What does that actually mean? Most things happen on land, so anything that happens at sea is going to be strange by default anyway, isn't it. Hey guess what, something just happened away out there in the middle of the atlantic ocean! Really? Well that's strange because normally it's just waves swishing around and the odd ship that passes in the night. See what I mean? Whoever thought that saying up didn't think it through properly enough.
I think it's a sailors expression from the old days, referring to the fact that when there's a bunch of men on a boat together for long periods of time, strange things happen. Plus the sea monsters and Bermuda triangle kinda stuff.
See my Sandy Claws post. http://www.hipforums.com/newforums/showthread.php?p=6663852&posted=1#post6663852 .
Actually, unless you're referring to things that happen to humans, way more things happen in the ocean, where there are many more life forms, than happen on land.