Wanderlust World Wanderlust World Seawater's salinity isn't a single event—it's a planetary-scale, billion-year accumulation of dissolved minerals. Here's the step-by-step cycle:
Rain (slightly acidic from dissolved CO₂) falls on continents, chemically weathering rocks. It picks up ions—sodium, chloride, magnesium, sulfate, calcium, potassium—and carries them via streams and rivers to the ocean.
At mid-ocean ridges, seawater seeps into fractured crust, superheats, reacts with basalt, and erupts through black smokers loaded with dissolved metals and sulfides. This submarine "reverse weathering" contributes significantly to ocean chemistry.
The ocean is a closed basin for salts. Water evaporates (leaving salts behind); rain and river inflow add fresh water. Over geologic time, inputs ≈ outputs for water, but salts accumulate because they don't evaporate.
| Ion | Concentration (g/kg) | % of Dissolved Solids |
|---|---|---|
| Chloride (Cl⁻) | 19.35 | 55% |
| Sodium (Na⁺) | 10.76 | 30.6% |
| Sulfate (SO₄²⁻) | 2.71 | 7.7% |
| Magnesium (Mg²⁺) | 1.29 | 3.7% |
| Calcium (Ca²⁺) | 0.41 | 1.2% |
| Potassium (K⁺) | 0.39 | 1.1% |
Together: >99% of all dissolved solids. Ratios are remarkably constant globally (Forchhammer's Principle).
Salinity drives thermohaline circulation (the global conveyor belt), determines sound speed (sonar), controls marine physiology (osmoregulation), and records past climate in foraminifera shells. The salt in your tears is a direct chemical echo of this 4-billion-year cycle.