### Clue: Essentially, it's why sea, sky and current give that in which we have information (3,4)
### Answer: THE KNOW 
 ### Explanation: Definition: that in which we have information
 **The central letters, respectively, of**(Essentially) "it's why sea, sky" **plus**(and) NOW(current;the present time).
Defn: From the phrase "in the know".