The road crews in this area (Ohio, USA) use brine to pretreat roads when icing conditions are expected. Some trucks are also equipped to spray brine onto the granular material as it is spread on the roads. Either Calcium or Sodium Chloride is used depending on many factors.

Fresh water freezes at about 32˚f, (0˚c). Sea water typically freezes at about 28.4˚f (-2˚c). I am thinking that sea water would not be an effective ice melting solution, except in a very narrow temperature window. Granular sodium chloride is effective down to 20˚f (-7c), while granular calcium is effective down to -20˚f (-29˚c)