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Ocean Water. Salts and Gases. The Dissolving Power of Water. Dissolving power results from polar nature of H 2 O molecule. Na + and Cl - are held together by ionic bonds (attraction of opposite charges). H 2 O reduces the ionic bonding and pulls Na + and Cl - apart.

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ocean water

Ocean Water

Salts and Gases

the dissolving power of water
The Dissolving Power of Water
  • Dissolving power results from polar nature of H2O molecule
  • Na+ and Cl- are held together by ionic bonds (attraction of opposite charges)
  • H2O reduces the ionic bonding and pulls Na+ and Cl- apart
salinity in oceans
Salinity in Oceans
  • Salinity
  • Total amount of dissolved solids expressed in grams in 1 kg of water
  • Average salinity in oceans = 35 ‰
  • 35 parts per thousand (ppt)
  • 35 g/kg
  • Salinity variations
  • Due to differences in local rates of evaporation and precipitation (water budget)
constituents of sea water
Constituents of Sea Water
  • Most abundant seawater elements are sodium (Na+) + chloride (Cl-)
  • Major constituents: SO42-,Mg2+, Ca2+, K+, and HCO3-
  • Minor and trace elements also present
salts in the ocean
Salts in the Ocean

Why is the ocean salty?

  • Salts come from:
  • Rocks = cations
  • Gases from mantle
  • Why is the ocean not getting saltier?
  • Salts going in = salts going out
salts going out
Salts Going Out
  • Sea Sra
  • Sea Spray
  • Evaporites
  • Biological
    • Fecal pellets
    • Shell formation
  • Adsorption
  • Mid-ocean ridge magma
principle of constant proportions
Principle of Constant Proportions
  • The amount of salt varies, but the relative proportions of ions are constant
  • Because of this principle, it is necessary to test for 1 salt ion (usually Cl) to determine total amount of salt present
determining salinity
Determining Salinity

1. Calculating Salinity

  • Salinity=1.8065 x chlorinity (‰)

2. Salinometers

Cl-

Na+

  • Salinity determined by the electrical conductivity produced by dissolved salts

Deionized water

with salt

factors affecting salinity
Factors Affecting Salinity
  • Precipitation
  • Evaporation
  • Run off
  • Freezing
residence times
Residence Times
  • Average length in time that a substance remains in solution in seawater
  • Ions with longer residence times are most abundant in ocean
effects of salinity
Effects of Salinity
  • Freezing point depression; boiling point elevation
  • Disrupts Hydrogen bonding

(freezing point of seawater =-2°C)

2. Changes density

  • Pure water density = 1 kg/l
  • Seawater density = 1.024 kg/l

3. Changes vapor pressure

  • ↑ ‰, ↑ P
desalination
Desalination
  • Fresh H20 from Salt H20
  • Methods
  • Distillation
  • Electrodialysis
  • Reverse Osmosis
gases in seawater
Gases in Seawater
  • Major Gases: N2, O2 and CO2
  • O2 and CO2 important for life processes
co 2 and o 2 with depth
CO2 and O2 with depth
  • Surface (0m)
  • Oxygen (O2) abundant gas
  • Photosynthesis dominant
  • ~ 200m - ~1,000m
  • Oxygen (O2) ↓
  • Carbon Dioxide (CO2) ↑
  • Respiration dominant
  • Organic matter decay
  • 1,000m – 4,000m
  • O2↑ slightly
  • Oxygenated bottom waters
  • Cold salty oxygenated H2O sinks in polar region transported to depth
  • CO2continues to ↑
  • Organic matter decay
gases summary
GasesSummary
  • Photosynthesis
  • CO2 consumed; O2 produced
  • Therefore, O2 more abundant than CO2 in photic zone
  • Respiration
  • O2 consumed; CO2 produced
  • Organic matter (OM) decay
  • O2 consumed; CO2 produced
  • Respiration and OM decay
    • = ↑ CO2 below photic zone
the ph scale
The pH Scale
  • An acid has excess [H+] (Hydrogen ions)
  • A base has excess [OH-] (Hydroxyl ions)
  • CO2 controls acidity
  • ↑ CO2 = ↑ acidity
  • ↓ CO2 = ↓ acidity

pH of seawater = 7.5-8.5; Average = 7.8

gases in seawater carbonate buffering system
Gases in SeawaterCarbonate Buffering System
  • Dissolved CO2 in water acts as a buffer
  • Prevents large shifts in pH
  • Seawater too basic:
    • H2CO3 HCO3- + H+ (pH drops)
  • Seawater too acidic:
    • HCO3- + H+ H2CO3 (pH rises)
gas cycling
Gas Cycling
  • Photosynthesis produce O2
  • Respiration & decomposition of O.M. use O2
  • O.M. buried doesn’t consume all O2
  • Rocks consume O2
  • O2 Cycling
  • CO2 Cycling
  • Organisms use CO2 for tissue
  • Decay of organic matter releases CO2 back to ocean
nutrients and organics
Nutrients and Organics
  • Required for plant growth
  • Cycled by plant growth and decay
  • Organics used by organism or buried
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