The Properties of Seawater - Jones & Bartlett Learning

Water is just not water. It is a

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

© Jones & Bartlett Learning, LLC vital substance, the earth’s NOT FOR SALE OR DISTRIBUTION blood, something of rich and infinite variety. ~ L. Watson, The Water Planet, 1988







The Properties of Seawater © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION


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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, LL and dynamic.” (H.C. Berg, Random Walks in Biology, 1983.) NOT FOR SALE OR DISTRIBUT 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 basis & of Bartlett this chapter. Here, we LLC will examine the chemical and physical&nature of seawater and LLC lay Jones Learning, © Jones Bartlett Learning, the fNOT oundation later discussions of ocean circulation and marine life. TheFOR concluding of the chapFORforSALE OR DISTRIBUTION NOT SALEsection OR DISTRIBUTION ter 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


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

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One of the most obvious properties of seawater

Electron

© Jones & Bartlett Learning, LLC shells © Jones & Bartlett is its saltyLearning, taste. If youLLC believe that its taste is due to NOT FOR SALE OR DISTRIBUTION NOT FOR SALE ORsalt, DISTRIBUTION dissolved you are correct, and this is what makes the water of the oceans different from the water of lakes and rivers. Seawater is made up mainly of l iquid water (about 96.5 percent by weight) in which chloride Jones & Bartlett (Cl) and sodium©(Na) are the dominantLearning, dissolved LLC chemicals. The common tableSALE salt youOR useDISTRIBUTION to flavor NOT FOR your food is composed of precisely the same elements. Before continuing our discussion about the chemistry of water, we must, however, become familiar with a few basic chemical and physical concepts. So let’s begin.

© Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION 4-1 Basic Chemical Notions

Nucleus

Nucleus

© Jones & Bartlett Learning, LL NOT FOR SALE OR DISTRIBUT proton (+ charge) neutron (0 charge) (a) ATOM

© Jones & Bartlett Learning, LLC NOT FOR SALE OR Oxygen DISTRIBUTION Hydrogen

All matter is composed of “building blocks” termed atoms. An atom is the smallest unit of a substance that © Jones & Bartlett LLCproperties. For example,©aJones & Bartlett Learning, LLC retains allLearning, of its chemical NOT FOR SALE NOT FOR SALE OR DISTRIBUTION singleOR atomDISTRIBUTION of hydrogen possesses all of the chemical Shell has a maximum Outer shell has a characteristics of a large collection of hydrogen atoms. 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 the properties of aLearning, hydrogen LLC © Jones & Bartlett © Jones & Bartlett Learning, LL atom. Atoms that are chemically bonded to one another Hydrogen NOT FOR SALE OR DISTRIBUT NOT FOR SALE OR DISTRIBUTION comprise a molecule. Or, if you prefer, a molecule is a 0 neutrons 1 neutron 2 neutrons chemical substance that can be separated into distinct 1 2 3 H H H atoms. Sodium chloride (NaCl) is a molecule of salt that can be separated into a positively charged atom + © Jones & Bartlett Learning, © Jones & Bartlett Learning, LLC ) and a negatively charged atom ofLLC (Cl-). (Na NOT SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION TheFOR internal structure of any atom consists of 8 neutrons 9 neutrons 10 neutrons elementary particles that possess mass and electric 16 17 18 O O O 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 all of its mass: protons with a positive electric charge © Jones & Bartlett Learning, LLC © Jones &depicts Bartlett Learning, LLC atom a nucleus of protons and neutrons, surrounded by and neutrons with no electrical charge (FIGURE 4–1a). NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION shells of orbiting electrons. (b) A depiction of electrons within Surrounding the nucleus are collections of orbiting the shells of hydrogen (one electron) and oxygen (eight electrons) electrons that have little mass and carry a negative atoms. (c) The isotopes of an element have a variable number of electrical charge. The electron orbits are not randomly neutrons. Hydrogen isotopes have zero, one, or two neutrons; distributed around the nucleus but are confined to oxygen isotopes have eight, nine, or ten neutrons. discrete levels termed electron shells. AllLearning, elements LLC © Jones & Bartlett © Jones & Bartlett Learning, LL (except for one type of hydrogen that OR does DISTRIBUTION not have NOT FOR SALE OR DISTRIBUT NOT FOR SALE neutrons) contain protons, neutrons, and electrons, hand, contains eight protons in its nucleus, balanced and differ from one another because of the number electrically by eight orbiting electrons. So hydrogen and structural arrangement of these fundamental atoms consist of a single proton and a single e lectron, subatomic particles. A stable atom of an element is © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC and oxygen atoms of eight protons and eight electrons. electrically neutral, indicating that the positive charges NOT FOR SALE OR DISTRIBUTION NOTareFOR SALE DISTRIBUTION If electrons either addedOR or removed from any from the protons are balanced by the negative charges single atom, the atom is no longer electrically balfrom the electrons. anced. Atoms with more electrons than protons have Let’s be specific. Hydrogen (FIGURE 4–1b) possesses a net negative charge. Atoms with more protons than one proton in its nucleus; the positive charge from electrons have aLearning, net positiveLLC charge. An atom with its single proton is neutralized by the negative charge © Jones & Bartlett Learning, LLC © Jones & Bartlett eitherSALE a positive a negative charge is called an ion. from its orbiting electron. Oxygen, on the other NOT FOR SALE ORone DISTRIBUTION NOT FOR ORorDISTRIBUTION

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For example, when NaCl dissolves in water, it separates

Although an ice cube appears inert to the naked eye,

& Bartlett Learning, LLC © Jones into & Bartlett Learning, LLCcharge of an ion is the © Jones + the ions Na and Cl-. The it is not inert on an atomic scale. Its molecules are NOT FOR OR DISTRIBUTION NOT FORsingle SALE OR DISTRIBUTION most important reason for its ability to bond vibratingSALE back and forth 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 © Jones Bartlett LLC temperature of ice, the©back-and-forth Jones & Bartlett of neutrons in its nucleus can vary.& Because the nLearning, eutron melting motions Learning, LL carries no electrical charge but has mass, OR variations of the molecules are so vigorous that they SALE exceed the NOT FOR OR DISTRIBUT NOT FOR SALE 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 cryselement 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 FOR SALE ORunlike DISTRIBUTION either zero, one, or two neutrons (FIGURE 4–1c). Oxygen free to moveNOT relative to one another, 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 neumore energetically. Some of these molecules contain so trons and the Learning, most abundant oxygen isotope has eight. © Jones much kinetic energyLearning, that they escape © Jones & Bartlett LLC & Bartlett LLCfrom the liquid surface become gas (FIGURE 4–2c); this process NOT FOR SALE OR DISTRIBUTION NOT FORand SALE ORaDISTRIBUTION is called evaporation. At 100°C, the boiling tempera4-2 Basic Physical Notions ture 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,collisions, LLC © Jones & Bartlett Learning, LL physical concept of heat, the property that one meaand are the least ordered of the three states NOT NOTand FOR SALE DISTRIBUTION sures with a thermometer that resultsOR from the of matter because of their very highFOR kineticSALE energy.OR DISTRIBUT physical vibrations of atoms and molecules. These The kinetic theory of heat has important implicaphysical 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 of its and Learning, molecules. LLC gases. Imagine thermometer, whichLearning, is nothing more © Jones & atoms Bartlett © aJones & Bartlett LLC Let’ s consider a specific example. A block of ice than a narrow glass tube filled with mercury. If we wish NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 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 NOT FOR SALE OR DISTRIBUTION Molecular structure

Ice

Water

Gas



Polymer

© Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION (a) SOLID WATER

(b) LIQUID WATER

© Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION (c) 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. Polymers are bits ofLearning, crystalline structure its melting (c) Gaseous water (gas) is made up of © Jones & Bartlett LLCthat can exist in liquid water©near Jones & temperature. Bartlett Learning, LLC moving molecules. NOT FORindependently SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

