Ocean acidity is increasing according to a new study

01/25/10 Matthew Cimitile
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In addition to making oceans warmers, greenhouse gasses like CO2 in the atmosphere are making oceans more acidic. More acidic oceans could hamper the growth and survival of shell-building organisms like corals and clams. By comparing pH readings from seawater in the northeastern Pacific Ocean between 1991 and 2006, a team of scientists found the first direct evidence of ocean acidification across an entire ocean basin.

WMNF sat down with Robert Byrne, a seawater chemist at the University of South Florida - St. Petersburg and principal investigator of the research team to talk about the implications of these findings, which are published in the current edition of the American Geophysical Union’s journal “Geophysical Research Letters”.

WMNF: The first question I have is, some people may view the effects of climate change and the pumping of CO2 into the atmosphere as more of a problem that will appear down the road, but this report shows us that it’s already having real effects on ocean chemistry; can you talk about the findings of this research?

Byrne: It is having an effect that is immediate. As we are putting CO2 in the atmosphere, one of the things that this study shows is that the pH change in the ocean, pH is being lowered, is changing in lockstep in near surface water with the CO2 changes in the atmosphere. We are seeing contemporary changes and in particular our study shows observations over the past 15 years across a whole ocean basin are showing substantial acidification effects. In the upper mix layer of the ocean down to maybe perhaps 100 meters or so, we are seeing an increase in this 15 year period of about 6 percent in the extent of ocean acidity.

WMNF: What effects does a lowering of pH have on oceans and marine organisms?

Byrne: There are many effects and those are some of the biggest questions that we have. What the quantitative effects are actually going to be. One of the most important effects is another chemically one, immediately. And that is that the carbonate ion concentration goes down correspondingly. Shells are made out of calcium and carbonate and so when levels of carbonate in the upper ocean decrease, calcareous organisms, organisms that calcify to make their structural parts are put in jeopardy and their shells can more easily dissolve. And these organisms experience greater difficulties in calcifying and building those shells as well.

WMNF: You compared data between 1991 and 2006, is it fair to say then that, being 2010, ocean area in this region could be even more acidic today?

Byrne: Yes, I think there is really no doubt about that. What the study showed was in the upper ocean, observations were in very close agreement with predictions. Predictions based upon what is happening to CO2 in the atmosphere would say that the pH should increase on a yearly basis by .0017 per year. So the overall change that we saw over the 15 year period was very close to predictions that would be based on what the CO2 compositions, what the carbon dioxide concentration was in the atmosphere in 1991 and what it got to be in 2006. So what that says is that our observations are in very close agreement with thermodynamics, what we would expect from equilibration with the Upper Ocean. So with the extra years that have gone by now, I think there is no question that the acidity is even greater, the pH is going down, and will continue to do so.

WMNF: Has pH been this low before or as low as what models project for the future?

Byrne: Well ph, according to models, hasn’t been this low for something on the order of a million years and maybe quite a bit more than that. Basically, over that period of time, you can make predictions like that, just from a knowledge of carbon dioxide levels in the atmosphere. We have an understanding of carbon dioxide levels in the atmosphere going back at least 800,000 years from looking at the CO2, the carbon dioxide composition in Antarctic ice cores. Carbon dioxide gets trapped in snow and that gets compressed and becomes part of the record, part of the chemical record in ice cores.

WMNF: Looking towards the future, are we looking at oceans continuing to take in more CO2 and become more acidic or is there a level at which the oceans can no longer take in anymore CO2, in which case that CO2 will remain in the atmosphere?

Byrne: It is predicted that based upon CO2 levels in the atmosphere, by the end of the next century, if we have a business as usual model for putting CO2 in the atmosphere and then have concentrations as high as 800 parts per million, that we could decrease the pH between now and the end of the century by another three-tenths of a pH unit approximately. Since pre-industrial times we have already decreased the pH by about a one-tenth of a pH unit. So the overall change, pre-industrial to the end of the century, if CO2 levels go to where they look like they might go with a business as usual model, that would be an overall change of about four-tenths of a pH unit and that means those calcite levels that I talked about could be decreased by a factor of 2.5 or so.

WMNF: My last question is how do we reduce the impact acidification is having on oceans?

Byrne: That is a great question and one that is very difficult to answer. Right now for the most part, what we are doing is trying to document what the changes are and to help us make projections through time. But the schemes for decreasing the impact of CO2, some of these schemes would involve certainly carbon sequestration. One of the best things that we can do of course is to decrease the rates at which we put CO2 into the atmosphere. One of the important aspects in all of this is just that our rates of change, of carbon dioxide in the atmosphere, are just remarkably fast, almost unprecedented at least over very long periods of time – 800,000 years maybe even millions of years and maybe even unique through Earth history, possibly. So it is these rapid changes through time that really are endangering ecosystems. So whatever we might do to slow down the rate that we put CO2 in the atmosphere would certainly help to damp a little bit the rate of change. CO2 rates of change in the atmosphere are going to continue to increase and our study shows for the most part, pH changes are going to move in lockstep with that. One of the points I’d like to make here is that pH is an extremely important ocean variable. It controls many kinds of processes; the ones I have talked about so far are just the carbonate ions concentration levels. But pH influences the ability potentially of organisms to require nutrients, it changes the rate of oxidation reduction reactions, there are just a myriad of effects that pH governs in the oceans.

Direct observations of basin-wide acidification of the North Pacific Ocean

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Hello Robert

Hello Robert This is indeed depressing reading. I think I experienced it to a certain degree when I was visiting Great Barrier Reef in July 2006. My daughter and I went snorkling in the surface and we did not see any colored corals, only grey and dead mussels. However it was close to an island and that might be the reason. Hope you are well and happy. I got this link for Tricia. Lots of regards from Lisbeth in DK