Geography and Oceanography - Chapter 10 ppsx

Temperature vs HeatTemperature 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 ch

The Properties of Sea Water

What makes water so special?

Why is the ocean salty?

Where’s the Water?

Reservoir Volume (106 km3) Percent

Where did the water in the

Oceans come from?

Outgassing (H2O, CO2) 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

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)

ice water vapor

liquid waterExists in three states on the planet surface

Changes of state

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

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

Energy removed from surface (evaporation)

Energy liberated into the atmosphere (condensation)

Major source of energy to power

the Earth’s weather systems

Density of Pure Water

Consequences…

Surface tension - measure of how

difficult it is to stretch or break the

surface of a liquidWater 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 vaporizationTremendous dissolving power

Dissolving Power of Water

Why is the Ocean Salty?

Total dissolved solids (called “salinity”)About 3.5% by weight (average

seawater)

Usually expressed as 35 0/00 (parts per thousand, ppt)

Varies geographically according to

Evaporation, Precipitation, and Rivers

The Most Abundant Ions

Ions in Sea Water

Anions are negatively charged examples: Cl-, SO4-

Cations are positively charged examples: Na+, K+, Ca++, Mg++

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 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 how “reactive”

Residence Time: The average time spent by

a substance in the Ocean =

Amount in Sea Rate entering or exiting

Proportions?

Adding salt lowers the

freezing temperature:

Seawater freezes at about -2 oCFreezing removes fresh water, leaves salt

The Hydrologic Cycle

Salt in the Ocean increases its density

Ocean Surface salinities

Evaporation vs Precipitation

Which processes change the

Which ocean is the saltiest?

The Atlantic!

In spite of the fact that many 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 plus input from the Mediterranean Sea

Surface salinities

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

Water is a polar molecule unique

properties (melting pt, heat capacity, dissolving power, water denser than ice)

Salinity is the total dissolved solids

Salinity in the surface ocean varies by Evaporation - Precipitation

Principle of Constant Proportions