[Vidéo en Français] Invited by the Midis MINATEC, Eric Maréchal relives the astonishment of explorers from Antiquity to the present day, when confronted with a unique phenomenon: the red colouring of snow! We walk with them, until they understand that this colouring comes from microalgae, revealing an ocean hidden in these red snows, but also in the white snows… Eric Maréchal presents the ALPALGA project (https://alpalga.fr​), resulting from the collaboration of 5 Grenoble laboratories, which are exploring this little-known ocean, with the support of the Agence Nationale de la Recherche and the Kilian Jornet Foundation.