Diurnal CO2 Flux Variations Above an Alkaline Playa

The carbonate mineral deposits at Atlin, British Columbia, known as hydromagnesite‐magnesite playas, are unique in the world. The playas have been forming from carbon and magnesium dissolved in the groundwater for millennia and are exposed to the elements at the Earth's surface. Since carbon is present in the groundwater and minerals, CO₂ gas can be exchanged with the atmosphere. Understanding physical and chemical processes governing CO₂ exchange between predominantly unvegetated carbonate deposits and their importance in the carbon cycle is essential in the current climate.

Using dynamic closed chambers, researchers continuously measured CO₂ exchange between the playa and the atmosphere. They found that the CO₂ fluxes had a distinct diurnal oscillation with emissions of CO₂ in the daytime balanced by similar uptake of CO₂ at nighttime. At 1‐m depth in the playa, CO₂ concentrations exceeded 8000 ppm, and the researchers found minimal net exchange of carbon across the playa‐atmosphere interface despite the large source of CO₂ just below the surface.

These findings provide insights into the factors controlling CO₂ fluxes in an inorganic carbon system and guidance for future application of these flux methods to measure CO₂ capture and storage in engineered mineral systems.