Where’s the Water?Where’s the Water? ReservoirReservoir Volume (10Volume (1066 km km33)) PercentPercent

OceanOcean 13701370 97.3 97.3Ice (polar)Ice (polar) 29 29 2.1 2.1GroundwaterGroundwater 5 5 0.4 0.4LakesLakes 0.1 0.1 0.01 0.01AtmosphereAtmosphere 0.01 0.01 0.001 0.001RiversRivers 0.0010.001 0.00010.0001

Where did the water in Where did the water in the Oceans come from?the Oceans come from?

Outgassing (HOutgassing (H22O, COO, CO22) of the ) of the Earth from Earth from volcanoesvolcanoes, early , early in its historyin its history

Sedimentary rocks as old as Sedimentary rocks as old as 3.8 billion years!3.8 billion years!

A much smaller amount from A much smaller amount from cometscomets that pass by that pass by

The Water MoleculeThe Water Molecule

Water is a “Polar” Water is a “Polar” MoleculeMolecule

Weak electrical attraction makes Weak electrical attraction makes for “sticky” moleculesfor “sticky” molecules

This explains its unique This explains its unique properties:properties:heat capacityheat capacitysurface tensionsurface tensiondissolving powerdissolving power

Temperature vs HeatTemperature vs Heat

TemperatureTemperature is a measure of is a measure of how fast the molecules in a how fast the molecules in a substance are movingsubstance are moving

HeatHeat is a measure of how much is a measure of how much energy has to be put into (or energy has to be put into (or gotten out of) a substance to gotten out of) a substance to change its temperature, or change its temperature, or “state” (solid, liquid, gas)“state” (solid, liquid, gas)

Sensible Heat vs Latent Sensible Heat vs Latent HeatHeat

Sensible heatSensible heat is what we sense is what we sense from different temperaturesfrom different temperatures

Latent heatLatent heat is the energy needed is the energy needed to change state (ice to water, to change state (ice to water, water to vapor)water to vapor)

Table 4.2 (6th edition)

iceice

water water vaporvapor

liquid liquid waterwater

Exists in three states on the planet surfaceExists in three states on the planet surface

Changes of state

Water co-exists on the Earth in 3 physical states:

solidsolid liquidliquid gasgas

Changes of state always occur Changes of state always occur at at constant temperatureconstant temperature

The heat needed for a change of state The heat needed for a change of state

is called is called latent heatlatent heat

Heat and the three Heat and the three Physical States of Physical States of

Water:Water:

EvaporationEvaporation from lakes, from lakes, oceans, rivers, etc. occurs oceans, rivers, etc. occurs for temperatures lower than for temperatures lower than

100 100 ooCCBut it But it

requires requires more more

energy to energy to do sodo so

Density of Pure Water

Consequences…

Consequences

Bottom temperature of deep, cold lakes is always 4 oC.

Ice floats on the water surface, so fish survive.

Pipes (or beer bottles) can freeze and burst.

Surface tensionSurface tension - measure - measure of how difficult it is to of how difficult it is to

stretch or break the surface of stretch or break the surface of a liquida liquid

Water has the highest surface tension of all Water has the highest surface tension of all common liquidscommon liquids

Energy removed from surface Energy removed from surface (evaporation)(evaporation)

Energy liberated into Energy liberated into the atmosphere the atmosphere (condensation)(condensation)

Major source of energy to Major source of energy to power power

the Earth’s weather systemsthe Earth’s weather systems

Special Properties of Special Properties of WaterWater

Density of solid is less than Density of solid is less than liquidliquid

Melting and boiling points are Melting and boiling points are very highvery high

Highest heat capacity Highest heat capacity High heat of fusion and High heat of fusion and vaporizationvaporization

Tremendous dissolving powerTremendous dissolving power

Dissolving Power of Dissolving Power of WaterWater

Why is the Ocean Why is the Ocean Salty?Salty?

Total dissolved solids (called Total dissolved solids (called “salinity”)“salinity”)

About 3.5% by weight (average About 3.5% by weight (average seawater)seawater)

Usually expressed as 35 Usually expressed as 35 00//0000 (parts per thousand, ppt)(parts per thousand, ppt)

Varies geographically according Varies geographically according to Evaporation, Precipitation, to Evaporation, Precipitation, and Riversand Rivers

The Most Abundant IonsThe Most Abundant Ions

Chloride (ClChloride (Cl--)) 19.0 g/kg19.0 g/kg Sodium (NaSodium (Na++)) 10.6 “10.6 “ Sulfate (SOSulfate (SO44

2-2-)) 2.6 “ 2.6 “ Magnesium (MgMagnesium (Mg2+2+) ) 1.2 “ 1.2 “ Calcium (CaCalcium (Ca2+2+)) 0.4 “ 0.4 “ Potassium (KPotassium (K++)) 0.40.4 “ “

