Is this why oceans are salty? From noaa.gov's Ocean facts:


  Salt in the ocean comes from rocks on land.
  
  The rain that falls on the land contains some dissolved carbon dioxide from the surrounding air. This causes the rainwater to be slightly acidic due to carbonic acid (which forms from carbon dioxide and water).


But...if this is the case wouldn't our rivers be even saltier from seasonal downpours and snowpack melt?
No, because fresh rainfall has no salt in it, so as long as the river keeps moving the salt has no time to accumulate.

Only stagnant sources of water on land, like lakes with no outlet, can become saline.