Measuring Diapycnal Mixing in the Upper Ocean therMocline using Noble Gas Supersaturation

在这个项目中，华盛顿大学海洋学院的研究人员将开发一种新方法，利用溶解惰性气体的自然分布来限制海洋中横等环流混合的速率。他们将应用这一方法来确定亚热带海洋通风温跃层的内旋混合率，在那里，长期以来对向光带提供营养物质的物理机制存在不确定性。惰性气体不受生物学的影响，因此它们在海洋中的分布完全由物理过程决定。因为这些气体的平衡浓度是温度的非线性函数，所以在不同温度下与大气平衡的水之间的混合会引起气体的过饱和。最近，分析方法的进步使得测量这种混合信号成为可能，并且理解它的理论基础也刚刚发展起来。该理论指出，自从水包离开地表以来，惰性气体的过饱和度随着时间的推移而积累，并且它对海洋通风的温跃层中的潜流混合最为敏感。因此，这种示踪剂记录了数十年时间尺度上的深周期混合的影响，并补充了持续数月至一年的有目的的示踪剂释放实验和代表数百年的整个海洋温跃层混合分析。该项目将分析研究与理论研究相结合。研究小组将通过世界上三个通风的温跃层剖面测量Ne、Ar、Kr和Xe的浓度。通过北太平洋中部和南太平洋东部的两个经向剖面，以及横跨北大西洋南部的一个纬向样带，我们预计稀有气体示踪剂将显示出不同程度的过饱和度，这是由于底旋混合造成的。该提案的理论/建模方面侧重于使用一系列海洋全球环流模型来帮助分离导致惰性气体过饱和的不同物理过程。然后，该模型将用于确定由惰性气体示踪剂推断出的双周期混合率对亚热带海洋中营养物向热带区输送的影响。利用这种跨学科的方法，研究小组将评估高饱和度过饱和度作为海洋温跃层中深层混合的示踪剂的效用，并促进我们对海洋学中一个经典问题的理解。预计该项目将产生一系列更广泛的影响。通过开发一种量化海洋温跃层中周期混合率的新方法，该项目将有助于解决依赖于这一基本数量的许多问题，从确定生物生产力及其控制到了解翻转环流背后的驱动力。更好地限制混合率和广泛传播用于其他数据/模式比较的观测数据集，将改进对海洋人为二氧化碳吸收和全球变暖引起的生物生产力变化的预测，这两个主题都是社会明显感兴趣的。该项目还将促进教育，由主要研究人员共同指导一名研究生，并通过与日本和加拿大同事建立联合实地研究和分析研究，加强国际科学合作。

In this project, researchers at the University of Washington School of Oceanography will develop a new method of constraining the rate of diapycnal (cross-isopycnal) mixing in the ocean using the natural distributions of dissolved noble gases. They will apply this method to determine the diapycnal mixing rate in the ventilated thermocline of the subtropical oceans where there is long-standing uncertainty about the physical mechanisms supplying nutrients to the euphotic zone. Noble gases are not affected by biology, so their distribution in the ocean is determined purely by physical processes. Because the equilibrium concentrations of these gases are non-linear functions of temperature, mixing between waters equilibrated with the atmosphere at different temperatures induces a supersaturation in the gases. Advances in analytical methodology have recently made it possible to measure this mixing signal, and a theoretical basis for understanding it has also just been developed. The theory indicates that noble gas supersaturation accumulates over the time since the water parcel left the surface and that it is most sensitive to diapycnal mixing in the ventilated thermocline of the ocean. Thus, this tracer records the effect of diapycnal mixing over time scales of decades and compliments purposeful tracer release experiments that last months to a year and whole-ocean analyses of thermocline mixing that represent hundreds of years. The project will combined analytical and theoretical research. The research team will measure the concentrations of Ne, Ar, Kr and Xe in transects through three sections of the world's ventilated thermocline. Two meridional sections through the central North Pacific and eastern South Pacific and a zonal transect across the southern North Atlantic cross contrasting regions where we expect the noble gas tracers to reveal different degrees of supersaturation due to diapycnal mixing. The theoretical/modeling aspect of the proposal focuses on using a series of ocean global circulation model runs to help separate the different physical processes causing noble gas supersaturation. The model will then be used to determine the effect of the diapycnal mixing rates deduced from the inert gas tracers on the transport of nutrients to the euphotic zone in the subtropical oceans. Using this interdisciplinary approach the team will evaluate the utility of noble supersaturation as a tracer of diapycnal mixing in the ocean thermocline and advance our understanding of a classic problem in oceanography. The project is expected to have a number of broader impacts. By developing a new method of quantifying diapycnal mixing rates in the ocean's thermocline, this project should help to solve the many issues that depend on this fundamental quantity, from determining biological productivity and its controls to understanding the driving forces behind the overturning circulation. Better constraints over mixing rates and wide dissemination of the observational dataset for other data/model comparisons will lead to improved predictions for anthropogenic CO2 uptake by the ocean and for changes in biological productivity caused by global warming, both topics of clear interest to society. The project will also promote education by involving a graduate student that will be jointly advised by the principle investigators and will enhance international scientific collaboration by establishing joint field and analytical research with Japanese and Canadian colleagues.