Humans and the Ocean

The Ocean as a Carbon Sink

Earth’s oceans play a major role in regulating the planet’s climate by acting as carbon sinks—they absorb and store large amounts of carbon dioxide (CO₂) from the atmosphere. In fact, the oceans have taken in about one-fourth of the CO₂ released by human activities since the Industrial Revolution.

When CO₂ from the air comes into contact with the surface of the ocean, some of it dissolves into the water, forming carbonic acid. This process helps remove CO₂ from the atmosphere. Once in the ocean, the carbon can take several paths:

Physical (solubility) Pump

Cold, dense water near the poles absorbs more CO₂ and sinks to the deep ocean, carrying the carbon with it. This water can stay trapped for hundreds or even thousands of years before resurfacing.

2. Biological Pump

Tiny ocean organisms called phytoplankton use CO₂ during photosynthesis to make food. When these organisms die, some sink to the ocean floor, locking carbon away in sediments. Other marine animals like corals and shellfish use carbon to build shells and skeletons made of calcium carbonate. When they die, these materials can also become part of ocean sediments, storing carbon long-term. In many cases, the hard parts of marine organisms can be compacted and cemented together on the ocean floor creating new bioclastic sedimentary rocks.

Ocean Acidification

The oceans help regulate Earth’s climate by absorbing carbon dioxide (CO₂) from the atmosphere. But when too much CO₂ enters the ocean, it changes the water’s chemistry—a process called ocean acidification.

Here’s how it happens: When CO₂ dissolves in seawater, it reacts with water molecules to form carbonic acid. This weak acid breaks apart into hydrogen ions and bicarbonate ions. The extra hydrogen ions make the water more acidic and lower the ocean’s pH. Even a small drop in pH means the ocean is becoming more acidic than normal.

Ocean acidification has several serious consequences:

Shell-building Problems

Many marine organisms—like corals, clams, oysters, and some plankton—use calcium carbonate to build their shells and skeletons. Acidic water means less calcium carbonate is available for marine organisms. It makes it harder for the organisms to form these structures, and in severe cases, it can even dissolve existing shells.

2. Coral Reef Damage

Coral reefs depend on stable conditions to grow. As acidity increases, coral skeletons weaken and reefs can erode faster than they can rebuild, threatening entire reef ecosystems.

3. Food Chain Disruption

Because many small shell-forming organisms are at the base of the food web, their decline can affect fish, marine mammals, and even humans who rely on seafood.

4. Ecosystem Balance

Acidification can change the behavior and survival of marine species, leading to shifts in ocean biodiversity.

The Great Pacific Garbage Patch

The Great Pacific Garbage Patch is a massive area in the Pacific Ocean where large amounts of floating plastic, fishing nets, and other debris have collected. Estimates suggest it covers about 1.6 million square kilometers (around 620,000 square miles). That’s roughly twice the size of Texas or three times the size of France. It’s not a solid island of trash, but rather a huge zone filled with tiny bits of plastic, called microplastics, mixed into the water. These pieces are often too small to see easily, but together they make the area look like a thin soup of debris.

The patch is located between Hawaii and California and was created by a system of ocean currents known as the North Pacific Gyre. These circular currents trap floating trash that comes from rivers, ships, and coastlines around the Pacific. Once plastics enter the ocean, they don’t break down easily. Instead, sunlight and waves slowly turn them into smaller and smaller pieces.

Most of the garbage in the Great Pacific Garbage Patch comes from human activities on land and at sea. Here are the main sources:

Land-based Litter (About 80%)

Trash from cities, streets, and rivers is washed into the ocean by rain or wind. Plastic bags, bottles, food wrappers, and packaging materials are common items. Once they reach the ocean, currents carry them into the patch.

2. Marine Sources (About 20%)

This includes waste from ships, fishing boats, and offshore platforms. Lost or discarded fishing nets, ropes, and gear—called ghost nets—make up a large part of the floating debris and can trap marine animals.

