oceanography test number two

What is the chemical formula of water?

H2O: 2 hydrogen atoms and 1 oxygen atom.

What kind of bonds hold a water molecule together?

Covalent bonds.

Why is water a polar molecule?

One end (hydrogen) is slightly positive and the other end (oxygen) is slightly negative.

What is a hydrogen bond?

A weak attraction between the positive hydrogen of one water molecule and the negative oxygen of another.

What happens when you put a drop of water vs rubbing alcohol on a penny?

Water beads up into a half-sphere. Alcohol flattens out. This shows hydrogen bonds.

What is surface tension?

The "skin" on water caused by hydrogen bonds. It lets a paperclip or mosquito sit on water.

Name two properties of water caused by hydrogen bonds.

Surface tension and high specific heat.

What is specific heat?

The heat needed to raise 1 unit of mass of a material by 1 degree.

What is heat capacity?

The heat needed to raise the temperature of a whole object by 1 degree.

What does specific heat depend on?

The type of material.

What does heat capacity depend on?

The total mass.

What is the specific heat of water?

1.00 calorie per gram per °C.

What does a high specific heat mean for heating and cooling?

The substance heats up and cools down slowly.

Why does water have a high specific heat?

Hydrogen bonds absorb heat energy, so it takes more heat to raise the temperature.

Which heats up faster: land or ocean? Why?

Land. Rock and soil have a lower specific heat than water.

Which has the highest specific heat: water, air, or rock?

Water (1.00). Air is 0.25 and rocks are about 0.17 to 0.47.

What is density?

Mass per unit volume. Denser fluids sink below less dense fluids.

At what temperature is pure water most dense?

About 3.98°C (roughly 4°C).

What happens to pure water's density as it cools from warm down to 4°C?

It increases.

What happens to pure water's density as it cools from 4°C to 0°C?

It decreases.

What happens to water's density when it freezes?

It decreases, so ice floats.

Does water's density change in a straight line with temperature?

No, it is not linear.

How does depth (pressure) affect density?

Density increases slightly with depth. Pressure rises about 1 atmosphere every 10 m.

How does winter cooling affect the water column?

Surface water cools and gets denser, so it sinks and mixes the water column.

How does summer warming affect the water column?

Surface water warms and gets less dense, so it floats and the layers stay separate (stratified).

On the Effect of Salt graph, what does the pink line show?

The temperature of maximum density.

On the Effect of Salt graph, what does the black/blue line show?

The temperature at which water freezes.

As salt is added, what happens to the temperature of maximum density?

It decreases.

As salt is added, what happens to the freezing temperature?

It decreases.

What is the freezing temperature of pure water?

0°C.

Why is salt put on roads in winter?

Salt lowers the freezing temperature, so the water doesn't freeze as easily.

At about what salt content do the pink and black lines meet?

About 24.7 g/kg (at -1.332°C). Ocean water is about 35 g/kg.

What happens to ocean water (above 24.7 g/kg salt) as it cools?

It keeps getting denser until it freezes. There is no density maximum above freezing.

What does the Temperature-Salinity (T-S) diagram show?

Lines of equal density for different temperatures and salinities.

What is true about any two points on the same line of a T-S diagram?

They have the same density.

On a T-S diagram, which lines have the highest density?

The lines toward the lower right (colder and saltier).

Why do scientists use the T-S diagram?

Temperature and salinity are easy to measure, and the diagram converts them into density.

Where does cold, salty (dense) water end up?

On the bottom. Warm, fresh water floats on top.

What processes make surface salinity lower?

Freshwater added: precipitation, runoff, and melting ice.

What processes make surface salinity higher?

Freshwater removed: evaporation and freezing.

What happens to salinity if evaporation is greater than precipitation?

The water gets saltier.

Why is salinity low at 60°N?

Precipitation is higher than evaporation there.

Where is sea surface salinity highest?

In the mid-latitudes, where evaporation is greater than precipitation.

Where do most of the salts in the ocean come from?

The land.

What are the inputs of salts to the ocean?

Rivers, volcanism, the ridge system, and decay.

What are the outputs (removal) of salts from the ocean?

Adsorption and precipitation, sea spray, biological uptake, and sediments.

What is residence time?

How long a substance stays in the ocean (total amount divided by rate of input or output).

What are the residence times of sodium and iron?

Sodium: about 68 million years. Iron: about 200 years.

Why does sodium chloride build up in the ocean?

It has a very long residence time, so it stays in the ocean.

What are calcite and aragonite?

Two forms of calcium carbonate (CaCO3).

How are calcite and aragonite similar?

Both are CaCO3 minerals that organisms use to build shells and skeletons.

What is the main difference between calcite and aragonite?

