A discussion of salinity that means the salt content of the oceans requires an understanding of these important concepts:

• The present-day oceans are considered to be in a state where it receives as much salt as they lose.
• The salty oceans have been mixed with each other over such a long time period that their composition of sea salt is actually the same everywhere.

The reason salinity doesn’t change much across space or time is because the salt content stays pretty consistent. We’re talking about an estimated range of 33 to 37 grams of salt per kilogram. Generally, the average is around 35 PSU (Practical Salinity Units), but sometimes it shifts a bit due to what’s happening on the Earth’s surface. Places with lots of evaporation end up with saltier surfaces, while spots with more rainfall have less salty surfaces. Near the shore, especially close to big sources of freshwater, salinity can go down because of dilution. It’s like when a part of the ocean is separated from the open sea by land – that area gets influenced by the freshwater nearby.

Salinity of the Ocean 

Salt in the ocean originates two sources:

• Runoff from the land.
• Openings in the seafloor.

You know, the rocks chilling on the Earth’s surface are like the VIPs of salt production for our oceans. So, when rain decides to drop by, it’s a bit acidic and starts chatting up the rocks, causing them to erode. This erosion lets out ions, which hitch a ride to streams and rivers, ending up in the ocean. The cool thing is, sea life uses some of these ions, making the water cleaner. But, you see, not all ions get this VIP treatment, and their gang in the water gets bigger over time. Oh, and there’s another salt source party happening underwater! Hydrothermal fluids, or ocean floor vents, are like secret salt suppliers. Ocean water sneaks into these underwater cracks, gets cozy with Earth’s magma, and they start a hot chemical dance.

During this dance, the water loses some stuff like oxygen and magnesium, but gains metals like iron, zinc, and copper from nearby rocks. Then, the hot water throws a party and releases these metals through the ocean floor vents. It’s like a direct delivery of minerals to the ocean! Now, when it comes to the ocean’s ion guest list, chloride and sodium are the rock stars, making up a whopping 85%. Magnesium and sulfate are like the cool sidekicks, adding another 10%. The rest of the ions are just tiny party crashers in the grand ocean celebration.

Read Also: Why Is Salinity Important in the Ocean?