From carbon dioxide sink to acid bath

Leading journals knocked back Bradley Opdyke in the early 1990s when he tried to publish research giving some of the first hints that ocean acidification due to high atmospheric carbon dioxide levels could wreak havoc on marine ecosystems.
The work by the young scientist, then based at the University of Michigan, was zeroing in on a problem that researchers now fear will hit marine life hard: aberrations in ocean chemistry caused by surges in dissolved carbon dioxide.

It is now known that the casualties could be organisms such as coral and clams, which extract calcium carbonate from seawater to form their exoskeletons and shells.



The calcium carbonate shields of these organisms accumulate on the seafloor and eventually form big limestone deposits. Opdyke, now at the Australian National University, had compared marine limestone accumulation rates across the world with chemical signatures locked in the rocks to gauge the impact of ocean chemistry on the calcifying organisms. He focused on geological records stretching back 12,000 years to the start of the present interglacial, the Holocene epoch.

He found the limestone accumulation rate, typically up to 2m every 1000 years during the epoch, depended strongly on the carbonate chemistry of the ocean.

The implications were serious, but the world was only just starting to become conscious of the effect of increased atmospheric carbon dioxide levels on the temperature of the globe. It was deaf to warnings of another looming crisis, now dubbed “the other carbon dioxide problem”.

The American Journal of Science, the oldest scientific journal in the US that has been published continuously, eventually published the paper. However, it was not until Opdyke and colleagues published further research in the respected US journal Science in 1999 that the scientific community started to take notice. That team, led by Joan Kleypas of the National Centre for Atmospheric Research in Colorado, warned that changes in ocean chemistry due to rising carbon dioxide levels could threaten coral reefs by the middle of the 21st century.

Ten years after the Science paper, the scientific community is on board and scientists worldwide are stepping up their research effort on ocean acidification amid alarming projections for carbon dioxide emissions.

But there are big gaps in the knowledge and the problem is only now starting to register on the political radar. And, as in the early stages of the global warming argument, the ocean acidification debate has spawned a coterie of sceptics.

Even scientists worried about the problem are reluctant to sound the alarm until more results are in.

The oceans are a sink for carbon dioxide, taking up about 30 per cent of emissions caused by human activities. The burning of fossil fuel and deforestation could deliver marine ecosystems a double whammy: ocean warming due to the greenhouse effect and changes to ocean chemistry.

At worst, a shift in the delicate chemical balance of the oceans could cause an ecosystem crash, with the effect rippling through the food chain from plankton to whales. Australia’s multi-billion-dollar fishery and tourism industries are at risk. There are already signs that the Great Barrier Reef, which generates $4 billion in revenue a year, is being affected.

Cheryl Jones, The Australian, 5 August 2009. Article.

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