Possible Clues:

• A grass mutates like this into a weed
• With 11-Down, area between the Azores and the Caribbean
• Name of N. Atlantic sea
• 'Wide -- Sea' (Jean Rhys novel)
• Wide __ Sea, Jean Rhys's prequel to Jane Eyre
• There's no C in ___
• Sea known for seaweed
• Agar's prepared with source of seaweed like this?
• Uncertain gas soars in the Atlantic
• Sea, a region of the western Atlantic Ocean between the Azores and the Caribbean