The Properties of Seawater 89 © Jones & Bartlett Learning, LLC

Water is just not water. It is a © Jones & Bartlett Learning, LLC © Jones & Bartlettvital substance, Learning, the earth’s LLC NOT FOR SALEblood, somethingOR DISTRIBUTION of rich and NOT FOR SALE OR DISTRIBUTION infinite variety. ~ L. Watson, The Water Planet, 1988 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

The© Jones & BartlettProperties Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION of Seawater 4 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Preview Water is everywhere. Its presence on our planet is crucial for the existence of life. “Biology,” said Berg, “is wet © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC and dynamic.” (H.C. Berg, Random Walks in Biology, 1983.) NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION What exactly are the chemical and physical properties of water generally and seawater specifically? How variable are these properties over time and space? How do chemical elements enter the oceans, and—once there—how do they interact with other substances, both living and nonliving? A discussion of these questions forms© the Jones basis &of Bartlettthis chapter. Learning, Here, we LLCwill examine the chemical and© Jones physical & nature Bartlett of seawater Learning, and LLClay the foundationNOT FOR for SALE later discussions OR DISTRIBUTION of ocean circulation and marine life.NOT The FOR concluding SALE section OR DISTRIBUTION of the chapter integrates these ideas into the global water cycle and examines the ocean as a complex and dynamic biogeochemical system.

© Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES One of the most obvious properties of seawater Electron © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLCshells is its salty taste. If you believe that its taste is due to NOT FOR SALE OR DISTRIBUTION NOT FOR SALEdissolved OR salt,DISTRIBUTION you are correct, and this is what makes Nucleus the water of the oceans different from the water of Nucleus lakes and rivers. Seawater is made up mainly of liquid water (about 96.5 percent by weight) in which chloride (Cl) and sodium© (Na) Jones are the& Bartlettdominant Learning, dissolved LLC © Jones & Bartlett Learning, LLC chemicals. The commonNOT FOR table SALE salt you OR use DISTRIBUTION to flavor NOT FOR SALE OR DISTRIBUTION your food is composed of precisely the same elements. Before continuing our discussion about the chemistry proton (+ charge) of water, we must, however, become familiar with a few neutron (0 charge) basic chemical and physical concepts. So let’s begin. (a) ATOM © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOTHydrogen FOR SALE OR OxygenDISTRIBUTION 4-1 Basic Chemical Notions

All matter is composed of “building blocks” termed atoms. An atom is the smallest unit of a substance that © Jones & Bartlettretains all Learning, of its chemical LLC properties. For example,© a Jones & Bartlett Learning, LLC NOT FOR SALEsingle OR atom DISTRIBUTION of hydrogen possesses all of the chemicalNOT FOR SALE OR DISTRIBUTION characteristics of a large collection of hydrogen atoms. Shell has a maximum Outer shell has a of two electrons maximum of eight If you tried to divide a single hydrogen atom into electrons simpler units, you could do so, but these bits of matter (b) ELECTRON SHELLS would no longer display© Jones the properties& Bartlett of aLearning, hydrogen LLC © Jones & Bartlett Learning, LLC atom. Atoms that areNOT chemically FOR SALE bonded OR to one DISTRIBUTION another HydrogenNOT FOR SALE OR DISTRIBUTION comprise a molecule. Or, if you prefer, a molecule is a chemical substance that can be separated into distinct 0 neutrons 1 neutron 2 neutrons 1 2 3 atoms. Sodium chloride (NaCl) is a molecule of salt H H H that can be separated into a positively charged atom (Na© Jones+) and a negatively& Bartlett charged Learning, atom of LLC (Cl-). © Jones & Bartlett Learning, LLC NOTThe FOR internal SALE structure OR DISTRIBUTION of any atom consists of NOT FOR SALE OR DISTRIBUTION 8 neutrons 9 neutrons 10 neutrons elementary particles that possess mass and electric 16O 17O 18O charge. The center of an atom, the nucleus, is composed (c) ISOTOPES of two distinct kinds of particles that contain essentially FIGURE 4–1 Atomic structure. (a) A simplified version of an © Jones & Bartlettall of its mass:Learning, protons LLC with a positive electric charge© Jones & Bartlett Learning, LLC and neutrons with no electrical charge (FIGURE 4–1a). atom depicts a nucleus of protons and neutrons, surrounded by NOT FOR SALESurrounding OR DISTRIBUTION the nucleus are collections of orbitingNOT FORshells SALEof orbiting OR electrons. DISTRIBUTION (b) A depiction of electrons within electrons that have little mass and carry a negative the shells of hydrogen (one electron) and oxygen (eight electrons) electrical charge. The electron orbits are not randomly atoms. (c) The isotopes of an element have a variable number of distributed around the nucleus but are confined to neutrons. Hydrogen isotopes have zero, one, or two neutrons; discrete levels termed© Jones electron & Bartlett shells. All Learning, elements LLCoxygen isotopes have eight, nine,© Jonesor ten neutrons. & Bartlett Learning, LLC (except for one typeNOT of hydrogenFOR SALE that ORdoes DISTRIBUTIONnot have NOT FOR SALE OR DISTRIBUTION neutrons) contain protons, neutrons, and electrons, and differ from one another because of the number hand, contains eight protons in its nucleus, balanced and structural arrangement of these fundamental electrically by eight orbiting electrons. So hydrogen subatomic© Jones particles.& Bartlett A stable Learning, atom of LLC an element is atoms consist© Jones of a single & Bartlett proton andLearning, a single electron, LLC electrically neutral, indicating that the positive charges and oxygen atoms of eight protons and eight electrons. fromNOT the FOR protons SALE are balanced OR DISTRIBUTION by the negative charges If electronsNOT are FOR either SALE added OR or removedDISTRIBUTION from any from the electrons. single atom, the atom is no longer electrically bal- Let’s be specific. Hydrogen (FIGURE 4–1b) possesses anced. Atoms with more electrons than protons have one proton in its nucleus; the positive charge from a net negative charge. Atoms with more protons than © Jones & Bartlettits single Learning,proton is neutralized LLC by the negative charge© Joneselectrons & Bartlett have aLearning, net positive LLC charge. An atom with NOT FOR SALEfrom itsOR one DISTRIBUTION orbiting electron. Oxygen, on the otherNOT FOReither SALE a positive OR or DISTRIBUTION a negative charge is called an ion.

88 CHAPTER 4 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES For example, when NaCl dissolves in water, it separates Although an ice cube appears inert to the naked eye, © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC into the ions Na+ and Cl-. The charge of an ion is the it is not inert on an atomic scale. Its molecules are NOT FORsingle SALE most OR important DISTRIBUTION reason for its ability to bond NOTvibrating FOR SALE back and OR forth DISTRIBUTION even though they are locked with other elements. together into a crystalline framework. If we add heat The story does not end there though. Although the to the ice cube, the molecules vibrate faster and move number of protons is fixed for any element, the quantity farther back and forth in the crystal. Above 0°C, the of neutrons in its nucleus© Jones can vary. & Because Bartlett the neutron Learning, meltingLLC temperature of ice, the© back-and-forth Jones & Bartlett motions Learning, LLC carries no electrical chargeNOT FORbut has SALE mass, ORvariations DISTRIBUTION of the molecules are so vigorousNOT that FOR they SALEexceed theOR DISTRIBUTION in the number of neutrons change the weight of the strength of the electrical bonds holding the molecules element, but not its basic chemistry. Atoms of the same in place in the crystal. At that temperature, the crys- element that differ in weight due to variable numbers tal’s structure disintegrates (melts), and the solid ice of neutrons are called isotopes. Hydrogen has three becomes liquid water (FIGURE 4–2b). Liquids are loose © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC isotopes. Each isotope contains a single proton, but aggregates of molecules that are in contact, but are NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION either zero, one, or two neutrons (FIGURE 4–1c). Oxygen free to move relative to one another, unlike the fixed similarly has three isotopes containing either eight, molecules in a solid. As more heat is added to the liquid nine, or ten neutrons in its nucleus (see Figure 4–1c). water, its temperature rises as its molecules vibrate The most abundant hydrogen isotope has zero neu- more energetically. Some of these molecules contain so © Jones &trons Bartlett and the Learning,most abundant LLC oxygen isotope has eight. © Jonesmuch kinetic & Bartlett energy Learning, that they escape LLC from the liquid NOT FOR SALE OR DISTRIBUTION NOTsurface FOR and SALE become OR a DISTRIBUTIONgas (FIGURE 4–2c); this process 4-2 Basic Physical Notions is called evaporation. At 100°C, the boiling temperature of water, all of the molecules are highly energized Another important notion that we must consider and thus are vaporized (converted into gas). Free gas in order to understand the behavior of water is the molecules move independently of one another between © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC physical concept of heat, the property that one mea- collisions, and are the least ordered of the three states sures with a thermometerNOT andFOR that SALE results OR from DISTRIBUTION the of matter because of their veryNOT high FOR kinetic SALE energy. OR DISTRIBUTION physical vibrations of atoms and molecules. These The kinetic theory of heat has important implica- physical vibrations represent energy of motion, called tions for measuring temperature and understanding the kinetic energy. The more heat in a material, the greater density of materials, whether they be solids, liquids, or the agitation© Jones of its& atomsBartlett and Learning,molecules. LLC gases. Imagine© aJones thermometer, & Bartlett which Learning,is nothing more LLC Let’sNOT consider FOR SALE a specific OR example. DISTRIBUTION A block of ice than a narrowNOT glass FORtube filled SALE with OR mercury. DISTRIBUTION If we wish consists of an orderly, rigid arrangement of water to determine the temperature of a water sample, we molecules (FIGURE 4–2a) that are held firmly in place stick the thermometer in the liquid. What happens? by strong electrical bonds between the molecules. The mercury in the tube rises and eventually stops. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION MolecularNOT structure FOR SALE OR DISTRIBUTION Ice Water Gas

Polymer

© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION (a) (b) (c) SOLID WATER LIQUID WATER GASEOUS WATER FIGURE 4–2 States of matter. Water occurs in three states, which depend on temperature and pressure. (a) Solid water (ice) consists of ordered molecules that are tightly bonded to one another. (b) Liquid water consists of molecules that move relative to one another. Poly- © Jones &mers Bartlett are bits of Learning, crystalline structure LLC that can exist in liquid water© near Jones its melting & temperature.Bartlett Learning, (c) Gaseous water LLC (gas) is made up of NOT FORindependently SALE OR moving DISTRIBUTION molecules. NOT FOR SALE OR DISTRIBUTION The Properties of Seawater 89 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES It is then an easy matter to read the temperature of could not have formed, and life could not have devel- © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC the water off the thermometer’s scale. But what exactly oped. In fact, H2O is the only substance that can coexist NOT FOR SALEdoes theOR rise DISTRIBUTION of mercury in the tube represent inNOT a FORnaturally SALE as aOR gas, DISTRIBUTION a liquid, and a solid on the Earth’s physical sense? Well, it’s quite simple, provided you surface. Therefore, it is not surprising to discover how grasp the kinetic theory of heat. Recall that the water fundamental it is to all forms of life. molecules are vibrating at a rate that depends on the Water also has an unusually high heat capacity and water’s temperature.© Jones When the & thermometerBartlett Learning, is placed LLCtremendous solvent power.© JonesHeat capacity & Bartlett is defined Learning, LLC in the liquid, waterNOT molecules FOR SALE strike theOR tube; DISTRIBUTION these as the quantity of heat requiredNOT FOR to raise SALE the tempera OR DISTRIBUTION- collisions add energy to the molecules of the tube, so ture of 1 gram of a substance by 1°C. More energy is they vibrate faster. This in turn transfers kinetic energy required to raise the temperature of a substance with to the atoms of mercury. The atoms of mercury begin to high heat capacity than one with low heat capacity. vibrate vigorously and collide with one another harder In other words, adding the same amount of heat will © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC and harder, forcing them on the average farther apart raise the temperature of a substance with a low heat thanNOT they FOR were SALE before OR the additionDISTRIBUTION of kinetic energy capacity NOTto a greater FOR degree SALE than OR one DISTRIBUTION with a high heat from the water. Therefore, the mercury expands and capacity. The high heat capacity of water explains why rises in the tube of the thermometer, which is calibrated so much energy is required to heat water. precisely to read temperature. In addition to its unusually high heat capacity, © Jones & BartlettTemperature Learning, controls LLC another fundamental prop©- Jonesthe &capability Bartlett of Learning,liquid water LLCto dissolve material, its NOT FOR SALEerty of OR matter DISTRIBUTION called density—the amount of massNOT FORsolvent SALE power OR, is unsurpassedDISTRIBUTION by any other substance. contained in a unit volume, expressed as grams (mass) In fact, chemists refer to water as the “universal solvent,” per cubic centimeter (volume), that is, g/cm3. The more meaning that virtually anything can be dissolved to mass that is contained in a cubic centimeter, the more some extent in liquid water. dense is the material. The amount of heat contained in Water possesses other unusual properties as well, © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC a substance determines how vigorously the molecules but the case for this substance’s chemical uniqueness in that substance vibrateNOT FOR and collide SALE with OR one DISTRIBUTION another. should be clear. To accountNOT for FORwater’s SALE singular OR prop DISTRIBUTION- The harder they vibrate, the farther apart they tend to erties, we must examine the physical structure of the

be, which controls directly the amount of mass that water molecule, H2O. The molecule’s asymmetrical is contained in a unit volume. This means that 10°C shape is as important as the chemical identities of the water© Jones is denser & Bartlett than 15°C Learning, water and that LLC warm air is two elements© Jones H and O.& TheBartlett two hydrogen Learning, atoms, LLC rather lessNOT dense FOR than SALE cold air OR at theDISTRIBUTION same pressure. than beingNOT attached FOR SALEsymmetrically OR DISTRIBUTION to either side of Now that we have a solid conceptual understanding the oxygen atom, are separated from each other by an of the structure of atoms, of the kinetic theory of heat, angle of 105 degrees for water in the liquid and gaseous and of temperature and density, we can examine the states (FIGURE 4–3c). This molecular architecture re- chemical and physical properties of water in general, sembles a mouse’s “head” with hydrogen “ears.” The © Jones & Bartlettand seawater Learning, in particular. LLC Let’s start by inspecting© Joneshydrogen & Bartlett and oxygen Learning, atoms shareLLC electrons, and this

NOT FOR SALEthe common OR DISTRIBUTION molecule on the Earth that we referNOT to FORcovalent SALE bond OR creates DISTRIBUTION the water molecule H2O. Each simply as water. hydrogen atom within the molecule possesses a single positive charge; the oxygen atom, a double negative

4-3 The Water Molecule charge. As such, the H2O molecule is electrically neu- © Jones & Bartlett Learning, LLCtral because of the balance© betweenJones &the Bartlett positive andLearning, LLC Most people knowNOT that the FOR chemical SALE formula OR DISTRIBUTION for water negative charges. However,NOT the FORstructural SALE asymmetry OR DISTRIBUTION is H2O. This formula means that water consists of two of the molecule imposes a slight electrical imbalance atoms of hydrogen (H) that are chemically bonded to because the positive hydrogen atoms are bonded to one one atom of oxygen (O) (FIGURE 4–3a). However, despite end of the oxygen atom and the electrons associated its simple chemical composition, water is a complex with that atom are concentrated on the other side. substance© Jones with & Bartlett truly remarkable Learning, physical LLC properties. This gives© Jonesrise to a &dipole Bartlett (two-pole) Learning, structure LLC (see ForNOT example, FOR SALE the melting OR DISTRIBUTIONand boiling temperatures Figure 4–3c).NOT Thus,FOR there SALE is a ORresidual DISTRIBUTION positive charge of water are much higher than expected when com- at the hydrogen end of the molecule and a residual pared with chemically related hydrogen compounds negative charge at the oxygen end, despite the overall (FIGURE 4–3b). This is fortunate; otherwise, water would electrical neutrality of the water molecule. Conse- © Jones & Bartlettbe able to Learning, exist only as LLC a gas at the temperatures that© Jones quently, & Bartlett liquid water Learning, is not merely LLC a collection of freely NOT FOR SALEprevail OR at the DISTRIBUTION Earth’s surface. Consequently, the oceansNOT FORmoving SALE molecules. OR DISTRIBUTION Rather, its dipole structure causes

90 CHAPTER 4 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES 100© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Measured values NOT FOR SALE OR DISTRIBUTION NOT FOR SALE ORx DISTRIBUTIONExpected values 105° 50 S Sulfur H2O Se Selenium Hydrogen Te Tellurium 0 H Hydrogen © Jones & Bartlett Learning, LLC Boiling © Jones & Bartlett Learning, LLC temperatures H2Te

NOT FOR SALE OR DISTRIBUTION (°C) Temperature NOT FOR SALE OR DISTRIBUTION –50 H2Se H S x 2 Melting x temperatures –100 Oxygen 0 50 100 150 © Jones & Bartlett Learning, LLC Molecular© Jones weight (moles) & Bartlett Learning, LLC

NOT(a) FORH2O MOLECULE SALE OR DISTRIBUTION(b) MELTING AND BOILING NOTTEMPERATURES FOR SALEOF WATER OR DISTRIBUTION

Cumulative positive charge Hydrogen Hydrogen 100 © Jones & Bartlett Learning,+ LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION105° NOT FOR SALE OR DISTRIBUTION

Oxygen O molecules per cluster

– 2 © Jones & BartlettFree H Learning,2O LLC © Jones & Bartlett Learning, LLC CumulativeNOT FOR SALEmolecules OR DISTRIBUTION A cluster of H 0 NOT FOR SALE OR DISTRIBUTION negative H2O molecules 0 50 100 with hydrogen bonds charge Temperature (°C) (c) DIPOLE STRUCTURE (d) CLUSTERS OF WATER (e) SIZE OF WATER CLUSTERS

