Observations of elemental and isotopic ratios of atmospheric major components and its application to detect atmospheric circulation and ocean heat uptake changes

Abstract:

Gravitational separation of the atmospheric constituents has been observed by analyzing the stratospheric air samples for Ar/N₂ ratio and stable isotopic ratios of N₂, O₂ and Ar (Ishidoya et al., 2008, 2013, 2018; Sugawara et al., 2018). By applying the precise measurements to the tropospheric air samples, we have also reported seasonal and interannual variations in the surface Ar/N₂ ratio around Japan and in Antarctica (Ishidoya et al., in review). Gravitational separation of the stratospheric air is weakened (enhanced) due to an enhancement (weakening) of the atmospheric circulation by a balance between mass-independent transport and mass-dependent molecular diffusion. Therefore, gravitational separation can be used as an indicator of the Brewer-Dobson circulation. In addition, an enhancement of the stratospheric gravitational separation will induce an increase of heavier molecules at the surface. Such increase is negligibly small for the atmospheric components with significant chemical and/or biological processes, however, it cannot be ignored for the components with the very small secular changes such as Ar/N₂ ratio, which is driven by changes in the solubility in seawater and reflects the spatiotemporally-integrated air-sea heat flux or ocean heat content (OHC). In this presentation, we will review our past studies on gravitational separation in the stratosphere briefly and discuss recent progress in the observations and interpretation of the Ar/N₂ ratio variations at the surface and in the stratosphere.