Processes drIving Submarine Canyon fluxES

驱动海底峡谷通量的过程ES

• 批准号: NE/W005441/1
• 负责人: Rob Hall
• 金额: $ 63.12万
• 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: 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%2FW005441%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架通过一个陡峭的大陆斜坡与深海相连，这个斜坡从海面下几千米上升到只有几百米。陆架海中的浮游植物（微型植物）依赖于大陆斜坡上的深海水流，为它们提供生长和繁殖所需的营养。浮游植物的光合作用是陆架海洋食物网的基础，因此所有生物，包括商业上重要的鱼类，都受到上坡洋流的影响。沿大陆斜坡流下的水流同样至关重要。深海营养物质允许的额外光合作用使大气中的二氧化碳减少到大陆架水域，如果这些碳随后被运出大陆架并锁在深海中，那么它们只能有效地长期缓冲人为排放。洋流在大陆斜坡上上下流动的机制尚不清楚，用于预测未来气候的数值模式也无法准确模拟。在大陆斜坡笔直而平坦的地方，由于水流通常沿着斜坡而不是穿过斜坡，所以跨坡运输有限。然而，在大陆架被海底峡谷切割的地方，沿着斜坡的水流被峡谷陡峭的壁阻挡。这通过两个关键的物理过程增强了通过峡谷的跨坡运输。第一种是上升流和下升流——由沿着斜坡的水流在陡峭的岩壁上变得不稳定并转向或离开大陆架引起的。第二个过程是内部潮汐和湍流混合——由地下波撞击陡峭的岩壁引起。这就产生了湍流，并将深海水和峡谷边缘上方的浅水混合在一起。这两个过程都是具有挑战性的观察和破译由于他们的小尺度和峡谷几何的复杂性。海底峡谷在世界范围内的大陆边缘很常见，它们是由高密度的、富含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的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现实地近似它们。为了实现这些目标，我们将深入研究惠塔德峡谷的物理过程，这是一个切割凯尔特海大陆架的大型分支系统。在峡谷的不同分支内，这两种过程在跨坡养分运输中可能或多或少地发挥作用：部分分支可能以上升流和下升流为主；其他分支由内部潮汐和湍流混合而成。我们将使用广泛的技术，包括尖端的自动驾驶汽车、各种船载和系泊仪器，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，测量洋流速度、溶解的营养物质浓度和湍流混合，以确定营养物质通过峡谷的运输。这些滑翔机是由浮力而不是螺旋桨驱动的，所以它们可以用一块电池监测峡谷环境几个月。观测结果和高分辨率模式模拟将是互补的，因此我们可以：(1)研究峡谷几何形状如何控制这两个过程；(2)确定了惠塔德峡谷和整个欧洲西北陆架断裂的主导过程；(3)评估沿坡水流速度、潮汐能和海洋分层变化对坡间养分运输的影响；(4)改进全球海洋和气候模式对这些过程的模拟。