FIGURE 4–3 The water molecule. (a) The chemical bonding of two hydrogen atoms and one oxygen atom produces a water (H 2O) molecule. (b) The© observed Jones (o) & melting Bartlett and boiling Learning, temperatures LLC of water are much higher than ©theory Jones (x) indicates. & Bartlett (Adapted Learning, from Horne, R. LLC A. MarineNOT Chemistry: FOR The SALEStructure ofOR Water DISTRIBUTION and the Chemistry of the Hydrosphere. John WileyNOT & Sons, FOR 1969). SALE(c) The two OR small DISTRIBUTION hydrogen atoms are separated from each other at their points of attachment to the large oxygen atom by an angle of 105 degrees, so that the molecule resembles the familiar caricature of a mouse’s head. This structure creates a dipolar molecule with a residual positive charge at one end and a

residual negative charge at the other end. (d) A cluster of H 2O molecules with hydrogen bonds is contrasted here with free H 2O molecules. © Jones &(e) BartlettThe size of the Learning, clusters decreases LLC with increasing temperature.© Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

the negative end of the molecule to be attracted to liquid water and to melt ice because hydrogen bonds

and become electrically bonded to the positive end of that link H2O molecules to H2 molecules must first be a nearby water molecule.© Jones This electrostatic & Bartlett bonding, Learning, broken LLC before the solid can melt© Jones and the & liquidBartlett can Learning, LLC called hydrogen bondingNOT, producesFOR SALE irregular OR chains DISTRIBUTION vaporize. This is also the reasonNOT for FOR water’s SALE high heat OR DISTRIBUTION and clusters of H2O molecules (FIGURE 4–3d). The size of capacity. When heat is added to water, only a fraction water-molecule clusters decreases with increasing tem- of this energy is actually used to increase the vibra- perature (FIGURE 4–3e). Although hydrogen bonding tions of the molecules, which would be detected as a is only 4 percent as strong as the covalent bonds that rise of temperature. Much of the added heat is used to © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC hold the atoms of the molecule together, it is directly break hydrogen bonds that link the H2O molecules into responsibleNOT FOR for many SALE of water’s OR extraordinaryDISTRIBUTION physical irregular clusters.NOT Thus, FOR as SALE water is OR heated, DISTRIBUTION its tempera- properties. Let’s examine how this comes about. ture rises slowly relative to the amount of energy used. The higher-than-expected melting and boiling Conversely, when cooled, water releases more heat temperatures of water (see Figure 4–3b) depend than expected from the decrease in its temperature. © Jones &directly Bartlett on the Learning, dipole structure LLC of the H2O molecule. © JonesThe & unusually Bartlett high Learning, heat capacity LLC of water prevents NOT FORMore SALE energy OR isDISTRIBUTION required than expected to vaporize NOTextreme FOR variationsSALE OR in DISTRIBUTIONthe temperature of the oceans The Properties of Seawater 91 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES and explains why the climates of coasts and islands keeps the cations separated from the anions, a process © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC experience less extreme temperature variations than known as hydration. In other words, water acts as a NOT FOR SALEthose ORof land DISTRIBUTION located far from the ocean or large lakes.NOT FORsolvent SALE by preventing OR DISTRIBUTION the chemical recombination of During the summer, large bodies of water absorb solar Na+ and Cl- to form the solid halite. heat, helping keep air temperatures cool. During the The density of water is yet another unusual prop- winter, large lakes and the ocean radiate great quanti- erty of this familiar substance. Ice floats on water! All ties of stored heat© toJones the atmosphere & Bartlett as theirLearning, water LLCother solids sink in their own© Jones liquids. & It’s Bartlett hard to imag Learning,- LLC cools, warming theNOT adjacent FOR shoreline. SALE OR DISTRIBUTIONine a solid bar of steel floatingNOT inFOR a vat SALEof molten OR steel. DISTRIBUTION The high solvent power of liquid water likewise Once again, water behaves in a peculiar way. Why is depends on the dipole structure of its molecule. this so? Sodium and chloride are the most common elements At the freezing point, solids crystallize from liquids dissolved in seawater. Sodium is a positively charged because the thermal vibrations of molecules are low © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC atom (Na+) called a cation. In contrast, chloride is a enough so that chemical bonding can occur and a crys- negativelyNOT FOR charged SALE atom OR (Cl DISTRIBUTION-) called an anion. When tal forms.NOT The FORloose assortmentSALE OR of DISTRIBUTION molecules in the these two ions come into contact, they are attracted to liquid is reconstructed into a rigid solid. Because the each other because of their opposing charges and can molecules in the solid vibrate less than do the molecules be held together by ionic bonds to form halite (rock in the liquid, they are more tightly packed and denser © Jones & Bartlettsalt or common Learning, table salt). LLC When halite crystals are put© Jonesin the& Bartlettsolid than Learning,in the liquid LLCstate. Therefore, solids, NOT FOR SALEin water OR ( FIGUREDISTRIBUTION 4–4), the negatively charged endNOT of FORbecause SALE of their OR higher DISTRIBUTION density, sink in their own liq- + the H2O dipole dislodges sodium ions (Na ) from the uids. Water does not behave in the same way because

solid, and the positive end of the H2O molecule tears ice molecules are arranged into an open crystal frame- off chloride ions (Cl-). Dissolution (the noun form of work (FIGURE 4–5a), whereas liquid water molecules the verb to dissolve) continues until either the entire are packed into snug clusters by the hydrogen bonds © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC crystal of halite is gone or the volume of water can no between molecules (see Figure 4–3d). Also, the angle longer accommodateNOT more FOR ions SALE of salt OR because DISTRIBUTION it is of separation between theNOT two hydrogen FOR SALE atoms ,OR which DISTRIBUTION saturated, meaning there is physically no more “room” is 105 degrees in liquid and gaseous water, expands to for the sodium and chloride in the water. (By way of 109.5 degrees in ice. This makes ice about 8 percent

an analogy, think about what happens when you keep less dense than water. The H2O molecules in ice are adding© Jones spoonful & Bartlett after spoonful Learning, of sugar LLC to your cup of ordered ©into Jones a porous & hexagonBartlett (a Learning, six-sided structure) LLC coffee.)NOT FOR In solution, SALE the OR sodium DISTRIBUTION and chloride ions are by the hydrogenNOT FOR bonds SALE between OR oppositelyDISTRIBUTION charged surrounded by water molecules (see Figure 4–4). This ends of neighboring molecules (Figure 4–5a). When

NOT FOR SALE OR DISTRIBUTION NOTHydration FOR SALE OR DISTRIBUTIONH2O H O sheath 2 Small H O water 2 H2O Hydrated – cluster Cl H O chloride 2 © Jonesion & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC H2O H2O NOT FOR SALE OR DISTRIBUTION– H2ONOT FOR SALE OR DISTRIBUTION Na+ Cl Na+ – – – Cl Cl Cl Na+ Na+ Cl– Na+ Na+ – H O Cl– Cl H O © Jones & Bartlett2 Learning, LLC Na+ © Jones &2 Bartlett Learning, LLC – Cl + NOT FOR SALE OR DISTRIBUTIONCl– Na+ NOT FORNa SALE OR DISTRIBUTION Na+ – Hydrated H2O Cl H2O sodium ion Halite crystal

+ - © Jones & BartlettFIGURE 4–4 Learning, Halite (rock LLCsalt). The dipole structure of the H©2O Jones accounts &for Bartlettits unsurpassed Learning, properties asLLC a solvent. Na and Cl ions NOT FOR SALEare dislodged OR DISTRIBUTION from the halite crystal by, respectively, the negativelyNOT and FOR positively SALE charged OR ends DISTRIBUTION of the water dipole.

92 CHAPTER 4 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES Hydrogen © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Covalent bond Oxygen Maximum density (3.98°C) NOT FOR SALE OR DISTRIBUTION NOT1.000 FOR SALE OR DISTRIBUTION 0.998 ) 3 0.996 Liquid water 0.994 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Ice

NOT FOR SALE OR DISTRIBUTIONDenstiy (g/cm 0.9174 NOT FOR SALE OR DISTRIBUTION 0.9172 0.9170

0 3.98 5 10 15 © Jones & Bartlett Learning, LLC © JonesTemperature & Bartlett (°C) Learning, LLC (a) HEXAGONALNOT FOR CRYSTAL SALE STRUCTURE OR DISTRIBUTION OF ICE (b) DENSITY OF WATERNOT FOR SALE OR DISTRIBUTION

FIGURE 4–5 Properties of water. (a) The open network of the hexagonal structure of ice crystals is shown here. (b) Because of the open-crystal structure of solid water, ice is less dense than liquid water. Water attains its maximum density at a temperature of 3.98°C; polymers exist in liquid water colder than this temperature. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION ice is warmed to 0°C, it begins to melt as thermal The dissolving agent, the liquid water, is the solvent vibrations of the molecules cause the crystalline struc- and the dissolved substances, the salt ions, are the ture to break apart. Because of hydrogen bonds, the solute. Seawater also contains minor to trace amounts freed H2O molecules in© the Jones liquid become& Bartlett more Learning,closely ofLLC dissolved metals, nutrients,© gases, Jones and organic& Bartlett com- Learning, LLC packed together than NOTthey were FOR in theSALE solid, OR resulting DISTRIBUTION pounds of seemingly infiniteNOT variety. FOR SALE OR DISTRIBUTION in an increase of density (more mass per unit volume). Before examining the chemistry of seawater Water does not, however, reach its maximum density solutions, we need to determine the amount of until it is warmed to 3.98°C (FIGURE 4–5b) because material that is dissolved in seawater so that we can loose aggregates of molecules that resemble the open compare samples taken from different parts of an crystalline© Jones structure & Bartlett of ice (see Learning, Figure 4–2b), LLC termed ocean or, for© that Jones matter, & fromBartlett different Learning, oceans. WeLLC polymersNOT, FORpersist SALE in water OR cooler DISTRIBUTION than that critical can taste seawaterNOT FORsamples SALE and say OR qualitatively DISTRIBUTION that temperature. Above 3.98°C, the density of water this sample tastes “saltier” than this other one. But decreases with increasing temperature, as expected. this is a rather subjective technique, and a scientist Below 3.98°C, however, the density of water decreases needs to know exactly and precisely how salty a parcel © Jones &as temperatureBartlett Learning, decreases until LLC it freezes into ice. © Jonesof water & is. Bartlett Oceanographers Learning, specify LLC the concentra- What we have learned so far about seawater is that tion of a solute in seawater in units called parts per NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION it consists dominantly of H2O, a chemical substance thousand, represented by either the abbreviation that can occur in a solid, liquid, and gaseous state at ppt or, as preferred by marine scientists, the symbol the temperatures and pressures that exist at the Earth’s ‰. Although oceanographers also express salinity surface. Although we find water everywhere on the as a dimensionless unit in terms of PSS78—Practical planet, its unusual chemical© Jones and &physical Bartlett properties Learning, Salinity LLC Scale 1978—we will© Jonesuse ppt. & Average Bartlett or Learning, LLC should not be taken forNOT granted; FOR it is SALE these very OR proper DISTRIBUTION- “normal” seawater has a salinityNOT of aboutFOR 35‰.SALE This OR DISTRIBUTION ties that have enabled life to appear and evolve through means that the dissolved salt occurs in a concentra- geologic history. We can now proceed to examine sea- tion of 35 parts per thousand (ppt). That is, the salt water’s other chemical ingredients. comprises 3.5 percent (divide 35 by 1,000, and con- © Jones & Bartlett Learning, LLC vert it to a percentage© Jones &by Bartlettmultiplying Learning, it by 100) LLC of The Solutes of Seawater the sample, the rest (96.5 percent or 965 parts per NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION thousand) being H2O molecules. (Notice that 965 + Chemical analyses of samples from all over the world 35 = 1,000.) This signifies that a volume of seawater show that seawater consists of a small quantity of salt weighing 1,000 grams (or 1 kilogram) with a salinity dissolved in water. The salt occurs as charged particles, of 35‰ contains 35 grams of solute. Obviously, a © Jones &cations Bartlett and anions, Learning, that are LLC dispersed among the mol- © Jones100-gram & Bartlettsample of Learning,seawater with LLC a salinity of 35‰ NOT FORecules SALE of liquidOR DISTRIBUTION water. Seawater is a chemical solution. NOTcontains FOR SALE3.5 grams OR of DISTRIBUTIONdissolved salts. The Properties of Seawater 93 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES As you know, because of its high solvent power in the ocean. Because the concentrations of these major © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC (ability to dissolve), ocean water dissolves many types constituents in seawater vary little over time at most NOT FOR SALEof chemicals, OR DISTRIBUTION and most are found in minute quantiNOT- FORlocalities, SALE they OR are DISTRIBUTION described as conservative ions of ties. All these solutes can be grouped into five broad the ocean. categories: major constituents, nutrients, gases, trace Nutrients elements, and organic compounds. A review of the Nutrients are essential for plant growth, as any- general characteristics© Jones of each & group Bartlett follows. Learning, LLC © Jones & Bartlett Learning, LLC body who has fertilized a lawn or garden knows. All Major ConstituentsNOT FOR SALE OR DISTRIBUTIONplants, including those NOTthat live FOR in the SALE ocean, OR con DISTRIBUTION- In terms of quantity, the primary solutes in seawater vert nutrients into food (organic compounds such as are cations and anions. By weight, chloride (Cl-) and sugar) by photosynthesis. Nutrients in seawater are sodium (Na+) together comprise more than 85.65 per- compounds that consist primarily of nitrogen (N), cent© Jones (TABLE 4–1& )Bartlett of all the dissolvedLearning, substances LLC in sea- phosphorous© Jones (P), and& Bartlett silicon (Si).Learning, Representative LLC water.NOT WhenFOR SALEthese two OR ions DISTRIBUTION bond chemically into concentrationsNOT FOR of these SALE nutrients OR DISTRIBUTION in the ocean are a solid, they form halite and give seawater its most listed in TABLE 4–2; note that the concentrations are distinctive property—its saltiness. Surprisingly, the six specified inparts per million (ppm). Most plants most abundant ions—chloride (Cl-), sodium (Na+), cannot use elemental nitrogen and phosphorus and sulfate (SO42-), magnesium (Mg2+), calcium (Ca2+), so satisfy their nutrient needs by absorbing phos- © Jones & Bartlett Learning,+ LLC © Jones & Bartlett3- Learning, LLC- and potassium (K )—make up over 99 percent of all phate (PO4 ) and nitrate (NO3 ). Silicon is used by NOT FOR SALEof seawater’s OR DISTRIBUTION solutes. The addition of five more solutesNOT FORimportant SALE groups OR DISTRIBUTION of microscopic plants (diatoms) - - to the list—bicarbonate (HCO3 ), bromide (Br ), boric and animals (radiolaria) to precipitate silica (SiO2) 2+ - acid (H3BO3), strontium (Sr ), and fluoride (F )— shells around their fragile cells. Because of biological elevates the quantity of dissolved ingredients in sea- uptake and release, the concentrations of nutrients water to 99.99 percent© Jones (see Table& Bartlett 4–1). This Learning, means, LLCin seawater, as on land, vary© Jones from place & Bartlett to place andLearning, LLC of course, that everythingNOT FOR else SALE dissolved OR in DISTRIBUTION seawater over time at any one place.NOT Thus, FOR oceanographers SALE OR DISTRIBUTION occurs in trace amounts and collectively comprises refer to these substances as nonconservative ions only 0.01 percent! But what appears to be insignificant of seawater, signifying that levels of these substances cannot be ignored because, even in tiny quantities, are not constant in water but vary over time and from many of these chemicals are absolutely critical for life place to place. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

TABLE 4–1 MAJOR SOLUTES IN SEAWATER © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALESalt OR Ion DISTRIBUTIONIons in Seawater* (‰)NOT FORIons SALE by Weight OR DISTRIBUTION (%) Cumulative (%) Chloride (Cl-) 18.980 55.04 55.04 Sodium (Na+) 10.556 30.61 85.65

2- Sulfate (SO4 ) 2.649 7.68 93.33 Magnesium (Mg2+)© Jones & Bartlett1.272 Learning, LLC 3.69 © Jones & 97.02Bartlett Learning, LLC Calcium (Ca2+) NOT FOR SALE 0.400OR DISTRIBUTION 1.16 NOT FOR SALE98.18 OR DISTRIBUTION Potassium (K+) 0.380 1.10 99.28

- Bicarbonate (HCO3 ) 0.140 0.41 99.69 Bromide (Br-) 0.065 0.19 99.88 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Boric acid (H3BO3) 0.026 0.07 99.95 NOTStrontium FOR (Sr SALE2+) OR DISTRIBUTION0.013 NOT 0.04FOR SALE OR DISTRIBUTION99.99 Fluoride (F-) 0.001 0.00 99.99 Total 34.482 99.99 99.99

© Jones & Bartlett*The gram Learning, weight of ions per LLC1 kg of seawater, or g/kg. © Jones & Bartlett Learning, LLC NOT FOR SALESource: OR Adapted DISTRIBUTION from Sverdrup, H. U., Johnson, M. W., and Fleming, R. H.NOT The Oceans FOR (Englewood SALE Cliffs, N.J.:OR Prentice-Hall, DISTRIBUTION 1942).

94 CHAPTER 4 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES © Jones & TABLEBartlett 4–2 Learning, LLC © JonesTABLE & Bartlett 4–4 Learning, LLC NOT FOR SALENEAR-SURFACE OR DISTRIBUTION NUTRIENT NOT FOREXAMPLES SALE OF OR TRACE DISTRIBUTION ELEMENTS CONCENTRATIONS IN SEAWATER IN SEAWATER

Nutrient Element Concentration (ppm)* Trace Element Concentration (ppb)* Phosphorus (P) 0.07 Lithium (Li) 170 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Nitrogen (N) 0.5 Iodine (I) 60 NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Silicon (Si) 3 Molybdenum (Mo) 10 Zinc (Zn) 10 *ppm = parts per million Iron (Fe) 10 Aluminum (Al) 10 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Copper (Cu) 3 Gases NOT FOR SALE OR DISTRIBUTION Manganese NOT(Mn) FOR SALE OR2 DISTRIBUTION Listed in order of decreasing abundance (TABLE 4–3), Cobalt (Co) 0.1 gases in seawater include nitrogen (N2), oxygen (O2), Lead (Pb) 0.03 carbon dioxide (CO2), hydrogen (H2), and the noble gases argon (Ar), neon (Ne), and helium (He). Nitro- Mercury (Hg) 0.03 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC gen and the three noble gases are inert (unreactive) Gold (Au) 0.004 NOT FORand SALE rarely OR involved DISTRIBUTION directly in plant photosynthesis. NOT FOR SALE OR DISTRIBUTION

In contrast, levels of dissolved O2 and CO2 are greatly *ppb = parts per billion influenced by photosynthesis and respiration of organisms. Therefore, they vary greatly in space and time depending on the activities© Jones of plants & Bartlett and animals Learning, and OrganicLLC Compounds © Jones & Bartlett Learning, LLC are regarded as nonconservative.NOT FOR SALE OR DISTRIBUTIONOrganic compounds are large,NOT complex FOR molecules SALE pro OR- DISTRIBUTION duced by organisms. They include substances such as Trace Elements lipids (fats), proteins, carbohydrates, hormones, and Trace elements are all chemical ingredients that oc- vitamins. Typically, they occur in low concentrations cur in minute (trace) quantities in the oceans. Most and are produced by metabolic (physical and chemi- trace© elements, Jones such& Bartlett as manganese Learning, (Mn), LLClead (Pb), cal processes© in Jones the cell &of Bartlettan organism Learning, that produce LLC mercuryNOT (Hg), FOR gold SALE (Au), OR iodine DISTRIBUTION (I), and iron (Fe), living matter)NOT and FORdecay processesSALE OR of organisms.DISTRIBUTION For occur in concentrations of less than 1 ppm (part per example, vitamin complexes are vital for promoting the million) (TABLE 4–4). Many occur in quantities of less growth of bacteria, plants, and animals, as shown by

than 1 part per billion (ppb) and even at 1 part per the control that thiamine and vitamin B12 have on the trillion. These low concentrations make certain trace growth rate, size, and number of microscopic plants © Jones &elements Bartlett difficult Learning, and sometimes LLC even impossible to © Jonesgrown in& laboratoryBartlett Learning,experiments. LLC NOT FORdetect SALE in seawater.OR DISTRIBUTION However, despite their extremely NOT FORNow SALEthat we ORhave DISTRIBUTION a general understanding of the low concentrations, trace elements can be critically chemical makeup of seawater—a solution of mainly important for marine organisms, either by helping to water with some salts, and tiny quantities of nutrients, promote life or by retarding or killing life (toxicity). gases, trace elements, and organic compounds—we can © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION TABLE 4–3 QUANTITIES OF GAS IN AIR AND SEAWATER

In Surface Ocean Gas© Jones & Bartlett Learning,In Dry LLCAir (%) Water© (%)Jones & BartlettWater–Air Learning, Ratio LLC

