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

南极底层水（AABW）是全球海洋中最主要的深海水体。它是在南极大陆架上形成的非常寒冷、稠密的水作为密度外流下沉到大陆坡时产生的，在下沉时夹带着周围的深海水团。最近在了解其他主要密度流，特别是北欧海和边缘海的密度流的动力学和建模方面取得了进展。然而，在了解南极密度流方面取得的进展较少，主要是由于缺乏详细的实地数据。因此，我们没有，在这个时候，有一个明确的答案，以下两个基本问题：什么是相对重要的过程被认为是决定生产率和水文特征的AABW在南极洲周围的主要形成地点？为什么南极外流保持足够的密度对比下沉到深海海底，而大多数其他外流夹带足够有力，以达到中性密度在中间深度？基于2003-2005年在西北罗斯海南极斜坡（AnSlope）现场项目期间在能量密度外流内和周围获得的广泛剖面和系泊数据集，调查人员定义了一个可以解决上述问题的数值模拟研究。对实地数据的分析和探索性建模工作表明，南极外流受到以下因素的显著影响：（1）小规模（亚罗斯比半径）地形变率（2）流出与横坡平流的非线性相互作用以及与潮汐等“独立的”能量过程有关的混合;（3）非线性物态方程效应，特别是热压效应。一个广泛的数值研究，使用谱元素大涡模拟（LES）模型将进行研究的敏感性流出动态和AABW生产这些因素。这些模型将由南极实地数据（AnSlope和威德尔海南部的补充方案）指导，但将适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生产率的参数化，并使用区域海洋建模系统的粗分辨率区域海洋模型的框架内测试这些。该研究将解决的首要目标，提高代表性的AABW形成气候系统models.Intellectual优点：该项目是第一个已知的应用程序的LES模式的气候学上的重大问题，全球底层水形成南极洲周围。我们将使用这个工具来量化的主要因素的相对重要性，影响生产率和性能的AABW的参数范围内，涵盖了主要的南极外流。结果将进行比较，并与外流在世界其他地方ocean.Broader影响：参数化，我们将开发将提高我们的能力，模拟AABW生产在地球气候系统模型，不能解决小的空间和时间尺度的外流及其夹带过程。AABW是纬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支持这笔赠款。地球和空间研究（ESR）合作研究员将继续为西俄勒冈州大学提供科学监督，以开发K-12课程并教育气候科学教师。将在年度培训讲习班、俄勒冈州和国家科学教师协会会议上作演讲。ESR和迈阿密大学都有专门的教育和外联网页。

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.