A study of port (4)
I believe the answer is:
aden
'port' is the definition.
(port in Yemen)
'a study' is the wordplay.
'study' becomes 'den' (term for a study or office).
'a'+'den'='ADEN'
'of' is the link.
(Other definitions for aden that I've seen before include "Yemeni gulf" , "Strange Dane to be in the Yemen" , "Dane in seaport of Yemen" , "Dean is out in the Middle Eastern port" , "Yemen's chief port" .)