Main •
John Lynch as Dr. Arthur Wilde (seasons 1-3), a famous biologist. 8 years prior to the events of the series, he and Annika discovered a bacterium that feeds on . On Polaris VI, he continues the research in order to fight climate change. Although he does not lead the research station, as head scientist he does have some authority over the staff. At first classified as missing, he is another survivor. He is a brilliant but manipulative narcissist whose unethical pursuit of a climate solution drives the conflict across all three locations. •
Katharine O'Donnelly as Dr. Maggie Mitchell (seasons 1-3), the station doctor during winter. She is new to Polaris VI with Aki and Heather, and becomes close to Aki. Upon their return, the summer team finds her hiding and afraid as one survivor next to two missing and seven dead team members. She tries to reconstruct the past events while being worn-out physically and mentally. The story she tells leads Johan's search for his wife. Initially appearing as a traumatized survivor, she is later revealed to be a vengeful and highly intelligent strategist hunting Arthur Wilde to the ends of the Earth. •
Olivia Morris as Rachel Russo (seasons 2–3), a marine biologist and the estranged daughter of Arthur Wilde. She joins the
Alexandria in season 2 to reconcile with her father but becomes a vital player in the high-stakes human trials in the Sahara.
Season 1 •
Alexandre Willaume as Johan Berg (season 1), the station's summer commander. His wife Annika remains in the station during winter and is missing when Johan returns after six months, having lost communications for three weeks. He tries to figure out what happened and find his wife. •
Richard Sammel as Erik Osterland (season 1), the winter commander of Polaris VI. He has a military background and tries hard to keep the team safe and together. He has a relationship with Ebba, the station's nurse. •
Tomohisa Yamashita as Aki Kobayashi (main, season 1; guest, season 2), a young, ambitious biologist who works on his PhD. He admires Arthur Wilde and his work and is proud to work for him. Like Maggie and Heather, he is new at the station. Aki and Maggie are very close, and he's protective of her, even more so when the killings begin. •
Laura Bach as Annika Lundqvist (season 1), an ambitious and very dedicated biologist who discovered the bacterium together with Arthur. She remained at Polaris VI because she is determined to work on this crucial research and be acknowledged as well in a world very dominated by men. Upon Johan's return, Annika is missing, and he tries hard to find her. •
Álvaro Morte as Ramón Lazaro (season 1), the station cook who has repeatedly returned to the station for many years now. He gets along with the crew, but can also become choleric and aggressive.
Season 2 •
Moe Dunford as Alec Kurtz, a security expert on the
Alexandria who finds himself outmatched by the psychological warfare occurring on the ship. •
Josefin Neldén as Amy, a dedicated scientist working under Wilde who begins to suspect the true nature of the research and the identity of the killer. •
Hovik Keuchkerian as Charlie, the ship's head of security. A former professional boxer, he uses his physical presence and intuition to hunt the murderer on board. •
Sota Fukushi as Yuto Nakajima, a computer specialist from Japan responsible for the freighter's technical infrastructure and data security.
Season 3 •
Ben Cura as Liam Ruddock (main season 3, guest season 2). •
Stanley Weber as Pierre. •
Clara Galle as Alba. •
Riko Nakazono as Keiko. •
Godehard Giese as Horst. •
Johnny Grodan as Joe. •
Lochlann Ó Mearáin as Sean.
Supporting and recurring •
Chris Reilly as Nils Hedlund (season 1), the station's Technician who is shown as conflicted, drinking a lot and more and more affected by
polar T3 syndrome. • Tom Lawrence as Miles Porter, the communications officer and one of the longest serving staff at Polaris VI. •
Sandra Andreis as Ebba Ullman (season 1), the station nurse who has spent many winters on Polaris VI already. She misses her kids and her family, but also has an affair with Erik, which is straining on her. •
Amelia Hoy as Heather Blake (season 1), a Computer Officer from Texas who is very athletic and competitive. She is the third newbie on the station, along with Maggie and Aki. •
Mónica López as Astrid Casado (season 1) •
Hannes Fohlin as Gus (season 1) • Andreas Rothlin as Dr. Micke Karlsson (season 1) • Philippe Jacq as Damian Fowles (season 1) •
Nora Ríos as Gloria (season 2), a crew member and researcher on the
Alexandria. •
Enrique Arce as Óscar (season 2), a cynical technician on the cargo ship. •
Olwen Fouéré as Lauren (season 2 and 3), a mysterious figure with deep ties to the corporate interests funding Wilde's research. •
Lolu Ajayi as Jamal, part of the facility's security. == Production ==