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
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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