RAPID: Quantifying turbulent mixing and heat flux in the Mackenzie Canyon and across the Beaufort continental slope in the Arctic Ocean

RAPID：量化麦肯齐峡谷和北冰洋波弗特大陆坡的湍流混合和热通量

• 批准号: 2042692
• 负责人: Amy Waterhouse
• 金额: $ 7.13万
• 依托单位: University of California-San Diego Scripps Inst of Oceanography
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-08-15 至 2023-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2042692&HistoricalAwards=false
• 关键词: RAPID; Quantifying; turbulent; mixing; heat

The Arctic Ocean is the one place in the world where the warm, salty waters from the Atlantic Ocean meet the colder and fresher waters of the Pacific Ocean. Because the Pacific Water is fresher, it is lighter and floats above Atlantic Water (AW), which is warm but heavy and sinks to fill the depths of the Arctic Ocean. As such, the Pacific waters act as a physical barrier that prevents warm Atlantic waters from reaching the surface where they can cause increased melting of sea ice. Because the flow of Atlantic Water is approximately ten times stronger than the flow of Pacific Water, it represents a huge potential for influencing sea ice coverage. However, because it is salty and heavy, Atlantic waters cannot reach the ocean surface unless they are actively drawn to the surface. The ocean’s tides and winds provide energy sources for lifting these heavy waters and the mechanisms for raising these waters to the surface are not well understood. This project studies how the Mackenzie Canyon - a submarine canyon - can act as a conduit to draw up the deep, warm Atlantic Water to the shallow shelves, and mix it into shallow, near-surface water masses where it may influence sea-ice processes. Redistribution of heat by turbulent mixing plays an important role in controlling the ocean climate in the Arctic. This is a unique opportunity that documents the dynamics and mechanisms during a time where ice-cover and the Arctic Ocean structure is rapidly evolving. For this project, the research team uses special custom-made mixing sensors and a commercially available acoustic instrumentation aboard an already-planned field experiment to allow characterization of the rate at which heat is being drawn to the Arctic Ocean’s surface through turbulent mixing processes. The individual processes and sources of energy responsible for this heat transfer (e.g., tides, winds, and mean flow) vary depending on how details of the forcing combine, often creating geographic hotspots of mixing that dominate the net turbulent heat fluxes. Continental slopes have been identified as one such conduit for heat. This project determines how much and by what mechanism warmer Atlantic Water (AW) is modified and upwelled due to the presence of the slope-incising topography of the Mackenzie Canyon, compared to the smoother Beaufort continental slope. Aims include providing turbulent instrumentation added to the Arctic Observing Network (AON) conductivity, temperature, and depth (CTD) survey sections to estimate turbulent dissipation rate and heat fluxes within the canyon and across the AON hydrographic transects of the Beaufort Sea, where there are relatively few known turbulence observations. As a result of this work, the project obtains a comprehensive map of the turbulent heat flux and dissipation rate across the Beaufort slope via the AON transects and within the Mackenzie Canyon. This work is important for measuring ocean dynamics and increases understanding of the influence of incising topography to the upward heat flux from the Atlantic Water in the Arctic Ocean. While canyons represent a small percentage of the coastline in the Arctic, this project’s measurements quantify their contribution to the modification and transport of heat in the Beaufort Sea. On a larger scale, this work contributes to refining methods for calculating turbulent quantities using two different CTD-mounted instruments in the Arctic, a region rich with warm lateral intrusions and significant heat flux across regions of variable and complex topography.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

北冰洋是世界上唯一一个大西洋的温暖咸水与太平洋的寒冷淡水交汇的地方。因为太平洋的水更新鲜，更轻，漂浮在温暖但沉重的大西洋水（AW）之上，下沉到北冰洋深处。因此，太平洋水域充当了一个物理屏障，阻止温暖的大西洋海水到达海面，从而导致海冰融化加剧。由于大西洋水流的强度大约是太平洋水流的十倍，因此它对海冰覆盖的影响潜力巨大。然而，由于大西洋是咸的和重的，除非它们被积极地吸引到海面上，否则它们不能到达海洋表面。海洋的潮汐和风为抬升这些重水提供了能量，而将这些水抬升到水面的机制尚不清楚。这个项目研究麦肯齐峡谷——一个海底峡谷——如何作为一个管道，将深而温暖的大西洋水吸引到浅层大陆架，并将其混合成浅层的近地表水团，在那里它可能会影响海冰的形成。湍流混合引起的热量重新分配在控制北极海洋气候方面起着重要作用。这是一个独特的机会，可以记录冰盖和北冰洋结构迅速演变期间的动态和机制。在这个项目中，研究小组在一个已经计划好的现场实验中使用特殊的定制混合传感器和商用声学仪器，以表征通过湍流混合过程将热量吸引到北冰洋表面的速率。负责这种热传递的各个过程和能量来源（例如潮汐、风和平均流量）因强迫的细节如何结合而变化，通常会产生控制净湍流热通量的混合地理热点。大陆斜坡已被确定为这样一个热通道。该项目确定了与平缓的波弗特大陆斜坡相比，由于麦肯齐峡谷的斜坡切割地形的存在，温暖的大西洋水（AW）被修改和上涌的程度和机制。目的包括为北极观测网络（AON）的电导率、温度和深度（CTD）调查部分提供湍流仪器，以估计峡谷内和波弗特海AON水文断面上的湍流耗散率和热通量，那里已知的湍流观测相对较少。作为这项工作的结果，该项目获得了通过AON横断面和麦肯齐峡谷穿越波弗特斜坡的湍流热通量和耗散率的综合地图。这项工作对于测量海洋动力学和增加对地形上升对北冰洋大西洋水上升热通量的影响的理解是重要的。虽然峡谷只占北极海岸线的一小部分，但这个项目的测量量化了它们对波弗特海热量变化和传输的贡献。在更大的尺度上，这项工作有助于改进在北极地区使用两种不同的ctd安装仪器计算湍流量的方法，北极地区具有丰富的温暖横向侵入和跨越可变和复杂地形区域的显著热通量。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。