The Properties of Seawater


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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 LLC s scale. But what exactly the waterLearning, off the thermometer’ oped. In fact, H2O is the only substance that can coexist NOT FOR SALE NOT FOR SALE OR DISTRIBUTION does the rise of mercury in the tube represent in a naturally 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 © Jones &thermometer Bartlett Learning, © Jones & Bartlett Learning, LL water’s temperature. When the is placed LLC tremendous solvent power. Heat capacity is defined in the liquid, water molecules strike the these as the quantity of heat required to raise the temperaNOT FOR SALE OR DISTRIBUT NOT FOR SALE ORtube; 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 NOT FOR SALE OR DISTRIBUTION FORdegree SALEthan ORone DISTRIBUTION than they were before the addition of kinetic energy capacityNOT to a greater 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, Temperature controls another fundamental propthe& capability liquid water LLC to dissolve material, its © Jones & Bartlett Learning, LLC © Jones Bartlettof Learning, solvent power, is unsurpassed by any other s ubstance. erty ofOR matter called density—the amount of mass NOT FOR SALE DISTRIBUTION NOT FOR SALE OR DISTRIBUTION In fact, chemists refer to water as the “universal s olvent,” contained in a unit volume, expressed as grams (mass) meaning that virtually anything can be dissolved to per cubic centimeter (volume), that is, g/cm3. The more some extent in liquid water. mass that is contained in a cubic centimeter, the more Water possesses other unusual properties as well, dense is the material. The amount of heat contained in © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LL but the case for this substance’s chemical uniqueness a substance determines how vigorously the molecules NOT DISTRIBUT NOT FOR SALE OR should be clear. To account for FOR water’sSALE singularOR propin that substance vibrate and collide with oneDISTRIBUTION another. erties, we must examine the physical structure of the The harder they vibrate, the farther apart they tend to water molecule, H2O. The molecule’s asymmetrical be, which controls directly the amount of mass that shape is as important as the chemical identities of the is contained in a unit volume. This means that 10°C two elements H and O. two hydrogen atoms,LLC rather water is denser than 15°CLearning, water and that warm air is © Jones & Bartlett LLC © Jones & The Bartlett Learning, than being attached symmetrically to either side of less dense than cold air at the same pressure. NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 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 states (FIGURE 4–3c). This molecular architecture reand of temperature and density, we can examine the sembles a mouse’s “head” with hydrogen “ears.” The chemical and physical properties of water in general, © Jones & Bartlett Learning, LLC Let’s start by inspecting © Jones & Bartlett Learning, LLCelectrons, and this hydrogen and oxygen atoms share and seawater in particular. NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION covalent bond creates the water molecule H2O. Each the common molecule on the Earth that we refer to hydrogen atom within the molecule possesses a single simply as water. positive charge; the oxygen atom, a double negative charge. As such, the H2O molecule is electrically neu4-3 The Water Molecule tral theBartlett positive and © Jones & Bartlett Learning, LLC because of the balance © between Jones & Learning, LL negative charges. However, the structural asymmetry Most people knowNOT that the chemical formula for water NOT FOR SALE OR DISTRIBUT FOR SALE OR DISTRIBUTION of the molecule imposes a slight electrical imbalance is H2O. This formula means that water consists of two because the positive hydrogen atoms are bonded to one atoms of hydrogen (H) that are chemically bonded to end of the oxygen atom and the e lectrons a ssociated one atom of oxygen (O) (FIGURE 4–3a). However, despite with that atom are concentrated on the other side. its simple chemical composition, water is a complex © Joneswith & Bartlett Learning, LLC © Jones Bartlett Learning, LLC This gives rise to a & dipole (two-pole) structure (see substance truly remarkable physical properties. NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Figure 4–3c). Thus, there is a residual positive charge For example, the melting and boiling temperatures at the hydrogen end of the molecule and a residual of water are much higher than expected when comnegative charge at the oxygen end, despite the overall pared with chemically related hydrogen compounds electrical n eutrality of the water molecule. Conse(FIGURE 4–3b). This is fortunate; otherwise, water would quently, liquid water is not merely be able toLearning, exist only asLLC a gas at the temperatures that © Jones & Bartlett © Jones & Bartlett Learning, LLCa collection of freely moving molecules. Rather, its dipole structure causes prevail at the Earth’s surface. Consequently, the oceans

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© Jones & Bartlett Learning, LLC Measured values NOT FOR SALE ORx DISTRIBUTION Expected values

© Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION Temperature (°C)

105°

Hydrogen

50

S Se Te H

H2O

0

Boiling © Jones & Bartlett Learning, LLC temperatures NOT FOR SALE OR DISTRIBUTION –50

–100

Oxygen

x x

H2S

0

Sulfur Selenium Tellurium Hydrogen

© Jones & Bartlett Learning, LL H2Te NOT FOR SALE OR DISTRIBUT

H2Se Melting temperatures

50

100

150

Molecular weight (moles) © Jones & Bartlett

© Jones & Bartlett Learning, LLC Learning, LLC (a) FOR H2O MOLECULE NOT SALE OR DISTRIBUTION FOR SALE (b) MELTING AND BOILINGNOT TEMPERATURES OF WATEROR DISTRIBUTION

© Jones & Bartlett 105° NOT FOR SALE OR DISTRIBUTION

Oxygen – © Jones & Bartlett LLC Free HLearning, 2O A cluster of Cumulative molecules H2O molecules negative NOT FOR SALE OR DISTRIBUTION with hydrogen bonds charge (c) DIPOLE STRUCTURE

100


(d) CLUSTERS OF WATER

H2O molecules per cluster

Hydrogen

Cumulative positive charge Hydrogen + Learning, LLC

50

0

0

© Jones & Bartlett Learning, LL NOT FOR SALE 50 100OR DISTRIBUT Temperature (°C)

(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 (H2O) molecule. ©observed Jones(o)&melting Bartlett Learning, LLC Jones & Bartlett LLC (b) The and boiling temperatures of water are much higher than © theory (x) indicates. (AdaptedLearning, from Horne, R. A. FOR DISTRIBUTION NOT OR MarineNOT Chemistry: The SALE Structure ofOR Water and the Chemistry of the Hydrosphere. John Wiley & Sons,FOR 1969). SALE (c) The two smallDISTRIBUTION 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 H2O molecules with hydrogen bonds is contrasted here with free H2O molecules. (e) The size of the clusters decreases with increasing temperature.



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 and the can Learning, LL a nearby water molecule. This electrostatic bonding, © Jones & Bartlett Learning,broken LLC before the solid can melt © Jones & liquid Bartlett vaporize. This is also the reason for water’ s high heat called hydrogen bonding, produces irregular chains NOT FOR SALE OR DISTRIBUT NOT FOR SALE OR DISTRIBUTION capacity. When heat is added to water, only a fraction and clusters of H2O molecules (FIGURE 4–3d). The size of water-molecule clusters decreases with increasing temof this energy is actually used to increase the vibraperature (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 & the Bartlett Learning, © Jones & Bartlett Learning, LLC molecules into hold© theJones atoms of molecule together, itLLC is directly break hydrogen bonds that link the H2O NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION irregular clusters. Thus, as water is heated, its temperaresponsible for many of water’s extraordinary physical ture rises slowly relative to the amount of energy used. properties. Let’s examine how this comes about. Conversely, when cooled, water releases more heat The higher-than-expected melting and boiling than expected from the decrease in its temperature. temperatures of water (see Figure 4–3b) depend directly on the dipole structure The&unusually heat capacity of water prevents © Jones & Bartlett Learning, LLC of the H2O molecule. © Jones Bartletthigh Learning, LLC More energy is required than expected to vaporize extreme variations in the temperature of the oceans NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION



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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 SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION those of land located far from the ocean or large lakes. solvent by preventing the chemical recombination of

