Earth's Hydrosphere and Cryosphere
Domain V examines the movement and storage of water in oceans, ice, groundwater, and the atmosphere, and the interactions that link them. Items emphasize reservoirs and residence times, ocean circulation and tides, cryospheric change, and human impacts on water resources.
Reservoirs and the water cycle
About 97% of water is saline; of the freshwater, most is in glaciers and ice sheets, with groundwater next and surface water a small fraction. Residence times are long in oceans and ice and short in the atmosphere (days). Transfers include evaporation, transpiration, condensation, precipitation, infiltration, runoff, and discharge.
Oceans
Salinity averages about 35 per mille; density increases with salinity and with cold. Wind plus Coriolis produces subtropical gyres, western boundary currents, and coastal upwelling. Thermohaline circulation is driven by density contrasts from deep water formed in the North Atlantic and around Antarctica. Tides are chiefly lunar: spring tides at new and full moon reinforce Sun and Moon, neap tides at quarters partly cancel them.
Cryosphere
Alpine glaciers differ from continental ice sheets (Greenland, Antarctica). Sea ice is floating and forms from seawater; ice shelves float but are fed by land ice; permafrost is frozen ground. Glacial mass balance compares accumulation with ablation, and the equilibrium line divides them. Land-ice melt plus thermal expansion raises sea level.
Groundwater
Recharge fills aquifers; the water table is the upper saturated boundary; pumping draws a cone of depression and can reverse flow directions.
Worked example
A coastal town pumps heavily from an aquifer whose water table sits near sea level. Freshwater forms a lens floating on denser saltwater. Heavy pumping lowers hydraulic head, so freshwater pressure falls and seawater migrates inland and upward into wells. Remedies: reduce pumping, recharge with treated water, or move wells inland.
Traps
Assuming floating sea ice melting raises sea level (it displaces nearly its own weight); confusing sea ice with ice sheets; treating groundwater as inexhaustible; and mixing up spring and neap tides.