Ocean acidification: Oceans passing critical CO2 threshold

From an article by Stephen Leahy on IPS News:

UXBRIDGE, Canada, Nov 24 (IPS) - An apparent rapid upswing in ocean acidity in recent years is wiping out coastal species like mussels, a new study has found.

"We're seeing dramatic changes," said Timothy Wootton of the Department of Ecology and Evolution at the University of Chicago, lead author of the study published Monday in the Proceedings of the National Academy of Sciences. The study shows increases in ocean acidity that are more than 10 times faster than any prediction.

"It appears that we've crossed a threshold where the ocean can no longer buffer the effects of CO2 in the atmosphere," Wootton told IPS.

For millions of years, the levels of carbon dioxide in the atmosphere and the ocean were in balance, but the burning of fossil fuels and deforestation has put more CO2 into the atmosphere over the last 150 years. The oceans have absorbed one-third -- about 130 billion tonnes -- of those human emissions and have become 30 percent more acidic as the extra CO2 combines with carbonate ions in seawater, forming carbonic acid.

Each day, the oceans absorb 30 million tonnes of CO2, gradually and inevitably increasing their acidity. There is no controversy about this basic chemistry; however, there is disagreement about the rate at which the oceans are becoming acidic and the potential impact.

The ocean's pH -- the measure of acidity or alkalinity -- has been declining, or becoming more acidic, at a rate of about 0.02 per decade since 1980, said Ulf Riebesell, a biological oceanographer at the Leibniz Institute of Marine Sciences in Kiel, Germany.

"We're just starting to realise the far-reaching impacts of ocean acidification," Riebesell told IPS, noting that the term ocean acidification was coined just four years ago.

Wootton and colleagues measured a massive pH decline of 0.4 units in just eight years off the northwest tip of Washington State in the U.S. And that abrupt increase has had a major impact on marine species in the tide pool on Tatoosh Island where the study was conducted.

"Large shell species like mussels and goose barnacles were dying at a faster rate and being replaced by other species," he said.

Increased seawater acidity means there is less calcium carbonate in the water for corals and shell-forming species like mussels and phytoplankton to grow or maintain their skeletons. The once verdant mussel beds in the study area were being replaced by algae, Wootton said.