Class The Oceans SALINITY AND COMPOSITION OF SEA WATER Water's solvent properties- reviewWater's solvent properties- review SalinitySalinity Composition of dissolved saltsComposition of dissolved salts –"Constant proportions" –"Conservative" and "nonconservative" species Salinity distribution in surface ocean watersSalinity distribution in surface ocean waters –-- controlling factors

WATER IS AN EXCELLENT SOLVENT -- Dissolves many substances H 2 O molecule is “polar” Negative H 2 O end -- attracts + ions (cations)Negative H 2 O end -- attracts + ions (cations) Positive H 2 O end -- attracts - ions (anions)Positive H 2 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 H 2 O’s overcomes ionic bonding in solids --> solids dissolveThe attraction of the H 2 O’s overcomes ionic bonding in solids --> solids dissolve How and Why Do Various Elements Dissolve in Water?

SALINITY (review) Ave. S = 35 g/kg; range = g/kgAve. S = 35 g/kg; range = g/kg Variations due to gains vs. losses of H 2 OVariations due to gains vs. losses of H 2 O COMPOSITION OF DISSOLVED SALTS Dissolved substances are ionsDissolved substances are ions – 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”... Which ions are found in seawater and how much of each is there?

These are the Major Elements in SeawaterThese are the Major Elements in Seawater –Others -- "minor" or "trace”elements Major elements: "constant proportions"Major elements: "constant proportions" –[Na + ] / [Cl - ] = a constant value everywhere –[Na + ] / Salinity = “““

Why does this occur? Oceans are “well stirred”Oceans are “well stirred” i.e., Mixing time (<2,000 yr) is much less than the time for much addition/removali.e., Mixing time (<2,000 yr) is much less than the time for much addition/removal Most minor and trace species are NOT present in constant proportions --Most minor and trace species are NOT present in constant proportions -- –“non-conservative”species –removed rapidly from sea water –some removed by living organisms

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... temperate latitudes. (~40-50˚)temperate latitudes. (~40-50˚) equatorial regionsequatorial regions near coastsnear coasts Where is salinity high? Where is it low?

Sea Surface Salinities (Fig. 5-21)

Is salt added in certain areas and not in others?Is salt added in certain areas and not in 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 place to place 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… –Temperate + equatorial: E low S –Subtropics (Dry!): E > P ---> high S Salinity near continentsSalinity near continents –Runoff from major rivers --> low S –Semi-enclosed seas of high E --> high S Overview of salinity-controlling processes:

Sea Surface Salinities (Fig. 5-21)

Sea Surface Salinities

Ocean currents modify the salinity pattern --Ocean currents modify the salinity pattern -- Ex. #1: Gulf Stream: warm, saline water transported North and WestEx. #1: Gulf Stream: warm, saline water transported North and West Ex. #2: SE Pacific: cool, less saline water transported Northward, then WestwardEx. #2: SE Pacific: cool, less saline water transported Northward, then Westward

Sea Surface Salinities (Fig. 5-21)

Why is salinity so important? High S water is more dense than low S water. Convection is driven by the sinking of cold, high salinity water masses. Deep Ocean currents driven by convection These currents carry heat from low to high latitudes and influence global climate strongly

From Before..... Convection in the Oceans- Salinity is critical too. CoolingHeating North Atlantic Equator Evap. Sea Ice