The Finite Ocean

This is the fifth chapter in Living in the Age of Humans, a series of stories examining the planet-wide impacts of our species. If this is new to you, read the  introductory story  to learn more about the series, or browse the other chapters — The Human Reach, The Living Land, A World of Forests, and The Diversity of Life — in  this collection .

With every drop of water you drink, every breath you take, you’re connected to the sea. No matter where on Earth you live.

Our terrestrial existence makes it easy for most of us to forget that ours is a water planet. The ocean covers 71 percent of Earth's surface. The ocean formed early in our planet's history, and life originated in it. For more than 3 billion of Earth's 4.5-billion-year history, the ocean was the sole cradle of life. We are the descendants of the ocean. Before we were born, we floated in salt water. Salt courses through our veins. We breathe oxygen that the ocean provides.

For most of human existence, the ocean seemed infinite and inexhaustible. We harvested its riches with little regard for our impact on its dynamic processes and abundant ecosystems. Early warnings, like the hunting of whales to near extinction in the 19th and 20th centuries, did little to alter our profligate habits. The great explosion of human populations and economies of the past century have made it clear that the ocean is indeed finite, and that our activities are having profound impacts on its health.

Human activities are having multiple effects on the ocean and the life it harbors. Burning of fossil fuels is raising ocean temperatures and altering its chemical composition, damaging coral reefs and other ecosystems. Thousands of tons of plastics are washing into the ocean every year, and fisheries are being over-exploited, risking collapse of commercially important species.

The map above estimates the change in human impact to global marine ecosystems from 2003 to 2013. The most heavily impacted areas — as determined by 12 different human-made stressors, which range from vessel traffic to sea temperature change — are shown in bright yellow, while the least impacted areas appear blue.

The pressure to feed an ever-growing human population has, perhaps inevitably, led to overfishing and other unsustainable fishing practices. The harvesting of fish at rates that exceed their ability to maintain healthy populations is an increasing concern in many regions around the world. The UN Food and Agriculture Organization bottom (FAO) estimated that a third of global fish stocks were being overfished in 2019.

Compounding the overfishing issue is illegal, unreported, and unregulated fishing, which undermines efforts to manage and conserve fisheries. Fishing without proper licenses, catching protected species, and exceeding quotas threatens the sustainability of marine ecosystems.

Many fish stocks have been depleted or are at risk of depletion due to overfishing. Some prominent examples include Atlantic cod and bluefin tuna. Depleted fish stocks not only harm the environment but also affect the livelihoods of millions of people who depend on fishing for their income and food security.

Some fishing techniques have serious unintended impacts. Bottom trawling can scrape seafloor communities clean, and drift nets often capture non-target species in what's known as bycatch. These practices result in the destruction of sensitive ecosystems like coral reefs and contribute to the decline of marine species. 

Farm-raised fish can help alleviate overfishing of wild stock, but in many cases aquaculture raises significant environmental concerns. Farming of Atlantic salmon, for instance, causes pollution from chemical treatments and excessive fish feces.

Conservation efforts, including initiatives to address overfishing and promote sustainable fisheries management, are increasing. Many countries have implemented fishing quotas, established marine protected areas, and adopted sustainable fishing practices to rebuild fish populations and protect marine biodiversity.

About three percent of Earth's global greenhouse gas emissions come from maritime cargo vessels. That may seem like a modest number, but if the industry were a country, it would rank as the world's sixth largest emitter.

As ocean transport continues to increase, undersea noise levels rise. Whales are among the species that use sound to communicate over long distances; noise from ship engines and propellers can disrupt this communication. The mere presence of large ships can disrupt foraging behaviors.

Commercial vessels, including cargo ships and cruise ships, may inadvertently transport invasive species in their ballast water, which is water held in tanks to add weight and stability when a ship is carrying less cargo, and which is typically taken on in one port and discharged in another. This water can contain a variety of organisms, including bacteria, viruses, algae, and even small fish and other marine animals. When discharged in a new port, these organisms can sometimes outcompete native species, damaging ecosystems and reducing marine biodiversity.

A poster child for marine invasives is the lionfish. Native to the South Pacific, they are popular with collectors. In this case a few individuals were released off the Florida coast in the 1980s. Lionfish have since spread throughout the Gulf of Mexico, Caribbean, and the U.S. east coast, threatening to displace many native species and damaging coral reef ecosystems.

Because the oceans cover three-fifths of the planet, it's perhaps unsurprising that the deep ocean is estimated to hold more mineral reserves than all land-based deposits. The potential for mining and resource extraction of ocean-floor minerals is enormous — as are the potential environmental consequences.

The global marine mining industry was valued at only $1.6 billion in 2021, but this figure could increase to $31.5 billion by the end of 2031 due to rising demand for the rare earth metals and minerals in undersea deposits.

The heavy machinery used in deep sea mining and oil and gas extraction can cause significant damage to delicate deep-sea habitats such as seamounts, hydrothermal vents, and cold-water coral reefs. Mining activities can release pollutants and toxins into the water, including chemical-laden sediment that can travel long distances and potentially smother marine life. 