During the summer, large bodies of water absorb solar Na+ and Cl- to form the solid halite. The density of water is yet another unusual propheat, helping keep air temperatures cool. During the erty of this familiar substance. Ice floats on water! All winter, large lakes and the ocean radiate great quanti©toJones & Bartlett Learning, © Jones Learning, LL other solids sink in their own liquids.& It’sBartlett hard to imagties of stored heat the atmosphere as their water LLC ine a solid bar of steel floating a vat of molten steel. cools, warming the adjacent NOTinFOR SALE OR DISTRIBUT NOT FORshoreline. SALE OR DISTRIBUTION Once again, water behaves in a peculiar way. Why is The high solvent power of liquid water likewise this so? depends on the dipole structure of its molecule. 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 crysNOT FOR SALE OR DISTRIBUTION NOT SALE ORofDISTRIBUTION negatively charged atom (Cl ) called an anion. When tal forms. The FOR loose assortment molecules in the these two ions come into contact, they are attracted to liquid is reconstructed into a rigid solid. Because the molecules in the solid vibrate less than do the molecules each other because of their opposing charges and can in the liquid, they are more tightly packed and denser be held together by ionic bonds to form halite (rock in the solid thanLearning, in the liquid LLC state. Therefore, solids, salt or common table salt). When halite crystals are put © Jones & Bartlett Learning, LLC © Jones & Bartlett 4–4), the negatively charged endNOT of FOR because of their density, sink in their own liqin water NOT FOR SALE OR(FIGURE DISTRIBUTION SALE ORhigher DISTRIBUTION 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 frameoff chloride ions (Cl-). Dissolution (the noun form of work (FIGURE 4–5a), whereas liquid water molecules are packed into snug clusters by the hydrogen bonds the verb to dissolve) continues until either the entire © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LL between molecules (see Figure 4–3d). Also, the angle crystal of halite is gone or the volume of water can no FOR SALE DISTRIBUT NOTmore FORions SALE DISTRIBUTION of separation between theNOT two hydrogen atoms,OR which longer accommodate of saltOR because it is is 105 degrees in liquid and gaseous water, expands to saturated, meaning there is physically no more “room” 109.5 degrees in ice. This makes ice about 8 percent for the sodium and chloride in the water. (By way of less dense than water. The H2O molecules in ice are an analogy, think about what happens when you keep ordered © into a porous six-sided structure) adding spoonful after spoonful of sugarLLC to your cup of © Jones & Bartlett Learning, Jones & hexagon Bartlett(aLearning, LLC by the hydrogen bonds between oppositely charged coffee.) In solution, the sodium and chloride ions are NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION ends of neighboring molecules (Figure 4–5a). When surrounded by water molecules (see Figure 4–4). This


© Jones & Bartlett Learning, LLC Hydration H2O NOT FOR SALE OR DISTRIBUTION sheath

H2O Cl–

Hydrated chloride ion Jones &

Small water cluster

H2O

© Bartlett Learning, LLC H2O NOT FOR SALE OR DISTRIBUTION – Na+ Cl

Cl–

Na+

Na+

H2O © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION Cl– H2O

Cl– Na+

Cl–

H2O

Na+

Cl– Na+

H2O H2O

© Jones & Bartlett Learning, LL NOT FOR SALE OR DISTRIBUT H2O

Cl– Na+

Cl–

Na+

Cl– Na+

Cl–

© Jones H&2OBartlett Learning, LLC Na+SALE OR DISTRIBUTION NOT FOR H2O

Hydrated sodium ion

Halite crystal

FIGURE 4–4 Halite (rockLLC salt). The dipole structure of the H accounts & forBartlett its unsurpassed properties as a solvent. Na + and Cl - ions © Jones & Bartlett Learning, ©2OJones Learning, LLC are dislodged from the halite crystal by, respectively, the negatively positively charged of the water dipole. NOT FOR SALE OR DISTRIBUTION NOTand FOR SALE ORends DISTRIBUTION

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Hydrogen

© Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION Maximum density (3.98°C) 1.000 Denstiy (g/cm3)

© Jones & Bartlett Learning,Covalent LLC bond Oxygen NOT FOR SALE OR DISTRIBUTION

0.998 0.996 0.994

Liquid water

© Jones & Bartlett Learning, LLC Ice 0.9174 NOT FOR SALE OR DISTRIBUTION


0.9172 0.9170 0

3.98 5

10

15

Temperature (°C) © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC (a) HEXAGONAL CRYSTAL STRUCTURE OF ICE (b) DENSITY OF WATER NOT FOR SALE OR DISTRIBUTION NOT 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.



The dissolving agent, the liquid water, is the solvent ice is warmed to 0°C, it begins to melt as thermal and the dissolved substances, the salt ions, are the vibrations of the molecules cause the crystalline strucsolute. Seawater also contains minor to trace amounts ture to break apart. Because of hydrogen bonds, the ofLLC dissolved metals, nutrients,©gases, and organic com- Learning, LL liquid become more Learning, closely freed H2O molecules in©the Jones & Bartlett Jones & Bartlett pounds of seemingly infinite NOT variety.FOR SALE OR DISTRIBUT packed together than NOT they were in the solid,OR resulting FOR SALE DISTRIBUTION Before examining the chemistry of seawater in an increase of density (more mass per unit volume). s olutions, we need to determine the amount of Water does not, however, reach its maximum density material that is dissolved in seawater so that we can until it is warmed to 3.98°C (FIGURE 4–5b) because compare samples taken from different parts of an loose aggregates of molecules that resemble the open © Jones & Bartlett Learning, LLC Jones & from Bartlett Learning, LLC ocean or, for©that matter, different oceans. We crystalline structure of ice (see Figure 4–2b), termed NOT FOR OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION can taste seawater samples and say qualitatively that polymers, persistSALE in water cooler than that critical this sample tastes “saltier” than this other one. But temperature. Above 3.98°C, the density of water this is a rather subjective technique, and a scientist decreases with increasing temperature, as expected. needs to know exactly and precisely how salty a parcel Below 3.98°C, however, the density of water decreases of water is. Oceanographers specify the concentraas temperature decreases until it freezes into ice. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC tion of a solute in seawater in units called parts per What we have learned so far about seawater is that NOT FORit SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION thousand, represented by either the abbreviation consists dominantly of H2O, a chemical substance ppt or, as preferred by marine scientists, the symbol that can occur in a solid, liquid, and gaseous state at ‰. Although oceanographers also express salinity the temperatures and pressures that exist at the Earth’s as a dimensionless unit in terms of PSS78—Practical surface. Although we find water everywhere on the use ppt.&Average or Learning, LL © Jones Bartlett Learning,Salinity LLC Scale 1978—we will © Jones Bartlett planet, its unusual chemical and& physical properties “normal” seawater has a salinity of about should not be taken forNOT granted; it isSALE these very properNOT FOR 35‰. SALEThis OR DISTRIBUT FOR OR DISTRIBUTION means that the dissolved salt occurs in a concentraties that have enabled life to appear and evolve through tion of 35 parts per thousand (ppt). That is, the salt geologic history. We can now proceed to examine seacomprises 3.5 percent (divide 35 by 1,000, and conwater’s other chemical ingredients. vert it to a percentage by multiplying it by 100) of © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC the sample, the rest (96.5 percent or 965 parts per TheNOT Solutes of Seawater FOR SALE OR DISTRIBUTION SALE OR DISTRIBUTION thousand) b NOT eing HFOR 2O molecules. (Notice that 965 + 35 = 1,000.) This signifies that a volume of seawater Chemical analyses of samples from all over the world weighing 1,000 grams (or 1 kilogram) with a salinity show that seawater consists of a small quantity of salt of 35‰ contains 35 grams of solute. Obviously, a dissolved in water. The salt occurs as charged particles, 100-gram sample of Learning, seawater withLLC a salinity of 35‰ cations and anions, that are dispersed among the mol© Jones & Bartlett Learning, LLC © Jones & Bartlett contains 3.5 grams dissolved salts. of liquid water. Seawater is a chemical solution. NOT NOT FORecules SALE OR DISTRIBUTION FOR SALE ORof DISTRIBUTION



