An Ecological Perspective
(BIOL 346)
Talk Ten:
Ocean acidification
So, what is it?
• The ongoing decrease in the pH of the Earth's oceans,
caused by the uptake of carbon dioxide (CO2) from the
atmosphere.
• An estimated 30–40% of the carbon dioxide released by
humans into the atmosphere dissolves into oceans, rivers
and lakes.
• To achieve chemical equilibrium, some of it reacts with the
water to form carbonic acid.
• Some of these extra carbonic acid molecules react with a
water molecule to give a bicarbonate ion and a hydronium ion,
thus increasing ocean "acidity" (H+ ion concentration).
So, what is it?
• Between 1751 and 1994 surface
ocean pH is estimated to have
decreased from approximately
8.25 to 8.14, representing an
increase of almost 30% in H+
ion concentration in the
world's oceans.
• Earth System Models project
that within the last decade
ocean acidity exceeded
historical predictions
• Could undermine the functioning
of marine ecosystems and many
ocean goods and services
Estimated change in sea water pH caused by human
created CO2 between the 1700s and the 1990s, from
the Global Ocean Data Analysis Project (GLODAP) and
the World Ocean Atlas
How much CO2 can the ocean
absorb?
• The total amount of any gas seawater can absorb
depends on temperature and salinity
• Salinity is a measure
of the dissolved salt
content of water
Remember this relationship!
Temperature
or
Salinity
Amount of gas
seawater can absorb
Increases in temperature and salinity can decrease the
amount of gas seawater can absorb.
4
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Life on Earth would not be
possible without water
Its chemical and physical
properties actually defy some
fundamental laws of physics
Almost all biochemical reactions
require water!
How does water support life?
– Water is cohesive
– Water can moderate
temperature of surrounding
environment
– Ice floats
– Versatility of water as a
solvent
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Water
Water has hydrogen bonding
potential
• H-bonds are non-covalent,
weak interactions
• H2O is both a Hydrogen
donor and acceptor
• One H2O can form up to
four H-bonds
• (A) Hydrogen bonds
between water
molecules results in
local aggregations of
water molecules
• (B) Theses are very
short lived, break up
rapidly to form more
random
configurations
• Due to temperature
variations in water
Water
Density
• Another property of water is
density during phase changes.
– The density of most
substances increases when
a liquid becomes a solid.
Solid water is actually less
dense than liquid water.
• It is for this reason that ice
floats.
– The fact that ice floats is
essential for the survival
of many aquatic
ecosystems and ultimately
life on Earth.
Hydrogen bond
Ice
Stable hydrogen bonds
Liquid water
Hydrogen bonds
constantly break
and re-form
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Capillary Action & Surface tension
• Cohesion of water causes capillary
attraction, which is the ability of water to
move upward in small spaces.
• Cohesion makes it possible for water to
move up the fibers of a plant.
•
– In addition, it moves water upwards in
soil.
– Allows water to be taken into human
cells attached to other molecules
• Cohesion of water also causes surface
tension, water's invisible skin which allows
water striders to walk on water
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pH and buffers
• Measure of the acidity or basicity of an aqueous solution.
– Solutions with a pH less than 7 are said to be acidic
– Solutions with a pH greater than 7 are basic or alkaline.
– Pure water has a pH very close to 7
•
•
•
•
Acid
A chemical compound that donates H+ ions to solutions.
Base
A compound that accepts H+ ions and removes them from solution.
• Remember H3O+ and OH-?
• The H3O+ donates H+ to a solution and the OH- removes H+ from a
solution
• If an equal number of these ions are present in a solution the pH
will not change as it is said to be buffered.
The pH scale
• To describe the acidity of
a solution, we use the pH
scale.
• Acids have a low pH, so
they have a high
concentration of H+
• Bases have a high pH, so
they have a low
concentration of H+
Used with permission from purewaterproducts.com
• The ocean absorbs
carbon dioxide from the
atmosphere
• Human activities release
carbon dioxide into the
atmosphere
• Too much carbon dioxide
in the ocean has the
potential to harm marine
organisms and
ecosystems
How is atmospheric CO2 responsible for
ocean acidification?
When CO2 dissolves in seawater, carbonic acid is produced via the reaction:
This carbonic acid dissociates in the water, releasing hydrogen ions and bicarbonate:
The increase in the hydrogen ion concentration causes an increase in acidity, since acidity is
defined by the pH scale, where pH = -log [H+] (so as hydrogen increases, the pH
decreases). This log scale means that for every unit decrease on the pH scale, the
hydrogen ion concentration has increased 10-fold.
