Possible Clues:

• Little that's visible
• A sign of trouble below
• Lettuce's wrinkle? There's much more underneath
• Hint of the whole
• Bit that's visible
• Small indication of a large problem
• Little sign of danger, but it's freezing
• Arctic tern's nesting area?
• There's a lot more, in fact, in the main car:- female article; gems; and black work unit
• Small part that's visible