Water and Ocean Structure Chapter 6

The Water Molecule Molecule Molecule –Group of atoms held together by chemical bonds Covalent bonds Covalent bonds –Pairs of electrons are shared –Sharing leads to an unequal distribution of charge  o bond angle (H-O-H)

The Water Molecule Having a “+ end” and a “- end” makes water a polar molecule Having a “+ end” and a “- end” makes water a polar molecule –Makes water able to separate molecules held together by opposite electrical charges Salts Salts –Water = universal solvent –Makes water able to attract similar molecules Forms H bond with nearby water molecules Forms H bond with nearby water molecules

The Water Molecule Cohesion Cohesion –The sticking together of individual water molecules Surface tension Surface tension Adhesion Adhesion –The sticking of water to solids Makes thing wet Makes thing wet Both lead to capillary action Both lead to capillary action

Water and Heat Heat Heat –The energy produced by the random vibration of atoms or molecules How many and how rapidly How many and how rapidly Temperature Temperature –An object’s response to and input (or removal) of heat Different substances = different responses Different substances = different responses How rapidly How rapidly More heat energy – Hot bath or candle flame? More heat energy – Hot bath or candle flame?

Degrees Degrees –Temperature measurement Celsius vs. Fahrenheit Celsius vs. Fahrenheit –1 o C = 1.8 o F Conversions Conversions – o C  o F  o F = o C x (9/5) + 32  o F = 20 o C x (9/5) + 32 = 68 o F – o F  o C  o C = ( o F – 32) x 5/9  o C = (60 o F – 32) x 5/9 = 15.6 o C

Water and Heat Heat Capacity Heat Capacity –A measure of the heat required to raise the temperature of 1g of a substance by 1 o C Calories per gram Calories per gram –Calorie  The amount of heat required to raise the temperature of 1g of water by 1 o C –Heat capacity of water one of the highest of all substances Can absorb (or release) large amounts of heat without large changes in temperature Can absorb (or release) large amounts of heat without large changes in temperature

Water Temp. and Density Density = mass per unit volume Density = mass per unit volume –Most substances become denser as they get colder Water becomes more dense as heat is removed… Water becomes more dense as heat is removed…

Water Temp. and Density …until it approaches its freezing point Density quickly decreases as it turns from water to ice Density quickly decreases as it turns from water to ice –Freezing  Bond angle changes from o to 109 o  Forms regular hexagons  Water expands by ~9%

Latent Heats Latent heat of fusion Latent heat of fusion –Heat removed during freezing that does not change the temperature 80 calories of heat per 1g of water at 0 o C to form ice 80 calories of heat per 1g of water at 0 o C to form ice Latent heat of vaporization Latent heat of vaporization –Heat added during evaporation that produces a change in state but does not cause a change in temperature 540 calories per 1g of water at 20 o C 540 calories per 1g of water at 20 o C –Highest on Earth

Seawater vs. Pure Water Seawater Seawater –96.5% pure water –3.5% dissolved solids and gasses Lower its latent heat by ~4% Lower its latent heat by ~4% Act as a natural antifreeze Act as a natural antifreeze –Salinity goes up  freezing point goes down  Freezing point of seawater = -1.9 o C (28.6 o F)

Seawater vs. Pure Water Both freezing and evaporating seawater leaves salt behind Both freezing and evaporating seawater leaves salt behind –Leftover dense water sinks to the bottom Seawater evaporates more slowly than freshwater Seawater evaporates more slowly than freshwater –3.3 cubic feet of the sea evaporates per year Left over heat powers wind  waves, storms, and currents Left over heat powers wind  waves, storms, and currents

Global Thermostatic Effects Thermostatic properties Thermostatic properties –Properties of water that act to moderate changes in temperature Thermal inertia Thermal inertia –Resisting temperature changes with the input or loss of heat –Temp differences Land – 250 o F Land – 250 o F Ocean – 61 o F Ocean – 61 o F

Effects of Water and Air Movement Why doesn’t the water at the equator boil away or the oceans at the poles entirely freeze solid? Why doesn’t the water at the equator boil away or the oceans at the poles entirely freeze solid? –Currents move heat in water/air from tropics to poles Equalizes polar-tropical heat imbalance Equalizes polar-tropical heat imbalance

Effects of Air and Water Movement Example – Gulf Stream Example – Gulf Stream –“outgoing” water is 10 o C warmer than “incoming” water  10 million calories/meter 3  Flow = 55 million meter 3 /second  550 trillion calories moved North/second –Energy used to evaporate ocean is released to make water vapor Usually at a distance Usually at a distance –Cools Cuba  warms Canada

Density Structure of the Ocean Liter of seawater – 2% to 3% more dense than pure water Liter of seawater – 2% to 3% more dense than pure water –Density of seawater = – g/cm 3 –Dissolved solids (“salt”) Density goes up when the… Density goes up when the… –Temperature goes down –Pressure goes up –Salinity (how salty) goes up

Density Structure of the Ocean Density zones Density zones –Surface zone (mixed layer) (2%) Least dense Least dense Temp and salinity mostly constant throughout Temp and salinity mostly constant throughout –Pycnocline (18%) More dense More dense Density increases with depth Density increases with depth –Deep zone (80%) Most dense (below 1,000m) Most dense (below 1,000m) Little change in density with depth Little change in density with depth

Density Structure of the Ocean Temperature and stratification Temperature and stratification –Pycnocline changes density so rapidly due to temperature change Thermocline Thermocline –Regional differences? Factors? –Tropical regions – deep thermocline –Polar regions – no thermocline

Density Structure of the Ocean Salinity and stratification Salinity and stratification –Low salinity creates stratification Wherever precipitation exceeds evaporation Wherever precipitation exceeds evaporation –Creates the halocline  Zone of rapid salinity increase with depth Thermocline (temp) + Halocline (salinity) = Pycnocline (density) Thermocline (temp) + Halocline (salinity) = Pycnocline (density) –Water mass