To address rising atmospheric carbon dioxide levels, a primary driver of global warming, geoengineering methods are being explored alongside decarbonization and energy-saving strategies. The ocean absorbs approximately one-quarter of human-produced carbon dioxide and stores roughly 50 times more carbon dioxide than the atmosphere, underscoring its potential as a significant site for carbon absorption and storage. Marine Carbon Dioxide Removal (mCDR) encompasses geoengineering techniques designed to artificially enhance the ocean's capacity for carbon absorption. mCDR includes the following approaches: (1) nutrient fertilization, (2) artificial upwelling and downwelling, (3) seaweed cultivation, (4) marine ecosystem restoration, (5) ocean alkalinity enhancement, and (6) electrochemical engineering. Although these methods are conceptually promising, limited knowledge and experience prevent their large-scale implementation in ocean waters to achieve meaningful reductions in atmospheric carbon dioxide. This report summarizes the findings from feasibility studies on the first four biogeochemical mCDR methods-nutrient fertilization, artificial upwelling and downwelling, seaweed cultivation, and marine and coastal ecosystem restoration-conducted by the National Academies of Sciences, Engineering, and Medicine. The summary is based on the original report and additional insights from the author.