Seawater Chemistry. Components of Seawater water’s ability to dissolve crustal material as it...
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Seawater Chemistry. Components of Seawater water’s ability to dissolve crustal material as it cycles from ocean to atmosphere have added solids and gases
Components of Seawater waters ability to dissolve crustal
material as it cycles from ocean to atmosphere have added solids
and gases to the ocean ~97.2% of 1,370 million cubic kilometers
(329 million cubic miles) is salt
Slide 3
Components of Seawater by mass seawater about 96.5% water about
3.5% dissolved substances if the oceans waters could evaporate,
remaining salts would cover the entire planet to a depth of 45 m
(150 ft)
Slide 4
Slide 5
Salinity The total quantity (concentration) of dissolved
inorganic solids in water About 3.5-3.7% by mass in oceans Average
~3.5% or 35 ppt or 35 % 0
Slide 6
How do ions modify the physical properties of water? Heat
capacity decreases with increased salinity Less heat is needed to
raise the temperature of seawater
Slide 7
How do ions modify the physical properties of water? As
salinity increases, the freezing point of water decreases Dissolved
salts disrupt hydrogen bonding Sea ice forms at a lower temperature
than freshwater ice
Slide 8
How do ions modify the physical properties of water? Seawater
evaporates more slowly than fresh water Dissolved salts attract
water molecules Osmotic pressure increases with increasing
salinity
Slide 9
Components of Seawater About 3.5% of seawater consists of
dissolved substances Boiling 100 kg of seawater yields 3.5
kilograms of residue Oceanographers use parts per thousand (o/oo)
or ppt
Slide 10
Major Constituents of Seawater Nearly every element present in
the crust & atmosphere is also in oceans Water96.5% total
percent by mass Oxygen85.8%(by mass) Hydrogen10.7% Ions 3.4% total
percent by mass
Slide 11
Major Constituents of Seawater at 34.4 ppt Over 99% of seawater
salinity comes from 6 ions: Chloride55% Sodium32% Sulfate 8%
Magnesium 3% Calcium 1% Potassium 1%
Slide 12
Slide 13
Sources of Oceans Salts Weathering and erosion of crustal rocks
accounts for some (not the only source) Salts in the ocean are
different concentration than those in river water
Slide 14
Sources of Oceans Salts Upper mantle appears to contain more of
the substances found in seawater (including water itself) than are
found in surface rocks their proportions are about the same as in
the ocean
Slide 15
Sources of Oceans Salts Combination of weathering (ex, sodium)
and outgassing (ex, chloride) Differences in expected seawater
concentrations may be the result of interactions at mid ocean rifts
(hydrothermal vents) All the water in the oceans cycles through the
seabed every 1 to 10 million years
Slide 16
Slide 17
Slide 18
Principle of Constant Proportions The percentage of salts in
seawater is the same in samples from many places, regardless of how
salty the water is Same proportions for 33 ppt and 37 ppt
Slide 19
The Ocean is in Chemical Equilibrium The proportion and amounts
of dissolved salts per unit volume are nearly constant what goes in
must go out
Slide 20
The Ocean is in Chemical Equilibrium Ions are added to the
ocean at the same rate the are removed Additions from the mantle or
from weathering are balanced by subtractions being bound into
sediments
Slide 21
Residence Time Concept of helps explain why ocean is not
getting saltier Chemically active ions have shorter residence times
See Table 7.3 page 169 (Oceanography book) If an ion remains in the
ocean longer than the oceans mixing time (~1600 years) it becomes
evenly distributed
Slide 22
Slide 23
Dissolved Gases Seawater also contains dissolved gases Most
gases in the air dissolve readily in seawater at the surface Plants
and animals need dissolved gases to survive
Slide 24
Dissolved Gases Major gases nitrogen, oxygen & carbon
dioxide Gases dissolve better in cold water Cold polar water
contains more gases that warm tropical water
Slide 25
Dissolved Gases Nitrogen 48% of the gases in ocean (78% in
atmosphere) Source diffusion of atmospheric nitrogen Upper layers
saturated with nitrogen gas
Slide 26
Dissolved Gases Living organisms require nitrogen to build
proteins Nitrogen gas cant be used by organisms until it is
attached to oxygen in a process called nitrogen fixation Blue-green
algae convert nitrogen gas to a useable form that animals need for
building proteins and amino acids
Slide 27
Dissolved Gases Oxygen 36% of the gases in the ocean (21% in
atmosphere) Average of 6 ppm (6 mg/L) Source photosynthesis and
diffusion of atmospheric oxygen Living organisms require oxygen for
respiration