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/X014754/1
• 负责人: Rob Hall
• 金额: $ 9.78万
• 依托单位: University of East Anglia
• 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%2FX014754%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零星但大量的沉积物、对气候具有重要意义的有机碳和污染物通过连接世界各地大陆架和深海的海底峡谷的理解发生重大变化。世界上所有的水下边缘都有9000个巨大的海底峡谷，在规模上常常使河流系统相形见绌。这样的峡谷可以转移大量的自然沉积物、有机碳和维持重要生态系统的营养物质，并且越来越多地被认为是海底污染的热点，威胁着它们所承载的生物多样性。沿着峡谷移动的沉积物流速度快、密度大，会破坏支撑全球通信的电缆。因此，重要的是要了解这种流动何时以及如何被触发，被运输的物质的数量，以及至关重要的是，这些在不同类型的峡谷之间是如何变化的。对浊度流的监测主要集中在由河流或长岸漂流形成的“陆地附着”峡谷上，在这些地方，强大的浊度流已被证明能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%，但陆地分离的峡谷（远离海岸）仍未受到监测，这暴露了我们对全球颗粒输送的理解上的一个主要空白。这种偏见源于一种长期持有的观点，即与陆地分离的峡谷与目前海平面下的沉积物输入是分离的。Whittard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范式，揭示了与陆地分离的峡谷可以具有与陆地连接的主要峡谷相似的频率和功率的浊度流。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颗粒通过陆地分离的海底峡谷向深海转移的机制和通量。如果峡谷的源头远离现在的沉积物供应，浊流怎么会频繁发生呢？我们将在大陆架和惠塔德峡谷头内部署一系列传感器，以测量浊流之前和同时的条件，并将反复绘制海底地图，以确定沉积物如何以及在哪里被运送到峡谷头。然后，我们将沿着陆地分离的峡谷进行第一个源汇测量，然后是世界上任何主要深海峡谷的第二个源汇测量，因此，这本身将代表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？与陆上峡谷相比如何？我们将分析海底和沉积物陷阱样本，以确定沿峡谷运输的有机碳和污染物的数量，以及由于掩埋而在海底有效锁定的程度。在春天和夏天，当浑浊流最频繁的时候，浮游植物在惠塔德峡谷的源头大量繁殖，提供新鲜的（海洋）有机碳，其方式与河流洪水将新鲜碳输送到附着陆地的峡谷的方式相似。我们还观察了移动垃圾的积累，因此将测试浑浊流运输污染物和有机碳的程度以及其分布与海底生物多样性热点的关系。除了构成生态威胁外，微塑料等污染物可能有效地充当“示踪剂”，证明了当代峡谷水流的存在。有多少自然的和人为的物质通过与陆地分离的峡谷转移？全球存在颗粒向海洋和跨海洋运输的预算，但没有一个包括与陆地分离的峡谷。我们将提供一级计算来评估陆地分离峡谷的全球意义，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，以确定现有全球预算中缺失的内容。