New Method Measures How Ocean Acidification Impacts Marine Ecosystems

As carbon dioxide continues to enter out Earth's atmosphere, the ocean is continuing to acidify. Now, scientists have developed a new way to measure how this acidification is affecting marine ecosystems over an entire oceanic basin.

When CO2 enters our atmosphere, it also mixes with seawater. This accumulation of CO2 is slowly acidifying the surface waters of the ocean over time, making it more difficult for shelled organisms, such as corals, to build their calcium carbonate skeletons; the acidic waters eat away at these shells.

In order to better understand how ocean acidification impacts large areas, the scientists studied a 5,000 km stretch of ocean crossing the Red Sea, the Gulf of Aden and the Western Indian Ocean. They developed a new method to simultaneously assess the overall calcification rates of coral reefs and open sea plankton over a whole oceanic basin, based on variations in surface water chemistry.

The variations in water chemistry result from the tendency of organisms that precipitate calcium carbonate skeletons to replace some of the calcium with other elements, such as strontium. These replacements depend on growth conditions and are typical for each group of organisms.

In this case, the scientists estimated that plankton precipitate 80 percent of the Red Sea calcium carbonate and coral reefs precipitate 20 percent. This data in particular is crucial for tracking the effects of human activity over time, since it's not possible to see the change without having a baseline.

The findings are important for better understanding ocean acidification and how it's impacted reefs and other organisms over time. This could be especially important in the future as carbon dioxide concentrations continue to increase.

The findings are published in the journal Proceedings of the National Academy of Sciences.