OEAS 306 Exam 2

What causes deviations from equilibrium gas concentrations between the ocean and atmosphere?

(Answer) > All do Rapid change in atmospheric pressure Biology (Photosynthesis, Respiration, Denitrification) Rapid change in surface water temperature Breaking waves and air entrainment

The hydrogen bonds of water molecules account for which of the following?

(Answer) > All the answers provided are relevant Water is the universal solvent Water has a high heat capacity Water has a high boiling point Water has a high surface tension

The depth to which light can penetrate the ocean depends on:

(Answer) All of the statements are true: The amount of particles suspended in the water The turbidity of the water The angle at which light hits the ocean surface The smoothness or roughness of the sea surface (e.g., waves and bubbles)

What is the average pH of today's ocean?

8

The most abundant dissolved gas in seawater is:

nitrogen

The most pronounced thermoclines occur in:

the tropics

What is the oxidation state of Cr in Cr2O72-?

+6

Because of the increase in atmospheric CO2, the ocean is:

Becoming more acidic

In general, the water column is vertically stable because:

It is density stratified

The pE of the ocean describes the:

the activity of electrons

You dissolve 1 mole of NaCl in 500 mL water. What is the molarity (M) of Na+ and Cl- are in solution?

2 M of Na+, and 2 M of Cl-

The wavelengths of light that penetrate deepest into the ocean are:

green and blue

What is the average salinity of the oceans?

About 35 o/oo (parts per thousand) or grams/kg

Which of the following statements about pH is not true?

As a whole, the pH of the ocean is mildly acidic

There is always a down-gradient flux of CO2 into the ocean. Why is that? (2 points) What maintains the influx of CO2 from the atmosphere to the oceans? (2 points)

Atmospheric concentrations of CO2 are always higher than surface water concentrations driving the flux in. This is because CO2 immediately reacts with water and is converted to carbonic acid then bicarbonate. The equilibrium reactions keep CO2 concentrations lower in the water

At the current pH of the ocean, most of the inorganic carbon in seawater is present in the ocean as:

Bicarbonate (HCO3-) ions

The minimum velocity layer for sound is important because:

Sound is trapped in this layer so can be transmitted very efficiently for long distances there

Describe to ocean's biological C pump and how it works. (4 points) Name at least 4 steps What is the fate of this carbon and can carbon be sequestered permanently through the biological pump? (4 points) Name at least 2 fates.

CO2 from the atmosphere dissolves in the ocean where it is taken up by phytoplankton which are grazed on by zooplankton and can sink. While most of the C is recycled in the euphotic zone, some of the dead phytoplankton, zooplankton, their fecal pellets and organic material sink from the euphotic zone where remineralization is slower (but still happens) and some of this material can become DOM. These deep C pools can be removed from atmosphere for 1000s of years and a portion of it can be buried.

Depth profiles of CO2 show that:

CO2 is enriched in deeper waters

The oceans are said to be in chemical equilibrium because:

Chemically, what comes in is about equal to what goes out

Describe the ocean's solubility pump, how it works, and where it happens in the ocean? (4 points) Where does this CO2 go? (2 points)

Cold water can hold more gas and when water cools at the poles, more CO2 is dissolved and this high CO2 water then sinks to form deep water bringing the CO2 with it. It gets upwelled somewhere else and goes back to the atmosphere.

Why is the pH of the deep ocean lower than that in surface waters? (2 points) How can the pH in the surface of the ocean change dramatically on short time scales (e.g., days)? (2 points)

Higher CO2 concentrations (cold temps and high pressure) photosynthesis/respiration

The amount of gas that seawater can hold in solution (or the gas solubility) is greater:

In colder water

The salinity of the ocean, at the present time, seems to be:

In equilibrium, with dissolved components entering equal to dissolved components leaving

With respect to controlling atmospheric carbon dioxide, the "solubility pump" is most important:

In polar waters

If I were to draw a vertical profile of pH in the ocean, pH would be highest at what depth?

