Geosciences 40: The Sea Around Us
Midterm Study Guide
1. What is the "Goldilocks Principle” as applied to Earth and the Oceans?
The Goldilocks Principle suggests that 1) Earth has just the right position- not too close to the sun &
not too far away and 2) When it was forming, Earth had just the right mass, large enough to retain
2. Which is greater - the average depth of the ocean, or the average elevation of the continents?
The average depth of the ocean is about 4 ½ times the average height of the continents above sea
3. Why do we say there is one world ocean? Over time, does water from the Atlantic and Pacific Oceans
mix with waters from the Baltic and Mediterranean seas?
We say that there is one world ocean because even though we have four oceans, they are all
connected. Over time, water from most all bodies of water mix due to the processes of
photosynthesis, evaporation, and precipitation.
4. Surface water on Earth most likely came from where?
Two major hypotheses: 1) Emission (degassing) of materials (volatiles) from Earth’s surface millions
of years ago; i.e. volcanic eruptions, hot springs, sea floor vents, etc. 2) E.T. such as cometary or
meteorite impacts. Models show that the entire ocean could have degassed in the first .5 billion years
or less. (Most likely 4 billion years ago)
5. How is Ocean deep water different from shallow water?
Deep water has a lower temperature, a higher salinity and a higher density than shallow water.
Respiration also occurs more so in deep water than it does in shallow water. Deep water makes up
80% of the total water in the ocean while surface water only makes up 2%.
6. Why is water a polar molecule? What properties of water derive from its polar nature?
Water is a polar molecule because it contains opposite charges. Because of its polar nature, water is
very strongly bonded together; therefore the boiling point of water is very high as well as its freezing
point. Water also acts as a “global thermostat” and has the remarkable ability to dissolve more
substances than any other natural solvent. Polarity is responsible for surface tension.
7. What did Rachel Carson suggest about how ocean chemistry may have changed over geologic time
(millions of years)? What did she think about the connections between river chemistry and ocean
Rachel Carson suggested that rain and other factors weather the continents and that rivers deliver
dissolved rock, including elements such as Ca, Na, & Cl, to the world ocean, which caused changes
in ocean chemistry over time (hyrdologic cycle). Ocean chemistry also changes due to volcanic gases
and the interaction of seawater with the seafloor.
8. How did geosc040 get it’s name: “The Sea Around Us” ?
Rachel Carson’s 1951 book titled “The Sea Around Us.”
9. What affect does photosynthesis have on the concentrations of CO and O in seawater? How do the
concentrations of CO an2 O vary2with depth in the oceans?
Photosynthesis occurs primarily in ocean surface water therefore there is more O in su2face water
and less CO (O is produced and CO is consumed by photosynthesis). Respiration occurs more
2 2 2 primarily in deep waters therefore there is more CO and 2ess O in de2p waters (Respiration
consumes O and2produces CO ). Deep2water also contains more CO because the2solubility of CO 2
increases as temperature decreases and deep-water creatures respire CO 2.
10. How is heat different than temperature?
Heat is a measure of how many molecules of a substance are vibrating, and how rapidly they are
vibrating. Temperature records only how rapidly the molecules of a substance are vibrating.
11. What is heat capacity? What is latent heat? What’s the difference between sensible heat and latent heat?
Heat capacity is defined as the number of heat units needed to raise the temperature of a body by one
degree. Latent heat is the heat released or absorbed by a chemical substance during a change of
phase, i.e. the energy required to change ice to liquid or the energy released when water vapor
condenses to form rain. Sensible heat is the amount of energy released or absorbed by a chemical
substance during a change of temperature.
12. How does the addition of salt to water change the freezing (boiling) point of water?
When you add nonvolatile substance like NaCl to water, it breaks down into positive sodium ions and
negative chloride ions. The ions do not evaporate therefore the energy needed to break the attractions
between water molecules is taken up by these nonvolatile particles and the boiling point rises.
13. What is residence time of an element in seawater? How do you calculate resident time?
The residence time of an element in seawater is the average time a substance remains dissolved. It is
calculated by dividing the total amount in seawater (kg) by the input rate (kg/year), where the input
rate equals the average concentration in rivers.
14. How do temperature and salinity influence the solubility of gas in seawater?
Decreased temperatures and decreased salinity increase the solubility of gasses in seawater, i.e. a gas
would be most soluble in fresh cold water as opposed to salty warm water.
15. Why does ice float?
Ice floats because it has approximately a 9% lower density than liquid water, which reaches its
maximum density at 4 degrees Celsius (40 degrees Fahrenheit).
16. How is the ocean stratified by density? What physical factors are involved? What names are given to
the ocean's density zones?
Since deep-water masses have a narrow range of temperature and salinity, the ocean is density
stratified. The ocean is stratified into three zones by density: the surface zone (mixed layer), the
pycnocline (zone of rapid density change with depth) and the deep zone. The physical factors
involved in the levels of density include temperature and salinity, with the ocean being denser in
areas of low temperature and high salinity.
17. What are the thermocline, halocline, and pycnocline? Are they the same in all places in the ocean?
The thermocline is the zone of abrupt temperature change in the ocean, the halocline is the zone of
abrupt salinity change and the pycnocline is the zone of abrupt density change.
18. Read the Chapter Summaries and Key Concepts on our book’s web site
• The most abundant ions dissolved in seawater are chloride, sodium, and sulfate.
• The Coriolis effect modifies the courses of currents, with currents turning clockwise (right) in
the Northern Hemisphere, counterclockwise (left) in the Southern Hemisphere.
• Latitudes below 40 degrees N & S do NOT receive more solar energy than they lose.
• Marine animals do NOT break down water molecules to obtain O 2 • Water has a low viscosity, high surface tension, low compressibility, high heat capacity & high
• Latent heat of melting is 80 cal/gram
• Latent heat of vaporization or condensation is 540 cal/gram
- + -2 +2 +2 +
• Cl, Na , S0 ,4Mg , Ca , K order of most abundant elements in seawater
19. What are the main factors that influence plankton blooms?
The two main factors that influence plankton blooms include a readily available supply of sunlight
and nutrients, which leads to the second factor of increased and rapid reproduction.
20. What are the connections between large-scale wind patterns and the pattern of surface ocean
Due to both the Coriolis Effect and the Ekman Spiral, large-scale wind patterns, such as the North
Atlantic Gyre, cause ocean surfaces to circulate to the right of the wind direction in the northern
hemisphere and to the left of the wind direction in the southern hemisphere.
21. What is a gyre? What factors determine the large-scale pattern of surface ocean circulation in the N.
A gyre is a large-scale circular current system that flows clockwise in the northern hemisphere and
counterclockwise in the southern hemisphere. The factors, or currents, that determine the large-
scale pattern of surface ocean circulation in the N. Atlantic include the North Equatorial Current,
the Gulf Stream, the North Atlantic Current and the Canary Current, which all collectively make
up the North Atlantic Gyre.
22. Are there any differences between the flow of surface waters on the Eastern and Western side of ocean
basins? If so, what are they?