NitrogenNOT (NFOR2) SALE OR DISTRIBUTION78.03 47.5NOT FOR SALE OR DISTRIBUTION0.6

Oxygen (O2) 20.99 36.0 1.7

Carbon dioxide (CO2) 0.03 15.1 503.3

Argon (Ar), hydrogen (H2), 0.95 1.4 1.5 © Jones & Bartlettneon (Ne), and Learning, helium (He) LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION The Properties of Seawater 95 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES proceed to examine the nature of salinity and its effect on regardless of population size. This means that the total © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC the properties of water, as well as the factors that control number of people in the population can vary, but the NOT FOR SALEthe saltiness OR DISTRIBUTION of the ocean. In other words, why are theNOT FORrelative SALE proportion OR ofDISTRIBUTION females to males does not change. oceans salty, why are there variations in the salinity of In other words, the ratio of females to males is constant the oceans, both on its surface and within its depths, and and is independent of population size. Just so, the ratio how does dissolved salt affect the physical properties of any two major salt constituents in ocean water is of water? Answers© to Jones such questions & Bartlett are easy Learning, to grasp, LLCconstant and is independent© Jones of salinity. & Bartlett Learning, LLC provided that youNOT understand FOR theSALE concepts OR justDISTRIBUTION intro- This important discovery,NOT FOR made SALE during OR the DISTRIBUTION duced. Also, the boxed feature “Chemical Techniques” Challenger expedition, is termed the principle of reviews a few of the methods that chemists employ to constant proportion or constant composition, and measure the properties of seawater while at sea and in was a major breakthrough in determining salinity of the laboratory. seawater in a rapid, accurate, and economical man- © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC ner. In theory, all that need be done to quantify salin- NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 4-4 Salinity ity is to measure the amount of only a single major ion dissolved in a sample of seawater because all the A simple way to determine salinity is to evaporate wa- other major constituents listed in Table 4–1 occur in ter from a container of seawater and then compare fixed amounts relative to that ion. Chemists chose to © Jones & Bartlettthe weight Learning, of the solid LLC residue left behind in the bot©- Jonesmeasure & Bartlett Cl- for Learning,determining LLCthe salinity of seawater NOT FOR SALEtom of OR the DISTRIBUTIONcontainer—the salts—to the weight of theNOT FORbecause SALE it is the OR most DISTRIBUTION abundant solute in seawater and original sample of seawater. Unfortunately, the method its concentration is easily determined. is neither precise nor accurate because salt crystals Today, oceanographers rely on a variety of methods, including the electrical conductivity of seawater, to hold on to variable amounts of H2O molecules, and make routine determinations of salinity. The electrical that affects the weight© Jones of the &salt Bartlett residue. Learning,In order to LLC © Jones & Bartlett Learning, LLC conductivity of a solution is its ability to transmit an compare accuratelyNOT salinity FOR data SALE gathered OR from DISTRIBUTION many NOT FOR SALE OR DISTRIBUTION parts of the ocean and measured in many different electrical current directly proportional to the total ion laboratories and ships, chemists have adopted a stan- content of the water at a given temperature, which, of dardized and what seems to nonchemists to be a rather course, is its salinity. A salinometer indirectly mea- cumbersome definition ofsalinity : the total mass ex- sures salinity by measuring the electrical conductivity pressed© Jones in grams & Bartlett of all the Learning, substances LLCdissolved in 1 of seawater.© Jones Its calibrations & Bartlett allow Learning, oceanographers LLC to kilogramNOT FOR of seawater, SALE whenOR DISTRIBUTION all the carbonate has been determineNOT salinity FOR directly SALE and OR quickly DISTRIBUTION by inserting an converted to oxide, all the bromine and iodine have electrical probe into the water, a very simple matter been replaced by chlorine, and all organic compounds compared with the rather laborious chemical deter- have been oxidized at a temperature of 480°C. Because mination of chlorinity. we are not chemical oceanographers, we can simplify © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC the definition of salinity as follows to suit our more Factors that Regulate NOT FOR SALEgeneral OR purpose: DISTRIBUTION the total weight in grams of dissolvedNOT FORthe SALESalinity OR of DISTRIBUTIONSeawater salts in 1 kilogram of seawater expressed as ‰ (parts per thousand). There is a lot of dissolved salt in the ocean. An important question is, what supplied all this material to the Principle of Constant© Jones Proportion & Bartlett Learning, LLCsea? The answer is straightforward© Jones (TABLE & Bartlett 4–5). Rivers Learning, LLC NOT FOR SALE OR DISTRIBUTIONdisgorge huge volumes ofNOT fresh FOR water SALEinto the OR ocean DISTRIBUTION Salinity determinations from the world’s oceans have every year. Chemical analyses of water samples from revealed an important, unexpected finding. Although rivers all over the world indicate that they contain a salinity varies quite a bit because of differences in the variety of dissolved substances in concentrations of total© Jones amount & of Bartlett dissolved salts,Learning, the relative LLC proportions ppm (TABLE© Jones 4–6). Rivers & Bartlett have a dissolved Learning, load of LLCchemi- of the major constituents are constant. In other words, cals because of the chemical weathering of rocks on theNOT ratio FOR of any SALE two major OR DISTRIBUTION constituents dissolved in the land.NOT These FOR rocks SALE are made OR up DISTRIBUTION of an assemblage + + - 2- seawater, such as Na /K or Cl /SO4 , is a fixed value, of minerals composed predominantly of the elements whether the salinity is 25, 30, 35‰, or whatever. To silicon, aluminum, and oxygen. Acidic water breaks put it in more familiar terms, let’s imagine that the down these rocks into their component elements.

© Jones & Bartlettratio of females Learning, to males LLC in a population is ¼ (1 female© JonesWhen & Bartlett carbon dioxide Learning, (CO2) LLCis dissolved in water, it NOT FOR SALEfor every OR 4DISTRIBUTION males) and that this ratio never changesNOT FORreacts SALE with H OR2O molecules DISTRIBUTION to produce H2CO3, a weak

96 CHAPTER 4 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES © Jones & TABLEBartlett 4–5 Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALESOURCES OR DISTRIBUTIONAND SINKS OF SOME SEAWATER COMPONENTSNOT FOR SALE OR DISTRIBUTION

Chemical Component Sources Sinks Chloride (Cl-) Volcanoes Evaporative deposition as NaCl (rock salt) River influx Net air transfer © Jones & Bartlett Learning, LLC Pore-water burial © Jones & Bartlett Learning, LLC Sodium (Na+) NOT FOR SALERiver influx OR DISTRIBUTION Evaporative depositionNOT as NaCl FOR (rock SALEsalt) OR DISTRIBUTION Net air transfer Cation exchange with clays Basalt-seawater reactions Pore-water burial Potassium© Jones (K+) & Bartlett Learning,River influx LLC Uptake© Jones by clays & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTIONVolcanic-seawater reactions Volcanic-seawaterNOT FOR SALEreactions OR DISTRIBUTION (high temperature) (low temperature) Calcium (Ca2+) River influx Biogenic secretion of shells Volcanic-seawater reactions Evaporitic deposition of gypsum

Cation exchange (CaSO+ z 2H2O) © Jones & Bartlett Learning, LLC © Jones & BartlettPrecipitation Learning, as calcite LLC Silica (H4SiO4) River influx Biogenic secretion of shells NOT FOR SALE OR DISTRIBUTION Basalt-seawater reactionsNOT FOR SALE OR DISTRIBUTION

2- 3- Phosphorus (HPO4 , PO 4 , River influx Burial as organic P - H2PO4 , organic P) Rainfall and dry fallout Adsorption on volcanic ferric oxides Formation of phosphorite rock © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Source: Adapted from Berner,NOT E. K., and FOR Berner, SALER. A. The Global OR Water DISTRIBUTION Cycle (Englewood Cliffs, N.J.: Prentice-Hall, 1987). NOT FOR SALE OR DISTRIBUTION

acid called carbonic acid. In turn, this acid separates Notice that the reaction yields free ions of H+, + - into hydrogen (H ) and bicarbonate (HCO3 ) ions. which because of their small size and high chemical + + The specific© Jones chemical & Bartlett reactions Learning, are reversible, LLC are quite reactivity, replace© Jones cations & such Bartlett as Na Learning, and K that areLLC simple, and are represented by + NOT FOR SALE OR DISTRIBUTION bound to mineralsNOT inFOR rocks. SALE The amount OR DISTRIBUTION of H is a mea sure of the acidity of the water. This process—the bath- +− HO22++CO HC23OHHCO3 . ing of rocks in acidic water—slowly weathers minerals,

Substance Concentration (ppm) Concentration (%)

- 2- Bicarbonate/carbonate (HCO3 /CO3 ) 58.8 48.7 Calcium (Ca2+) © Jones & Bartlett Learning,15.0 LLC © Jones12.4 & Bartlett Learning, LLC Silica (SiO ) 13.1 10.8 2 NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 2- Sulfate (SO4 ) 1.2 9.3 Chloride (Cl-) 7.8 6.5 Sodium (Na+) 6.3 5.2 Magnesium© Jones (Mg 2&+) Bartlett Learning, LLC 4.1 © Jones & Bartlett 3.4Learning, LLC PotassiumNOT FOR(K+) SALE OR DISTRIBUTION 2.3 NOT FOR SALE OR 1.9 DISTRIBUTION - Nitrate (NO3 ) 1.0 0.8

Iron aluminum oxide [(Fe, Al)2 O3] 0.9 0.8 Remainder 0.3 0.3 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALESource: Livingstone, OR DISTRIBUTION D. A. Chemical composition of rivers and lakes, U.S. GeologicalNOT Survey, FOR Professional SALE Paper 440-GOR (U.S.DISTRIBUTION Government Printing Office, 1963). The Properties of Seawater 97 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTIONTHE OCEAN SCIENCESNOT FOR SALE OR DISTRIBUTION CHEMISTRY Chemical Techniques

In trying to characterize© Jones and &explain Bartlett the chemical Learning, prop- LLCtrapping a sample of seawater.© JonesA messenger & Bartlett attached to Learning, LLC erties of seawater,NOT marine FOR chemists SALE findOR itDISTRIBUTION critically a clamp beneath the first bottleNOT is FOR then released,SALE ORdrop- DISTRIBUTION important to collect sufficient and appropriate seawater ping and triggering the next bottle below. The procedure samples, prevent their chemical contamination, deter- is repeated until all the bottles on the cable have been mine sampling depths, and use accurate and precise closed. Depending on the nature of the study, chemists analytical procedures. usually collect seawater volumes of between 1 and 3 liters © Jones & Bartlett Learning, LLC (~1.06 and© 3.17 Jones quarts) & with Bartlett these bottle Learning, samplers. LLC Sample Collection NOT FOR SALE OR DISTRIBUTION A moreNOT elaborate FOR SALEsample-bottle OR DISTRIBUTION configuration is Seawater samples for chemical analysis are collected known as the rosette cluster. It consists of a rigid frame in metallic or plastic cylindrical bottles. The metallic that holds a number of collection bottles upright, arranged bottles have interior liners composed of inert plastic in a circular pattern (FIGURE B4–2). The bottles can be set © Jones & Bartlettto prevent Learning, contamination LLC of the sample by metal ions.© Jonesto open & Bartlett and close automatically, Learning, or LLC a technician can trigger NOT FOR SALEOne OR such DISTRIBUTION sampling device, the Niskin bottle, has valvesNOT FORany of SALE the bottles OR electronically DISTRIBUTION from a shipboard console. on both ends that are opened and attached to a cable Sampling Depths (FIGURE B4–1). Typically, several open bottles are attached at predetermined positions on the cable. After the Chemists must establish the exact sampling depth bottles are lowered, a weight, known as a messenger, is for each bottle. Otherwise, the analytical work, no mat- fastened to the cable© Jones and released. & Bartlett When the Learning, messenger LLCter how accurate, is of limited© useJones in determining & Bartlett the ex Learning,- LLC strikes the first NOTwater FORbottle, itSALE causes itOR to closeDISTRIBUTION tightly, act chemical structure of theNOT water FOR column. SALE A common OR DISTRIBUTION technique is to measure the length of the cable between the ocean surface and the depth at which the bottle was triggered by the messenger. However, the cable rarely © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOTFIGURE FOR B4–1 SALE Niskin ORbottles. DISTRIBUTION Open Niskin bottles are NOT FOR SALE OR DISTRIBUTION attached to a cable and lowered to water depths where FIGURE B4–2 A rosette cluster. Water collecting bottles seawater samples are to be obtained for chemical analysis. A are arranged around a rigid, circular frame in a rosette pat- metal messenger “ trips” each bot tle on the cable individually, tern. Technicians are able to close the bottles individually © Jones & Bartlettcausing itLearning, to fill with water LLC and close securely. © Jones as& the Bartlett array is lowered Learning, or raised through LLC the water column. NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

98 CHAPTER 4 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES © Jones & hangsBartlett straight Learning, down because LLC of the drift of the ship rela- © Jonesat frequencies & Bartlett that depend Learning, on temperature. LLC These NOT FOR SALEtive to theOR bottles DISTRIBUTION on the cable. Depth corrections are NOTsignals FOR are SALE transmitted OR electronicallyDISTRIBUTION to the ship. This applied by measuring the angle of the cable and by not- allows the temperature of the water to be monitored ing the difference between the temperature readings continuously as the instrument is lowered. on the pressure-protected and unprotected thermom- Because the composition of seawater is constant, eters mounted on the© samplingJones bottles.& Bartlett (Temperature Learning, chemistsLLC traditionally have determined© Jones water & Bartlett salinity Learning, LLC discrepancies are indicatorsNOT FOR of water SALE pressure, OR which DISTRIBUTION is by chemical titration—the processNOT of standardizingFOR SALE sil -OR DISTRIBUTION a function of water depth.) When near-bottom water ver nitrate against a normal seawater sample of known samples are collected, it is customary to attach a pinger chemical composition. The electrical conductivity of sea- (a pulsing sound source) to the free end of the cable. water, which is proportional to the total concentration Sound signals reflected off the seafloor and transmitted of dissolved ions, is now used routinely to determine to ©the Jones ship are used& Bartlett to determine Learning, the distance LLC between salinity rapidly.© The Jones salinometer & Bartlett compares Learning, the electri -LLC theNOT pinger FOR and the SALE bottom OR to within DISTRIBUTION a meter or so. cal conductivityNOT of an FOR unknown SALE sample OR with DISTRIBUTION that of a known, standard sample of seawater and converts the Analytical Procedures difference into a salinity value after correcting for tem- Analytical procedures reveal the temperature and perature effects. An important instrument called the © Jones & Bartlettsalinity of water.Learning, Reversing LLC thermometers, which are © JonesCTD (conductivity, & Bartlett temperature, Learning, depth) LLC consists of a NOT FOR SALEfastened OR to water-samplingDISTRIBUTION bottles, are used to mea- NOTsalinometer, FOR SALE an electronic OR DISTRIBUTION thermometer, and a pressure sure the temperature of water in situ. Better precision sensor. As it is lowered through the water column, the (up to 0.0001°C) is obtained by using temperature- CTD transmits electronic signals to the ship, where they sensitive materials, such as quartz crystals, which vibrate are stored in a shipboard computer for analysis later. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION releasing ions, which go into solution and become part response by most people is that the amount could of a river’s dissolved chemical load (Table 4–6). not be much because the concentration of solutes Let’s firm up our understanding of weathering by in rivers is low (that’s why freshwater doesn’t taste examining© Jones the chemical & Bartlett breakdown Learning, of an actual LLC min- salty), and it’s© Jones dissolved, & Bartlett so you can’t Learning, see it (how LLC

eral, NOTorthoclase FOR (KAlSi SALE3O 8OR), the DISTRIBUTION common potassium- can anythingNOT that FORcan’t be SALE seen amountOR DISTRIBUTION to much?). bearing feldspar of granite. The chemical reaction is It turns out that the annual river input of material in solution to the oceans is somewhere between + 15 15 15 2KAlSi3O8 + 2H + H2O 2.5 × 10 and 4 × 10 grams. True, 10 (10 mul- © Jones & Bartlett (Learning,orthoclase) LLC © Jonestiplied &by Bartlett itself fifteen Learning, times) seemsLLC to be quite a → 2K+ + Al Si O (OH) + 4SiO . big number. But how big is it, really? This rate of NOT FOR SALE OR DISTRIBUTION2 2 5 4 2 NOT FOR SALE OR DISTRIBUTION (kaolinite) (dissolved silica) influx, 1015 grams per year, is about equivalent to the mass of mud supplied each year to the oceans by This formula indicates that the mineral orthoclase the rivers of North America, South America, Africa, in the presence of acidic water (H+) is broken down into and Europe combined! Although dissolved material + potassium ions (K ), silica© Jones (SiO2), & and Bartlett aluminum Learning, sili- is LLC invisible to the naked eye,© itJones represents & Bartlett a major Learning, LLC

cates. The latter compoundNOT bondsFOR withSALE H2O, OR forming DISTRIBUTION annual input of mass to the oceans,NOT FOR all of SALE it derived OR DISTRIBUTION another mineral, the clay kaolinite. Rivers transport by the chemical weathering of rocks on land. In addi- these materials to the ocean in two distinct states: as a tion to the supply from rivers, the Earth is degassing. + dissolved load (K and SiO2) and as a suspended load This means that volcanoes on the crests of spreading (particles of kaolinite). The dissolved K+ and SiO con- ocean ridges and in the volcanic arcs of subduction © Jones & Bartlett Learning, LLC2 © Jones & Bartlett Learning, LLC tribute to the salinity of seawater; the clay accumulates zones spew large quantities of cations (including NOT FOR SALE OR DISTRIBUTION 2+ +NOT FOR SALE OR DISTRIBUTION2- - as sediment on the ocean floor. So what was a solid Ca and K ) and anions (including SO4 and Cl ) mineral in rocks on land becomes, by the processes into the water column, although the exact amount of chemical weathering and transport, dissolved salts of this input has yet to be determined reliably. in the ocean and mud on the sea bottom. The fossil record and sedimentary rocks them- © Jones & BartlettHow much Learning, mass is actually LLC added to the ocean © Jonesselves indicate & Bartlett that oceansLearning, have existed LLC on the Earth NOT FORby SALE the river OR influx DISTRIBUTION of dissolved matter? The first NOTfor FOR at least SALE as long OR as 3.4DISTRIBUTION billion years. Geochemical The Properties of Seawater 99 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES data indicate that the salinity of the oceans has changed Organisms help maintain the steady-state equilib- © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC little over the past 1.5 billion years. This constant rium of the ocean’s salinity as well. We already know NOT FOR SALEocean OR salinity DISTRIBUTION despite the tremendous annual supplyNOT FORthat diatomsSALE ORhave DISTRIBUTION silica shells and forams carbonate of dissolved chemicals to the oceans by rivers can only shells that are precipitated from the uptake of Si4+ and mean that on average a similar quantity of salt must Ca2+, respectively, from seawater. Once these organisms be removed from the oceans each year. Otherwise, the die, their hard parts may settle to the sea bottom to salinity of the world’s© Jones oceans & would Bartlett have Learning, increased LLCform deep-sea oozes. Also,© Jones many species & Bartlett of animals Learning, LLC over geologic time.NOT This FOR balance SALE between OR inputs DISTRIBUTION and extract certain chemical substancesNOT FOR that SALE are dissolved OR DISTRIBUTION outputs of salt to the ocean is called a steady-state in seawater. Some of these chemicals are concentrated equilibrium. in fecal pellets that sink to the ocean floor and become Oceanographers refer to inputs of material as incorporated in sediment. sources and their outputs as sinks. We’ve already iden- Let’s synthesize all that we have learned about © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC tified several of the principal sources of the salt ions steady-state equilibrium, sources and sinks of salt toNOT the ocean. FOR Let’sSALE now OR examine DISTRIBUTION the principal sinks of ions, andNOT geologic FOR cycles. SALE The OR salt DISTRIBUTION ions dissolved in dissolved salt in the ocean (see Table 4–5). The removal ocean water are derived largely from the weather- of salt occurs by both inorganic and organic processes. ing and erosion of rocks on land. Because the aver- Evaporation is an excellent example of an inorganic age chemical composition of seawater has remained © Jones & Bartlettprocess and, Learning, as discussed LLC in the boxed feature, “Desali©- Jonesremarkably & Bartlett stable Learning, (in a steady LLC state) over geologic NOT FOR SALEnation,” OR is DISTRIBUTIONa technique for producing drinkable waterNOT FORtime, SALE the inputs OR of DISTRIBUTION salt must be balanced by the out- from seawater. In arid climates, evaporation rates are puts. The river-supplied ions remain in ocean water high. Evaporation removes water from the ocean but for a long time, but eventually are extracted by innot the dissolved salt ions. This indicates that, with organic and organic processes and become part of time, the concentration of salt will rise by the evapora- the ocean’s sedimentary record. These sediments, as © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC tion of water molecules, creating a brine, or a very salty they are buried, become cemented into sedimentary solution. The DeadNOT Sea and FOR the GreatSALE Salt OR Lake, DISTRIBUTION both in rocks and eventually areNOT subducted FOR SALEalong the OR col DISTRIBUTION- arid settings, are fine examples of this very process. As liding boundaries of lithospheric plates. Some of more and more water molecules are evaporated from these sedimentary units are melted and intruded as the water, the solution eventually becomes saturated, igneous rocks, others are crumpled and raised into which© Jones means & that Bartlett the solution Learning, is holding LLC as much mate- large mountain© Jones belts, & where Bartlett chemical Learning, attack by LLC acidic rialNOT in a FORdissolved SALE state ORas it canDISTRIBUTION for the temperature and water onceNOT again FOR releases SALE these OR ions DISTRIBUTION to the sea. In ef- pressure conditions of the water. The removal of more fect, this is a grand sedimentary cycle (FIGURE 4–6). water creates a supersaturated solution (a solution Elements bonded into solid minerals in rocks are put containing a quantity of dissolved ions that exceeds the theoretical saturation value). This leads to the pre- © Jones & Bartlettcipitation Learning, of evaporite LLCminerals from seawater, notably© Jones & Bartlett Learning, LLC Erosion NOT FOR SALEhalite OR(NaCl) DISTRIBUTION and gypsum (CaSO4 z H2O). PrecipitationNOT FOR SALE OR DISTRIBUTION of evaporite minerals from seawater represents a sink

because dissolved salt ions are being removed from the Transport ocean to form sedimentary deposits on the seafloor. Wind also blows© Jones onshore & aBartlett large amount Learning, of sea LLC Uplift © Jones & Bartlett Learning, LLC spray, which on evaporation forms a coating of salt Deposition NOT FOR SALE OR DISTRIBUTION Compression NOT FOR SALE OR DISTRIBUTION on land—as anybody who wears glasses and lives by the seashore can attest. In addition, freshly extruded Lithospheric plate basalt lavas on the ocean floor are quite reactive and Intrusion extract dissolved ions, such as Mg2+ and SO 2-, from 4 Sedimentary beds the© Jonesseawater & that Bartlett comes inLearning, contact with LLC the hot lava. © Jones & Bartlett Learning, LLC Finally,NOT FOR adsorption SALE (the OR “sticking” DISTRIBUTION of ions to a surface) FIGURE 4–6NOT Sedimentary FOR SALE cycle. Over OR geologic DISTRIBUTION time, mountains of cations like K+ and Mg2+ by certain clay minerals in are leveled by rivers. The weathering products are dispersed into the ocean and the formation of hydrogenous miner- the ocean and collect on the sea bottom, forming sedimentary als, such as ferromanganese nodules, remove a large, beds. Eventually, these accumulations of sediment are deformed © Jones & Bartlettunknown Learning, quantity of LLCions from the sea. All of these© Jones and &uplifted Bartlett into mountain Learning, ranges by LLC plate tectonics. Then a new NOT FOR SALErepresent OR chemical DISTRIBUTION sinks for ions dissolved in seawater.NOT FORcycle ofSALE river erosion OR begins.DISTRIBUTION

