Download Midterm Exam II

Midterm Exam II
October 28, 2:10 – 3:25 pm, HW714
Guide to study: answer the questions from the
Concept Check (CC) boxes in textbook:
¾ Chapters 4 (4.13 – 4.18), 5, 6 and part of 7
¾ 60 multiple choice questions
¾ this exam constitutes 22% (only) of your total (overall)
grade
Remember to bring pencils!!! (No. 2) and to follow the
instructions about writing your names on both exam and
answer sheets, as well as to ‘bubble’ your names (no IDs!) on
the appropriate place of the answer sheet (on the back).
Chapter 4: 13, 14,17, 19 and 20.
Chapter 5: 1, 2, 3, 4, 7 through 12, 13, 16 through 21.
Chapter 6: 1, 2, 3, 4, 5 through 11, 16, 17, 18, 19, 27, 28, and
29.
Chapter 7: 1, 2, 3, 4, 6, 6, 8, 9, 10.
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Chapter 4 – Ocean Basins
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Basins Æ
Features of the Sea floor
sections of the abyssal plain separated
by continental margins, ridges, and rises.
Oceanic Ridges
Hydrothermal Vents
Abyssal Plains and Abyssal Hills
Seamounts and Guyots
Trenches and Island Arcs
Seafloor:
Seafloor: 4000 – 6000 m water depth, 30% of the
Earth’
Earth’s surface
Abyssal Plain: vast, flat plain extending from the base of
the continental slope.
Ocean Basins: sections of the abyssal plain separated by
continental margins, ridges, and rises.
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Sea floor features
FlatFlat-topped seamounts eroded by
wave action are called guyots.
guyots.
Seamounts are volcanic projections from the ocean floor that do not
rise above sea level. FlatFlat-topped seamounts eroded by wave action are
called guyots
Abyssal hills are small, extinct volcanoes or
rock intrusions near the oceanic ridges.
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Abyssal hills are flat areas of sedimentsediment-covered ocean floor found
between the continental margins and oceanic ridges. Abyssal hills are
small, extinct volcanoes or rock intrusions near the oceanic ridges.
ridges.
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MidMid-Ocean Ridges and Rises
Hydrothermal vents are sites where superheated water containing
dissolved minerals and gases escapes through fissures, or vents. Cool
water (blue arrows) is heated as it descends toward the hot magma
magma
chamber, leaching sulfur, iron, copper, zinc, and other materials
materials from
the surrounding rocks. The heated water (red arrows) returning to
to
the surface carries these elements upward, discharging them at
hydrothermal springs on the seafloor.
An oceanic ridge is a mountainous chain of young,
basaltic rock at an active spreading center of an ocean.
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Major ocean trenches
Island Arcs
There are two ways in which a group of islands can form.
1) As a lithospheric slab is being subducted, the slab melts when the
edges reach a depth which is sufficiently hot. Hot, remelted
material from the subducting slab rises and leaks into the crust,
forming a series of volcanoes. These volcanoes can make a chain of
islands called an "island arc". Examples of island arcs are the
Japanese islands, the Kuril Islands, and the Aleutian Islands of
Alaska, shown here.
Trenches are arcarc-shaped depressions in the ocean floor caused by the
subduction of a converging ocean plate.
Most trenches are around the edges of the active Pacific. Trenches
Trenches are the
deepest places in Earth’
Earth’s crust, 3 to 6 kilometers (1.9 to 3.7 miles) deeper than
the adjacent basin floor. The ocean’
ocean’s greatest depth is the Mariana Trench
where the depth reaches 11,022 meters (36,163 miles) below sea level.
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level.
2) The second way in which islands are formed is via plumes or hot
spots in the lithosphere. The Hawaiian Islands are an example of this
type of island formation. In this case, there is no associated subducting
slab.
Island Arcs are formed on the opposing edge of a subducted slab.
For each case, there is an associated subducting slab and a trench.
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Chapter 4 - Summary
• Seafloor features result from a combination of
tectonic activity and the processes of erosion and
deposition.
• The submerged outer edge of a continent is called
the continental margin. The deepdeep-sea floor beyond
the continental margin is called the ocean basin
• Features of the deepdeep-ocean basins include oceanic
ridges, hydrothermal vents, abyssal plains and hills,
seamounts, guyots,
guyots, trenches, and island arcs.
Formation of a volcanic island chain as an oceanic plate moves over a
stationary mantle plume and hot spot. In this example, showing the
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formation of the Hawai’ian Islands, Loihi is such a newly forming island.