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As you know, because of its high solvent power

in the ocean. Because the concentrations of these major

© Jones & Bartlett Learning, LLC © Jones & Bartlett LLC (ability toLearning, dissolve), ocean water dissolves many types c onstituents in seawater vary little over time at most NOT FOR SALE OR NOT FOR SALE OR DISTRIBUTION of chemicals, and most are found in minute quantilocalities, they areDISTRIBUTION 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© Jones Bartlett Learning, LLC © Jones & Bartlett Learning, LL general characteristics of each&group follows. body who has fertilized a lawn or garden knows. All FOR SALE OR DISTRIBUT NOT FOR SALE OR DISTRIBUTION Major Constituents plants, including those NOT that live in the ocean, conIn 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 percompounds that consist primarily of nitrogen (N), TABLE 4–1 ) of all the dissolved substances in seacent ( phosphorous (P), and silicon (Si). Representative © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC water. these two bond chemically into concentrations of these nutrients in the ocean are NOT When FOR SALE ORions DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 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 in parts per million (ppm). Most plants most abundant ions—chloride (Cl-), sodium (Na+), cannot use elemental nitrogen and phosphorus and 22+ 2+ sulfate (SO4 ), magnesium (Mg ), calcium (Ca ), so satisfy their nutrient needs by absorbing phos© Jones & Bartlett Learning, LLC up over 99 percent of © & Bartlett Learning, LLC allJones and potassium (K+)—make nitrate (NO phate (PO43-) and 3 ). Silicon is used by NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION of seawater’s solutes. The addition of five more solutes important groups 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 seauptake and release, the concentrations of n utrients water to 99.99 percent (see Table 4–1). This means, LLC in seawater, as on land, vary from place to place and © Jones & Bartlett Learning, © Jones & Bartlett Learning, LL of course, that everything else dissolved in seawater over time at any one place. Thus, oceanographers NOT FOR SALE OR DISTRIBUT NOT FOR 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.



TABLE 4–1

MAJOR SOLUTES IN SEAWATER

© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Salt Ion Ions in Seawater* (‰) by Weight (%) Cumulative (%) NOT FOR SALE OR DISTRIBUTION NOT FORIons SALE OR DISTRIBUTION Chloride (Cl-)

18.980

55.04

55.04

Sodium (Na+)

10.556

30.61

85.65

2.649

7.68

93.33

Sulfate (SO42-) Magnesium (Mg )©

3.69

Calcium (Ca )

1.16

2+

2+

1.272 Jones & Bartlett Learning, LLC NOT FOR SALE 0.400 OR DISTRIBUTION

© Jones & 97.02 Bartlett Learning, LL NOT FOR SALE 98.18 OR DISTRIBUT

0.380

1.10

99.28

Bicarbonate (HCO3 )

0.140

0.41

99.69

Bromide (Br )

0.065

0.19

99.88

Fluoride (F-)

0.001

0.00

99.99

34.482

99.99

99.99

Potassium (K+) -

-

© Boric Jones &3BO Bartlett Learning, LLC 0.026 acid (H 3) NOT FOR SALE OR DISTRIBUTION 2+ 0.013 Strontium (Sr ) Total

© Jones 0.07 & Bartlett Learning, 99.95 LLC NOT 0.04 FOR SALE OR DISTRIBUTION 99.99

© Jones & Bartlett © Jones & Bartlett Learning, LLC *The gramLearning, weight of ions per LLC 1 kg of seawater, or g/kg. Source: Adapted from Sverdrup, H. U., Johnson, M. W., and Fleming, R. H. The Oceans (Englewood Cliffs, N.J.: 1942). NOT FOR SALE OR DISTRIBUTION NOT FOR SALE ORPrentice-Hall, DISTRIBUTION

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© Jones & Bartlett Learning, LLC TABLE 4–4 NOT FOR SALE OR DISTRIBUTION EXAMPLES OF TRACE ELEMENTS

© Jones & TABLE Bartlett4–2 Learning, LLC NOT FOR SALE OR DISTRIBUTION NEAR-SURFACE NUTRIENT

IN SEAWATER

CONCENTRATIONS IN SEAWATER Nutrient Element Phosphorus (P) Nitrogen (N) Silicon (Si)

Concentration (ppm)*

Trace Element

0.07

Concentration (ppb)*

Lithium (Li)

170

© Jones & Bartlett Learning, LLC 0.5 Iodine (I) NOT FOR SALE OR DISTRIBUTION Molybdenum (Mo) 3

*ppm = parts per million

© Jones & Bartlett Learning, LLC GasesNOT FOR SALE OR DISTRIBUTION

© Jones & Bartlett Learning, LL 60 NOT 10FOR SALE OR DISTRIBUT

Zinc (Zn)

10

Iron (Fe)

10

Aluminum (Al)

10

© Jones & Bartlett Learning, LLC Copper (Cu) 3 NOT FOR SALE OR DISTRIBUTION Manganese (Mn) 2

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 Mercury (Hg) 0.03 gases argon (Ar), neon (Ne), and helium (He). Nitro© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Gold (Au) 0.004 gen and the three noble gases are inert (unreactive) NOT FORand SALE DISTRIBUTION rarelyOR involved 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 Organic depending on the activities of plants and animals and © Jones & Bartlett Learning, LLC Compounds © Jones & Bartlett Learning, LL Organic compounds are large, complex molecules proare regarded as nonconservative. NOT FOR SALE OR DISTRIBUT NOT FOR SALE OR DISTRIBUTION duced by organisms. They include substances such as lipids (fats), proteins, carbohydrates, hormones, and Trace Elements vitamins. Typically, they occur in low concentrations Trace elements are all chemical ingredients that ocand are produced by metabolic (physical and chemicur in minute (trace) quantities in the oceans. Most © Jones & Bartlett Learning, LLC Learning, LLC cal processes©inJones the cell& of Bartlett an organism that produce trace elements, such as manganese (Mn), lead (Pb), living matter) and FOR decay processes of organisms. For mercury gold (Au),OR iodine (I), and iron (Fe), NOT(Hg), FOR SALE DISTRIBUTION NOT SALE OR DISTRIBUTION example, vitamin complexes are vital for promoting the occur in concentrations of less than 1 ppm (part per growth of bacteria, plants, and animals, as shown by million) (TABLE 4–4). Many occur in quantities of less the control that thiamine and vitamin B12 have on the than 1 part per billion (ppb) and even at 1 part per growth rate, size, and number of microscopic plants trillion. These low concentrations make certain trace © Jones & Bartlett Learning, LLC even impossible to © Jones & laboratory Bartlett Learning, grown in experiments. LLC elements difficult and sometimes NOT FORdetect SALE OR DISTRIBUTION NOT FOR SALE OR Now that we haveDISTRIBUTION a general understanding of the in seawater. However, despite their extremely chemical makeup of seawater—a solution of mainly low concentrations, trace elements can be critically water with some salts, and tiny quantities of nutrients, important for marine organisms, either by helping to gases, trace elements, and organic compounds—we can promote life or by retarding or killing life (toxicity).