The 2010 Deepwater Horizon oil spill was the largest marine oil spill in the history of the petroleum industry, and was so extensive that it was visible from space. Many of the affected ecosystems have not yet recovered fully. Among many other impacts, the spill killed an estimated 167,000 sea turtles. Spilled oil also entered the food chain, and was eventually detected even in land mammals and birds. 

As the ocean absorbs heat from the atmosphere, sea surface temperatures rise and the ocean's chemical composition changes. The combination of warming and acidification has profound impacts on ocean ecosystems, especially coral reefs, which are among the Earth's richest and most diverse ecosystems.

Corals are tiny organisms, billions of which create vast reefs that harbor many life forms. Coral polyps have a symbiotic relationship with microscopic algae. When temperatures reach a critical point, coral bleaching occurs; the algae are expelled by the coral, causing it to turn a ghostly white. Reefs usually recover from a single bleaching event, but repeated bleaching makes the coral more susceptible to disease and increases the risk that entire reef ecosystems may collapse.

High sea surface temperatures often cause hurricanes and typhoons to become stronger and more destructive, resulting in severe storm surge events. In September 2022, Hurricane Ian crossed the eastern Gulf of Mexico as it approached the west coast of Florida. Unusually warm surface waters — nearing 90 degrees Fahrenheit — caused the hurricane to rapidly intensify. It struck the coast north of Fort Myers as a high category four storm. Scientists predict that, although the frequency of storms may not increase, their intensity likely will.

The greater rates of warming in polar regions are boosting concerns about sea level rise caused by increased melting of glaciers in Antarctica and Greenland. A recent study indicates that the rate of warming in Antarctica is more rapid than climate models have been predicting.

The Thwaites Glacier in West Antarctica, the world's widest, is melting into the ocean at alarming rates. The glacier currently contributes 4 percent of all sea level rise; its collapse could worsen impacts on coastal cities worldwide. Sea levels along U.S. coastlines are already projected to rise by 10 to 12 inches between 2020 and 2050.

Relative sea level change is a combination of global sea level rise and local vertical land motion. The map below shows relative sea level rise as measured by tide gauges. A negative trend does not mean that the ocean is not rising. Instead, it indicates that the land is rising even faster than the ocean. These shifts will dramatically increase the severity of storm-related flooding in many locations.

Perhaps the greatest pollution-related threat to oceans is from discarded plastic and trash. Most plastics are derived from petroleum; the large molecules in plastics biodegrade extremely slowly. Currents carry plastic trash for thousands of kilometers, where some eventually accumulates in five "garbage patches," the largest of which is in the central Pacific and is roughly twice the size of Texas.

Marine species may become entangled in plastic waste; ingesting plastic can cause suffocation, and disrupts food chains and ecosystems. Large plastic objects eventually break down into small particles called microplastics which, although largely invisible, continue to wreak havoc on ocean environments. Despite increased awareness of the problem, the amount of plastic waste entering the ocean continues to increase.

Oil spills tend to attract media attention, but far more oil — two to three times as much, in fact — enters the ocean as polluted runoff from roads, cities, and other sources. In addition to oil, runoff may carry fertilizers, pesticides, and animal waste. Fertilizer in particular can result in huge algae blooms, depleting areas of the ocean of oxygen. A recurring "dead zone" appears in the summer off the mouth of the Mississippi River. Most fish can simply swim away from these areas, but less mobile species die off.

The World Wildlife Fund estimates that animal agriculture accounts for approximately 60 percent of global marine eutrophication (which refers to the enrichment of nutrients and depletion of oxygen in an ecosystem). Animal waste can also contain harmful bacteria and pathogens, such as E. coli and salmonella, which contaminate animal and human food supplies.

Pesticides, primarily from farming operations, can harm marine organisms. Toxic chemicals can enter the marine food chain and can have a cumulative effect on predators consuming contaminated prey.

Coastal development can alter hydrology and water quality, and can result in habitat destruction and fragmentation, erosion, and increased pollution from runoff and sewage. This can negatively affect the health of both marine ecosystems and the people who depend on them for food and income. 

Continuing coastal development not only causes pollution, but destroys tidal marshes and mangrove swamps, both of which are important nurseries for many marine species and serve as buffers against storm surge. A NASA study showed that nearly 3,400 square kilometers (1,300 square miles) of mangroves, or two percent of the world's mangroves, were lost between 2000 and 2016. Wetlands are also threatened by sea level rise.

Concerns have been raised that MPAs can reduce access to commercially valuable fish stocks. But in many cases MPAs have resulted in increased catches by providing areas where populations of marine species can replenish.

Previous goals to protect 10 percent of the Earth's oceans by 2010 and 2020 both went unmet. A current goal to protect 30 percent of the planet's lands and waters by 2030 has gained wide international support, yet progress toward this ambitious target has been slow.

The ocean is life, not only for all of its creatures but for each and every one of us, no matter WHERE on this planet we live. "He kapu ka moana" [the ocean is sacred].

Humankind — Homo sapiens — is the sole species in Earth's 4.5-billion-year history to have had a profound impact on the entire planet. It is also the only species with awareness of its impacts and — theoretically — the ability to strive intentionally toward a future that achieves harmony with nature.

It's up to us to find ways to live in balance with the natural world, including the oceans, upon which we are utterly dependent.

You can help protect Earth's marine resources by supporting these organizations.

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Explore the map data in greater detail: