The levels of carbon dioxide and other greenhouse gases like methane and nitrous oxide have been steadily rising for many years due to a variety of human activities, like the burning of fossil fuels and changes in land use. These levels aren't only rising in the air; they are also rising in the oceans. According to the National Oceanic and Atmospheric Administration (NOAA), the oceans are absorbing around thirty percent of atmospheric carbon dioxide (CO2), which is increasing oceanic CO2 levels as well.
Different chemical reactions occur in seawater during the absorption of CO2, increasing the levels of hydrogen ions, and reducing carbonate ion levels in the water. Together, water (H2O) and CO2 form carbonic acid (H2CO3), which is a weak acid that breaks apart into hydrogen ions (H+) and bicarbonate ions (HCO3), and the process changes the pH of the ocean. The pH scale is logarithmic, so even tiny changes can have big impacts. Since the start of the industrial revolution about 200 years ago, sea surface pH has dropped by 0.1 pH units, which translates into roughly a thirty percent increase in acidity. These changes are stressing a variety of animals and plants in the oceans.
Scientists have now developed a three dimensional model of the world's oceans to learn more about how deeply ocean acidification is moving into the depths of the sea. The investigators used the model to estimate the concentrations of CO2 at different depths over time. The work showed that ocean acidification has continued to move deeper into the oceans over time, reaching an average depth of 1,000 meters by 2014. The findings have been reported in Science Advances.
This research also showed that the depth of ocean acidification was dependent on various factors as well, such as churning. In some places the depth of ocean acidification was estimated to be deeper, at around 1,500 meters.
The study authors noted that as acidification gets deeper, it will affect more marine animals. Many sea creatures with shells that are made of calcium are already impacted, since those shells dissolve is more acidic water. But those impacts will reach even more animals as it penetrates deeper into the ocean.
Sources: National Oceanic and Atmospheric Administration (NOAA), Phys.org, Science Advances