Ocean Acidification is one of the three things that our delegation wanted to spread the word about at this conference. It has turned out to be a major theme among the scientists at the conference since the handful of other ocean science groups also realized that there was a need for outreach on this topic.
Ocean Acidification is also known as the “other CO2 problem.” It refers to the chemical reaction between water and carbon dioxide to form a weak acid. This is not quite the same thing as “acid rain” since that term generally refers to the creation of much stronger acids being formed in un-buffered rain water interacting with sulfur and nitrogen based compounds. The ocean is reasonably well buffered against (resistant to) changes in its pH from the addition of acids, but it is not immune to the effects.
There are layers of complexity, but the simplest picture is still fundamentally correct: more carbon dioxide in the atmosphere means more carbon dioxide in the oceans, more carbon dioxide in the oceans means more acid formation in the ocean, more acid formation means a lower ocean pH a.k.a. a more acidic ocean.
The extra CO2 that we’ve added to the atmosphere has made its way into the oceans already, and the pH has dropped by about 0.1 units already in response to our emissions. The pH scale is a little strange, so a drop of 0.1 units means that the water is actually about 30% more acidic. The ocean is slightly on the basic end of the scale on average (a bit over 8 at the surface, a bit over 7.5 at the bottom), so becoming a little more acidic isn’t going to melt the casual swimmer’s eyes or anything bizarre like that. However, as you might expect, life in the ocean has evolved to thrive in these higher pH conditions.
The main cause for concern comes from the reaction of this water-and-carbon-dioxide acid with a molecule in seawater called “carbonate” to form another common molecule in seawater called “bicarbonate.” This decreases the concentration of carbonate floating around. This is the same carbonate that could otherwise be used to form calcium carbonate, or the stuff found in chalk. Chalk and limestone are actually the calcium carbonate shells of tremendous numbers of dead microscopic plankton. Several very common varieties of modern plankton also make their shells out of calcium carbonate. When you consider that some of these plankton types are key components of the base of the food web in the ocean, the potential problem becomes apparent. Experimentation suggests that these organisms are increasingly going to make shells at a slower rate and with greater difficulty as carbonate becomes more scarce. Experiments using the carbon dioxide concentrations expected by the end of the century suggest that these shells will eventually dissolve in some surface seawater. Any ocean life that relies on a shell is also likely to have similar problems, and I understand that some oysters and clams show greatly reduced shell thicknesses already in modern conditions. Coral polyps also make their homes in calcium carbonate structures (the coral), and the reduced calcification rates are a likely additional threat to these species (along with warming induced bleaching, nutrient runoff, turbidity, dynamite fishing, and over fishing higher up in the food chain leading to over-predation…corals have it rough these days). Collectively acidification has a very real potential to rearrange the base of most ocean ecosystems. Ecosystems are known to adapt when change comes gradually but, as with global warming, this pH change is happening faster than any dramatic past ocean pH change we have record of. Naturally, past more-gradual acidification events also marked widespread mass-extinctions. It’s not definite that this will be large problem for humanity, but it is clear that it could be an enormous problem for the oceans and the ~50% of humanity that relies on the sea for its primary source of protein. We really need to take a closer look at how ocean ecosystems respond to the plight of it’s shell-formers. In the mean time, it is one heck of another big reason to stop dumping carbon dioxide into the atmosphere.
As I alluded to in a past entry there was an interesting exchange regarding ocean acidification at an early meeting…sadly my notes are nigh-illegible so the italicized text from here on out is paraphrases of my tattered memories. First the IPCC scientists presented acidification in their briefing as something that is almost definitely going to be in the next IPCC report (AR5). Two scientists in the audience then asked whether any mention of ocean acidification has been made to the decision makers formally and, if not, why not. They responded that no, the mandate of the IPCC is to release the reports on a preset time table after the standard multi-year review process and that to go beyond that would be to overstep their bounds.
At the same Q and A the question was asked how can you claim to not be involved in advocacy and still say ‘urgent action is needed (with respect to climate change).’ Rajendra Pachauri (I think) then responded that the full sentence that the reporter was quoting was urgent action is needed if the temperature increase is to be limited to 2 degrees C and that that is one of several exact questions of science which the IPCC is charged with answering. I appreciate this guy for his ability to competently deal with attacks…this is the same guy that pointed out that the UAE scientist’s enemy’s work made it into the IPCC. My favorite bit from him came when asked if he is concerned that Saudi Arabia has been making such a big deal of the UAE leak…I would be concerned if they hadn’t! It is said that politics and oil mix well, but I’m not sure that oil and science mix so well. Yes, I’ll leave it at that.
–Brendan Carter, Scripps Oceanography graduate student