SeaChem.ppt

• Atoms are the smallest unit

which display all of the

properties of the material.

• Atoms are composed of:

– Nucleus - the center of the atom consisting of:

• positively charged particles (protons) • neutrally charged particles

(neutrons)

–

particles that orbit the nucleus in discrete electron shells

.

• Electrically stable atoms have the same

number of electrons as protons.

• Ions are atoms with either more or fewer

electrons than protons.

• Isotopes are atoms containing the same number of

protons, but different numbers of neutrons.

– Therefore, they have different atomic weights.

– For example, O-16 and O-18. Both have 8 protons, but differ in neutrons, one has 8 the other 10. (This can be used to determine climate temperature…sediments have greater amounts of O-18 during colder periods since O-16 that was locked up in ice because it evaporated more easily has returned to the ocean)

•

Heat

results from the vibrations of

atoms (

kinetic energy

). Heat is

the

total

energy present

•

Temperature

is the

average

Kinetic Energy

of molecules.

• In

solids,

the atoms or molecules:

– vibrate weakly

– are rigidly held in place

• In liquids, the atoms or molecules:

– vibrate more rapidly – move farther apart

– are free to move relative to each other

• In gases, the atoms or molecules:

– are highly energetic – move far apart

•

Melting

is the transition from solid to liquid;

freezing

is the reverse.

•

Evaporation

(vaporization) is the transition from

liquid to gas;

condensation

is the reverse.

– Evaporation requires heat input – Condensation releases heat

•

Temperature

controls density.

– As temperature increases:

• atoms or molecules move farther apart

The water molecule is unique in structure and

properties.

• H₂O is the chemical formula for water.

• Unique properties of water include:

– Higher melting and boiling point than other hydrogen compounds.

– High heat capacity (amount of heat needed to raise the temperature of one gram of water 1oC).

– Greater solvent power than any other substance.

• Water molecules are asymmetrical is shape:

• Asymmetry of a water molecule and distribution of electrons result in a dipole structure.

• The oxygen end of the molecule is negatively charged.

• The hydrogen end of the molecule positively charged.

• Dipole structure of water molecule produces an

• The dipole structure of water makes it an exceptional solvent.

• Na+ and Cl- ions are removed from the halite crystal by the

negative and positive ends of the water dipole.

• Ice floats in water because all of the

molecules in ice are held in hexagons.

– The center of the hexagon is open space,

making ice 8% less dense than water.

•

Fresh water

reaches its maximum density

at 3.98

C.

– Below this temperature increasing numbers of

water molecules form hexagonal polymers and

decrease the density of the water.

Hydrogen bonding is responsible for many of the unique properties of water.

This is because energy is required to break the hydrogen bonds and separate the water molecules.

High Heat of Fusion (energy needed to melt/form ice 80 cal/g)

High Heat of Vaporization (energy needed to vaporize water; 540 cal/g)

• Water dissolves salts by:

– surrounding the atoms in the salt molecule

– neutralizing the

ionic bond

holding the

molecule together.

• Dissolved salts form

cations

(positively

charged ions) and

anions

(negatively

charged ions).

Seawater consists predominantly of water with

various materials dissolved within it.

• The

solvent

is the material doing the dissolving.

– In seawater it is the water.

• The

solute

is the substance being dissolved.

•

Salinity

is the total amount of salts dissolved in

the water.

– It is measured in parts of salt per thousand parts of

salt water and is expressed as ppt (parts per thousand) or abbreviated as o/oo.

• Salt sources include:

– weathering of rocks on land

– the reaction of lava with seawater OR outgassing, primarily at vents/rifts

• Weathering mainly involves the chemical reaction between rock and acidic

rainwater.

– Acid rain is produced by the interaction of carbon dioxide and rainwater, which forms carbonic acid, or between Pollutants like SO

3, NO,

Figure 5-6 Sedimentary Cycle - Weathering

• 99.9% of all the salt ions in the sea are:

– chloride (Cl-) (18.98 ppt)

– sodium (Na+) (10.556 ppt)

– sulfate (SO₄-2) (2.649 ppt)

– magnesium (Mg+2) (1.272 ppt)

– calcium (Ca+2) (0.400 ppt)

– potassium (K+) (0.380 ppt)

– Bicarbonate (HCO₃-) (0.140 ppt)

• Sodium and chloride alone comprise about 86% of

the salt in the sea.

• The major chemical constituents of seawater

display little variation over time and are a

• Trace elements occur

in minute quantities.

– They are usually

measured in parts per

million (ppm) or parts

per billion (ppb).

• Even in small

Addition of salt modifies the properties of water.

• Pure water freezes at 0oC.

• Adding salt increasingly lowers the freezing point.

– This is because salt ions interfere with the formation of the hexagonal structure of ice.

• Density of water increases as salinity increases.

