Download - Ocean, water and Seawater Oceanography
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Chapter 6: Water and Seawater
Fig. 6-19
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Atomic structure Nucleus Protons and neutrons Electrons Ions are charged atoms
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Water molecule H2O Two hydrogen, one oxygen Bonded by sharing electrons Bend in geometry creates polarity Dipolar molecule
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Dipolar molecule Weak negative charge at O end Weak positive charge at H end Hydrogen bonds Weak bonds between water molecules and ions Explains unusual properties of water
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Fig. 6-3
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Two unusual properties High surface tension
Hydrogen bonding creates “skin” Important for living organisms
Capillarity Universal solvent
Electrostatic bond between dipolar water and ions
Ocean is salty
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Fig. 6.4
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Fig. 6-5b
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Thermal properties of water Solid, liquid, gas on Earth’s surface Water has high freezing point Water has high boiling point Water has high heat capacity Water has high latent heats
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Fig. 6-7
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Heat capacity Heat absorbed or released with
changes in state Latent heats of
Melting; freezing Vaporization, evaporation Condensation
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Global thermostatic effects Moderate global temperature Evaporation removes heat from
oceans Condensation adds heat to
atmosphere Heat re-distributed globally
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Differences in day and night temperatures
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Water density Maximum density at 4oC Ice less dense than liquid water
Atomic structure of ice Ice floats
Increased salinity decreases temperature of maximum density
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Fig. 6-10
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Fig. 6-8
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Seawater Salinity=total amount of solid material
dissolved in water (g/1000g) Typical salinity is 35 o/oo or ppt Brackish (hyposaline) < 33 ppt Hypersaline > 38 ppt
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Measuring salinity Evaporation Chemical analysis
Principle of Constant Proportions Chlorinity
Electrical conductivity (salinometer)
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Dissolved substances Added to oceans
River input (primarily) Circulation through mid-ocean ridges
Removed from oceans Salt spray Recycling through mid-ocean ridges Biogenic sediments (hard parts and fecal pellets) Evaporites
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Residence time Average length of time a substance remains dissolved in
seawater Long residence time = unreactive
Higher concentration in seawater Short residence time = reactive
Smaller concentration in seawater Steady state
Ocean salinity nearly constant through time
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Dissolved gases Solubility depends on temperature, pressure, and ability
of gas to escape Gases diffuse from atmosphere to ocean
Wave agitation increases amount of gas Cooler seawater holds more gas Deeper seawater holds more gas
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Conservative vs. nonconservative constituents
Conservative constituents change slowly through time Major ions in seawater
Nonconservative constituents change quickly due to biological and chemical processes Gases in seawater
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Oxygen and carbon dioxide in seawater Nonconservative O2 high in surface ocean due to
photosynthesis O2 low below photic zone because of
decomposition O2 high in deep ocean because source is
polar (very cold) ocean
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CO2 low in surface ocean due to photosynthesis
CO2 higher below photic zone because of decomposition
Deeper seawater high CO2 due to source region and decomposition
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Acidity and alkalinity Acid releases H+ when dissolved in water Alkaline (or base) releases OH- pH scale measures acidity/alkalinity
Low pH value, acid High pH value, alkaline (basic) pH 7 = neutral
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Carbonate buffering Keeps ocean pH about same (8.1) pH too high, carbonic acid releases H+ pH too low, bicarbonate combines with
H+ Precipitation/dissolution of calcium
carbonate CaCO3 buffers ocean pH Oceans can absorb CO2 from
atmosphere without much change in pH
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Fig. 6-17
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How salinity changes Salinity changes by adding or removing
water Salinity decreases by
Precipitation (rain/snow) River runoff Melting snow
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Salinity increases by Evaporation Formation of sea ice
Hydrologic cycle describes recycling of water
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Hydrologic cycleFig. 6-19
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Horizontal variations of salinity Polar regions: salinity is lower, lots of
rain/snow and runoff Mid-latitudes: salinity is high, high rate of
evaporation Equator: salinity is lower, lots of rain Thus, salinity at surface varies primarily with
latitude
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Fig. 6-20
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Vertical variations of salinity Surface ocean salinity is variable Deeper ocean salinity is nearly the same
(polar source regions for deeper ocean water)
Halocline, rapid change of salinity with depth
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Density of seawater 1.022 to 1.030 g/cm3
Ocean layered according to density Density of seawater controlled by temperature,
salinity, and pressure Most important influence is temperature Density increases with decreasing temperature
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Salinity greatest influence on density in polar oceans
Pycnocline, rapid change of density with depth
Thermocline, rapid change of temperature with depth
Polar ocean is isothermal
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Layers of ocean Mixed surface
layer Pycnocline Deep ocean
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End of Chapter 6: Water and Seawater