Student: Julie C.
ASSIGNMENT #3 –
Seawater Properties, Surface Winds, and
Ocean Currents Due date: 10/14/07 (NOTE: reference citations are in parentheses, and “Book” =
Garrison textbook)
Topic #1 - Describe
and Discuss the Key Physical and Chemical Properties of Water (10 points total)
(From lecture “Properties of Seawater” slides
1-10, Book sections 6.1-6.7)
a) Provide a brief yet concise definition of what water is –
as a chemical compound.
A water molecule is made up of one oxygen atom
covalently bonded to two hydrogen atoms.
H2O
CORRECT
b) Describe the geometry and type of bonding between the
three atoms in the water molecule.
Indicate how the bonding relationship makes water a polar molecule. (Book Figure 6.1,
section 6.2) The three atoms form a
rough triangle with an angle of 105°. The atoms are bound covalently, which means
that they are sharing electrons. The electrons spend more time near the more
strongly-positive oxygen nucleus, thus polarizing that end of the molecule to a
negative charge. Near the hydrogen
nuclei, the molecule is positively charged.
CORRECT
c) Provide a brief yet
concise definition of hydrogen bonding.
Indicate how the polar nature of the water molecule causes this type of
bonding. (Book section 6.2) Hydrogen bonds are weak bonds formed by
weakly negative and weakly positive electron fields – opposite charges
attracting. Because each water molecule
has a negative and a positive side, water molecules form hydrogen bonds with
each other, oxygen-side to hydrogen-side.
CORRECT
d) Briefly describe and explain the amazing thermal
properties of water. Be sure to touch on
the following items: (Book fig. 6.8, section 6.8)
1) heat capacity – Water has an
enormous heat capacity, and can absorb a lot of heat energy without changing
temperature.
INCORRECT – IN TERMS OF HEAT
CAPACITY, WATER CAN ABSORB ALOT OF HEAT WHILE CHANGING LITTLE IN
TEMPERATURE – ANY HEAT ADDED TO THE WATER WILL CHANGE IT’S TEMPERATURE WITHIN A
SINGLE PHASE, LIKE HEATING WATER FROM 20 TO 3O DEGREES.
- 1 POINT
2) latent heat of fusion – At 80
calories per gram of water, this refers to the amount of heat energy it takes
to freeze water or to melt ice.
CORRECT, EXCEPT THAT WHEN YOU
FREEZE, YOU ARE NOT TAKING, BUT INSTEAD, GIVING OFF HEAT… AND WITHOUT A CHANGE IN THE TEMPERATURE OF
THE SYSTEM.
- ˝ POINT
3) latent heat of vaporization – At
540 calories per gram, the highest of any known substance, this is the amount
of heat energy it takes to vaporize liquid water or condense water vapor.
CORRECT, EXCEPT THAT WHEN YOU
CONDENSE, YOU ARE NOT TAKING, BUT INSTEAD, GIVING OFF HEAT… AND WITHOUT A CHANGE IN THE TEMPERATURE OF
THE SYSTEM.
- ˝ POINT
4) Freezing and melting temperatures – The Celsius temperature scale is based on the freezing point
of water (0°C) and its boiling point (100°C).
CORRECT
5) Indicate if the values are relative high or low compared
to similar compounds. The heat capacity, latent heat
of fusion and particularly the latent heat of vaporization of water are all
very high or the highest compared to similar compounds. The boiling and melting temperatures are
“unusually high, allowing water to exist as a liquid on most of Earth” (copied
from table 6.2).
CORRECT
e) Give a brief explanation as to why the ocean’s water plays
a central role in maintaining long-term moderate climate conditions on Earth. (Book section 6.11)
The ocean buffers the Earth against large temperature swings by
transporting heat in ocean and wind currents from the equatorial regions to the
poles. Heat loss is stored in ice at the
poles.
CORRECT
Topic #2 - Describe
and Discuss Seawater Salinity (10
points total)
a) Provide a brief yet concise definition of salinity. (Book section 7.4)
Salinity is the amount of solids dissolved in
water in grams per kilogram.
CORRECT
b) List the major (six of them) constituents of salinity and
each of their percentage of total salinity. (Slide 28,
lecture notes) The Lecture notes at
Oceansci.com state, “they almost always consist of 55% sodium ion, 31%
chloride, 8% sulfate, 4% magnesium ion, 1% calcium ion, and 1% potassium ion.”
CORRECT
c) List and briefly discuss the various sources from where
the dissolved sea salts in the ocean are derived. Cite at least two distinct sources. (Slide 34, Book
section 7.6, figure 7.4)
1. The crust – land erosion –
rivers and rain wash continental salts and sediments into the ocean.
2. Thermal vents – water
leaches into cracks near spreading centers, is superheated and dissolves a lot
of minerals as it boils back out as a
distinctive “black smoker”
CORRECT
d) List and briefly discuss the various sinks to where the
dissolved sea salts in the ocean leave the ocean. Cite at least two distinct sinks. (Book figure 7.4)
1. sedimentation to the ocean
bottom – falling marine snow traps salts and precipitates them to the bottom
2. subduction of ocean crust
– subducting ocean plate carries a lot of water and sediments into the
asthenosphere and out of the ocean.
