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Dissolution and mass transfer at gas liquid interfaces are central to many industrial and environmental issues. All these applications aim at predicting the transfer velocities between the two phases, and the dependency of these velocities on several factors such as pressure, temperature, flow regime and so on. The goal of the present study is to understand the physical phenomena acting in the liquid phase during the dissolution and transfer of a gas at a flat two-phase interface; and to measure the influence of these phenomena on mass exchanges. To that end, an oscillating grid apparatus is used to generate a controlled liquid side turbulence. The dissolution of an atmospheric sparingly soluble gas, carbon dioxide, is considered. Optical measurement techniques are used simultaneously in order to gain further insight on the hydrodynamics influence on dissolved gas mixing. The phenomena responsible for mass transfer acceleration are found to happen in thin characteristic depth scales under the interface. In those regions, a complex combination of dissolved gas injection and diffusion layers renewing events is observed. The analysis of velocity fields highlights their strongly three dimensional aspects, and simultaneous measurements, lead to the conclusion that these three-dimensional effects have an impact on dissolved scalar concentration structures, and consequently on mass transfer.