100 CHAPTER 4 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES into solution and transported to the ocean by rivers, alert person.) By contrast, many of the principal ions © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC where organic and inorganic processes cause them in river water are characterized by short residence NOT FORto SALE be precipitated OR DISTRIBUTION into solids (such as halite, and NOTtimes FOR in SALEthe oceans OR becauseDISTRIBUTION they are much more silica and carbonate shells) and reincorporated into reactive or are important for biological cycles. For sedimentary rocks that become uplifted by tectonic example, many marine organisms require dissolved 2+ processes and weathered once again, repeating this Ca to secrete their carbonate (CaCO3) shells. These grand cycle. © Jones & Bartlett Learning, calciumLLC ions are in constant© demand Jones by & the Bartlett marine Learning, LLC If rivers are the primaryNOT FOR source SALE of salt ionsOR toDISTRIBUTION the biota, so calcium has a relativelyNOT low FOR residence SALE time OR DISTRIBUTION oceans, why aren’t the ionic compositions of fresh- of 8 × 106 years. water and seawater similar? They clearly are not, as a Long residence times also help to explain the comparison of Tables 4–1 and 4–6 shows. Shouldn’t principle of constant proportions. Water is stirred they be, if one is supplying material directly to the and mixed by ocean currents, much as stirring a pot © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC other? The difference in the relative composition of of soup with a spoon creates eddies and swirls (tur- solutesNOT in seawater FOR SALE and river OR water DISTRIBUTION is a result of the bulence) thatNOT mix the FOR ingredients. SALE OR Studies DISTRIBUTION of currents residence time of ions in the ocean, which is simply indicate that mixing rates in the oceans are on the the average length of time that an ion remains in order of a thousand (103) years or less. This rate is solution there. It ranges between 2.6 × 108 years for much lower than are the residence times of the major © Jones &sodium Bartlett and 1.5 Learning, × 102 years LLC for aluminum (TABLE 4–7). © Jonesions of &seawater, Bartlett which Learning, range from LLC millions (106) to NOT FORThis SALE is no OR different DISTRIBUTION from saying that your “residence NOThundreds FOR SALE of millions OR DISTRIBUTION(108) of years (see Table 4–7). time” in your bedroom, asleep in bed, is eight hours a Thus, rapid mixing and very long residence times of day. Note that the two most abundant components of salt ions in seawater assure that these substances are seawater (Na+ and Cl-) have long residence times, on distributed uniformly throughout the oceans. A more the order of hundreds of million years. Their persis- familiar way to think about this is to imagine yourself © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC tence in a dissolved state in ocean water reflects their making a cake. Slowly adding dye along the edge of a low geochemical and NOTbiochemical FOR reactivity;SALE OR in DISTRIBUTIONother bowl (this is equivalent to a riverNOT supplying FOR SALE ions at theOR DISTRIBUTION words, they are essentially inert. (To carry our anal- edge of an ocean basin) to a cake batter that is being ogy one step further, an inert, listless person would rapidly stirred by an electric beater (this is equivalent tend to spend more time in bed and have a longer to mixing by ocean currents) quickly distributes the residence© Jones time in & the Bartlett bedroom Learning, than would LLC an active, dye molecules© Jonesevenly throughout & Bartlett the Learning, batter, so that LLC NOT FOR SALE OR DISTRIBUTION its color (thisNOT is equivalent FOR SALE to the OR ocean’s DISTRIBUTION salinity) is uniform (FIGURE 4–7).

TABLE 4–7 Effects of Salinity on the Properties © Jones & BartlettRESIDENCE Learning, IN OCEAN LLC WATERS © Jonesof Water & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTIONResidence Time NOT FOR SALE OR DISTRIBUTION In the previous sections, we learned a great deal Substance (3 106 yr) about the structure of the water molecule and the - Chloride (Cl ) ∞ salinity of the ocean. Now we are ready to exam- Sodium (Na+) 260 ine the effect dissolved ions have on the physical Lithium (Li+) © Jones & 20Bartlett Learning,properties LLC of water. As you might© Jones guess, &the Bartlett addition Learning, LLC Strontium (Sr2+) NOT FOR SALE19 OR DISTRIBUTIONof salt modifies some of theNOT properties FOR SALEof water OR in DISTRIBUTION Potassium (K+) 11 a number of significant ways. Most of these chang- Calcium (Ca2+) 8 es come about because the ions are hydrated (see Figure 4–4), which modifies the chemical behavior Zinc (Zn2+) 0.18 of the H2O molecules in the solution. Let me explain Barium© Jones (Ba2+) & Bartlett Learning,0.084 LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION by examiningNOT some FOR specific SALE water OR properties DISTRIBUTION as they Cobalt (Co2+) 0.018 are affected by solutes. Chromium (Cr) 0.00035 Aluminum (Al) 0.00015 Freezing Point Pure freshwater freezes at 0°C. The addition of salt to the water lowers its freezing point. For example, sea- © Jones & BartlettSource: Adapted Learning, from Wentworth, C. LLC K. A scale of grade and class terms © Jones & Bartlett Learning, LLC NOT FOR SALEfor clastic sediments,OR DISTRIBUTION Journal of Geology 30 (1922): 377–392. NOTwater FOR with SALE a salinity OR of DISTRIBUTION 35‰ freezes at a temperature The Properties of Seawater 101 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

© Jones & BartlettFIGURE 4–7 Learning, Rapid mixing LLCspreads dye evenly throughout the© cake Jones batter. & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION of -1.91°C (FIGURE 4–8). The reason that the freezing Density temperature of seawater is depressed relative to that of Because solutes have a greater atomic mass than do

freshwater is quite simple. The hydrated salt ions “hold H2O molecules, the density of water increases with on” to individual H O molecules, interfering with their salinity. This means that freshwater floats on salt- ©2 Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC water. For salinities >24.7‰ (see Figure 4–8), the rearrangement intoNOT an ordered FOR SALE ice crystal. OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION temperature of maximum density (3.98°C for fresh

4 water; see Figure 4–5b) is below the freezing point (0°C). Vapor Pressure 3 © Jones & Bartlett Learning, LLC The vapor© pressureJones &on Bartletta liquid surface Learning, is the pressure LLC Maximum-density exerted by its own vapor. When a liquid such as water NOT2 FOR SALEtemperature OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION is placed in a closed container, some of the molecules

1 will vaporize, decreasing the amount of liquid. Once equilibrium is reached, the vapor pressure is the pres- 0 sure exerted by the molecules in the vapor phase. As © Jones & Bartlett Learning, LLC © Jonesthe &salinity Bartlett of water Learning, increases, LLC vapor pressure drops; –1 Freezing-point NOT FOR SALETemperature (°C) OR DISTRIBUTION NOT FORthis meansSALE that OR freshwater DISTRIBUTION evaporates at a faster rate temperature than does seawater. The depression of vapor pressure –2 in seawater is directly related to the total number of Average solute molecules. This effect is a consequence of the –3 seawater © Jones & Bartlett Learning, LLChydrated ions, which “hold© on” Jones to the &water Bartlett molecules, Learning, LLC making their vaporization more difficult. –4 0 10NOT FOR 20 SALE OR 30 DISTRIBUTION 40 NOT FOR SALE OR DISTRIBUTION Salinity (‰) 4-5 Chemical and Physical Structure FIGURE 4–8 Effects of salinity on the maximum-density and of the Oceans freezing-point© Jones temperatures& Bartlett of Learning,seawater. The addition LLC of dissolved © Jones & Bartlett Learning, LLC ions to water lowers the initial freezing point temperature of the Oceanographers have acquired a great deal of informa- NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION solution because the hydrated ions interfere with the rearrange- tion about variations in the fundamental properties

ment of the H2O molecules into an ordered ice structure. Also, an of ocean water, including the regional distribution of increase in salinity depresses the maximum-density temperature of temperature, salinity, and density along the sea sur- seawater. Consequently, the temperature of maximum-density of face and throughout the ocean’s depths. This section © Jones & Bartlettaverage seawater Learning, is well below LLC its freezing point. This means that© Jonessummarizes & Bartlett and Learning, explains the LLC general distribution of NOT FOR SALEseawater OR of averageDISTRIBUTION salinity will freeze before it will sink. NOT FORthese SALE three important OR DISTRIBUTION parameters of ocean water. This

102 CHAPTER 4 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES will provide the background necessary to understand insolation varies with the seasons, the surface-water © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC variations in the ocean’s content of gases, the important temperature changes with time as well. The intense NOT FORtopic SALE of the OR following DISTRIBUTION section. NOTsunlight FOR SALEin the tropicsOR DISTRIBUTION and subtropics produces a broad band of water with a temperature higher than Temperature 25°C that shifts north or south depending on the season (see Figure 4–9). Water in the polar oceans is Latitude exerts a strong© Jones control &on Bartlett the surface Learning, tem- veryLLC cold, much of it being near© Jones or even & below Bartlett 0°C. Learning, LLC perature of the oceanNOT because FOR the SALEamount ORof insola DISTRIBUTION- Seasonal shifts of the isothermsNOT are minor FOR in SALE the ocean OR DISTRIBUTION tion (the solar energy striking the Earth’s surface) off Antarctica but are significant in the North Pacific decreases poleward. Surface-water temperatures, and North Atlantic Oceans. therefore, are highest in the tropics and decrease Ocean currents that flow around the periphery of with distance from the equator. Isotherms, imagi- each ocean affect the distribution of surface-water tem- © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC nary contour lines that connect points of equal water perature. For example, the strips of >25°C water in the temperature,NOT FOR generally SALE trend OR east–west, DISTRIBUTION parallel to the tropical AtlanticNOT and FOR Pacific SALE Oceans OR are DISTRIBUTION much broader lines of latitude (FIGURE 4–9). Because the amount of at their western than at their eastern margins. This

Arctic Circle © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC

NOT FOR SALE OR DISTRIBUTION NOT FOR SALE60° NOR DISTRIBUTION

Equator 0°

Sea-Surface Currents © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC (a) SEA-SURFACENOT FOR TEMPERATURE SALE OR IN DISTRIBUTIONAUGUST NOT FOR SALE OR DISTRIBUTION FIGURE 4–9 Sea-surface temperatures. Because water is heated by the sun, and solar radiation decreases with distance from the equator, sea-surface temperatures vary directly with latitude. Deep blue indicates cold water (0–1°C) and orange, warm water (24°C+). Large-scale ocean circulation transports warm water poleward at the western edges of the ocean basins and cold water equatorward at © Jones &their Bartlett eastern peripheries. Learning, (a) Global LLC sea-surface temperature (SST)© is Jonesshown for &August. Bartlett (b) Global Learning, SST is shown LLC for February. (Adapted NOT FORfrom SALE Sverdrup, OR H. DISTRIBUTION U., et al. The Oceans. Prentice-Hall, 1942.) NOT FOR SALE OR DISTRIBUTION The Properties of Seawater 103 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES 90 °E 120 °E 150° E 180° 150° W 120° W 90° W 60° W 30° W 0° 30° E60° E © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

Arctic Circle © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC 60° N NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

30° N © Jones & Bartlett Learning, LLC © Jones & BartlettTr opic of CancerLearning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

Equator 0°

Tr opic of Capricorn © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC 30° S NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC (b) SEA-SURFACE TEMPERATURE IN FEBRUARY NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION FIGURE 4–9 (Continued) Sea-surface temperatures.

© Jones & Bartlettdistortion Learning, is produced LLC by currents that move warm© Jones so familiar& Bartlett to sailors Learning, and tourists, LLC but the deeper water water poleward along the western side of oceans and below the thermocline, where temperatures are near NOT FOR SALEcold waterOR DISTRIBUTION equatorward along their eastern sides (seeNOT FORfreezing SALE even OR at the DISTRIBUTION equator! Figure 4–9). Because of solar heating during the summer, a sea- Investigations of water temperature with water sonal thermocline appears at a depth of between 40 depth reveal that the oceans in the middle and lower and 100 meters (~132 and 330 feet) in the oceans of latitudes have a layered© Jones thermal & structure Bartlett (FIGURE Learning, 4–10). LLCthe mid-latitudes (FIGURE ©4–11 Jones). The daily & Bartlett thermoclines Learning, LLC A layer of warm water,NOT several FOR hundredSALE OR to a thousandDISTRIBUTION that occur at very shallowNOT water FOR depths SALE (<12 meters;OR DISTRIBUTION meters thick, floats over colder, denser water that fills ~39 feet) are diurnal. Unlike the surface water, where up the rest of the basin. The two water masses are temperature changes with the hour, the day, and the separated from each other by a band of water that season, water below the permanent thermocline main- has© Jones a sharp temperature& Bartlett gradientLearning, (meaning LLC that tem- tains a low,© Jones stable temperature& Bartlett overLearning, time, averaging LLC perature changes rapidly with depth); it is called the <4°C for most of the ocean (see Figure 4–10). thermoclineNOT FOR SALE(see Figure OR 4–10).DISTRIBUTION The thermocline is NOT FOR SALE OR DISTRIBUTION a permanent hydrographic feature of temperate and Salinity tropical oceans, and ranges in water depth between 200 and 1,000 meters (~660 to 3,300 feet). Surpris- The salinity of the ocean’s surface water, although more © Jones & Bartlettingly, in termsLearning, of volume, LLC the most typical water© of Jonescomplicated & Bartlett in detail Learning, than the patternLLC of the sea-surface NOT FOR SALEthe tropics OR DISTRIBUTION is not the warm, thin surface-water layerNOT FORtemperature, SALE ORalso showsDISTRIBUTION a clear latitudinal dependence

104 CHAPTER 4 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES Te mperatu re (° C) © Jones & Bartlett05 Learning,10 15 LLC 20 © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALEThermoclin OR eDISTRIBUTION 0 25 20 10 15 10 1 1 5 5 Thermoclin e 4 2 2 Po© la r Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Deep water Te mperate

ter depth (km ) ter depth (km 3 NOT FOR) ter depth (km SALE3 OR DISTRIBUTION (<4° C) NOT FOR SALE OR DISTRIBUTION Tr op ical Wa Wa Sea bottom 4 4

5 5 © Jones & Bartlett Learning, LLC60° S40° S2 0° S0© Jones ° & Bartlett 20° N4 Learning,0° N LLC NOT FOR SALE OR DISTRIBUTION LatitudeNOT FORVer SALE tical exaggeration OR DISTRIBUTION ~ 1000X (a) TEMPERATURE PROFILES (b) TEMPERATURE DISTRIBUTION (°C) IN CENTRAL PACIFIC OCEAN

FIGURE 4–10 Temperature profiles. (a) These vertical profiles depict variations of temperature with water depth. Note the prominent thermocline that separates cold, deep water from warm surface water. (b) A longitudinal profile of the average temperature distribu- © Jones &tion Bartlett in the Pacific Learning, Ocean using isothermsLLC indicates that the bulk of© all Jonesocean water & isBartlett colder than Learning, 4° Celsius. (Adapted LLC from Reid, J. L., Jr., NOT FORIntermediate SALE OR Waters DISTRIBUTION of the Pacific Ocean. Johns Hopkins Press, 1965.)NOT FOR SALE OR DISTRIBUTION

(FIGURE 4–12a). The highest salinity values occur FIGURE 4–12b shows exactly how ocean salinity between 20 and 30 degrees north and south latitude changes with latitude. Maximum salinity values oc- and decrease toward the© equatorJones and & Bartlettthe poles. SalinityLearning, curLLC in the subtropics and minimum© Jones values & Bartlett near the Learning, LLC

variations are caused byNOT the addition FOR SALE or removal OR of DISTRIBUTION H2O equator and the polar regions.NOT The dashedFOR SALE line in this OR DISTRIBUTION

molecules from seawater. Processes that remove H2O figure is a plot of the latitudinal difference between molecules from seawater include evaporation and the evaporation and precipitation—that is, evaporation

formation of ice. Precipitation (rain, snow, sleet), river (removal of H2O) minus precipitation (addition of runoff,© andJones ice melting & Bartlett add H2 OLearning, molecules, diluting LLC the H2O). To calculate© Jones this value & Bartlett for any latitude, Learning, the total LLC salinityNOT of seawater FOR SALE and reducing OR DISTRIBUTION its density. Because amount of evaporationNOT FOR for SALE one year OR is subtracted DISTRIBUTION from these processes are dependent to a large degree on the total precipitation for that same year. If the result climate, and climate varies with latitude, the salinity of the calculation is a positive value, then evapora- of surface seawater varies directly with latitude. tion has exceeded precipitation, and salinity in this

May June August August 20 20 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC March September 40 NOT FOR SALE OR DISTRIBUTION40 NOT FOR SALE OR DISTRIBUTION

60 60 November Water Depth (m) Water Depth (m)

80© Jones & Bartlett Learning, LLC 80 © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FORJanuary SALE OR DISTRIBUTION

100 100 (a) GROWTH OF SEASONAL THERMOCLINE (b) DECAY OF SEASONAL THERMOCLINE

FIGURE 4–11 Seasonal thermocline. (a) Beginning in March, when there is no ver tical change in the temperature of the upper water column, © Jones &the Bartlettthermocline develops;Learning, it is most LLC pronounced in August. (b) After August,© Jones the thermocline & Bartlett weakens Learning, with the onset LLCof winter and disappears NOT FORby SALE March (see OR part DISTRIBUTION a). (Adapted from Open University Course Team,NOT Seawater: FOR Its Composition, SALE Properties, OR DISTRIBUTION and Behavior. Pergamon Press, 1989.) The Properties of Seawater 105 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES © Jones & Bartlett120° E Learning,150° E 180° LLC 150° W 120° W 90° W © Jones 60° W & 30° Bartlett W 0° Learning, 30° E LLC 60° E 90° E 120° E NOT FOR SALE OR DISTRIBUTION NOT33 FOR SALE OR DISTRIBUTION

Arctic Circle 34 60° N 32

©33 Jones & Bartlett Learning, LLC 35 © Jones & Bartlett Learning, LLC 33 34 NOT FOR SALE OR DISTRIBUTION 36 NOT FOR SALE OR DISTRIBUTION

30° N 37 Tropic of Cancer 35 34 36 32 35 33 32 36 35 33 © Jones0° Equator & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR34 SALE OR DISTRIBUTION34 Tropic of 35 Capricorn 36 37 30° S 35 36 35 35 34 © Jones & Bartlett Learning, LLC 34 © Jones & Bartlett Learning, LLC

NOT FOR SALE OR DISTRIBUTION34 NOT FOR SALE OR DISTRIBUTION 60° S Antarctic Circle

+50 36

( Salinity Salinity

NOT FORDry SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

0 °

°° )

Wet Evaporation – precipitation © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC –50 34 NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Evaporation – precipitaton (cm) Evaporation – precipitaton

40°N30°N20°N10°N0° 10°S20°S30°S40°S 50°S (b) LATITUDINAL VARIATIONS IN SALINITY AND “DRYNESS”

FIGURE 4–12 Salinity© variations. Jones (a) & The Bartlett surface salinity Learning, of the world’s LLC oceans in parts per thousand (‰)© Jones during August & Bartlett shows a regular Learning, LLC pattern that depends NOTon latitude, FOR with SALE maximum OR values DISTRIBUTION in the center of each ocean and minimal valuesNOT at the equatorFOR SALEand polar ORregions. DISTRIBUTION (Adapted from Sverdrup, H. U., et al. The Oceans. Prentice-Hall, 1942.) (b) A comparison of evaporation and precipitation rates accounts for the maximum salinity levels in the subtropics and the minimum salinity levels near the equator and the polar regions. This profile is a global average.

© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC region will be higher than normal. A negative value being highest in the tropics and subtropics. By con- denotesNOT FOR the converse, SALE OR that DISTRIBUTION is, precipitation exceeds trast, rainfallNOT maximaFOR SALE occur ORin the DISTRIBUTION tropics and tem- evaporation, and salinity here is lower than normal. perate latitudes, and minima in the subtropics and The rate of evaporation depends strongly, although high latitudes. Therefore, during the course of a year, not exclusively, on temperature and, thus varies di- there is a net excess of precipitation over evaporation © Jones & Bartlettrectly with Learning, latitude, being LLC very low in the polar and© Jones in the& Bartletttropics and Learning, temperate latitudes,LLC and an excess NOT FOR SALEsubpolar OR regions, DISTRIBUTION rising in the middle latitudes, andNOT FORof evaporation SALE OR over DISTRIBUTION precipitation between 20 and

106 CHAPTER 4 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES 35 degrees latitude, where, not surprisingly, most of (FIGURE 4–13b). Water stratification (layering) is evi- © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC the major land deserts occur. dent between 40°N and 40°S latitudes, where a lens NOT FOR SALENotice OR in FigureDISTRIBUTION 4–12b that the two curves rep- NOTof high-salinityFOR SALE (35‰) OR DISTRIBUTION surface water is separated from resenting evaporation minus precipitation and sea- less saline water below by a sharp halocline. Also, two surface salinity are quite similar in shape. This suggests tongues of water with salinities of <34.74‰ extend that the major control on the surface salinity of the northward from the Antarctic region: one at about a world’s oceans is the© relative Jones effect & Bartlett of evaporation Learning, 1,000-meterLLC (~3,300-feet) depth,© Jones the other & Bartlett along the Learning, LLC and precipitation—inNOT other FOR words, SALE of climate. OR DISTRIBUTION The deep-sea bottom. These tonguesNOT indicate FOR SALE that their OR DISTRIBUTION maximum salinity levels in the subtropical oceans are water originated at the sea surface in the south polar produced by a strong excess of evaporation over pre- seas and are separated from each other by a water mass cipitation. At the equator, evaporation rates are high, that flowed southward out of the North Atlantic Ocean but rainfall is even greater, leading to the lower surface (see Figure 4–13b). What is truly remarkable about © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC salinity in these waters. In the midlatitudes, rainfall this North Atlantic water below a depth of 2 kilometers ratesNOT surpass FOR evaporation SALE OR rates DISTRIBUTION to an even greater (~1.2 miles)NOT is its uniformFOR SALE salinity OR of ~DISTRIBUTION34.9‰. This degree than they do in the tropics, which reduces condition reflects the fact that once water sinks, it is no salinity to less than 34‰. Surface salinity in the polar longer in contact with the atmosphere, where precipita- seas fluctuates as ice forms and melts with the chang- tion and evaporation alter the salinity. Thus, the salinity © Jones &ing Bartlett seasons. TheLearning, water of LLCthe coasts and continental © Jonesof deep & water Bartlett remains Learning, relatively stable LLC (unchanging) NOT FORshelves SALE is ORdiluted DISTRIBUTION by the freshwater of rivers. A case NOTover FOR time, SALE although OR very DISTRIBUTION slow mixing processes, not in point is the Amazon River, which injects more than well understood, do eventually change the salinity of 5 × 1012 cubic meters (~1.8 × 1014 cubic feet) of fresh water masses. water into the western South Atlantic Ocean each year, lowering the salinity there. © Jones & Bartlett Learning, DensityLLC © Jones & Bartlett Learning, LLC As was the case for temperature, sharp salinity gradients characterizeNOT the water FOR column SALE of theOR world’s DISTRIBUTION Density, the amount of massNOT per FOR unit SALE volume OR DISTRIBUTION oceans (FIGURE 4–13a). These gradients are termed halo- (g/cm3), depends on the temperature, salinity, and clines and, like temperature, represent boundary zones pressure of seawater. Because water is essentially between distinct water masses. A north–south longitu- incompressible, pressure affects density only in the dinal© profile Jones of &salinity Bartlett in the Learning, western Atlantic LLC Ocean deepest parts© of Jones the ocean & andBartlett can be Learning, ignored for ourLLC revealsNOT a well-developed FOR SALE OR layering DISTRIBUTION of water masses purposes. It NOTshould, FOR however, SALE be ORnoted DISTRIBUTION that, if water

Inferred water motion 34 36 38 Halocline 0 0 35.5 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC 35.5 NOT FOR SALE OR DISTRIBUTION NOT FOR SALE34.5 OR DISTRIBUTION Halocline 1 2 35.0

4 Sea bottom

3 © Jones & Bartlett Learning,60° LLC S 40° S 20°© S Jones &0° Bartlett 20°Learning, N LLC NOT FOR SALE OR DISTRIBUTION LatitudeNOT FOR SALE OR DISTRIBUTION (a) SALINITY PROFILES (b) SALINITY DISTRIBUTION (‰) IN THE WESTERN ATLANTIC OCEAN

FIGURE 4–13 Salinity profiles. (a) Vertical profiles of salinity show that sea-surface water may be more or less saline than the water below it. Note the prominent haloclines. (b) Isohalines (lines connecting points of equal salinity) in a longitudinal profile of the western © Jones &Atlantic Bartlett Ocean revealLearning, distinct water-mass LLC stratification and a prominent© Jones halocline. & BelowBartlett a 2-kilometer Learning, depth, the LLC water has a remarkably NOT FORuniform SALE salinity, OR ranging DISTRIBUTION between 34.7 and 34.9‰. (Adapted from Tolmazin,NOT FOR D. Elements SALE of Dynamic OR OceanographyDISTRIBUTION. Allen and Unwin, 1985.) The Properties of Seawater 107 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES was absolutely incompressible, sea level would be 50 is warm fresh water. The conversion of temperature © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC meters (~165 feet) higher than it presently is! Water and salinity data to water density can be done simply NOT FOR SALE OR DISTRIBUTION NOT FOR SALEdensity OR controls DISTRIBUTION the vertical structure of the water col- by consulting either tables or graphs (FIGURE 4–14a). umn, with the more dense water underlying the less It is possible to have high-salinity water overlie dense water. Basically, the density of water is increased low-salinity water, provided that the temperature of by dropping its temperature and raising its salinity. the surface water is much higher than the temperature This means that cold,© Jones saline water& Bartlett is more Learning,dense than LLCof the deep water. Thus, warm© Jones water with& Bartlett high salinity Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

3 3 3 3 3 3

3 10

l Freezing a

Temperature (°C) Temperature n temperatures c y

o 1.030 g/cm

s 0 I © Jones & Bartlett Learning, LLC Ice © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION 010203NOT FOR SALE04 OR DISTRIBUTION0

(a) SEAWATER DENSITY

Temperature Salinity Water density © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

Thermocline Halocline Pycnocline

Surface layer 0 ocline layer 1 Pycn © Jones & Bartlett Learning,Deep LLC layer © Jones & Bartlett Learning, LLC NOT FOR SALE2 OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Sinking of cold, 3 dense water Sinking of cold, dense water

Water depth (km) Water 4 Sea bottom 5 © Jones & Bartlett Learning,60° LLC N 30° N0° 30°© S Jones 60° S& Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION Latitude NOT FOR SALE OR DISTRIBUTION (c) DENSITY STRUCTURE OF THE OCEANS

FIGURE 4–14 Density of seawater. (a) This plot shows the variation of seawater density as a function of temperature and salinity. Note that water parcels of different temperatures may have identical densities, provided that salinity counters the temperature effect. (b) Verti- © Jones & Bartlettcal gradients Learning, of both temperature LLC and salinity create pycnoclines© Jonesin the water & column.Bartlett (c) Based Learning, on density, LLCthe oceans can be separated NOT FOR SALEinto a three-tieredOR DISTRIBUTION structure, with the pycnocline layer isolatingNOT the deep FOR layer SALE from the OR surface DISTRIBUTION layer.

108 CHAPTER 4 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES levels can overlie cold water with low salinity—a water- with the frigid polar atmosphere. This cold (<4°C) © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC mass arrangement that is common in the ocean of the polar water sinks to the ocean bottom because of its NOT FOR SALE OR DISTRIBUTION NOT FORlow SALE and middle OR DISTRIBUTION latitudes (see Figure 4–13a), where high density, and flows slowly equatorward, supplying high evaporation rates increase the salt content of sur- the depths of the ocean with water that was once near face water relative to subsurface water. the ocean’s surface. If vertical gradients of water temperature (ther- We can now discuss the nature and distribution of moclines) and salinity© (haloclines) Jones & existBartlett in the Learning,ocean, gasesLLC dissolved in the ocean. ©As Jonesyou will &see, Bartlett gas con- Learning, LLC then it stands to reasonNOT that FORdensity SALE will show OR a DISTRIBUTIONsimi- centrations depend a great dealNOT on the FOR density SALE structure OR DISTRIBUTION lar gradient because it depends directly on variations of the water column. of temperature and salinity. A sharp density gradient with depth is called a pycnocline (FIGURE 4–14b). Den- 4-6 Gases in Seawater sity stratification of the ocean imposes a three-layered © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC structure on the water column: a surface layer, a pyc- NOT FOR SALE OR DISTRIBUTION To understandNOT better FOR the SALE levels andOR distributionDISTRIBUTION of nocline layer, and a deep layer (FIGURE 4–14c). gases in seawater, we need a thorough grasp of certain Surface Layer chemical concepts. The first is saturation value, which This topmost layer, the surface layer, is thin, averag- refers to the amount of gas at equilibrium that can be ing about 100 meters (~330 feet) in thickness, and dissolved by a volume of water at a specific salinity, © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC represents about 2 percent of the ocean’s volume. Being temperature, and pressure. The higher the saturation NOT FORat SALE the surface, OR DISTRIBUTIONit is the least dense water of the water NOTvalue FOR is for SALE a gas, ORthe greater DISTRIBUTION is its solubility, which is column, largely because of its warm temperatures. the property of being dissolved and going into solu- Because it is in contact with the atmosphere, its water tion. The solubility of gases increases with a drop in is affected by weather and climate, which cause diurnal, either water temperature or salinity and a rise in pres- seasonal, and annual fluctuations© Jones & of Bartlettsalinity and Learning, water sureLLC (FIGURE 4–15a). This means© Jones that cold, & Bartlett brackish Learning, LLC temperature. Light penetratesNOT FOR to theSALE bottom OR of DISTRIBUTION this (slightly salty) water can dissolveNOT more FOR gas SALE than canOR DISTRIBUTION zone, allowing plant photosynthesis to occur wher- warm, saline (salty) water at the same pressure. If a ever nutrient levels are adequate. In the polar regions, parcel of water is saturated with a gas, a change of water cooling of the surface water produces dense water that temperature or salinity will cause the quantity of gas sinks. This sinking process prevents the formation of a to be below or above the water’s new saturation value, pycnocline© Jones in the & oceans Bartlett of the Learning, high latitudes. LLC conditions called© Jones undersaturation & Bartlett and Learning, supersatura LLC- NOT FOR SALE OR DISTRIBUTION tion, respectively.NOT FORWater SALEthat is undersaturatedOR DISTRIBUTION can Pycnocline Layer dissolve more gas, whereas water that is supersaturated The boundary zone between the surface-water and can release gas from solution (bubbles may form under deep-water layers is the pycnocline layer, where a the right conditions). sharp density gradient exists. It is not really a distinct At this point, it is necessary to specify the types © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC water mass, but a transition zone where the surface- of units that chemists use to characterize the quan- NOT FORwater SALE layer OR grades DISTRIBUTION into the deep-water layer. (Because NOTtity FOR of dissolved SALE gasesOR DISTRIBUTIONin water. We will use a volume temperature is the dominant control of water density measure expressed as milliliters—that is, a thousandth in the pycnocline, many oceanographers commonly (10-3) of a liter—of gas dissolved in 1 liter of water, refer to this layer as the thermocline.) Water in this expressed as ml gas/l. Those of you who have taken a transition zone amounts© Jones to about & 18Bartlett percent Learning, of the course LLC in chemistry realize that© Jonesthe amount & Bartlett of gas in Learning, LLC ocean’s volume. In theNOT low latitudes,FOR SALE the pycnocline OR DISTRIBUTION a 1-milliliter volume dependsNOT on the FOR temperature SALE and OR DISTRIBUTION corresponds to the permanent thermocline, which is pressure of the system. Therefore, the concentration created by the strong and persistent heating of the of a gas dissolved in 1 liter of water is specified for a water by the tropical sun. In the midlatitudes, the standard temperature of 0°C and a standard pressure pycnocline weakens and coincides with the halocline, of 1 atmosphere (equivalent to the pressure exerted © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC which is produced by the abundant rainfall that di- by the weight of the atmosphere, which is the pressure lutesNOT the salinity FOR ofSALE the water OR in DISTRIBUTION the surface layer (see that we feel NOTat sea level).FOR SALE OR DISTRIBUTION Figure 4–12b). The processes that produce, consume, and regu- Deep Layer late gas concentrations in the ocean are summarized About 80 percent of the total volume of the oceans is in in TABLE 4–8 and depicted in FIGURE 4–15b. Enormous © Jones &the Bartlett deep layer Learning,. The bulk of LLC this deep water originates © Jonesquantities & Bartlett of gases are Learning, exchanged LLCbetween the ocean NOT FORin SALE the high OR latitudes, DISTRIBUTION where it is cooled while in contact NOTand FOR the atmosphereSALE OR near DISTRIBUTION the sea surface (see boxed The Properties of Seawater 109 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES Breaking © Jones & Bartlett12 Learning, LLC © Jones & Bartlett Learning,Diffusion LLC Air wave NOT FOR SALE OR DISTRIBUTION Fresh water NOT FOR SALE OR DISTRIBUTION (ml/l) 2 8 0 Photosynthesis Seawater Respiration 4 Bubbles Decomposition Dissolved O Dissolved © Jones & Bartlett Learning, LLC Pycnocline© Jones layer & Bartlett Learning, LLC 0 1 0 NOT6 FOR 12SALE OR18 DISTRIBUTION 24 NOT FOR SALE OR DISTRIBUTION Temperature (°C) Respiration (a) SOLUBILITY OF OXYGEN 2 © Jones & Bartlett Learning, LLC depth (km) Water © Jones & Bartlett AdvectionLearning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Volcanic emanations 3

Respiration © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLCDecomposition Sea bottom NOT FOR SALE OR DISTRIBUTION NOT FOR4 SALE OR DISTRIBUTION (b) SOURCES AND SINKS OF GASES

FIGURE 4–15 Gases in seawater. (a) The solubility of oxygen decreases as water temperature and salinity rise. (b) Dissolved gases in the oceans are derived from both external and internal sources and organic and inorganic processes. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION feature “The Sea-Surface Microlayer”). Ordinarily, large storms, drive air bubbles downward into the surface seawater is near saturation with respect water, where water pressure dissolves some of the

to the common atmospheric gases (O2, N2, CO2). bubbles before they can ascend back to the surface. However, gases diffuse across the air-sea interface, In fact, this very process—the passage of air bubbles as© theJones temperature & Bartlett and salinity Learning, of the LLC water change through© water—is Jones &used Bartlett to aerate Learning, water in your LLC fish orNOT as organisms FOR SALE produce OR or DISTRIBUTION consume gases, creating aquarium.NOT Oxygen FOR diffuses SALE outOR ofDISTRIBUTION air bubbles into supersaturated or undersaturated conditions. Also, the aquarium water where fish can then use it to breaking waves, particularly those associated with “breathe.”

© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALETABLE OR DISTRIBUTION 4–8 NOT FOR SALE OR DISTRIBUTION SUMMARY OF FACTORS THAT REGULATE THE CONCENTRATION OF GASES IN WATER

Factors Effects Wave and current Increases the exchange of seawater gases with the atmosphere. turbulence © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Difference in gas NOTGases FOR diffuse SALE across OR the air-seaDISTRIBUTION interface from high to low areas of concentrationNOT FOR until chemical SALE equilib OR- DISTRIBUTION concentration rium is attained. Temperature A drop in water temperature increases the solubility of gases. Salinity A rise in salinity decreases the solubility of gases. © PressureJones & BartlettA rise Learning, in pressure increasesLLC the solubility of gases. © Jones & Bartlett Learning, LLC

NOTPhotosynthesis FOR SALE ORIncreases DISTRIBUTION concentration of O2; decreases concentrationNOT of CO FOR2. SALE OR DISTRIBUTION

Respiration Increases concentration of CO2; decreases concentration of O2.