CORRECT
e) Provide a brief yet concise definition of the Principle of
Constant Proportion, in terms of the composition and concentration of the major
dissolved ions in seawater. Define in
terms of the steady-state nature of salinity – what’s coming versus what’s
going out at what given constant rate. (Slide 35, Book
section 7.7) The Principle of Constant
Proportions, discovered in 1865 by Georg
Forchhammer [and further codified by Dittmar in 1884], is that the percentage
of dissolved salts in any seawater sample will be the same, no matter how
concentrated or diluted the sample is.
The ocean has a steady state (same salinity for 3.4 billion years)
because these ions are being added and removed at the same rate via weathering,
outgassing, evaporation. and other physical and biological processes.
CORRECT
Topic #3 – Describe
and Explain the Major Global-Scale Surface Winds (10 points total)
a) What causes the global surface winds
and their associated circulation cells in the atmosphere?
(Book, 8.4 and Ch. 8 introduction) Heat from the sun and the Earth’s
rotation.
CORRECT – more specifically, differential heating of
the surface by the sun
b) List and describe the three major surface wind belts found
in both the Northern and Southern Hemispheres.
Note their current direction and latitudinal extent over the globe -
where they originate and where they end.
(Slide 13 from “Atmospheric Circulation”, Book
table 8.13, sections 8.9-11)
1. Hadley cells – strong, steady wind blows from
the northeast at the surface in Northern hemisphere, and from the SE in the
Southern, these are called the trade winds at ~ 15°. Hadley cells are located between the equator
and 30° latitude.
2. Ferrel cells – surface wind blows from the west
in the Northern hemisphere, and from the west in the Southern: the
“Westerlies”. Ferrel cells are located between 30° and 50°-60° latitude.
3. polar cells – located from 50°-60° latitude to
the poles, surface “polar easterlies” winds.
CORRECT
c)List and briefly describe the atmospheric conditions along
regions where the major surface wind belts meet:
|
|
c) atmospheric conditions |
1) pressure |
2) typical weather * |
|
1) at the equator |
convergent warmed air masses meet at the equator
and rise forming Hadley cells |
equatorial doldrums; low |
stormy, wet, hot; light winds |
|
2) at 30 degrees N and S Latitude |
divergent cooling equatorial masses descend and
flow back to the equator or divert into Ferrel cells |
subtropical high |
warm, mild, dry; variable winds; horse latitudes |
|
3) at 60 degrees N and S Latitude |
convergent Ferrel and polar cells |
subpolar low |
stormy, wet, cool; heavy precipitation, winter
fronts |
|
4) at both poles |
divergent cold, high pressure air pushes from
the poles towards lower latitudes |
polar high |
cold, harsh, dry; variable winds; polar jet
stream |
(Slides 13-14, 16, book table 8.1) It seems like the Ferrel cells are the
result of the two stronger forces of the high-pressure cold polar regions and
the hot, low pressure equatorial belt duking it out. The Ferrel cells are sort
of the go-between for these two strong systems.
CORRECT - EXCELLENT
d) Briefly describe and explain the Coriolis Effect (Book 8.7, 8.8) As the Earth rotates east, the equatorial
regions have the highest rotational velocity compared to regions to the north
and south. This relative difference
causes air masses to rotate in enormous cells: clockwise in the Northern
hemisphere and counterclockwise in the Southern hemisphere. As rising air moves
from the warmer equatorial regions to cooler polar regions, the earth rotates
more slowly beneath the air (which has maintained its equatorial rotational
velocity) as it heads to higher latitudes, thus causing a deflection from true
north or south to an observer on the ground.
1) Its general effect on surface winds and the formation of
storm systems? “The
Coriolis force makes cyclones spiral and maintains the low pressure of the
disturbance.” (Slide 27) Its general effect on surface winds is in causing
clockwise rotation in the Northern hemisphere and counterclockwise rotation in
the Southern hemisphere.
2) What causes this effect?
The Earth’s rotation… points closer to the
equator have a greater velocity than points closer to the poles to rotate
through the same 360° each day.
3) How is it different comparing the Northern versus the
Southern Hemisphere?
They move in opposite clockwise directions.
CORRECT – VERY GOOD
e) Give a simple
compare and contrast review of tropical cyclones (hurricanes) versus
extra-tropical cyclones (winter storms).What are the key features of each? What
are the key differences between the two?
(Slides 26-33, Book section 8.14-18) Tropical cyclones (hurricanes) form at a
latitude of 8°-15°, while extra-tropical cyclones (winter storms) form at the
polar front at 30°-55°. Both are formed by
air spinning rapidly into a low pressure center, and both can be incredibly
destructive, like Hurricane Katrina. Tropical cyclones form from one air mass,
while extra-tropical cyclones form from two. Tropical cyclones form in the
summer, while extra-tropical cyclones form in the winter. TCs move west until
they hit higher latitudes while ETCs move easterly.
