Ocean WaterOcean Water

Salts and GasesSalts and Gases

The Dissolving Power of The Dissolving Power of WaterWater

•Dissolving power results from Dissolving power results from polarpolar nature of H nature of H22O moleculeO molecule

– NaNa++ and Cl and Cl-- are held together by are held together by ionic bondsionic bonds (attraction of (attraction of opposite charges)opposite charges)

– HH22O reduces the ionic bonding and pulls NaO reduces the ionic bonding and pulls Na++ and Cl and Cl-- apart apart

Salinity in OceansSalinity in Oceans

– Total amount of dissolved Total amount of dissolved solids expressed in grams in 1 solids expressed in grams in 1 kg of waterkg of water

•Average salinity in oceans = 35 Average salinity in oceans = 35 ‰‰

• Salinity variationsSalinity variations– Due to differences in local Due to differences in local

rates of evaporation and rates of evaporation and precipitation (water budget)precipitation (water budget)

– 35 parts per thousand (ppt)35 parts per thousand (ppt)– 35 g/kg35 g/kg

•SalinitySalinity

Constituents of Sea WaterConstituents of Sea Water

•Most abundant seawater elements are sodium (NaMost abundant seawater elements are sodium (Na++) + chloride (Cl) + chloride (Cl--))

• Minor and trace elements also presentMinor and trace elements also present

• Major constituents: SOMajor constituents: SO442-2-,, MgMg2+2+, Ca, Ca2+2+, K, K++, and HCO, and HCO33

- -

Seawater versus River Seawater versus River WaterWater

Chemical ConstituentChemical ConstituentPercent of total salt contentPercent of total salt content

OceanOcean RiverRiver

Silica (SiOSilica (SiO22))

Iron (Fe)Iron (Fe)

Calcium (Ca)Calcium (Ca)

Magnesium (Mg)Magnesium (Mg)

Sodium (Na)Sodium (Na)

Potassium (K)Potassium (K)

Bicarbonate (HCOBicarbonate (HCO33))

Sulfate (SOSulfate (SO442-2-))

Chloride (Cl)Chloride (Cl)

Nitrate (NONitrate (NO33))

Bromide (Br)Bromide (Br)

TOTALTOTAL

--

--

1.191.19

3.723.72

30.5330.53

1.111.11

0.420.42

7.677.67

55.1655.16

--

.02.02

100.00100.00

14.5114.51

0.740.74

16.6216.62

4.544.54

6.986.98

2.552.55

31.9031.90

12.4112.41

8.648.64

1.111.11

--

100.00100.00

Salts in the OceanSalts in the OceanWhy is the ocean salty?Why is the ocean salty?

– Salts going in = salts going outSalts going in = salts going out

• Salts come from:Salts come from:

– Rocks = cationsRocks = cations

– Gases from mantleGases from mantle

• Why is the ocean not Why is the ocean not getting saltier?getting saltier?

Salts Going OutSalts Going Out

• Sea SraSea Sra • Sea SpraySea Spray

• BiologicalBiological– Fecal pelletsFecal pellets– Shell formationShell formation

• Mid-ocean ridge magmaMid-ocean ridge magma

• EvaporitesEvaporites

• AdsorptionAdsorption

Principle of Constant Principle of Constant ProportionsProportions

– Because of this principle, it is Because of this principle, it is necessary to test for 1 salt ion necessary to test for 1 salt ion (usually Cl) to determine total (usually Cl) to determine total amount of salt presentamount of salt present

– The amount of salt varies, but the The amount of salt varies, but the relative proportions of ions are constantrelative proportions of ions are constant

Determining SalinityDetermining Salinity

1.1. Calculating Salinity Calculating Salinity

– Salinity=1.8065 x chlorinity (Salinity=1.8065 x chlorinity (‰)‰)

2.2. Salinometers Salinometers

– Salinity determined by the Salinity determined by the electrical conductivity electrical conductivity produced by dissolved saltsproduced by dissolved salts

Cl-

Na+

Deionized water with salt

Factors Affecting SalinityFactors Affecting Salinity

•PrecipitationPrecipitation

• EvaporationEvaporation

• Run offRun off

• FreezingFreezing

Residence TimesResidence Times• Average length in time that a substance remains in Average length in time that a substance remains in

solution in seawatersolution in seawater

IonIon Time in yearsTime in yearsChloride (ClChloride (Cl--))

Sodium (NaSodium (Na++))

Magnesium Magnesium (Mg(Mg2+2+))

Sulfate (SOSulfate (SO442-2-))

Potassium (KPotassium (K++))

Calcium (CaCalcium (Ca++))

Manganese (Mn)Manganese (Mn)

