Sea Water ChemistrySea Water Chemistry

Chapter 7Chapter 7

Sea Water ChemistrySea Water Chemistry

determine many important determine many important oceanographic phenomena oceanographic phenomena including :including :

Global patterns of oceanic and Global patterns of oceanic and atmospheric circulation, and the atmospheric circulation, and the growth and distribution of marine growth and distribution of marine organisms. organisms.

Life on earth probably evolved Life on earth probably evolved in water in water

Most animals are 50-65% Most animals are 50-65% waterwater

water exists in all three water exists in all three physical states of matter: physical states of matter: solid, liquid, and gas solid, liquid, and gas

71% of the Earth Surface - Sea 71% of the Earth Surface - Sea WaterWater

regulates the climate, dilute regulates the climate, dilute wastewaste

major habitat for living major habitat for living creaturescreatures

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polarity of water molecules polarity of water molecules results in hydrogen bondingresults in hydrogen bonding

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1. has cohesive behavior 1. has cohesive behavior 2. resists changes in 2. resists changes in

temperature temperature 3. has a high heat of 3. has a high heat of

vaporization and cools surfaces vaporization and cools surfaces as it evaporates as it evaporates

4. expands when it freezes 4. expands when it freezes 5. is a versatile solvent5. is a versatile solvent

Characteristics of HCharacteristics of H2200

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1. Surface tension 1. Surface tension – measure of how difficult it is to measure of how difficult it is to

stretch or break the surface of a stretch or break the surface of a liquid liquid

– water has a greater surface water has a greater surface tension than most liquidstension than most liquids

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2-3. Water's high heat of 2-3. Water's high heat of vaporization:vaporization:

moderates the earth's climate.moderates the earth's climate. solar heat absorbed by tropical solar heat absorbed by tropical

seas dissipates when surface seas dissipates when surface water evaporates water evaporates

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4. Oceans and lakes don't 4. Oceans and lakes don't freeze freeze

because of hydrogen bonding, because of hydrogen bonding, water is less dense as a solid water is less dense as a solid than it is as a liquid.than it is as a liquid.

consequently, ice floats.consequently, ice floats.

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5. water is a versatile solvent 5. water is a versatile solvent owing it to the polarity of the owing it to the polarity of the water molecule water molecule

ionic compounds dissolve in ionic compounds dissolve in waterwater

Major Components of Major Components of SeawaterSeawater

dissolved salts - hydrated dissolved salts - hydrated anions anions and and cations (Table 7.1;, f. 7.3)cations (Table 7.1;, f. 7.3)

dissolved gases - nitrogen, oxygen, dissolved gases - nitrogen, oxygen, carbon dioxidecarbon dioxide

organic and inorganic - dissolved organic and inorganic - dissolved organic materials suspended organic materials suspended particulate matterparticulate matter

Major Ions in Typical SeawaterMajor Ions in Typical Seawater

Ion Parts per thousand by weight ‰ (ppt)(Table Ion Parts per thousand by weight ‰ (ppt)(Table 7.1)7.1)

Cl- Cl- 18.98 18.98 SOSO44-2 -2 2.649 2.649 HCOHCO33- - 0.140 0.140 Na+ Na+ 10.556 10.556 MgMg2+2+ 1.272 1.272 Ca+Ca+ 0.400 0.400 K+K+ 0.380 0.380

On average, concentration of dissolved salts, On average, concentration of dissolved salts, i.e., i.e., the salinity, in seawater is 3.5% or the salinity, in seawater is 3.5% or 3535‰.‰.

The relative abundances of the ions listed The relative abundances of the ions listed above does not change, even though salinity above does not change, even though salinity does; are said to be conservative.does; are said to be conservative.

