Explanation for lord byron's poem?

10 roll on, thou deep and dark blue ocean – roll!
ten thousand fleets sweep over thee in vain;
man marks the earth with ruin – his control
stops with the shore; upon the watery plain
the wrecks are all thy deed, nor doth remain
15 a shadow of man’s ravage, save his own,
when, for a moment, like a drop of rain,
he sinks into thy depths with bubbling groan,
without a grave, unknelled, uncoffined, and unknown.
3
and i have loved thee, ocean! and my joy
20 of youthful sports was on thy breast