A pair of environmental physicists at the Institute of Biogeochemistry and Pollutant Dynamics, ETH Zurich, has built a 3D model of the world's oceans and their currents to learn more about the depths that ocean acidification has reached due to increasing levels of carbon dioxide in the atmosphere. In their paper published in the journal Science Advances, Jens Müller and Nicolas Grube describe the factors that went into their model and what it showed them about ocean acidification around the globe.

Prior research has shown that in addition to warming the atmosphere, carbon emissions are also leading to warming of the world's oceans. Carbon dioxide in the air increases acidification of the oceans—the same process that makes carbonated beverages taste more acidic. Such increased acidification has led to problems for a variety of sea life, most notably corals, which have been dying.

In this new study, the research pair wanted to know how deep the acidification has gone, starting with the beginning of the industrial age. To find out, they built a model that emulates the world's oceans and the impacts of ever-increasing amounts of exposure to atmospheric carbon dioxide.

To create their model simulation, the researchers started with a standard ocean model. They added CO2 estimates for the years 1800, 1994, 2004 and 2014, using three signals for ocean acidification; proton concentrations, pH levels and aragonite saturation states. This allowed the model to calculate estimates of CO2 concentrations in the water at various depths over time.

The researchers found acidification moved deeper into the world's oceans over the study years, with an average depth of 1,000 meters by 2014. They also noted the depth varied depending on circumstances—the acidification went deeper, for example, in parts of the Atlantic meridional overturning current due to churning. In such places, increased acidification was seen as deep as 1,500 meters.

The researchers note that as acidification moves ever deeper, more ocean creatures will be affected. Pteropods, for example, may be most at risk because their shells are made from calcium, which dissolves in more acidic water.