Relative abundances of minor and trace Relative abundances of minor and trace constituents do varyconstituents do vary

Determining SalinityDetermining Salinity

Evaporation of water to weight the salt is Evaporation of water to weight the salt is an imprecise methodan imprecise method

Because of the constancy of composition if Because of the constancy of composition if we measure one component we can get a we measure one component we can get a more precise measurementmore precise measurement

Salinity ppt = 1.80655 x Chlorinity in pptSalinity ppt = 1.80655 x Chlorinity in ppt If chlorinity is 19.2 ppt, what is the salinity If chlorinity is 19.2 ppt, what is the salinity

of sea water?of sea water? 34.7 ppt = 35 ppt34.7 ppt = 35 ppt

Sources of SaltSources of Salt

Rivers (winds and glaciers are a less Rivers (winds and glaciers are a less important, indirect source)important, indirect source)

Weathering of oceanic crustWeathering of oceanic crust Hydrothermal Vents associated with Hydrothermal Vents associated with

Mid-ocean ridges and other submarine Mid-ocean ridges and other submarine volcanoesvolcanoes

SinksSinks

Biologic activityBiologic activity Interaction with Particulate matter: clays Interaction with Particulate matter: clays

and organic matter absorb dissolved and organic matter absorb dissolved metalsmetals

Direct PrecipitationDirect Precipitation

Hydrothermal Activity: (fig. 7.4)Hydrothermal Activity: (fig. 7.4) Reaction between seawater and new Reaction between seawater and new

oceanic crustoceanic crust Minerals like magnesium is incorporated Minerals like magnesium is incorporated

into depositsinto deposits Calcium is added to sea waterCalcium is added to sea water

Physical and Chemical Physical and Chemical Properties of WaterProperties of Water

Heat Capacity -Heat Capacity - energy added to energy added to raise temperature of 1 gram of raise temperature of 1 gram of substance by substance by °C°C

adding energy breaks H-bonds, adding energy breaks H-bonds, increases fraction of free waterincreases fraction of free water

important in thermal buffering and important in thermal buffering and heat transport to higher latitudesheat transport to higher latitudes

Latent Heats and EvaporationLatent Heats and Evaporation

heat input or release associated heat input or release associated with phase changes (ice - liquid, with phase changes (ice - liquid, liquid - vapor)liquid - vapor)

changes in water structure, H-changes in water structure, H-bonding with phase changesbonding with phase changes

important in thermal buffering, important in thermal buffering, heat transport and heat exchange heat transport and heat exchange with atmospherewith atmosphere

Density -Density - mass per unit volume mass per unit volume (grams/cm(grams/cm33))

density of water phases (ice, liquid, density of water phases (ice, liquid, vapor) due to structural changes at vapor) due to structural changes at molecular levelmolecular level

density maximum at density maximum at °C in pure water°C in pure water Major role in deep ocean circulation and Major role in deep ocean circulation and

water column structure and stabilitywater column structure and stability

Light TransmissionLight Transmission

transparent in visible part of transparent in visible part of spectrumspectrum

Absorbed as is goes deeper in the Absorbed as is goes deeper in the water columnwater column

strongly absorbs infrared (heat) and strongly absorbs infrared (heat) and ultraviolet (prevents damage to ultraviolet (prevents damage to DNA)DNA)

Dissolving PowerDissolving Power

hydration of solutes - interactions hydration of solutes - interactions between solutes and free waterbetween solutes and free water

decreases H-bonding, increases order decreases H-bonding, increases order of free water, increases densityof free water, increases density

exclusion of solutes on freezing and exclusion of solutes on freezing and evaporationevaporation

other effects of solutes: freezing point other effects of solutes: freezing point depression, boiling point elevationdepression, boiling point elevation

pH (acidity or alkalinity)pH (acidity or alkalinity)

measure of the dissociation of measure of the dissociation of water into ions (H+, OH), (fig. 7.9)water into ions (H+, OH), (fig. 7.9)

pH = - log [H+]pH = - log [H+] pH effects on biological and pH effects on biological and

geochemical reactionsgeochemical reactions

Conservative vs. Non Conservative vs. Non Conservative PropertiesConservative Properties

