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

北冰洋是世界上唯一一个来自大西洋的温暖咸水与太平洋更冷更新鲜的海水相遇的地方。因为太平洋水更新鲜，它更轻，漂浮在大西洋水(AW)之上，大西洋水温暖但重，下沉到北冰洋的深处。因此，太平洋水域起到了物理屏障的作用，阻止温暖的大西洋海水到达表面，在那里它们可能导致海冰融化增加。因为大西洋水的流动强度大约是太平洋水的十倍，所以它代表着影响海冰覆盖的巨大潜力。然而，由于大西洋海水又咸又重，除非它们被积极地吸引到海面上，否则它们无法到达海面。海洋的潮汐和风为抬升这些重水提供了能源，而将这些水抬高到水面的机制还不是很清楚。这个项目研究了麦肯齐峡谷--一个海底峡谷--如何发挥管道的作用，将温暖的深大西洋水引向浅海大陆架，并将其混合成可能影响海冰过程的浅水近地表水团。湍流混合引起的热量再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，研究小组使用了特殊的定制混合传感器和商业上可用的声学仪器，安装在已经计划好的实地实验中，以便能够表征通过湍流混合过程将热量吸引到北冰洋表面的速度。负责这种热量传输的个别过程和能源(例如潮汐、风和平均气流)根据强迫的细节如何结合而有所不同，通常产生主导净湍流热通量的混合的地理热点。陆坡已被确定为这样的热量管道之一。该项目确定了由于麦肯齐峡谷的斜坡切割地形与更为平坦的波弗特大陆斜坡相比，变暖的大西洋水(AW)被修改和上升的程度和机制。目标包括向北极观测网络(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，在这些断面上，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内穿过Beaufort坡面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很重要，并增加了对切割地形对北冰洋大西洋水向上热通量的影响的了解。虽然峡谷只占北极海岸线的一小部分，但该项目的测量结果量化了它们对波弗特海热量变化和运输的贡献。在更大的范围内，这项工作有助于改进在北极使用两种不同的安装在CTD上的仪器计算湍流量的方法，北极地区拥有丰富的温暖侧向侵入和显著的热通量，跨越多变和复杂的地形区域。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.