3. Improper Waste Management

In some regions, garbage dumps are near rivers or coastlines, and trash easily escapes into waterways.

4. Storms and Natural Disasters

Floods, hurricanes, and tsunamis can sweep huge amounts of plastic and debris from land into the sea.

This pollution harms marine life. Sea turtles, fish, and seabirds can mistake the plastic for food, which can make them sick or even kill them. Some plastics also release harmful chemicals into the water.

Visit The Ocean Cleanup to learn more about the Great Pacific Garbage Patch

Prevention and Cleanup

Stopping the Great Pacific Garbage Patch from growing—and eventually cleaning it up—requires both prevention and active cleanup efforts. Here’s how scientists, organizations, and individuals can help:

Reduce Plastic Use

The best way to stop more trash from entering the ocean is to use less single-use plastic. Choosing reusable bottles, bags, and containers keeps waste from starting its journey to the sea.

2. Improve Waste Management

Many countries are upgrading recycling systems and building better landfills to prevent trash from leaking into rivers and oceans.

3. Prevent Litter

Simple actions like properly disposing of trash, joining local cleanups, and keeping storm drains clear help stop waste before it reaches waterways.

4. Fishing Gear Recovery

Programs that collect or recycle old fishing nets and gear can prevent “ghost nets” from drifting into the ocean and harming marine life.

5. Cleanup Projects

Organizations such as The Ocean Cleanup are developing technologies that use large floating barriers to collect plastics from the surface of the ocean and from rivers before they spread further.

6. Education and Laws

Teaching people about the problem and passing laws to ban ocean dumping can make a big difference.

Overfishing

Overfishing happens when people catch fish faster than the populations can reproduce. This has become a major global problem, threatening ocean ecosystems and the livelihoods of millions of people who depend on fishing for food and income.

Modern fishing technology—like giant nets, sonar, and factory ships—allows boats to catch enormous numbers of fish. While this makes seafood widely available, it also means many fish species are being removed from the ocean too quickly.

Here are some key numbers to show the scale of the overfishing problem worldwide:

Global Fishing Stocks

According to the FAO (Food and Agriculture Organization), about 33% of the world’s fish stocks are overfished, meaning fish are being caught faster than they can reproduce. Another 60% are fished at maximum sustainable levels, leaving very little room for error. Only around 7% are underfished.

2. Decline of Popular Species

Some species have suffered dramatic drops:

- Bluefin tuna populations have declined by over 90% in the last 50 years.
- Atlantic cod stocks collapsed in the early 1990s by about 95%.

Both Bluefin tuna and Atlantic Cod populations have rebounded slightly in more recent years, but recovery has been slow.

3. Economic Impact

Overfishing costs the global economy an estimated $83 billion per year in lost revenue from depleted fish populations.

4. Bycatch Problem

Up to 40% of the fish caught worldwide are not the intended species. These “bycatch” animals—like dolphins, turtles, and sharks—are often thrown back dead or dying.

5. Projected Seafood Shortages

If current overfishing trends continue, the UN's Food and Agriculture Organization (FAO) warns that many major fish stocks could collapse by 2050, threatening food security for over 3 billion people who rely on fish as a primary protein source.

When too many fish are taken, the entire food web is affected. Predators lose their prey, and smaller species can overpopulate, throwing ecosystems out of balance. Coral reefs and coastal habitats also suffer because fish play important roles in maintaining healthy environments.

To solve overfishing, scientists and governments are working together to create sustainable fishing practices. These include setting catch limits, protecting certain areas from fishing, banning destructive methods like bottom trawling, and promoting aquaculture (fish farming) done in environmentally responsible ways.

Consumers can help too by choosing sustainably sourced seafood—look for labels like the Marine Stewardship Council (MSC) certification. If people around the world fish responsibly, the oceans can recover and continue providing food for generations to come.

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