Presentation on theme: "Where’s the Water? F ReservoirVolume (10 6 km 3 )Percent Ocean1370 97.3 Ice (polar) 29 2.1 Groundwater 5 0.4 Lakes 0.1 0.01 Atmosphere 0.01 0.001 Rivers0.0010.0001."— Presentation transcript:
Where’s the Water? F ReservoirVolume (10 6 km 3 )Percent Ocean1370 97.3 Ice (polar) 29 2.1 Groundwater 5 0.4 Lakes 0.1 0.01 Atmosphere 0.01 0.001 Rivers0.0010.0001
Where did the water in the Oceans come from? F Outgassing (H 2 O, CO 2 ) of the Earth from volcanoes, early in its history F Sedimentary rocks as old as 3.8 billion years! F A much smaller amount from comets that pass by
Water is a “Polar” Molecule F Weak electrical attraction makes for “sticky” molecules F This explains its unique properties: heat capacity surface tension dissolving power
Temperature vs Heat F Temperature is a measure of how fast the molecules in a substance are moving F Heat is a measure of how much energy has to be put into (or gotten out of) a substance to change its temperature, or “state” (solid, liquid, gas)
Sensible Heat vs Latent Heat H Sensible heat is what we sense from different temperatures H Latent heat is the energy needed to change state (ice to water, water to vapor)
Consequences F Bottom temperature of deep, cold lakes is always 4 o C. F Ice floats on the water surface, so fish survive. F Pipes (or beer bottles) can freeze and burst.
Surface tension - measure of how difficult it is to stretch or break the surface of a liquid Water has the highest surface tension of all common liquids
Energy removed from surface (evaporation) Energy liberated into the atmosphere (condensation) Major source of energy to power the Earth’s weather systems
Special Properties of Water F Density of solid is less than liquid F Melting and boiling points are very high F Highest heat capacity F High heat of fusion and vaporization F Tremendous dissolving power
Why is the Ocean Salty? F Total dissolved solids (called “salinity”) F About 3.5% by weight (average seawater) F Usually expressed as 35 0 / 00 (parts per thousand, ppt) F Varies geographically according to Evaporation, Precipitation, and Rivers
The Most Abundant Ions F Chloride (Cl - )19.0 g/kg F Sodium (Na + )10.6 “ F Sulfate (SO 4 2- ) 2.6 “ F Magnesium (Mg 2+ ) 1.2 “ F Calcium (Ca 2+ ) 0.4 “ F Potassium (K + ) 0.4 “ 35.2 g/kg
Ions in Sea Water F Anions are negatively charged Cl -, SO 4 - F Cations are positively charged Na +, K +, Ca ++, Mg ++
Measuring Salinity F Principle of Constant Proportions e.g., SO 4 2- /Cl - is a constant, independent of salinity F This means we need measure only one ion to get salinity; i.e., Cl - F Today salinity is measured quickly by electrical conductivity of sea water
Where does Salinity come from? F Terrigenous input (rivers, dust, ash) F Hydrothermal vents F Dissolving old sediments (evaporites) F Steady State: Inputs equal Outputs
Weathering of Rocks F H 2 O + CO 2 ---> H 2 CO 3 (carbonic acid) F “acid” rain, pH ~4-5; environmental concerns (HCl, HF, H 2 SO 4 ) F Dissolves rock minerals into ions, which travel down rivers to the ocean
Residence Time F How long do the various dissolved ions stay in the ocean? Depends on how “reactive”. Residence Time: The average time spent by a substance in the Ocean = Amount in Sea Rate entering or exiting
Residence Time F For water entering through rivers, the residence time is about Volume = 1370x10 6 km 3 (oceans) Flux 0.037x10 6 km 3 /yr (rivers) = 35,000 years. For Cl -, the residence time is 100 Ma! For Fe 2+, the residence time is 200 yr Which is likely to obey Constant Proportions?
Adding salt lowers the freezing temperature: Seawater freezes at about -2 o C Freezing removes fresh water, leaves salt
Which ocean is Saltiest? In spite of the fact that many more big rivers empty into the Atlantic than the Pacific, the Atlantic is actually significantly saltier because of the evaporation-precipitation cycle and the Isthmus of Panama; the Indian is intermediate
Surface salinities Evaporation, precipitation, and wind patterns explain high/low salinity of Atlantic/Pacific.
Summary: è Water is a polar molecule -- unique properties (melting pt, heat capacity, dissolving power, water denser than ice) è Salinity is the total dissolved solids è Salinity in the surface ocean varies by Evaporation - Precipitation è Principle of Constant Proportions è Residence Time in the Oceans