Processes drIving Submarine Canyon fluxES

驱动海底峡谷通量的过程ES

• 批准号: NE/W00528X/1
• 负责人: Jeff Polton
• 金额: $ 24.3万
• 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: 2022
• 资助国家: 英国
• 起止时间: 2022 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FW00528X%2F1
• 关键词: Processes; drIving; Submarine; Canyon; fluxES

The shallow shelf seas that surround all the continents are connected to the deep open ocean by a steep continental slope, which rises from thousands of metres beneath the ocean surface to just a few hundred. Phytoplankton (microscopic plants) in shelf seas are reliant on flows of deep ocean water up the continental slope to provide them with the nutrients they require to grow and reproduce. Photosynthesis by phytoplankton is the foundation of the shelf sea food web, so all organisms, including commercially important fish species, are influenced by up-slope currents. Flow down the continental slope is equally critical. Drawdown of atmospheric carbon dioxide into shelf waters by the extra photosynthesis allowed by deep ocean nutrients is only an effective long-term buffer to anthropogenic emissions if the carbon is then transported off the shelf and locked away in the deep ocean.The mechanisms that allow currents to flow up and down the continental slope are poorly understood and are not accurately simulated by the numerical models used to predict future climate. Where the continental slope is straight and smooth, there is limited cross-slope transport because currents generally flow along the slope rather than across it. However, where continental shelves are incised by submarine canyons, along-slope currents are blocked by the canyons' steep walls. This results in enhanced cross-slope transport through the canyons by two key physical processes. The first is upwelling and downwelling - caused by along-slope currents becoming unstable over the steep walls and being turned onto, or off, the shelf. The second process is internal tides and turbulent mixing - caused by subsurface waves breaking against the steep walls. This creates turbulence and mixes deep ocean water with shallow water above the canyon rim. Both processes are challenging to observe and decipher due to their small scales and the complexity of canyon geometry. Submarine canyons are common along continental margins worldwide - created by high-density, sediment-laden currents rather than rivers - so they have the potential to make a major contribution to the total transport of nutrients onto continental shelves globally. This project aims to observe, understand and predict these two crucial canyon processes so that they can be accurately simulated, or realistically approximated, by the next generation of global models. To achieve these aims, we will intensively study both physical processes in Whittard Canyon, a large, branching system that incises the Celtic Sea continental shelf. Within the different limbs of the canyon, the two processes are expected to play greater or lesser roles in cross-slope nutrient transport: some limbs are expected to be dominated by upwelling and downwelling; other limbs by internal tides and turbulent mixing. We will use a broad range of technologies, including cutting-edge autonomous vehicles, a wide variety of ship-board and moored instruments, and state-of-the-art high-resolution ocean models, to measure critical ocean properties and help us understand the dominant processes. Specifically, we will use autonomous ocean gliders equipped with bespoke sensors measuring current velocity, dissolved nutrient concentration, and turbulent mixing, to determine nutrient transport through the canyon. These gliders are driven by buoyancy instead of a propeller, so they can monitor the canyon environment for months on a single battery. The observations and high-resolution model simulations will be complementary so that we can: (1) investigate how canyon geometry controls the two processes; (2) determine which processes dominate in Whittard Canyon and along the whole European northwest shelf break; (3) assess how cross-slope nutrient transport is affected by along-slope current speed, tidal energy, and changes in stratification (layering of the ocean); and (4) improve the simulation of these processes by global ocean and climate models.

环绕所有大陆的浅海陆棚通过陡峭的大陆坡与开阔深海相连，大陆坡从洋面以下数千米上升到几百米。陆架海中的浮游植物（微型植物）依赖于深海水沿大陆坡向上流动，为其提供生长和繁殖所需的营养。浮游植物的光合作用是大陆架海洋食物网的基础，因此所有生物，包括具有重要商业价值的鱼类，都受到上坡流的影响。沿大陆坡流下的水流也同样严重。深海营养物质所允许的额外光合作用将大气中的二氧化碳吸入大陆架沃茨，如果这些碳随后被运离大陆架并被锁在深海中，那么这种吸入只能是对人为排放的一种有效的长期缓冲，人们对洋流沿大陆坡上下流动的机制知之甚少，用于预测未来气候的数值模型也没有准确模拟。在大陆坡平直的地方，跨坡迁移有限，因为海流一般是沿着大陆坡流动，而不是横穿大陆坡;但是，在大陆架被海底峡谷切割的地方，顺坡海流被峡谷陡峭的岩壁阻挡。这导致通过两个关键的物理过程增强了穿越峡谷的跨坡运输。第一种是上升流和下降流--由顺坡水流在陡峭的岩壁上变得不稳定而转向或离开大陆架造成的。第二个过程是内潮和湍流混合-由地下波撞击陡峭的墙壁引起。这就产生了湍流，并将深海水与峡谷边缘上方的浅水混合在一起。这两个过程是具有挑战性的观察和破译，由于其规模小，峡谷几何形状的复杂性。海底峡谷是世界各地沿着大陆边缘常见的峡谷--是由高密度、充满沉积物的洋流而不是河流形成的--因此它们有可能对全球大陆架上营养物质的总运输做出重大贡献。该项目旨在观察、理解和预测这两个关键的峡谷过程，以便下一代全球模型能够准确地模拟或真实地近似。为了实现这些目标，我们将深入研究Whittard峡谷的物理过程，这是一个切割凯尔特海大陆架的大型分支系统。在不同的肢体的峡谷，这两个过程预计将发挥或大或小的作用，在跨坡营养输送：一些肢体预计将占主导地位的上升流和下降流;其他肢体的内部潮汐和湍流混合。我们将使用广泛的技术，包括尖端的自动驾驶汽车，各种船上和系泊仪器，以及最先进的高分辨率海洋模型，来测量关键的海洋特性，并帮助我们了解主导过程。具体来说，我们将使用配备定制传感器的自主海洋滑翔机，测量流速，溶解营养物浓度和湍流混合，以确定营养物通过峡谷的运输。这些滑翔机是由浮力而不是螺旋桨驱动的，因此它们可以用一块电池监测峡谷环境数月。观测和高分辨率模式模拟将是互补的，以便我们能够：（1）研究峡谷几何形状如何控制这两个过程;（2）确定Whittard峡谷和沿着整个欧洲西北陆架断裂带的主导过程;（3）评估沿坡流速、潮汐能和分层变化如何影响跨坡营养物输送（4）改进全球海洋和气候模式对这些过程的模拟。