Tuesday, December 28, 2010

Coastal upwelling

You wouldn't think that the oceans around Antarctica would have a lot of exciting marine animals. But it does! The shores around Antarctica have quite a variety of marine life, because it is a zone of coastal upwelling.

The water in the ocean doesn't stay in one place. Water moves. You're probably familiar with currents and tides, which are a couple ways that water moves around in the ocean. But water also moves up and down in the ocean, not just around the surface. Here's how.

Water that is on the ocean surface gets pushed around by the wind. When the surface water is pushed away from an area, other water has to move in to replace it. Along the coast of a piece of land, there's no surface water to replace it, so the bottom waters have to rise up to replace that water. Where the bottom waters come up to the surface is called "upwelling".

The surface waters being pushed away will move around the surface and eventually sink to the bottom. It will then eventually upwell to become part of the surface ocean again. It's a big conveyor belt that moves water up and down, in addition to around the surface.

While water is on the bottom of the ocean, it collects a lot of nutrients. The nutrients come from dead things that sink to the bottom and start to decompose. So, at areas where bottom water is rising to the surface, it is bringing along with it a lot of nutrients that had been collecting. Those nutrients are important for living organisms at the surface.

Around the coast of Antarctica, the westerly winds push water away, and it is replaced by the cold, nutrient-rich water below. The high level of nutrients in the upwelled water around McMurdo mean that there is a lot of productivity. There's a lot of phytoplankton in the water that use those nutrients to photosynthesize. Because there's a lot of phytoplankton, there are a lot of animals that eat the phytoplankton, and therefore a lot of animals that eat those animals... a whole food chain! So, there's a lot of animals living off the coast of McMurdo. Some of them are very colorful, just like in the tropics!

The marine biologists here at McMurdo keep a touch tank with some of the animals they catch. Here's what I saw in the touch tank:There's a lot of different types of animals in there, of different shapes and colors. And they all live right here near McMurdo! It's all of this life that lets the oceans support the larger ocean animals that you might be more familiar with:(See the whale and the penguins at the ice edge?)

Even though it's so cold and icy, the oceans are home to several species of whales, penguins, and seals. They can live here because of the upwelling that brings all of those rich nutrients to support the entire food chain in ocean around Antarctica.

[Photo credit: upwelling diagram from sonoma.edu]