Conservative Properties of SeawaterConservative Properties of Seawater those properties that can only be those properties that can only be

altered at the sea surface: altered at the sea surface: temperature, salinity, inert gasestemperature, salinity, inert gases

properties not altered by biological properties not altered by biological or geochemical reactionsor geochemical reactions

importance in water mass importance in water mass identification, tracing and mixingidentification, tracing and mixing

Nonconservative Properties of Nonconservative Properties of SeawaterSeawater

those properties that can be those properties that can be altered anywhere in the water altered anywhere in the water columncolumn

properties altered by biological properties altered by biological and geochemical reactionsand geochemical reactions

Dissolved GasesDissolved Gases The proportions of gases in the The proportions of gases in the

atmosphere is not the same as their atmosphere is not the same as their proportions in seawater, (Table 7.4)proportions in seawater, (Table 7.4)

There is less NThere is less N22 (nitrogen gas) in the ocean (nitrogen gas) in the ocean than in the atmosphere, than in the atmosphere,

much more oxygen, much more oxygen, and even more COand even more CO22. . All this COAll this CO22 in the oceans keeps CO in the oceans keeps CO22 from from

being in the atmosphere and causing being in the atmosphere and causing global warming. global warming.

The colder the water, the more gas The colder the water, the more gas can dissolve in itcan dissolve in it. .

When you leave your can of coke in the When you leave your can of coke in the car in the sun, then open it, what car in the sun, then open it, what happens? happens?

Coke sprays all over you. Coke sprays all over you. That's because the gas has exsolved That's because the gas has exsolved

(come out of solution); a lot has (come out of solution); a lot has accumulated in the little space at the accumulated in the little space at the top of the can. top of the can.

Very active fish, such as trout and salmon, Very active fish, such as trout and salmon, require very cold water to live in because require very cold water to live in because they have high oxygen requirements. they have high oxygen requirements.

They literally suffocate when the water gets They literally suffocate when the water gets too warm, and the oxygen levels drop. too warm, and the oxygen levels drop.

This explain why these fish don't live down This explain why these fish don't live down south.south.

'Thermal pollution' occurs when electric 'Thermal pollution' occurs when electric plants put warm water into streams, plants put warm water into streams, lowering lowering the oxygen levelthe oxygen level..

COCO22 is important because it is needed is important because it is needed by plants so they can photosynthesize. by plants so they can photosynthesize.

OO22 is important because animals need is important because animals need it for respiration.it for respiration.

PhotosynthesisPhotosynthesis: : COCO22 + H + H22O + energy [from the sun] O + energy [from the sun] O O22

+ sugar (organic matter)+ sugar (organic matter)

Respiration (the reverse of Respiration (the reverse of photosynthesis): photosynthesis):

OO22 + sugar + sugar COCO22 + H + H22O + energyO + energy

Dissolved OxygenDissolved Oxygen

seawater\atmosphere exchange at seawater\atmosphere exchange at air water interface only (fig.7.8)air water interface only (fig.7.8)

biological processes that affect Obiological processes that affect O22 concentration: photosynthesis and concentration: photosynthesis and respirationrespiration

typical distribution of Otypical distribution of O22 in water in water column and processes that control column and processes that control this distributionthis distribution

Phytoplankton NutrientsPhytoplankton Nutrients

inorganic sources of N, P, S and inorganic sources of N, P, S and other atoms required for other atoms required for phytoplankton growthphytoplankton growth

photosynthesis and respiration photosynthesis and respiration contributes in nutrient distributioncontributes in nutrient distribution

Especially important, because so much is Especially important, because so much is needed, are needed, are N (nitrogen) and P (phosphorus). N (nitrogen) and P (phosphorus).

Si (silica)Si (silica) is also important for all the siliceous is also important for all the siliceous organisms we‘ll discuss: diatoms, radiolarians, organisms we‘ll discuss: diatoms, radiolarians, and siliceous sponges.and siliceous sponges.

