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不断上升的世界里，沿海植被生态系统中的碳汇可以在地质时间尺度上隔离二氧化碳，现在被称为“蓝碳”。海洋巨藻是一种高产的大型植物，目前覆盖约350万平方公里的沿海海底，每年为全球提供1521亿吨碳当量的净初级产量。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，这可以防止富含碎屑的沉积物的积累。但是，虽然MA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，为沿海带以外的海洋海底生态系统提供了重要的碳补贴和/或促进了海洋海底的长期碳埋藏。大陆架海以其丰富的碳储量而闻名，海洋峡湾最近被提议作为具有全球意义的主要碳汇，尽管它们的面积覆盖率很低，仅占全球年碳固存的11%。每单位面积，峡湾的有机碳埋藏率是全球海洋平均水平的100倍，峡湾沉积物的有机碳含量是海洋上升流区域下的生物沉积物的两倍。北极峡湾的研究表明，CMA对碳固存的贡献高达60%，这将使大型藻类成为蓝碳固存和全球生物地球化学循环的主要贡献者。然而，CMA的再矿化和固存都受到了很差的限制，而MA碎屑的实际重要性，以及因此CMA作为深层异源（汇）底栖生物群和沉积物的主要生态系统服务，仍然需要通过定量的、地理上受限的调查来解决。该项目将量化MA碳对碳固存的贡献，以及作为对深kongsjorden底栖动物的食物补贴，kongsjorden是研究最深入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Smeaton等人（2017）的方法建立MA衍生蓝碳的清单。现场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年的船期已经确定。虽然该项目将收集英国以外的数据，但其结果与英国直接相关，并且在苏格兰蓝碳论坛上展示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，提高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，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.