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Study of Sediments is important to
oceanography because:
Chapter 5 - Sediments
ƒ Distribution of sediments on the sea
floor
ƒ Seabed Resources
1. Sediments and volcanism are the most
important agents of physical change on the
deep-ocean floor
Sediments are particles of organic or inorganic matter
2. Study o sediments is important to ocean’s
chemistry, morphology and history as well
as to Earth’s climate (paleoclimate)
that accumulate in a loose, unconsolidated form.
Record of geologic/oceanographic history
The position and nature of sediments provide important
clues to Earth's recent history, and valuable resources can
sometimes be recovered from them.
ƒ Types (Classification)
ƒ Location or distribution of sediments
ƒ Rates of Deposits/Accumulation
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Sediment Classification
The Sediment Cycle.
Over geological time,
mountains rise as
lithospheric (crustal)
plates collide, fuse, and
subduct. Water and wind
erode the mountains and
transport resulting
sediment to the sea. The
sediments are deposited
on the seafloor, where
they travel with the plate
and are either uplifted or
subducted. Thus, the
material is eventually
made into mountains again.
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* according to particle size
Large (L)
Medium (M)
Small (S)
How far sediments go horizontally and how long it takes to get to
bottom of sea depends on size. Shape is also important to how
sediments go around and settle in the bottom.
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Sediment Classification
* according to location – where sediment is found
Neritic: near continental
margins & islands – contains
mainly terrigenous
sediments
Pelagic: deep sea floor – can
contain a larger amount of
biogenous sediments.
* according to source and chemistry
Type
Terrigenous (Lithogenous) Æ
Biogenous Æ
Hydrogenous Æ
Cosmogenous Æ
Source
pre-existing rock (land derived material)
living organisms
precipitation from sea water
space
Review information
in these two tables
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Compare:
Rates of Sedimentation
Continental Margin: rapid, neritic sediments
Major Rivers:
Bays:
Ganges, Yangtse,
Yangtse, Yellow, Brahmaputra
8 m/yr
¼ of all land derived sediment
•
1. Rivers 800,000 cm/1000 years
2. Bays
500 cm/1000 years
3. Shelf
40 cm/1000 years
500 cm/ 1000 years (0.5 cm/yr)
Shelf/Slope:
Neritic Sediments
10 – 40 cm/ 1000 years
Ocean Basins: slow, pelagic sediments
0.5 – 1.0 cm/ 1000 years
Average Accumulation 500 – 600 m
(during geological history, in about 100 my)
Thickness depends on age
Oldest sea floor is 200 million years
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•
Pelagic Sediments
1 cm/1000 years!
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Lithogenous
Biogenous
From rocks, wood, waste sludge, volcanic stuff
Oozes – sediment containing at least 30% biogenous
material. Dominant on deep-ocean floor, 2 types of oozes:
Results from erosion by air & water Transported by
winds, water, ice and gravity. Also by glaciers and
icebergs
Neritic or pelagic – dominates the neritic sediments
because it is the largest source for these
Pelagic lithogenous sediments Æ abyssal clay (about
75% of clay), very slow accumulation, rich in Fe Æ
red clay
* Calcareous (CaCo3) oozes
formed by organisms which contain calcium
carbonate in their shells or skeletons – dominant
pelagic sediment (cocolithophorids, pteropods, foraminifera)
* Siliceous (SiO2) oozes
formed by organisms that contain silica in their
shells. Diatoms are one type of organism whose
remains contribute to siliceous oozes. The ocean is
under-saturated with respect to Si, so it can
dissolve everywhere.
(large contribution from photosynthetic organisms)
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Hydrogenous
Calcareous Oozes
Originate from chemical reactions with water that occur in
the existing sediment. Hydrogenous sediments are often
found in the form of nodules containing manganese and iron
oxides. Hydrogenous sediments can be:
CCD (~4500 meters) depth where rate of dissolution of calcium
carbonate is equals to its rate of accumulation
Carbonates
Æ direct deposition
Phosphorites
Æ abundant in continental shelf
Salts Æ by evaporation
Evaporites - salts that precipitate as evaporation occurs.
Evaporites include many salts with economic importance.
Evaporites currently form in the Gulf of California, the Red Sea,
and the Persian Gulf
Manganese nodules Æ Mn, Fe, Cu, Ni, Co. These are found in abyssal
seafloor and continental margins, around ocean ridges and
seamounts (but at higher concentrations than those found on
land). The Co (cobalt) content is of strategic importance to US
(used in aircraft’s manufacture).
