Possible Clues:

• Arctic ecosystem
• When so frozen below, it's difficult to crack the cockney back here
• Vast level Arctic region with frozen subsoil
• Cold plain
• Doctor tucked into fish in northern region
• Frozen plain fish -- doctor tucks in
• Vast Artic region with frozen sub-soil
• Artic treeless plain
• Treeless area
• Area with frozen subsoil