Why is the sea salty?

Ah, the ocean. What is it that is so calming about the sea?

The small one and I spend as much time as we can next to it, on it, in it, looking at it, talking about it, learning about it, trying to protect it.

Lately I’ve been on the receiving end of a ton of questions about octopus and squid – Mr Three is fascinated by the idea of an ink-assisted quick getaway. And then there’s the tentacles, the suckers, the camouflage, the mystery of the colossal squid, the epic battles with sperm whales – all irresistible fodder for a small and curious mind. “Let’s talk about octopus and squid, Mummy” has been the constant refrain for some time now, and I’m starting to come to the end of my tales about squishy marine life!

Soooo it was with some relief that I fielded a somewhat ‘easier’ question the other week, in a splutter while swimming together –  “Why is the sea salty?”

The waters of the oceans largely come from rivers, rushing over rocks and silt and full of the mineral stories of the places they’ve come from. Mountain passes, slow-grinding glaciers, simmering rainforests, cool alpine bush, polar tributaries, swampy estuaries…we tried to think of all the different kinds of places rivers flow from and through.

Each of these rivers is pouring mineral-rich waters into the sea day and night, I explained. The rivers themselves don’t taste salty, but as all of this water accumulates in the ocean the mineral blend becomes richer. And then, evaporation takes place, which concentrates the salty sea even more – the sun’s heat works upon the water’s surface to vaporise it into gas and become part of the air. But the minerals don’t evaporate, and what is left behind is a salty sea that we DON’T particularly want to swallow as we’re swimming, right?!

He agreed. And then said, “Let’s talk about octopus and squid, Mummy!”


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