N is necessary to make proteins. N is necessary to make proteins. P is necessary to make new cells (it's part of the P is necessary to make new cells (it's part of the

cell wall), and also genetic material, DNA and cell wall), and also genetic material, DNA and RNA.RNA.

N is useful for plants only in these forms: N is useful for plants only in these forms: NONO33

-- nitratenitrate NONO22

-- nitritenitrite NHNH44

++ ammoniumammonium NN22, the gas, is not usable by most plants. , the gas, is not usable by most plants. Only a few bacteria can break this very strong Only a few bacteria can break this very strong

molecule apart and turn it into nitrate. molecule apart and turn it into nitrate. These are 'nitrogen-fixing bacteria'.These are 'nitrogen-fixing bacteria'. P is useful in the form of P is useful in the form of phosphatephosphate, PO, PO44

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Thus weathering, sedimentation, and Thus weathering, sedimentation, and ocean chemistry are all closely linked.ocean chemistry are all closely linked.

Other ions in seawater, such as Cl Other ions in seawater, such as Cl –– and and SOSO4 4 , are not derived from weathering, , are not derived from weathering,

but from volcanic degassing.but from volcanic degassing.

The Carbonate System in The Carbonate System in SeawaterSeawater

COCO22 in seawater is controlled by: ( f.7- in seawater is controlled by: ( f.7-

10-11)10-11) Exchange with the atmosphereExchange with the atmosphere Photosynthesis/Respiration: Photosynthesis/Respiration: 6CO6CO22 + 6H + 6H22 O O CC66 H H1212 O O66 + 6O + 6O22

The Carbonate BufferThe Carbonate Buffer

Carbon Dioxide: COCarbon Dioxide: CO22 , ,

Carbonic Acid: HCarbonic Acid: H22COCO33 , ,

Bicarbonate: HCOBicarbonate: HCO33 , ,

Carbonate: COCarbonate: CO332-2-

COCO22 + H + H22O O HH22COCO33 . .

HH22COCO33 HCOHCO33 + H+ H+2.+2.

HCOHCO33 COCO332-2-+ H + H +3.+3.

Another important reaction is the dissolution Another important reaction is the dissolution and precipitation of calcium carbonate:and precipitation of calcium carbonate:

COCO33 + Ca+ Ca+2+2 CaCO CaCO334.4...

Importance of these reactionImportance of these reactions:s: Maintain constant pH (seawater is said to be Maintain constant pH (seawater is said to be

buffered). buffered). Few marine organisms can tolerate a pH very Few marine organisms can tolerate a pH very

different from 8.different from 8.

Biological ProductivityBiological Productivity

In general, shells of organisms are likely In general, shells of organisms are likely to be preserved where their production to be preserved where their production rate is high, rate is high,

Siliceous shells are preserved only Siliceous shells are preserved only where the production rate is high. where the production rate is high.

Siliceous oozes occur where Siliceous oozes occur where productivity rate is high and terrigenous productivity rate is high and terrigenous sedimentation rate low.sedimentation rate low.

Carbonate shells: the oceans are Carbonate shells: the oceans are supersaturated with respect to CaCOsupersaturated with respect to CaCO33 at the at the surface and become increasingly surface and become increasingly undersaturated with depth.undersaturated with depth.

Shells more likely to be preserved at shallow Shells more likely to be preserved at shallow depth.depth.

Lysocline: depth at which rapid dissolution of Lysocline: depth at which rapid dissolution of CaCOCaCO33 begins. begins.

This is deeper than the depth where ocean This is deeper than the depth where ocean becomes undersaturated.becomes undersaturated.

CCDCCD

Carbonate Compensation Depth (or Carbonate Compensation Depth (or ‘snow line’): ‘snow line’):

depth where dissolution>supply of depth where dissolution>supply of CaCOCaCO33 and and

below which CaCObelow which CaCO33 shells are not shells are not

preserved in sediment.preserved in sediment.