Rising levels of carbon dioxide could increase the volume of oxygen-depleted 'dead zones' in tropical oceans by as much as 50% before the end of the century — with dire consequences for the health of ecosystems in some of the world's most productive fishing grounds....In one of my earlier posts on ocean acidification, I had questioned whether algal blooms caused by more CO2 might be a bad thing for this very reason. (Some sceptics argue that more algae operating as a carbon sink will be a good thing. But obviously, it has a massive down side.)
A team led by Andreas Oschlies of the Leibniz Institute of Marine Sciences in Kiel, Germany, has now used a global model of climate, ocean circulation and biogeochemical cycling to extrapolate existing experimental results of the effects of altered carbon and nutrient chemistry on dissolved oxygen to the global ocean1. They found that a CO2-rich world will only have a small impact on waters at middle and high latitudes. But in all tropical oceans the volume of 'oxygen-minimum' zones will substantially increase as ocean bacteria feed on the algae that will flourish as a result of the elevated CO2 levels.
"Carbon dioxide fertilizes biological production," says Oschlies. "It's really like junk food for plants. When the carbon-fattened excess biomass sinks it gets decomposed by bacteria which first consume the oxygen, and then the nutrients."
Again, as far as I can see, this is an ocean danger story that is getting little press attention. Bah.
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