Photo: Pondering the power of an acidified ocean

Some organisms will fare better than others in an acidified ocean: some will be clear winners, others will be losers. (Credit: Ian Knauer via Flickr)

By Carin Bondar

Carin Bondar is a biologist, TV host and science communicator with a PhD in population ecology from the University of British Columbia. She blogs for Scientific American and Huffington Post and has appeared in a scientific capacity on various international television networks. Her writing has been featured online at National Geographic Wild, Jezebel, Forbes, The Guardian, The Daily Beast and the Richard Dawkins Foundation. Find Dr. Bondar online, on twitter or on her Facebook page. Look for her blogs on science topics in the coming weeks on the David Suzuki Foundation website.

I recently had the pleasure of attending the 2012 American Association for the Advancement of Science meeting in Vancouver, B.C. Among the largest gatherings of scientists from all corners of the globe, this year's conference saw coverage of a wide variety of topics. Cutting-edge science was presented in areas from medicine to physics, and environment to communication. As a biologist, I chose to attend sessions that focused on animal behaviour and ecosystem health. I especially enjoyed the session on ocean acidification. It was presented by leading experts from several universities, each addressing the topic from a different perspective. Much fascinating work is taking place in this area, and I'll be discussing the latest results and trends in subsequent posts here on the Healthy Oceans Blogs. However, I'd like to begin my coverage by providing a general introduction and clarifying some common myths about ocean acidification.

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What exactly is ocean acidification?

It's no secret that mean levels of atmospheric CO2 are significantly higher than they have been on our planet for the past 600,000 years. Burning fossil fuels is the largest contributor to the rise, and all of this "extra" carbon dioxide in the atmosphere is having many effects all over the planet. Approximately 25 per cent of atmospheric CO2 is absorbed by the surfaces of the world's oceans, and the resulting change in pH is what scientists have termed ocean acidification. To be clear: the term acidification is not meant to describe a future ocean that is composed of acid as opposed to water. The shift in pH from historic levels of 8.25 to predicted levels of 8.14 and lower is movement toward the acidic end of the pH spectrum; however, it is far from the level of something like lemon juice (with a pH of 2.4). Despite the fact that sea life will not be subjected to living in actual acid, the change (which is measured on a logarithmic scale and therefore represents a 100 to 150 per cent decrease in ocean pH) will have massive implications.

Winners and losers

According to Christopher Harley at UBC, some organisms will fare better than others in an acidified ocean: some will be clear winners, others losers. Researchers are racing to identify which organisms will be hit hardest by these environmental changes. Animals that have calcareous shells are in big trouble. For example, molluscs like mussels, clams and snails secrete their own shells by drawing on calcium carbonate in the seawater. Hard corals and sea urchins do the same to construct their skeletons. Due to a sequence of fairly simple chemical reactions, calcium carbonate is not as bioavailable in an acidified ocean. Quite simply, organisms that require it for skeletal or shell formation during development are going to suffer drastic consequences.

Why does this matter?

Peggy Olive Your initial reaction may not be one of complete alarm. Large animals tend to rule when it comes to tugging on our heartstrings, and a mussel isn't exactly a polar bear or an orca. However, the potential for changes to ecosystem functions is massive. For example, mussel beds provide habitat to hundreds of marine species and food for many marine and terrestrial predators. Sea urchins are a major component of the diet of seals and sea lions, and hard corals provide a subtidal home to countless fish and invertebrates. Moving a few steps up the food chain we will undoubtedly see that orcas and other top predators will be affected by ocean acidification too.

Looking ahead

In a subsequent post I'll look at some complex predictive modelling being undertaken at the National Oceanic and Atmospheric Administration in the U.S. that is providing insight into how these changes will reverberate through oceanic food chains. For now, suffice it to say that due to ocean acidification, aquatic ecosystems in 2112 will look substantially different than those of today.

March 5, 2012

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Mar 05, 2012
4:36 PM

I should think that the presence of so much decaying calciferous material in the ocean would act as a pH buffer. In addition, since most carbonates form precipitates and settle out of the ocean water, the formation of these precipitates also acts as a buffer. The combined effects are perhaps equal and more to the task of maintaining ocean pH within narrow bounds even in the presence of 500 ppm atmospheric CO2.

Aren't clams and mollusks found around hot smokers and volcanic vents in the ocean now? Why doesn't the excess carbonic acid cause them to die out there?

Mar 06, 2012
7:52 AM

To what extent might all this diminish the seas capacity to function as a CO2 sink?

Mar 07, 2012
6:43 PM

Thank you for your comments! John, from what I gather the capacity of the surface waters of the ocean to act as a sink for CO2 will not be diminished in the next few centuries — meaning that the pH of the water will continue to fall. Ken, you've got an interesting point about the buffering effect…I'd have to research that in greater detail. The production of carbonic acid, and resulting production of bicarbonate means that less calcium carbonate is formed — and this is bad news for organisms that need access to that calcium! I'm really glad you brought up the point about naturally acidic upwellings — this will be the topic of one of my future posts on the subject. Stay tuned!

