Ocean Uncharted: Exploring the Wonders Below

Ocean Uncharted: Exploring the Wonders Below

Covering over 70% of the Earth’s surface, the ocean is a realm of immense depth and diversity, with an average depth of 3,688 meters (12,100 feet).¹ Beneath the waves lies a world full of intricate ecosystems that have fascinated scientists and adventurers for centuries. However, human activities are leaving an increasingly visible mark on even the most remote corners of the ocean. 

In recent years, researchers like Dr. Alan Jamieson have found evidence of human impact in the hadal zone, the deepest region of the ocean. Plastics and harmful chemicals like polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs)—banned decades ago—have been discovered in animals living in the Mariana Trench. In some areas, the amount of plastic found far exceeds the number of marine animals. This startling reality underscores the urgency of protecting our oceans, from the sunlit surface to the deepest trenches.

The open ocean is commonly classified into different zones based on depth, each with unique characteristics and life forms. Understanding these zones is key to protecting the ocean’s ecosystems as they face increasing threats. This blog explores facts about each zone and highlights the immense pressures at various depths.

Epipelagic

• Ocean surface down to 200 m (~660 ft)
• Surface temperature can range from 36 °C (97 °F) to -2 °C (28 °F)²
• Sunlight supports photosynthetic organisms, the foundation of the marine food web
• Rich with life, from small fish to massive whales

Mesopelagic

• 200 m (~660 ft) to 1,000 m (~3,300 ft)
• Temperature sharply decreases, and sunlight diminishes, leading to a realm of perpetual twilight²
• 90% of the fish in the world (by mass) are found here³—many feature larger, upward-directed eyes to see food sources above²

Bathypelagic

• 1,000 m (~3,300 ft) to 4,000 m (~13,000 ft)
• Sunlight is absent, and the temperature is almost constant at 4 ºC (39 ºF)²
• Most hydrothermal vents—geysers on the seafloor that spew hot, mineral-rich water—are located in this zone⁴
• Specialized adaptations for survival include bioluminescence, such as anglerfish that uses a bioluminescent “lure” to attract prey⁵

Abyssopelagic

• 4,000 m (~13,100 ft) to 6,000 m (19,700 ft)
• ~75% of the deep ocean floor is in this zone²
• “Marine snow”, bits of organic debris such as decaying organisms, rain down from above, serving as a food source⁶
• Marine animal adaptations include slow metabolism, flexible stomachs, big mouths⁷, and the lack of gas-filled spaces (e.g., swim bladders) due to the intense pressure⁸

Hadal

• 6,000 m (~19,700 ft) to the deepest point at 10,994 m (36,070 ft)
• Only occurs in deep-ocean trenches where one of Earth’s tectonic plates is sliding beneath another. When combined across all oceans, these make up an area about the size of Australia⁹
• The deepest observed fish (8,336 m; 27,349 ft),¹⁰ squid (6,212 m; 20,381 ft),¹¹ and octopus (6,957 m; 22,825 ft)¹² were recently discovered in deep-ocean trenches

Feeling the Pressure

• At sea level, the pressure we feel is equal to 1 atm (14.7 psi)¹³
• Pressure increases by 1 atm for every 10 m (33 ft) of water. At 10 m, the pressure a diver would feel is double what they feel at the ocean’s surface¹³
• The Titan submersible that imploded in June 2023 lost contact at ~3,500 m (~11,500 ft); due to the immense pressure, the implosion likely occurred within one millisecond¹⁴
• At the deepest point (10,994 m; 36,070 ft), pressure is about 1,100 times greater than at sea level. If you were at the bottom of the ocean, it would feel like 100 adult elephants were standing on your head¹⁵

Looking Ahead

Exploring the ocean’s depths is both a scientific challenge and an adventure. Each layer presents unique environments that reveal the resilience of marine life. As human influence on the ocean grows, understanding, respecting, and protecting these remarkable ecosystems becomes even more critical—from the sunlit surface to the darkest trenches.