Chapter 6: Water and Seawater Fig. 6-19. Atomic structure Nucleus Protons and neutrons Electrons...
Transcript of Chapter 6: Water and Seawater Fig. 6-19. Atomic structure Nucleus Protons and neutrons Electrons...
Chapter 6: Water and Seawater
Fig. 6-19
Atomic structure
Nucleus Protons and neutrons Electrons Ions are charged atoms
Water molecule
H2O Two hydrogen, one oxygen Bonded by sharing electrons Bend in geometry creates
polarity Dipolar molecule
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
Fig. 6-3
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
Fig. 6.4
Fig. 6-5b
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
Fig. 6-7
Heat capacity
Heat absorbed or released with changes in state
Latent heats of Melting; freezing Vaporization, evaporation Condensation
Global thermostatic effects
Moderate global temperature Evaporation removes heat
from oceans Condensation adds heat to
atmosphere Heat re-distributed globally
Differences in day and night temperatures
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
Fig. 6-10
Fig. 6-8
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
Measuring salinity
Evaporation Chemical analysis
Principle of Constant Proportions
Chlorinity Electrical conductivity
(salinometer)
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
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
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
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
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
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
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
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
Fig. 6-17
How salinity changes
Salinity changes by adding or removing water
Salinity decreases by Precipitation (rain/snow) River runoff Melting snow
Salinity increases by Evaporation Formation of sea ice
Hydrologic cycle describes recycling of water
Hydrologic cycleFig. 6-19
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
Fig. 6-20
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
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
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
Layers of ocean
Mixed surface layer
Pycnocline Deep ocean
End of Chapter 6: Water and Seawater