Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Journal topic
Volume 13, issue 6
Biogeosciences, 13, 1753–1765, 2016
https://doi.org/10.5194/bg-13-1753-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Biogeosciences, 13, 1753–1765, 2016
https://doi.org/10.5194/bg-13-1753-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 21 Mar 2016

Research article | 21 Mar 2016

Historical reconstruction of ocean acidification in the Australian region

Andrew Lenton1, Bronte Tilbrook1,2, Richard J. Matear1, Tristan P. Sasse3, and Yukihiro Nojiri4 Andrew Lenton et al.
  • 1CSIRO Oceans and Atmosphere, Hobart, Australia
  • 2Antarctic Climate and Ecosystems Co-operative Research Centre, Hobart, Australia
  • 3Climate Change Research Centre, Kensington Campus, University of New South Wales, Sydney, Australia
  • 4National Institute for Environmental Studies, Tsukuba, Japan

Abstract. The ocean has become more acidic over the last 200 years in response increasing atmospheric carbon dioxide (CO2) levels. Documenting how the ocean has changed is critical for assessing how these changes impact marine ecosystems and for the management of marine resources. Here we use present-day ocean carbon observations, from shelf and offshore waters around Australia, combined with neural network mapping of CO2, sea surface temperature, and salinity to estimate the current seasonal and regional distributions of carbonate chemistry (pH and aragonite saturation state). The observed changes in atmospheric CO2 and sea surface temperature (SST) and climatological salinity are then used to reconstruct pH and aragonite saturation state changes over the last 140 years (1870–2013). The comparison with data collected at Integrated Marine Observing System National Reference Station sites located on the shelf around Australia shows that both the mean state and seasonality in the present day are well represented, with the exception of sites such as the Great Barrier Reef. Our reconstruction predicts that since 1870 decrease in aragonite saturation state of 0.48 and of 0.09 in pH has occurred in response to increasing oceanic uptake of atmospheric CO2. Large seasonal variability in pH and aragonite saturation state occur in southwestern Australia driven by ocean dynamics (mixing) and in the Tasman Sea by seasonal warming (in the case of the aragonite saturation state). The seasonal and historical changes in aragonite saturation state and pH have different spatial patterns and suggest that the biological responses to ocean acidification are likely to be non-uniform depending on the relative sensitivity of organisms to shifts in pH and saturation state. This new historical reconstruction provides an important link to biological observations that will help to elucidate the consequences of ocean acidification.

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We reconstruct the observed variability and mean state in pH and aragonite saturation state around Australia at high spatial resolution and reconstruct the changes that have occurred in the Australian region over the last 140 years. We find that large changes in aragonite saturation state and pH have very different spatial patterns, which suggests that the biological responses to ocean acidification are likely to be non-uniform and dependent on the relative sensitivity of organisms to change.
We reconstruct the observed variability and mean state in pH and aragonite saturation state...
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