Projected acidification of the Great Barrier Reef could be offset by ten years

The research, by CSIRO Oceans and Atmosphere, Hobart, used a high-resolution model developed for the Great Barrier Reef region to study the impact of artificial ocean alkalinization on the acidity of the waters in the Great Barrier Reef. The study is based on the use of existing shipping infrastructure to inject a source of alkalinity into the ocean, which could also be considered as an acceleration of the chemical weathering of minerals through natural processes. Their results are published today in the IOP Publishing journal Environmental Research Letters.

The Great Barrier Reef is a globally significant coral reef system that supports productive and diverse ecosystems. At present, it is facing unprecedented stress from ocean warming, tropical cyclones, sediment and nutrient runoff, marine pests, and ocean acidification. Among these stressors, ocean acidification represents one of the most significant threats to the long-term viability of the reef, since it impacts the ability of the corals to build and repair their hard structures and recover from bleaching events.

In response to the declining health of coral reef ecosystems, a wide range of potential intervention concepts and technologies are currently under consideration, with the goal of minimising environmental pressures and enhancing the resilience of the coral reef ecosystem. These include active and direct environmental engineering approaches, such as artificial ocean alkalinization, a technique to offset or ameliorate the changes associated with ocean acidification and enhance oceanic carbon uptake. Essentially, artificial ocean alkalinization involves adding a source of alkalinity, such as olivine, to seawater, thereby "reversing" the shift in the carbon chemistry equilibrium process that occurs when the ocean takes up anthropogenic carbon. Olivine is an abundant mineral resource, which is already mined near the Great Barrier Reef.

The goal of this study was to investigate the reduction of the impact of ocean acidification on a scale hitherto unconsidered. According to the authors, "The majority of the artificial ocean alkalinization modeling studies to date have focused on the potential for alkalinization as a carbon dioxide removal technique. Few studies have explored the role of alkalinization with a focus on offsetting the changes associated with ocean acidification at a regional scale." The study therefore used a recently developed 4 km-resolution coupled hydrodynamic-biogeochemical model, validated for the Great Barrier Reef region, which allowed the simulation of the impact of the alkalinity injection on individual reefs along the length of the Great Barrier Reef (~2,000 km) for the first time. The results showed that by releasing the alkalinizing agent from an existing shipping lane, the resulting de-acidification would reach almost the whole of the Great Barrier Reef.

This report describes the novel and timely use of a regional model as a testbed for an ocean acidification mitigation technique. The study found that, by assuming the use of existing shipping infrastructure (a bulk carrier releasing 30,000 tons per day) as the alkalinity delivery mechanism, artificial ocean alkalinization would offset or ameliorate the projected acidification by ten years on 250 reefs. In doing so, it would also sequester 35,000 t of carbon in the ocean per year, or 0.0001% of the current global CO₂ emissions.