Decomposition Increases concentration of CO2; decreases concentration of O2. - 2- pH Controls the relative concentrations of the various species of CO2 in water (H2CO3, HCO3 , CO 3 ). © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALESource: OR Adapted DISTRIBUTION from Parker, H. S., Exploring the Oceans (Englewood Cliffs,NOT N.J.: Prentice-Hall, FOR SALE 1985). OR DISTRIBUTION

110 CHAPTER 4 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES The primary regulator of gas concentrations in Gases other than oxygen and carbon dioxide are © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC subsurface water is the activity of organisms (see also released and taken up by physical and biological NOT FORTable SALE 4–8). OR When DISTRIBUTION light and nutrient conditions are NOTprocesses. FOR SALE For example, OR DISTRIBUTION the decay of unstable radioac- adequate, plants photosynthesize. This complex bio- tive elements contained in the minerals of deep-sea chemical process of photosynthesis converts water muds produces a variety of gases, including helium

(H2O) and carbon dioxide (CO2) into organic matter (He), radon (Rn), and argon (Ar). Some gases, such as

and liberates oxygen (O©2 )Jones as a product & Bartlett of the reactions. Learning, carbonLLC dioxide and helium, are© Jones spewed &out Bartlett of active Learning, LLC Thus, plants simultaneouslyNOT FORreduce SALE the dissolved OR DISTRIBUTION con- submarine volcanoes on spreadingNOT FOR midocean SALE ridges OR DISTRIBUTION

tent of CO2 and augment the levels of dissolved O2 as (FIGURE 4–16). These gases are then slowly transported they conduct photosynthesis in the upper, sunlit part hundreds, perhaps thousands, of kilometers by deep- of the water column during daylight hours. In contrast, sea currents before mixing dilutes them to such a de- respiration, the chemical breakdown of food in cells gree that they are no longer distinguishable in the © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC for the release of energy, is conducted by both plants water column. Such gases can be used to trace the and animalsNOT FOR in surface SALE water, OR DISTRIBUTIONand by animals at all flow path ofNOT currents FOR near SALE the sea OR bottom, DISTRIBUTION even very

depths of the ocean. This results in the uptake of O2 sluggish ones. Also, ocean basins filled withanoxic

and the release of CO2 as organisms oxidize food for nu- water (water without dissolved oxygen) are not popu- tritional purposes. As you sit reading this passage, you lated by normal communities of plants and animals © Jones &are Bartlett respiring, Learning,“burning” food LLC in the presence of oxygen, © Jonesbecause & theseBartlett organisms Learning, cannot LLC survive without

NOT FORwhich SALE releases OR DISTRIBUTION the energy that your body requires to NOTO 2FOR. However, SALE specialized OR DISTRIBUTION anaerobic bacteria, which live. Consequently, these life-sustaining processes— live without free oxygen, inhabit such waters. They photosynthesis and respiration—have a profound im- use the oxygen atoms that are chemically bonded to 2- pact on the concentrations of dissolved CO2 and O2 sulfate ions (SO4 ) for conducting their metabolic in the oceans, an important topic that we will cover in processes, which yields the toxic gas hydrogen sulfide © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC subsequent chapters on biological oceanography. Last, (H2S) as a reaction byproduct. Although anaerobic dead organic matter andNOT excrement FOR areSALE decomposed OR DISTRIBUTION by conditions rarely develop in theNOT well-mixed, FOR SALE and thus OR DISTRIBUTION microbes, chiefly bacteria. Enzymes that are secreted by well-ventilated, water of the open ocean, they do occur microbes chemically “attack” organic matter and break in some restricted basins where circulation is sluggish it down into simpler chemical compounds by the pro- and the supply of oxygen is limited. For example, cess of© oxidationJones &, aBartlett chemical Learning,reaction that LLCconsumes water trapped© inJones the small & Bartlett basins that Learning, are part of theLLC O2 andNOT produces FOR COSALE2 and ORother DISTRIBUTION gases. continental NOTshelf ofFOR southern SALE California OR DISTRIBUTION commonly

0 Units in parts per million © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC 1 NOT FOR SALE OR DISTRIBUTION 210 NOT FOR SALE OR DISTRIBUTION

2 280 245 315 350 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC 3 210 NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Water depth (km)

4 East Pacific Rise © Jones & Bartlett5 Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 135° E 160° E 175° W 150° W 125° W 100° W Longitude

FIGURE 4–16 Helium-3. A large plume of water enriched in helium-3 extends westward from the East Pacific Rise, tracing the flow of © Jones &water Bartlett at mid-depth Learning, in the Pacific LLC Ocean. Volcanic emissions are clearly© Jones the source & ofBartlett this gas, which Learning, originated deep LLC in the Earth’s mantle. NOT FOR[Adapted SALE from OR Jenkins, DISTRIBUTION W. J., Oceanus 35 (1992): 47–56.] NOT FOR SALE OR DISTRIBUTION The Properties of Seawater 111 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES is anoxic because of sluggish bottom currents and of the ample food supply, and, as they respire, they © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC poor mixing. deplete the O2 content of the water. Also, bacteria NOT FOR SALEIn OR order DISTRIBUTION to firm up our understanding of the NOTgas FORthere SALE decompose OR DISTRIBUTIONthe abundant dead organic matter,

chemistry of the oceans, we will consider in the next which further reduces the dissolved O2. The sharp

two sections the sources, sinks, and distribution of O2 pycnocline indicates that the water column is stable

and CO2—two gases vital for the ocean’s biota. Both and that vertical mixing of water is minimal at these are considered to© be Jones nonconservative & Bartlett substances Learning, in LLCintermediate water depths.© Jones Thus, the & Bartletthigh demand Learning, LLC

seawater because theirNOT concentrations FOR SALE vary OR greatly DISTRIBUTION over for dissolved O2 by animalsNOT and FOR bacteria SALE that are OR feed DISTRIBUTION- short time and distance scales. ing on the dead and living organic matter, combined with a relatively slow rate of water mixing and thus of

Oxygen O2 replenishment, produces the O2-minimum layer with O concentrations of <2 milliliters per liter (see © Jones & Bartlett Learning, LLC 2 © Jones & Bartlett Learning, LLC The vertical distribution of O2 in the ocean of the Figure 4–17a). lowNOT and FOR middle SALE latitudes OR DISTRIBUTIONshows a distinct pattern BelowNOT the pycnocline,FOR SALE water OR is sparselyDISTRIBUTION populated (FIGURE 4–17a). A warm surface-water layer with a because food is scarce. The biological demand for dis-

high content of dissolved O2 is separated from cold, solved O2 is low here, and O2 concentrations rise with relatively well-aerated deep water by a distinct oxygen- depth to between 3 and 5 milliliters per liter. Because © Jones & Bartlettminimum Learning, layer at about LLC 150 to 1,500 meters (~495© to Jonesoxygen & Bartlett production Learning, is restricted LLC to surface water, the

NOT FOR SALE4,950 OR feet) DISTRIBUTION below the sea surface. This vertical oxygenNOT FORdissolved SALE O2 ORfound DISTRIBUTION in this deep layer must have been profile reflects inputs and outputs of gases by a variety derived from shallow depths. Temperature and salinity of processes. Let’s examine them. data (see Figure 4–13b) indicate that deep water in all

There are two principal sources of O2 for the the ocean basins is derived from the polar regions. In oceans—gas diffusion across the air-sea interface the high latitudes, surface water is cooled, which raises © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC and plant photosynthesis. Both of these processes its gas-saturation values. These cold, O2-rich water are limited to theNOT uppermost FOR SALE levels OR of theDISTRIBUTION water masses sink because of theirNOT high FOR densities. SALE They OR flow DISTRIBUTION column and account for the high concentrations of equatorward, ventilating the depths of all the ocean

dissolved O2, typically in excess of 5 milliliters per basins (FIGURE 4–17b). Although this advection pro-

liter, in the surface-water layer. The O2-minimum cess (the horizontal and vertical movement of a fluid) zone© Jones coincides & Bartlett with the Learning,pycnocline layer;LLC this im- is slow, it© occurs Jones at a& rate Bartlett that satisfactorily Learning, meets LLC the pliesNOT a FORconnection SALE between OR DISTRIBUTION the two. Organisms of respirationNOT requirements FOR SALE of the OR scanty DISTRIBUTION populations of all kinds are drawn to the pycnocline layer because deep-sea fauna.

[O2] (ml/l) 6 O2 diffusion O2 diffusion 0 0 © Jones & Bartlett Learning, LLC Surface© Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION layerNOT FOR SALE OR DISTRIBUTION Pycnocline O -rich 1 1 layer 2 O2-minimum layer O2-rich water water

2 2 © Jones & Bartlett Learning, LLC Advection© Jones & Bartlett Learning, LLC

3 NOT FOR SALE3 ORDeep DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Water depth (km) Water depth (km) layer Advection

4 4

(a) VERTICAL O2 PROFILES IN (b) O2-ADVECTION PATTERN IN THE ATLANTIC OCEAN THE ATLANTIC OCEAN FIGURE 4–17 Dissolved oxygen. (a) Vertical profiles of dissolved oxygen reveal a distinct pattern consisting of well-ventilated surface

NOT FOR SALEadvection OR of DISTRIBUTIONcold, dense, O2-rich polar water. NOT FOR SALE OR DISTRIBUTION

112 CHAPTER 4 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR THEDISTRIBUTION OCEAN SCIENCESNOT FOR SALE OR DISTRIBUTION CHEMISTRY Desalination

Fresh water is a precious© Jones commodity & Bartlett that is essential Learning, LLC © Jones & Bartlett Learning, LLC for all living organisms.NOT Its distributionFOR SALE on theOR Earth DISTRIBUTION is NOT FOR SALE OR DISTRIBUTION variable. In arid regions, the amount of fresh water is very limited, making desalination, the production of drinkable water from seawater, very important. Unfor- tunately, desalination requires a great deal of energy, which© Jones means that & Bartlettit is an expensive Learning, process. LLC © Jones & Bartlett Learning, LLC NOTIf seawater FOR SALEconsists OR overwhelmingly DISTRIBUTION of water NOT FOR SALE OR DISTRIBUTION (about 96.5 percent on the average), why is it so expensive to purify it into drinkable fresh water? The answer

is related to the dipole structure of H2O molecules, © Jones & Bartlettwhich results Learning, in tightly bonded LLC clusters that must be © Jones & Bartlett Learning, LLC NOT FOR SALEdisrupted OR for DISTRIBUTION desalination to occur. NOT FOR SALE OR DISTRIBUTION Desalination relies on five general techniques: 1. Distillation. The evaporation of seawater produces water vapor, which is then cooled to form a liquid-water© Jones condensate. & Bartlett Learning, FIGURELLC B4–3 Reverse osmosis. ©At Jonesa desalination & Bartlett plant in Learning, LLC 2. Freezing. As seawater begins to freeze, Cyprus, seawater is forced through a series of membranes in NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION the H2O molecules arrange themselves the blue tubes shown. By the time seawater reaches the last into a crystal structure, leaving behind the tube, it is fresh enough to drink. salt ions in a highly concentrated brine. The pure ice must then be separated from © Jonesthe brine. & Bartlett Learning, LLC expensive, and© mostJones widely & Bartlettemployed Learning,one is distilla -LLC NOT3. Reverse FOR osmosis.SALE Seawater,OR DISTRIBUTION under an applied tion. In Kuwait,NOT Saudi FOR Arabia, SALE Israel, ORGreece, DISTRIBUTION Pakistan, pressure, is forced through a semiperme- Australia, India, and Chile, as well as in the United able membrane. Only the H O molecules 2 States in Texas, southern California, and the Florida are able to pass through the membrane, Keys, fresh water is obtained by distillation. A large which separates them from the salt ions salt water pond is covered with plastic, glass, or even © Jones & Bartlett(FIGURE Learning, B4–3). LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOTcanvas. FOR Solar SALE radiation OR DISTRIBUTIONheats the enclosed volume of 4. Electrodialysis. Electrically charged, semiper- salt water. Evaporation produces water vapor, which meable membranes draw salt ions out of the rises, cools, and condenses on the covering fabric of the seawater solution, leaving behind fresh water. structure (FIGURE B4–4). This condensed water then This technique is most effective for brackish trickles down the underside of the sloping roof, and is (low-salinity)© water. Jones & Bartlett Learning,collected LLC in large receptacles. In© Kuwait, Jones the &heat Bartlett of the Learning, LLC 5. Salt absorption.NOT Chemically FOR SALEactive resins OR orDISTRIBUTION sun combined with waste heat generatedNOT FOR by petroleum- SALE OR DISTRIBUTION charcoals are used to draw off the dissolved fired power plants greatly increases evaporation and the salt ions from seawater, producing fresh production rate of fresh water at little additional cost. water.

© AllJones of these & Bartlett techniques Learning, are currently LLC in use Visit http://science.jbpub.com/oceanlink6e© Jones & Bartlett Learning, LLC somewhereNOT FOR in the SALE world. OR Perhaps DISTRIBUTION the simplest, least for more NOTinformation. FOR SALE OR DISTRIBUTION

© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION The Properties of Seawater 113 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Solar NOT FOR SALE OR DISTRIBUTION energy NOT FORPlastic SALE OR DISTRIBUTION Condensation

FIGURE B4–4 Distillation of seawater. A widely used technique for desalination (taking salt out of seawater) involves the evaporation of seawater from a pool, the condensation of fresh water on a covering fabric, and its collection in a storage vat. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

of 7 is, by definition, a neutral solution consisting of Carbon Dioxide equal parts (10-7) of OH- and H+ (see Figure 4–18). © Jones & Bartlett Learning, LLC © JonesRaising & Bartlett the amount Learning, of H+ to LLC 10-6—remember that NOT FOR SALECarbon OR dioxide DISTRIBUTION (CO ) is a gas that is actively involvedNOT in FOR-7 SALE+ OR DISTRIBUTION 2 10 , one H ion in 10 million of the H2O molecules, photosynthesis and respiration. Plants cannot produce is a much smaller value than 10-6, which is one H+ food and survive in its absence. Animals release CO 2 ion in a million H2O molecules—lowers the pH to as they break down food for energy by the chemical 6, a solution that is no longer neutral but acidic (see process of respiration. Also, CO regulates the acidity -6 © Jones & Bartlett2 Learning, LLCFigure 4–18). The log to© the Jones base 10& Bartlettof 10 is Learning,the LLC of seawater. Let’s examine this latter chemical property -6 NOT FOR SALE OR DISTRIBUTIONexponent -6; thus, the negativeNOT FOR log ofSALE 10 is OR -(- 6)DISTRIBUTION of seawater. or 6. Low concentrations of H+ that impart a higher The degree to which water provides a suitable pH than the neutral level of 7 create a basic solution, habitat for marine biota is determined, in part, by in which the amount of OH- surpasses the amount of the concentration of dissolved hydrogen ions (H+), a H+ (see Figure 4–18). measure© Jones termed & Bartlett the pH of Learning, water. In pure LLC water (water It’s important© Jones that & Bartlettyou understand Learning, the preceding LLC containingNOT FOR nothing SALE but OR H2O DISTRIBUTION molecules) at 25°C, a very discussion.NOT Let’s FOR review SALE what we’ve OR learnedDISTRIBUTION so far about -7 tiny fraction of the H2O molecules, about 10 , or one pH. A neutral solution has a pH of 7, which means that in 10 million (107), spontaneously dissociates (breaks the H+ concentration is 10-7. A basic solution has a pH apart) into a hydroxyl (OH-) and a hydrogen (H+) ion. value that is greater than 7 (remember that this means The free hydrogen ions are what control the acidity of + © Jones & Bartlett Learning, LLC © Joneslow & concentrations Bartlett Learning, of H ) and LLC an acidic solution has water. The formal definition of pH is a pH value that is lower than 7 (high H+ concentra- NOT FOR SALE OR DISTRIBUTION NOT FORtions). SALE So the OR pH DISTRIBUTION scale, to a first approximation, is pH = −log (H+). 10 nothing more than a measure of the content of H+ in At first glance, this formula looks quite difficult the water. Because the H+ ion is so reactive with other to grasp, but it need not be. Remember that the pH of compounds, acid water (water with a pH of less than water is, to a first ©approximation, Jones & Bartlett merely aLearning, measure of LLC7 and thus a relatively high© Jones concentration & Bartlett of H+ ),Learning, is LLC the concentration NOTof the HFOR+ ion. SALE The parentheses OR DISTRIBUTION in the a powerful dissolution agent,NOT ableFOR to SALEweather OR rocks DISTRIBUTION preceding equation can be equated to the concentra- chemically. Also, plants and animals living in the ocean tion of H+, although technically they refer to the chemi- are affected by the content of H+ in the water they in- cal activity of this ion, which is an indirect function habit because many metabolic activities are regulated of© itsJones concentration & Bartlett level. Learning, Now, if we goLLC back to our by the seawater’s© Jones pH. & BartlettThe question Learning, remaining LLC to be example of pure water, measurements indicate that answered is, what exactly determines the amount of NOT-7 FOR SALE OR DISTRIBUTION + NOT FOR SALE OR DISTRIBUTION 10 H2O molecules (one in 10 million) are separated H in the ocean? -7 into their ionic components. If we substitute 10 , the The pH of water is directly linked to the CO2 sys- + concentration of H , into the formula and solve for its tem. When CO2 is added to water, most of it is rapidly

negative log, we get a pH value of 7 (FIGURE 4–18). The converted into carbonic acid (H2CO3) as it bonds with © Jones & Bartlettlog to the Learning, base ten of LLC10-7 is the exponent -7; thus,© Jones water & Bartlettmolecules Learning, (hydration). LLC This acid then rapidly -7 - NOT FOR SALEthe negative OR DISTRIBUTION log of 10 is -(-7) or 7. Water with a pHNOT FORdissociates SALE into OR bicarbonate DISTRIBUTION (HCO3 ) and carbonate

114 CHAPTER 4 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES © Jones & Bartlett Learning, LLC pH [H+] © Jones [OH–] & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION 1 10–1 NOT10 –13FOR SALEHydrochloric OR acid DISTRIBUTION 2 10–2 10–12 Lime juice 3 10–3 10–11 Acetic acid –4 –10 Acidic 4 10 10 Tomato juice Solutions © Jones & Bartlett5 Learning,10–5 10LLC–9 Black coffee © Jones & Bartlett Learning, LLC NOT FOR SALE6 OR 10DISTRIBUTION–6 10–8 Milk NOT FOR SALE OR DISTRIBUTION Neutral 7 10–7 10–7 Pure water 8 10–8 10–6 Seawater 9 10–9 10–5 Borax solution © Jones & Bartlett Learning,10 LLC10–10 10–4 © Jones & Bartlett Learning, LLC –11 –3 NOT FOR SALE ORBasic DISTRIBUTION11 10 10 MilkNOT of magnesia FOR SALE OR DISTRIBUTION Solutions 12 10–12 10–2 Household ammonia 13 10–13 10–1 Lye 14 10–14 10–0 Sodium hydroxide © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FORFIGURE SALE 4–18 OR The DISTRIBUTION pH scale. The concentration of H+ in water is specifiedNOT FOR by pH. SALEA pH of 7 ORdenotes DISTRIBUTION that the H+ concentration is 10 –7, or one part in 10 million. Solutions with low pH values (high concentrations of H+) are acidic. Solutions with high pH values (low concentrations of H+) are basic.

2- + (CO3 ) ions, which yields H ions, making the water essentially a stable solution with a pH that rarely ranges acidic. The specifics ©of theJones chemical & Bartlett reaction are Learning, belowLLC 7.5 or above 8.5. This condition© Jones is &described Bartlett as Learning, LLC buffered, meaning that the mixture of compounds and NOT FOR SALE– OR+ DISTRIBUTION NOT FOR SALE OR DISTRIBUTION CO2 + H2O → H2CO3 → HCO3 + H the nature of the reactions are such that the pH of the 2− + solution is hardly affected despite an input or output → CO3 + 2H . of H+. Let me explain. Increasing the level of H+, which This formula summarizes each step of the reaction should lower the pH (make the water more acidic), © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC when CO2 is dissolved in water. Notice that the free ions causes the reactions (see FIGURE 4–19c) to shift to the left; of H+NOT lower theFOR pH SALEof the water. OR Therefore,DISTRIBUTION we conclude as a consequence,NOT HFOR+ is removed SALE asOR it complexes DISTRIBUTION with - that the addition of dissolved CO2 tends to lower the HCO3 to form H2CO3, buffering the solution (keeping pH of water. At equilibrium, the proportion of each of the pH near its original value, FIGURE 4–19d). Conversely, - 2- + the carbon compounds (H2CO3, HCO3 , and CO3 ) reducing the level of H (making the solution more ba- depends on the pH of the water. At the pH of normal sic by raising the pH) reverses the reactions. There is a © Jones & Bartlett Learning, LLC © Jones & Bartlett+ Learning, LLC seawater (7.8 to 8.2), about 88.9 percent of the carbon rapid release of H into solution, as H2CO3 dissociates NOT FOR SALE OR DISTRIBUTION- NOT FOR -SALE OR DISTRIBUTION+ compounds occur as HCO3 (FIGURE 4–19a). A change in to HCO3 and releases H (see Figure 4–19d). The end the amount of any of these carbon substances disrupts result is that the pH is stable despite changes in the rela-

the balance of the CO2 system, and reactions occur to tive amounts of the carbon species in the CO2 system; reestablish equilibrium. For example, the removal of the system is basically self-regulating or buffered.

