Ocean Acidification: Saturation State

Ocean Acidification: Saturation State thumbnail

Description

Ocean acidification is an often overlooked consequence of humankind's release of carbon dioxide emissions into the atmosphere from fossil fuel burning. Excess carbon dioxide enters the ocean and reacts with water to form carbonic acid, which decreases ocean pH (i.e., makes seawater less basic), and lowers carbonate ion concentrations. Organisms such as corals, clams, oysters, and some plankton use carbonate ions to create their shells and skeletons. Decreases in carbonate ion concentration will make it difficult for these creatures to form hard structures, particularly for juveniles. Ocean acidification may cause some organisms to die, reproduce less successfully, or leave an area. Other organisms such as seagrass and some plankton species may do better in oceans affected by ocean acidification because they use carbon dioxide to photosynthesize, but do not require carbonate ions to survive. Ocean ecosystem diversity and ecosystem services may therefore change dramatically from ocean acidification.

This datasets shows computer model simulations of surface ocean aragonite saturation state from 1861 to 2100, based on historical data and future projections of carbon dioxide emissions, with continents and coral reefs in purple marked. Aragonite saturation state is commonly used to track ocean acidification because it is a measure of carbonate ion concentration. Aragonite is one of the more soluble forms of calcium carbonate and is widely used by marine calcifiers (organisms with calcium carbonate structures). Corals and other calcifiers are more likely to survive and reproduce when the saturation state is greater than three. When aragonite saturation state falls below 3, these organisms become stressed, and when saturation state is less than 1, shells and other aragonite structures begin to dissolve. The predicted pH decrease of approximately 0.3 units during the 21st century would be a greater change than possibly at any time in the last 300 million years.

The model simulation is driven with atmospheric emissions based on records of atmospheric carbon dioxide levels for past dates, and the CMIP5 IPCC RCP 8.5 scenario for future dates (approx. 950 ppm atmospheric CO2 by 2100).

Notable Features

  • Decreases in carbonate ion concentration will make it difficult for these creatures to form hard structures, particularly for juveniles
  • Aragonite saturation state is commonly used to track ocean acidification because it is a measure of carbonate ion concentration.
  • When aragonite saturation state falls below 3, these organisms become stressed, and when saturation state is less than 1, shells and other aragonite structures begin to dissolve.

Related Datasets