In surface water

The ocean is slow to heat and slow to cool. This is related to a property of water known as:

high heat capacity

What are pycnoclines, haloclines, and thermoclines? (3 points) Describe how the thermoclines look in tropical, temperate, and polar oceans (3 points). Would you expect the water column to be more stable in polar, tropical or temperate oceans? (1 point) Why? (2 point)

In vertical profiles of density, salinity, and temperature, the region where these properties change dramatically/steeply with depth Tropical thermoclines are steepest because surface waters are warmest, temperate thermoclines are less steep and there can be a secondary seasonal thermocline, polar thermoclines are nearly non-existent because surface water temperatures are low. Deep water is uniformly cold everywhere so the steepness of the thermocline depends on surface water temperatures More stable water columns in the tropics because surface water is much less dense than deep water. Least stable in polar waters because there is not much difference between surface and bottom waters so they are easy to mix.

The transmission of sound by water can best be described by which of the following statements:

It is faster than transmission through air

Once an element or dissolved substance reaches the ocean:

It may stay or be removed depending on the fluxes affecting the residence time of that particular element

If a compound is at chemical equilibrium in seawater, what two things do I need to know to calculate its residence time? (2 points)

Its concentration and either the input or output (they are equal when a system is in equilibrium)

The property of water that accounts for the ability of liquid water to absorb heat without a change in temperature is called

Latent heat

Which transfers more heat?

Latent heat of vaporization

Which form of water is most dense?

Liquid salt water

If our planet were without its ocean, but otherwise the same as it is today, would surface temperatures be more extreme than they are now (that is, higher high temperatures in summer, and lower low temperatures in winter), less extreme, about the same or what. Why do you think that? (2 points)

More extreme because temps would not be moderated by water's high heat capacity.

Which is the best example of a non-conservative constituent in seawater:

Nitrate (NO3-)

Nonconservative constituents of seawater are:

Often tied to biological cycles

Which gases in water are most influenced by biology? (2 points)? What biological processes influence their distribution? (2 points) Describe their concentrations and the processes that control their concentrations in surface (upper 100m) (2 points), subsurface (~200-1000m) (2 points) and deep water (>2000m) (2 points)?

Oxygen and CO2 Photosynthesis and respiration Oxygen is higher and CO2 lower in surface waters because of photosynthesis. CO2 is higher and oxygen lower in subsurface waters due to respiration. Both increase in deep water due to low temperature and high pressure increasing their solubility

Microbes mediate much of the chemistry in the ocean. What types of reactions do they mediate and name one. (4 points)

Redox reactions. Photosynthesis-respiration

Other than the hydrogen and oxygen in the water molecules themselves, what are the two most abundant ions in seawater?

Sodium (Na+) and chloride (Cl-)

The residence time of element in the ocean is:

The average length of time an element spends in the ocean

We can determine salinity if we know:

The conductivity of a water sample

Which of the following directly contributes to the oxygen minimum layer?

The decomposition of organic matter

Increases in acidity in the ocean can result in:

The dissolution of carbonate minerals or carbonate skeletons/shells of organisms

The Principle of Constant Proportions states that:

The ratio of major salts in seawater from different places in the ocean is constant

What do light and sound have in common?

They both bend when they move between media of different densities

Which is true about hydrogen bonds?

They occur between hydrogen and oxygen atoms of neighboring water molecules

During photosynthesis, water is:

an electron donor

The pH of the ocean is buffered primarily by what acid-base pair?

bicarbonate-carbonate

The hydrogen and oxygen atoms within a water molecule are held together by:

covalent bonds

Gas transfer velocity (K in cm/hr) increases with:

increasing wind speed

Water reacts with/dissolves ions because:

it is polar

The buffer capacity of the ocean maintains its:

pH

The pH is defined as:

pH = - log [H+]

The ocean's deep sound channel (SOFAR layer) is characterized as a zone in which:

sound is trapped in a horizontal band at the velocity minimum layer

The pH of the ocean describes the:

the activity of protons

Most of the world ocean has the temperature properties of:

the deep and bottom waters

Acid-base equilibrium reactions in seawater are important because:

they can buffer seawater from changes in pH

Why are the components of oceanic salinity different from those in freshwater? (4 points)

water circulates through the mantle at spreading centers and loses and gains chemical constituents through exchanges between super-heated water and the mantle and precipitation of other elements when the water cools.

The density of a parcel of seawater will increase:

when the salinity increases