Geography and Oceanography - Chapter 10 ppsx

The Properties of Sea Water What makes water so special? Why is the ocean salty? Where’s the Water?  Reservoir Volume (10 6 km 3 ) Percent Ocean 1370 97.3 Ice (polar) 29 2.1 Groundwater 5 0.4 Lakes 0.1 0.01 Atmosphere 0.01 0.001 Rivers 0.001 0.0001 Where did the water in the Oceans come from?  Outgassing (H 2 O, CO 2 ) of the Earth from volcanoes, early in its history, but continuing today  Sedimentary rocks as old as 3.8 billion years!  A much smaller amount from comets that pass by The Water Molecule Water is a “Polar” Molecule  Weak electrical attraction makes for “sticky” molecules  This explains its unique properties: heat capacity surface tension dissolving power Temperature vs Heat  Temperature is a measure of how fast the molecules in a substance are moving  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  Sensible heat is what we sense from different temperatures; energy needed to raise T (or released to decrease T)  Latent heat is the energy needed to change state (ice to water, water to vapor) [...]... seawater) Usually expressed as 35 0/00 (parts per thousand, ppt) Varies geographically according to Evaporation, Precipitation, and Rivers The Most Abundant Ions Chloride (Cl-) Sodium (Na+) Sulfate (SO4 2-) Magnesium (Mg2+) Calcium (Ca2+) Potassium (K+) 19.0 g/kg 10. 6 “ 2.6 “ 1.2 “ 0.4 “ 0.4 “ 35.2 g/kg Ions in Sea Water Anions are negatively charged examples: Cl-, SO4Cations are positively charged examples:... residence time is about Volume = 1370x106 km3 (oceans) Flux 0.037x106 km3/yr (rivers) = 35,000 years For Cl-, the residence time is 100 Ma! For Fe2+, the residence time is 200 yr Which is likely to obey Constant Proportions? Adding salt lowers the freezing temperature: Seawater freezes at about -2 oC Freezing removes fresh water, leaves salt The Hydrologic Cycle Evaporation - Precipitation Over the oceans,... fish survive 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 Special Properties of Water Density of solid is less than liquid Melting and boiling points are very high Highest heat capacity High heat of fusion and vaporization Tremendous dissolving power... Proportions e.g., SO4 2-/ Cl- is a constant, independent of salinity This means we need measure only one ion to get salinity; i.e., Cl Today salinity is measured quickly by electrical conductivity of sea water Where does Salinity come from? Terrigenous input (rivers, dust, ash) Hydrothermal vents Dissolving old sediments (evaporites) Steady State: Inputs equal Outputs Weathering of Rocks H2O + CO2 -> H2CO3 (carbonic...Changes of state always occur at constant temperature The heat needed for a change of state is called latent heat Heat and the three Physical States of Water: Evaporation from lakes, oceans, rivers, etc occurs for temperatures lower than 100 oC But it requires more energy to do so Major source of energy to power the Earth’s weather systems Energy liberated into the atmosphere... Terrigenous input (rivers, dust, ash) Hydrothermal vents Dissolving old sediments (evaporites) Steady State: Inputs equal Outputs Weathering of Rocks H2O + CO2 -> H2CO3 (carbonic acid) “acid” rain, pH ~ 4-5 ; environmental concerns (HCl, HF, H2SO4) Dissolves rock minerals into ions, which travel down rivers to the ocean Residence Time How long do the various dissolved ions stay in the ocean? Depends on... Surface salinities Evaporation vs Precipitation Which processes change the surface salinities ? saltier fresher ⇒ evaporation ⇒ precipitation ⇒ sea ice formation ⇒ sea ice melting ⇒ freshwater runoff from land Which ocean is the saltiest? . the water surface, so fish survive. Pipes (or beer bottles) can freeze and burst. Surface tension Surface tension - - measure of how measure of how difficult it is to stretch or break. heat Heat and the three Physical States of Water: Evaporation Evaporation from lakes, oceans, from lakes, oceans, rivers, etc. occurs for rivers, etc. occurs for temperatures lower than 100 . Water  Density of solid is less than liquid  Melting and boiling points are very high  Highest heat capacity  High heat of fusion and vaporization  Tremendous dissolving power Dissolving