• Vapor pressure is the pressure exerted by the gaseous

phase on the liquid phase of a material.

– It is proportional to the amount of material in the gaseous phase. (In other words, the saltier the water, the slower the evaporation.)

Effects of Salinity on the Maximum-Density and

Freezing-Point Temperatures of Seawater

Figure 5-8

Because the solute lowers the freezing point, it turns out that seawater

• Salinity is the total mass (in grams) of all

substances dissolved in one kilogram of sea

water when:

– all carbonate has been converted to oxide

– all bromine and iodine has been replaced by

chlorine

• The

Principle of constant proportion

states that:

(Forchhammer’s Principle)

The absolute amount of salt in sea water varies, but

the relative proportions of the ions is constant.

• Because of this principle, it is necessary to test for only one salt ion, usually chloride, to determine the total amount of salt

•

Chlorinity

is the amount of halogens in seawater

and is expressed as grams/kilogram or o/oo

(ppt).

• Halogens are determined by titration

• chlorine • bromine • iodine • Fluorine

• Salinity is equal to 1.8065 times chlorinity.

•

Salinometers

determine salinity from the

electrical conductivity produced by the dissolved

salts.

•

Refractometers

use refraction of light in different

• Salinity in the ocean is in a steady-state

condition.

• This is because the amount of salt added to

the ocean (input from source) equals the

•

Salt sinks

(

remove salts

) include the following:

– Wind-blown spray carries minute droplets of saltwater inland.

– Adsorption of ions onto clays and some hydrogenous minerals. (Adsorption is the binding of molecules or particles to a surface, must be distinguished from absorption, the filling of pores in a solid)

– Shell formation by organisms. (These become uplifted or subducted…)

•

Evaporation removes only water

molecules.

– Remaining water becomes increasingly saline, eventually producing a salty brine.

– If enough water evaporates, the brine becomes

• Lack of similarity between relative composition of river

water and the ocean is explained by residence time.

– Residence time is average length of time that an ion remains in solution in the ocean.

• Ions with long residence times tend to accumulate in the

sea. (Chloride has the longest RT)

• Ions with short residence times are removed. (Iron has the

least RT)

• Rapid mixing (as compared to residence time) and long

Gases are also dissolved in the Ocean

• In order of decreasing abundance the major gases

in the sea are:

– nitrogen (N₂) - Greatest quantity

– oxygen (O₂)

– carbon dioxide (CO₂) - quickly reacts with water

– the noble gases:

• argon (Ar) • neon (Ne) • helium (He)

Sources and Sinks of Gases

5-6 Gases in Seawater

• The surface layer is usually saturated in

atmospheric gases because of direct gas

exchange with the atmosphere.

• Below the surface layer, gas content reflects

the relative importance of:

– Respiration

– Photosynthesis

– Decay

– Infusion from volcanic vents

• The solubility and saturation value of gases in sea water increase as: – temperature decreases

– salinity decreases – pressure increases

• Solubility is a measure of a substance's tendency to dissolve and go into solution.

5-6 Gases in Seawater

•

Saturation value

is the equilibrium amount of gas

dissolved in water at an existing temperature,

salinity and pressure.

– Water is undersaturated when it has the capacity to

dissolve more gas.

• This means that its gas content is below the saturation value.

– Water is saturated when it contains as much dissolved

gas as it can hold in equilibrium.

• Gas content is at its saturation value.

– Water is supersaturated when it contains more

dissolved gas than it can hold in equilibrium.

• Gas content is then above its saturation value and excess gas will come out of solution.

Nutrients are chemicals essential for life.

• Major nutrients in the sea are compounds of:

– phosphorus 0.07 ppm

– nitrogen 0.5 ppm

– Silicon 3 ppm

• Because of usage,

nutrients

are scarce at the

surface and their

concentrations are

measured

in parts per million (

ppm

).

• Concentration of nutrients vary greatly over

time and because of this they are considered a

• Marine organic compounds occur in low

concentrations and consist of large complex

molecules, such as:

– Fat

– Proteins

– Carbohydrates

– Hormones

– Vitamins

Carbon dioxide is of major importance in

controlling the

acidity

of seawater

• Major sources of carbon dioxide are respiration and decay.

• Major sinks are photosynthesis and construction of carbonate shells.

5-6 Gases in Seawater

Acidity of sea water

•

• A solution is basic if it has excess OH- (hydroxyl) ions.

• pH measures how acid or base water is.

– - pH of 0 to 7 is acidic. – - pH of 7 is neutral.

– - pH of 7 to 14 is basic.

The pH Scale

Carbon Species and the CO

system in the oceans

• Dissolved carbon appears in water in 3 forms:

–

–

3

-₎

– Carbonate (CO₃2-₎

• Basic solutions are dominated by carbonate.

• Acidic solutions are dominated by carbon dioxide.

