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

南极底水是全球海洋中占主导地位的深海水团。它的产生是因为南极大陆架上形成的非常冷、密度高的水随着密度的流出而下沉到大陆坡上，在下降时卷走了周围的深海水团。最近在理解动力学和模拟其他主要密度流方面取得了进展，特别是北欧和边缘海的密度流。然而，在理解南极密度流方面取得的进展较少，主要是因为缺乏详细的实地数据。因此，目前我们对以下两个基本问题没有明确的答案：据信决定南极洲周围主要形成地点AABW产量和水文特征的工艺的相对重要性是什么？为什么南极的外流保持了足够的密度对比而沉入深海海底，而大多数其他的外流却足够强烈地卷积到中等深度的中性密度？基于2003-2005年在罗斯海西北部的南极坡度(AnSlope)现场计划期间获得的大量剖面和系泊数据集，研究人员定义了一个能够解决上述问题的数值模拟研究。对现场数据的分析和探索性的模拟工作表明，南极的外流受到以下因素的显著影响：(1)小尺度(亚Rossby半径)地形变化(波纹、等深线收敛、大陆坡曲率、陡坡)；(2)外流与跨坡平流的非线性相互作用和与潮汐等“独立”能量过程有关的混合；以及(3)非线性状态方程效应，特别是热压性。将利用谱元素大涡模拟(LES)模式进行一系列广泛的数值研究，以研究外流动力学和AABW产量对这些因素的敏感性。这些模型将以南极现场数据(Anslope，以及南部韦德尔海的补充计划)为指导，但将应用于理想化的地形和水文场。我们将开发南极密度外流和AABW生产率的参数化，并使用区域海洋模拟系统在较高分辨率的区域海洋模式框架内对它们进行测试。这项研究的首要目标是改善AABW形成在气候系统模型中的表现。智力优势：该项目是已知的第一个将LES模型应用于南极周围具有气候意义的全球底层水形成问题的项目。我们将使用这一工具来量化影响AABW产量和特性的主要因素在涵盖主要南极外流的参数范围内的相对重要性。结果将与世界海洋其他地方的外流进行比较和对比。更广泛的影响：我们将开发的参数化将提高我们在无法解决外流及其夹带过程的小空间和时间尺度的地球气候系统模型中模拟AABW生产的能力。AABW是经向翻转环流的重要组成部分，也是全球深海通风的主要贡献者。一名研究生将在RSMAS/UM由这笔助学金资助。地球和空间研究(ESR)联合调查员将继续为西俄勒冈大学的一项拨款提供科学监督，以开发K-12课程和教育气候科学教师。报告将在年度培训研讨会、俄勒冈州和全国科学教师协会会议上发表。ESR和迈阿密大学都有侧重于教育和外展的特定网页。

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.