The ocean is a giant buffering system: heat and gases are exchanged at the air–ocean interface, helping to regulate Earth's climate. One-third of all anthropogenic CO2 released to the atmosphere has been soaked up by the oceans, significantly mitigating the climate impacts of increasing anthropogenic emissions. This service, however, comes at a cost: the increased CO2 uptake has resulted in shifts in seawater chemistry. Acidity has increased and the saturation state of carbonate minerals — the building blocks for the shells of marine organisms — has decreased. The impacts of this effect, known as ocean acidification, include shell dissolution in marine organisms and alteration of food webs, as well as other potential ecosystem-level changes that are not yet fully understood.
To constrain the sub-seasonal to interannual variability of carbonate chemistry, Adrienne Sutton and colleagues compile a set of high-frequency observations from twelve moorings across three different oceanic regions: open ocean (subtropical and subarctic), coastal ocean and coral reefs. They determine the monthly surface seawater pH and aragonite saturation state at each of these sites since 2010 and compare them with estimates of pre-industrial conditions. In this way they identify regions where current variability goes beyond pre-industrial bounds (Biogeosciences 13, 5065–5083; 2016).
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