IMS 7 - Water & Seawater

Properties of water

-          Chemical recombination restricted by surrounding hydrogen molecules

-          Ice density 0.9170 g/cm³ is ~8% lesser than liquid water

-          Salinity lowers freezing point, salt interferes ordered crystal rearrangement

-          35‰ salinity with freezing point -1.91°C

-          Seawater contains dissolved substance

Salinity

-          Total solid material dissolved, including dissolved gases, excluding suspended fine particles

Seawater constituents

-          70 elements, 6 major elements make 99%: Na, CI, SO₄, Mg, Ca, K

Salt Ion	Ions in Seawater (‰)	Ions by Weight (%)	Cumulative (%)
Chloride (Cl-)	18.980	55.04	55.04
Sodium (Na+)	10.556	30.61	85.65
Sulfate (SO42-)	2.649	7.68	93.33
Magnesium (Mg2+)	1.272	3.69	97.02
Calcium (Ca2+)	0.400	1.16	98.18
Potassium (K+)	0.380	1.10	99.28
Bicarbonate (HCO3-)	0.140	0.41	99.69
Bromide (Br-)	0.065	0.19	99.88
Boric Acid (H3BO3)	0.026	0.07	99.95
Strontium (Sr2+)	0.013	0.04	99.99
Fluoride (F-)	0.001	0.00	99.99
Total	34.482	99.99	99.99

Trace Elements

• -          0.001‰; 1ppm
• -          manganese (Mn), lead (Pb), gold (Au), iron (Fe), iodine (I)

Seawater composition

• -          Dissolved gases, Nutrient (N, Si, P), Organic compounds (fat, protein, carbohydrate)
• -          NO₃^- and PO₄^3- utilized by photosynthesizers
• -          Biological uptake & release, non-conservative (highly varied [con])

Non-conservative

• -          Seawater dissolved substances tied to biological/seasonal/geological cycles (short Residence Times)

Residence Times

• -          Avr. time a substance remains in specified region of space

Salinity variation

• -          Avr. 33 – 38ppt
• -          Baltic Sea 10ppt
• -          Red Sea & Persian Gulf 42ppt
• -          Dead Sea 330ppt (hypersaline inland lake)
• -          Great Salt Lake, Utah 280ppt (hypersaline inland lake)

Salinity Determination

• -          Evaporate weight amount of seawater & weigh salt
• -          Ocean well-mixed; Exact same proportion of major dissolved constituents everywhere
• -          550.4‰ chlorinity; easy to measure
• -          Salinity (‰) = 1.80655 x Chlorinity (‰) or conductivity

Conductivity

• -          Measures strength of nutrient solution

Processes Decreasing Salinity

-          Precipitation

-          Runoff

-          Melting icebergs

-          Melting sea ice

Salinity regulator

• -          River bring dissolved salts 2.5 – 4.5 x 10¹⁵ g/yr
• -          Atmospheric volcanic gas & hydrothermal circulation release cations (Ca²⁺ , K⁺) and anions (SO₄^2-, Cl^-)

Chemical equilibrium factors

• -          Chemical precipitation & evaporite minerals (CaCO₃, NaCl, CaSO₄)

-          Evaporation & supersaturation

• -          Marine aerosols

-          Salt coatings nearshore

• -          Ion Adsorption by clay minerals (authigenic mineral formation)

-          Al, Fe, Mg

• -          Biological precipitation

-          Hard part secretion (Ca²⁺, Sr²⁺), Eg: shells

• -          Drawn into mantle & subduction zone

Gas	Dry Air (%)	Surface Ocean (%)
Nitrogen (N2)	78.03	47.5
Oxygen (O2)	20.99	36.0
Carbon Dioxide (CO2)	0.03	15.1
Hydrogen (H2)	Trace	Trace
Argon (Ar)	Trace	Trace
Neon (Ne)	Trace	Trace
Helium (He)	0.95	1.4

CO₂ + H₂O + Light » CH₂O + O₂  (Photosynthesis)
CH₂O + O₂ » CO₂ + H₂O + Energy (Respiration)

-          Gas diffusion across air-sea interface & planktonic photosynthesis (high 0₂)

-          Organic matter accumulation, feeding organism respiration, bacterial decomposition (Low 0₂)

-          Low BOD, cold gas-saturated water, hydrothermal vent (Increasing 0₂)

pH = - log₁₀ [H⁺]

Seawater as Buffer (pH 8)

-          CO₂ + H₂O à H₂CO₃ (Mostly)

-          H₂CO₃ à H⁺ + HCO₃^- (Bicarbonate – further dissociation)

-          HCO₃^- à H⁺ + CO₃^2- (Carbonate – further dissociation)

-          CO₃^2- + Ca²⁺ --> CaCO₃