A new study from the Carnegie Institute has found that ocean acidification will, more and more frequently, increase the risk to marine organisms by heightening normal ocean chemistry changes as they occur overnight. 

The research involved a highly refined set of measurements made in tide pools, and it indicates that the organisms that are hit the hardest by the changes will likely be any creatures with shells or skeletons made from calcium carbonate. 

Acidification results when cars' and power plants' carbon dioxide emissions are absorbed into oceans. This alters the water chemistry, causing it to be more acidic. As the balance changes, organisms that usually make their outer protection (shells and exoskeletons) from calcium carbonate have a more difficult time building up those layers of protection. These creatures include oysters and mussels. If enough acid is present in an area, such shells and outer layers can dissolve completely. 

Tide pools are set off from the open ocean in low tide periods, separated by rocks from the larger wave action. During the day, oceans are acidified less because there's a counter action taking place. Plants are using a photosynthesis-like method to turn the energy from the sun and Earth's atmospheric carbon dioxide into sugar. This produces oxygen, draws carbon dioxide out of the seawater, and reverses the acidification. 

Nights are a different story. At that point, animals and plants respirate in their normal way, which uses oxygen and puts off carbon dioxide. With more CO2 entering the ocean water and no counter balance to the process, the risk to calcifying creatures increases. 

The research team team looked at several rocky, natural tide pools in the area contained by the UCDavis Bodega Marine Laboratory, 65 miles north of San Francisco. The study authors discovered that the pools' water at night was, indeed, very different than during the day. The pools in those hours grew acidic to the point of corroding calcium carbonate exoskeletons and shells. They learned that the rate at which the outer layers dissolved in nighttime periods was highly affected by the chemistry of the seawater. 

"Unless carbon dioxide emissions are rapidly curtailed, we expect ocean acidification to continue to lower the pH of seawater," noted Lester Kwiatkowski, the study's lead author. "This work highlights that even in today's temperate coastal oceans, calcifying species, such as mussels and coralline algae, can dissolve during the night due to the more-acidic conditions caused by community respiration."

The situation will likely progress, too. "If what we see happening along California's coast today is indicative of what will continue in the coming decades, by the year 2050 there will likely be twice as much nighttime dissolution as there is today. Nobody really knows how our coastal ecosystems will respond to these corrosive waters, but it certainly won't be well," co-author Ken Caldeira said. 

The findings were published in the March 18 issue of the journal Scientific Reports.

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