An Ecological Perspective (BIOL 346)

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An Ecological Perspective (BIOL 346)

• Talk Ten
• Ocean acidification

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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 3040 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).

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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
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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

Increases in temperature and  salinity can
decrease the amount of gas seawater can absorb.
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Life on Earth would not be possible without
water Its chemical and physical properties
actually defy some fundamental laws of
physicsAlmost all biochemical reactions require
water!
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How does water support life?

• Water is cohesive
• Water can moderate temperature of
  surroundingenvironment
• Ice floats
• Versatility of water as a solvent

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Water
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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

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Water

• (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

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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.

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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.

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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
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• 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

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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.

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Battle for carbonate!

• Organisms must use more energy or make less hard
  part material
• Existing hard parts dissolve (chemical reaction
  goes the wrong way)

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Hgm,

• dgdfg

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• 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
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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
Normal
Acidic
Albright et al. 2010
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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.

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Simpson et al. 2011
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• 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
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Ocean acidification Impacts on individual marine
organisms

• 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

Photosynthesis
Growth
Amount of dissolved carbon
Chen Durbin 1994
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The Solutions
What can we do about ocean acidification?
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A possible geoengineering solution Add CaCO3 to
the ocean.
Reduce CO32- under-saturation caused by excess
CO2 dissolving in ocean water.
Shells are made of CaCO3
Ca2 CO32-
Shells are made of CaCO3
Ca2 CO32-
H CO32-
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Sounds great, but..
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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.
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What about Fe fertilization to take care of CO2
already in the atmosphere?
Biological Pump
Phytoplankton - Forams
Fe fertilization removes CO2 from the
atmosphere, but may have decreased effectiveness
due to damage to phytoplankton that use calcium
carbonate to build shells
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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.

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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) cant 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.

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Oh yes, Stop adding CO2 to the atmosphere!
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The End!

• Any Questions?