1. Ocean Acidification

2. Ocean Acidification
Overview – Processes were understood by chemists 100 years ago

3. pH Scale pH Scale measures acidity Pure water has pH of 7
Lower pH is acidic
Higher pH is basic
Logarithmic scale:
Each step is 10x more
acidic or basic
If students have not already taken chemistry, it will be hard to go into full detail and stay on time (it isn’t covered until halfway through the class and has to build up to it). Cover the basics of how to use the scale, but not necessarily the underlying reasons behind it.
All of the solutions with pH 0-14, the solution is mostly water (pH 7 is water)
pH scale actually continues in both directions (<0 & >14), but outside of a chem lab, we don’t see them in daily experience
We call things with a pH of 1, like sulfuric acid deadly. When the pH reaches 2, we call if food.
At a pH of 4, oceans and lakes are dead.
Background info for instructor:
pH = -log[H+], where [H+] is the molar concentration of H+ in solution
If ab=c then loga(c)=b (if the log’s base, “a” in this example, isn’t explicitly listed, then it is the standard log of base 10)
The “p” in pH was a mathematical operator from the pre-calculator days of sliderules, where calculations with large numbers was performed using logarithms
the “p” is an operator that means “take the negative log of a number/variable”
Acid – (BrØwnsted-Lowry definition) Molecule that donates an H+ ion when dissolved in water
Base - (BrØwnsted-Lowry definition) Molecule that donates an OH- ion when dissolved in water
Water acts as both a very weak acid and very weak base (in equal amounts)
EPA

4. Natural Carbon Cycle
Plants take in carbon from carbon dioxide during photosynthesis
Animals take in carbon by eating plants
Animals release carbon dioxide by breaking down carbohydrates to release their energy
The amount of carbon and the proportions of elements in the atmosphere change over geologic time (increasing/decreasing)
Amounts present are a function of the equilibrium established by various species at the time
Humans are artificially changing the equilibrium
Carbohydrates include all sugars and fibers (difference between them is the various lengths/shapes of CH2O chains strung together)
Carbon Sequestration – The process of removing carbon from the carbon cycle.
Plants that are buried before they are eaten remove carbon, while volcanos emit carbon dioxide

5. Human Caused CO2 in the Environment
Burning fossil fuels adds
extra CO2 to atmosphere
4 lbs. of CO2 from fossil
fuel adds 1 lbs. of
dissolved CO2
24,000,000,000,000 lbs.
CO2 released from fossil
fuels in 2011
CO2 vapors seek dynamic equilibrium with dissolved CO2 in the ocean
Burning wood does not add extra CO2 Source of the wood’s carbon was the atmosphere,
When a new tree grows back, an equal amount of CO2 will be absorbed to create new wood
Burning fossil fuels adds extra CO2
Source of fossil carbon is plants and animals that absorbed CO2 from atmosphere millions of years ago
By testing air trapped in ancient rock, we know that atmospheric CO2 has never been higher than today
Total CO2 emissions in 2011 from
Percent of CO2 emissions from fossil fuel based on 57% of total
As CO2 from fossil fuels is released into the atmosphere,
more CO2 dissolves in the ocean to maintain dynamic equilibrium

6. Ocean Acidification
Only 1/3 of CO2 added to the atmosphere is dissolves into the ocean, then very little of that actually forms carbonic acid.
…But in 2011 alone we put an extra 24 trillion pounds of CO2 into the atmosphere by burning fossil fuels
The ocean is slightly basic (pH=8.2). When we say “ocean acidification” this means that the ocean is becoming more acidic or less basic
Ocean Acidification: Dissolved CO2 reacts to form carbonic acid, lowering the ocean’s pH
As more CO2 is added to the air, more dissolves into the ocean and more converts to H2CO3

7. Effects of Ocean Acidification
Effects on shells
Right: Healthy pteropod
with clear shell
Far right: Shell partially
dissolved by ocean acidification
NOAA
Effects on corals
Shells are energetically easy to form, which means they are also energetically easy to destroy
As the pH drops (becomes more acidic), the dynamic equilibrium of CaCO3 (calcium carbonate that shells and coral are made of) begins to favor the dissolved ionic form rather than its solid form
Far left: Healthy coral in “normal” water
Left: Dead coral in acidic waters off
Puerto Rico
At today’s CO2 emissions rate, ocean pH will drop from 8.2 to 7.9 by year NOAA

8. Summary pH Scale Natural Carbon Cycle Human Caused CO2
Ocean Acidification
Effects of Ocean Acidification