Not surprisingly, it's a ring of land (5)
I believe the answer is:
atoll
'land' is the definition.
The definition and answer can be both natural objects as well as being singular nouns.
Perhaps you can see a link between them that I don't see?
'not surprisingly it's a ring' is the wordplay.
'not surprisingly' becomes 'a' (I can't explain this - if you can you should believe this answer much more).
'it's a ring' becomes 'toll' (ring a bell).
'a'+'toll'='ATOLL'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for atoll that I've seen before include "Circular coral reef" , "Coral island surrounding a lagoon" , "Key" , "Coral island(s) surrounding a lagoon" , "Ring-shaped coral reef enclosing a lagoon" .)