Aluminum (Al)Aluminum (Al)

Iron (Fe)Iron (Fe)

80 million80 million

60 million60 million

10 million10 million

9 million9 million

6 million6 million

1 million1 million

7 thousand7 thousand

1 hundred1 hundred

1 hundred1 hundred

• Ions with longer residence times are most abundant in oceanIons with longer residence times are most abundant in ocean

Effects of SalinityEffects of Salinity

1.1.Freezing point depression; boiling point elevationFreezing point depression; boiling point elevation– Disrupts Hydrogen bonding Disrupts Hydrogen bonding (freezing point of seawater =-(freezing point of seawater =-

22°C)°C)

2.2. Changes densityChanges density– Pure water density = 1 kg/lPure water density = 1 kg/l

– Seawater density = 1.024 kg/lSeawater density = 1.024 kg/l

3. 3. Changes vapor pressureChanges vapor pressure– ↑ ‰↑ ‰, , ↑↑ P P

DesalinationDesalination•Fresh HFresh H220 from Salt H0 from Salt H2200

• MethodsMethods

– Reverse OsmosisReverse Osmosis

– ElectrodialysisElectrodialysis

– DistillationDistillation

Gases in SeawaterGases in Seawater

•Major Gases: NMajor Gases: N22, O, O22 and CO and CO22

• OO22 and CO and CO22 important for life processes important for life processes

COCO22 and O and O22 with depth with depth

• Surface (0m)Surface (0m)

– Photosynthesis dominantPhotosynthesis dominant• ~~ 200m - 0m - ~1,000m~1,000m

– Oxygen (OOxygen (O22) ) ↓↓– Carbon Dioxide (COCarbon Dioxide (CO22) ↑) ↑

– Oxygen (OOxygen (O22) abundant gas) abundant gas

– Respiration dominantRespiration dominant

• 1,000m – 4,000m1,000m – 4,000m– OO22 ↑ slightly↑ slightly

– Organic matter decayOrganic matter decay

• Oxygenated bottom watersOxygenated bottom waters

– COCO22 continues to continues to ↑↑• Organic matter decayOrganic matter decay

• Cold salty oxygenated Cold salty oxygenated HH22O sinks in polar O sinks in polar region transported to region transported to depthdepth

GasesGasesSummarySummary

• PhotosynthesisPhotosynthesis

– COCO2 2 consumed; Oconsumed; O22 produced produced

– Therefore, OTherefore, O22 more more abundant than COabundant than CO22 in in photic zonephotic zone• RespirationRespiration

• Organic matter (OM) decayOrganic matter (OM) decay

– OO22 consumed; CO consumed; CO22 produced produced

– OO22 consumed; CO consumed; CO22 produced produced

• Respiration and OM Respiration and OM decay decay

= = ↑ CO↑ CO22 below photic zone below photic zone

The pH ScaleThe pH Scale

• COCO22 controls acidity controls acidity

• An acid has excess [HAn acid has excess [H++] ] (Hydrogen ions)(Hydrogen ions)

• A base has excess [OHA base has excess [OH--] ] (Hydroxyl ions)(Hydroxyl ions)

pH of seawater = 7.5-8.5; Average = 7.8pH of seawater = 7.5-8.5; Average = 7.8

– ↑ ↑ COCO22 = ↑ acidity = ↑ acidity

– ↓↓ COCO22 = ↓ acidity = ↓ acidity

Gases in SeawaterGases in SeawaterCarbonate Buffering SystemCarbonate Buffering System

• Seawater too basic: Seawater too basic: HH22COCO33 HCO HCO33

-- + H + H++ (pH drops) (pH drops)

• Seawater too acidic: Seawater too acidic: HCOHCO33

-- + H + H++ H H22COCO33 (pH rises) (pH rises)

• Dissolved CODissolved CO22 in water acts as a buffer in water acts as a buffer

• Prevents large shifts in pHPrevents large shifts in pH

Gas CyclingGas Cycling

•OO22 Cycling Cycling

• COCO22 Cycling Cycling– Organisms use COOrganisms use CO22

for tissuefor tissue– Decay of organic Decay of organic

matter releases COmatter releases CO22 back to oceanback to ocean

– Photosynthesis produce OPhotosynthesis produce O22

– Respiration & Respiration & decomposition of O.M. decomposition of O.M. use Ouse O22– O.M. buried doesn’t O.M. buried doesn’t consume all Oconsume all O22

– Rocks consume ORocks consume O22

Nutrients and OrganicsNutrients and Organics

• Required for plant growthRequired for plant growth

• Cycled by plant Cycled by plant growth and decaygrowth and decay

• Organics used by Organics used by organism or buriedorganism or buried