Syllabus concepts to know

• 4.1.1 Movements of water in the hydrosphere are driven by solar radiation and gravity.
• 4.1.2 The global hydrological cycle operates as a system with stores and flows.
• 4.1.3 The main stores in the hydrological cycle are the oceans (96.5%), glaciers and ice caps (1.7%), groundwater (1.7%), surface freshwater (0.02%), atmosphere (0.001%), organisms (0.0001%).
• 4.1.4 Flows in the hydrological cycle include transpiration, sublimation, evaporation, condensation, advection, precipitation, melting, freezing, surface run-off, infiltration, percolation, streamflow and groundwater flow.
• 4.1.5 Human activities, such as agriculture, deforestation and urbanization, can alter these flows and stores.
• 4.1.6 The steady state of any water body can be demonstrated through flow diagrams of inputs and outputs.
• 4.1.7 Water has unique physical and chemical properties that support and sustain life.
• 4.1.8 The oceans act as a carbon sink by absorbing carbon dioxide from the atmosphere and sequestering it.
• 4.1.9 Carbon sequestered in oceans over the short term as dissolved carbon dioxide causes ocean acidification; over the longer term, carbon is taken up into living organisms as biomass that accumulates on the seabed.
• 4.1.10 The temperature of water varies with depth, with cold water below and warmer water above.
• 4.1.11 Stratification occurs in deeper lakes, coastal areas, enclosed seas and open ocean, with a thermocline forming a transition layer between the warmer mixed layer at the surface and the cooler water below.
• 4.1.12 Global warming and salinity changes have increased the intensity of ocean stratification.
• 4.1.13 Upwellings in oceans and freshwater bodies can bring cold, nutrient-rich waters to the surface.
• 4.1.14 Thermohaline circulation systems are driven by differences in temperature and salinity.