The deep ocean, spanning everything beyond the sunlit surface layer, is Earth’s largest and most mysterious ecosystem, covering over 60% of our planet’s surface. The most profound regions of the Earth’s oceans are called the hadal zone. Named after Hades, the Greek deity associated with the realm of the dead, it is a menacing location that lives up to its ominous title. Comprising profound trenches and troughs, it goes down 11 km (6.8 miles) beneath the surface of the Earth’s oceans. This vast, dark expanse remains unexplored mainly due to the technical challenges posed by extreme pressures, frigid temperatures, and pitch darkness. Yet, despite its ominous reputation, the deep ocean plays a pivotal role in supporting life on Earth, contributing to climate stability, biodiversity, and even potential medical breakthroughs.
ECOLOGICAL SIGNIFICANCE: BIODIVERSITY & UNIQUE ECOSYSTEMS
The deep ocean is far from lifeless. Despite the absence of sunlight, it sustains diverse forms of life with fascinating adaptations, enabling species to endure crushing pressures, freezing temperatures, and total darkness. Hydrothermal vents, cold seeps, and deep-sea coral reefs host unique ecosystems where organisms rely on chemosynthesis rather than photosynthesis. Hydrothermal vent communities, for instance, support organisms like the giant tube worm (Riftia pachyptila) and Pompeii worm (Alvinella pompejana), which flourish by converting inorganic compounds into energy. These ecosystems reveal remarkable biological adaptability, providing insights into resilience that could inform conservation and medical advances.


Cold seeps and deep-sea corals are similarly unique, contributing to biodiversity by supporting life forms specially adapted to stable, nutrient-poor environments. The sheer diversity in the deep ocean is astounding, with many undiscovered species likely still hidden in these extreme environments. The continued exploration of these regions may yield species with unique biochemical compounds, some with the potential for applications in medicine, biotechnology, and environmental science.
MARINE FOOD WEBS
The deep ocean plays a central role in marine food webs, especially in sustaining species that are commercially significant. Many fish species—such as tuna, swordfish, and deep-sea snappers—rely on the deep sea at different life stages. These nutrient-rich depths provide a foundation for the marine food web, supporting phytoplankton and zooplankton that form its base. Through vertical migrations, deep-sea species also transport nutrients to the ocean’s upper layers, enhancing the productivity of surface waters and supporting fisheries.


All Images Courtesy: Dr Biju Dharmapalan
In addition to supporting food webs, the deep ocean acts as a sink for organic matter, recycling nutrients that are essential to the health of marine ecosystems. This nutrient cycling directly affects the sustainability of marine fisheries, which are crucial to the economy and global food security. Conservation strategies focused on understanding and preserving these ecosystems are vital for managing marine resources effectively.
CLIMATIC SIGNIFICANCE
Carbon Sequestration
The deep ocean serves as a major carbon sink, absorbing large amounts of carbon dioxide (CO2) and playing a vital role in regulating the Earth’s climate. Through the biological carbon pump, phytoplankton in surface waters convert CO2 into organic matter via photosynthesis. When these organisms die, they sink as ‘marine snow’, transferring carbon to the deep ocean floor. This process is complemented by the physical carbon pump, in which CO2 is absorbed in cold, dense waters at high latitudes and then transported to deeper layers through thermohaline circulation.
The sequestration of carbon in the deep ocean has significant climate implications, as it reduces the amount of CO2 in the atmosphere, helping to mitigate climate change. Without this carbon-capturing ability, atmospheric CO2 levels would rise at a much faster rate. Protecting the deep ocean’s carbon storage capacity is therefore essential for addressing global warming and maintaining climate stability.
Heat Distribution
The deep ocean also regulates the Earth’s climate by distributing heat. Ocean currents, driven by wind, temperature differences, and salinity, circulate heat across the globe, influencing climate and weather patterns. The thermohaline circulation, also called the ‘global conveyor belt’, transfers cold, dense water from polar regions to warmer equatorial areas, maintaining a balance in global temperatures.


The ocean’s ability to store vast amounts of heat acts as a buffer against extreme temperature changes in the atmosphere. This distribution of heat helps moderate global climate, contributing to weather stability and reducing the intensity of temperature fluctuations. As climate change continues to affect ocean temperatures, preserving the deep ocean’s natural ability to store and transfer heat is vital for climate resilience.
ECONOMIC SIGNIFICANCE
Resource Extraction
The deep ocean holds a wealth of mineral and biological resources with immense economic potential. Seafloor mining, though nascent, targets valuable metals like copper, nickel, cobalt, and rare earth elements. These minerals are found in polymetallic nodules, hydrothermal vent deposits, and cobalt-rich crusts on the ocean floor and are essential for modern technologies, including electronics, renewable energy systems, and electric vehicles.
Bioprospecting—the search for valuable compounds in living organisms—has uncovered unique molecules in deep-sea species with potential applications in medicine, such as antibiotics, anti-cancer agents, and enzymes. While the economic benefits of these resources are clear, responsible management is crucial to minimise the environmental impact of resource extraction and ensure that deep ocean remains a viable source for future generations.
Fisheries


Deep-sea fisheries contribute significantly to global food security and the economy. Many deep-sea species, such as the Orange roughy (Hoplostethus atlanticus), grenadiers, and deep-sea shrimps, are commercially valuable. However, deep-sea fishing poses challenges due to the slow growth and reproductive rates of many deep-sea species, making them vulnerable to overfishing.
Sustainable management of deep-sea fisheries is essential to balance economic benefits with conserving deep-sea ecosystems. Implementing measures such as catch limits, protected areas, and monitoring programmes can help ensure the long-term viability of deep-sea fisheries and the health of marine ecosystems.


