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Unlock This CourseOur oceans are like giant sponges that soak up carbon dioxide from the atmosphere. When CO₂ dissolves in seawater, it creates a chemical reaction that makes the water more acidic. This process is happening right now in oceans around the world and it's having major effects on marine life.
Understanding how carbon dioxide affects seawater pH is crucial for marine science because it helps us predict what will happen to ocean ecosystems as atmospheric CO₂ levels continue to rise.
Key Definitions:
Seawater is naturally slightly basic with a pH around 8.1. When we say oceans are becoming more "acidic," we mean the pH is dropping towards neutral (7.0). Even small changes in pH represent huge changes in acidity because the pH scale is logarithmic - a drop of 0.1 pH units means a 26% increase in acidity!
When carbon dioxide from the atmosphere meets the ocean surface, it doesn't just sit there - it gets busy creating a whole chain of chemical reactions that change the water's chemistry.
Here's what happens step by step when CO₂ enters seawater:
Carbon dioxide gas dissolves directly into the seawater at the surface, just like fizzy drink bubbles dissolving in water.
The dissolved CO₂ reacts with water molecules to form carbonic acid (H₂CO₃), which is unstable and quickly breaks down.
Carbonic acid releases hydrogen ions (H⁺) and bicarbonate ions (HCO₃⁻), making the water more acidic.
The more CO₂ that dissolves, the more hydrogen ions are released and the lower the pH becomes. This is why rising atmospheric CO₂ levels directly lead to more acidic oceans.
The oceans absorb about 25% of all the CO₂ that humans put into the atmosphere each year. That's roughly 22 million tonnes of CO₂ every single day! Without this ocean absorption, atmospheric CO₂ levels would be much higher than they are now.
Scientists have been tracking ocean pH for decades and the results show clear patterns of acidification happening worldwide.
Since the Industrial Revolution began around 1750, ocean pH has dropped by about 0.1 units globally. This might sound small, but remember - it represents a 26% increase in acidity across all the world's oceans.
Ocean pH was stable at around 8.2 for thousands of years. Marine ecosystems evolved and adapted to these consistent chemical conditions.
Average ocean pH is now around 8.1 and continuing to drop. The rate of change is faster than anything seen in the geological record for millions of years.
Not all parts of the ocean are experiencing the same pH changes. Some regions are becoming acidic faster than others due to local conditions.
The Arctic Ocean is experiencing some of the most rapid acidification on Earth. Cold water absorbs more CO₂ than warm water and melting ice is adding fresh water that has different chemical properties.
In Alaska's Bering Sea, pH levels have dropped so much that some areas now have water that's corrosive to shell-building organisms. Crab fishermen have reported finding crabs with damaged shells and some fish populations are showing signs of stress from the changing water chemistry.
Areas where deep, CO₂-rich water rises to the surface (like off the coasts of California and Peru) are experiencing particularly severe acidification. These waters were already more acidic and additional CO₂ is pushing them to extreme levels.
Changing ocean pH doesn't just affect water chemistry - it has direct impacts on the creatures that call the ocean home.
Many marine animals build their shells and skeletons from calcium carbonate, which becomes harder to form as water becomes more acidic.
Oysters, mussels and clams struggle to build strong shells in acidic water. Young shellfish are especially vulnerable during their early development.
Corals find it harder to build their calcium carbonate skeletons, leading to weaker reef structures that are more easily damaged by storms.
These spiny creatures have trouble forming their protective shells, making them more vulnerable to predators and environmental stress.
Even fish without shells are affected by changing pH. Acidic water can interfere with their nervous systems, affecting their ability to smell, navigate and avoid predators.
Research on the Great Barrier Reef has shown that clownfish raised in more acidic water lose their ability to recognise the smell of their home anemone. This makes it much harder for young fish to find safe places to live, potentially disrupting entire reef communities.
Scientists use various tools and techniques to track ocean pH changes and understand their effects.
Modern oceanographers use sophisticated equipment to measure pH with incredible precision.
Ships equipped with automated pH sensors travel regular routes, collecting continuous data about ocean chemistry changes over time.
Floating instruments anchored in key locations provide real-time pH data, helping scientists track rapid changes in ocean chemistry.
Based on current trends and climate models, scientists can predict how ocean pH will continue to change in the coming decades.
If current CO₂ emission trends continue, ocean pH could drop by another 0.3-0.4 units by 2100. This would represent a total change of 150% in ocean acidity since pre-industrial times.
Some marine ecosystems may reach critical thresholds where they can no longer function normally, leading to collapse of local food webs.
Changes in ocean chemistry could affect global weather patterns, fish populations that billions of people depend on for food and coastal protection from coral reefs.
While ocean acidification is a serious challenge, understanding the problem is the first step towards solutions. Some marine organisms are showing signs of adaptation and reducing CO₂ emissions can slow the rate of change, giving ecosystems more time to adjust.