Recent ocean acidification trends from boron isotope (δ11B) records of coral: role of oceanographic processes and anthropogenic CO2 forcing

Abstract

Anthropogenic CO2 emission has resulted in lowering of surface ocean pH referred as ‘Ocean acidification (OA)’ which posed a serious threat to calcifying marine organisms. Several attempts have been made to assess the role of anthropogenic CO2 forcing against oceanographic factors/processes contributing to the recent OA trend; however, such attempts were hindered by the dearth of long-term pH records. Boron isotopic composition (δ11B) of corals has been used as a robust proxy for seawater pH records. In the present study, we have compiled available coral δ11B-pH records from the Indian, Pacific and Atlantic oceans and assessed regional trends, variability, forcing factors and their relative roles. Most of these δ11B-pH records show a discernable decline trend in recent decades with large variability. Our assessment of the Pacific records reveals that atmospheric CO2 forcing explains maximum pH variability followed by physical oceanographic factors/processes modulated by Pacific oscillations, e.g., ENSO and PDO. In addition, coral metabolic processes might control a large portion of the pH variability; however, they require detailed laboratory-based studies. Further, our investigation reveals a significant increase in pH variability (pH extremes) since ~1970s associated with ENSO events which might be critical for the resilience and adaptability of corals and other calcifiers.

Research Highlights

  • Since the industrial era (~1850), Coral δ11B-pH records show a discernible decreasing trend and a rapid decline since 1970.
  • Oceanographic processes control large inter-annual pH variability, whereas the long-term declining trend is driven by atmospheric CO2 forcing.
  • The pH extremes are predicted to increase in future warming scenarios, a threat to coral ecosystem.

Tarique M. & Rahaman W., 2022. Recent ocean acidification trends from boron isotope (δ11B) records of coral: role of oceanographic processes and anthropogenic CO2 forcing. Journal of Earth System Science 131: 165. doi: 10.1007/s12040-022-01907-z. Article (subscription required).

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