Historical clue formulations

• Sea with no land boundaries — 2018-12-08
• Floating brown algae — 2010-04-09
• ___ Sea, in the North Atlantic — 2000-03-20
• Gulfweed — 1998-11-29
• Gulfweed — 1998-06-25
• Sea in a Jean Rhys title — 1997-12-19