One result of the release of hydrogen ions is that they combine with any carbonate ions in
the water to form bicarbonate:
This removes carbonate ions from the water, making it more difficult for
organisms to form the CaCO3 they need for their shells.
All CaCO3 shells are not created equal
Aragonite
(orthorhombic)
Calcite
(hexagonal)
Calcite
Aragonite
10 g
10 g
Decreased
ocean pH
(more acidic water)
Calcite
Aragonite
8 g
5 g
“Battle” for carbonate!
• Organisms must use more
energy or make less hard
part material
• Existing hard parts
dissolve (chemical
reaction goes “the wrong
way”)
From the wikimedia free licensed media file
repository
Hgm,
• dgdfg
•
First-sale revenues from U.S.
commercial fisheries totaled about $4
billion.
•
Four groups of animals contributed
almost equally to that total.
•
Two groups are calcifiers, which means
they make shells, spines, or exoskeletons
out of calcium carbonate: crustaceans
(lobsters, crabs, shrimp) and mollusks
(clams, oysters, mussels, scallops, and
other non-crustacean calcifiers).
•
The other two groups are animals that
prey on calcifiers (such as flounder and
octopus) and top predators that eat the
calcifiers’ predators (such as salmon and
tuna).
•
Of these groups, the mollusks appear
most vulnerable to direct effects of
ocean acidification. But a decline in
those species could cause problems for
predators above them on the food
chain.dvsdv
Used with permission from the Woods
Hole Oceanographic Institution
Ocean acidification: Impacts on individual marine organisms
Reduced fertilization of gametes in corals and other marine organisms
• Deformed flagellum in sperm that impacts their swimming
• Fitness effect: lower population growth
Natural range in the ocean
Albright et al. 2010
Ocean acidification: Impacts on individual marine organisms
Reduced hearing ability in anemone fish (clown fish) larvae
• Deformed morphology of CaCO3 fish ear bones (otoliths)
• Disruption of acid-base balance in neuro-sensory system
• Fitness effect: lower survival due to higher predation.
Simpson et al. 2011
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file repository
Ocean acidification: Impacts on ecological communities
Tropical Oceans Predictions:
• Corals will become increasingly rare
• Algae will become more abundant
• Because coral reefs support so many animals,
biodiversity will decline
Hoegh-Guldberg et al. 2007
Ocean acidification: Impacts on individual marine organisms
Growth
Photosynthesis
Non-calcifying marine algae: Increased photosynthesis and growth
• Lower pH means more dissolved CO2 for photosynthesis to fuel growth
• Fitness effect: higher survival and population growth
Amount of dissolved carbon
Chen & Durbin 1994
The Solutions
What can we do about ocean acidification?
A possible geoengineering solution: Add CaCO3 to the ocean.
Reduce CO32- under-saturation caused by excess CO2 dissolving in ocean water.
2+
2Shells
3 32Shells are
are made
made of
of CaCO
CaCO33 =
= Ca
Ca2+ ++ CO
CO
H+
CO32-
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Sounds great, but……………..
To counteract 2 gigatons of carbon/yr input of CO2, would
need 20 gigatons of CaCO3/yr.
White Cliffs of Dover would be
rapidly consumed.
Limestone Rock (CaCO3)
• Limestone mining would be expensive and would cause
ecological damage.
• All the energy needed to move massive amounts of rock into
the ocean would likely add more CO2 to the atmosphere.
What about Fe fertilization to take care of CO2 already in
the atmosphere?
Phytoplankton - Forams
Biological Pump
Fe fertilization – removes CO2 from the atmosphere, but may have decreased
effectiveness due to damage to phytoplankton that use calcium carbonate to
build shells
What about Fe fertilization to take
care of CO2 already in the atmosphere?
• Foraminifera, commonly referred to as
forams, are photosynthetic organisms
that live in the surface of the ocean
and take up CO2 during photosynthesis.
• The CO2 that they take up during
photosynthesis becomes part of their
biomass and, therefore, they help
remove CO2 from the atmosphere.
• When they die, they sink to the bottom
of the ocean and with them goes the
biomass. This overall process helps
decrease the amount of CO2 in the
atmosphere.
What about Fe fertilization to take
care of CO2 already in the atmosphere?
• However, these organisms will be
unable to function properly in more
acidic oceans.
• However, if plankton using the Fe (such
as forams) can’t function properly, then
Fe fertilization will not work.
– There is incomplete shell growth and
malformed shell plates of foraminifera
under more acidic conditions.
• The chemical composition of the sea
urchin spine is 94 percent mineral
(calcium carbonate, magnesium
carbonate and silica) and 6 percent
organic matter.
Oh yes,
Stop adding CO2 to the atmosphere!
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The End!
Any Questions?