The magnesium amount. More magnesium makes aragonite instead of calcite.

What is an aragonite sea vs a calcite sea?

Aragonite sea: high Mg/Ca ratio. Calcite sea: low Mg/Ca ratio.

Has seawater composition always been the same?

No. It changes over time. Fossils show an on/off switch between calcite and aragonite.

How do scientists learn about ancient seawater chemistry?

Fluid inclusions (tiny bubbles of very old seawater) in rock salt, plus fossils.

Why are calcite and aragonite important in the ocean?

Organisms build shells with them, they store carbon, and they record past seawater chemistry.

What are the four parts of the marine carbonate system?

CO2, carbonic acid, bicarbonate, and carbonate.

What is the carbonate system equation?

CO2 + H2O

What does the carbonate system do for the ocean?

It is a natural buffer that keeps ocean pH in a healthy range.

What does adding CO2 do to the carbonate system?

pH drops (more acidic) and the amount of carbonate ion decreases.

What is neutral pH?

7.

What do low and high pH mean?

Low pH = acidic. High pH = basic (alkaline).

What is the pH of a healthy ocean?

About 8 (about 8.2 on the slides). Slightly basic.

What is the typical pH range of seawater?

About 7.5 to 8.5.

Is there more carbonate ion at pH 8 or pH 7?

At pH 8. The amount drops at pH 7.

What is ocean acidification?

A drop in ocean pH caused by the ocean absorbing CO2 from the atmosphere.

How does CO2 make seawater acidic?

CO2 dissolves in water and grabs a water molecule to form carbonic acid.

How much has ocean acidity risen since the industrial revolution?

About 30%.

What is the common building block of shells?

Carbonate ion.

Why does ocean acidification make it hard to build shells?

CO2 reduces the carbonate ion available, so shells are harder to make.

How does a shortage of carbonate ion hurt organisms?

They have less energy to eat, mate, and survive.

Where will shells dissolve first?

The Southern Ocean and Arctic Ocean.

Why is ocean acidification a problem for the food web?

Small organisms are at risk, so the food web gets weaker.

How can we stop ocean acidification?

Emit less carbon dioxide.

What was the PETM?

The Paleocene-Eocene Thermal Maximum, about 55 million years ago. A rapid CO2 input that acidified the ocean.

In PETM sediment cores, what does the sharp color change mean?

It marks the beginning of the CO2 input.

Why are PETM cores red at the sharp color change?

Almost no calcium carbonate shells were left (they dissolved).

In PETM sediment cores, what does the gradual lightening of color mean?

Slow recovery (brown/red back to grey/beige).

How long did the ocean take to recover from the PETM?

About 200,000 years.

Why was slow CO2 input in the past less harmful than fast input?

If CO2 is added slowly, Earth can fix it. If added quickly, Earth can't keep up.

What are the major nutrients for ocean productivity?

Nitrogen and phosphorus.

What other nutrients does the ocean need?

Carbon and iron.

What is the Redfield ratio?

The fixed ratio of nutrients phytoplankton use: C : N : P : Fe = 106 : 16 : 1 : 0.01.

Why can nutrients limit productivity?

Phytoplankton need a specific recipe. If one nutrient runs out, growth stops.

What do red, orange, and yellow mean on the productivity map?

High productivity (lots of algae growing).

Why is nitrate zero at the ocean surface?

Organisms use it all up.

Where do ocean nutrients come from?

The land. High nutrients are found along the continents.

4-part graph: what does organic matter look like with depth?

Lots at the surface and very little below.

4-part graph: what does oxygen look like with depth?

High at the surface, lowest at mid-depth (oxygen minimum zone), higher again in the deep.

Why is there an oxygen minimum zone?

Bacteria use up oxygen breaking down sinking organic matter.

4-part graph: what does nitrate look like with depth?

Zero at the surface, highest at mid-depth.

Why is nitrate highest at mid-depth?

Breaking down organic matter releases nutrients back into the water.

4-part graph: what does total dissolved carbon look like with depth?

Low at the surface and highest at mid-depth, where organic matter breaks down.

How are organic matter, oxygen, and nitrate connected?

Breaking down organic matter uses oxygen and releases nitrate (nutrients).

What determines how much oxygen is in the ocean?

Supply (physical processes) and consumption (biological processes).

Why does cold, high-latitude water hold more oxygen?

Cold water dissolves oxygen more easily. Warm low-latitude water holds less.

How does oxygen get into the ocean interior?

Currents carry it from the surface down. This is called ventilation.

What is ventilation?

The process that delivers oxygen-rich surface water into the ocean interior.

What takes oxygen out of the ocean?

Consumption (organisms using it up).