THE OCEAN IS AN ESSENTIAL ELEMENT OF OUR PLANET AND PLAYS A VITAL ROLE IN SUPPORTING LIFE AS WE KNOW IT.
The ocean, which stretches from the coast to the open seas and from the surface to the abyssal depths, covers approximately 70% of the Earth's surface and is home to an astonishing diversity of marine life, ranging from the microscopic, such as viruses and bacteria, to the majestic, like whales and large mammals.
The ocean consists of distinct zones that vary in their proximity to the coast, seabed depth, light availability, water temperature, and the types of organisms that inhabit them. Depending on their distance from the coastline, marine zones can be categorized as neritic, which refers to the shallow part of the ocean near the coast and includes the continental shelf (approximately 1/4 of the global seafloor), or pelagic, which pertains to the open sea. The term "pelagic" originates from the Greek word "pelagos," which means "of or relating to the open sea." The pelagic zones are further classified based on their vertical position in the water column and are commonly referred to as the epipelagic, mesopelagic, bathypelagic, abyssopelagic, and hadalpelagic zones.
Open ocean zones
image courtesy: National Oceanic and Atmospheric Administration (NOAA)
OCEAN IS A DYNAMIC ENVIRONMENT SHAPED BY THE INTERPLAY OF PHYSICAL, CHEMICAL AND BIOLOGICAL FORCES.
THE EPIPELAGIC ZONE SERVES AS A PRIMARY SOURCE OF OXYGEN PRODUCTION THROUGH PHOTOSYNTHESIS, WHICH IS VITAL FOR SUSTAINING BOTH MARINE AND TERRESTRIAL ECOSYSTEMS
The epipelagic zone, often referred to as the "sunlight" or euphotic zone, constitutes the uppermost layer of the ocean that spans from the surface down to approximately 200 meters (656 feet) in depth. This zone derives its name from the presence of sunlight, a vital component for photosynthesis, which fuels the rich biodiversity found here.
Within the epipelagic zone, phytoplankton take centre stage as the primary producers. These microscopic, plant-like organisms form the foundation of the marine food web. Phytoplankton harness the sun's energy to convert carbon dioxide and nutrients into organic matter, making them essential for the sustenance of marine life and for their significant role in the global carbon cycle. By absorbing substantial amounts of carbon dioxide from the atmosphere and transforming it into organic material, phytoplankton contribute to carbon sequestration, which plays a pivotal role in regulating the Earth's climate.
Phytoplankton
photo courtesy: NOAA MESA Project
ocean surface - 656 feet
Phytoplankton
photo courtesy: NOAA MESA Project
ocean surface - 656 feet
Moreover, the epipelagic zone is not just a hotspot for marine biodiversity; it also serves as a habitat for an array of fascinating species, including fish, marine mammals, and seabirds.
These creatures rely on the abundant zooplankton, which feeds on phytoplankton, creating a complex web of predator-prey relationships that shape the intricate balance of life in this sunlit realm.
The epipelagic zone supports some of the most valuable fisheries on the planet, making it indispensable for commercial fishing and providing sustenance for billions of people.
Zooplankton - Copepod with eggs
photo credit: Matt Wilson/Jay Clark; Affiliation: NOAA NMFS AFSC
ocean surface - 656 feet
Zooplankton - an assortment of crustaceans
photo credit: Matt Wilson/Jay Clark; Affiliation: NOAA NMFS AFSC
ocean surface - 656 feet
THE MESOPELAGIC ZONE CONTRIBUTES TO CLIMATE REGULATION BY SEQUESTERING CARBON DIOXIDE THROUGH THE DAILY VERTICAL MIGRATION OF ITS RESIDENT ORGANISM, HELPING TO MITIGATE CLIMATE CHANGE.
Hawaiian bobtail squid (Euprymna scolopes)
photo source: Canva.com
The mesopelagic zone, often referred to as the twilight zone, is situated between the epipelagic zone (near the ocean's surface) and the bathypelagic zone (the deep-sea region).
This intriguing zone extends from approximately 200 meters (656 feet) to around 1000 meters (3281 feet) below the ocean's surface. As its name suggests, the mesopelagic zone receives only faint traces of sunlight, creating a dimly lit environment similar to twilight.
This unique lighting condition has given rise to a diverse population of bioluminescent organisms. These organisms produce light through chemical reactions to aid in camouflage, attract prey, or communicate with others. In some cases, this bioluminescence is achieved through a symbiotic relationship with bioluminescent bacteria.
656 - 3281 feet
656 - 3281 feet
Southern Bobtail squid (Euprymna tasmanica)
photo source: Canva.com
Northern shortfin squid (Illex illecebrosus) actively feeding on a large swarm of crustaceans
photo courtesy: NOAA Office of Ocean Exploration and Research
656 - 3281 feet
Beyond its intriguing features, the mesopelagic zone plays a crucial role in facilitating the movement of organic matter (OM) and carbon through the oceanic water column. Many organisms exhibit vertical diurnal migrations, ascending to the epipelagic zone at night to feed on plankton and descending to the mesopelagic zone during the day to evade predators. This daily migration not only regulates interactions between predators and prey but also promotes the transport of nutrients. This is achieved through the excretion of faeces and urine, followed by the subsequent bacterial decomposition of this organic matter. Additionally, this movement promotes carbon sequestration in the deep ocean. When organisms that have consumed organic material sink and die, they transport carbon downward in a process known as the 'biological pump.'
This phenomenon contributes to carbon sequestration in the deep ocean, playing a pivotal role in regulating carbon dioxide levels on Earth.
Biological pump
image courtesy: E.L. Cavan, A. Belcher, A. Atkinson, S. L. Hill, S. Kawaguchi, S. McCormack, B. Meyer, S. Nicol, L. Ratnarajah, K. Schmidt, D. K. Steinberg, G. A. Tarling & P. W. Boyd; https://www.nature.com/articles/s41467-019-12668-7
THE BATHYPELAGIC AND ABYSSOPELAGIC ZONES PRESENT SOME OF THE MOST EXTREME CONDITIONS ON EARTH AND SERVE AS TESTAMENTS TO THE ASTONISHING ADAPTABILITY OF LIFE IN THE OCEAN'S DEPHTS.
The bathypelagic and abyssopelagic zones, located below the euphotic zone (the uppermost layer of the ocean where sunlight can penetrate), are two of the most enigmatic and least explored ocean regions.
The bathypelagic zone, known as the midnight zone, extends from approximately 1,000 meters (3,280 feet) to 4,000 meters (13,123 feet) below the ocean's surface. It is characterized by darkness, high pressure (at 4,000m depth, it can reach as much as 411 Kg/cm²), and a low but stable temperature of around 4°C. Creatures in this zone must adapt to a life with minimal food resources, which often leads to them having slow metabolisms. They typically rely on marine snow, which is a mix of organic matter and debris that drifts down from above. The inhabitants of this zone have squishy bodies and slimy skin, which helps them survive the extreme pressures of the deep ocean.
Marine snow
photo credit: Henk-Jan Hoving/GEOMAR
3281-13123 feet
Fish faecal pellets
photo credit: Grace Saba
3281-13123 feet
The abyssopelagic zone is the region of the ocean that lies below the bathypelagic zone, typically starting around 4,000 meters (13,123 feet) and extending down to about 6,000 meters (19,685 feet) below the ocean's surface. Animals inhabiting this extreme depth must withstand immense pressures, which can be up to 600 times greater than what is experienced at sea level, and they have developed highly specialized adaptations for survival.
One of the most remarkable species found on the seafloor of this zone is the tripod fish. These unique creatures can pump fluid into their elongated fins, effectively transforming them into rigid stilts, resembling a tripod. These extended fins can reach several feet in height, allowing the tripod fish to perch above the seafloor and patiently wait for passing prey. This adaptation helps them navigate and hunt in the challenging environment of the abyssopelagic zone, where food resources are scarce and the pressures are extreme.
The tripod fish (Bathypterois viridensis) was observed during Dive 6
image courtesy of the NOAA Office of Ocean Exploration and Research, Exploring Deep-sea Habitats off Puerto Rico and the U.S. Virgin Islands.
