Collaborative research: Modeling control of Antarctic Bottom Water production by small-scale bathymetry and tides

南极底水（AABW）是全球海洋中占主导地位的深海水体。它是由南极大陆架上形成的非常寒冷、密度很大的水形成的，这些水以密度较大的流出物的形式向大陆斜坡下沉，在下降的过程中夹带着周围的深海水团。最近在了解其他主要密度洋流的动力学和建模方面取得了进展，特别是在北欧和边缘海域。然而，由于缺乏详细的实地数据，在了解南极密度流方面取得的进展较少。因此，我们目前对以下两个基本问题没有明确的答案：在南极洲周围的主要形成地点，被认为决定AABW的产量和水文特征的过程的相对重要性是什么？为什么南极流出物保持了足够的密度，从而下沉到深海底，而大多数其他流出物却在中等深度剧烈运动，达到中性密度？根据2003-2005年在西北罗斯海的南极坡（anslop）野外项目中获得的大量剖面和系泊数据集，研究人员定义了一个可以解决上述问题的数值模拟研究。野外数据分析和探索性模拟工作表明，南极外流受到以下因素的显著影响：(1)小尺度（亚罗斯比半径）地形变异性（波纹、等深线辐合、大陆坡曲率、陡坡）；(2)外流与坡面平流的非线性相互作用，以及与潮汐等“独立”能量过程相关的混合；(3)非线性状态方程效应，特别是热压效应。将使用谱元大涡模拟（LES）模型进行一系列广泛的数值研究，以研究流出动力学和AABW产量对这些因素的敏感性。这些模型将以南极野外数据（anslop和威德尔海南部的补充项目）为指导，但将应用于理想化的地形和水文领域。我们将开发南极密度外流和AABW产生速率的参数化，并在使用区域海洋模拟系统的粗分辨率区域海洋模式框架内对这些进行测试。该研究将解决在气候系统模式中改善AABW形成的总体目标。知识价值：该项目是已知的第一个将LES模型应用于南极洲周围全球底水形成的重要气候问题的项目。我们将使用这一工具，在涵盖南极主要外流的参数范围内，量化影响南极冰冰产生速率和性质的主要因素的相对重要性。结果将与世界海洋其他地方的流出进行比较和对比。更广泛的影响：我们将开发的参数化将提高我们在地球气候系统模式中模拟AABW产生的能力，这些模式不能解决小空间和时间尺度的流出及其携带过程。AABW是经向翻转环流的重要组成部分，是全球深海通风的主要贡献者。一名研究生将在RSMAS/UM获得这项资助。地球与空间研究（ESR）的联合研究员将继续为西俄勒冈大学提供科学监督，以开发K-12课程，并对教师进行气候科学教育。报告将在年度培训研讨会，以及俄勒冈州和国家科学教师协会会议上进行。ESR和迈阿密大学都有专门的网页，重点是教育和推广。

Antarctic Bottom Water (AABW) is the dominant abyssal water mass in the global ocean. It is produced as very cold, dense water formed over the Antarctic continental shelves sinks down the continental slope as a density outflow, entraining ambient deep-ocean water masses as it descends. There has been recent progress in understanding the dynamics and modeling other major density currents, notably those in the Nordic and marginal seas. However, less progress has been made in understanding Antarctic density flows, hampered primarily by a lack of detailed field data. As a consequence we do not, at this time, have a clear answer to two following fundamental questions: What is the relative importance of processes believed to determine the production rate and hydrographic characteristics of AABW at the primary formation sites around Antarctica? Why do Antarctic outflows retain sufficient density contrast to sink to the deep ocean floor, whereas most other outflows entrain sufficiently vigorously to reach neutral density at intermediate depths?Based on an extensive profile and mooring data set obtained in and around an energetic density outflow during the Antarctic Slope (AnSlope) field program in 2003-2005 in the NW Ross Sea, the investigators have defined a numerical modeling study that can address the above questions. Analyses of the field data, and exploratory modeling efforts, suggest that Antarctic outflows are significantly impacted by the following factors: (1) small-scale (sub-Rossby radius) topographic variability (corrugations, isobath convergence, continental slope curvature, steep slopes); (2) nonlinear interaction of the outflow with cross-slope advection and mixing associated with 'independent' energetic processes such as tides; and (3) nonlinear equation-of-state effects, notably thermobaricity. An extensive set of numerical studies using a spectral element Large Eddy Simulation (LES) model will be carried out to study the sensitivity of outflow dynamics and AABW production to these factors. The models will be guided by Antarctic field data (AnSlope, and complementary programs in the southern Weddell Sea), but will be applied to idealized topographies and hydrographic fields. We will develop parameterizations of Antarctic density outflows and AABW production rates, and test these within the framework of coarser-resolution regional ocean models using Regional Ocean Modeling Sysytem. The study will address the overarching objective of improving the representation of AABW formation in climate system models.Intellectual Merits: This project is the first known application of an LES model to the climatologically significant problem of global bottom water formation around Antarctica. We will use this tool to quantify the relative importance of the principal factors influencing the production rate and properties of AABW over parameter ranges that cover the major Antarctic outflows. Outcomes will be compared and contrasted with outflows elsewhere in the world ocean.Broader Impacts: The parameterizations that we will develop will improve our ability to simulate AABW production in earth climate system models that cannot resolve the small spatial and temporal scales of the outflow and its entrainment processes. AABW is a critical component of the meridional overturning circulation and is the dominant contributor to ventilation of the global deep ocean. One graduate student will be supported at RSMAS/UM by this grant. The Earth and Space Research (ESR) Co-investigator will continue to provide scientific oversight for a Western Oregon University grant to develop K-12 curricula and educate teachers in climate science. Presentations will be given at annual training workshops, and Oregon and National Science Teacher Association meetings. Both ESR and the University of Miami maintain specific web pages focused on education and outreach.