Israeli scientists devise way to measure acidification for whole oceans

It’s easy to measure changes in acidity, and how it affects life, at one point. A whole ocean basin is a different kettle of fish.

Climate change is no longer controversial, and neither is the runaway acidification of the oceans. Accurately measuring the degree of acidification and its effect on marine life is easy to do for isolated spots. It’s very difficult to do for a whole ocean.

Now Israeli scientists at the Hebrew University of Jerusalem have announced a way to estimate acidification and its effect on a whole ocean basin, never mind that their paper comes 16 years after their fateful Red Sea cruise.

As the concentration of carbon dioxide in the air rises, more of the gas gets absorbed by the sea. The result is ocean acidification.

As the water becomes more acid, the concentration of calcium-based minerals that sea creatures – from oysters to corals to plankton – use to build shells and skeletons becomes scarcer.

Their shells and skeletons become more fragile, too. In acidic water, reefs develop a condition comparable to osteoporosis, which means that a big storm or even just big waves can cause them to shatter, leading to whole ecosystems to collapse.

Ecosystems on the brink of collapse are things people ought to know in advance, but obtaining data on global scales had been impossible. The breakthrough by the Hebrew University of Jerusalem team was achieved by sailing 5,000 kilometers, from the Red Sea resort city of Eilat through the Gulf of Aden to the Seychelles in the Indian Ocean, taking samples from the water surface for chemical testing as they went.

By the way, this cruise was in 1998. They haven’t been able to repeat it for political reasons.

The swashbuckling group was led by professors Boaz Lazar and Jonathan Erez and graduate student Zvi Steiner, with Prof. Amitai Katz, all from the Fredy and Nadine Herrmann Institute of Earth Sciences at the Hebrew University of Jerusalem, together with Prof. Aldo Shemesh and Dr. Ruth Yam of the Weizmann Institute of Science.

Only one thing changing

Lazar makes the point that the basic data is the same now as in 1998, so the delay in its analysis doesn’t matter. “The Red Sea is stable,” explains the professor, by which he means: the various parameters measured in the 1960s and in 1998, salinity for example, were much the same – with the exception of the water’s acidity.

Given that the other parameters are stable, the change in acidity cannot be because of change in circulation: “Not at all. It’s all because more C02 is getting into the water,” says Lazar.

They’d love for a new ship to sail the same route and get fresh measurements, but nobody seems to find the thought of a scientific cruise down the Red Sea “appetizing,” the professor understates.

Collapsing corals and pitiful plankton

As said, it’s trivial to obtain measurements at a single point. Making estimations for whole oceans is a whole other matter and to measure change in the oceanic carbon cycle, first one has to map the carbon cycle of life.

The team discovered that in the Red Sea, corals – which live only by the coasts and are rare relative to deep-sea plankton – are nonetheless responsible for a huge 20% of all calcium carbonate precipitation, with plankton responsible for the other 80%.

Knowing these ratios gives science a tool to monitor exactly how the rising concentration of carbon dioxide affects ocean acidification, Lazar explains.

It had been known how ocean acidification affected reefs – previous work the Hebrew University team did in Australia showed that from the 1960s to 2008-2009, the Great Barrier Reef’s rate of growth slowed by 30%, Lazar says. But until now, nobody knew how acidification affected the greatest part, the plankton in the open seas.

“We can say how much calcium carbonate deposition per year by plankton in the open sea versus the reefs on the margins, for the whole basin, giving us a tool to monitor how the rising concentration of carbon dioxide affects ocean acidification and ocean life as a whole,” Lazar explains.

This is an urgently needed tool. Since the Industrial Revolution began some 200 years ago, the acidity of the ocean surface has increased by 30% – and there’s a delay factor. The sea will take more time to absorb the carbon dioxide already in the air. Even if man were to cease all greenhouse-gas emissions today, the globe will get warmer and the oceans more acidic.

At a worst-case scenario, by this century’s end, the ocean surface could be 150 percent more acid than at the start of the industrial revolution, according to the U.S. National Oceanographic and Atmospheric Administration. We need to know that before it happens, not after.

Ruth Schuster, Haaretz, 27 November 2014. Article.

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