13123 - 19685 feet
13123 - 19685 feet
Sperm whale VS Giant squid
image credit: Ryan Somma from Occoquan, USA
The abyssopelagic zone is home to nektonic species like giant squids, occasionally attracting sperm whales for hunting. Whales have evolved remarkable adaptations for deep diving, including efficient lung capacity, reduced oxygen consumption through slowed heart rate and selective blood flow, myoglobin-rich muscles for oxygen storage, and the ability to regulate gas levels. These adaptations enable whales to explore this extreme environment and hunt elusive prey like giant squids.
THE HADALPELAGIC ZONE IS THE DEEPEST PART OF THE OCEAN, AND IT PRESENTS SOME OF THE MOST EXTREME ENVIRONMENTAL CONDITIONS ON OUR PLANET.
Xenophyophore
photo courtesy of IFE, URI-JAO, Lost City Science Party, and NOAA.
The hadalpelagic zone, also known as the hadal zone or hadal region, spans from depths of approximately 19,700 feet (6,000 meters) to the very bottom of the Mariana Trench, which reaches an astounding depth of 36,070 feet (10,994 meters). This trench represents the deepest known part of the Earth's oceans.
The pressure experienced in the hadalpelagic zone is staggering, primarily due to the immense weight of the water column above. At its deepest points, the pressure can reach levels exceeding 1,000 times the atmospheric pressure at sea level, exerting an incredible force on everything in this extreme environment. This immense pressure poses a formidable challenge to the survival of any organisms that venture into these depths.
In addition to the immense pressure, the hadalpelagic zone features frigid water temperatures, hovering around the freezing point and staying in the range of 1-4°C (34-39°F). These cold temperatures further complicate the survival of organisms, necessitating their adaptation to the extreme cold and pressure conditions unique to this extraordinary environment.
Some of the most intriguing and unique creatures on Earth are found in the Hadal zone. These include amphipods, giant single-celled organisms known as xenophyophores, and various species of fish and invertebrates that have evolved special adaptations to thrive in this harsh environment.
THE OCEAN HELPS DISTRIBUTE HEAT AND NUTRIENTS AROUND THE PLANET THROUGH SURFACE AND DEEP OCEAN CURRENTS, INFLUENCING WEATHER PATTERNS AND MAINTAINING GLOBAL CLIMATE STABILITY.
THIS WATER MASS "HEATING SYSTEM" IS NAMED CONVEYOR BELT.
The ocean is a vast and dynamic system with complex circulation patterns consisting of horizontal and vertical currents. These currents are vital for maintaining the ocean's health and significantly impact Earth's climate.
There are two types of currents: surface currents, which affect the top layers of water (about 10% of the ocean), and deep currents. Various factors contribute to the formation of ocean currents, including wind patterns, tides, changes in water density due to temperature and salinity, and the rotation of the Earth. Surface and deep currents work together to facilitate the movement and distribution of heat around the planet, playing a crucial role in regulating the climate.
They absorb heat from the surface of the ocean and distribute it globally.
The totality of the ocean currents acts together like a large Conveyor Belt, transporting nutrients and oxygen produced in the poles to the other lower latitudes via deep currents and upwelling systems and redistributing the heat absorbed near the equator to higher latitudes by releasing it gradually as it moves across the various oceans and seas.
Ocean surface currents
image credit: Dr Michael Pidwirny
Gyres are massive circular ocean current systems that significantly influence the circulation of water masses across different continental shelves. There are five major gyres worldwide, which are crucial components of the global ocean circulation system. These major gyres include the North Atlantic Gyre, South Atlantic Gyre, North Pacific Gyre, South Pacific Gyre, and Indian Ocean Gyre. Each of these gyres plays a vital role in the circulation of ocean waters on a global scale and contributes to the functioning of the Great Conveyor Belt, an essential part of Earth's climate system.
A summary of the path of the thermohaline circulation. Blue paths represent deep-water currents, while red paths represent surface currents
image credit: Robert Simmon, NASA Earth Observatory
