Hydrosphere: Ocean Relief, Salinity, Temperature, Currents and Tides
Hydrosphere: Ocean Relief, Salinity, Temperature, Currents and Tides
This domain tests ocean floor features, the controls of salinity and temperature, current systems and tide types. Expect map-based identification and simple causal explanations.
Core rules and concepts
- Ocean relief: continental shelf (shallow, fisheries, oil), continental slope, continental rise, abyssal plain, mid-ocean ridge, seamount/guyot and trench (deepest).
- Average ocean salinity is about 35 parts per thousand. It is highest in the subtropics where evaporation exceeds rainfall; lower near the equator and at river mouths; the Baltic is very low, the Red Sea high.
- Temperature decreases with depth. A thermocline separates warm surface water from cold deep water; polar water is coldest and densest.
- Currents are driven by winds, density differences and Coriolis deflection; they form gyres. Warm currents raise coastal temperatures; cold currents cool them and encourage fog and upwelling.
- Tides are caused mainly by the Moon's gravity, with the Sun modifying range. Spring tides occur at new and full moon; neap tides at quarter phases.
Worked example
Why is salinity lower at the equator than at 20°–30° latitude? Reasoning: equatorial rainfall and large river discharge add fresh water, while cloud cover reduces evaporation. In the subtropics, clear skies and descending air give high evaporation with little rain, so salinity rises. Temperature alone does not decide salinity; the rainfall–evaporation balance does.
Traps
The deepest ocean feature is a trench, not an abyssal plain. Spring tides are not a season. Cold currents flow toward the equator on the western sides of continents in low latitudes. Do not confuse salinity (ppt) with density.