TABLE 4–3

QUANTITIES OF GAS IN AIR AND SEAWATER

© Jones Gas

& Bartlett Learning, In DryLLC Air (%) Nitrogen ) 78.03 NOT (N FOR SALE OR DISTRIBUTION 2

In Surface Ocean ©(%) Jones Water 47.5 NOT

& Bartlett Learning, Water–Air RatioLLC FOR SALE OR 0.6 DISTRIBUTION

Oxygen (O2)

20.99

36.0

1.7

Carbon dioxide (CO2)

0.03

15.1

503.3

Argon (Ar), hydrogen (H2), neon (Ne), helium (He) LLC Bartlettand Learning,

0.95

1.4

1.5

© Jones & NOT FOR SALE OR DISTRIBUTION




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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 SALE OR of DISTRIBUTION NOT FOR SALE OR DISTRIBUTION the saltiness of the ocean. In other words, why are the relative proportion 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 & Bartlett Learning, © Jones & Bartlett Learning, LL of water? Answers©toJones such questions are easy to grasp, LLC constant and is independent of salinity. provided that youNOT understand concepts introThis important discovery, made during NOT FOR SALE ORthe DISTRIBUT FOR the SALE OR just DISTRIBUTION duced. Also, the boxed feature “Chemical Techniques” Challenger expedition, is termed the principle of c onstant proportion or constant composition, and reviews a few of the methods that chemists employ to was a major breakthrough in determining salinity of measure the properties of seawater while at sea and in seawater in a rapid, accurate, and economical manthe laboratory. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC ner. In theory, all that need be done to quantify salinNOT FOR SALE OR DISTRIBUTION FOR DISTRIBUTION ity is to NOT measure the SALE amountOR of only a single major 4-4 Salinity ion dissolved in a sample of seawater because all the other major constituents listed in Table 4–1 occur in A simple way to determine salinity is to evaporate wafixed amounts relative to that ion. Chemists chose to ter from a container of seawater and then compare determining LLC the salinity of seawater measure Cl- for Learning, © Jones & Bartlett Learning, LLC © Jones & Bartlett the weight of the solid residue left behind in the botbecause it is the abundant solute in seawater and NOT FOR SALE NOT FOR SALE ORmost DISTRIBUTION tom ofOR the DISTRIBUTION container—the salts—to the weight of the its concentration is easily determined. original sample of seawater. Unfortunately, the method Today, oceanographers rely on a variety of methis neither precise nor accurate because salt crystals ods, 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 of the & saltBartlett residue. Learning, In order to LLC © Jones © Jones & Bartlett Learning, LL conductivity of a solution is its ability to transmit an compare accurately salinity data gathered from many FOR SALE ORion DISTRIBUT NOT FOR SALE OR DISTRIBUTION electrical current directlyNOT proportional to the total parts of the ocean and measured in many different content of the water at a given temperature, which, of laboratories and ships, chemists have adopted a stancourse, is its salinity. A salinometer indirectly meadardized and what seems to nonchemists to be a rather sures salinity by measuring the electrical conductivity cumbersome definition of salinity: the total mass exof seawater. Its calibrations allowLearning, oceanographers © Jones & Bartlett Learning, LLC © Jones & Bartlett LLCto pressed in grams of all the substances dissolved in 1 determine salinity directly and quickly by inserting an NOT FOR SALE when OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION kilogram of seawater, all the carbonate has been electrical probe into the water, a very simple matter converted to oxide, all the bromine and iodine have compared with the rather laborious chemical deterbeen replaced by chlorine, and all organic compounds mination of chlorinity. have been oxidized at a temperature of 480°C. Because we are not chemical oceanographers, we can simplify © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Factors that Regulate the definition of salinity as follows to suit our more NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR general purpose: the total weight in grams of dissolved the Salinity of DISTRIBUTION Seawater 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 4–5). Rivers sea? The answer is straightforward © JonesProportion & Bartlett Learning, LLC © Jones(TABLE & Bartlett Learning, LL Principle of Constant disgorge huge volumes ofNOT freshFOR water SALE into theOR ocean DISTRIBUT NOT FOR SALE OR DISTRIBUTION every year. Chemical analyses of water samples from Salinity determinations from the world’s oceans have rivers all over the world indicate that they contain a revealed an important, unexpected finding. Although variety of dissolved substances in concentrations of salinity varies quite a bit because of differences in the ppm (TABLE 4–6). Rivers have a dissolved load of chemitotal amount of dissolved salts, the relative proportions © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC cals because of the chemical weathering of rocks on of the major constituents are constant. In other words, NOT FOR SALE OR DISTRIBUTION ORupDISTRIBUTION the land.NOT TheseFOR rocksSALE are made of an assemblage the ratio of any two major constituents dissolved in 2+ + of minerals composed predominantly of the elements seawater, such as Na /K or Cl /SO4 , is a fixed value, silicon, aluminum, and oxygen. Acidic water breaks whether the salinity is 25, 30, 35‰, or whatever. To down these rocks into their component elements. put it in more familiar terms, let’s imagine that the is dissolved in water, it When carbon dioxide (CO2) LLC ratio of females to males in a population is ¼ (1 female © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, to produce H2CO3, a weak reactsSALE with HOR for every males) and that this ratio never changes NOT FOR SALE OR 4DISTRIBUTION NOT FOR DISTRIBUTION 2O molecules

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© Jones & Bartlett Learning, LLC © Jones & TABLE Bartlett4–5 Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION SOURCES AND SINKS OF SOME SEAWATER COMPONENTS Chemical Component

Sources

Sinks

Chloride (Cl )

Volcanoes River influx

Evaporative deposition as NaCl (rock salt) Net air transfer © Jones & Bartlett Pore-water burial

-

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

Sodium (Na+)

Potassium (K+) © Jones

River influx & Bartlett Learning, LLC Volcanic-seawater reactions NOT FOR SALE OR DISTRIBUTION (high temperature) River influx Volcanic-seawater reactions Cation exchange

Calcium (Ca2+)

© Jones & Bartlett Learning, LLC Silica (H4SiO4) NOT FOR SALE OR DISTRIBUTION

Learning, LL OR DISTRIBUT

Uptake by clays & Bartlett Learning, LLC © Jones Volcanic-seawater reactions NOT FOR SALE OR DISTRIBUTION (low temperature) Biogenic secretion of shells Evaporitic deposition of gypsum (CaSO+ z 2H2O) Precipitation as calcite

© Jones & Bartlett Learning, LLC Biogenic secretion of shells FOR SALE OR DISTRIBUTION

River influx NOT Basalt-seawater reactions River influx Rainfall and dry fallout

Phosphorus (HPO42-, PO43-, H2PO4-, organic P)

FOR Evaporative depositionNOT as NaCl (rock SALE salt) Net air transfer Cation exchange with clays Basalt-seawater reactions Pore-water burial

Burial as organic P Adsorption on volcanic ferric oxides Formation of phosphorite rock


Source: Adapted from Berner, E. K., and Berner, R. A. The Global Water Cycle (Englewood Cliffs, N.J.: Prentice-Hall, 1987).

acid called carbonic acid. In turn, this acid separates into hydrogen (H+) and bicarbonate (HCO3-) ions. The specific chemical reactionsLearning, are reversible, are quite © Jones & Bartlett LLC simple, and are represented by

NOT FOR SALE OR DISTRIBUTION H2O + CO2 H2CO3 H + + HCO3 − .


Notice that the reaction yields free ions of H+, which because of their small size and high chemical and K+ that are reactivity, replace cations as Na+Learning, © Jones &such Bartlett LLC bound to minerals in rocks. The amount of H+ is a mea NOT FOR SALE OR DISTRIBUTION sure of the acidity of the water. This process—the bathing of rocks in acidic water—slowly weathers minerals,

© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC TABLE 4–6 NOT FOR SALE OR DISTRIBUTION DISSOLVED SUBSTANCES IN RIVER WATER NOT FOR SALE OR DISTRIBUTION Substance

Concentration (ppm)

Concentration (%)

Bicarbonate/carbonate (HCO3 /CO3 )

58.8

48.7

Calcium (Ca )

15.0

-

2+

2-

12.4 © Jones & Bartlett Learning, LL NOT 10.8 FOR SALE OR DISTRIBUT

© Jones & Bartlett Learning, LLC 13.1 NOT FOR SALE OR DISTRIBUTION

Silica (SiO2)

1.2

Sulfate (SO42-) Chloride (Cl ) -

Sodium (Na+)

9.3

7.8

6.5

6.3

5.2

Bartlett Learning, LLC Potassium (K ) SALE OR DISTRIBUTION NOT FOR

4.1

Nitrate (NO3 )

1.0

0.8

Iron aluminum oxide [(Fe, Al)2 O3]

0.9

0.8

Remainder

0.3

0.3

Magnesium (Mg & ) © Jones 2+

+

-

2.3

© Jones & Bartlett 3.4 Learning, LLC 1.9DISTRIBUTION NOT FOR SALE OR

© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Source: Livingstone, D. A. Chemical composition of rivers and lakes, U.S. Geological Survey, Professional Paper 440-G Government Printing Office, 1963). NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR (U.S. DISTRIBUTION



