The world’s oceans, covering over 70% of Earth’s surface, are home to diverse ecosystems and regulate the planet’s climate. Human activities have led to growing ocean pollution, posing a significant threat to marine environments globally.
Pinpointing the Most Polluted Ocean
The Pacific Ocean is considered the most polluted, due to significant plastic accumulation. The North Pacific Subtropical Gyre, ocean currents, draws in and traps marine debris, forming the Great Pacific Garbage Patch between Hawaii and California. This patch is not a solid island of trash, but a vast area of concentrated plastic particles, from large items to microplastics.
The Great Pacific Garbage Patch is the largest accumulation of ocean plastic, covering an estimated 1.6 million square kilometers (twice the size of Texas). Approximately 1.8 trillion plastic pieces (100,000 tonnes) are found here. Most of this debris (80%) originates from land-based activities in North America and Asia, with the rest from ocean sources like ships. While microplastics are abundant, larger objects account for most of the patch’s mass.
Types of Ocean Contaminants
Ocean pollution takes various forms. Microplastics, plastic fragments under five millimeters, are a pervasive contaminant. These include primary microplastics, manufactured for products like cosmetics, and secondary microplastics, resulting from the breakdown of larger items. Trillions of these tiny particles float on the ocean surface, with more in deeper waters.
Chemical pollutants are another threat, including persistent organic pollutants (POPs), heavy metals (e.g., mercury, lead), and nutrients from agricultural runoff and sewage. Oil spills introduce harmful petroleum products. Noise from shipping, oil drilling, and military sonar also disrupts marine animals’ communication and navigation. Discarded fishing gear, known as “ghost fishing” gear, traps and kills marine life after being lost.
Primary Sources of Ocean Pollution
Most ocean pollutants originate from human activities, primarily from land-based sources. Urban runoff, carrying litter and chemicals, flows into waterways and the ocean. Untreated sewage and industrial discharge release contaminants. Agricultural runoff, with fertilizers and pesticides, contributes to nutrient pollution and harmful chemicals. Littering on land is a direct source, as trash is blown or carried into the sea.
Sea-based activities also contribute to ocean pollution. Shipping leads to oil spills and noise pollution. Fishing activities are a source of marine debris, particularly abandoned gear. Offshore oil and gas operations cause spills and noise pollution. These diverse sources collectively introduce billions of pounds of trash and other pollutants into the oceans annually.
Impact on Marine Environments
Ocean pollution seriously impacts marine life and ecosystems. Plastics pose a significant threat, as marine animals mistake plastic for food, leading to ingestion. This can cause internal injuries, digestive blockages, starvation, and death. Thousands of marine animals, including seabirds, sea turtles, and mammals, are killed each year after ingesting plastic.
Entanglement in plastic, especially fishing gear, is another severe consequence. Animals caught in loops or nets suffer deep lacerations, strangulation, drowning, or become vulnerable to predators. This “ghost fishing” harms marine life long after the gear is lost. Chemical pollutants, like heavy metals and persistent organic pollutants, accumulate in marine animal tissues through biomagnification, affecting human seafood consumers. These toxins cause reproductive issues, immune suppression, and behavioral changes in marine organisms.
Ecosystems are also impacted. Nutrient pollution leads to harmful algal blooms that deplete oxygen, creating “dead zones” where marine life cannot survive. Coral reefs degrade from pollution and climate change, threatening biodiversity. Noise pollution disrupts marine mammals’ communication, navigation, and food finding, potentially altering migration routes or forcing habitat abandonment.