Planet Earth/5c. Earth’s Oceans (Warehouses of Water)

The Earth’s Oceans

Tracy Caldwell Dyson in the Cupola module of the International Space Station observing the Earth’s vast oceans below her in 2010.

The majority of your existence with be spent on one of the Earth’s continents, despite the fact that the majority of Earth’s surface is covered by water. Over 361 million square kilometers (139 million square miles) of Earth’s surface is covered by liquid water, representing 71% of Earth’s surface. This warehouse of liquid water is amazingly gigantic, yet rarely factors into our daily lives unless you are crossing one of these gigantic expanses of water. The Earth is called the “Blue Planet” because the blue color of these ocean waters dominates Earth’s overall color from outer space. Since all of Earth’s oceans are connected, the divisions of the World’s Ocean into geographically named regions are somewhat arbitrary, but typically divided into five oceans; the Pacific, Atlantic, Indian, Southern (Antarctic), and Arctic Oceans. However, each of these oceans are interconnected allowing water to circulate globally between these regions of Earth. The World’s Ocean exhibits an average depth of 3.7 kilometers, about 2.3 miles deep. As a major feature of Earth, the oceans are extremely important in regional weather patterns and climate far inland, and has a major factor in Utah’s weather, despite being almost 1 megameters from the nearest coastline.

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  Pacific Ocean
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  Atlantic Ocean
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  Indian Ocean
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  Southern (Antarctic) Ocean
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  Arctic Ocean

The ocean surface at the Marshall Islands in the Pacific Ocean.

Exploring the Ocean Floor

Victor Vescovo

With long hair and a gray beard Victor Vescovo is an alumnus of some of the most prestigious universities in the United States; earning degrees from Harvard, Stanford and MIT, but rather than science, Vescovo specialized in degrees in business and political science. He was recruited by the ill-fated Lehman Brothers where he worked on advising the Saudi Arabian government on business investments, but also served in the U.S. Navy Reserve as an intelligence officer until 2013. In 2001 he started a company offering credit and loans to members of the United States military, and later co-founded an investment company called Insight Equity. His financial banking experiences afforded him wealth that he put into extremely lofty personal goals, hiking the highest peaks on all seven continents including Mt. Everest, and reaching both the North and South Poles on skis. Having achieved these goals, Vescovo pushed on with an even greater personal goal to reach the five deepest points in the five oceans of the World. In May 2019 on board the submarine DSV Limiting Factor Victor Vescovo dived down to the deepest point on Planet Earth, the Challenger Deep within the Mariana Trench in the South Pacific. Discovered and named by the British Royal Society’s ship, the HMS Challenger in the 1870s, the Challenger Deep site reaches a depth near 10.9 kilometers below sea level.

The DSV Limiting Factor, the Triton Submarine that made the journey 10,925 meters below the ocean’s surface at Challenger Deep in 2019.

Most of Earth is covered by water, and rarely visited by humans.

A descent just a few meters deep into the ocean results in an increase of pressure, as the water above pushes down as a hydrostatic pressure, measured as force per unit area, crushing any submarine that descends to this depth. The deeper the descent the more pressure is exerted. A dive to the deepest point on Earth results in pressures over 108 million Pascals, or over a thousand times greater than atmospheric pressure at sea level. To make the dive, the Deep Five Expedition, uses a specially designed Triton 36000/2 model submarine. Previously only two other manned expeditions have made dives into the Challenger Deep, in 1960 Don Walsh and Jacques Piccard dived onboard a submarine named Trieste to a depth of 10.912 kilometers, and in 2012 filmmaker James Cameron onboard the submarine Deepsea Challenger reached a depth of 10.908 kilometers. Victor Vescovo piloted multiple dives into the Challenger deep, as well as other members of the Five Deeps Expedition team, including Patrick Lahey, Jonathan Struwe, the submarine designer John Ramsay, and scientist Alan Jamieson. They recorded each dive and made some remarkable observations of animals at these deep depths beneath the ocean. The deepest point reached was 10.928 kilometers below sea level, within the Hadopelagic zone of the ocean.

The zones of the ocean deep.

Oceanographers divide the ocean into a pelagic zone, the open water column, equivalent to the sky, and the benthic zone, the ocean floor, equivalent to the ground. Pelagic animals are animals that swim or float in the open water, while benthic animals are animals that crawl on the sea floor or are sessile, held to the ocean floor by attachments or burrows. The benthic zone is the ocean or sea floor no matter its depth, and can be used to refer to both shallow and deep depths, the same is true for the pelagic zone. Hence, oceanographers use modifiers to denote depth beneath the sea surface.

Epipelagic Zone

The Epipelagic Zone is the zone where sunlight is able to penetrate the water, and where there is enough sunlight for photosynthesis. This zone is also known as the Photic Zone. Most ocean animals live within this zone since there is an abundance of phytoplankton that use photosynthesis and needs sunlight to live. These light-loving phytoplankton, including dinoflagellates, diatoms, cyanobacteria, algae like coccolithophores, cryptophytes and other microscopic organisms, are an important food source for larger animals in the ocean. The Epipelagic Zone extends to depths of 200 meters below sea level.

Schools of fish within the photic zone of the ocean (Epipelagic Zone).

Mesopelagic Zone

The Mesopelagic Zone is the twilight zone where sunlight dims to less than 1% of its surface brightness. As a dark zone, the Mesopelagic Zone is dominated by heterotrophic bacteria, and eukaryotic plankton that eat or scavenge on decaying dead organisms that sink down from the biologically rich photic zone. In the nearly continuous darkness, the only sources of light come from bioluminescence, flashes of light produced by animals to lure prey. Many animals adapted to the darkness rise at night to feed within the Epipelagic Zone above. The Mesopelagic Zone extends to depths of 1 kilometer below sea level.