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© Jones & Bartlett Learning, LLC THE OCEAN NOT FOR SALE OR DISTRIBUTION

© Jones & Bartlett Learning, LLC

SCIENCES NOT FOR SALE OR DISTRIBUTION

CHEMISTRY Chemical Techniques

In trying to characterize and & explain the chemical prop- LLC trapping a sample of seawater. A messenger attached toLearning, LL © Jones Bartlett Learning, © Jones & Bartlett erties of seawater, marine chemists find it critically a clamp beneath the first bottle is then released, dropNOT FOR SALE OR DISTRIBUT NOT FOR SALE OR DISTRIBUTION important to collect sufficient and appropriate seawater ping and triggering the next bottle below. The procedure samples, prevent their chemical contamination, deteris 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 ©3.17 Jones Bartlett Learning, (~1.06 and quarts)&with these bottle samplers.LLC Collection NOTSample FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION A more elaborate sample-bottle configuration is known as the rosette cluster. It consists of a rigid frame Seawater samples for chemical analysis are collected that holds a number of collection bottles upright, arranged in metallic or plastic cylindrical bottles. The metallic in a circular pattern (FIGURE B4–2). The bottles can be set bottles have interior liners composed of inert plastic to and close automatically, a technician can trigger to prevent contamination Bartlett Learning, LLCof the sample by metal ions. © Jonesopen & Bartlett Learning,orLLC any of the bottles electronically from a shipboard console. One such sampling device, the Niskin bottle, has valves



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© Jones & Bartlett © use Jones & Bartlett fastened to the cable and released. When theLearning, messenger LLC ter how accurate, is of limited in determining the ex-Learning, LL NOT SALE OR DISTRIBUT NOTbottle, FORitSALE DISTRIBUTION strikes the first water causes itOR to close tightly, act chemical structure of the waterFOR column. A common 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 NOT FOR SALE DISTRIBUTION FIGURE B4–1 Niskin OR bottles. Open Niskin bottles are attached to a cable and lowered to water depths where seawater samples are to be obtained for chemical analysis. A metal messenger “trips” each bottle on the cable individually, causing it to fill with water and close securely. Bartlett Learning, LLC ©


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© Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION FIGURE B4–2 A rosette cluster. Water collecting bottles are arranged around a rigid, circular frame in a rosette pattern. Technicians are able to close the bottles individually array is lowered or raised through Jonesas&theBartlett Learning, LLC the water column.



2ND PAGES

& Bartlett Learning, LLC © Jones & hangs Bartlett Learning, LLC straight down because of the drift of the ship rela- © Jones at frequencies that depend on temperature. These NOT FOR SALE OR DISTRIBUTION NOT FOR SALE ORbottles DISTRIBUTION tive to the on the cable. Depth corrections are signals are transmitted electronically to the ship. This

applied by measuring the angle of the cable and by notallows 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 thermomBecause the composition of seawater is constant, eters mounted on the sampling bottles. (Temperature chemists water salinity Learning, LL © Jones & Bartlett Learning, LLC traditionally have determined © Jones & Bartlett discrepancies are indicators of water pressure, which is by chemical titration—the process of standardizing sil-OR DISTRIBUT NOT FOR SALE NOT FOR SALE 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 & Bartlett Learning, LLC ©The Jones & Bartlett Learning, to © theJones ship are used to determine the distance between salinity rapidly. salinometer compares the electri-LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION the pinger and the bottom to within a meter or so. cal conductivity of an unknown sample with that of a known, standard sample of seawater and converts the Analytical Procedures difference into a salinity value after correcting for temperature effects. An important instrument called the Analytical procedures reveal the temperature and CTD (conductivity, © Jones & Bartlett Learning, LLC & Bartletttemperature, Learning,depth) LLCconsists of a salinity of water. Reversing thermometers, which are © Jones salinometer, an electronic thermometer, and a pressure fastenedOR to water-sampling bottles, are used to mea- NOT FOR SALE OR DISTRIBUTION NOT FOR SALE DISTRIBUTION sensor. As it is lowered through the water column, the sure the temperature of water in situ. Better precision CTD transmits electronic signals to the ship, where they (up to 0.0001°C) is obtained by using temperatureare stored in a shipboard computer for analysis later. sensitive materials, such as quartz crystals, which vibrate



releasing ions, which go into solution and become part of a river’s dissolved chemical load (Table 4–6). Let’s firm up our understanding of weathering by © Jones & Bartlett Learning, LLC minexamining the chemical breakdown of an actual FOR(KAlSi SALE OR DISTRIBUTION eral, NOT orthoclase 3O8), the common potassiumbearing feldspar of granite. The chemical reaction is

response by most people is that the amount could not be much because the concentration of solutes in rivers is low (that’s why freshwater doesn’t taste © Jones & Bartlett Learning, LLC salty), and it’s dissolved, so you can’t see it (how NOT SALE OR DISTRIBUTION can anything that FOR can’t be seen amount to much?). It turns out that the annual river input of material in solution to the oceans is somewhere between 2KAlSi3O8 + 2H+ + H2O 2.5 × 1015 and 4 × 1015 grams. True, 1015 (10 mul (orthoclase) tiplied by itself fifteen times) seems to be quite a © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC → 2K+ + Al2Si2O5(OH)4 + 4SiO2. big number. But how big is it, really? This rate of NOT FOR SALE OR DISTRIBUTION NOT FOR10 SALE ORperDISTRIBUTION 15 (kaolinite) (dissolved silica) grams year, is about equivalent to influx, 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 + (SiO2),&and aluminum silipotassium ions (K ), silica isLLC invisible to the naked eye, represents a major Learning, LL © Jones Bartlett Learning, © itJones & Bartlett forming cates. The latter compound H2O, annual input of mass to the oceans, all ofSALE it derived NOT FOR OR DISTRIBUT NOT bonds FOR with SALE OR DISTRIBUTION another mineral, the clay kaolinite. Rivers transport by the chemical weathering of rocks on land. In addithese 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 SiO2 conocean ridges and in the volcanic arcs of subduction © Jones & Bartlett Learning, LLC © 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 FOR SALE OR SO DISTRIBUTION 2as sediment on the ocean floor. So what was a solid ) and anions (including and Cl-) Ca2+ and K+NOT 4 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 themHow much mass is actually added to the ocean selves that oceans have existed © Jones & Bartlett Learning, LLC © Jonesindicate & Bartlett Learning, LLC on the Earth the river of dissolved matter? The first NOT forFOR at least as long as 3.4 billion years. Geochemical NOT FORbySALE ORinflux DISTRIBUTION SALE OR DISTRIBUTION



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data indicate that the salinity of the oceans has changed

