Southern Ocean acidification revealed by Biogeochemical-Argo floats


Ocean acidification has potentially large impacts on calcifying organisms and ecosystems. Argo floats equipped with biogeochemical (BGC) sensors have been continuously measuring Southern Ocean pH since 2014. These BGC-Argo floats were deployed as part of the Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) project. Here we present a SOCCOM-era Objectively Mapped pH (SOM-pH) 2014-2019 climatology and explain the method for constructing this product. We show example SOM-pH fields demonstrating the spatial and temporal structure of Southern Ocean pH. Comparison with previous ship-based measurements reveals decreases in pH of up to 0.02 per decade, with a structure decaying with depth. An assessment of the trend structure reveals a pattern indicative of the meridional overturning circulation. Upwelling waters that have not been in recent contact with the atmosphere show negligible or small trends, while surface and downwelling waters that have had more exposure to the atmosphere show the strongest trends. Thus comparison of this new BGC-Argo mapped pH estimate to historic observations allows quantifying the structure of Southern Ocean acidification.

Key Points

  • We present a novel 12-month Southern Ocean pH mapped product, made possible by the Biogeochemical-Argo array initiated in 2014.
  • Comparing to ship-based measurements above 1500 m reveals a decrease in pH of up to 0.02 per decade.
  • pH changes are widespread with varying magnitudes reflecting the pattern of the meridional overturning circulation.

Mazloff M. R., Verdy A., Gille S. T., Johnson K. S., Cornuelle B. D. & Sarmiento J., 2023. Southern Ocean acidification revealed by Biogeochemical-Argo floats. Journal of Geophysical Research: Oceans 128: e2022JC019530. doi: 10.1029/2022JC019530. Article (subscription required).

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