CORRECT
Topic #4 – Describe
and Explain what an Ocean Gyre is and the Forces that Create and Sustain a Gyre
a) Briefly describe an ocean gyre – include breaking it down
into its four surface current components. (Lecture
notes on “Ocean Circulation,” section IV, book section 9.4-6) An ocean gyre is a persistent surface
current which flows in a roughly circular shape around the edges of ocean
basins. It is made up of four
interconnected currents that flow into each other: transverse currents along
the equator and at ~50° latitude, and western and eastern boundary currents.
CORRECT
b) Name the primarily factors (forces and processes) that
create and sustain an ocean gyre. You
should have a list of five factors. (From
http://earth.usc.edu/~stott/Catalina/Oceans.html, book fig. 9.2) Steady surface winds (trade winds and
Westerlies), the Coriolis effect, solar energy, gravity and surface circulation.
CORRECT, EXCEPT FOR LAST ONE –
LANDMASS BARRIERS CORRECT ANSWER
- ˝ POINT
c) Briefly explain how the primarily factors that drive an
ocean gyre work together to sustain the gyre current. (From
http://earth.usc.edu/~stott/Catalina/Oceans.html, book 9.4) Solar energy causes equatorial waters to
expand and rise up a very small amount (8cm). Surface winds also cause the
water to move and “pile up,” keeping the currents to the ocean margins. Gravity
pulls the water down the equatorial small slope to higher latitudes. The Coriolis effect causes the moving water
to deflect to the right in the Northern hemisphere and to the left in the
Southern. The trade winds and Westerlies
also help push the surface water in a big loop of surface circulation
.MOSTLY/PARTIALLY CORRECT –
LOOKING FOR AN EXPLANATION OF HOW THE INWARD MOVEMENT OF THE EKMAN TRANSPORT IS
BALANCED BY THE GRAVITY-FORCED OUTWARD WATER MOVMENT FROM THE PRESSURE GRADIENT
“HILL OF WATER” FINALLY, THE LANMASS BARRIERS
CAUSE CURRENT DEFLECTION.
- ˝ POINT
d) List the names of
the specific ocean basin gyres found around the globe – Note: there are five of them. (From lecture notes)
Northern Atlantic, South Atlantic, North Pacific, South Pacific and
CORRECT
a) Briefly define each boundary current in terms of its
position in an ocean gyre. (Book 9.6) They are defined by their geographical
position in a gyre: western boundary currents are located on the western edge,
and eastern boundary currents are located on the eastern edge of the sea basin.
CORRECT
b) List and briefly describe the key characteristics for each
of the two boundary currents – features such as temperature, flow rate, current
width and depth. (Lecture notes, book 9.6, table 9.1)
Western boundary currents are narrow at <100 km and are the fastest
and deepest, running up to 10 km/hr and to a depth of 1500 m. They move warm
waters towards the poles, and their water is clear, blue and doesn’t carry many
nutrients. Eastern boundary currents are
broad, slower and shallower at up to 2 km/hr and at most a third of the
greatest depth of the Western boundary current at < 500m deep. They can be
1000 km wide and move cold water towards the equator.
CORRECT
c) List the name of the specific boundary currents found
around the globe – categorize them as
either western or eastern boundary. (Lecture notes, slide 15 of “Ocean Circulation”, book 9.6)
North Atlantic
South Atlantic
North Pacific
South Pacific East
Australian Current
CORRECT
d) Briefly describe the boundary current we have off our
coastline here in
CORRECT
a) Briefly describe the Great Ocean Conveyor – include
breaking it down into its cold deep and shallow warm components. (Book 9.19, fig.
9.26) The Great Ocean Conveyor describes a “global pattern of deep circulation”
in the world ocean. From page 254, “The
slow, steady, three-dimensional flow of water... distributes dissolves gases
and solids, mixes nutrients, and transports the juvenile stages of organisms
among ocean basis.” A complete circuit
can take about 1,000 years. The cold
deep water masses are formed at the poles, and are called Antarctic Bottom
Water and North Atlantic Deep Water. The
shallow warm components are portions of the surface gyres, like the
CORRECT
b) Briefly explain what primarily drives the Great Ocean
Conveyor – Where does it get started and by what process(es)? (internet, Slide 35,
book 9.20) “the driving force of the Conveyor is the cold, salty water of the
CORRECT
c) How does
temperature, salinity and density affect this global-scale thermohaline
circulation loop? (Book 9.16) Because the density of
seawater is dependent on its salinity and temperature, differences in water
masses causes them to move, with denser masses sinking. These density differences drive the
circulation in the deep ocean.
CORRECT
d) Briefly explain how might changes in the Great Ocean
Conveyor affect global climate.
In
http://www.columbia.edu/cu/record/23/11/13.html , if the Coveyor were to
collapse or change as a result of greenhouse gases, the climate of
CORRECT
TOTAL POINT = 57 POINTS
– VERY CONSISTENT, OUTSTANDING WORK.