Mar 08, 2012
1:49 AM

Ken Brody — why should buffering suddenly become a magic panacea when it hasn't worked to prevent ancient ocean acidification events?

There have been a number of peer-reviewed papers on this topic in the last decade. Sadly, the dissolution of of carbonate minerals, like the chemical silicate and carbonate rock weathering process, only works on the timescales of hundreds of thousands to millions of years. Alkalinity supplied back to the ocean at that rate is going to be a tad useless to humans and marine life living today, and the foreseeable future.

Indeed, what we observing is a decline in ocean pH (increased acidity) matching the rate of increase in atmospheric CO2. The ALOHA (Hawaii) and BATS (Bermuda) stations are seeing an increase in acidity of around 5% per decade (IIRC).

The oceans only acidify when the rate of increase of atmospheric CO2 is too rapid for the chemical weathering process to supply alkalinity back to the ocean. That is why the oceans were not corrosive when CO2 levels were higher than today and the climate was in 'steady states'. With slow changes the chemical weathering process is able to keep up. Again, there is a vast amount of scientific literature on this topic — see work by Wally Broecker, James Kasting, Robert Berner and Lee Kump.

I have a number of posts coming up at Skeptical Science (SkS), over the next few months, covering all these lame canards about ocean acidification. It's quite interesting how contradictory all the skeptic objections are — whereas the mainstream science is internally consistent, and all fit coherently into a broad conceptual framework.

And finally, your claims are self-contradictory. The formation of calcium carbonate releases CO2 into the ocean, whereas the dissolution of calcium carbonate consumes CO2 — hence the buffering effect over geological timescales.

Mar 08, 2012
10:32 AM

John — see the FAQ section at EPOCA. There is a collection of explanations for the most common ocean acidification myths, and the site is managed by bona fide world experts on the subject.

The oceanic carbon sink will reduce in time, but not to any appreciable extent sufficient to diminish ocean acidification.

Mar 08, 2012
10:57 AM

Carin — "The production of carbonic acid, and resulting production of bicarbonate means that less calcium carbonate is formed — and this is bad news for organisms that need access to that calcium!"

It's the reduction in carbonate ion availability (activity) that impinges on the ability of marine life to build/secrete calcium carbonate shells and skeletons, not calcium. The calcium ion concentration is, for all intents and purposes a fixed value. It does change over the course of millions of years due to 'volcanic processes' however. In other words, the calcium 'building block' is still freely available, but the carbonate 'building block' is being steadily reduced.

And thanks for writing about this. Ocean acidification is yet to appear on most peoples radar, but its effects on marine life are likely to be extremely dire. We are already seeing that on the Pacific coast of North America (an area of strong natural upwelling of cold, acidified deep water), where juvenile Pacific oysters have been dissolving in the last 5 years because the waters there are so corrosive.

Mar 09, 2012
6:10 AM

I feel there is a very gross false assumption. We are assuming that the increase in ocean acidity is due to absorption of atmospheric C02. The waters ability to absorb C02 is reliant on low temperature. When subsuming C02 into H20 the temperature must be low (lower than 5c, I forget exactly) whereas the temperatures on average of the worlds oceans are much higher, closer to 15c. The only areas of ocean surface cold enough to direct absorb C02 from the atmosphere would be in the Northernmost latitudes. Though the oceans of the world are all connected would it not be counter intuitive to assume that C02 absorption in less than 20% of the worlds surface area would lead to a quick change in the levels throughout all the wolrds ocean? Fluids do not move instantly. Please do not attack my argument as I believe there are arguements to possibly explain what Dr. Suzuki refers to but they are really lacking from the published reports. Please refer to a published article on it that gives more detail. As well as that would they be able to eliminate from the results the direct pollution of the oceans through industrial chemicals such as those used in the manufacture of most consumer goods.

Mar 10, 2012
11:56 PM

Considering that the CO2 levels are the highest in the past 600,000 years then one has to wonder how life in the ocean survived when the atmospheric CO2 levels were higher — perhaps 700,000 years ago. Not unlike saying temperatures are the highest they've been in 1,000 years! Of course this is neglecting to mention they were higher over 1000 years ago. And considering the ocean is not 'acidifying' when in fact it is actually neutralizing — moving incredibly slowly towards 7ph — one can really only claim that it is is becoming marginally less alkaline. However "Oceans marginally less alkaline" is not as striking a headline as "Oceans acidifying" is it? This is not to say that local and global climates do not change — they are ALWAYS changing. The herring fisheries of the middle ages changed when the fish moved due to climate changes, the Mayan civilization collapsed due to climate change as others rose and fell accordingly. And local climates are always changing, the question is — what are the underlying causes? And how can these influences be predicted or is it like earthquakes and at best can be commented on as it happens?

Mar 14, 2012
2:42 PM

Hey Rob — good point regarding the Ca , I should have described it as 'bioavailable' calcium. I'm so glad to have many participants in this discussion — I have the next two pieces ready to go. Some of the cutting edge work being done now (and presented at AAAs) will definitely cover some of the interesting points being covered here.

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