Collaborative Research: Reacting Tracers in a Turbulent Mixed Layer

碳酸盐化学物种和浮游生物等活性示踪剂在确定海洋的地球化学方面发挥着关键作用，海洋是地球系统中最大的短时间内活跃的碳库。这些示踪剂主要在混合层中反应，在那里发生海气交换，光充足，有利于光合作用。这些示踪剂的混合是参数化的大尺度，中尺度涡分辨模拟的全球碳循环和气候，但到目前为止，它们的反应和流动物理之间的耦合没有表示。理解这种耦合在上层海洋是复杂的湍流过程的存在跨越了广泛的尺度，包括垂直混合米级朗缪尔湍流和更大规模的搅拌亚中尺度涡，锋，和细丝。因此，即使在混合层中，反应性示踪剂也没有完全混合到在所有尺度下具有零梯度的点。这导致了异质性，还是？斑，？示踪剂的空间分布;这种不均匀性的程度和光谱特性由湍流混合与生物或化学反应之间的相互作用决定。描述真实混合层湍流对具有不同反应动力学和速率的反应示踪剂的影响，是理解海洋中物理过程与生物和化学物种之间相互作用的一个基本挑战。本项目将利用大涡模拟研究多尺度湍流过程对海洋混合层中活性示踪剂的影响，尺度从几米（朗缪尔）到几十公里（次中尺度锋和不稳定性）。研究人员将通过借鉴他们以前研究朗缪尔湍流，亚中尺度特征，反应流和全球碳循环的经验来研究混合层示踪剂动力学。相对较少的工作湍流和海洋示踪剂反应在这一范围内的尺度是现存的，但小尺度湍流混合的时间尺度类似的化学过程（如CO2水合），和亚中尺度涡演变的时间尺度类似的浮游生物水华。许多以前的研究反应示踪剂依赖于简单的流场（如二维或准地转湍流）。该项目将解决上层海洋湍流的全三维复杂性。首先，将使用相对简单的示踪反应，建立更真实的生物和化学模型。这种方法将允许基本的毒性示踪剂的相互作用，以了解之前引入过于复杂的反应模型。该项目将汇集基本湍流物理学、化学和生物反应流以及物理海洋学的概念。更广泛的影响：三名研究生将在海洋物理学、生物学和化学的联系方面接受培训。从该项目中获得的见解将直接关系到大气和海洋之间界面的气体和碳预算，以及海洋上层的生物动态。这两个过程在全球有机和无机碳循环中起着关键作用，因此对理解和预测大气CO2水平和气候变化有直接影响。虽然这项研究将侧重于基本过程，重点是物理海洋学和理想化的反应模型，但在化学和生物海洋学问题上有明确的应用。特别是，在目前的研究中开发的数值框架，诊断和基本的理解，反应示踪剂的研究可以在未来扩展到更复杂的模型，在海洋上层的生物和化学反应。研究人员团队在建模和参数化开发的更多应用方面也有经验，因此将确保基础工作的实用性。从这些模拟中获得的数据将公开提供，以支持对上层海洋反应示踪剂的进一步研究。

Reactive tracers such as carbonate chemical species and plankton play key roles in determining the biogeochemistry of the ocean, which is the largest reservoir of carbon in the Earth system active on short timescales. These tracers react primarily in the mixed layer, where air-sea exchange occurs and light is plentiful for photosynthesis. The mixing of these tracers is parameterized in large-scale, mesoscale eddy-resolving simulations of the global carbon cycle and climate, but so far the coupling between their reactions and flow physics is not represented. Understanding this coupling in the upper ocean is complicated by the presence of turbulent processes spanning a wide range of scales, including vertical mixing by meter-scale Langmuir turbulence and kilometer-scale stirring by submesoscale eddies, fronts, and filaments. As such, reactive tracers are not fully mixed to the point of having zero gradients at all scales, even in the mixed layer. This leads to heterogeneity, or ?patchiness,? in the spatial distribution of tracers; the degree and spectral properties of this heterogeneity are determined by the interactions between turbulent mixing and biological or chemical reactions. Characterizing the effects of realistic mixed layer turbulence on reactive tracers with different reaction dynamics and rates is a fundamental challenge in understanding the interplay between physical processes and biological and chemical species in the ocean.Intellectual Merit: This project will use large eddy simulations (LES) to study the effects of multiscale turbulent processes on reactive tracers in the oceanic mixed layer, spanning scales from meters (Langmuir) to tens of kilometers (submesoscale fronts and instabilities). The investigators will examine mixed layer tracer dynamics by drawing on their prior experience studying Langmuir turbulence, submesoscale features, reacting flows, and the global carbon cycle. Relatively little work on turbulence and oceanic tracer reactions over this range of scales is extant, yet small-scale turbulent mixing has time scales similar to those of chemical processes (such as CO2 hydration), and submesoscale eddies evolve on time scales similar to those of plankton blooms. Many prior studies of reactive tracers have relied on simple flow fields (such as two-dimensional or quasi-geostrophic turbulence). This project will address the full three dimensional complexity of upper ocean turbulence. At first, relatively simple tracer reactions will be used, building toward more realistic biological and chemical models. This approach will allow fundamental turbulence-tracer interactions to be understood before introducing overly complex reaction models. This project will bring together concepts from fundamental turbulence physics, chemical and biological reacting flows, and physical oceanography.Broader Impacts: Three graduate students will be trained at the nexus of oceanic physics, biology, and chemistry. Insights obtained from this project will be directly relevant to gas and carbon budgets at the interface between the atmosphere and ocean, as well as biological dynamics in the upper ocean. Both of these processes play a critical role in the organic and inorganic global carbon cycles, and thus have a direct impact on understanding and predicting atmospheric CO2 levels and climate change. Although this study will be focused on fundamental processes, with an emphasis on physical oceanography and idealized reaction models, there are clear applications to problems in chemical and biological oceanography. In particular, with the numerical framework, diagnostics, and fundamental understanding developed in the current study, the study of reactive tracers can be extended in the future to more complicated models of biological and chemical reactions in the upper ocean. The team of investigators is also experienced in more applied aspects of modeling and parameterization development, and so will ensure the practical utility of the fundamental work. The data obtained from these simulations will be made publicly available to support further research on reactive tracers in the upper ocean.