Transcript 103-20a-ChemicalCompositionSeawater

CHEMICAL COMPOSITION
OF
SEAWATER
GEOL 1033
(Lessons 22-23, 25, and parts of Lesson 24)
(ppt file 103-20a)
Chemical Oceanography
• Chemical oceanographers are interested in
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Composition of seawater
Distribution of chemical elements (How they vary)
Causes of these distributions
Chemical reactions in the oceans
Chemical cycles, e. g., carbon cycle, nitrogen cycle, etc.
Use of chemistry to solve problems in oceanography
Involved in biochemical and geochemical investigations
Etc.
• Need:
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Water sampling devices
Storage for water samples
Techniques to detect & measure elements, etc.
Measurements of certain physical properties of seawater, too
Etc.
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A Water sampling Device
Must be large enough (amount varies with what measuring)
Locatable as to depth
No contamination – stainless steel, teflon, etc.
Nansen bottle
– Vertical & open at both ends until triggered with a messenger
– Thermometers for temperature and depth determinations
Rosette
• A rosette permits collecting
many water samples
• Nansen-like bottles are
electronically triggered
• Records other information
at same time:
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Temperature
Depth
Salinity
O2 probe
Suspended particulate matter
(laser nephelometer
determines light scattering
and converts measurements to
concentrations)
Storage
• Water libraries
– Water samples are stored in large containers
– May be cooled
– Available to members of the scientific community
WATER DISTRIBUTION ON EARTH'S SURFACE
• ~98% of Earth's surface and near-surface water is in the
oceans as liquid or sea ice (1.37 x 109 km3)
• ~97-98% of this water is saline.
• Remember: Frozen seawater excludes salts, leaves a cold
brine as a residue, and forms freshwater when it melts.
• Average salinity is about 34.482 o/oo (=34.482 g/kg)
Water Molecule – A Polar Molecule
Hydrogen Bonds in Liquid Water
• Forms
"structured
water"
What is the Source of the Water in the Oceans?
• Volcanic outgassing from the mantle early in Earth
history?
– 72% of volcanic gases is water vapour today!
• Cosmogenic?
– Many small comets strike Earth’s upper atmosphere per year
– Would have been much more frequent in the distant past about
4 billion years ago
• Why has the volume remained nearly constant for about
4 billion years?
– Plate tectonic recycling between Earth's surface and its mantle
may have established a dynamic equilibrium.
Generalized Periodic Table of the Elements
What are the
major elements
in sea salt?
Seawater Salt = Mostly Sodium Chloride
Salt in Aqueous Solution
WHAT ARE THE OTHER MAJOR ELEMENTS
IN SEA SALT?
ELEMENT ABUNDANCE IN THE CRUST
• Abundance of elements in the crust by percentage weight:
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Oxygen
Silicon
Aluminum
Iron
Calcium
Sodium
Potassium
Magnesium
all others
O
Si
Al
Fe
Ca
Na
K
Mg
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1.5
Constituents of Seawater
• 96.5% water (96.5% = 965 ppt)
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Chloride
Sodium
Sulfate
Magnesium
Calcium
Potassium
• Bicarbonate
Constituents of Seawater
• Parts per thousand = ppt
Constituents of Seawater
• Major ions = ppt
• Minor components =
ppm
• Trace elements = ppb
What is the Source of the Salts in Seawater?
• Weathering and erosion on land provides many ions, e.g., sodium,
calcium, potassium, etc.
• Hydrologic cycle carries these ions to the sea
• Volcanic outgassing from the mantle provides many ions, e. g.,
chloride.
River Water vs. Seawater Constituents
• Many ions are in river water, but in much lower
amounts & in different proportions
trace
trace
trace
Residence Time
• Residence times
help to explain
why some ions
are more
abundant than
others
END OF FILE
• Unit = mL/L
• At 1 atm at sea level
• STP = standard temperature & pressure
ELEMENT ABUNDANCE IN THE CRUST and WHOLE EARTH
• Abundance of elements in the crust by percentage weight:
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Oxygen
Silicon
Aluminum
Iron
Calcium
Sodium
Potassium
Magnesium
all others
O
Si
Al
Fe
Ca
Na
K
Mg
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3.6
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• Whole Earth order of abundance:
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Iron
Oxygen
Silicon
Magnesium
Nickel
Sulfur
Calcium
Aluminum
all others
Fe
O
Si
Mg
Ni
S
Ca
Al
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<1
CHARACTERISTICS OF THE WORLD OCEAN
• Oceans cover 71% of Earth's surface (This is equal to
about 361 100 000 km2 or 3.611 x 108 km2)
• Oceans represent about 98% of Earth's surface and
near-surface water (1.37 x 109 km3)
• Average depth of the oceans is about 3.8 km (~12,450').
• Average temperature of the oceans is about 4 deg. C.
• Average salinity is about 34.482 o/oo (=34.482 g/kg)
HEAT CAPACITY OF COMMON MATERIALS
CROSS SECTIONS OF EARTH
• Core (2 layers)
• Mantle (3 layers)
• Crust (2 types)
Outer core is liquid
CROSS SECTIONS OF EARTH
Upper mantle/crustal layers:
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lithosphere
asthenosphere
upper mesosphere
OVERVIEW OF PLATE TECTONIC PROCESSES
Thermal Convection