Oceans, Atmosphere, and Climate
Ocean structure and circulation
Seawater density increases with salinity and decreases with temperature, so cold, salty water is densest and sinks at high latitudes, driving thermohaline circulation. Distinguish the surface mixed layer, thermocline, and deep zone. Winds plus the Coriolis effect create gyres; Ekman transport moves surface water roughly 90° to the wind, and offshore-directed transport produces coastal upwelling. El Niño weakens or reverses the trade winds, warm water spreads east, and Peruvian upwelling collapses, bringing drought to Indonesia and Australia and wetter conditions to Peru; La Niña is the reverse. Keep tides (mostly lunar), wind waves, and density currents separate.
Atmosphere and energy
Know composition (N₂ ≈78%, O₂ ≈21%, argon, trace CO₂), the vertical layers, and the temperature trend in each - decreasing with height in the troposphere, increasing in the stratosphere where ozone absorbs ultraviolet. Uneven insolation drives Hadley, Ferrel, and Polar cells, the jet streams, and prevailing winds. Greenhouse gases absorb and re-emit infrared, warming the surface; this is not the same process as ozone depletion. Front and air-mass questions require source regions and the fact that warm air holds more water vapor.
Climate and feedbacks
Climographs pair monthly temperature and precipitation; check hemisphere (July–August warm means northern), total rainfall, and seasonality. Ice-albedo is a positive feedback. Milankovitch cycles (eccentricity ~100 kyr, obliquity ~41 kyr, precession ~23 kyr) redistribute sunlight rather than changing total solar output.
Traps: "the ozone hole causes the greenhouse effect"; "Coriolis is strongest at the equator" (it is zero there); "El Niño means warm water in the western Pacific"; "weather and climate are the same." Rule of thumb: cold + salty = dense = sinking, which is why deep water forms at high latitudes.
Worked example
Sea-surface temperatures rise off Peru and trade winds slacken. Predict: wetter Peru and drought in Australia - the classic El Niño pattern.