The line shows the calcium carbonate (CaCO3) compensation depth (CCD). At
this depth, usually about 4,500 meters (14,800 feet – about the height of
some of the peaks in the Colorado Rocky Mountains, known as ‘the fourteeners’ ), the rate at which calcareous sediments accumulate equals the rate at
which those sediments dissolve.
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Distribution of sediments is determined by climate
(temperature), environmental factors (nutrients, possible
chemical reactions, activity of physical environment), supply,
size and rate of accumulation.
Map of distribution of sediment
Recall (from Chapter 4) that turbidity currents can deposit
Turbidites – Where would you expect to find turbidites?
• Terrigenous sediments are deposited along the coastal boundaries
• 75% of marine sediments are from land – coarser sediments closer to coasts
and finer sediments at farther distances offshore
• Higher latitudes – coarser sediments; lower latitudes – finer sediments
• At higher latitudes rafting by glaciers and ice contribute significant amounts
of sediments from land (coarse)
• Red clay (fine, pelagic lithogenous) found where there is not much of anything
else – deep ocean basins
• Calcareous are not found in deep-sea areas below 4500 m or where ocean
primary productivity is low. Fund in warm, tropical latitudes, shallow areas
(Caribbean), elevated ridges and seamounts
The general pattern of sediments on the ocean floor. Note the
dominance of diatom oozes at high latitudes.
What differences in the type and distribution of sediments do you
note between the Atlantic Ocean and the Pacific Ocean?
• Siliceous (photosynthesis) found below areas of very high biological
productivity - abound in areas of N. Pacific and Antarctic Ocean: cold but
nutrients and sun light good for photosynthesis.
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Chapter 5 – Sediments - Summary
Resources
Sediment is particles of organic or inorganic matter that accumulate in a
loose, unconsolidated form. Sediment may be classified by grain size of by
the origin of the majority of the particles.
Sand and Gravel Æ construction
Phosphorite Æ fertilizers
Sulfur Æ sulfuric acid for industry
Coal Æ energy
Oil and Gas Æ energy, transportation
(20(20-25% of US production comes from
offshore areas)
ƒ Maganese Nodules Æ Mn,
Mn, Fe, Co, Cu, Ni
ƒ Gas Hydrates Æ energy in the future?
ƒ
ƒ
ƒ
ƒ
ƒ
Marine sediments are broadly classified by origin into four categories:
(a)Terrigenous sediments are materials that originate from rocks on land
and arise on the continents or islands near them; they are the most
abundant. (b) Biogenous sediments are of biological origin. (c)
Hydrogenous sediments are formed directly from seawater. (d) Of less
importance are cosmogenous sediments, which come from space.
Though there are exceptions, the sediments of continental margins tend
to be mostly terrigenous, whereas the generally finer sediments of the
deep-ocean floor contain a larger proportion of biogenous material.
Deep sea oozes (calcareous and siliceous) form of biogenous sediment:
remains of some of the ocean's most abundant and important organisms.
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Sediment deposited on a quiet seabed can provide a sequential record of
events in the water column above. In a sense sediments act as the recent
memory of the ocean. The memory does not extend past about 200 million
years because seabeds are relatively young and recycled into Earth at
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subduction zones.
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ƒA molecule is a group of atoms held together by chemical bonds.
ƒ Water is a polar molecule, having a positive and a negative side.
Chapter 6
Water and Ocean Structure
H2O
Some basic concepts:
• Covalent bonds: shared pairs of electrons
• Hydrogen bonds: bonds between water molecules due
to polar structure
Compounds – substances that contain two or more
different elements in fixed proportions
Element – a substance composed of identical particles
that cannot be chemically broken down into simpler
substances
Atoms – the particles that make up elements
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Temperature, Heat, Heat Capacity, Calories
Hydrogen Bonds
Temperature
ƒ Measure of av. kinetic
energy (motion) of
molecules (KE=1/2mv2)
ƒ unit is degrees C, F or K
(Kelvin)
Hydrogen bonds form when the
positive end of one water molecule
bonds to the negative end of
another water molecule.
Heat
ƒ Measure of the total kinetic
energy of the molecules in a
substance
ƒ Unit is the calorie
Two important properties of water
molecules:
* Heat Capacity = is a measure of the heat required to raise
the temperature of 1g of a substance by 1°C.
Cohesion – the ability of water
molecules to stick to each other,
creating surface tension.
