The most common and most likely answer to this crossword clue is the 9 plus 4 letter word COOMASSIE BLUE
C
O
O
M
A
S
S
I
E
B
L
U
E
Buddy explains!
The straight part
We know that "imbues cool sea when dispersed (13, 2 words)" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case imbues cool sea when dispersed (13, 2 words) = coomassie blue.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.