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the “other” CO₂ problem

NOAA

Ocean Acidification

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Phenomenon: What’s Happening to the Coral Reefs?

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Why is it the first CO₂ problem?

Global temperatures in 2050?

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Global surface temperature anomalies – June 2018

What do you notice?

Are there any patterns to the warmings (or coolings)?

Where is there the least warming?

Changes in ocean temp = small

But changes in ocean chemistry = more significant

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Ocean Acidification

As ocean pulls carbon dioxide out of atmosphere how does it affect the ocean?

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Ocean acidification

CO₂ is readily soluble in water and ∼30-40% of anthropogenic CO₂ released into atmosphere dissolves into the oceans

CO₂ reacts with water molecules for form carbonic acid

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Fate of anthropogenic CO₂ emissions

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Dissolved ions regulate ocean acidity and alkalinity

If excess OH- in solution = Basic/alkaline
If excess H+ in solution = Acidic
pH scale measures acidity/alkalinity

Low pH value - acidic
High pH value - alkaline (basic)
pH 7 = neutral

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Ph of oceans = 8 (slightly alkaline)

Log scale (8 to 9 = ten-fold change)

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Where does ocean acidity come from?

CO₂ + H₂O ←→ H₂CO₃ ←→ H⁺ + HCO₃^-←→ H⁺+ CO₃^-2

as CO₂ increases, decrease in pH of the ocean

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Patterns?

Over time?

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Change in sea surface pH (1700’s-1990)

Change of 0.1 ph = 30% increase in acidity

It is thought that the pH of ocean surface water will decrease by about 0.2 by 2100.

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Effect of increasing acidity

Shell forming organisms will have trouble making their shell from CaCO3

Will affect entire food chain

Pteropod shells are dissolving & damaged

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Effect of increasing acidity

Photosynthetic organism will benefit from increased CO₂

Calcifying (shell forming) species will suffer

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Food and Agriculture Organization of the United Nations

OA will cause decline in commercial fisheries.

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Coral at Risk

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Coral Bleaching

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Symbiotic relationship between coral and algae

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Symbiotic relationship between coral and zooxanthellae

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Coral Bleaching

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Half of Great Barrier Reef has died since 2016

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Carbon Cycle

Organic (derived from the biosphere)
Inorganic (containing no C-H or C-C bonds)

Inorganic carbon is responsible for ocean acidification.

CO₂ is readily exchanged between the atmosphere and ocean.

Wikimedia User: Hgrobe

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Carbonate Buffering System

To demonstrate how carbonation affects pH of the oceans, we need to study the following chemical reaction. We’ll start by reading it from the left.Carbon Dioxide + water combine to create carbonic acid, which then dissociates by losing one H+ ion and becoming bicarbonate, a negative ion. Bicarbonate further dissociates by losing one more H+ ion (now we have two) and becomes a carbonate ion. this equation can and does move in both directions in an attempt to reach an equilibrium or balance When the system is NOT in equilibrium or balanced, one side gets weighed down. The result? The equation will move in the direction necessary to undo that imbalance. And therein lies the importance of this equation to the oceans. Notice that carbon dioxide is on the left and the hydrogen-plus ion that leads to increased acidity in on the right. Whenever one of these is increased or decreased, the equation will move in the direction necessary to undo that change. We call this particular reaction a BUFFERING reaction, because its equilibrium regulates the ocean concentrations of H-plus and hence ocean pH. It is VERY difficult, therefore, to change the pH of the oceans. So this chemical equation buffers and thus maintains a steady pH in the oceans.Is there any way to change ocean pH?Look closely at the equation. With an understanding of equilibrium, what is one thing I could do to make the oceans more acidic? I could add more carbon dioxide!

This equation maintains EQUILIBRIUM in the oceans, which means:�Whenever you try to change the ocean’s H+ or CO2 content, the above equation will work in whatever directions UNDOES the change, so the system goes back to being in balance.

Buffering keeps the ocean from becoming too acidic or too basic.
Precipitation or dissolution of calcium carbonate, CaCO₃, buffers ocean pH.
Oceans can absorb CO₂ from the atmosphere without much change in pH.
CO2is of major importance in controlling the acidity of seawater

CO₂ dissolves in water to make carbonic acid
The ocean is loaded with calcium carbonate
Calcium carbonate neutralizes acid, carbonic acid neutralizes base
If acid is added, it dissolves calcium carbonate and the pH is stabilized
If base is added, it is neutralized by carbonic acid so the pH stabilized
pH of ocean is constant at 8.1

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Yellow numbers are natural fluxes.

Red are human contributions (gigatons/year).

White numbers indicate stored carbon.

Movement of carbon between land, atmosphere, and oceans.

Source: U.S. DOE, Biological and Environmental Research Information System.

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Wikimedia User:BeAr

As CO₂ is added to the oceans, bicarbonate and carbonate ions are produced. This increases the H ions (acidity) in solution in the ocean’s waters.

To maintain chemical equilibrium, carbonate is converted to bicarbonate. Thus, the dissolution of CaCO₃ (calcite and aragonite) contained in the shells of organisms favored.

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What has caused these changes?

1. Increased CO2 in atmosphere means more CO2 in the ocean since there is continual exchange between the atmosphere upper part of the ocean.

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What has caused these changes?

What patterns do you see in each graph?

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What has caused these changes?

1. Increased CO₂ in atmosphere means more CO₂ in the ocean, since there is continual exchange between the atmosphere and the upper part of the ocean.

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What has caused these changes?

2. As ocean temperatures increase, its ability to hold CO₂ is reduced (in solubility).