Towards a theory of the abyssal circulation

关于海洋环流的最深处，一幅经过修正的图景正在浮现。在粗糙的地形上，使稠密的海底水变轻并使其上升到中等深度所需的混合作用得到了强烈增强。该项目将致力于建立一个动力学理论，捕捉边界转换与内部流动和分层之间的相互作用。这项工作很重要，因为深海有储存大量热量和碳的能力。更全面地了解形成其环流的动力过程将有助于气候模式捕捉其在气候变化中的行为和作用。在解释冰河时期大气中二氧化碳的减少时，深渊被认为起着关键作用。对深海环流动力学的更深入了解也将有助于更好地了解它在地球历史上的这些时期和其他时期可能有何不同。提出的工作将建立深海环流对斜坡上底部强化混合的响应的动力学模型层次，重点关注地形斜坡上的边界层与深渊内部之间的双向相互作用。这种相互作用将用边界层理论明确地表示出来。该方法将从斜坡上的局部一维动力学开始，然后在简单的二维示例中考虑它们与大规模背景的耦合，随后扩展到理想化和日益现实的三维设置。这将把最近关于斜坡上底部强化混合的研究与深海倾覆的尺度理论联系起来，这些理论基于底部平坦、侧壁垂直的海洋盆地。这些动力学将使用行星地转模型进行探索，其减少的动力学允许直接的动力学洞察和控制的数值解决方案，解决所有特征，包括地形斜坡上所有重要的边界层。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。

A revised picture is emerging of the deepest portion of the ocean's circulation. The mixing required to lighten dense bottom waters and that allows them to rise to mid-depth is strongly enhanced over rough topography. This project will work toward a dynamical theory that captures the interplay between the boundary transformations and interior flows and stratification. This work is important because the abyssal ocean has the capacity to store vast amounts of heat and carbon. A more complete understanding of what dynamical processes shape its circulation will help climate models capture its behavior and role in a changing climate. A pivotal role has been ascribed to the abyss in explaining the drawdown of atmospheric carbon dioxide during ice ages. Deeper insight into the dynamics of the abyssal circulation will also help understand better how it may have been different during these and other periods of Earth's history.The proposed work will build a hierarchy of dynamical models of the response of the abyssal circulation to bottom-intensified mixing on slopes with a focus on the two-way interaction between boundary layers on topographic slopes and the interior of the abyss. This interaction will be expressed explicitly using boundary layer theory. The approach will start with the local one-dimensional dynamics on slopes, then consider their coupling to the large-scale context in simple two-dimensional examples, and subsequently extend to idealized and increasingly realistic three-dimensional setups. This will connect recent work on bottom-intensified mixing on slopes to scaling theories for the abyssal overturning that are based on ocean basins with a flat bottom and vertical sidewalls. These dynamics will be explored using a planetary geostrophic model, whose reduced dynamics allow for direct dynamical insight and controlled numerical solutions that resolve all features, including the all-important boundary layers on topographic slopes.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.