THE HISTORY OF DEEP OCEAN EXPLORATION
Humanity’s understanding of the deep sea has evolved through centuries of scientific curiosity, technical advancements, and exploration. Ancient civilisations like the Greeks and the Romans saw the ocean as mysterious, often associating it with myths and deities. Early efforts to study marine life, such as Aristotle’s observations, were rudimentary, as the technology of that era limited exploration.
The Age of Exploration (16th-18th centuries) marked a pivotal phase in expanding oceanic knowledge. Navigators like Ferdinand Magellan, James Cook, and Christopher Columbus undertook voyages primarily to discover trade routes and new territories but also laid the groundwork for modern oceanography.
Technological progress began to transform deep-sea exploration. The first submarine, built in 1620 by Cornelis Drebbel, could only navigate shallow waters. True breakthroughs came with the development of sonar in the 20th century. A historic milestone was achieved in 1960 when the bathyscaphe Trieste descended to the Challenger Deep, over 35,800 feet below the surface, enduring immense pressures equivalent to ‘50 jumbo jets’ worth’.
The 1970s and 1980s witnessed the advent of Remotely Operated Vehicles (ROVs), unmanned, tethered devices equipped with cameras and sensors, revolutionising deep-sea exploration. Human-occupied vehicles (HOVs) complemented ROVs, enabling direct observation and interaction with the underwater environment. James Cameron’s 2012 solo dive to the Mariana Trench aboard Deep Sea Challenger provided valuable scientific insights and imagery, reaffirming the importance of human involvement in exploration.


Recent expeditions have unveiled new species, ecosystems, and geological formations, offering insights into the Earth’s history and the origins of life. The Five Deeps Expedition (2018-2019), led by Victor Vescovo, reached the deepest points in the world’s five oceans using the submersible DSV Limiting Factor, revealing critical data about these extreme environments.
INDIA’S INITIATIVES
India is advancing its marine research capabilities through initiatives in oceanography. The National Institute of Ocean Technology (NIOT) in Chennai has developed a range of deep-sea exploration tools, including a 6,000-meter-rated ROV, an Autonomous Underwater Vehicle (AUV), and an Autonomous Coring System (ACS). These technologies have allowed India to explore its exclusive economic zone and contribute to global marine research.
India’s Samudrayaan Mission, part of the Ministry of Earth Sciences’ efforts, aims to deploy the manned submersible MATSYA 6000 to a depth of 6,000 meters. This mission places India among a select group of countries with the capability for deep-sea exploration, including the United States, Russia, Japan, France, and China. One of Samudrayaan’s primary objectives is to locate and analyse polymetallic nodules in the Central Indian Ocean Basin. Rich in manganese, nickel, cobalt, and copper, these nodules are essential for electronics, batteries, and renewable energy technologies. India’s exploration efforts can potentially contribute to the global demand for these resources while developing its marine science expertise.


THREATS TO DEEP OCEANS
The deep ocean faces numerous threats from human activity, including pollution, habitat destruction, and climate change. Deep-sea mining, while economically promising, poses significant risks to fragile ecosystems. Mining disrupts seafloor habitats, creates sediment plumes, and releases toxic substances, which can harm marine life and disrupt ecosystem functions.
Pollution is another major concern. Plastics, chemicals, and even noise pollution from submersibles and ROVs can reach the deep ocean, affecting organisms adapted to its dark and quiet environment. Additionally, climate change is altering the deep ocean through warming, acidification, and deoxygenation. These changes disrupt biological processes, alter species distributions, and threaten the health of deep-sea habitats.
CONSERVATION EFFORTS AND INTERNATIONAL COLLABORATION
Conserving the deep ocean requires global cooperation, as its ecosystems are often located beyond national jurisdictions. Marine Protected Areas (MPAs) effectively preserve biodiversity, providing safe havens where marine life can thrive. However, protecting deep-sea ecosystems on a global scale requires a coordinated approach.
The Biodiversity Beyond National Jurisdiction (BBNJ) Agreement, recently signed by India, represents a significant step toward protecting marine biodiversity in international waters. This treaty aligns with the United Nations Convention on the Law of the Sea (UNCLOS) and aims to regulate marine resource conservation and sustainable use.
REV Ocean, founded by Norwegian entrepreneur Kjell Inge Røkke and marine biologist Nina Jensen, exemplifies a dedicated approach to ocean conservation. The organisation collaborates with key partners to tackle pollution, overfishing, and climate change issues. Equipped with advanced scientific tools, the REV Ocean vessel supports research and solutions to safeguard the ocean’s health for future generations.
CONCLUSION
The deep oceans are paramount to our planet’s health and sustainability. Their ecological, climatic, economic, and scientific significance underscores the need for continued exploration, research, and conservation efforts. Protecting the deep oceans is vital for preserving biodiversity and ecosystem services and ensuring our planet’s long-term resilience to environmental challenges. By addressing the challenges of deep-sea exploration, scientists and engineers develop technologies and methods that are directly transferable to space exploration, enhancing our ability to explore, understand, and eventually inhabit other worlds.
As we continue to explore and understand the deep oceans, it is imperative to balance the use of their resources with the protection of their fragile ecosystems. By fostering international cooperation, advancing scientific research, and promoting sustainable practices, we can safeguard the deep oceans for future generations and unlock the mysteries of this final frontier. The future of our planet and the myriad life forms that call it home depend on a healthy and vibrant deep ocean.
*The writer is the Dean (Academic Affairs) at Garden City University, Bangalore, and an Adjunct Faculty at the National Institute of Advanced Studies, Bangalore. He can be contacted at bijudharmapalan@gmail.com