What you’ll learn14 learning objectivesChoose one objective for a focused lesson, or study the complete topic.4.1.1Water movement drivers• Solar radiation and gravity• Heat for evaporation, gravity for drainageSyllabus objective4.1.2Hydrological cycle• System with stores and flows• Stores: boxes; flows: arrowsSyllabus objective4.1.3Hydrological cycle stores• Oceans (96.5%), glaciers/ice caps (1.7%), groundwater (1.7%)• Surface freshwater (0.02%), atmosphere (0.001%), organisms (0.0001%)Syllabus objective4.1.4Hydrological cycle flows• Transpiration, sublimation, evaporation, condensation, advection, precipitation• Melting, freezing, run-off, infiltration, percolation, streamflow, groundwater flowSyllabus objective4.1.5Human activity impacts• Agriculture, deforestation, urbanization alter flows and stores• Reduced evapotranspiration, increased run-off → flash floodsSyllabus objective4.1.6Water body steady state• Flow diagrams of inputs and outputs• Calculate sustainable harvesting ratesSyllabus objective4.1.7(HL)—Water properties• Polarity, cohesion, adhesion, solvent properties• Transparency, high specific heat capacity• Density variations with temperature• Gas solubility variationsSyllabus objective4.1.8(HL)—Oceans as carbon sink• Absorb atmospheric CO₂ and sequester it• Moderates atmospheric CO₂ increases• Saturation point may be reachedSyllabus objective4.1.9(HL)—Ocean carbon sequestration• Short-term: dissolved CO₂ → ocean acidification• Long-term: biomass accumulates on seabed → fossil fuelsSyllabus objective4.1.10(HL)—Water temperature and density• Cold water below, warmer above• Density differences restrict mixing → stratification• Water densest at 4°C → freezing from surface downSyllabus objective4.1.11(HL)—Stratification• Occurs in deeper lakes, coastal areas, seas, ocean• Thermocline: transition layer between warm surface and cold deep water• Differences in dissolved oxygen and mineral nutrientsSyllabus objective4.1.12(HL)—Ocean stratification increase• Global warming and salinity changes• Most pronounced in upper 200mSyllabus objective4.1.13(HL)—Upwellings• Bring cold, nutrient-rich waters to surface• Mass vertical movement from depths• Seasonal cycles in stratified lakes and ENSOSyllabus objective4.1.14(HL)—Thermohaline circulation• Driven by temperature and salinity differences• Ocean conveyor belt distributes heat globally• Affects climateSyllabus objective
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