According to this list: http://travel.cnn.com/explorations/life/worlds-15-highest-bungee-jumping-sites-479316
and crossing it with the description here: http://www.skybreakers.com/eng/suomenkorkein_eng.htm
apparently the highest bungee jump above/over the sea is in Kaivopuisto, Helsinki, Finland. The jump is done from 150 mts high.
It's very likely that other jumps over the sea, from higher heights, have been done. This is the highest commercial one (commercial in the sense - schedule or arrive, pay, do!).
