During a recent visit to the beach, my 5-year-old asked why the sea is salty. We sat there stumped for a moment, debating how we should tackle this question. Ultimately, my wife took the lead and came up with the following explanation:
“Long ago, the sea wasn’t salty at all. In fact, the sea was sweet, and all the fish were getting cavities. The jellyfish tasted like gelatin, and the eels tasted like gummy worms. Well, the fish and the eels and the jellyfish got fed up with all of the sweetness, and they asked the whales to help. So the whales dug up all the salt buried beneath the ocean and stirred up the water until the sea tasted salty.”
Almost every culture has developed some tall tale to explain how the oceans became salty. Nordic myths talk of magic millstones that grind salt aboard a sunken ship at the bottom of the ocean. Polynesian legends describe a giant whose foot lands on an ant colony; the giant shakes his leg, dropping villagers and their sacks of salt into the sea. In Hindu mythology, the powerful sage Agastya slurps up the sea and then spews or urinates it out.
Of course, the truth is much simpler and far less imaginative: The salt in the ocean comes from rocks on land and from openings in the ocean floor. Here is how it works.
Water is an excellent solvent and contains many dissolved substances. The salt in the sea exists in the form of charged particles called ions. The most common of these are sodium and chloride ions, the components of ordinary table salt. Other common ions include magnesium, potassium, calcium, and sulfate.
Ions arrive to the oceans through various natural mechanisms. For instance, as rainwater passes through soil and filters through rocks, it dissolves the minerals that it picks up along the way; this is called weathering. The rainwater, now equipped with a small amount of dissolved salts, flows down streams and into rivers and eventually reaches the sea.
Imagine a gust of wind blowing dust from the land onto the ocean’s surface, or volcanic ash drifting down to the sea. Chemical ions are deposited into the sea through these methods as well.
Beneath the surface, minerals released from hydrothermal vents and submarine volcanoes also provide salts to the oceans. Hydrothermal vents are openings in the sea floor out of which heated water flows. In these places, seawater reacts with hot rocks and dissolves some of the mineral constituents.
You might be thinking, “Won’t the sea become saltier?”
Not likely. There are also sinks for every type of ion—processes that remove these ions from the sea—such as salt spraying onto the land and the precipitation of various ions onto the seafloor as mineral deposits.
Today, the salt content of the oceans has reached a “steady state.” Dissolved salts are removed from seawater at the same rate that weathering and hydrothermal systems provide new salts.
My son sat there in the sand, listening to his mother’s explanation with a grain of salt. Though he suspects it’s not true, I know he prefers his mother’s fable to my dense scientific explanation. (Ions and the processes that move them are no match for gelatin jellyfish and good-doing whales.) Still, I encourage him to explore and examine and ask these questions. My hope is that he’ll continue to be curious about the sea and its inhabitants—and that, one day, that curiosity will grow into a passion for and a profound interest in preserving our oceans.
Author’s Bio
Leopoldo Llinas is a forward-thinking father who hopes to educate the young men and woman who will make this world a better place. He holds a PhD in Marine Biology and Fisheries from the University of Miami Rosenstiel School of Marine and Atmospheric Science. leollinas@gmail.com
