To keep global surface warming below 1.5°C by 2100, the portfolio of cost-effective CDR technologies must expand. To evaluate the potential of macroalgae CDR, we developed a kelp aquaculture bio-techno-economic model in which large quantities of kelp would be farmed at an offshore site, transported to a deep water “sink site”, and then deposited below the sequestration horizon (1,000 m). We estimated the costs and associated emissions of nursery production, permitting, farm construction, ocean cultivation, biomass transport, and Monitoring, Reporting, and Verification (MRV) for a 1,000 acre (405 ha) “baseline” project located in the Gulf of Maine, USA. The baseline kelp CDR model applies current systems of kelp cultivation to deep water (100 m) exposed sites using best available modeling methods. We calculated the levelized unit costs of CO₂eq sequestration (LCOC; $ tCO₂eq^-1). Under baseline assumptions, LCOC was $17,048 tCO₂eq^-1. Despite annually sequestering 628 tCO₂eq within kelp biomass at the sink site, the project was only able to net 244 C credits (tCO₂eq) each year, a true sequestration “additionality” rate (AR) of 39% (i.e., the ratio of net C credits produced to gross C sequestered within kelp biomass). As a result of optimizing 18 key parameters for which we identified a range within the literature, LCOC fell to $1,257 tCO₂eq^-1 and AR increased to 91%, demonstrating that substantial cost reductions could be achieved through process improvement and decarbonization of production supply chains. Kelp CDR may be limited by high production costs and energy intensive operations, as well as MRV uncertainty. To resolve these challenges, R&D must (1) de-risk farm designs that maximize lease space, (2) automate the seeding and harvest processes, (3) leverage selective breeding to increase yields, (4) assess the cost-benefit of gametophyte nursery culture as both a platform for selective breeding and driver of operating cost reductions, (5) decarbonize equipment supply chains, energy usage, and ocean cultivation by sourcing electricity from renewables and employing low GHG impact materials with long lifespans, and (6) develop low-cost and accurate MRV techniques for ocean-based CDR.

为了到 2100 年将全球地表温度保持在 1.5°C 以下，必须扩大具有成本效益的 CDR 技术组合。为了评估大型藻类 CDR 的潜力，我们开发了一种海带养殖生物技术经济模型，在该模型中，大量海带将在近海养殖场，运输到深水“汇点”，然后沉积在封存范围以下（1,000 米）。我们估算了位于缅因湾的 1,000 英亩（405 公顷）“基线”项目的苗圃生产、许可、农场建设、海洋养殖、生物质运输以及监测、报告和验证 (MRV) 的成本和相关排放， 美国。基线海带 CDR 模型使用最佳可用建模方法将当前的海带栽培系统应用于深水 (100 m) 暴露地点。我们计算了 CO 的平准化单位成本₂ eq 封存（LCOC；$ tCO ₂ eq ^-1）。在基线假设下，LCOC 为 17,048 美元 tCO ₂ eq ^-1。尽管每年在汇点的海带生物质中封存 628 tCO ₂ eq，但该项目每年只能净获得 244 C 信用（tCO ₂ eq），真正的封存“附加”率（AR）为 39%（即产生的净碳信用额与封存在海带生物量中的总碳的比率）。由于优化了我们在文献中确定的范围的 18 个关键参数，LCOC 降至 $1,257 tCO ₂ eq ^-1和 AR 提高到 91%，这表明可以通过流程改进和生产供应链的脱碳来大幅降低成本。海带 CDR 可能受到高生产成本和能源密集型操作以及 MRV 不确定性的限制。为了解决这些挑战，研发必须 (1) 降低农场设计的风险，最大限度地利用租赁空间，(2) 自动化播种和收获过程，(3) 利用选择性育种来提高产量，(4) 评估配子体的成本效益苗圃文化既是选择性育种的平台，也是降低运营成本的驱动力，(5) 通过从可再生能源采购电力和使用低温室气体影响的长寿命材料，使设备供应链、能源使用和海洋养殖脱碳，