how does salinity in the oceans vary over the globe and what is the likely reasons for this?

Answer 1

The major variable regarding ocean salinity is the 'Water Cycle.' Only pure water evaporates from oceans, lakes and seas. Not salt water. So, any body of water tends to get more salty over time. If all the water evaporates, all that is left is salt. That is why Utah has the great salt flats. The huge lake Bonneville evaporated and left behind miles and miles of salt.

But in the Water Cycle, the water that evaporates does not just stay up in the air. It forms clouds, rain or snow falls to Earth and flows down rivers back into the oceans, seas and lakes. The water that falls from the sky - not counting any pollution! - is pure water. The rivers and glaciers carry this water - with dissolved minerals and salts - back into the sea.

The concentration of dissolved minerals and salts of the rivers or glaciers is far less than that in the oceans. So near where fresher water is flowing into the oceans the salinity is lower than that out in the parts of the ocean where there is less rainfall.

;-D There is a lot of water on planet Earth, but not much of it is drinkable! Don't waste water!