This week, we deep dive into a paper recently published in Environmental Research Communications. The study was led by H. J. Anderson from the Environment Research Unit of CSIRO in Hobart (Australia).
This study investigates Ocean Alkalinity Enhancement (OAE) as a marine carbon dioxide removal strategy. OAE involves adding alkaline substances to seawater to increase its capacity to absorb atmospheric CO₂, thereby mitigating climate change and ocean acidification. The authors focus on a high-resolution (200 m) simulation of OAE in a coastal channel near Woodbridge, Tasmania, where a field trial is planned.
The study reveals that the effectiveness of OAE in capturing atmospheric carbon dioxide is closely tied to seasonal ocean conditions. During summer months, the coastal waters near Woodbridge, Tasmania, become more stratified, meaning that surface and deeper waters mix less, which significantly enhances the efficiency of carbon uptake. In this period, around 60% of the added alkalinity is converted into dissolved inorganic carbon (DIC), indicating a strong sequestration potential. In contrast, during winter, when stratification weakens and mixing increases, the efficiency drops to about 46%. Interestingly, physical forces such as tidal currents and wind-induced mixing were found to have a secondary influence on the sequestration process compared to seasonal stratification. This highlights the importance of timing and local environmental conditions when planning OAE interventions.
In terms of environmental impact, the authors find that increasing the alkalinity of seawater leads to predictable and proportional increases in pH. This means that the chemical response of the water is well understood and can be controlled: for instance, the rate of alkalinity addition can be adjusted to remain within safe environmental limits, such as Australia’s regulatory threshold of a 0.2 unit pH increase. Simulations also show that these pH changes are not permanent. Natural processes, such as water movement and the ocean’s own uptake of carbon, help return pH levels to their original state over time. This suggests that, when carefully managed, OAE can be a reversible and environmentally safe method for carbon removal.
Here is a list of the main takeaways of this paper:
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Seasonal timing matters: OAE is more effective in summer due to stronger water column stratification, with differences in sequestration efficiency of over 30% between seasons.
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Local dynamics drive results, with wind and tides having less impact than expected, underscoring the need for high-resolution, site-specific modeling.
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Predictable chemical response: The relationship between alkalinity addition and pH change is linear and controllable, allowing for fine-tuning.
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Impacts are reversible: pH levels return to baseline as water mixes and absorbs CO₂ naturally, suggesting OAE can be safe and transient if properly managed.
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The study advances tools for monitoring, reporting, and verifying coastal OAE, bridging the gap between experimental trials and scalable climate solutions.
Read the full paper here: Ocean alkalinity enhancement in a coastal channel: simulating localised dispersion, carbon sequestration and ecosystem impact