CO2 from water by plant© photosynthesisJones & Bartlett (FIGURE Learning, 4–19b) LLCWith this background, we© Jonescan now & explain Bartlett the Learning, LLC

or by solar heating, whichNOT reduces FOR itsSALE saturation OR DISTRIBUTIONvalue dissolution of CaCO3 shells inNOT cold, FOR deep SALE water butOR DISTRIBUTION and causes bubbles to form, initiates a series of chemical not in warm, shallow water, and the ocean’s carbonate responses that shift the reactions specified in the formula compensation depth (CCD). Recall that the pH level

to the left. This results in the production of CO2. Respira- of water is inversely proportional to the concentration tion, in contrast, releases CO into the water (see Figure of dissolved CO . This means that the higher the CO © Jones & Bartlett2 Learning, LLC © Jones2 & Bartlett Learning, LLC2 4–19b). This process causes the reactions in the formula content of the water is, the lower the pH (or, if you NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION to move to the right, which increases the concentrations prefer, the greater the content of H+). Cold water has

of the other chemical species at the expense of CO2. a higher gas-saturation value than does warm water Organisms are sensitive to pH, quite a few extremely because of its low temperature (see Figure 4–15a). Also, so. Fortunately, the many rapid chemical reactions with- the saturation value of gases in water increases with in-

© Jones &in theBartlett CO2 system Learning, (Figure 4–19)LLC prevent large fluctua- © Jonescreasing & pressure Bartlett and Learning,therefore water LLC depth. This means NOT FORtions SALE in the OR pH DISTRIBUTIONlevels of the world’s oceans. Seawater is NOTsimply FOR that SALE the cold, OR denseDISTRIBUTION water that fills the ocean The Properties of Seawater 115 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES Normal pH range © Jones & Bartlett Learning, LLC © Jonesof seawater & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION100 NOT FOR SALE OR DISTRIBUTION

2 © Jones & BartlettC O Learning, LLC © Jones & Bartlett Learning, LLC NOT60 FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 3 HCO

2 – r centage % centage r 40 3

Pe CO © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR20 DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

0 04 56 7 8 9101 11 2 © Jones & Bartlett Learning, LLC © JonespH & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION Fresh waterNOT FORNormal SALE seawater OR DISTRIBUTION (a) DISTRIBUTION OF C ARBON SPECIES IN WA TE R

Ai r

NOT FOR SALE OR DISTRIBUTION6C O 2 + 6H 2 O + energy C6 HNOT 12O 6 + FOR 6O 2 SALE OR DISTRIBUTION (dissol ve d (water) (glucose) (oxygen) carbon di ox ide)

FIGURE 4–19 Carbon species and the CO2 system in the oceans. (a) Carbon dissolved in water occurs in the form of carbon dioxide (CO2), - 2- bicarbonate (HCO3 ), and carbonate (CO3 ). At equilibrium, the relative proportion of these carbon species depends on the pH of the water. 2- - Basic solutions are dominated by CO3 ; acidic solutions, by CO2. At the pH of normal seawater, HCO3 makes up about 80 percent of the © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC carbon species. (b) The CO2 system is also involved in biological processes, notably photosynthesis, which removes dissolved CO2 from the

water, and respiration,NOT which liberatesFOR SALECO2 into theOR water. DISTRIBUTION Thus, the CO2-carbonate cycle influences andNOT is influenced FOR bySALE both chemical OR DISTRIBUTIONand life processes. (c) Carbon dioxide diffuses from the atmosphere into the oceans, where it complexes with water to form weak carbonic acid + 2- (H2CO3) and hydrogen (H ) ions. Some of the bicarbonate ions dissociate into carbonate (CO3 ) ions, which may complex with calcium 2+ (Ca ) to form calcium carbonate (CaCO3). (d) The pH of seawater (7.8) is buffered by the CO2-carbonate cycle. If the pH rises, H2CO3 dissociates and yields H+, reversing the trend. If the pH drops, H+ complexes with HCO -, causing the pH to rise again. © Jones & Bartlett Learning, LLC © Jones3 & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

depths contains high levels of dissolved gases like O2 CaCO3 shells that sink to the deep-sea floor. Shallow

(see Figure 4–17b) and CO2. More importantly, respira- water, on the other hand, is relatively warm and has a

tion in the deep layer of the ocean releases CO2 into the lower concentration of CO2 at saturation than does the

© Jones & Bartlettwater. The Learning, high CO2 concentration LLC of the deep water© Jonesdeep, & coldBartlett water. Learning,This raises the LLC water’s pH level, which 2- NOT FOR SALElowers OR the DISTRIBUTIONpH, making the water acidic and dissolvingNOT FORreleases SALE carbonate OR DISTRIBUTION ions (CO3 ) that chemically bond

116 CHAPTER 4 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES (carbon di ox ide) © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning,CO 2LLC gas NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTIONAi r

Water (water) (carbonic acid) (bicarbonate) (hydr ogen) – + CO 2 + H 2O H 2CO 3 HCO 3 + H ©(dissol Jones ve d & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOTcarbon FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION di ox ide)

2– 2+ CaCO 3 CO 3 + Ca (dissol ve d (carbonate) (calcium) calcium + © Jones & Bartlett Learning, LLCcarbonate) H + © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION (hydr o gen) NOT FOR SALE OR DISTRIBUTION dissolution © Jones & Bartlett Learning, LLC ecipitation pr © Jones & Bartlett Learning,Water LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Sediment

(c) THE© Jones CO 2 SY STEM& Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

Seawater H CO HCO – + H + pH drop s too basic: 2 3 3 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Seawater HCO – + H + H CO pH rises NOT FOR SALEtoo acidic: OR DISTRIBUTION3 2 3 NOT FOR SALE OR DISTRIBUTION (d) C ARBONATE BUFFER

FIGURE 4–19 (Continued) Carbon species and the CO2 system in the oceans.

NOT FORCaCO SALE3. Therefore, OR DISTRIBUTION carbonate oozes tend to accumulate NOTon FOR land, whenceSALE itOR returns DISTRIBUTION to the ocean as river runoff. in relatively shallow water of the deep sea above the Dwelling in this watery wilderness is an incredible CCD because water below the CCD is cold and acidic variety of life-forms: delicate, lacy plants; spindly legged

and dissolves shells composed of CaCO3. shrimp; swift, powerful sharks and tuna; microscopic, © Jones & Bartlett Learning,floating LLC algae; and solidly anchored© Jones oysters. & BartlettWe marvel Learning, LLC at the ability of these creatures to live in the ocean, but 4-7 The Ocean NOTas a PhysicalFOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION many of us fail to realize that we, as terrestrial inhabit- Chemical System ants, live in an ocean as well. We dwell on land beneath an ocean of air that is an order of magnitude (differs by For teaching purposes, in a previous chapter we treat- a factor of 10) deeper than the deepest seas and that, ed the oceans separately, as if each were a self-contained © Jones & Bartlett Learning, LLC because of its© weight, Jones exerts & Bartlett considerable Learning, pressure LLCon basin of water, separated cleanly from the others. But NOT FOR SALE OR DISTRIBUTION us. For thoseNOT of you FOR who are SALE technically OR DISTRIBUTIONinclined, atmo- such is not the case. Water does flow across geographic spheric pressure at sea level is about 1,013 millibars, or boundaries, both near the sea surface and at depth. H O molecules in seawater are not even confined to 6 2 2 ~1,013 × 10 dynes/cm , the oceans, but are passed into the atmosphere by © Jones &evaporation; Bartlett windsLearning, and air LLC masses then transport this © Jones & Bartlett Learning,or LLC NOT FORvapor, SALE some OR of DISTRIBUTIONit across great distances. Eventually, the NOT FOR SALE ~OR10 metric DISTRIBUTION tons/m2. The Properties of Seawater 117 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES This transparent envelope of fluid—the gaseous of water, both as gas and as droplets (clouds), that far © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC atmosphere—is in direct contact with the surface of exceeds the volume of water stored in rivers. Finally, a NOT FOR SALEall the OR land DISTRIBUTION and oceans and is a crucial element of theNOT FORminuscule SALE quantity OR DISTRIBUTION of water is stored in the biosphere, planet’s water cycle. The atmosphere and hydrosphere, in the cells and tissues of plants and animals. which enclose the Earth’s crust, interact through a vast Although the values cited in Table 4–9 are accu- network of processes. Powered by the energy of the rate for the present, they do not reflect the quantities sun, water is exchanged© Jones among & Bartlett the oceans, Learning, the at- LLCthat existed in some of these© Jones reservoirs & inBartlett the geologic Learning, LLC mosphere, and theNOT landmasses FOR SALE through OR evaporation, DISTRIBUTION past. During glacial ages,NOT for example, FOR SALE seawater OR that DISTRIBUTION precipitation, river flow, groundwater (subterranean evaporated from the oceans fell as snow on land and water) percolation, ocean circulation, and a host of was converted into ice, forming enormous ice caps related and intertwined processes. Some of these and mountain glaciers. So, at that time, the volume operate quickly; others, quite slowly. However, be- of water stored in the ice reservoir was much greater © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC fore we examine the workings of this immense global than it is at present. Obviously, water does not reside waterNOT cycle, FOR we SALE need toOR consider DISTRIBUTION the distribution of indefinitelyNOT in FOR any one SALE state ORor reservoir; DISTRIBUTION rather, it is water on the Earth. continually changing back and forth, from gas to liquid to solid, and shifting from one reservoir to another. At Reservoirs of Water present, global warming is causing a worldwide melt- © Jones & Bartlett Learning, LLC © Jonesing &of Bartlettmountain Learning,glaciers and iceLLC sheets. Let’s examine some specific processes that control the flux of water NOT FOR SALEWater OR covers DISTRIBUTION more than 60 percent of the Earth’s surNOT- FOR SALE OR DISTRIBUTION on the Earth. face in the Northern Hemisphere and over 80 percent in the Southern Hemisphere. Not surprisingly, most of the water on the Earth—in fact, 97.25 percent of it The Global Water Cycle by volume—is found© Jones in the oceans & Bartlett (TABLE 4–9Learning,). It may LLC © Jones & Bartlett Learning, LLC astonish some of youNOT to discoverFOR SALE that rivers OR andDISTRIBUTION lakes, The exchange of water amongNOT FOR the ocean, SALE the OR land, DISTRIBUTION which are so familiar and so indispensable to the activi- and the atmosphere is termed the hydrologic cycle ties of humans, are of little significance in the Earth’s (FIGURE 4–20). The sun’s heat evaporates surface water overall water inventory. In fact, groundwater —the from the ocean and the land. (Just leave a glass of water water below the ground surface that saturates the void in sunlight for a few weeks and see what happens!) space© Jones in soil, & sediment, Bartlett and Learning, rock—exceeds LLC the com- Evaporated© Jones water enters & Bartlett the atmosphere Learning, as vapor LLC and binedNOT volume FOR SALE of water OR in lakes, DISTRIBUTION rivers, and the atmo- most of thisNOT returns FOR directly SALE to OR the seaDISTRIBUTION as precipitation. sphere by one order of magnitude (see Table 4–9). Air currents transport the remainder of this water va- Also, the atmosphere contains a significant quantity por over land, where it condenses and falls as rain or snow (FIGURE 4–21). This precipitation flows as runoff © Jones & Bartlett Learning, LLC © Jonesinto & rivers, Bartlett collects Learning, temporarily LLC in lakes, ponds, and wetlands, infiltrates the ground (groundwater) only NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION TABLE 4–9 to emerge later in rivers and lakes, or remains in solid EARTH’S WATER RESERVOIRS form as snow or ice. With time, all of this water finds its way back to the oceans, either as river outflow, Water melting glaciers and icebergs, groundwater seepage, Volume Total Water Reservoir ©(10 Jones6 km 3&) Bartlett(%) Learning, LLCor evaporation and precipitation,© Jones thereby & Bartlett closing Learning,the LLC hydrologic cycle. In effect, the same molecules of water Oceans NOT1370 FOR SALE OR97.25 DISTRIBUTION NOT FOR SALE OR DISTRIBUTION are being continually recycled from reservoir to reser- Ice masses 29 2.05 voir, the rates of flux and the quantity exchanged and Groundwater 9.5 0.68 stored depending on climate. Lakes 0.125 0.01 © Jones & Bartlett Learning, LLC Over© the Jones oceans, & evaporationBartlett Learning, exceeds precipita LLC - Atmosphere 0.013 0.001 tion, and the balance of water is maintained by river NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Rivers 0.0017 0.0001 inflow. On all the land combined, in contrast, precipi- Biosphere 0.0006 0.00004 tation far exceeds evaporation, and the excess water Total 1408.64 99.99 travels to the ocean by river and groundwater flow. Estimates of these various fluxes are summarized in TABLE 4–10 © Jones & BartlettSource: Adapted Learning, from Berner, LLC E. K., and Berner, R. A. The Global Water © Jones & Bartlett. These Learning, calculations LLC assume that the total NOT FOR SALECycle OR (Englewood DISTRIBUTION Cliffs, N.J.: Prentice-Hall, 1987). NOT FORvolume SALE of water OR DISTRIBUTIONon the planet is fixed on a global

118 CHAPTER 4 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Wind

Sun

Evaporation Evaporation Rain© Jones and snow & Bartlett Learning, LLC Transpiration © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

River © JonesIce & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

Ocean

FIGURE 4–20 Hydrologic cycle. The hydrologic cycle incorporates the major pathways for the transport and exchange of water among the various reservoirs of the earth. Basically, water circulates and changes phases (solid, liquid, gas) continually. In the gaseous state, water is supplied to the atmosphere by the evaporation of surface liquid water, much of it from the oceans, and by transpiration, the passage of water © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC vapor through the surface of leaves. Condensation then causes the atmosphere to release this water as a liquid (rain) and as a solid (snow). These liquid and solid formsNOT of water FOR eventually SALE return OR to the DISTRIBUTION oceans by river runoff and groundwater flowage,NOT closing FOR the hydrologic SALE cycle.OR DISTRIBUTION

© Jones &FIGURE Bartlett 4–21 RecyclingLearning, of water. LLC Water evaporated from the ocean© Jones condenses & asBartlett clouds that Learning, drop rain onto LLCthese mountains. River NOT FORrunoff SALE and groundwaterOR DISTRIBUTION flow discharge this water into the ocean, NOTclosing FORthe hydrologic SALE cycle. OR DISTRIBUTION The Properties of Seawater 119 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES scale (a perfectly reasonable supposition on a short © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC TABLE 4–10 time scale), so that precipitation and evaporation are NOT FOR SALEWATER OR DISTRIBUTION FLUXES NOT FORbalanced SALE for ORthe planet DISTRIBUTION as a whole. Water Flux The Ocean as a Biogeochemical System Process (km3/yr) Evaporation from© land Jones & Bartlett Learning,72,900 LLCNow that we have examined© Jones the chemistry & Bartlett of seawa Learning,- LLC Precipitation on landNOT FOR SALE OR110,300 DISTRIBUTIONter and the physical natureNOT of theFOR water SALE column, OR weDISTRIBUTION Precipitation on oceans 385,700 can combine them into a generalized biogeochemical system (FIGURE 4–22). Rivers supply the ocean with Evaporation from oceans 423,100 most of its dissolved ions, these being derived mainly Total precipitation on Earth 496,000 © Jones & Bartlett Learning, LLC from the© chemical Jones weathering& Bartlett of Learning, rocks on land. LLC The Total evaporation on Earth 496,000 driving force underlying the ocean’s biogeochemical NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION system is the sun. Solar radiation absorbed by ocean Source: Adapted from Berner, E. K., and Berner, R. A. The Global Water water raises its temperature and stratifies the water Cycle (Englewood Cliffs, N.J.: Prentice-Hall, 1987). column. A thermocline, separating the warm surface water from the cold deep water, forms. In addition, © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

e U THERMOCLINE c

P o

W m Animals Death

E p L o Detritus L s i I t N i o organic © Jones & Bartlett Learning, LLC G n© Jones & Bartlett Learning, LLC inorganic Death NOT FOR SALE OR DISTRIBUTION NOTBacteria FOR SALE OR DISTRIBUTION

Cold water

NOT FOR SALE OR DISTRIBUTION Sedimentation NOT FOR SALE OR DISTRIBUTION

Animals

Bacteria Sediment © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION FIGURE 4–22 Biochemical recycling of matter. Inorganic nutrients are converted into food by plant photosynthesis in the surface- water layer of the ocean. Animals eat plants and one another. When plants and animals die, their organic matter settles through the water column, where it is converted into simple nutrients by bacterial decomposition. This nutrient-charged water is then returned slowly to the surface by upwelling currents, completing the biochemical recycling of key nutrients. [Adapted from Repeta, D. J., et © Jones & Bartlettal. Oceanus Learning, 35 (1992): 38–46.] LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

120 CHAPTER 4 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTIONTHE OCEAN SCIENCESNOT FOR SALE OR DISTRIBUTION CHEMISTRY The Sea-Surface Microlayer

The seawater surface ©is a Jonesunique interface & Bartlett where chemicals Learning, anLLC answer to this question is not© aJones simple matter. & Bartlett The Learning, LLC are exchanged betweenNOT the FORocean andSALE the atmosphere.OR DISTRIBUTION definition of the surface microlayerNOT is FOR quite looseSALE and OR DISTRIBUTION This actual surface, called the surface microlayer, is depends on the research interests of the chemists, physi- incredibly thin—a few hundred micrometers (~0.0039 cists, and biologists who study ocean phenomena at the inch)—and, although regarded as being important for the air-sea interface. Most oceanographers would probably chemistry of the upper ocean, has not been examined agree that the surface microlayer extends from 3 Ang- extensively© Jones because & Bartlett of the difficulties Learning, of sampling LLC such stroms (10 -10 meters),© Jones the diameter& Bartlett of a water Learning, molecule, LLC a tinyNOT vertical FOR section SALE of the OR water DISTRIBUTION column. However, it to a depth of NOTabout 3FOR millimeters SALE (~ 0.1OR inch) DISTRIBUTION or so, the represents a critical link between the atmosphere and lower limit of nonturbulent (smooth or laminar) water the ocean (FIGURE B4–5). The surface microlayer receives flow in the absence of a wind. Using a log scale to plot and transmits energy, gases, and solids and collects mat- a vertical profile of the ocean lets us expand the sur- © Jones & Bartlettter transported Learning, by winds fromLLC above and by water from © Jonesface microlayer & Bartlett so that Learning, it occupies about LLC half the water NOT FOR SALEbelow. Ferren OR DISTRIBUTION MacIntyre (1974) aptly states, “Through the NOTdepth FOR on SALEthat diagram OR (DISTRIBUTIONFIGURE B4–6). Some chemists ocean’s 360 million square kilometers of surface pass 70 and physicists believe that this 3-millimeter-thick (~0.1- percent of the solar energy that the earth absorbs, most inch) surface layer may provide as many research prob- of its supply of freshwater, a large fraction of the annual lems as has the remainder of the ocean! Biologists refer production of carbon dioxide and oxygen, a huge tonnage to the organisms that inhabit the surface microlayer as of particulate matter© and Jones unmeasured & Bartlett volumes ofLearning, man- theLLC neuston and that thin habitat© Jones as the &neuston Bartlett Learning, LLC made pollutants.” Clearly,NOT an FORunderstanding SALE of OR the chemiDISTRIBUTION- layer (see Figure B4–6). NOT FOR SALE OR DISTRIBUTION cal and physical processes that occur across the surface Three processes transport matter to the ocean’s microlayer of the ocean is essential for an understanding surface from below: molecular diffusion, convective of processes of global proportion. motion, and rising air bubbles. Diffusion is a slow process © WhatJones exactly & Bartlett is meant byLearning, the ocean’s LLCsurface? In and comes about© Jones by the random & Bartlett motion Learning, of molecules. LLC other words, how thick is this surface? Actually, providing Convection refers to the vertical circulation of water that NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION results in the transfer of heat and both dissolved and

