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

在这个项目中，华盛顿大学海洋学学院的研究人员将开发一种新的方法，利用溶解的稀有气体的自然分布来限制海洋中的稀有气体混合的速度。他们将应用这种方法来确定亚热带海洋通风温跃层中的昼夜混合率，在那里，向真光带提供营养物质的物理机制长期存在不确定性。稀有气体不受生物影响，因此它们在海洋中的分布完全由物理过程决定。由于这些气体的平衡浓度是温度的非线性函数，在不同温度下与大气平衡的水之间的混合会导致气体的过饱和。最近，分析方法的进步使测量这种混合信号成为可能，理解它的理论基础也刚刚发展起来。该理论表明，稀有气体的过饱和度自水团离开海面以来随着时间的推移而积累，它对海洋通风温跃层中的昼夜混合最敏感。因此，这个示踪剂记录了数十年时间尺度上昼夜混合的影响，并补充了持续数月至一年的有目的的示踪剂释放实验，以及代表数百年的温跃层混合的全海洋分析。该项目将结合分析和理论研究。研究小组将通过世界通风温跃层的三个部分测量横断面中的Ne、Ar、Kr和Xe的浓度。穿过北太平洋中部和南太平洋东部的两个经向断面和横跨北大西洋南部的纬向断面横跨不同的区域，我们预计稀有气体示踪剂将揭示由于昼夜混合而产生的不同程度的过饱和。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式运行，以帮助分离导致惰性气体过饱和的不同物理过程。然后，该模型将被用来确定从惰性气体示踪剂推导出的昼夜混合率对营养物质向亚热带海洋真光层输送的影响。使用这种跨学科的方法，该小组将评估贵重过饱和度作为海洋温跃层中昼夜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些更广泛的影响。通过开发一种量化海洋温跃层中昼夜混合率的新方法，该项目应该有助于解决依赖于这一基本量的许多问题，从确定生物生产力及其控制到理解颠覆环流背后的驱动力。对混合速率的更好限制和其他数据/模型比较的观测数据集的广泛传播将改进对海洋人为二氧化碳吸收和全球变暖造成的生物生产力变化的预测，这两个主题显然都是社会感兴趣的。该项目还将促进教育，由一名研究生参与，由主要研究人员共同提供建议，并将通过与日本和加拿大的同事建立联合实地和分析研究来加强国际科学合作。

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.