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生物地球化学中起着关键作用，海洋是地球系统中短时间内活动的最大碳库。这些示踪剂主要在混合层发生反应，在混合层发生海气交换，有充足的光进行光合作用。这些示踪剂的混合在全球碳循环和气候的大尺度、中尺度涡旋解析模拟中得到了参数化，但到目前为止，它们的反应与流动物理之间的耦合还没有得到表征。理解上层海洋的这种耦合是复杂的，因为存在着跨越大尺度的湍流过程，包括米尺度的Langmuir湍流的垂直混合和亚中尺度涡旋、锋面和细丝的千米尺度的搅拌。因此，即使在混合层中，活性示踪剂也不能完全混合到在所有尺度上都具有零梯度的程度。这就导致了异质性，或者说是“补丁性”，在示踪剂的空间分布上；这种非均质性的程度和光谱性质是由湍流混合和生物或化学反应之间的相互作用决定的。描述具有不同反应动力学和速率的真实混合层湍流对反应性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基本挑战。智力优势：该项目将使用大涡模拟（LES）来研究多尺度湍流过程对海洋混合层反应性示踪剂的影响，范围从米（朗缪尔）到几十公里（亚中尺度锋面和不稳定性）。研究人员将利用他们先前研究朗缪尔湍流、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。在这个尺度范围内，关于湍流和海洋示踪反应的研究相对较少，但小规模湍流混合的时间尺度与化学过程（如二氧化碳水合作用）相似，而亚中尺度涡旋的演化时间尺度与浮游生物大量繁殖的时间尺度相似。先前对反应性示踪剂的许多研究都依赖于简单的流场（如二维或准地转湍流）。这个项目将解决海洋上层湍流的全部三维复杂性。首先，将使用相对简单的示踪反应，建立更现实的生物和化学模型。这种方法将允许在引入过于复杂的反应模型之前了解基本的湍流-示踪剂相互作用。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、生物和化学的联系方面接受培训。从这个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，以及上层海洋的生物动力学。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二氧化碳水平和气候变化具有直接影响。虽然这项研究将侧重于基本过程，强调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也有明显的应用。特别是，随着当前研究中发展的数值框架，诊断和基本理解，反应性示踪剂的研究可以在未来扩展到更复杂的上层海洋生物和化学反应模型。研究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际效用。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性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.