Distribution of Carbon Species in Water

Figure 5-19a Distribution of Carbon Species in Water

The CO

System

Figure 5-19c The CO₂ System

• pH is related to the amount of CO

dissolved in

water.

• CO

combines with the water to produce carbonic

acid, which releases H

ions.

CO2 + H2O ←→ H2CO3 ←→ H+ + HCO3-←→ H+ + CO3-2

– H₂CO₃ is carbonic acid

– HCO₃- is the bicarbonate ion

– CO₃-2 is the carbonate ion

CO

+ H

O ←→ H

CO

←→ H

+ HCO

←→ 2H

+ CO

-2

• Changing the amount of CO

shifts the reaction to

either the right or left of the equation.

– Adding CO₂ shifts the reaction to the right and produces more H+ ions.

• This makes the water more acidic.

– Removing CO₂ shifts the reaction to the left,

combining H+ ions with carbonate and bicarbonate ions.

• This makes the water less acidic.

• Dissolved CO₂ in water acts as a buffer

– A buffer is a substance that prevents large shifts in pH.

5-6 Gases in Seawater

• Dissolution of carbonate shells in deep water occurs because:

– cold water under great pressure has a high saturation

value for CO₂

– the additional CO₂ releases more H+ ions making the

water acidic

• Carbonate sediments are stable and do not dissolve in warm, shallow water because the water:

– is under low pressure

– contains less dissolved CO₂

– is less acidic than the deep water.

Water is recycled continually between the

ocean and the land

• The reservoirs of free water include:

– Oceans:

• cover 60% of the northern hemisphere • cover 80% of the southern hemisphere • contain 97% of Earth’s water

– Rivers, lakes and glaciers

– Groundwater

• contains a larger volume of water than all of the combined water in lakes and rivers

• Ocean surface temperature strongly correlates with

latitude.

– This is because insolation – the amount of sunlight

striking Earth’s surface – is directly related to latitude.

• Ocean

isotherms

– lines of equal temperature –

generally trend east-west except where deflected

by currents.

• Ocean currents carry warm water poleward on the western side of ocean basins.

Sea Surface Temperatures

• Insolation and ocean-surface water temperature vary with the season.

• Ocean surface temperature is highest in the tropics (25oC) and decreases poleward.

• Tropical and subtropical oceans are permanently

layered with warm, less dense surface water

separated from cold, dense deep water by a

thermocline

.

– The thermocline is a layer in which water temperature and therefore density change rapidly.

Salinity changes with latitude due to variations in

precipitation and evaporation

• Highest ocean salinity is between 20-30o north and south of the

equator, because evaporation exceeds precipitation.

• Salinity at the equator and poleward of 30o is low because

evaporation is less than precipitation.

Figure 5-12b Latitudinal Variations in Salinity and “Dryness”

• In some places surface water and deep water are

separated by a

halocline

.

– The halocline is a zone of rapid change of

salinity, and therefore density, with water

depth.

Density of sea water is a function of

temperature, salinity and pressure

• Density increases as

– temperature decreases

– salinity and pressure increase.

• Pressure increases regularly with depth, but

temperature and salinity are more variable.

• Higher salinity water can rest above lower salinity water if:

– the higher salinity water is sufficiently warm – the lower salinity water is sufficiently cold

• Pycnocline is a layer within the water column where water density changes rapidly with depth.

Figure 5-14a Seawater Density

Note that the

isopycnals (equal density lines) are curved - this is

because salinity must increase (which

increases density) as temperature increases (which lowers density) to maintain a given

Thermocline, Halocline, and Pycnocline

Figure 5-14b

Decreased Temp = Increased Salinity = Two Pycnoclines here increased Density increased density where density changes with

• The water column in the ocean can be divided into the:

– surface layer – pycnocline – deep layer

The

Surface Layer

• About 100m thick

• Comprises about 2% of the ocean volume

• Is the most variable part of the ocean because it is

in contact with the atmosphere.

• Is

less dense

than the layers below because of its

The Pycnocline

• Is transitional between the surface and deep layers.

• Comprises 18% of the ocean basin.

• In the low latitudes, the pycnocline coincides with

the thermocline.

The Deep Layer

• Represents 80% of the ocean volume.

• Water in the deep layer originates at the surface

in high latitudes, where it:

– cools

– becomes dense

– sinks to the sea floor

Helium-3

Figure 5-16 Helium-3

• Oxygen tends to be abundant in the water of the surface layer and deep layer, and lowest in the pycnocline.

• Surface layer is rich in oxygen because of photosynthesis and diffusion from the atmosphere layer.

• Oxygen minimum layer occurs at about 150 to 1500m below the surface and coincides with the pycnocline.

5-6 Gases in Seawater

The Oxygen Minimum Layer

• Sinking food particles settle into this layer and are

slowed down by the sharp density gradient.

