Oxygen decreasing in ocean waters

Saturday 25 February 2012 12:44PM (view full episode)


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Robyn Williams: Another aspect of climate change, possibly, is a worrying depletion of oxygen dissolved in the ocean, especially in the tropics. Lisa Levin is a professor at the Scripps Institution of Oceanography in La Jolla, California.

Lisa Levin: This work comes from long time-series studies. Some of it has happened in the north-east Pacific, some of it was from the California cooperative fisheries investigation program, about a 60-year time-series of California. Other work comes from analysing the global datasets in various ways, looking at data collected 40 years ago and comparing it to the present.

Robyn Williams: How much is it going down?

Lisa Levin: In some places the oxygen is going down significantly; 30% decline in the last 22 years at water depths of 200 to 300 metres off Southern California. That's a fairly extreme example but that gives you a feel for what can happen. It doesn't mean that it hasn't happened in the past, but usually these changes happen at a much slower rate.

Robyn Williams: Any idea why it's going down?

Lisa Levin: We believe that declines in oxygen are related to both a warming of the water, because warm water holds less oxygen than cold water, and also to stratification or layering of the waters as a result of being warmer, and also from the melting of the polar ice caps, which adds a salinity gradient. And when there is more stratification there is less vertical mixing of oxygen from the surface into the interior of the ocean. And so normally oxygen is replenished inside the ocean, and we believe that that has been reduced, leading to apparent declines.

Robyn Williams: Yes, I was going to ask you about that. Declines in what way? You've studied the wildlife effects. What are they?

Lisa Levin: Low oxygen areas, some of which occur naturally in the ocean, appear to...well, we know they exhibit a lower species diversity, they are mostly occupied by soft-bodied organisms on the seafloor, and so calcareous species are often absent. We also know that they are smaller-bodied animals than in more oxygenated areas. So the changes we expect to see as low oxygen areas expand include a loss of diversity and a change in species composition, and also a redistribution of species with many moving into shallower depths seeking better oxygenated water.

Robyn Williams: There are some areas that you've suggested where the oxygen is going up. Are there many?

Lisa Levin: There are areas where statistically increases in oxygen have happened. Most of the oxygen declines are in tropical and subtropical waters between about 200 and 700 metres water depth, sometimes a little bit shallower. Some of the areas where oxygen is going up is in more higher latitude regions.

Robyn Williams: How much of this is a general concern as a trend where oxygen seems to be going down substantially across areas of the ocean? Personally does it worry you?

Lisa Levin: Yes, it does. I think that the loss of oxygen has not gotten sufficient attention amongst scientists or among the public. We tend to be a little bit more aware of processes like the acidification of the oceans. I think that in certain areas it's going to have a very major economic impact. We already know regions like Peru which experience El Niños and have major oxygen fluctuations, we know that the entire ecosystems can change in response to that. And it's quite likely that our fisheries are going to be affected, we have fisheries moving into shallower waters, we have fishes moving northward, so they are being redistributed. In some cases they are becoming more easily caught by fishermen, but it's a difficult situation because we have trouble telling if the densities are going up or animals are simply being compressed in their habitat and it's looking like there is more available than there really are.

Robyn Williams: Of course the ocean is a gigantic place, vast numbers of different ecosystems. What were you doing exploring around New Zealand?

Lisa Levin: I was on the Tangaroa with a group of people, some based at NIWA in Wellington, and we were looking for methane seeps, areas where methane is being squeezed and emitted from the seafloor on the continental margin. Fishermen and others had found evidence of this but we actually had the first real look at these places.

Robyn Williams: What was it like down there near the bottom? Did you see evidence of trawling, for example?

Lisa Levin: There was intense trawling. All of the nine sites that we discovered had evidence of trawler activities, either trawl marks or fishing gear that had been stranded or rubble that had been created by the trawling activity. So there is intense trawling on the New Zealand continental margin and many other margins around the world, and we really run the risk of damaging ecosystems and organisms before we even discover them.

Robyn Williams: Yes, even at such depths.

Lisa Levin: Yes, these are at depths of 500, 800, 1000 metres where this commonly occurs.

Robyn Williams: Quite extraordinary. How are you following up this work yourself?

Lisa Levin: I would say right now I'm trying to raise public awareness about the types of human intervention that's going on in the deep sea, and I'm also trying to establish a dialogue between economists, policy people, regulators, stakeholders, the industry, to try to encourage better stewardship of these environments.

Robyn Williams: Are they listening?

Lisa Levin: I hope so.

Robyn Williams: And so do we. That's Lisa Levin, distinguished professor at the Scripps Institution of Oceanography in La Jolla, California. And she had little to say, oddly enough, about Kevin Rudd or Julia Gillard.


Lisa Levin
Scripps Institution of Oceanography
La Jolla California


Robyn Williams
David Fisher

Comments (4)

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  • Trevor :

    27 Feb 2012 9:46:28pm

    I believe that atmospheric oxygen levels are also falling? Seems to be sometjing we don't hear much about. maybe we should.

      • JoeBloggs :

        29 Feb 2012 11:19:23am

        In time you will.

        As the acidification of the ocean increases and oxygen producing marine organisms fail to survive the production of planetary oxygen will diminish.

      • J Powell :

        29 Feb 2012 7:36:58pm

        Yes, this is far more concerning given that atmospheric concentrations are also decreasing. Just imagine the volume of oxygen being guzzled by airbuses every day! Personally, I feel these studies should be given high priority.

  • David Arthur :

    01 Mar 2012 12:11:14pm

    Regarding ocean stratification and consequent anoxia, how about constructing some kilometre-long pipes, tow them out to deep ocean, attach one end to a float and allow the other end to sink until the pipe is vertical? Deep ocean water can then be pumped to the surface, perhaps mechanically powered via windmills. The feasibility of this is supported by a Guardian (UK) article of 29 February 2012: "Windfarms that float – or fly – could be the future of energy generation", by Ian Sample.

    The idea is that this artificial enhancement of overturning circulation will help with ocean oxygenation, encourage CO2 uptake and bring nutrients to the surface to fertilise CO2 metabolism. Deep water is also colder, but the major beneficial effect will be through the enhancement of photosynthesis in the upper ocean.

    As an suggestion for geoengineering the climate to attempt to avert dangerous climate change, it would be a lot safer than deliberately contaminating the stratosphere with sulfate aerosols (air pollution).

    [I erroneously posted part of this comment after the story about fishermen and endangered species. Don't thank me for this idea, I've reporting the proposal from James Lovelock's "Revenge of Gaia"].