* Calorie = amount of heat to raise temperature of 1 gram
of pure water by 1°C (from 14.5 °C to 15.5 °C)
Adhesion – the tendency of water
molecules to stick to other
substances
* Latent Heat
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Water has a very high heat capacity, which means it resists
changing temperature when heat is added or removed Æ
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large thermal inertia
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States of matter
The relationship of density and temperature for pure water.
Note that points C and D both represent 0°C (32°F) but different
densities and thus different states of water. Ice floats because the
density of ice is lower than the density of liquid water.
The three common states of matter – solid, liquid, and gas. On Earth,
water can occur in all three states: gas, liquid, and solid.
• A gas is a substance that can expand to fill any empty container.
• A liquid is a substance that
flows freely in response to
unbalanced forces but has a
free upper surface in
container it does not fill.
Liquids compress only slightly
under pressure.
• Gases and liquids are classed
as fluids because both
substances flow easily.
• A solid is a substance that
resists changes of shape or
volume. A solid can typically
withstand stresses without
yielding permanently. A solid
usually breaks suddenly.
Temperature affects
water’s density
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Water Becomes Less Dense When It Freezes
The space taken by 24 water molecules in the solid lattice could be
occupied by 27 water molecules in liquid state, so water expands about
9% as the crystal forms.
Because molecules of liquid water are packed less efficiently, ice is less
dense than liquid water and floats.
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Changes of State-due to addition or loss of heat
(breaks H bonds)
The amount of energy required to break the bonds is termed the latent heat
of vaporization. Water has the highest latent heat of vaporization of any
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known substance.
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Things to remember:
* melting/evaporation requires addition of heat: 80
and 540 calories, respectively.
For 1 gram of H2O
* condensation/freezing release heat to the
environment: 540 and 80 calories, respectively.
Review information on Table 6.2
1. Can have liquid water at 0°C and below
(supercooled water)
2. Can change directly solid to gas - sublimation
3. Can boil water at temperature below 100°C (if
pressure decreases as when at the top of a high
mountain)
4. Evaporation removes heat from Earth’s surface
(it is a cooling mechanism)
5. Condensation in atmosphere releases heat that
will drive Earth’s weather cycle
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Density
ƒ density = mass per unit volume
ƒ measured in grams per cubic centimeters
density of pure water = 1 g/cm3
(determined at ~ 4°
4°C)
ƒ density increases as temperature drops to
4°C and then decreases as temperature goes
to 0°
0°C
ƒ ice is less dense than water
Adding salt to pure water
Æ Seawater
96.5% of pure water and
3.5% dissolved material
Æ Seawater
ƒ salt increases water’
water’s density
density of sea water > density of pure water
~ 1.03 g/cm3 at 4°
4°C
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I. add salt to water and observe
1. decrease freezing point (increase boiling point)
2. not much change in heat capacity & latent heats
3. increase surface tension (cohesion)
4. increase (of course) in density
II. increase temperature and observe
1. decrease in seawater density (very sensitive to T)
2. decrease in surface tension
III. but changes in pressure are mostly ignored by
physical properties of water - seawater is nearly
incompressible
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The Ocean Is Stratified by Density
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Table 6-3, p. 166
The Ocean Is
Stratified into Three
Density Zones by
Temperature and
Salinity
two samples of
water can have
the same density
at different
combinations of
temperature and
salinity!
a.The surface zone or
surface layer or mixed
layer
b.The pycnocline, or
thermocline or halocline
c.The deep ocean (~
80% of the ocean is
below the surface zone
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Fig. 6-17, p. 169
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Sound and light in Seawater
• Sound and light both travel in waves
• Refraction is the bending of waves, which occurs when
waves travel from one medium to another
• Refraction Can Bend the Paths of Light and Sound
through Water
• Light may be absorbed, scattered, reflected,
refracted and attenuated (decrease in intensity over
distance)
• Sunlight does not travel well in the ocean. Scattering
and absorption weaken light
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Sound Travels Much Farther Than Light
in the Ocean
Light
Refraction:
bending of
light due to
change in
density
between air
and water
ƒ Form of electromagnetic
radiation
ƒ Seawater transmits visible
portion of the electromagnetic
spectrum (water transmits blue light more
efficiently than red)
ƒ 60% is absorbed by 1 m depth
ƒ 80% absorbed by 10 m depth
ƒ No light penetration below 1000 m
ƒ Shorter wavelengths (blues) are transmitted to
deeper depths
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The so(sound)f(fixing)a(and)r(ranging) zone
The sofar
layer, in which
sound waves travel
at minimum speed.
