Collaborative Research: The impact of climate change on the physics and biology of the ocean on scales down to the submesoscale

上层海洋的物理结构对海洋-大气之间的动量、热量、淡水和二氧化碳等气体的交换具有重要的控制作用。它还调节营养物质的分布及其向阳光照耀的上层海洋的输送，从而调节植物生物量的生产，最终维持几乎所有海洋生物并调节关键的碳通量。确定构成上层海洋动力学的机制对于理解物理气候系统和生物地球化学循环如何发挥作用至关重要。此外，气候变化预计将对这些过程产生强烈影响；因此，至关重要的是发展一种能力，以预测它们在改变的强迫制度下的演变。这项工作不能用低分辨率的数值模式来完成，因为在大尺度上，海洋环流主要受地球自转的限制在水平面上。在较小的尺度上，这种限制会减少，垂直流动变得越来越有活力。该项目将为评估气候变化对全球和区域上层海洋过程的影响制定一个健全、高分辨率的数值框架。进行这类实验的工具和工作流程将编入共同体地球系统模型框架，从而可供其他研究人员使用。这项研究将对气候尺度模型和预测中通常不包括的尺度的重要性进行评估。因此，这项研究和任何后续研究的结果将有助于界定当前预测的可靠性，并有助于设计未来的研究。该项目还包括对一名研究生和一名博士后的培训和指导，他们将获得模型设计、数值实验和分析方面的技能，这些技能在未来的社会相关科学研究中至关重要。迄今为止，气候变化预测是通过粗分辨率海洋模型进行的。然而，最近的研究表明，在受地球自转限制较小的尺度上，次中尺度过程在决定上层海洋分层、混合层深度和表面到深度交换方面发挥着重要作用。关键是，气候变暖下海洋平均状态的变化很可能影响次中尺度活动，并对这些过程所调节的横向和垂直通量产生影响。该项目将使用数值模拟和观测相结合的方法，量化亚中尺度动力在当前气候条件下控制净初级生产和出口生产的作用；它还将审查在代表未来变暖的气候强迫下推动这些过程变化的机制。这是由一种新颖的实验设计实现的，该设计能够在高分辨率下进行计算上可行的气候变化实验。这涉及在当前和未来条件下将涡旋分辨(1/10度)全球海洋模型与生物地球化学相结合，使用从完全耦合的集合积分中提取的异常来定义气候扰动。嵌套在全球涡旋分辨区域内的区域模式将用于研究不同气候条件下不同海洋区域的次中尺度动力学。这项研究将产生一些与气候变暖条件下海洋系统变化有关的重要成果。将确定中尺度动力学在调节全球生物地球化学过程中的变化作用。将确定当今气候条件和气候变暖条件下若干不同地区的次中尺度活动。将量化次中尺度事件、其基本物理和相关热通量在当今气候条件和较暖气候条件下随季节变化的情况。将确定不同条件下亚中尺度活动对海洋生物地球化学的影响。将确定气候变暖条件下次中尺度活动的变化对上层海洋物理和生物地球化学的总体变化的影响程度。

The physical structure of the upper ocean is an important control on ocean-atmosphere exchange of momentum, heat, freshwater and gases such as carbon dioxide. It also regulates the distribution of nutrients and their delivery to the sunlit upper ocean, and therefore the production of plant biomass, which ultimately supports nearly all marine life and mediates key carbon fluxes. Determining the mechanisms structuring upper ocean dynamics is critical to understanding how the physical climate system and biogeochemical cycles function. Moreover, climate change is expected to strongly impact these processes; thus, it is crucial to develop a capacity to predict their evolution under altered forcing regimes. This work cannot be done with coarse resolution numerical models because at large scales ocean circulation is constrained mostly to the horizontal plane by the rotation of the Earth. This constraint is lessened at smaller scales and vertical flows become increasingly more energetic. This project will develop a sound, high-resolution numerical framework for evaluating climate change impacts on upper ocean processes globally and regionally. The tools and workflow for conducting such experiments will be codified in the Community Earth System Model framework and thus be available to other researchers. The study will provide an assessment of the importance of scales not normally included in climate scale models and projections. The results of this and any follow-on studies, will therefore be helpful in putting bounds on the reliability of current projections and in the design of future studies. The project also includes the training and mentoring of a graduate student and a postdoc, who will gain skills in model design, numerical experimentation, and analysis that are vitally important in future studies of societally relevant science.Climate change projections to date have been done with coarse-resolution ocean models. Recent research, however, has revealed that submesoscale processes, at scales where the constraint by the rotation of the Earth is lessened, play an important role in determining upper ocean stratification, mixed layer depths, and surface-to-depth exchange. Critically, changes to the ocean mean-state under a warming climate are very likely to impact submesoscale activity, with implications for the lateral and vertical fluxes mediated by these processes. This project will use a combination of numerical simulations and observations to quantify the role of submesoscale dynamics in controlling net primary production and export production under present-day climate conditions; it will also examine the mechanisms driving changes in these processes under climate forcing representative of future warming. This is made possible by a novel experimental design that enables computationally feasible climate-change experiments conducted at high-resolution. This involves integrating an eddy-resolving (1/10 degree) global ocean model with biogeochemistry under present-day and future conditions, using anomalies extracted from fully-coupled ensemble integrations to define the climate perturbation. A regional model, nested within the global eddy-resolving domain, will be used to investigate submesoscale dynamics in distinct oceanic regions under different climate conditions. There will be a number of important outcomes of this research relating to changes to the ocean system under a warmer climate. The changing role of mesoscale dynamics in mediating biogeochemical processes globally will be determined. The submesoscale activity in a number of contrasting regions in present-day and warmer climate conditions will be determined. Submesoscale events, their underlying physics and associated heat fluxes as a function of season in both present day and warmer climate conditions will be quantified. The impact of submesoscale activity on ocean biogeochemistry under varied conditions will be determined. The degree to which the changes in submesoscale activity in warmer climate conditions impacts the overall change to the upper ocean physics and biogeochemistry will be determined.