Increase in ocean acidity variability and extremes under increasing atmospheric CO2

Details

• Journal Title:
  Biogeosciences
• Personal Author:
  Burger, Friedrich A. ; John, Jasmin G. ; Frölicher, Thomas L.
• NOAA Program & Office:
  OAR (Oceanic and Atmospheric Research) ; GFDL (Geophysical Fluid Dynamics Laboratory)
• Description:
  Ocean acidity extreme events are short-term periods of relatively high [H+] concentrations. The uptake of anthropogenic CO2 emissions by the ocean is expected to lead to more frequent and intense ocean acidity extreme events, not only due to changes in the long-term mean but also due to changes in short-term variability. Here, we use daily mean output from a five-member ensemble simulation of a comprehensive Earth system model under low- and high-CO2-emission scenarios to quantify historical and future changes in ocean acidity extreme events. When defining extremes relative to a fixed preindustrial baseline, the projected increase in mean [H+] causes the entire surface ocean to reach a near-permanent acidity extreme state by 2030 under both the low- and high-CO2-emission scenarios. When defining extremes relative to a shifting baseline (i.e., neglecting the changes in mean [H+]), ocean acidity extremes are also projected to increase because of the simulated increase in [H+] variability; e.g., the number of days with extremely high surface [H+] conditions is projected to increase by a factor of 14 by the end of the 21st century under the high-CO2-emission scenario relative to preindustrial levels. Furthermore, the duration of individual extreme events is projected to triple, and the maximal intensity and the volume extent in the upper 200 m are projected to quintuple. Similar changes are projected in the thermocline. Under the low-emission scenario, the increases in ocean acidity extreme-event characteristics are substantially reduced. At the surface, the increases in [H+] variability are mainly driven by increases in [H+] seasonality, whereas changes in thermocline [H+] variability are more influenced by interannual variability. Increases in [H+] variability arise predominantly from increases in the sensitivity of [H+] to variations in its drivers (i.e., carbon, alkalinity, and temperature) due to the increase in oceanic anthropogenic carbon. The projected increase in [H+] variability and extremes may enhance the risk of detrimental impacts on marine organisms, especially for those that are adapted to a more stable environment.
• Keywords:
  Atmospheric Chemistry Carbon Dioxide Ocean Acidification Atmospheric Chemistry Carbon Dioxide Ocean Acidification
• Source:
  Biogeosciences, 17, 4633–4662, 2020
• DOI:
  https://doi.org/10.5194/bg-17-4633-2020
• Document Type:
  Journal Article
• Place as Subject:
  Antarctic Ocean
• Rights Information:
  CC BY
• Compliance:
  Submitted
• Main Document Checksum:
  urn:sha256:108dd8cd11b7e750a0379dc15186699a810493b215798b6ec68521b51b65406e
• Download URL:
  https://repository.library.noaa.gov/view/noaa/29810/noaa_29810_DS1.pdf
• File Type:
  [PDF - 12.42 MB ]