a) Evolution of the air-ice CO₂ flux (black corresponds to a period with the chamber not properly sealed, blue to a period with a correct sealing of the chamber) and temperature 2 cm above the air-ice interface (in red). The green horizontal step line corresponds to the flux calculated from the DIC anomaly. The shaded areas refer to working hours and the related increase of atmospheric pCO₂. b) Atmospheric (black line), ice surface (green triangles down) and seawater (blue triangles up) pCO₂. The ice surface pCO₂ corresponds to the first 5 cm of the bulk sea ice measured with the method of high vertical resolution.