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