Organisms help maintain the steady-state equilib-

© Jones & Bartlett Learning, LLC © Jones & Bartlett little overLearning, the past 1.5LLC billion years. This constant rium of the ocean’s salinity as well. We already know NOT FOR SALE OR NOT FOR SALE OR DISTRIBUTION ocean salinity despite the tremendous annual supply that diatoms haveDISTRIBUTION 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 Ca2+, respectively, from seawater. Once these organisms mean that on average a similar quantity of salt must die, their hard parts may settle to the sea bottom to be removed from the oceans each year. Otherwise, the © Jones Bartlett © Jones & Bartlett Learning, LL form deep-sea oozes. Also, many species of animals salinity of the world’ s oceans&would haveLearning, increased LLC extract certain chemical substances that are dissolved over geologic time. ThisFOR balance between and NOT FOR SALE OR DISTRIBUT NOT SALE ORinputs DISTRIBUTION in seawater. Some of these chemicals are concentrated outputs of salt to the ocean is called a steady-state in fecal pellets that sink to the ocean floor and become equilibrium. incorporated in sediment. Oceanographers refer to inputs of material as Let’s synthesize all that we have learned about sources and their outputs as sinks. We’ve already iden© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC steady-state equilibrium, sources and sinks of salt tified several of the principal sources of the salt ions NOT FOR SALE OR DISTRIBUTION FORcycles. SALE OR ions, andNOT geologic The saltDISTRIBUTION ions dissolved in to the ocean. Let’s now examine the principal sinks of ocean water are derived largely from the weatherdissolved salt in the ocean (see Table 4–5). The removal ing and erosion of rocks on land. Because the averof salt occurs by both inorganic and organic processes. age chemical composition of seawater has remained Evaporation is an excellent example of an inorganic remarkably stable (in a steady state) over geologic process and, as discussed in the boxed feature, “Desali© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC time,SALE the inputs salt must be balanced by the outnation,” a technique for producing drinkable water NOT FOR SALE ORis DISTRIBUTION NOT FOR ORofDISTRIBUTION puts. The river-supplied ions remain in ocean water from seawater. In arid climates, evaporation rates are for a long time, but eventually are extracted by inhigh. Evaporation removes water from the ocean but organic and organic processes and become part of not the dissolved salt ions. This indicates that, with the ocean’s sedimentary record. These sediments, as time, the concentration of salt will rise by the evapora© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LL they are buried, become cemented into sedimentary tion of water molecules, creating a brine, or a very salty FOR SALE ORcolDISTRIBUT FOR SALE DISTRIBUTION rocks and eventually areNOT subducted along the solution. The DeadNOT Sea and the Great SaltOR Lake, both in liding boundaries of lithospheric plates. Some of arid settings, are fine examples of this very process. As these sedimentary units are melted and intruded as more and more water molecules are evaporated from igneous rocks, others are crumpled and raised into the water, the solution eventually becomes saturated, large mountain belts, chemical attack byLLC acidic which means&that the solution is holdingLLC as much mate© Jones Bartlett Learning, © Jones &where Bartlett Learning, water once again releases these ions to the sea. In efrial in a dissolved state as it can for the temperature and NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION fect, this is a grand sedimentary cycle (FIGURE 4–6). pressure conditions of the water. The removal of more Elements bonded into solid minerals in rocks are put water creates a supersaturated solution (a solution containing a quantity of dissolved ions that exceeds the theoretical saturation value). This leads to the pre© Jones & Bartlett © Jones & Bartlett Learning, LLC cipitationLearning, of evaporite LLC minerals from seawater, notably Erosion OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION NOT FOR SALE halite (NaCl) and gypsum (CaSO4 z H2O). Precipitation 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. Uplift Wind also blows onshore large amount of sea LLC © Jones & aBartlett Learning, ©Deposition Jones & Bartlett Learning, LL spray, which on evaporation of salt Compression NOT FOR SALE OR DISTRIBUT NOT FOR forms SALEa coating OR DISTRIBUTION on land—as anybody who wears glasses and lives by Lithospheric plate the seashore can attest. In addition, freshly extruded basalt lavas on the ocean floor are quite reactive and Intrusion extract dissolved ions, such as Mg2+ and SO42-, from Sedimentary beds © Jones Bartlett Learning, LLC © Jones & Bartlett Learning, LLC the seawater&that comes in contact with the hot lava. NOT FOR SALE OR DISTRIBUTION NOT FOR SALE ORgeologic DISTRIBUTION Finally, adsorption (the “sticking” of ions to a surface) FIGURE 4–6 Sedimentary cycle. Over time, mountains + 2+ of cations like K and Mg by certain clay minerals in are leveled by rivers. The weathering products are dispersed into the ocean and the formation of hydrogenous minerthe 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 unknownLearning, quantity of LLC ions from the sea. All of these and & uplifted into mountain ranges byLLC plate tectonics. Then a new © Jones & Bartlett © Jones Bartlett Learning, represent chemical sinks for ions dissolved in seawater. cycle of river erosion begins.


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into solution and transported to the ocean by rivers,

alert person.) By contrast, many of the principal ions

& Bartlett Learning, LLC © Jones where & Bartlett Learning, LLCprocesses cause them © Jones in river water are characterized by short residence organic and inorganic NOT FOR OR because DISTRIBUTION NOT FORtoSALE OR DISTRIBUTION times in SALE the oceans they are much more be precipitated into solids (such as halite, and

reactive or are important for biological cycles. For silica and carbonate shells) and reincorporated into example, many marine organisms require dissolved sedimentary rocks that become uplifted by tectonic Ca2+ to secrete their carbonate (CaCO3) shells. These processes and weathered once again, repeating this © Jones & Bartlett Learning, calcium LLC ions are in constant©demand Jonesby&the Bartlett marine Learning, LL grand cycle. biota, so calcium has a relatively residence If rivers are the primary sourceSALE of salt ions the NOTlow FOR SALEtime OR DISTRIBUT NOT FOR OR to DISTRIBUTION of 8 × 106 years. oceans, why aren’t the ionic compositions of freshLong residence times also help to explain the water and seawater similar? They clearly are not, as a principle of constant proportions. Water is stirred comparison of Tables 4–1 and 4–6 shows. Shouldn’t and mixed by ocean currents, much as stirring a pot they be, if one is supplying material directly to the © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC of soup with a spoon creates eddies and swirls (turother? The difference in the relative composition of NOT FOR SALE OR DISTRIBUTION FOR SALE OR DISTRIBUTION bulence) thatNOT mix the ingredients. Studies of currents solutes in seawater and river water is a result of the indicate that mixing rates in the oceans are on the residence time of ions in the ocean, which is simply 3 order of a thousand (10 ) years or less. This rate is the average length of time that an ion remains in much lower than are the residence times of the major solution there. It ranges between 2.6 × 108 years for ions of & seawater, which range from millions (106) to for aluminum (TABLE 4–7). © Jones sodium and 1.5 × 102 yearsLLC © Jones & Bartlett Learning, Bartlett Learning, LLC hundreds of millions (108) of years (see Table 4–7). is noOR different from saying that your “residence NOT NOT FORThis SALE DISTRIBUTION FOR SALE OR DISTRIBUTION Thus, rapid mixing and very long residence times of time” in your bedroom, asleep in bed, is eight hours a salt ions in seawater assure that these substances are day. Note that the two most abundant components of distributed uniformly throughout the oceans. A more seawater (Na+ and Cl-) have long residence times, on familiar way to think about this is to imagine yourself the order of hundreds of million years. Their persis© Jones & Bartlett Learning, LLC a cake. Slowly adding©dye Jones making along & theBartlett edge of a Learning, LL tence in a dissolved state in ocean water reflects their NOT FOR SALE OR DISTRIBUT FOR reactivity; SALE OR bowl (this is equivalent to a river supplying ions at the low geochemical and NOT biochemical in DISTRIBUTION other edge of an ocean basin) to a cake batter that is being words, they are essentially inert. (To carry our analrapidly stirred by an electric beater (this is equivalent ogy one step further, an inert, listless person would to mixing by ocean currents) quickly distributes the tend to spend more time in bed and have a longer dye molecules evenly throughout batter, so that residence time in&the bedroom than wouldLLC an active, © Jones Bartlett Learning, © Jones & BartletttheLearning, LLC its color (this is equivalent to the ocean’ s salinity) is NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION uniform (FIGURE 4–7). TABLE 4–7

RESIDENCE IN OCEAN WATERS

© Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION Residence Time

Effects of Salinity on the Properties of Water © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION

In the previous sections, we learned a great deal about the structure of the water molecule and the Chloride (Cl-) ∞ salinity of the ocean. Now we are ready to exam260 Sodium (Na+) ine the effect dissolved ions have on the physical © Jones & 20 Bartlett Learning,pLLC © Jones Lithium (Li+) roperties of water. As you might guess, & theBartlett addition Learning, LL 2+ NOT FOR SALE NOT FOR SALE OR DISTRIBUTION 19 of salt modifies some of the properties of water OR in DISTRIBUT Strontium (Sr ) a number of significant ways. Most of these chang11 Potassium (K+) es come about because the ions are hydrated (see 2+ 8 Calcium (Ca ) Figure 4–4), which modifies the chemical behavior 0.18 Zinc (Zn2+) of the H2O molecules solution.Learning, Let me explain © Jones © Jonesin&the Bartlett LLC 0.084 LLC Barium (Ba2+) & Bartlett Learning, by examining some specific water properties as they NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 0.018 Cobalt (Co2+) are affected by solutes. Substance

