What you will learn in Oceanography

1. 1. The shape of the sea floor

   A drained ocean, drawn from a one-degree grid with its exaggeration always on screen. The mid-ocean ridge is the largest feature on the planet, and at true scale the whole sea floor goes flat — both are true at once.

2. 2. Salt

   Where the surface ocean is saltiest, and why: evaporation, rain, rivers and ice. Two independent datasets put the salinity maxima under the driest skies. The amount of salt varies; the recipe does not.

3. 3. Layers

   The temperature–salinity diagram, the oceanographer's own tool. Water masses as boxes, mixing as straight lines, density as curves — and two waters of equal density that mix into something denser.

4. 4. The conveyor

   Try to sink surface water to the abyss anywhere on Earth. The tropics are too warm, the Arctic too fresh, the Mediterranean too shut in. Two regions succeed, and they emerge from density rather than a label.

5. 5. Wind on water

   The Ekman spiral, transport at ninety degrees to the wind, the real winds piling water into the subtropics, and a gyre that turns lopsided the moment the Coriolis parameter is allowed to vary with latitude.

6. 6. Upwelling and life

   Wind along a coast moves surface water offshore and cold water rises to replace it. Reverse the wind and it stops. Keep the wind and deepen the nutricline, and the water that rises is barren: El Niño off Peru.

7. 7. Tides, and the ocean's chemistry problem

   One subtraction turns one tidal bulge into two. Then the same carbon dioxide that warms the planet dissolving into the sea: pH falling within the alkaline range, and carbonate saturation as the harm.