They carry goods south in stormy seas (5)
I believe the answer is:
asses
'they carry goods' is the definition.
The definition suggests an adverb but the answer is not.
'south in stormy seas' is the wordplay.
'south' becomes 'S' (abbreviation).
'in' is an insertion indicator.
'stormy' indicates anagramming the letters.
'seas' with letters rearranged gives 'ases'.
's' going inside 'ases' is 'ASSES'.
Can you help me to learn more?
(Other definitions for asses that I've seen before include "dim bulbs?" , "Small, sure-footed animals" , "Donkeys" , "Idiots" , "Fools; beasts of burden" .)