Drifters not mountain climbing around North Korea's capital (8)
I believe the answer is:
plankton
'drifters' is the definition.
(plankton drift through the ocean)
'not mountain climbing around north korea's capital' is the wordplay.
'mountain' becomes 'alp' (the Alps are a mountain range).
'climbing' says the letters should be written backwards (in a down clue, letters climb up).
'around' indicates putting letters inside.
'capital' suggests taking the first letters.
The initial letters of 'north korea' is 'nk'.
'not'+'alp'='notalp'
'notalp' written backwards gives 'platon'.
'platon' enclosing 'nk' is 'PLANKTON'.
(Other definitions for plankton that I've seen before include "Small organisms that float in water in great numbers" , "Minute fish food" , "Aggregate of small marine organisms" , "Drifting ocean organisms" , "Water micro-organisms" .)