Related Clues:

• Arctic navigation hazard
• Seagoing ice sheet
• Only about 10 percent of it is visible
• It keeps its head above water
• Penguin hangout
• Sea lane hazard
• Ice chunk
• Floating ice hunk
• ''Wozzeck'' composer
• Titanic downfall?
• Frozen sheet
• Hazard to navigation
• "Lulu" composer Alban
• Floating ice
• Chunk of ice