• The food draws large numbers of organisms which

respire, consuming oxygen.

• Decay of uneaten material consumes additional

oxygen.

• Density difference prevents mixing downward of

oxygen-rich water from the surface or upwards

from the deep layer.

• The deep layer is rich in oxygen because its

water is derived from cold surface waters

that sank to the bottom.

• Oxygen consumption by respiration is low

because there are fewer organisms in the

deep layer.

• Anoxic waters contain no oxygen and are

inhabited by anaerobic organisms (bacteria).

• The hydrologic cycle

describes the exchange of

water between ocean, land and atmosphere.

– On land precipitation exceeds evaporation.

– In the ocean evaporation exceeds precipitation.

Figure 5-20 Hydrologic Cycle

The ocean is part of a vast biogeochemical system

• Rocks on land undergo weathering.

• The products are transported to the sea.

• They may be deposited directly or used by organisms and later deposited as organic remains or organic wastes.

• These sedimentary deposits are buried, lithified and recycled by plate tectonics into new land

• The new land then undergoes weathering repeating the cycle.

Biochemical Recycling of Matter

Figure 5-22 Biogeochemical Recycling of Matter

• Water samples must be collected in inert

containers and isolated as they are

recovered so as to prevent contamination.

• The Niskin bottle has valves at each end.

– They automatically close when a weight (called

a

messenger

), is sent down the cable and

causes the bottle to flip over and seal itself.

• Sample depth can be determined from cable

inclination and length or with a pulsating

sound source.

Desalinization

is the process of producing

potable (drinkable) water from seawater using

one of the following methods

•

Distillation

is the evaporation of seawater and the

condensation of the vapor.

•

Freezing

produces salt-free ice which can be melted for

water.

The Ocean Sciences: Desalinization

•

Reverse osmosis

is placing seawater under

pressure and forcing water molecules

through a semi-permeable membrane,

leaving a brine behind.

•

Electrodialysis

is using electrically charged

surfaces to attract cations and anions,

leaving behind freshwater.

•

Salt absorption

is using resins and charcoal

to absorb ions from seawater.

• Sea ice is ice that forms by the freezing of sea

water.

– Icebergs are detached parts of glaciers.

• As ice forms, the salt remains in solution: – increasing salinity

– further lowering the freezing point of the water

• Depending upon how quickly the ice freezes, some salt may be trapped within the ice mass, but is gradually released.

As sea water

freezes, needles of ice form

The needles grow into platelets

The platelets

• Pancake ice

are rounded

sheets of flexible sea ice

that become abraded as

they collide.

• Sea ice thickens with time as snow freezes to its

surface and water to its bottom.

• The amount of light entering the ocean depends upon: – the height of the sun above the horizon

– the smoothness of the sea surface

• 65% of light entering the ocean is absorbed within the first meter and converted into heat.

• Only 1% of light entering the ocean reaches 100m.

• Water displays the selective absorption of light: – long wavelengths are absorbed first

– short wavelengths are absorbed last

• In turbid coastal waters

light rarely penetrates

deeper than 20m.

– The water appears

yellow to green because

particles reflect these

wavelengths.

• The

photic zone

is the part of the water

column penetrated by sunlight.

• The

aphotic

zone is the part of the water

column below light penetration and

permanently dark.

• The speed of sound in water increases as:

– Salinity increases

– Temperature increases

– Pressure increases

• In the ocean, the speed of sound is mainly a

function of temperature and pressure.

• Above the pycnocline, increasing pressure with

depth

increases the speed of sound

, despite the

gradual decrease in temperature.

• Within the pycnocline, the

speed of sound

decreases

rapidly because of the rapid decrease in

temperature and only slight increase in pressure.

• Below the pycnocline the speed of sound

•

SOFAR Channel

is located where sound speed is at a

minimum.

• Refraction of sound waves within the channel prevents

dispersion of the sound energy.

• Sound waves travel for 1000s of kilometers within the

channel.

Sound Speed Increases

• The

sea surface microlayer

is the water surface

to a depth of a few hundred micrometers.

• It is critical for the exchange of gases, liquids, and

solids between the atmosphere and the ocean.

• The

neuston layer

is the habitat of the sea surface

microlayer and is inhabited by

neuston.

• Processes that transport matter to the

surface layer from below are:

–

Diffusion

- random movement of molecules.

–

Convection

- vertical circulation resulting in

the transfer of heat and matter.

–

Bubbles

- the most important process because

bubbles absorb material and inject it into the air

as they bursts.

• Processes within the microlayer can be

divided into the:

–

Biological

- bacteria and plankton are more

densely concentrated in the neuston layer than

below.

–

Photochemical effect

- the interaction of

ultraviolet light and organic compounds.

Recycling of Water

Figure 5-21 Recycling of Water

Light Absorption