(3 10 yr) 6

Chromium (Cr)

0.00035

Aluminum (Al)

0.00015

© Jones & Bartlett LLC Source: AdaptedLearning, from Wentworth, C. K. A scale of grade and class terms for clastic sediments, Journal of Geology 30 (1922): 377–392. NOT FOR SALE OR DISTRIBUTION

Freezing Point Pure freshwater freezes at 0°C. The addition of salt to the water its freezing point.LLC For e xample, sea© Jones & lowers Bartlett Learning, water with a salinity 35‰ freezes at a t emperature NOT FOR SALE ORofDISTRIBUTION



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101







FIGURE 4–7 Rapid mixing spreads dye evenly throughout the cake batter. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

Density of -1.91°C (FIGURE 4–8). The reason that the freezing Because solutes have a greater atomic mass than do temperature of seawater is depressed relative to that of H2O molecules, the density of water increases with freshwater is quite simple. The hydrated salt ions “hold salinity. This means that freshwater floats on salt- on” to individual H2O molecules, interfering with their © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LL water. For salinities >24.7‰ (see Figure 4–8), the rearrangement into an ordered ice crystal. NOT FOR SALE OR DISTRIBUT NOT FOR SALE OR DISTRIBUTION temperature of maximum density (3.98°C for fresh water; see Figure 4–5b) is below the freezing point (0°C). 4

Vapor Pressure The vapor pressure on a liquid surface is the pressure © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Maximum-density exerted by its own vapor. When a liquid such as water 2 FOR SALE NOT OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION temperature is placed in a closed container, some of the m olecules will vaporize, decreasing the amount of liquid. Once 1 equilibrium is reached, the vapor pressure is the pressure exerted by the molecules in the vapor phase. As 0 the& salinity of water increases,LLC vapor pressure drops; © Jones & Bartlett Learning, LLC © Jones Bartlett Learning, Freezing-point this means evaporates at a faster rate NOT FOR SALE–1OR DISTRIBUTION NOT FOR SALEthat ORfreshwater DISTRIBUTION 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 seawater –3 hydrated ions, which “hold on” to the water molecules, © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LL making their vaporization more difficult. –4 Temperature (°C)

3

0

NOT 10

FOR DISTRIBUTION 20 SALE OR 30 40 Salinity (‰)

NOT FOR SALE OR DISTRIBUT

4-5 Chemical and Physical Structure

FIGURE 4–8 Effects of salinity on the maximum-density and of the Oceans freezing-point temperatures of seawater. The addition of dissolved © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Oceanographers have acquired a great deal of informaions to water lowers the initial freezing point temperature of the NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION tion about variations in the fundamental properties solution because the hydrated ions interfere with the rearrangeof ocean water, including the regional distribution of ment of the H2O molecules into an ordered ice structure. Also, an temperature, salinity, and density along the sea surincrease in salinity depresses the maximum-density temperature of face and throughout the ocean’s depths. This section seawater. Consequently, the temperature of maximum-density of summarizes andLearning, explains theLLC general distribution of average seawater is well below its freezing point. This means that © Jones & Bartlett Learning, LLC © Jones & Bartlett theseSALE three important parameters of ocean water. This seawater of average salinity will freeze before it will sink. NOT FOR SALE OR DISTRIBUTION NOT FOR OR DISTRIBUTION

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will provide the background necessary to understand

insolation varies with the seasons, the surface-water

& Bartlett Learning, LLC © Jones variations & Bartlett Learning, LLCof gases, the important © Jones in the ocean’s content temperature changes with time as well. The intense NOT FOR OR DISTRIBUTION NOT FORtopic SALE OR DISTRIBUTION of the following section. sunlight SALE in the tropics and subtropics produces a

broad band of water with a temperature higher than 25°C that shifts north or south depending on the season (see Figure 4–9). Water in the polar oceans is © Jones Learning, LLCcold, much of it being near © Jones Bartlett Latitude exerts a strong control & onBartlett the surface temvery or even&below 0°C. Learning, LL perature of the oceanNOT because the SALE amount OR of insolaSeasonal shifts of the isotherms are minor the ocean NOT FORinSALE OR DISTRIBUT FOR DISTRIBUTION off Antarctica but are significant in the North Pacific tion (the solar energy striking the Earth’s surface) and North Atlantic Oceans. decreases poleward. Surface-water temperatures, Ocean currents that flow around the periphery of therefore, are highest in the tropics and decrease each ocean affect the distribution of surface-water temwith distance from the equator. Isotherms, imagi© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC perature. For example, the strips of >25°C water in the nary contour lines that connect points of equal water NOT FOR SALE OR DISTRIBUTION NOT SALE OR tropical Atlantic andFOR Pacific Oceans areDISTRIBUTION much broader temperature, generally trend east–west, parallel to the at their western than at their eastern margins. This lines of latitude (FIGURE 4–9). Because the amount of

Temperature

© Jones & Bartlett Learning, 90°E 120 °E 150°E LLC 180° NOT FOR SALE OR DISTRIBUTION

150°W

120°W

© Jones &°WBartlett LLC 90°W 60 30°W Learning, 0° 30°E NOT FOR SALE OR DISTRIBUTION



60°E

Arctic Circle

© Jones & Bartlett Learning, LL 60°NOR DISTRIBUT NOT FOR SALE

© Jones & Bartlett Learning, LLC 30°N Tropic of Cancer NOT FOR SALE OR DISTRIBUTION Equator


0°

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


© Jones & Bartlett Learning, LL 60°S NOT FOR Antar SALE OR DISTRIBUT ctic Circle

Sea-Surface Currents

© Jones & Bartlett Learning, LLC


(a) SEA-SURFACE IN DISTRIBUTION AUGUST NOT FORTEMPERATURE SALE OR

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 their eastern peripheries. (a) Global sea-surface temperature (SST)©is Jones shown for & August. (b) Global SST is shownLLC for February. (Adapted © Jones & Bartlett Learning, LLC Bartlett Learning, Sverdrup, et al. The Oceans. Prentice-Hall, 1942.) NOT FORfrom SALE ORH. U., DISTRIBUTION NOT FOR SALE OR DISTRIBUTION



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103

90°E

120°E

150°E


180°

150°W

120°W

90°W

60°W

30°W

0°

30°E

60°E


Arctic Circle



© Jones & Bartlett60°Learning, LL N NOT FOR SALE OR DISTRIBUT

30°N © Jones & Bartlett Learning, LLC Tropic of Cancer NOT FOR SALE OR DISTRIBUTION Equator




© Jones & Bartlett Learning, LLC (b) SEA-SURFACE TEMPERATURE IN FEBRUARY NOT FOR SALE OR DISTRIBUTION

Tropic of Capricorn 30°S

S © Jones & Bartlett60°Learning, LL Antarctic Circle DISTRIBUT NOT FOR SALE OR


FIGURE 4–9 (Continued) Sea-surface temperatures.

distortion is produced by currents that move warm

0°

so familiar to sailors and tourists, but the deeper water

© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC water poleward along the western side of oceans and below the thermocline, where temperatures are near NOT FOR SALE OR DISTRIBUTION NOT FOR SALE DISTRIBUTION cold water equatorward along their eastern sides (see freezing evenOR at the equator!

Figure 4–9). Because of solar heating during the summer, a seaInvestigations 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 4–10). LLC 4–11 ). The daily thermoclines latitudes have a layered thermal (FIGURE the mid-latitudes (FIGURE © © Jones &structure Bartlett Learning, Jones & Bartlett Learning, LL A layer of warm water, to a thousand that occur at very shallowNOT waterFOR depths (

The Properties of Seawater - Jones & Bartlett Learning

The Properties of Seawater - Jones & Bartlett Learning

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