Water and SeawaterEver wonder why temperature extremes are found at places far from the ocean, while those close to the ocean are moderated?

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Winter in South Dakota…and Long Island

http://www.polarbearclub.org/polarbears/gallery_c.htm

Water and Seawater

• The mild climates found in coastal regions are made possible by water’s unique thermal properties

• These and other properties of water, which stem from the arrangement of its atoms and how its molecules ‘stick’ together, give water the ability to store vast quantities of heat, to stick together, and to dissolve almost anything

Some general chemistry….

• Water is a molecule– A molecule is a group of 2

or more atoms held together by mutually-shared electrons

– Water consists of 1 Oxygen atom and 2 Hydrogen atoms (H2O)

Some general chemistry….

• An atom is the smallest unit of matter; contains protons (+), electrons (-) and neutrons (=)• The protons and neutrons are

located in the atom’s nucleus

• An element contains a specific set of protons and electrons

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Nucleus: protons (+), neutrons (=)

electrons

General chemistry continued

• Elements in their pure form are quite rare in nature; instead they frequently combine to form compounds

• A compound consists of 2 or more elements• The electron arrangement determines the

chemical properties of an element– Atoms whose shells are incomplete tend to

interact with other atoms to gain, lose, or share electrons

My name is bond, ionic bond

• If an atom has 1 electron too many, it will donate that electron to an atom that is 1 electron short (of a complete outer electron shell)

• The donation of this electron, and its acceptance results in 2 charged atoms, or ions– The donating element has a (+) charge, having 1

more proton than it does electrons– The accepting element has a (-), having 1 more

electron than it does protons

NaSodium atom

Transfer ofelectron

ClChlorine atom

Na+

Sodium ionCl–

Chloride ion

Sodium chloride (NaCl)

+ –

Formation of an ionic bond

• The electrical attraction between the 2 ions (Na+ and Cl-) holds them together

My name is bond, covalent bond

• Two atoms may also share electrons• When atoms share their outermost electrons,

they form covalent bonds• The resulting compound is called a molecule• The resulting bond is very strong• Elements in need of 4 electrons, and those

with only 1 electron to share (=Hydrogen) frequently form covalent bonds

Water is covalently bonded• Water (H2O) is a covalently-bonded molecule,

in which Oxygen shares its electrons with 2 Hydrogen atoms (completes the outer electron shells of both the Hydrogen atoms and the Oxygen atom)

(–) (–)

O

HH

(+) (+)

A water molecule is a polar molecule

The oxygen atom in water is highly electronegative; it attracts the shared electrons much moreso than does the Hydrogen atoms, so the shared electrons spend more time near the Oxygen than the Hydrogen atoms

Water is a polar molecule

• A polar molecule results from the unequal distribution of electrical charges

• Atoms in a covalently-bonded molecule are in a constant ‘tug-o-war’ for their shared electrons

• An atom with a high electronegativity (its attraction for shared electrons) can pull electrons towards its nucleus and away from the other, sharing atom

Water is a polar molecule• The bonds that exist between 2 polar

molecules are called hydrogen bonds - very weak (compared to ionic and covalent) but collectively are very strong

Hydrogen bonds

I’m getting thirsty…

• Hydrogen bonds make water cohesive; its molecules tend to ‘stick’ together

• This cohesion allows plants to transport water and nutrients from their roots to their leaves (think of a giant redwood)

• Water has an extremely high surface tension (the measure of the difficulty to stretch or break the surface of a liquid)

A water strider walks on water

…and let’s not forget Jesus Christ Superstar, er, Lizard

http://www.youtube.com/watch?v=45yabrnryXk&feature=related

Water, water everywhere

• Water’s hydrogen bonds moderate temperature– Water is able to absorb a great deal of heat

energy without an increase in temperature because of its hydrogen bonds

– Heat must be absorbed to break hydrogen bonds and heat is released when hydrogen bonds form

– To increase temperature of water, heat energy must first disrupt the hydrogen bonds; when water is cooled, more hydrogen bonds form

