo).


The Mertz glacier tongue measures 150 km long and 50 km wide. The less-dense ice floats on the water and, in some places, rests on the ocean floor. One of the peculiarities of the Mertz glacier tongue is that it rests on the bottom at either end, like a bridge.

Edge of the Mertz glacier tongue.


Sorting operations on the rear deck of the Aurora Australis.


The CEAMARC collections are growing day by day. We are beginning to wonder about the volume of organisms collected. The problem is especially acute for the sponges because they are numerous and often very big.

Two big glass sponges.


Sponges grow very slowly (less than a millimeter a year!) in these cold waters. Their great size tells us that most of them are tens or even hundreds of years old (see the example of the Anoxycalyx (Scolymastra) joubini ).

Stefan Chilmonczyk shows us a sponge.


In spite of their stiffness and lack of mobility, sponges are very much animals, made up of different kinds of cells multicellular organisms) with siliceous or calcareous spicules. Most of the sponges collected during the CEAMARC mission have siliceous spicules.

Siliceous spicules of a sponge, removed with forceps and rinsed.


Antarctic waters contain a low level of carbonate ions, which could be a limiting factor for calcification in organisms and could explain the composition of marine communities : very few mollusks or crustaceans.



Sponges are filter feeders, that is to say, they create a current that draws water into their body’s chambers where food particles are absorbed then digested. Many organisms, like ophiuroids, crinoids and holothurians, use sponges as a support structure and fasten onto them temporarily.

Crinoids are attached to a sponge’s lamellar plate (background, left).


The sponges shelter many organisms in their cavity, like the little teleost fish that use the sponge to protect themselves and their eggs.

A sponge shelters a fish’s eggs.


The earliest sponges known have been found in earth dated to the Early Cambrian Period (-540 million years).

The next trawl is excitedly anticipated and is expected to start around midnight. It will prospect at a depth of approximately 1,200 m.

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