35.2 g/kg35.2 g/kg

Ions in Sea WaterIons in Sea Water

AnionsAnions are negatively are negatively chargedchargedClCl--, SO, SO44

--

CationsCations are positively are positively chargedchargedNaNa++, K, K++, Ca, Ca++++, Mg, Mg++++

Measuring SalinityMeasuring Salinity Principle ofPrinciple of Constant ProportionsConstant Proportionse.g., SOe.g., SO44

2-2-/Cl/Cl-- is a constant, is a constant, independent of salinityindependent of salinity

This means we need measure only This means we need measure only one ion to get salinity; i.e., Clone ion to get salinity; i.e., Cl--

Today salinity is measured Today salinity is measured quickly by quickly by electrical electrical conductivityconductivity of sea water of sea water

Where does Salinity come Where does Salinity come from?from?

Terrigenous input (rivers, Terrigenous input (rivers, dust, ash)dust, ash)

Hydrothermal ventsHydrothermal vents Dissolving old sediments Dissolving old sediments (evaporites)(evaporites)

Steady State: Inputs equal Steady State: Inputs equal OutputsOutputs

Weathering of RocksWeathering of Rocks

HH22O + COO + CO22 ---> H ---> H22COCO33 (carbonic (carbonic acid)acid)

““acid” rain, pH ~4-5; acid” rain, pH ~4-5; environmental concerns (HCl, environmental concerns (HCl, HF, HHF, H22SOSO44))

Dissolves rock minerals into Dissolves rock minerals into ions, which travel down rivers ions, which travel down rivers to the oceanto the ocean

Residence TimeResidence Time How long do the various dissolved ions How long do the various dissolved ions stay in the ocean? Depends on how stay in the ocean? Depends on how “reactive”.“reactive”.

Residence TimeResidence Time: The average time spent : The average time spent by a substance in the Ocean = by a substance in the Ocean =

Amount in SeaAmount in Sea Rate entering or exitingRate entering or exiting

Residence TimeResidence Time For water entering through rivers, the For water entering through rivers, the residence time is about residence time is about

VolumeVolume == 1370x101370x1066 km km3 3 (oceans) (oceans)

Flux 0.037x10 Flux 0.037x1066 km km33/yr (rivers)/yr (rivers)= 35,000 years.= 35,000 years.

For ClFor Cl--, the residence time is 100 Ma!, the residence time is 100 Ma!For FeFor Fe2+2+, the residence time is 200 yr, the residence time is 200 yr

Which is likely to obey Constant Which is likely to obey Constant Proportions?Proportions?

Adding salt lowers Adding salt lowers the freezing the freezing temperature:temperature:

Seawater freezes at about -2 Seawater freezes at about -2 ooCC

Freezing removes fresh water, Freezing removes fresh water, leaves saltleaves salt

The Hydrologic CycleThe Hydrologic Cycle

Evaporation - Evaporation - PrecipitationPrecipitation

Over the oceans, evaporation Over the oceans, evaporation exceeds precipitationexceeds precipitation

The balance is restored by The balance is restored by rain over the continents, rain over the continents, returning water via riversreturning water via rivers

Desalination -- fresh Desalination -- fresh water from the Oceanswater from the Oceans

Salt in the Ocean Salt in the Ocean increases its densityincreases its density

Ocean Surface Ocean Surface salinitiessalinities

Evaporation vs Evaporation vs PrecipitationPrecipitation

Which processes change the

surface salinities ?saltier fresher

evaporation precipitation

sea ice formation

sea ice melting

freshwater runoff from land

Which ocean is the Which ocean is the saltiest?saltiest?

Which ocean is Which ocean is Saltiest?Saltiest?

In spite of the fact that many In spite of the fact that many more big rivers empty into the more big rivers empty into the Atlantic than the Pacific, the Atlantic than the Pacific, the Atlantic is actually Atlantic is actually significantly saltier because significantly saltier because of the evaporation-of the evaporation-precipitation cycle and the precipitation cycle and the Isthmus of Panama; the Indian Isthmus of Panama; the Indian is intermediateis intermediate

Surface Surface salinitiessalinities

Evaporation, precipitation, and wind patternsexplain high/low salinity of Atlantic/Pacific.

Summary:Summary: Water is a polar molecule -- Water is a polar molecule -- unique properties (melting pt, unique properties (melting pt, heat capacity, dissolving power, heat capacity, dissolving power, water denser than ice)water denser than ice)

SalinitySalinity is the total dissolved is the total dissolved solidssolids

Salinity in the surface ocean Salinity in the surface ocean varies by Evaporation - varies by Evaporation - PrecipitationPrecipitation

Principle ofPrinciple of Constant ProportionsConstant Proportions Residence TimeResidence Time in the Oceans in the Oceans