How much heat required to induce evaporation

Water is a moderator of climate

The Oceans Moderate World Climate

• The huge amount of heat energy exchanged in the evaporation-condensation cycle help make life on Earth possible

• Oceans store heat energy from the sun; Evaporation removes heat energy from the oceans and carries it into the atmosphere, where it condenses as clouds and releases heat of condensation; transports heat from the low latitude oceans to heat-deficient higher latitudes

Hurricane path: Camille 1969

Day minus night temperature difference

Water’s amazing properties

• Water exists in all phases (gas, liquid, solid) on Earth

• Jeopardy question: What is the molecular formula of ice???

• Because of hydrogen bonds, ice is less dense than water– This prevents lakes, ponds, and even the ocean

from freezing solid; fish, dolphins, walruses very grateful

Thank you Hydrogen Bonds!!!

Water is the solvent of life

• Because of water’s polar properties (its hydrogen bonds), water is an incredible solvent

• A solvent is the dissolving agent of a solution, a liquid consisting of uniform mixture of 2 or more substances

• The substance that is being dissolved is called a solute

Ion insolution

Saltcrystal

Seawater

• Just how salty is seawater?• The oceans contain enough salt to cover the

entire planet with a layer more than 500 feet thick (the height of a 50-story skyscraper)! (but we have a lot of ocean….)

• The total amount of solid material dissolved in water is a measure of its salinity

Salinity of seawater

• The salinity of seawater is typically 3.5% • A salinity of 3.5% indicates that seawater

contains 96.5% pure water and 3.5% solutes• The major solutes of seawater are chlorine,

sodium, sulfur, magnesium, calcium, and potassium (=99% of the dissolved solutes), but >80 other elements have also been identified in seawater

Major dissolved components in seawater

Salinity of seawater

• Sodium and Chlorine make up 85% of the solutes found in seawater!

• Salinity is typically expressed in parts per thousand

• A salinity of 3.5% is equivalent to 35‰• 35‰ seawater has 35 grams of salt in every

1000 grams of seawater• But where does all this salt come from???

Could you please pass the salt?• Rivers supply most of the ‘salt’ to the oceans• Volcanic activity on land and underwater

(including hydrothermal vent activity!!!) contributes to the amount of ions in seawater

• The weathering of rocks by rainwater contribute sodium, magnesium and calcium (remember water is an incredible solvent!)

• Outgassing through volcanoes and rift vents provide carbon dioxide, chlorine, sulfur, hydrogen, fluorine, nitrogen and water vapor

The ocean as an Earth tea• Some of the ocean’s solutes

are hybrids of the weathering and outgassing processes; table salt (NaCl)

• Recent evidence suggests that mid-oceanic rifts increase the content of calcium and potassium of seawater, but may decrease the content of magnesium and sulfur– Water circulating through new ocean floor at these

sites is apparently stripped of these elements

The Principle of Constant Proportions

• When samples from the Challenger expedition were analyzed, the salinity of seawater changed slightly from location to location, but the relative amounts of ions did not vary significantly– Regardless of the salinity of seawater, the ratio of

solutes remain constant– How could this be so?

The Principle of Constant Proportions

• The addition of solutes (“sources”) is balanced by the removal of solutes (“sinks”)

• The sources = the sinks• The rate at which an element is added to the

ocean equals the rate at which it is removed (steady state condition)

• Materials added to the ocean are counteracted by processes that cycle dissolved substances out of seawater

How to measure salinity

• Because the ratio of solutes in seawater is constant, salinity can be measured by chlorinity; the measure of chlorine, bromine and iodine ions in seawater– Easy to measure– Salinity = 1.80655 x chlorinity

How to measure salinity

• Because increases in the amount of dissolved solutes increases the conductivity of water, the salinity of seawater is easily obtained by measuring the electrical conductivity (the ability of a substance to transmit electric current) of seawater– Very accurate

