...and what will rising carbon dioxide do to the world's seas?
Atmospheric carbon dioxide levels are rising fast, global temperatures are increasing, sea levels are encroaching and now the oceans are becoming more acidic. But is it really all such doom and gloom?
As a scientist researching climate change, I am interested in putting everything into perspective, and lucky for us, there is so much work taking place in all fields of climate science at the moment that our knowledge is expanding faster than ever.
One of the most interesting and hotly debated questions at the moment is: how acidic will the oceans become and what effect will this have on the creatures that live within them?
The oceans began acidifying around the same time as the Industrial Revolution. As carbon dioxide was pumped into the atmosphere owing to the burning of fossil fuels, some of it diffused into the oceans.
Since most of the surface ocean has a lower concentration of carbon dioxide than the atmosphere, it acts like a sponge, dissolving the carbon from the air. Over two hundred years, the ocean as a whole has only lowered in pH by 0.1 of a unit. This seems small but the pH scale is logarithmic, which means that sea water is now actually 30 per cent more acidic than before the Industrial Revolution began.
Acidifying the ocean is a very similar chemical process to producing carbonated drinks – except the ocean does not become fizzy… I have a very vivid memory of my parents dropping one of my baby teeth into a glass of fizzy drink and watching it dissolve; though I cannot say it put me off drinking carbonated drinks, it certainly demonstrated their acidic nature.
The chemistry behind this process is fairly simple; when CO2 dissolves it reacts with a water molecule to produce carbonic acid (H2CO3). This dissociates into a bicarbonate ion (HCO3-), and an acidic hydrogen ion (H+) which causes the water’s acidity level to rise. Fortunately, the ocean happens to be loaded with plenty of other negative ions, which can help mop up any excess hydrogen ions - but only up to a point.
Just like teeth, shells are made of readily-dissolvable material, most often calcite or in a few cases, aragonite, which are both forms of calcium carbonate. So animals that live within shells are vulnerable to any change in acidity. But how vulnerable they are also depends on where they live.
We can divide the oceans into three main environments; shallow coastal habitats, polar oceans and the rest, simply called "open ocean", where the majority of life-forms are microscopic and inhabit only the very top layer of sea water.
The shallow shelf areas are hugely productive. Here we find most of the large calcifying organisms; corals, brittle stars, star fish, molluscs and sea urchins. They can be quite vulnerable to changes in their habitat as they do not have much space to adapt; they require lots of light and a narrow range in temperature, so sudden changes can really stress certain species.
Corals, in particular, are thought to be at risk because they make their structure out of aragonite, which is even easier to dissolve than calcite. A group from Columbia University, in Arizona, have predicted that some coral species will almost halve the amount they can calcify by the time CO2 concentrations reach twice the pre-industrial revolution level; according to the Intergovernmental Panel on Climate Change (IPCC), this could be as early as 2045. Sea urchins and brittle starts are also at risk because the acidity affects the larval stage of their life cycle, although studies so far have found that some species are more at risk from rising temperatures than acidification.
However, there is a flip side to living near the coast. The natural acidity of these habitats varies quite a lot depending on the location. Species near estuaries and river mouths live happily in more acidic (lower pH) conditions than normal seawater, so these species are less likely to be affected by rising CO2 levels. This could give them a competitive advantage and they may even thrive in the future.
Polar species are predicted to be hit first. This is because CO2 dissolves most readily in cold water. You can observe this with fizzy drinks – less gas is released when you open a can that’s been the fridge compared with one left out in the warm. So the polar oceans will become more acidic more quickly.
There are teams of scientists funded by a European initiative called EPOCA, who are currently doing experiments with whole ecosystems in the Arctic. They envelop a parcel of sea water, along with all its inhabitants, in a giant 17m long tube called a mesocosm. They can then change the CO2 concentration, simulating higher atmospheric levels, while otherwise keeping the environment similar to the surrounding Arctic water. These experiments are still in their infancy, but will hopefully yield useful results and providing a more well-rounded view by virtue of assessing the responses of multiple species simultaneously.
The open ocean covers by far the largest area, but the inhabitants are mostly microscopic plants and animals. Many laboratories have been involved in culturing these tiny creatures under differing CO2 conditions and, so far, the results are contrasting. First, because plants take up carbon dioxide and use it to photosynthesise, these species tend to flourish in elevated CO2 conditions. But their hard-shelled animal counterparts, however, a group known as the coccolithophorids, may fare less well.
Recent experiments growing coccolithophorids demonstrate the need for such studies to replicate the natural world as closely as possible. For example, in one study seawater was acidified with dilute hydrochloric acid but plants reportedly failed to thrive. But another study used carbonic acid in place of hydrochloric, thereby simulating CO2-driven acidification, and the plants grew even better than under normal conditions.
So the jury is still very much out as to how much open ocean calcifying plants will suffer from increasing atmospheric CO2, and as with all habitats the effects will be species specific. One argument for coccolithophorid adaptation is they have a high degree of genetic diversity within each species, this may allow them to evolve quickly to changing environments.
