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- Title
Ocean Acidity Extremes Altered by Variability Changes.
- Authors
Burger, Friedrich Anton; Frölicher, Thomas L.; John, Jasmin G.
- Abstract
The uptake of anthropogenic CO2 by the ocean reduces the increase in atmospheric CO2,but causes ocean acidification, i.e. a decrease in both pH and calcium carbonatesaturation. On top of this secular change, recent studies suggest that the seasonalcycle in ocean acidity will strongly change over the 21st century because of thenonlinearity in carbonate chemistry of the ocean seawater. An increase in variabilitypotentially leads to more frequent and intense short-term ocean acidification extremeevents. Here, we use daily output from global warming simulations with a comprehensive fullycoupled Earth system model (GFDL ESM2M) to quantify the impact of changesin daily, seasonal and interannual variability in ocean acidity ([H+]) on changesin different extreme event characteristics. The impact of variability changes onextremes is isolated by adding the mean shift of the distribution from the secularchange to the preindustrial threshold (the 99th percentile). We show that an increasein the variability of [H+] leads to a strong increase in the occurrence of extremeevents and to large changes in their characteristics at the global scale. The number ofdays with extreme [H+] conditions for surface waters more than doubles by theend of the 21st century compared to present day under the RCP4.5 greenhousegas emission scenario. At the same time, the duration and maximal intensity ofindividual events increase by about 50%. At subsurface, where extreme events tendto be longer lasting and more intense, similar trends in duration and intensity aresimulated, but the model projects a six-fold increase in the number of extreme eventdays. In addition, the volume extent of individual extreme events in the upper 200mof the water column triples over the 21st century. We show that the increase inthe [H+] seasonality is the dominant driver of changes in [H+] extreme eventsat the surface, whereas changes in interannual and daily variability are of similarimportance at 200m depth. Present day in-situ [H+] observations are analysed toconstrain the model’s capability of representing short-term variability in seawateracidity. An increase in variability and extreme events in ocean acidity under futureglobal warming will probably increase the risk of severe and detrimental impacts onmarine organisms, especially on those that are adapted to a more stable environment.
- Subjects
OCEAN acidification; OCEAN; ACIDITY; WATER; GLOBAL warming; TWENTY-first century
- Publication
Geophysical Research Abstracts, 2019, Vol 21, p1
- ISSN
1029-7006
- Publication type
Article