Hydrosphere: Oceans, Water Resources and Hydrological Cycle
What this domain tests
Questions cover ocean temperature and salinity, currents, tides, and the stores and flows of the hydrological cycle, including water resources.
Core rules
- Average ocean salinity is about 35 parts per thousand. Salinity is highest in subtropical high-evaporation seas and lowest near large river mouths and high-rainfall equatorial zones.
- Temperature falls with depth; the thermocline is the zone of rapid decrease. Currents are driven by winds, density differences and Coriolis deflection, forming gyres.
- Tides are caused mainly by the Moon and Sun. Spring tides occur at new and full moon (syzygy); neap tides at quadrature.
- Hydrological cycle: evaporation, transpiration, condensation, precipitation, infiltration, runoff, groundwater storage.
Worked example
Why is surface salinity lower in the Bay of Bengal than in the Arabian Sea? The Bay receives huge freshwater discharge from the Ganga, Brahmaputra and other rivers and has high monsoon rainfall. The Arabian Sea has less river input and higher evaporation. Dilution lowers Bay salinity.
Traps
Spring tides are not a season; they occur twice a lunar month. Tides are not caused by Earth's rotation alone. Groundwater is part of the hydrological cycle, not separate from it. Salinity is not highest at the equator because heavy rainfall dilutes it.