A really important question is not just how each individual species will be affected, but whether ecosystems will be able to adapt? But this is a difficult question to answer when we still do not know that much at a species level. There are several groups using computer models to assess impacts on ecosystems. Their aim is not just to include environmental pressures like temperature and CO2 change, but also human interaction, such as fishing. So far, these models have not been very good at assessing shelf areas, mainly because they vary so much, and have the highest biodiversity. But since these models rely on actual scientific data, the more experiments are conducted, the better the models become.
In summary, ocean acidification is a daunting problem we will have to face. It has occurred several times before in Earth’s history, so not only can we use experiments to predict the outcome of the ocean, we can also learn from geological records which preserve past environmental conditions and species response.
It is extremely important that laboratory experiments replicate real environments, not only testing CO2 changes, but also temperature rises, competition for nutrients and sea level change – and this is no small task. We are only now learning that some areas of the ocean and different species will be affected more than others, and with ongoing world wide science collaborations and experiments, we will hopefully be able to tackle this problem head on.
This certainly is an issue worth looking into.
This could be a far greater, and more immediate problem, than rising sea levels. A small pH change could result in the total collapse of the ocean's food chain.
The carbonate equilibrium in sea water actually made up a large portion of my last midterm. We used acid-base equilibrium, the solubility of CaCO3, and various other information to determine the change in pH necessary to force the equilibrium far enough so that CaCO3 shells could no longer form. We assumed that all increase in pH was entirely from CO2 (which is inaccurate because chemical fertilizers also can have an effect). I think CliffordK is right. We used this article: http://www.sciencemag.org/content/305/5682/367.full.pdf Bill.D.Katt., Sun, 27th Feb 2011
Here's a link to the story about oyster farms in the Pacific NW.
We will see. Some points I would like to make.
"Phytoplankton use sunlight to convert carbon dioxide into carbon-based food. As small fish eat the plankton and bigger fish eat the smaller fish, an entire ecosystem develops. The Bering Sea is highly productive thanks mainly to diatoms, a large type of phytoplankton. "Because they're large, diatoms are eaten by large zooplankton, which are then eaten by large fish," Hutchins explained.
Yes, but what about the oysters? Geezer, Mon, 28th Feb 2011
Yeah, I read you Geezer. If I get it right its not the already grown oysters that are the problem, it's the oyster larvae that can't make their shells? I think that's another of the, rather simple, causality chains in nature that we haven't considered fully. We look on grown specimens forgetting that they all start weak. A worrying story that one. yor_on, Mon, 28th Feb 2011
... some are saying we have about 2 more generations... then Earth will no longer habitable for us... thanks to AGW denial... and now unstoppable
"some are saying we have about 2 more generations... then Earth will no longer habitable for us... thanks to AGW denial."
But you're right 'guest Larry' we do have a very serious issue in the Phytoplankton population shrinking. " "A measure of productivity is the net amount of carbon dioxide taken up by phytoplankton," said Jorge Sarmiento, a professor of atmospheric and ocean sciences at Princeton University in New Jersey. The one-celled plants use energy from the sun to convert carbon dioxide and nutrients into complex organic compounds, which form new plant material. This process, known as photosynthesis, is how phytoplankton grow.
Yoron - there's a good article in yesterday's nature on ocean acidification that you might be interested in. it's recent enough to still be open access on the nature website. if you cannot get hold of the article let me know by pm imatfaal, Fri, 11th Mar 2011
Geezer, you might like this one? Well, not like exactly, but it's interesting. On wild oysters, the headlines that came 100 years too late, and turning poop-water into salty Evian.
Not 50 % Clifford.
Yoron - I think Clifford is talking about a situation where the amount of oxygen is reduced by 50%. Geezer, Sat, 26th Mar 2011
A reduction of 50% from 21% would leave 10.5%, that's well into the range of "dizzy" according to that table and it would make it impossible to do anything. Even walking across the room would be impossible.
I think there are many different calculations.
http://hermosabeach.patch.com/articles/dead-sea-lion-found-near-hermosa-beach-pier Thought you might find this interesting. I read somewhere that there has been a 40% decline in Phytoplankton since 1950. When I read this article after the above to learn more http://earthobservatory.nasa.gov/Features/Phytoplankton/page2.php I became quite concerned considering the amount of marine deaths of late around the globe. Just wondered what your thoughts were? raven, Thu, 5th May 2011
Yep, there are some serious stuff going on. And you can backtrack it to the way we live and pollute. And then we have 'saviors' that reminds me more of fanatics than using common sense, wanting to fill the seas with tailored genes for cleaning it up. man-made organisms designed to pump out fuel and clean up waste. It's painfully obvious that some still believe Jules Verne to be fine and hearty. Also that 'Big Business' hope that this will let them make some real dough. All put together, with politicians that never hesitated to cut the Gordian knot, I'm sure we will see something like this soon enough. And when it backfire, as I expect it to do, those that did it will look at you and ask 'And what did you do ? Sat on your ass, didn't you. At least we tried.."