The efficacy and impacts of large-scale ocean alkalinity injection

Chair: Jessica Ericson

Andrew Lenton (1), David Keller (2), Viviane Scott (3), Naomi Vaughan (3)
1 CSIRO Oceans and Atmosphere, Hobart, Australia
2 GEOMAR, Helmholtz Centre for Ocean Research, Kiel, Germany
3 University of Edinburgh, School of Geosciences, Edinburgh, UK
4 University of East Anglia, Tyndall Centre for Climate Change Research, Norwich, UK

Background
Ocean alkalinity addition has been proposed as technique to both buffer ocean acidification and enhance oceanic carbon uptake. While limited modelling studies to date have suggested that ocean alkalinity injection may play a role in mitigating ocean acidification, it is recognised that any large-scale Climate Intervention will likely impact the ecosystem services (e.g. food production) provided by the ocean, there will certainly be positive and negative effects on human societies, and on their responses and strategies for adaptation to a changing climate. In this context there is an identified need for ongoing research to explore the short and longer-term impacts of ocean alkalinity injection.

Methods
Here we present simulations of the oceanic response to ocean alkalinity from the Carbon Dioxide Removal Model Intercomparison Project (CDRMIP). This involves injecting large amounts of alkalinity into the upper ocean, in conjunction with RCP 8.5, in the period 2020-2100. This allows the efficacy of ocean alkalinity injection to be quantified and the biogeochemical response to this injection to be explored. CDRMIP is made up of a suite of earth system and intermediate complexity models.

Findings
We discuss and quantify the degree to which CDR could help mitigate ocean acidification or reverse its effect, and discuss the potential effectiveness and risks/benefits of different ocean alkalinity injection proposals. We also explore the impact of cessation of alkalinity injection and quantify the time-scales associated with this.

Conclusions
This work provides key insights into the potential of this technique to offset ocean acidification, and identifies where future efforts should be directed. It also highlights that alkalinity injection will likely result in areas of potential negative impact on the marine ecosystem. This work does not consider important issues such as how alkalizing substances could be mined, processed, transported, and delivered to the ocean in a form that would easily dissolve and enhance alkalinity.