Using Noble Gases to Constrain the Impact of Water-Mass Formation Processes on Dissolved Gases

The bulk of global ocean gas concentrations are controlled at a few locations where deep-water formation occurs. High wind speeds, rapid cooling, and large swings in atmospheric pressure characterize these regions in the winter. These processes can have competing effects on gas saturations as bubble-mediated gas exchange drives saturations up, cooling and low atmospheric pressure drive saturations down, and diffusive gas exchange drives gases toward equilibrium. The noble gases have the proven potential to disentangle these competing effects, because each gas has different physical properties that make it more or less sensitive to these processes.

We present full water-column measurements of dissolved neon, argon, krypton, and xenon at six locations around the world spanning the North Atlantic, Southern Ocean, and North Pacific. We use a simple vector model to diagnose the importance of atmospheric pressure change, bubble injection, and cooling in creating the observed gas saturations. However, we find that the model is extremely sensitive to the choice of vector slopes. A one-dimensional model of convection in the Labrador Sea suggests that vectors based on a steady-state, in which a disequilibrium process is balanced by diffusive gas exchange, is more likely to represent the true system in nature. We extend our measurements and model to constrain the impact of physical air-sea disequilibria processes on nitrogen (N₂), which could be used to quantify the impact of denitrification throughout the ocean. Noble gas measurements should eventually provide a useful metric for comparison to climate models to evaluate the parameterization of deep-water formation processes on gases, including carbon dioxide.