Is macroalgal carbon sequestration the 'elephant in the Blue Carbon room' ?

海洋植物吸收二氧化碳，在大气二氧化碳水平上升的世界中，沿海植被生态系统中的碳汇可以在地质时间尺度上封存二氧化碳，现在被称为“蓝碳”。海洋大型藻类（MA）是高生产力的大型植物，目前覆盖约350万平方公里的亚沿海海底，并提供1521 Tg C年-1的净初级生产全球。然而，它们在很大程度上被排除在蓝碳固存的估计之外，因为它们主要生长在坚硬的基质上，这阻止了富含碎屑的沉积物的积累。但是，虽然海洋生物碳（CMA）不能在源生态系统内积累，但据估计，高达82%的CMA从源生态系统输出到更深的海底栖息地，为沿海区以外的海洋海底生态系统提供了显著的碳补贴，并/或有助于在海底长期埋碳。大陆架海以其重要的碳储量而闻名，海洋峡湾最近被提议作为具有全球意义的主要碳汇，尽管其面积覆盖率低，占全球年度碳封存的11%。每单位面积，峡湾有机碳埋藏率是全球海洋平均水平的100倍，峡湾沉积物中的有机碳含量是海洋上涌区生物沉积物的两倍。在北极峡湾的研究表明，CMA贡献了高达60%的固碳，这将使大型藻类的主要贡献者蓝色固碳，和全球生物地球化学循环一般。然而，CMA的矿化和封存都受到很大的限制，MA碎屑的实际重要性，因此CMA，作为一个主要的生态系统服务，深异地（汇）底栖生物群和沉积物仍然需要解决的定量，地理上受到很好的限制调查。该项目将量化MA碳对碳固存的贡献，并作为对Kongsfjorden深海底栖动物的食物补贴，这是研究最多的北极峡湾系统之一。Kongsfjord数字景观模型和现有的沉积碳数据将允许基于斯米顿等人（2017年）的方法建立MA衍生蓝碳清单。实地工作将与其他计划中的工作一起在波兰研究船RV Oceania上进行。2021年的发货时间已经确定。虽然该项目将收集英国以外的数据，但其结果对英国具有直接相关性，例如在苏格兰蓝碳论坛上介绍结果将有助于快速转化为国家气候减缓和适应政策。气候变化是一个全球性问题，改善对蓝碳生态系统的理解和管理是地球系统科学和可持续经济的几个主题的核心，并与联合国可持续发展目标3，13和14直接相关。

Marine plants draw down CO2, and in a world of rising atmospheric CO2 levels carbon sinks in vegetated coastal ecosystems can sequester CO2 on geological time scales and are now referred to as 'Blue Carbon'. Marine macroalgae (MA) are highly productive macrophytes that currently cover approximately 3.5 million km2 of sublittoral seabed and provide 1521 Tg C yr-1 of net primary production globally. Nevertheless, they have largely been excluded from estimates of blue carbon sequestration because they predominantly grow on hard substrates, which prevent the accumulation of detritus-rich sediments. But while MA carbon (CMA) cannot accumulate within the source ecosystem, it has been estimated that up to 82% of CMA is exported from the source ecosystem to seabed habitats at greater depths, providing a significant carbon subsidy to marine seabed ecosystems beyond the coastal zone and/or contributing to long-term carbon burial in the ocean seabed. Shelf seas are known for their significant stocks of carbon, and marine fjords have recently been proposed as major C sinks of global significance, despite their low area coverage accounting for 11 % of global annual carbon sequestration. Per unit area, fjord organic carbon burial rates are one hundred times as large as the global ocean average, and fjord sediments contain twice as much organic carbon as biogeneous sediments underlying the upwelling regions of the ocean. Studies in Arctic fjords suggest that CMA contributes up to 60% to C sequestration which would render macroalgae a major contributor to blue carbon sequestration, and global biogeochemical cycles in general. Both remineralisation and sequestration of CMA are poorly constrained, however, and the actual importance of MA detritus, and hence CMA, as a major ecosystem service to deep allochthonous (sink) benthic biota and sediments still needs to be addressed in a quantitative, geographically well-constrained investigation. This project will quantify the contribution of MA carbon to C sequestration and as food subsidy to benthic fauna in deep Kongsfjorden, one of the best-studied Arctic fjord systems. The Kongsfjord digital landscape model and already available sedimentary C data will allow to build an inventory of MA- derived blue carbon based on methodology on Smeaton et al (2017). Field work will take place alongside other planned work on board the Polish research vessel RV Oceania. Shiptime for 2021 has already been secured. While this project will gather data outside the UK, its results are of immediate relevance for the UK and presentation of results for example at the Scottish Blue Carbon Forum will facilitate quick translation into national climate mitigation and adaptation policy. Climate change is a global issue, and improved understanding and management of Blue Carbon ecosystems is central to several of the themes of Earth systems science and sustainable economies, and directly relevant to UN SDGs 3, 13 and 14.