Dissolved gases in seawater

• Gases in the air easily dissolve in seawater at the ocean’s surface

• Organisms living in the ocean require these dissolved gases to survive

• The major gases in seawater are:– Nitrogen– Oxygen– Carbon dioxide

Dissolved gases in seawater

• Nitrogen constitutes ~48% of the dissolved gases in seawater; the upper surface waters of the ocean are saturated (no additional Nitrogen can dissolve)

• Nitrogen is essential for organisms and can be a limiting factor for phytoplankton

• Most dissolved Nitrogen is unusable since it exists as N2 gas, a form that cannot be assimilated by most organisms

Dissolved gases in seawater

• Rather, nitrogen is readily recycled amongst living organisms as nitrite, nitrate and ammonium (we’ll come back to this…)

• Oxygen constitutes ~36% of the gases dissolved in seawater

• Oxygen is essential for all aerobic life forms• Dissolved oxygen comes from photosynthesis

and diffusion from the atmosphere

Dissolved gases in seawater

• Carbon dioxide is very soluble in water and comprises ~15% of the dissolved gases in seawater

• Because CO2 combines chemically with water to form H2CO3 (carbonic acid), water can hold a tremendous amount of CO2

• In fact, much more CO2 moves from the atmosphere into the ocean, than from the ocean to the atmosphere

Dissolved gases in seawater

• Carbon dioxide is used readily by marine plants and algae (phytoplankton) and is also incorporated into the shells and skeletons of living organisms

• In fact, the oceans are a carbon sink! Half of the anthropogenic (man-’made’) carbon dioxide has been absorbed by the oceans; very important!!!

• CO2 is used near the surface and produced at depth

• O2 is produced near the surface and used at depth

Dissolved gases in seawater

• Concentrations of oxygen and carbon dioxide vary with depth

• Moreover, gases dissolve more readily in cold water than warm

• Cold, polar water contains a greater volume of dissolved gases than warm, tropical water

• As a result, when deep, cold water is upwelled to the surface, it provides the nutrients many organisms need to survive (we return to this)

The Acid-Base Balance

• Water (H2O) can separate to form hydrogen ions (H+) and hydroxide ions (OH-), which will be present in equal concentrations in pure water

• An imbalance of these ions, however, produces an acidic or basic solution

• An acid is a substance that releases H+ ions in solution; a base is a substance that combines with a H+ ion in solution

The Acid-Base Balance

• The acidity or alkalinity (basic) of a solution is measured on a pH scale

• pH measures the concentration of H+ ions in solution; an excess of H+ ions makes the solution acidic; an excess of OH- ions makes the solution basic (alkaline)

• Seawater is slightly alkaline with an average pH of 7.8 – Why is this so?

The Carbonate Buffering System

• If CO2 readily dissolves into seawater and forms carbonic acid, why is seawater slightly alkaline, and not slightly acidic???

• When dissolved in seawater, CO is actually present in different forms; carbonic acid is only 1 of these

• Some carbonic acid, H2CO3 breaks down to produce H+ and the carbonate ion, HCO3

-

The Carbonate Buffering System

• In this way, carbonic acid and bicarbonate are buffers; if seawater becomes ‘too’ basic, reactions will proceed to produce more H+, increasing the acidity of the solution, and vice versa

• H2O + CO2 H2CO3 HCO3- + H+ H+ + CO3

-2

• More complex than other gases

Carbonic acid

Bicarbonate

Carbonate

The Ocean is density-stratisfied

• The density of water depends mainly on its temperature and salinity

• Freshwater is less dense than salt water• Warm water is less dense than cold water• Much of the ocean is divided into 3 density

zones:– Surface zone– Pycnocline– Deep zone

Temperature & salinity are ~constant

Density increases with increasing depth

Lies below the pycnocline; density changes little with increasing depth

Temperature and Salinity Affect Density

• The pycnocline’s rapid density increase with depth is due mainly to decreasing water temperature

• The surface zone is well mixed (by wind and surface currents) with little temperature change with depth

