Here’s an update and a bit of good news on the ocean acidification front.
This is a topic I’ve covered quite a bit (see “Ocean Basin Ocean Acidification,” “Ocean Acidification Time Bomb Is Ticking,” “Update: Thinner Shells Put Ocean on Thin Ice,” “Ocean Acidification Faster Sooner,” “Planetary Watch: An Unexpected Impact of Global Warming“), but for rapidly developing scientific areas like this one, there’s always new stuff. Here’s a report on the latest.
Ocean acidification is the result of our carbon habit. As we pump more and more carbon dioxide into the atmosphere, some of that CO2 gets taken up by the oceans. There, it is transformed into carbonic acid -- a weak acid that is slowly lowering the pH of seawater (the lower the pH, the higher the acidity). Lowering the pH of seawater is thought to be a problem because it will be increasingly harder for a wide variety of plants and animals to generate the calcium carbonate from seawater they need for their skeletons, exoskeletons, or shells.
We don't know precisely what that will mean for the ocean ecosystem, but it is not at all unlikely that problems encountered by the little critters will ripple up the food web impacting animals like us who sit at the top of it.
It's Surely Happening
That the ocean is acidifying is well established. As atmospheric CO2 concentrations have climbed, seawater measurements have shown falling pH's in the oceans in just about every corner of the world -- or at least pretty much everywhere we've looked (see here and here). And pumping more and more CO2 into the atmosphere isn't the only factor here. For reasons that are not entirely understood but are believed to be in part due to processes related to coasts and river runoff, acidification is happening faster in some areas than in others. (See also here.)
A Varied Response
It's all quite worrisome, but it's not clear that all is doom and gloom for our friends in the ocean. While data show that the shells of some species are getting thinner, other research shows some species appear to be largely unaffected. (See here and here.) And some studies suggest that certain species may be able to adapt to ocean acidification and survive. And there's even some evidence that "warming [temperatures] may mitigate ... [some] negative effects of acidification."
How great might we expect the variability of response to ocean acidification be from species-to-species and taxa-to-taxa?
In a paper published this week in the journal Nature Climate Change, Astrid Wittmann and Hans-O. Portner of the Alfred Wegener Institute in Germany attempt to answer this question. Sifting through 167 studies on the affects of acidification on 153 marine species, they found that extremely high values of CO2 concentrations (i.e., those greater than 10,000 parts per million) negatively affected "all animal groups we considered [corals, echinoderms, molluscs, crustaceans, fishes]." However, at more realistic concentrations in the 500 to 1,000 parts per million range -- concentrations we might expect to reach in this century -- the response was more variable. And for some species, especially echinoderms (think sea urchins and star fish) and crustaeceans (such as lobsters and crabs), the authors found that a small but significant fraction of the species studies actually reacted positively instead of negatively.
These findings suggest that ocean acidification will create marine winners and losers. It is not unreasonable to expect, therefore, that the distribution of biota in our progeny's ocean toward the end of this century may be quite different from that of today.
Is that good news or bad news? Definitely good news if you're worried that ocean acidification will lead to an ocean devoid of all life. The data studied by Wittman and Portner suggest that that is probably not on the horizon anytime soon, at least not from ocean acidification. But there's also a good deal of bad news -- or at least potentially bad news. We might find that brave new ocean community of the late 21st century to be far less palatable and perhaps even less suited to providing a critical source of protein to the 11 billion people expected to inhabit the planet in 2100.
A New Connection Between Ocean Acidification, Climate
Also, before getting too excited about living with ocean acidification, I should probably tell you about another paper by Katharina Six of the Max Planck Institute for Meteorology and colleagues also just published in Nature Climate Change. It suggests that ocean acidification might actually accelerate global warming.
Using data from seawater experiments (such as this one) that show that phytoplankton-generated dimethylysulfide, a biogenic sulfurous gas, is slowed as pH falls, the authors modeled how decreases in this gas impact the climate cycle. How so? Produced in the ocean, the gas then diffuses through the water column into the atmosphere (think of that ocean smell, and part of it is from this gas). In the atmosphere it is oxidized into tiny sulfate particles that help form clouds. Those clouds, in turn, reflect sunlight and cool the earth. And so more ocean acidity, less of that gas, less reflective clouds, warmer temperatures.
The more we study it, it seems we find that emitting CO2 can be an insidious exercise.