Bottom Boundary Layer Turbulence and Abyssal Recipes (BLT Recipes)

底部边界层湍流和深渊配方（BLT 配方）

• 批准号: NE/S001433/1
• 负责人: Alberto Naveira Garabato
• 金额: $ 113.26万
• 依托单位: University of Southampton
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2018
• 资助国家: 英国
• 起止时间: 2018 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FS001433%2F1
• 关键词: Bottom; Boundary; Layer; Turbulence; Abyssal

Since the seminal work of Walter Munk in the 1960s, oceanographers have believed that the upwelling of cold, abyssal waters that regulates the deep ocean's ability to sequester heat and carbon for decades to millennia (thereby shaping Earth's climate) is driven by centimetre-scale turbulent mixing associated with breaking waves in the ocean interior. Measurements of deep-ocean turbulence over the last two decades, however, starkly contest this scenario, and instead suggest that mixing by breaking waves drives *downwelling* of abyssal waters. Inspired by this conundrum, recent theoretical investigations have developed a tantalising alternative view of the role of mixing in sustaining deep-ocean upwelling. In this new view, upwelling is driven by highly localised turbulence within thin (typically tens of metres thick) layers near the seafloor, known collectively as the bottom boundary layer.In this proposal, we set out to assess the validity of this new paradigm, and figure out how it works, by obtaining the first set of concurrent, systematic measurements of (1) large-scale mixing and upwelling, (2) their interior and bottom boundary layer contributions, and (3) the processes underpinning these contributions, in a representative deep-ocean basin (the Rockall Trough, in the Northeast Atlantic). To this end, we will conduct a year-long field programme involving three research cruises, in close collaboration with a group of U.S. project partners.To measure (1), in the first cruise we will release a long-lived chemical tracer detectable at very low concentrations near the seafloor on the basin's eastern flank, where deep waters flow into the basin from the south. We will monitor how the tracer mixes and upwells as it fills the basin by sampling it at 6 and 12 months after its release, during the two subsequent cruises. To measure (2) and (3), we will adopt a two-pronged approach. First, we will assess mixing and upwelling in the ocean interior and the transition into the bottom boundary layer by deploying turbulence-measuring profilers at hundreds of sites throughout the basin, in the first and third cruises. Second, as these ship-deployed profilers are unsuitable to approach the seafloor closely, we will obtain targeted measurements of mixing and upwelling across the bottom boundary layer in two ways: (i) by conducting two 6-month-long deployments of a cluster of novel, turbulence-measuring instruments moored at the seafloor, at two sites on the basin's sloping boundary; and (ii) by performing a near-bottom release of a short-lived dye at each of the mooring deployment sites, and monitoring how the dye mixes and upwells over several days after its release.We will integrate our measurements of (1)-(3) into the design of a realistic numerical model of the circulation in the Rockall Trough, and use the model to conduct a rigorous, quantitative test of the new paradigm of ocean mixing. We expect this test to provide the first evidence of the dominance of bottom boundary layer turbulence in driving deep-ocean upwelling and, in so doing, trigger a profound transformation in our understanding and modelling of deep-ocean circulation.

自20世纪60年代沃尔特·芒克（Walter Munk）的开创性工作以来，海洋学家们一直认为，深海沃茨的上涌调节了深海在数十年至数千年内封存热量和碳的能力（从而塑造了地球的气候），这是由海洋内部破碎波相关的厘米级湍流混合驱动的。然而，过去20年来对深海湍流的测量结果与这一假设截然不同，相反，它们表明破碎波的混合驱动了深海沃茨的下降流。受到这个难题的启发，最近的理论研究已经发展出一种诱人的替代观点，即混合在维持深海上升流中的作用。在这种新的观点中，上升流是由薄层中高度局部化的湍流驱动的。在本提案中，我们着手评估这一新模式的有效性，并通过获得第一组同步、系统的测量结果来弄清楚它是如何工作的：（1）大规模混合和上升流，（2）它们的内部和底部边界层贡献，以及（3）支持这些贡献的过程，在一个有代表性的深海海盆（东北大西洋的罗卡尔海槽）中。为此，我们将与美国项目合作伙伴密切合作，开展为期一年的实地考察项目，包括三次考察航行。为了测量（1），在第一次考察中，我们将在盆地东侧海底附近释放一种长寿命的化学示踪剂，浓度很低，可检测到，那里的深层沃茨从南部流入盆地。我们将监测示踪剂如何混合和上升，因为它充满了盆地，在6个月和12个月后，它释放，在随后的两个巡航采样。至于第（二）及第（三）项措施，我们会双管齐下。首先，我们将在第一次和第三次巡航中，通过在整个盆地的数百个地点部署连续性测量剖面仪，评估海洋内部的混合和上升流以及向底部边界层的过渡。第二，由于这些部署在船上的剖面仪不适合近距离接近海底，我们将通过两种方式获得对整个底部边界层的混合和上升流的有针对性的测量：㈠在盆地倾斜边界的两个地点，在海底停泊一组新颖的连续测量仪器，部署两次，为期6个月;以及（ii）通过在每个系泊部署地点进行短寿命染料的近海底释放，并监测染料在释放后的几天内如何混合和上升。我们将整合我们对（1）-（3）的测量。罗卡尔槽环流的一个现实的数值模型的设计，并使用该模型进行严格的，海洋混合的新范式的定量测试。我们希望这次测试能够提供第一个证据，证明海底边界层湍流在驱动深海涌升方面的主导作用，并由此引发我们对深海环流的理解和建模的深刻转变。

项目成果

Sensitivity of Deep Ocean Mixing to Local Internal Tide Breaking and Mixing Efficiency

• DOI: 10.1029/2019gl085056
• 发表时间: 2019-12
• 期刊: Geophysical Research Letters
• 影响因子: 5.2
• 作者: L. Cimoli;Colm‐cille P. Caulfield;H. Johnson;D. Marshall;A. Mashayek;A. N. Naveira Garabato;C. Vic

Surface factors controlling the volume of accumulated Labrador Sea Water

控制拉布拉多海水积聚量的地表因素

• DOI: 10.5194/egusphere-2023-1564
• 发表时间: 2023
• 作者: Kostov Y