Modulation of Bubble-Mediated Gas Transfer due to Wave-Current Interactions

本项目将在综合建模框架内研究海气界面气体传输的空间变异性。理论研究和模拟研究在相对较小的尺度上一致认为，在较小的尺度上，流动不再受地球自转的支配，运动，特别是沿垂直方向的运动变得更加剧烈，对海洋生物地球化学和海气通量产生显著影响。然而，目前还没有研究集中在波流相互作用下的破波变异性和相关的气泡介导的气体传递。目前，大多数气体传递系数的参数化取决于风速，而不是更详细的波浪动力学表示，这导致了很大的不确定性。最近的参数化包括通过积分波参数的波效应，如有效波高或波龄，这两种参数都不能解释由于波流在尖锐锋的相互作用而引起的调制。最近开发的波浪破碎统计模型提供了一个框架，以明确地说明空气夹带和气泡介导的气体通量的破裂。该模型适用于耦合地球系统模拟，为研究波流相互作用对气泡介导的气体传输和通量变异性的影响提供了独特的机会。研究结果将直接应用于气候研究。它们可以解释沿海环境中观测到的气体通量的不确定性，有助于减少全球二氧化碳预算的不确定性。其他影响还包括培训学生。具体来说，一名本科生将参与这项研究。该项目将通过促进西班牙裔早期职业科学家的职业生涯，并通过向指定的西班牙裔服务机构UCSB的学生展示研究及其结果，加强代表性不足群体的参与。这项工作的首要目标是研究由于波流相互作用在亚中尺度气泡介导的气体传递的调制。模拟是基于表面波破裂和相关的海气通量的最新进展，这为模拟气泡介导的气体传递系数提供了一个基于物理的框架。实际的数值模拟将用于研究气泡介导的气体传输的空间变异性及其对气体通量（即CO2）的影响。初步的模式结果表明，由现实风和海流造成的破波统计证实了先前对海流调制波的观测和理论分析的发现，即在风与海锋倾斜的情况下，破波会增强。在亚中尺度上，随着模式分辨率的提高，电流的破波调制增强。亚中尺度锋面辐合和下流速度与斜风强迫下波浪破碎增强的区域重叠。据推测，在这些条件下，海气通量增强。这将在上升流条件下的东部边界流的数值模拟中进行测试。上升流区已显示出二氧化碳浓度的显著变化，但这一点尚不清楚。溶解二氧化碳的建模将忽略生物和化学反应，从背景平衡水平开始，然后用实际通量（包括气泡介导的转移系数）强制进行。该假设将通过使用仅依赖于风速的标准传递系数参数化，比较不同分辨率下的模型解与控制运行的模型解来验证。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This is project will study the spatial variability of gas transfer across the air-sea interface within a comprehensive modeling framework. Theoretical and modeling studies agree at relatively small scales, where the flow becomes less dominated by the rotation of the earth, motion, especially along the vertical direction becomes more energetic, with pronounced impacts on ocean biogeochemistry, and air-sea fluxes. However, no study has focused on wave breaking variability and related bubble mediate gas transfer due to wave-current interactions. Most parameterizations of gas transfer coefficients today depend on wind speed rather than more detailed representation of wave dynamics, resulting in large uncertainties. Recent parameterizations include wave effects through integral wave parameters such as significant wave height or wave age, neither which can explain the modulation due to wave-current interactions at sharp fronts. A recently developed model of wave breaking statistics provides a framework to explicitly account for breaking on air entrainment and bubble-mediated gas fluxes. The model is suitable for coupled earth system simulations providing a unique opportunity to study the effect of wave-current interactions on the variability of bubble-mediated gas transfer and fluxes. The results will have direct applications for climate studies. They can explain the uncertainty of the observed gas fluxes in coastal environments, helping to reduce the uncertainty of global CO2 budgets. Other impacts include training students. Specifically, an undergraduate student will participate in the research. The project will enhance the participation of underrepresented groups by contributing to the career of a Hispanic, early-career scientist, and by exposing the students at UCSB, a designated Hispanic-Serving Institution, to the research and its results. The overarching goal of the work is to investigate the modulation of bubble-mediated gas transfer due to wave-current interactions at submesoscales. The modeling is based on recent advances on surface wave breaking and related air-sea fluxes, which provide a physics-based framework to model bubble-mediated gas transfer coefficients. Realistic numerical simulations will be used to investigate the spatial variability of bubble-mediated gas transfer and their impact on gas fluxes (i.e., CO2). Preliminary model results show that wave breaking statistics forced by realistic winds and currents confirm previous findings from observations and theoretical analysis on the modulation of waves by currents, where wave breaking is enhanced in conditions with winds obliquely aligned with ocean fronts. The wave breaking modulation by currents is enhanced with increasing model resolution at submesoscales. Submesoscale frontal surface convergence and downwelling velocities overlap with areas with enhanced wave breaking with oblique wind forcing. It is hypothesized that under these conditions air-sea gas fluxes are enhanced. This will be tested with numerical simulations at an eastern boundary current during upwelling conditions. Upwelling areas have been shown to exhibit significant variability in CO2 concentrations that is not well understood. Dissolved CO2 will be modeled neglecting biological and chemical reactions starting from a background equilibrium level and then forced with realistic fluxes, including bubble-mediated transfer coefficients. The hypothesis will be tested by comparing model solutions at varying resolutions against a control run using standard transfer coefficient parameterizations that depend only on wind speed.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.