| Abstrakt: |
Ocean Alkalinity Enhancement (OAE) is an ocean‐based Carbon Dioxide Removal (CDR) method to mitigate climate change. Studies to characterize regional differences in OAE efficiencies and biogeochemical effects are still sparse. As subduction regions play a pivotal role for anthropogenic carbon uptake and centennial storage, we here evaluate OAE efficiencies in the subduction regions of the Southern Ocean, the Northwest Atlantic, and the Norwegian‐Barents Sea region. Using the ocean biogeochemistry model FESOM2.1‐REcoM3, we simulate continuous OAE globally and in the subduction regions under high (SSP3‐7.0) and low (SSP1‐2.6) emission scenarios. The OAE efficiency calculated by two different metrics is higher (by 8%–30%) for SSP3‐7.0 than for SSP1‐2.6 due to a lower buffer factor in a high‐CO2 ${\mathrm{C}\mathrm{O}}_{2}$ world. All subduction regions show a CDR potential (0.23–0.31; PgC CO2 ${\mathrm{C}\mathrm{O}}_{2}$ uptake per Pg alkaline material) consistent with global OAE for both emission scenarios. Calculating the efficiency as the ratio of excess dissolved inorganic carbon (DIC) to excess alkalinity shows that the Southern Ocean and the Northwest Atlantic are as efficient as the global ocean (0.79–0.85), while the Norwegian‐Barents Sea region has a lower efficiency (0.65–0.75). The subduction regions store a fraction of excess carbon below 1 km that is 1.9 times higher than the global ocean. The excess surface alkalinity and thus CO2 ${\mathrm{C}\mathrm{O}}_{2}$ uptake and storage follow the mixed‐layer depth seasonality, with the majority of the excess CO2 ${\mathrm{C}\mathrm{O}}_{2}$ flux occurring in summer at shallow mixed layer depths. This study therefore highlights that subduction regions can be efficient for OAE if optimal deployment strategies are developed. Plain Language Summary: Increasing atmospheric CO2 ${\mathrm{C}\mathrm{O}}_{2}$ concentrations demand urgent reductions in the anthropogenic greenhouse gas emissions to limit the increase in global air temperatures to ≤2° ${\le} 2{}^{\circ}$C relative to preindustrial conditions. To compensate for/counteract the small fraction of unavoidable emissions, it will also be necessary to implement a portfolio of carbon dioxide removal (CDR) methods. In this study, we focus on the ocean‐based CDR method Ocean Alkalinity Enhancement (OAE), which enhances oceanic carbon uptake and can thus aid in atmospheric CO2 ${\mathrm{C}\mathrm{O}}_{2}$ reduction. Oceanic subduction regions are key for anthropogenic carbon uptake and its centennial storage. Therefore, we simulate OAE in the deep and bottom water formation regions of the Southern Ocean, Northwest Atlantic and the Norwegian‐Barents Sea region to assess their carbon uptake and storage efficiency compared to the global ocean. We find that the subduction regions exhibit equivalent carbon uptake efficiency to the global ocean, and are nearly two times more effective in deep ocean carbon storage with respect to OAE. Seasonal mixed layer depth variability, however, influences the resulting surface alkalinity concentrations and thus CO2 ${\mathrm{C}\mathrm{O}}_{2}$ uptake and DIC accumulation. Therefore, our study emphasizes that the subduction regions can be efficient for OAE when appropriate deployment strategies are developed. Key Points: Southern Ocean and Northwest Atlantic Ocean Alkalinity Enhancement efficiencies are akin to the global ocean and larger than in the Norwegian‐Barents Sea regionThe subduction regions can store a fraction of excess carbon in the deep ocean that is nearly two times higher than in the global oceanSeasonal mixed layer depth variations govern excess surface alkalinity concentrations and thus the excess carbon uptake and storage [ABSTRACT FROM AUTHOR] |
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