On average:
ss in Air = 334 m/s
ss in Water = 1500 m/s
Sound transmission
is particularly
efficient - that is,
sounds can be
heard for great
distances - because
refraction tends to
keep sound waves
within the layer.
ss increases as
temperature and
pressure increase: sound
travels faster in warm
surface waters and then
again in deep (cold)
waters where pressures
are higher
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Chapter 6 – Summary
The shadow zone
Water is a polar chemical compound composed of two hydrogen atoms
and one oxygen atom. Its remarkable thermal properties result from the
large number and relatively great strength of hydrogen bonds between
water molecules.
Heat and temperature are not the same thing. Heat is energy produced
by the random vibration of atoms or molecules. Heat is a measure of how
many molecules are vibrating and how rapidly they are vibrating.
Sound velocity
(m/sec)
0
0
Sound bends up
Maximum
80 sound
velocity
120
200
300
400
Depth (ft)
Depth (m)
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Without water's unique thermal properties, temperatures on Earth's
surface would change dramatically with only minor changes in
atmospheric transparency or solar output. Water acts as a "global
thermostat.”
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Shadow
zone
Sound
bends
down
Water density is greatly influenced by changes in temperature and
salinity. Water masses are usually layered by density, with the densest
(coldest and saltiest) water on or near the ocean floor. Differences in
the density of water masses power deep ocean circulation.
Submarine
Light and sound are affected by the physical properties of water, with
refraction and absorption effects playing important roles
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Fig. 6-25, p. 178
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Ocean Salinity
Chapter 7
Ocean Chemistry
ƒ Salinity is the total quantity of dissolved
inorganic solids in water.
ƒ 3.5% salt on average
ƒ measured in g/kg (ppt
(ppt = parts per thousand)
About solutions and mixtures
A solution is made of two components, with uniform
(meaning ‘the same everywhere’
everywhere’) molecular properties:
Ocean salinities vary in space
The solvent, which is usually a liquid, and is the more
abundant component.
Processes that affect salinity: evaporation,
precipitation, runoff, freezing, and thawing
The solute, often a solid or gas, is the less abundant
component.
And recall that:
The heat capacity of water decreases with increasing salinity
As salinity increases, freezing point decreases
As salinity increases, evaporation slows (boiling point increases)
increases)
A mixture is different from a solution. In a mixture the
components retain separate identities, so it is NOT
uniform throughout.
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A few ions (charged particles) account for most of the
salinity of the oceans.
• Dissolved salts
™ Major constituents and trace elements
™ Conservative/nonconservative constituents
ƒ Major Constituents = [] > 1 part per million
™ Na+
™ Cl™ SO4™ Mg2+
™ Ca2+
™ K+
Sodium
Chloride
Sulfate
Magnesium
Calcium
Potassium
86 %
99 %
ƒ Trace Elements = [] < 1 part per million
See Table 7.2 for minor and trace elements in seawater
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Surface Salinity Northern Hemisphere Summer
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• Dissolved salts
™ Major constituents and trace elements
™ Conservative/nonconservative constituents
ƒ Major Constituents = [] > 1 part per million
™ Na+
™ Cl™ SO4™ Mg2+
™ Ca2+
™ K+
High = high evaporation
Low = coastal regions and high precipitation regions
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Sodium
Chloride
Sulfate
Magnesium
Calcium
Potassium
86 %
ƒ Trace Elements = [] < 1 part per million
99 %
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A few ions (charged particles) account for most of the
salinity of the oceans.
Seawater’
Seawater’s constituents may be conservative or
nonconservative
™ Conservative = concentration changes
only as a result of mixing, diffusion, and
advection
™ NonNon-conservative = concentration
changes as a result of biological or chemical
processes as well as mixing, diffusion, and
advection
See Table 7.2 for minor and trace elements in seawater
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Chapter 7 - Summary
The polar nature of the water molecule is responsible for water's
water's
remarkable ability to dissolve more substances than any other
natural solvent.
The most abundant ions dissolved in seawater are chloride,
sodium, sulfate.
The quantity of dissolved inorganic solids in water is its salinity.
salinity.
Constituents of seawater can be major constituents or trace
constituents.
Seawater’
Seawater’s constituents may be conservative or nonconservative
Ocean salinities vary in space.
Processes that affect salinity: evaporation, precipitation, runoff,
runoff,
freezing, and thawing.
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