ATMOSPHERE particulate matter. The most significant process in the Weathering Wind Erosion Forms: Gases surface microlayer by far is, however, the ascent and Liquids bursting of bubbles. Bubbles created by waves and wind Solids © Jones & Bartlett Learning, LLC © Jonesrise through & Bartlett seawater Learning, because of their LLC buoyancy and Evaporation Dry deposition adsorb or scavenge inorganic and organic matter in both NOT FOR SALE OR DISTRIBUTIONBubble bursting Wet deposition NOT FOR SALE OR DISTRIBUTION Wind spray Gas diffusion dissolved and solid states. When the bubble bursts, a portion of the scavenged material is ejected into the LAND SEA-SURFACE air, while the remainder collects in the surface micro- MASS MICROLAYER layer. Material also is added to the sea surface from the Biological Photochemical © Jones & Bartlett Learning,atmosphere LLC either as “wet” precipitation© Jones (rainfall & Bartlett and Learning, LLC NOTDiffusion FOR SALEWaves OR DISTRIBUTIONsnowfall) or as “dry” depositionNOT (particle FOR settlement SALE OR DISTRIBUTION Convection Dissolution Bubbles Settling and gas diffusion). The result of this atmospheric and oceanic flux of material is the enrichment of both dis- River OCEAN solved and particulate matter in the surface microlayer. Weathering Forms: Dissolved ©Erosion Jones & Bartlett Learning,Particulate LLC The concentrated© Jones materials & representBartlett a surfaceLearning, coating LLC NOT FOR SALE OR DISTRIBUTION that can reduceNOT significantly FOR SALE the transfer OR DISTRIBUTION of gases and FIGURE B4–5 Box model of the sea-surface microlayer. This water vapor across the air-sea interface, an effect that simple model shows how the sea-surface microlayer connects influences the chemistry of the lowermost atmosphere the atmosphere with the ocean. (Adapted from Liss, P. S. Chemi- and the uppermost ocean and, quite possibly, climate cal Oceanography. Academic Press, 1975.) in the long run. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION The Properties of Seawater 121 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC–10 NOT FOR SALE OR DISTRIBUTION10 NOT FOR SALE OR DISTRIBUTION Wet surfactants 10–8 Angstroms Sea-surface microlayer © Jones10–6 & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Bubble NOT FOR SALE OR DISTRIBUTIONbursting MicrometersNOT FOR SALE OR DISTRIBUTION Laminar 10–4 Gas diffusion Wind drag NEUSTON 10–2 Turbulent Millimeters © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Depth (meters) NOT FOR SALE OR DISTRIBUTION1 NOT FOR SALE OR DISTRIBUTION

SEASONAL THERMOCLINE Meters 102 PERMANENT THERMOCLINE DEEP-SEA TRENCHES © Jones & Bartlett Learning, LLC104 © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTIONKilometers

FIGURE B4–6 Profile of the ocean. This cross section of ocean depth is plotted on a logarithmic scale that expands the sea-surface microlayer,© Jones which & actually Bartlett extends Learning, no more than LLC3 millimeters below the sea surface,© relativeJones to &the Bartlett remainder Learning, LLC of the water column.NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

The processes that occur within the surface micro- organics that collect in the surface coating and suspends © layerJones can be & divided Bartlett into biological Learning, and photochemical LLC its eggs from© Jones a foam “raft.” & Bartlett Insects thatLearning, abound on LLC land NOTeffects FOR. Sampling SALE indicates OR DISTRIBUTION that bacteria and plankton are uncommonNOT FORin the ocean.SALE However, OR DISTRIBUTION five species of are more numerous in the surface microlayer than they sea striders, Halobates (FIGURE B4–7), live on top of the are in the water immediately below. These organisms surface microlayer, floating because air is trapped in their consume and produce a large variety of organic and in- body hair. Apparently, they feed on small organisms that © Jones & Bartlettorganic Learning, substances and, LLC presumably, influence the chem© -Jonesthey & encounter Bartlett in Learning, the surface film. LLC istry of this surface film of water. Evidence suggests that , Some organisms inhabit the neuston layer with NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION when microorganisms living in the surface microlayer their bodies protruding into the air above the water sur- wiggle their tiny flagella (whiplike appendages), the tiny face. Species with such habits, such as the Portuguese currents they induce can increase the rate of evapora- man-of-war (FIGURE B4–8), are termed pleuston. The tion by as much as a factor of 3. Field experiments have Portuguese man-of-war is a jellyfish or cnidarian and is demonstrated that© Jones microorganisms & Bartlett are scavenged Learning, by LLCactually a community of individual© Jones members & Bartlett that have Learning, LLC rising air bubblesNOT and are FOR ejected SALE into the OR air DISTRIBUTION when the evolved specialized functionsNOT that have FOR become SALE the variOR- DISTRIBUTION bubble bursts. Ultraviolet radiation is not attenuated in ous organs of the individual jellyfish (the community). the surface microlayer, and, in theory, this should lead to Using its long polyps, they can prey on fish just below photochemical reactions, such as the oxidation of organic the neuston layer. Incredibly, they move about using © compounds.Jones & BartlettFor example, Learning, it has been LLC suggested that the power© ofJones the wind & byBartlett extending Learning, an asymmetrical LLC photochemical reactions, as well as microbial processes, sail above the water surface. NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION are responsible for the production of much of the carbon Some marine chemists believe that human pollut- monoxide (CO) in the surface microlayer. ants may be enriched in the surface microlayer, and Besides bacteria and plankton, the neuston includes these are rapidly dispersed far from their point of macroscopic organisms. The snail Janthina prolongata is origin. For example, in the past, DDT, a toxic chlo- © Jones & Bartlettsuch a Learning,member, and apparentlyLLC it feeds directly on the© Jonesrinated & Bartlett hydrocarbon, Learning, was used LLC extensively in North NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

122 CHAPTER 4 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

FIGURE B4–7 The sea strider Halobates. This is a sketch of © Jones & oneBartlett of the few Learning, marine species LLC of insects that strides atop the © Jones & Bartlett Learning, LLC NOT FOR SALEsea-surface OR microlayer. DISTRIBUTION [Adapted from David, P. M., Endeavor NOT FORFIGURE SALE B4–8 ORPortuguese DISTRIBUTION Man-of-War. 24 (1965): 95–100.]

© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC America as a pesticideNOT to FORenhance SALE crop yield. OR DISTRIBUTIONSome transported DDT to the high latitudesNOT FORof the SouthernSALE OR DISTRIBUTION fraction of the DDT sprayed by planes on croplands Hemisphere. It accomplished this because it is a long- remained airborne, and winds transported this load distance migrant that feeds in the North Atlantic and eastward, and it rained down in the North Atlan- breeds on the Antarctic continent. By this mechanism, tic Ocean. Scientists surmise that much of the DDT DDT was dispersed rapidly across the globe, so that likely© Jones remained & inBartlett the surface Learning, microlayer LLC and be- even the ostensibly© Jones isolated & Bartlett Antarctic Learning, fauna (birds LLC cameNOT concentrated FOR SALE in neuston OR DISTRIBUTION organisms. Wilson’s and seals) becameNOT contaminated FOR SALE with OR the DISTRIBUTION exceedingly petrel, allegedly the most abundant bird in the world, toxic pollutant.

© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION sunlight is used by plants to convert carbon dioxide plant tissue by photosynthesis. Some of these mate- and nutrients into organic compounds (food) by pho- rials collect on the sea bottom as oozes, where they tosynthesis. Small marine animals that graze on the become buried and lithified into rock, and by the multiplying plants in turn© Jones serve as & food Bartlett for even Learning, larger process LLC of plate subduction, are© Jones deformed & andBartlett raised Learning, LLC animals. This results inNOT the transferFOR SALE of energy OR (radia DISTRIBUTION- to form a mountain belt (seeNOT Figure FOR 4–6). SALE As these OR DISTRIBUTION tion from the sun) and matter (nutrients from rocks) rocks are squeezed and uplifted by the tremendous through biological systems. When marine organisms forces of the colliding plates, they undergo chemical die, they sink below the permanent thermocline, tak- weathering and mechanical erosion until the chemi- ing with© Jones them nutrients& Bartlett (phosphorus Learning, and LLC nitrogen cals are released© Jones once more & Bartlett and transported Learning, by rivers LLC compounds) that are so crucial to plant photosyn- to the ocean. The result is a continuous biochemical thesis.NOT Bacteria FOR decompose SALE OR this DISTRIBUTION dead organic matter, recycling ofNOT elements FOR between SALE living OR DISTRIBUTIONand nonliving freeing these substances and producing nutrient-rich matter and between surface and subsurface water (see water. The vertical mixing of ocean water then slowly Figure 4–22). Much of the remainder of this book is transports this water and its dissolved load of chemi- devoted to examining the different physical, chemi- © Jones &cals Bartlett upward, Learning,reinfusing the LLC sunlit surface layer with © Jonescal, geologic, & Bartlett and biological Learning, pathways LLC involved in this NOT FORnutrients SALE that,OR onceDISTRIBUTION again, are incorporated into living NOTmajestic FOR planetarySALE OR cycle. DISTRIBUTION The Properties of Seawater 123 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

Study© Jones &Guide Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Key Concepts NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

1. The water molecule H2O has a dipole structure 5. The density of seawater depends largely on wa- (Figures 4–3a and c), which produces hydrogen ter temperature and salinity. Water tempera- © Jonesbonding & andBartlett allows Learning, water molecules LLC to collect ture© Jones is regulated & Bartlett by solar Learning, heating and LLC varies NOT intoFOR snug SALE clusters OR (Figures DISTRIBUTION 4–3d and e). This directlyNOT FOR with latitudeSALE OR(Figure DISTRIBUTION 4–9). Salinity dipole structure explains many of the curious depends on the relative effects of evaporation properties of water, including its elevated melt- and rainfall, and like temperature, varies with ing and boiling temperatures (Figure 4–3b), high latitude (Figure 4–12). Sharp vertical gradients power (Figure 4–4), of temperature are called thermoclines (Figures © Jones & Bartlettheat Learning, capacity, unusual LLC solvent © Jones & Bartlett Learning, LLC and the fact that ice, the solid form of water, is 4–10 and 4–11), of salinity are called haloclines NOT FOR SALE ORless DISTRIBUTIONdense than liquid water (Figure 4–5). NOT FOR SALE(Figure OR 4–13), DISTRIBUTION and of density are called pycno 2. The quantity of solutes in seawater, its salinity, clines (Figure 4–14b). is expressed as parts per thousand (‰). Aver- 6. Sources of gases in seawater include diffusion age seawater has a salinity of 35‰, meaning from the atmosphere and biological processes that a sample© Jones of seawater & Bartlett weighing Learning, 1,000 LLC (Figure 4–15b and© JonesTable 4–8). & Bartlett Plant photo Learning, LLC grams containsNOT 35 FOR grams SALE of dissolved OR DISTRIBUTION salt, col- synthesis uses up NOTCO2 and FOR releases SALE O 2OR; plant DISTRIBUTION lectively referred to as the major constituents and animal respiration consumes O2 and re-

of seawater (Table 4–1). Other solutes in the leases CO2. The production of O2 is limited to ocean include nutrients (such as compounds surface water where gas can diffuse across the of N, P, and Si) (Table 4–2), gases (such as O air-sea interface and where plants can photo- © Jones & Bartlett Learning, LLC 2 © Jones & Bartlett Learning, LLC and CO2) (Table 4–3), trace elements (such as synthesize. The sinking and advection (horizontal NOT metals)FOR SALE (Table OR 4–4), DISTRIBUTION and organic compounds transport)NOT FOR of cold, SALE dense, OR well-oxygenated DISTRIBUTION polar

(such as fats, proteins, and carbohydrates). water supply O2 to the deep levels of the ocean, 3. Salinity can be measured simply by determining ventilating the deepest parts of the ocean basins the amount of chloride (Cl-) in the seawater sam- (Figure 4–17). © Jones & Bartlettple. Learning, This is possible LLC because the relative amounts© Jones &7. Bartlett The hydrologic Learning, cycle (Figure LLC 5–20) describes the NOT FOR SALE ORof all DISTRIBUTION the major elements are fixed, regardlessNOT FOR SALEexchange OR of DISTRIBUTION water in gaseous, liquid, and solid of the total salt content of the seawater—a fact states among the various water reservoirs. Water expressed as the principle of constant proportion. is evaporated from the ocean’s surface, falls as Today, salinity is routinely determined by such precipitation on land, and returns to the oceans indirect techniques as electrical conductivity. as river runoff and groundwater flow, thereby 4. The salt content© Jones of the & ocean Bartlett is derived Learning, from LLC completing the hydrologic© Jones cycle. & Bartlett Learning, LLC the chemicalNOT breakdown FOR SALE of rocks OR DISTRIBUTION on land 8. Matter is recycled NOTthroughout FOR the SALE oceans OR (Fig DISTRIBUTION- (Table 4–6) and from volcanic outpourings ure 4–22). Through photosynthesis, plants

along the crests of spreading ocean ridges. The convert inorganic CO2 and nutrients into food. major elements dissolved in seawater have a long When consumed, this matter and energy are © Jonesresidence & Bartlett time in the Learning, ocean, meaning LLC that they passed© Jones on to &animals. Bartlett When Learning, marine organisms LLC NOT remainFOR SALE dissolved OR in seawaterDISTRIBUTION for between tens of die,NOT they FOR sink, SALE and their OR dead DISTRIBUTION tissues are de- millions and hundreds of millions of years before composed by bacteria, a process that releases they are removed from the system (Table 4–7). simple inorganic nutrients. The upwelling of Because mixing rates are on the order of tens to this nutrient-rich water recharges the surface thousands of years, elements with long residence water with vital elements that are once again © Jones & Bartletttimes, Learning, such as Na LLC+ and Cl-, are distributed in© a Jones & Bartlettconverted Learning, into food by LLC plants, initiating a new NOT FOR SALE ORfixed DISTRIBUTION ratio to one another throughout the oceans.NOT FOR SALEbiochemical OR DISTRIBUTION cycle. 124 CHAPTER 4 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES Keywords © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FORacidic SALE solution OR DISTRIBUTIONdeep layer isotherm residence time adsorption density ion respiration anaerobic dipole molecules salinity anion evaporation nonconservative ions solubility anoxic © Jonesgas & Bartlett Learning,nutrient LLC solute© Jones & Bartlett Learning, LLC atoms NOT FORgroundwater SALE OR DISTRIBUTIONoxidation solventNOT FOR SALE OR DISTRIBUTION basic solution halocline parts per thousand (ppt) steady state bicarbonate heat capacity pH surface layer buffered solution hydration photosynthesis thermocline carbonic© Jones acid & Bartletthydrogen Learning, bond LLC principle of constant© Jones & Bartlettvaporization Learning, LLC cation hydrologic cycle proportion water stratification NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION conservative ions insolation pycnocline

Questions

© Jones &Review Bartlett of Learning,Basic Concepts LLC © JonesCritical-Thinking & Bartlett Learning, Essays LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 1. What are some physical properties of water? 1. Why is the amount of dissolved Na+ in seawater How does one explain these singular physical constant over time, whereas the content of dis-

properties of water? solved CO2 is not? 2. Why does water attain its maximum density 2. Explain why the quantity of nutrients in ocean at 3.98°C, rather© Jones than at its& Bartlettfreezing point Learning, of LLC water often varies inversely© Jones with the & Bartlettmeasured Learning, LLC

0°C? What doesNOT salinity FOR do to SALE the freezing OR DISTRIBUTIONpoint amount of dissolved ONOT2 in the FOR water. SALE OR DISTRIBUTION of water? 3. Can the density of an ice cube vary? Explain 3. What are the major dissolved constituents your reasoning. (Hint: Think about kinetic of seawater? Why do they occur in fixed ra- energy.) 4. © tios,Jones despite & Bartlett variations Learning, in the salinity LLC of ocean Infer how© Jones the relative & Bartlett content ofLearning, dissolved CO LLC2 NOTwater? FOR SALE OR DISTRIBUTION in theNOT water FOR of a SALEtidal pool OR will DISTRIBUTION vary over a 4. Describe the important processes that change 24-hour period. Will variations in the level of

the salinity of seawater without altering the ratio dissolved CO2 affect the pH of this tidal pool of its dissolved salts. water? If so, how? If not, why not? 5. Why is sea-surface temperature strongly cor- 5. Would you expect the salinity of the oceans to © Jones & Bartlettrelated Learning, to latitude? LLC © Jones change& Bartlett during Learning, a geologic periodLLC when many NOT FOR SALE 6. What OR is DISTRIBUTION residence time for an element in sea- NOT FORcontinents SALE OR are DISTRIBUTIONcolliding and major mountain water, and what does it reveal about the element? belts are being raised worldwide? If so, how? If 7. List and discuss the mechanisms for the input not, why not? (Hint: Think about the control and output of elements in ocean water. Which that mountains exert on the content of dissolved of these input processes is the dominant sup- chemicals discharged into the ocean by rivers.) © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC plier of salt to the ocean? 6. What are some interconnections among global 8. What are thermoclines,NOT FOR haloclines, SALE and OR pycno DISTRIBUTION- plate tectonics, the hydrologicNOT FOR cycle, SALE seawater OR DISTRIBUTION clines? What is the relationship, if any, among salinity, and climate? the three? 7. What would happen to the hydrologic cycle if 9. How does the deep layer of the ocean get supplied water could not exist in the gaseous phase on © withJones dissolved & Bartlett oxygen, Learning, with dissolved LLC carbon the Earth’s© Jones surface? & Bartlett What would Learning, the implica LLC- NOTdioxide? FOR SALE OR DISTRIBUTION tions NOTbe for FORthe landmasses? SALE OR For DISTRIBUTION the oceans? 10. What exactly is pH? Explain how photosyn 8. If global warming occurs in the next century, thesis and respiration affect seawater pH. what will be the consequences, if any, of these 11. What is the hydrologic cycle, and in what ways elevated air temperatures for the salinity of the will global warming affect it? ocean? What is likely to happen in a quali- © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC 12. How are essential nutrients recycled in the ocean? tative sense to the volumes of water in the NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION The Properties of Seawater 125 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES various reservoirs listed in Table 4–9 in the in the deep water of the world’s oceans (see © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC event that the Earth does undergo warming Figure 4–17)? Explain. NOT FOR SALE ORin the DISTRIBUTION future? NOT FOR SALE OR DISTRIBUTION 9. Examine Figure 4–22. a. What is the role of the hydrologic cycle Tools for Learning (Figure 4–20) in biochemical recycling? Tools for Learning is an on-line review area located at this Explain.© Jones & Bartlett Learning, LLCbook’s web site OceanLink© ( http://science.jbpub.com/Jones & Bartlett Learning, LLC b. What isNOT the role FOR of theSALE sedimentary OR DISTRIBUTION cycle oceanlink6e). The review areaNOT provides FOR a SALE variety of OR activi DISTRIBUTION- (Figure 4–6) in biochemical recycling? ties designed to help you study for your class. You will Explain. find chapter outlines, review questions, hints for some of 10. If global warming significantly raises the sea- the book’s math questions (identified by the math icon), surface temperature of the polar oceans, what © Jones & Bartlett Learning, LLC web research© Jones tips for & selected Bartlett Critical-Thinking Learning, LLC Essay will likely happen to dissolved oxygen levels questions, key term reviews, and figure-labeling exercises. NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

126 CHAPTER 4 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALEA segment OR of DISTRIBUTION a bedrock shoreline encrusted with salt fragments.NOT FOR SALE OR DISTRIBUTION The Properties of Seawater 127 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. 2ND PAGES