A MISSING LINK between continental shelves and the deep sea: Addressing the overlooked role of land-detached submarine canyons

大陆架和深海之间缺失的联系：解决与陆地无关的海底峡谷被忽视的作用

• 批准号: NE/X014975/1
• 负责人: Mike Clare
• 金额: $ 110.23万
• 依托单位: NATIONAL OCEANOGRAPHY CENTRE
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2024
• 资助国家: 英国
• 起止时间: 2024 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FX014975%2F1
• 关键词: MISSING; LINK; between; continental; shelves

This ambitious project will enable a step change in understanding of the sporadic but large flows of sediment, climatically-important organic carbon, and pollutants through submarine canyons, which connect continental shelves worldwide to the deep-sea. >9000 large submarine canyons occur on all the world's submerged margins, often dwarfing river systems in scale. Such canyons can transfer large quantities of natural sediments, organic carbon and nutrients that sustain important ecosystems, and are increasingly recognised as hotspots for seafloor pollution that threatens the biodiversity they host. The sediment flows that travel along canyons can be fast and dense, breaking cables that underpin global communications. It is therefore important to understand when and how such flows are triggered, the amount of material that is transported, and crucially, how these vary between types of canyon.Monitoring of turbidity currents has focused on 'land-attached' canyons fed by rivers or long-shore drift, where powerful turbidity currents have been shown to effectively transport sediment and carbon over 1000s km. Despite accounting for >70% of canyons worldwide, land-detached canyons (that lie far from shore) remain un-monitored, exposing a major gap in our understanding of global particulate transport. This bias results from a long-held view that land-detached canyons are disconnected from sediment inputs during present day sea levels. New measurements in Whittard Canyon (in the Celtic Sea, 250 km from shore) challenge this paradigm, revealing that land-detached canyons can feature turbidity currents of similar frequency and power to major land-attached canyons. These surprising new results raise the following questions, and motivate our project, which aims to determine the mechanisms and fluxes of particulate transfer via land-detached submarine canyons to the deep-sea for the first time. How can frequent turbidity currents occur if a canyon head lies far from present day sediment supplies? We will deploy an array of sensors on the continental shelf and within the Whittard Canyon head to measure the conditions before and coincident with turbidity currents, and will repeatedly map the seafloor to identify how and where sediment is transported to the canyon head. We will then make the first source to sink measurements along a land-detached canyon, and the second of any major deep-sea canyon worldwide, hence in itself this will represent a significant scientific milestone. What is the nature, concentration and burial efficiency of organic carbon or pollutants, and how does this compare to land-attached canyons? We will analyse seafloor and sediment trap samples to determine what quantities of organic carbon and pollutants are transported along the canyon, and to what extent they remain effectively locked up in the seafloor as a result of burial. Phytoplankton blooms occur at the head of Whittard Canyon during spring and summer, when turbidity currents are most frequent, providing fresh (marine) organic carbon in a similar manner to how river floods convey fresh carbon to land-attached canyons. We also observe mobile litter accumulations so will test to what extent turbidity currents transport pollutants as well as organic carbon and how its distribution relates to seafloor biodiversity hotspots. As well as posing an ecological threat, pollutants such as microplastics may effectively act as 'tracers', evidencing contemporary canyon flows. What volumes of natural and anthropogenic material are transferred via land-detached canyons? Global budgets exist for particulate transport to and across the ocean, but none include land-detached canyons. We will provide a first order calculation to assess the global significance of land-detached canyons, first assessing the contribution to deep sea transport across the Celtic Margin, and then up-scaling our results to determine what is missing from existing global budgets.

这个雄心勃勃的项目将使人们对海底峡谷中零星但大量的沉积物、具有气候重要性的有机碳和污染物的认识发生一步变化，海底峡谷将世界各地的大陆架连接到深海。-gt；9000个大型海底峡谷分布在世界上所有的水下边缘，在规模上往往令水系相形见绌。这样的峡谷可以转移大量的天然沉积物、有机碳和营养物质，维持着重要的生态系统，并日益被认为是海底污染的热点，威胁到它们所拥有的生物多样性。沿着峡谷流动的泥沙流可能又快又密，破坏了支撑全球通信的电缆。因此，重要的是要了解这种水流何时以及如何被触发，被输送的物质的数量，以及至关重要的是，这些物质在不同类型的峡谷之间是如何变化的。对浑浊流的监测主要集中在由河流或长岸漂流供应的“陆上”峡谷，在那里，强大的浑浊洋流已被证明能够有效地将沉积物和碳输送超过1000公里。尽管占全球峡谷的70%，但与陆地分离的峡谷(远离海岸)仍然没有受到监测，暴露出我们对全球颗粒物传输的理解存在重大差距。这种偏见源于一种长期持有的观点，即在今天的海平面上，与陆地分离的峡谷与沉积物输入断开了联系。惠特塔德峡谷(位于凯尔特海，距离海岸250公里)的新测量结果挑战了这一模式，揭示了陆地分离的峡谷可以具有与主要陆地附着的峡谷相似的频率和功率的浑浊流。这些令人惊讶的新结果提出了以下问题，并激励了我们的项目，该项目旨在首次确定通过陆地分离的海底峡谷向深海转移颗粒物的机制和通量。如果峡谷的源头远离现在的沉积物供应，怎么会出现频繁的浑浊水流呢？我们将在大陆架和惠塔德峡谷头内部署一系列传感器，以测量浊流之前和与之重合的情况，并将反复绘制海底地图，以确定沉积物是如何以及在哪里被输送到峡谷头的。然后，我们将做出第一个沿着陆地分离的峡谷进行测量的震源，以及世界上任何主要深海峡谷中的第二个震源，因此这本身就代表着一个重要的科学里程碑。有机碳或污染物的性质、浓度和埋藏效率是什么，与陆地上的峡谷相比如何？我们将分析海底和沉积物陷阱样本，以确定沿着峡谷输送了多少有机碳和污染物，以及它们在多大程度上由于埋藏而被有效地锁在海底。浮游植物水华在春季和夏季出现在惠塔德峡谷的头部，这是浑浊水流最频繁的时候，提供新鲜(海洋)有机碳的方式类似于河流洪水将新鲜碳输送到与陆地相连的峡谷的方式。我们还观察到移动的垃圾堆积，因此将测试浑浊洋流在多大程度上输送污染物和有机碳，以及其分布如何与海底生物多样性热点地区有关。除了构成生态威胁外，微塑料等污染物可能有效地起到了‘示踪剂’的作用，证明了当代峡谷的流动。有多少数量的自然和人为物质通过与陆地分离的峡谷转移？全球存在往返于海洋的颗粒物运输预算，但没有一个预算包括与陆地分离的峡谷。我们将提供一个评估陆地分离峡谷的全球意义的一阶计算，首先评估对凯尔特边缘深海运输的贡献，然后扩大我们的结果，以确定现有的全球预算中缺少什么。