Chapter 7:

Ocean Chemistry

1

Housekeeping

• Website under construction in Moodle

(about halfway there)

• Extra credit for taking and sharing thorough

notes with the rest of the class

• Review of some exam material at end of

class (if time)

2

Water has unique properties

that enable life on Earth.

1. It’s a good solvent.

2. Ice floats.

3. Water has a high heat capacity.

4. Water helps the metabolism of organisms.

3

Learning Goals:

Water and Ocean Structure

• The properties of water moderate Earth’s temperatures and

enable life on Earth.

• Water resists rising in temperature as it is heated. Water

gives off heat when it freezes, and it absorbs heat as it

thaws.

• Seawater is mostly water molecules but has dissolved

substances.

• The ocean is stratified by density.

Density is driven mainly by temperature and salinity.

• Light is extinguished easily as it passes through water.

Sound is not.4

Learning Goals:

Water and Ocean Structure

• The properties of water moderate Earth’s temperatures and

enable life on Earth.

• Water resists rising in temperature as it is heated. Water

gives off heat when it freezes, and it absorbs heat as it

thaws.

• Seawater is mostly water molecules but has dissolved

substances.

• The ocean is stratified by density.

Density is driven mainly by temperature and salinity.

• Light is extinguished easily as it passes through water.

Sound is not.5

Learning Goals:

Ocean Chemistry

• Water is a powerful solvent.

Salinity: concentration of dissolved inorganic solids in water

• Salinity may vary with location.

However, the ratio of dissolved solids in seawater is

constant.

• Gases dissolve in seawater.

Cold water can hold more gas in solution than warm water.

• The ocean is a vast reservoir of carbon. It takes up carbon

from the atmosphere and so it is linked to climate.

• The ocean’s acid-base (pH) balance varies with depth and

dissolved components.

• Increases in carbon dioxide in the ocean are causing

ocean acidification.6

Learning Goals:

Ocean Chemistry

• Water is a powerful solvent.

Salinity: concentration of dissolved inorganic solids in water

• Salinity may vary with location.

However, the ratio of dissolved solids in seawater is

constant.

• Gases dissolve in seawater.

(Cold water can hold more gas in solution than warm water.)

• The ocean is a vast reservoir of carbon. It takes up carbon

from the atmosphere and so it is linked to climate.

• (The ocean’s acid-base (pH) balance varies with depth and

dissolved components.)

• Increases in carbon dioxide in the ocean are causing

ocean acidification.

(next class)

7

Photic Zone – thin region where sunlight penetrates: clarity of water,

surface smoothness & angle of Sun affects depth.

Aphotic Zone – no sunlight reaches

Light does not penetrate very deep into the ocean.

8

Reds absorbed first

Blues absorbed last

9

This fish was photographed in normal oceanic light – the

color blue predominates.

10

The same fish was photographed with a strobe light.

The flash contains all colors, and so the fish shows colors

that would otherwise be invisible.

11

Speed of sound is 5

times higher in water

than in air.

In water,

speed of sound is

affected by

temperature &

pressure.

Warm waters

High pressure

How does

sound move

in water?

12

Side-scan SONAR,

used for undersea mapping.

Does SONAR harm marine mammals?http://www.nmfs.noaa.gov/pr/pdfs/health/sonar_fact_sheet.pdf

13

14

Salinity• Salinity is defined

as the total

amount of

dissolved solids in

water including

dissolved gases

– Excludes

dissolved

organics

15

Earth’s Hydrologic Cycle

In other words,

these are processes that add or subtract

fresh water.16

Processes that Add/Subtract

Dissolved Substances

(in other words,

these processes

impact the

salinity of

seawater)

17

Salinity

18

Composition of Seawater

19

Processes Affecting Salinity

• Decreasing salinity – adding fresh water

to ocean

– Runoff, melting icebergs, melting sea ice

– Precipitation

• Increasing salinity – removing water from

ocean

– Sea ice formation

– Evaporation

20

Aquarius Satellite View of Global

Salinity, Aug.–Sept. 2011

21

Salinity is affected by evaporation and precipitation.

Near equator, more precipitation. 22

Aquarius Satellite View of Global

Salinity, Aug.–Sept. 2011

23

Water cannot dissolve oil; no polarity.

24

Halocline – where salinity increases rapidly.

25

Salinity Variation with Depth

• Low latitudes – salinity

decreases with depth

• High latitudes – salinity

increases with depth

• Deep ocean salinity

fairly consistent

globally

• Halocline – separates

ocean layers of

different salinity

26

Gases are also dissolved in the ocean.

• Carbon dioxide, or CO2, is one of the most

important gases in the ocean.

• As CO2 levels rise in the atmosphere, the

ocean absorbs it.

• The ocean absorbs ~30% of the carbon

dioxide in the atmosphere.

27

Questions about the following

three videos will appear on the

next exam.

28

Ocean Acidification:

the other carbon dioxide problem

Image from:

http://www.pmel.noaa.gov/co2/story/What+is+Ocean+Acidification%3F

Video: https://www.youtube.com/watch?v=Wo-bHt1bOsw

29

http://www.pbs.org/newshour/updates/climate-change-july-dec12-acidification_12-05/

How will ocean acidification impact Florida?

30

Hokulea: Sharing Hope for the World’s Corals

http://www.hokulea.com/sharing-hope-for-the-worlds-corals/

31

pH Scale

• Measures hydrogen ion concentration– pH value less than 7 = acid

– pH value greater than 7 = base (alkaline)

– pH 7 = neutral • Pure water

32

pH Scale

Acid releases a hydrogen ion

(H+) when dissolved in water.

Alkaline (or base) releases a

hydroxide ion (OH-) in water.

33

Ocean pH

• Seawater is slightly

alkaline

– Surface water average

pH 8.1

• Ocean water pH

decreases with depth

34

Carbonate Buffering System

Buffering

keeps the

ocean from

becoming too

acidic or too

basic.

Precipitation

or dissolution

of calcium

carbonate,

CaCO3,

buffers ocean

pH.

35