Assessing the technical aspects of ocean-alkalinity-enhancement approaches

Abstract

Abstract. Ocean alkalinity enhancement (OAE) is an emerging strategy that aims to mitigate climate change by increasing the alkalinity of seawater. This approach involves increasing the alkalinity of the ocean to enhance its capacity to absorb and store carbon dioxide (CO2) from the atmosphere. This chapter presents an overview of the technical aspects associated with the full range of OAE methods being pursued and discusses implications for undertaking research on these approaches. Various methods have been developed to implement OAE, including the direct injection of alkaline liquid into the surface ocean; dispersal of alkaline particles from ships, platforms, or pipes; the addition of minerals to coastal environments; and the electrochemical removal of acid from seawater. Each method has its advantages and challenges, such as scalability, cost effectiveness, and potential environmental impacts. The choice of technique may depend on factors such as regional oceanographic conditions, alkalinity source availability, and engineering feasibility. This chapter considers electrochemical methods, the accelerated weathering of limestone, ocean liming, the creation of hydrated carbonates, and the addition of minerals to coastal environments. In each case, the technical aspects of the technologies are considered, and implications for best-practice research are drawn. The environmental and social impacts of OAE will likely depend on the specific technology and the local context in which it is deployed. Therefore, it is essential that the technical feasibility of OAE is undertaken in parallel with, and informed by, wider impact assessments. While OAE shows promise as a potential climate change mitigation strategy, it is essential to acknowledge its limitations and uncertainties. Further research and development are needed to understand the long-term effects, optimize techniques, and address potential unintended consequences. OAE should be viewed as complementary to extensive emission reductions, and its feasibility may be improved if it is operated using energy and supply chains with minimal CO2 emissions.

Impact of marine carbon removal on atmospheric CO2

“…However, such shift necessitates a reevaluation of the energy considerations originally associated with stationary removal facilities and logistical management of by-products. For instance, electrolytic and electrodialytic processes of generating alkalinity from brine, by-products include gases and aqueous acids (Eisaman et al 2023). Managing these by-products, particularly in large quantities, poses environmental and safety risks.…”

“…There are significant variations in CDR methods, encompassing their development stages, removal mechanisms, carbon storage duration, and overall impacts (Mathesius et al 2015, Bach et al 2023. This spectrum ranges from emerging technologies like ocean alkalinisation (Eisaman et al 2023), which are still in their nascent stages, to more established practices like reforestation (Melnikova et al 2023). Understanding the benefits, risks, and trade-offs of each method is crucial for assessing the feasibility and effectiveness of different CDR approaches in the context of global climate goals.…”

Effects of grain size and seawater salinity on magnesium hydroxide dissolution and secondary calcium carbonate precipitation kinetics: implications for ocean alkalinity enhancement

“…Over long timescales, the natural CO2facilitated weathering of alkaline rocks supplies alkalinity to the oceans, influencing its CO2 uptake potential and storage. OAE builds upon this weathering feedback in the Earth System and can be accomplished by actively spreading pulverized alkaline minerals in and around marine environments or electrochemically removing acidity from seawater (Eisaman et al, 2023). In both cases, the seawater total alkalinity (TA) is increased thereby increasing the storage capacity of seawater for atmospheric CO2 (GESAMP, 2019, Kheshgi, 1995.…”

Ocean Alkalinity Enhancement (OAE) does not cause cellular stress in a phytoplankton community of the sub-tropical Atlantic Ocean

“…The subsequential alkalinity increase causes a change in the speciation of inorganic carbon in seawater, creating new space for the absorption of additional atmospheric CO2 (Hartmann et al, 2013). There are different methods of OAE to promote atmospheric carbon sequestration (Renforth and Henderson, 2017;Eisaman et al, 2023). OAE can be achieved through the weathering of limestone by the addition of carbonates, as hereby presented, through the weathering of silicate minerals such as the iron-containing mineral olivine, through electrochemical processes used to generate alkalinity from chloride brines and by additions of hydrated-carbonate-minerals to seawater and ground minerals to the shelf seafloor.…”