Ocean Acidification

MOSS LANDING — The same thing attributed to creating global warming is having an unexpected side effect: a noisier ocean.

As carbon dioxide is pumped into the atmosphere, which many scientists blame for global warming, it is also being absorbed into the oceans, which are becoming more acidic and therefore noisier, according to researchers at the Monterey Bay Aquarium Research Institute.

A louder ocean could be problematic for marine animals like whales and dolphins that rely on sonar to navigate and find food.

Keith Hester, a researcher with the aquarium’s ocean chemistry team, and his colleagues predict sounds will travel 70 percent farther in 2050 as a result of increased carbon dioxide in the ocean.

“Eighty-five percent of all the carbon dioxide emitted into the atmosphere will go into the ocean,” said Peter Brewer, a co-author on the paper and expert on ocean acidification.



As the carbon dioxide dissolves in the ocean, it reacts with seawater and decreases the pH. The result: Over the past 200 years, the oceans have become 30 percent more acidic, according to published studies.

That means trouble for ocean life. Increased acidity lowers the pH and results in less carbonate ion available for animals that build shells out of calcium, like corals and shellfish. Smaller animals like algae and planktonic snails face the threat of dissolving completely in the acidic water.

It turns out that increased acidity also makes for a noisier ocean, according to a study published in the journal Geophysical Research Letters by marine chemists from the Monterey Bay Aquarium Research Institute last week.

Sound travels in waves. As those waves move through the ocean, they interact with salts and other molecules that absorb some of the energy, influencing how far the sound can travel.

In the 1960s and 1970s researchers realized sound traveled differently in the Pacific and Atlantic oceans and that the difference correlated with a change in pH. Hester and his colleagues took that a step further.

Using Intergovernmental Panel on Climate Change predictions for carbon dioxide emissions, they calculated future pH levels in the ocean. Using well-established sound absorption equations, they predicted that by 2050, sound will travel up to 70 percent farther in the world’s oceans. The more acidic pH reduces sound absorption and allows sound waves to travel farther.

Hester said the 70 percent value is an approximation.

“It could be less, but likely more,” he said.

Brewer agreed the estimates are conservative.

“Carbon dioxide is going up far faster than all projections, so it will probably happen sooner,” he said.

Because sounds will travel farther, “communication will be easier,” said James Harvey, a professor and marine mammal expert at Moss Landing Marine Labs. “But human-made sounds that we already know are problematic will be propagated further.”

Sound from commercial ships are particularly harmful for marine mammals, interfering with their ability to navigate, reproduce and find food.

And those sounds are increasing rapidly, according to Brandon Southall, director of National Oceanic and Atmospheric Administration’s Ocean Acoustics Program, and will likely compound noise issues relating to marine chemistry.

“The problem for marine mammals is that anthropogenic environmental changes are happening at such a rapid pace,” Harvey said.

But evolution happens much slower than such man-made shifts; many animal species will be incapable of adapting fast enough to the changes and won’t survive, Harvey said.

Changing ocean acoustics is only one aspect of ocean acidification, Brewer warns.

“You don’t just change one thing,” said Brewer. “It’s like peeling away layers of an onion. There is a cascade of things we are disturbing that are going to emerge. We are just in the early stages of uncovering them.”
Contact Cassandra Brooks at 429-2436 or jcopeland@santacruzsentinel.com.

Cassandra Brooks, Santa Cruz Sentinel, 9 October 2008. Article.