To limit global warming below 2°C by 2100, we must drastically reduce greenhouse gas emissions and additionally remove ~100–900 Gt CO₂ from the atmosphere (carbon dioxide removal, CDR) to compensate for unavoidable emissions. Seaweeds (marine macroalgae) naturally grow in coastal regions worldwide where they are crucial for primary production and carbon cycling. They are being considered as a biological method for CDR and for use in carbon trading schemes as offsets. To use seaweeds in carbon trading schemes requires verification that seaweed photosynthesis that fixes CO₂ into organic carbon results in CDR, along with the safe and secure storage of the carbon removed from the atmosphere for more than 100 years (sequestration). There is much ongoing research into the magnitude of seaweed carbon storage pools (e.g., as living biomass and as particulate and dissolved organic carbon in sediments and the deep ocean), but these pools do not equate to CDR unless the amount of CO₂ removed from the atmosphere as a result of seaweed primary production can be quantified and verified. The draw-down of atmospheric CO₂ into seawater is via air-sea CO₂ equilibrium, which operates on time scales of weeks to years depending upon the ecosystem considered. Here, we explain why quantifying air-sea CO₂ equilibrium and linking this process to seaweed carbon storage pools is the critical step needed to verify CDR by discrete seaweed beds and nearshore and open ocean aquaculture systems prior to their use in carbon trading.

中文翻译：

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空气-海洋二氧化碳平衡：是否可以使用海藻来抵消碳去除？

为了到 2100 年将全球变暖幅度限制在 2°C 以下，我们必须大幅减少温室气体排放，并另外从大气中去除约 100–900 Gt CO ₂（二氧化碳去除，CDR）以补偿不可避免的排放。海藻（海洋大型藻类）自然生长在世界各地的沿海地区，对初级生产和碳循环至关重要。它们被认为是 CDR 的生物方法，并作为抵消在碳交易计划中使用。要在碳交易计划中使用海藻，需要验证将 CO ₂固定为有机碳的海藻光合作用会产生 CDR，并安全可靠地储存从大气中去除的碳 100 多年（封存）。关于海藻碳储存库的规模（例如，作为活生物量以及作为沉积物和深海中的颗粒和溶解有机碳）正在进行许多研究，但这些碳库并不等于 CDR，除非从海藻中去除的 CO 2_量海藻初级生产造成的大气环境可以量化和验证。大气CO ₂进入海水是通过气海CO ₂平衡实现的，其运行时间尺度为数周至数年，具体取决于所考虑的生态系统。在这里，我们解释了为什么量化海气CO ₂平衡并将这一过程与海藻碳储存池联系起来是在将离散海藻床以及近岸和公海水产养殖系统用于碳交易之前验证CDR所需的关键步骤。