Bathypelagic Zone

The Bathypelagic Zone is the completely dark zone dominated by scavenge heterotrophic bacteria, and cephalopods, like squid and cuttlefish that have neither skeletons nor complex internal skeletons. The calcite compensation depth (CCD) is within this zone, meaning that shelled organisms risk dissolution of their calcium carbonate skeletons at these depths. Beautiful glass sponges (Class Hexactinellida) construct their skeletons from silica spicules that are resistant to dissolution, and filter feed the detritus that falls from higher ocean zones. Sediments deposited on the ocean floor at these depths are enriched in organic carbon, forming black shales rather than limestone. The Bathypelagic Zone extends to depths of 4 kilometers below sea level.

Glass sponges of the class Hexactinellida (Euplectella aspergillum).

Abyssal Zone

The mid-ocean ridge that runs the length of the Indian Ocean across the Abyssal plain on the ocean floor.

A cusk eel (Spectrunculus grandis) on the Davidson Seamount in the Gulf of Mexico at 3,288 meters below the surface.

The Abyssal Zone forms both the abyssopelagic zone and abyssal plain, which covers more than 50% of Earth’s total surface area. The sea floor in depths less than 4,000 meters below sea level are referred to as the continental slope and shelf. In profile, these upper zones rise like skyscrapers, nearly vertical in profile, while the abyssal plain is more low laying and covers most of the ocean floor in the middle ocean basins. Mid Ocean Ridges near the central axis of the ocean’s center rise above these abyssal plains, but much of the ocean floor is at depths greater than 4,000 meters. The ocean floor here is composed mostly of basalt, volcanic igneous rock, and the water is pitch dark at these depths. Life survives in these deep zones on the “rain” of organic decaying matter that sinks from the zones above. Other organisms utilize chemosynthesis with complex ecosystems associated with deep hydrothermal vents, with bacteria utilizing sulfur and methane, rather than carbon dioxide and oxygen. Despite little oxygen and temperatures near 4°C, several fish have been observed at these depths, including cusk eels, the hadal snailfish, black lizardfish and abyssal spiderfish. Foraminiferans feed on the organic detritus of decaying organisms that sink down to these depths. Foraminferans (forams) are single celled benthic animals that feed on detritus that floats in the water. They compose their skeletons from calcium carbonate and prone to dissolution of those skeletons with depth, and changes in the CCD. However, these skeletons are frequently preserved as fossils in ocean floor sediments. The deeper living forams often compose their skeletons of shells of silica particles glued together with organic cements to avoid calcite dissolution with depth.

Crustaceans and polychaete worms are common at these depths. A unique group of mollusks, which have a single cap-like shell, in the class Monoplacophora are common on the abyssal plain, as well as the class Polyplacophora, like chitons which have single but segmented shells. The abyssal plain near the continental slopes are often affected by underwater landslides, called turbidity currents. These slopes are susceptible to sediment and mud participles to flow down these underwater slopes for great distances across the abyssal plains, often following the path of gigantic ocean deep canyons, hundreds of miles long. These flows are often triggered by earthquakes or overstepped slopes from sediment transport off the margins of continents. The Abyssal Zone extends to depths around 6 kilometers beneath sea level.

Hadopelagic Zone

The Marianas Trench Marine National Monument, the deepest part of the ocean.

Pseudoliparis swirei, hadal snailfish observed in the Mariana Trench.

The Hadopelagic Zone exists only in the deepest portions of the world’s oceans, and accounts for 0.25% of the ocean floor. Found within these deep trenches or gorges in narrow canyons, the hadopelagic zone forms from geological subduction along the oceanic plates, resulting in deep cavasses that extend just beyond 10 kilometers in ocean depth. The Mariana Trench, near Guam is one of these regions. The deepest living fish, the hadal snail fish (Pseudoliparis swirei), can live up to depths of 8 kilometers, although invertebrate and single celled protists can live at even more extreme depths. Amphipodan crustaceans, little shrimp-like creatures can live at depths found in the Mariana Trench, feeding on organic detritus in the pitch-black deep waters. They are uniquely adapted to the low oxygen environments, where fish are unable to live. The Hadopelagic Zone is mostly lifeless, especially for larger animals, like fish which require oxygen. As such, the life forms in these deep zones are mostly microscopic, including unique forms of bacteria that do not require either light or oxygen. The journey to the deepest bottom of the ocean takes nearly 4 hours, but once on the bottom Victor Vescovo guided the submarine around the bottom for 4 hours before making the 4-hour long journey back to the surface. The expedition set multiple records with numerous trips back down to the bottom, exploring the deepest ocean floor and collecting samples. But the most dramatic discovery on the nearly life-less Hadopelagic Zone was the presence of trash and garbage that had sunk to these depths. The isolated location of the deepest and darkest bottom point of the ocean was not immune from the effects of a planet dominated by humans. Samples of the amphipodan crustaceans, the tiny shrimp-like creatures showed high levels of pollutants, as the tiny shrimp were feeding not only on organic matter, but also the sinking refuse from human pollution dumped into global oceans. Even at these extraordinary depths, pollution was found (Jamieson et al. 2017: Nature Ecology & Evolution). Bits of trash and refuse poked out of the sandy bottom waters as the submarine recorded the near alien landscape transformed by a species dwelling at the surface.

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b. Properties of Earth’s Water (Density, Salinity, Oxygen, and Carbonic Acid).	c. Earth’s Oceans (Warehouses of Water).	d. Surface Ocean Circulation.