Class 17 -- The OceansClass 17 -- The Oceans

SALINITY AND COMPOSITION OF SEA WATERSALINITY AND COMPOSITION OF SEA WATER•Water's solvent properties- reviewWater's solvent properties- review•SalinitySalinity•Composition of dissolved saltsComposition of dissolved salts

–"Constant proportions""Constant proportions"–"Conservative" and "nonconservative" "Conservative" and "nonconservative" speciesspecies

•Salinity distribution in surface ocean waters Salinity distribution in surface ocean waters –-- controlling factors-- controlling factors

WATER IS AN EXCELLENT SOLVENT -- WATER IS AN EXCELLENT SOLVENT --

Dissolves many substancesDissolves many substances

HH22O molecule is “polar”O molecule is “polar”

•Negative HNegative H22O end -- attracts + ions (cations)O end -- attracts + ions (cations)

•Positive HPositive H22O end -- attracts - ions (anions)O end -- attracts - ions (anions)

•Many ions are “happy” in water because of thisMany ions are “happy” in water because of this

•The attraction of the HThe attraction of the H22O’s overcomes ionic bonding O’s overcomes ionic bonding

in solids --> solids dissolvein solids --> solids dissolve

How and Why Do Various ElementsHow and Why Do Various Elements Dissolve in Water? Dissolve in Water?

SALINITY (review)SALINITY (review)•Ave. S = 35 g/kg; range = 30-37 g/kgAve. S = 35 g/kg; range = 30-37 g/kg

•Variations due to gains vs. losses of HVariations due to gains vs. losses of H22O O

COMPOSITION OF DISSOLVED SALTSCOMPOSITION OF DISSOLVED SALTS•Dissolved substances are ionsDissolved substances are ions– cations (+) & anions (-)cations (+) & anions (-)

•99.7% of salinity is made up of only 7 ions99.7% of salinity is made up of only 7 ions–"major elements”... "major elements”...

Which ions are found in seawater Which ions are found in seawater and how much of each is there?and how much of each is there?

•These are the Major Elements in SeawaterThese are the Major Elements in Seawater–Others -- "minor" or "trace”elementsOthers -- "minor" or "trace”elements

•Major elements: "Major elements: "constant proportionsconstant proportions""–[Na[Na++] / [Cl] / [Cl--] = a constant value everywhere] = a constant value everywhere–[Na[Na++] / Salinity = “] / Salinity = “ ““ ““

Cations g/kg Anions g/kgNa+ 10.8 Cl- 19.4Mg2+ 1.3 SO42- 2.7Ca 2+ 0.4 HCO 3- 0.1K+ 0.4

Why does this occur? Why does this occur? •Oceans are “well stirred”Oceans are “well stirred”•i.e., Mixing time (<2,000 yr) is much less i.e., Mixing time (<2,000 yr) is much less than the time for much addition/removalthan the time for much addition/removal

•Most minor and trace species are NOT Most minor and trace species are NOT present in constant proportions -- present in constant proportions --

–““non-conservative”speciesnon-conservative”species–removed rapidly from sea water removed rapidly from sea water –some removed by living organismssome removed by living organisms

Highest S...Highest S...•center of oceans at ~ 25˚ lat.center of oceans at ~ 25˚ lat.•enclosed seas at same lat.enclosed seas at same lat.

Lowest S...Lowest S...•temperate latitudes. (~40-50˚)temperate latitudes. (~40-50˚)•equatorial regionsequatorial regions•near coastsnear coasts

Where is salinity high? Where is it low?Where is salinity high? Where is it low?

Sea Surface Salinities (Fig. 5-21)Sea Surface Salinities (Fig. 5-21)

• Is salt added in certain areas and not in Is salt added in certain areas and not in others?others?

• No…No…• It must be addition or loss of water.It must be addition or loss of water.

– Variations in the "water budget" from Variations in the "water budget" from place to placeplace to place

What causes these variations in salinity?What causes these variations in salinity?

The Global Hydrologic Cycle

Evaporation/ Precipitation Imbalance and Salinity

•Salinity variations with latitudeSalinity variations with latitude –E vs. P balance is the key…E vs. P balance is the key…–Temperate + equatorial: E < P ---> low STemperate + equatorial: E < P ---> low S–Subtropics (Dry!): E > P ---> high SSubtropics (Dry!): E > P ---> high S

•Salinity near continentsSalinity near continents–Runoff from major rivers --> low SRunoff from major rivers --> low S–Semi-enclosed seas of high E --> high SSemi-enclosed seas of high E --> high S

Overview of salinity-controlling processes:Overview of salinity-controlling processes:

Sea Surface Salinities (Fig. 5-21)Sea Surface Salinities (Fig. 5-21)

Sea Surface SalinitiesSea Surface Salinities

•Ocean currents modify the salinity patternOcean currents modify the salinity pattern -- --

•Ex. #1: Gulf Stream: warm, saline water Ex. #1: Gulf Stream: warm, saline water transported North and Westtransported North and West•Ex. #2: SE Pacific: cool, less saline water Ex. #2: SE Pacific: cool, less saline water transported Northward, then Westwardtransported Northward, then Westward

Sea Surface Salinities (Fig. 5-21)Sea Surface Salinities (Fig. 5-21)

Why is salinity so important?Why is salinity so important?

High S water is more dense than low S water.High S water is more dense than low S water.

Convection is driven by the sinking of cold, Convection is driven by the sinking of cold, high salinityhigh salinity water masses. water masses.

Deep Ocean currents driven by convectionDeep Ocean currents driven by convection

These currents carry heat from low to high These currents carry heat from low to high latitudes and influence global climate stronglylatitudes and influence global climate strongly

From Before..... Convection in the Oceans-From Before..... Convection in the Oceans-

Salinity is critical too.Salinity is critical too.

CoolingCooling Heating Heating

North AtlanticNorth Atlantic EquatorEquator

Evap.Evap.Sea IceSea Ice