Lunch Talk Series by Earth, Ocean and Atmospheric Sciences (EOAS) Thrust, HKUST (GZ) - Can Ocean Alkalinity Enhancement be used as a Negative Emission Technology?

With sustained year-on-year increases in anthropogenic CO2 emissions and a failure of existing policies to meet a target of limiting global warming to <1.5°C, there is increasing interest in Negative Emission Technologies (NETs). NETs are concepts to activity remove CO2 from the atmosphere. Marine-based NETs are potentially advantageous compared to lab-based NETs due to less competition for land space. However, whilst several concepts have been explored as potentially scalable carbon sinks, no marine-based NETs have yet been proven to be safe, cost-effective and viable at the gigaton CO2 year-1 scale. A relatively new NET concept is Ocean Alkalinity Enhancement. Ocean Alkalinity Enhancement proposes to artificially raise alkalinity in natural waters in order to stabilize higher concentrations of dissolved inorganic carbon and induce drawdown of CO2 from the atmosphere. Theoretically, Ocean Alkalinity Enhancement would be possible with low uncertainties compared to techniques using organic carbon sinks because it relies purely on a chemical process. Furthermore, the basic parameters required to measure and verify the underlying carbon fluxes (e.g. pCO2, TA, DIC) are widely measured in existing monitoring networks. But might the method have ecological or biogeochemical side-effects? How efficient will it prove under realistic field conditions? And where could we realistically source sufficient alkalinity from to supply a carbon negative Ocean Alkalinity Enhancement industry? In order to answer some of these questions, in 2023 we hosted two large 100,000 L scale incubation experiments in Daya Bay to test the basic theory of Ocean Alkalinity Enhancement using Mg(OH)2 additions to seawater under contrasting wet/dry season conditions. Dr Hopwood will present the first results from these experiments, evaluating the potential for undesired ecological/biogeochemical side-effects and constraining inefficiencies which require further analysis.

负排放技术（NET）可直接去除大气中二氧化碳，减少人为碳排放对气候的影响，而提高海洋水体碱度、提升海洋二氧化碳吸收能力是目前NET领域的研究和工程热点。本报告将展示在深圳大亚湾开展的两次大型现场实验，向海水中添加氢氧化镁以增强海水碱度，以对比干湿季节海洋吸收碳的潜力，进而对不良生态/生物地球化学副作用进行评估，探索进一步提高海洋固碳效率的手段。