Science News

Bad news for the Colossal squid’s home

Sun, 4th May 2008

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While we are still discovering such exciting things about illusive deep-sea creatures, there is also some worrying news this week about the state of the oceans that these creatures live in.

Oxygen Minimum ZoneScientists from the University of Kiel in Germany lead by Lothar Stramma have been studying the so-called ‘dead-zones’ of the oceans, and found that they are getting alarmingly bigger. These are areas where there is very little oxygen, and so most ocean life, including fish and those fantastic colossal squid are unable to survive – they are the equivalent of deserts in the ocean.

We’ve known for a while that in shallow seas the input of nutrients and pollutants from land can trigger these dead zones – there’s a particularly large dead-zone in the Gulf of Mexico, for example.

But now, Stramma and colleagues have revealed that in intermediate depths, around 300 to 700 metres, there is an expanding mass of oxygen-poor water. Using data from research vessels around the world and also special fixed buoys equipped with oxygen sensors, they have discovered that over the past fifty years, areas of ocean that used to be oxygen rich are now what they term ‘oxygen minimum zones’ – where oxygen levels are so low most sea life will suffocate and die.

Areas of particular concern are in the tropical Atlantic, off the west coast of Africa and around the equator in the Pacific Ocean.

We can’t be sure just what is causing the loss of oxygen; and there are natural fluctuations in levels due to global events like El Nino. But the finger of blame is pointing squarely at global warming and rising sea temperatures. Since warm water holds less oxygen and also does not sink like oxygen rich cold water, which would normally replenish oxygen deeper down.

The good news is that most fish can swim away and escape these dead zones. But if they are getting bigger and bigger perhaps soon there will be fewer places for them to escape to.

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