June 11: The trouble with acid oceans
Plankton in the northern oceans plays an important role in taking up CO2 from the atmosphere. Apart from that, it forms the basis of the marine food chain. The trouble is, these vital organisms are under threat from the unprecedented rise in atmospheric CO2-levels. The CarboOcean project, located in Bergen (Norway), is working to map out the consequences.
Algae in a fjord near Bergen (at Espeland) float in a time machine. Next to each other, algae live in glacial times, modern times and one century into the future. They all live in five meter deep nets hanging from a framework next to a wooden shed that houses some of the equipment. The nets are covered by sealed tents, which enables scientists to vary the CO2-level in the air above the water. These at glacial times live at a concentration of 190 ppm (parts per million) of CO2, the present concentration is at 370 ppm. The 2100 tent holds 700 ppm. This is the concentration the IPCC expects for the Earth by 2100 under one of the conservative scenario's.

High CO2 concentrations make the water more acid and this interferes with the formation of calcite shells by the algae. Professsor Truls Johannessen, professor at the CarboOcean project from the Bjerknes Centre for Climate Research in Bergen, shows two electron microscope pictures from coccolites, algae that cover themselves with small calcite disks. Normally they do this in a very symmetrical pattern. But the one from the future carries its lumpy irregular disks at odd angles. Something has gone seriously awry here. The simple experiment in the fjord reveals bad news that may have global consequences.
The CarboOcean project studies the uptake and release of CO2 by the oceans. The researchers do this by experiments, like in Espeland, by measurements aboard so-called 'ships of opportunity'. Mostly these are ships on regular routes that carry CO2-measurement equipment from the project registrating the CO2 pressure above and below the water. Also, they use satellite data for the determination of wind speed and sea water temperatures.
The result is an ever finer map of the oceans showing the CO2 fluxes into and out of the ocean. Broadly speaking, CO2 is taken up by the northern oceans, and released in waters at lower latitudes. On a yearly basis, 90 gigatonnes of carbon circulate through the ocean.
At least, that used to be the case. Now it is 92 going in and 90 coming out. The two extra come from human activities. When CO2 concentration was around 280 ppm (around the year 1750), the system was in balance. Now with CO2-levels approaching 400 ppm, it's on inbalance. But the good news is, it is taking up about 30 percent of the man-made CO2. Forests absorb another 20 percent, so that only half on the CO2 produced by humans stays in the atomosphere.
But that is about to change. The CO2-mopping mechanism of the oceans seems to be stalling. Truls Johannessen explains: “The colder the water is, the more CO2 it can take up. And the the less acidic, the more CO2. What is the direction today? The water is warming up and getting more acidic. So the ocean itself takes up less CO2, that means that more CO2 stays behind in the atmosphere and contributes to global warming. The natural systems that buffer CO2 in the natural world are getting weaker. Both the terrestrial system and the oceans take up less.”

This weakened uptake has not been taken into account the international panel on climate change, the IPCC. The science has to be beefed up beyond any reasonal doubt before the IPCC will include it in the projections. The CarboOcean team is working hard to get the data they need and to minimise the uncertainties. If they are right and CO2 uptake is indeed weakening, the next IPCC projections will be (even) less optimistic.
At the basis of it all lies the acidification of the oceans – a consequence of a shift in the global geobiochemic equilibrium of the oceans. As CO2 dissolves in ocean water, it forms carbonic acid (H2CO3). The carbonate part is bound by calcium as marine micro-organisms make shells of aragonite or calcite. Once the organism dies, the carbonate shells sink towards the sea-floor, thus taking the carbon out of the atmosphere for thousands of years.
So far so good. But the by-effect is excess of H+ (acid), making the oceans more acidic. In glacial times, the pH (degree for measuring acidity) of the oceans was 8.3. Now the value varies between 8,2 and 7,9. If that seems like a small difference, you should realise that 0,3 pH change means a doubling of H+ concentration.
Apart from the biological uptake by shell-forming micro-organisms, there is also the physical dissolving from CO2 in water, the so-called sea-air-exchange that is mainly governed by stirring up the water surface by the wind. Compared to the biological uptake however, the physical is four times less, according to Johannessen, and less permanent as well.
Johannessen is concerned about the acidification: “ If that is harmful to the organisms in the ocean, you get less biological production, and that means less deep uptake from the atmosphere. That is not yet sure, but models show that it is a plausible effect. That is why we do the experiments. To get more grip on that.”
The weakened uptake would be bad news for the climate change, as more of the emitted CO2 is expected to stay up in the atmosphere, thus amplyfying the greenhouse effect.
But that's not all. As the plankton is the first step in the food chain, it is essential for krill, which in turn is the main feed stock for predator fish like salmon, mackerel, herring, cod and baleen whales. Projections show that for example pteropods, one millimeter small snails, will not be able to form their aragonite shells by 2050, when atmospheric CO2 levels have reached twice the preindustrial level. Whether they will become extinct or migrate further south is anybody's guess.
Johannessen argues that the northern seas will face the worst acidification: “Arctic regions will go into trouble. As more CO2 gets into the cold water, acidification is stronger and organisms will suffer more. That's the simple reason.”
Accelerating global warming and warmer acidic oceans that spawn ever fewer fish. That's hardly a future to look out for. Remember, says Johannessen, these are projections. The projected CO2-rise of 700 ppm by 2100 can be prevented. Johannessen: “It is still possible to do something, but has to be done fast. A reduction of 50 to 80 percent (in greenhouse gas emissions) is needed.”
A recent setback for the CarboOcean research, and not only for them, is the announced closure of the world's last stationary wheathership MV Polarfront, located at 66 degrees latitude, some 450 kilometres off the Norwegian coast. It is of extraordinary importance for climate change research since it has provided long-term measurements. Closure would mean termination of these series, including Johannessen's CO2 measurement aboard. He hopes a recent article in Nature (June 11th, 2009) will help to convince the Norwegian government to revise or to postpone their decision.