• Between the surface zone and the deep zone also lies the thermocline; a zone in which temperature changes rapidly with depth (forms the pycnocline)

Temperature and Salinity Affect Density

• Low salinity can also contribute to the pycnocline, especially in regions where freshwater runoff mixes with the surface water

• The halocline is a zone of rapid salinity increase with depth

The Deep Zone

• The deep zone constitutes 80% of the ocean volume

• Water in the deep layer originates at the surface where it cools, becomes more dense, and sinks

• Very cold water; 1-3°C

Temperature and Salinity Affect Density

• Very cold and/or very salty water sinks to the seabed until it reaches a layer of water that is equally dense– Results from the formation of sea ice, or from a

high degree of evaporation• The pycnocline traps dense water masses at

depth and isolates 80% of the ocean water from surface circulation– Density differences power deep ocean currents

(we’ll come back to this….)

Hear no evil, see no evil…

• Light does not penetrate far through the ocean

• Light is a form of electromagnetic radiation that travels as waves through space, air and water (includes radio waves, infrared, ultraviolet and X-rays

• Water rapidly absorbs the visible wavelengths of light

Let there be light!

• When light is absorbed by water molecules (e.g., the ocean), the molecules vibrate and light energy is converted to heat

• Where light penetrates, photosynthesis proceeds; very important!

• The thin film of sunlit water at the top of the surface zone is the photic zone– <100 meters in open ocean– <40 meters in coastal regions– <600 meters in clear tropical regions

Hey, who turned off the lights???

• Ocean below the photic zone lies in blackness• Except for light generated by living organisms

(who ‘dat?!!?), the region is in perpetual darkness

• This dark water beneath the photic zone is the aphotic zone

Water transmits blue light more efficiently than red

• When light reaches surface waters, some of the energy is converted to heat

• The top meter of the ocean absorbs nearly all of the infrared radiation that reaches the ocean surface, warming it significantly

• This top meter also absorbs 71% of red light; the dimming light becomes bluer with depth as the red, orange, and yellow wavelengths are absorbed

Wavelength (nm)

10–5 nm

Increasing energy

Visible light

650nm

10–3 nm 1 nm 103 nm 106 nm 1 m 103 m

380 400 500 600 700 750

Radiowaves

Micro-waves

InfraredX-rays UVGammarays

Light waves with shorter wavelengths contain more energy and penetrate deeper than those with longer wavelengths. However, by 300 meters, even blue light has been converted into heat

Deep-sea shrimp

Sound travels much farther than light in the ocean

• Sound is a form of energy transmitted by rapid pressure changes

• Sound intensity decreases as it travels through seawater because of spreading, scattering, and absorption– Scattering occurs as sound bounces off bubbles,

suspended particles, organisms, the surface, the bottom, or other objects

– Sound is also absorbed by molecules into very small amounts of heat (sound is energy!)

Did you hear that?

• Sound travels nearly 5 times faster underwater than on land (in the air)

• In water, sound is transmitted by water molecules; since water molecules are densely packed (more so than molecules in air), they transmit sound more quickly– Sound causes a chain reaction of molecules

bumping into one another in a wave pattern,; closely packed molecules transmit sound more efficiently and as a result, faster

Do you hear what I hear?• Because of sound’s ability to travel so

effectively in water, we can use it to map ocean contours!!! (sound familiar???)

• And because sound waves travel more efficiently underwater than light waves, aquatic organisms frequently rely on sound (hearing), much more so than light (vision)– Other senses, too

A whale of a sound

• Whales regularly communicate with one another through sound– Breaching– Fin- and Tail- slapping– Bubbles– Vocalizations

• The larger the whale, the deeper the sound they can produce

Talk about singin’ the blues…

• Blue whales produce deep rumbling sounds; deep, low-pitched sounds that are the loudest noise produced by any animal

• You will feel a blue whale vocalization before you ever hear it

• Whale vocalizations can travel over entire ocean basins!!!

The Far Side by Gary Larson