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Ocean Acidification Basics

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Ocean Acidification Basics

Read the coastal-research scenario and data table to investigate how extra carbon dioxide changes seawater. Answer in your own words where appropriate.

A changing coast

A marine research team is studying a reef and nearby shellfish beds. They are investigating how carbon dioxide (CO₂) from human activities can affect ocean chemistry and organisms.

1.Multiple choice: Which process is the main driver of the recent increase in ocean acidification?

More carbon dioxide entering the atmosphere and dissolving into seawater
Tides mixing salt water with fresh water
The ocean absorbing more sunlight
Sea ice melting without any change in atmospheric gases

2.Short answer: When CO₂ dissolves in seawater, some reacts with water to form carbonic acid. What happens to the amount of hydrogen ions in the water?

3.True or false: Ocean acidification means that all seawater has become acidic, with a pH below 7.

TrueFalse

The monitoring record

Researchers measured the average surface-water pH at a coastal site. These readings are fictional data for this investigation.

Year

Average seawater pH

1980

8.15

2000

8.10

2020

8.05

4.Short answer: Describe the pattern in the coastal pH readings between 1980 and 2020. What does that pattern indicate about the water?

5.Short answer: Calculate the total change in pH from 1980 to 2020. Include the direction of change.

6.Multiple choice: Why might oysters and corals find it harder to build shells or skeletons as ocean acidification increases?

There may be fewer carbonate ions available to make calcium carbonate
Hydrogen ions turn all seawater into fresh water
The water loses all its dissolved oxygen
Salt disappears from the ocean

7.Explain why the pH readings alone do not prove that increased atmospheric CO₂ caused the change at this site. Give one other kind of evidence researchers could collect.

8.Short answer: Suggest one way ocean acidification could affect a food web, even if a predator is not directly sensitive to changing pH.

9.Fill in the blanks: When seawater pH decreases, hydrogen ion concentration generally . This makes seawater alkaline.

10.A coastal council wants to help limit ocean acidification. Propose one action that could reduce the amount of CO₂ added to the atmosphere, and explain how it could help.