Underwater environment
An underwater environment is a environment of, and immersed in, liquid water in a natural or artificial feature (called a body of water), such as an ocean, sea, lake, pond, reservoir, river, canal, or aquifer. Some characteristics of the underwater environment are universal, but many depend on the local situation.
Liquid water has been present on Earth for most of the
A number of human activities are conducted in the more accessible parts of the underwater environment. These include research, underwater diving for work or recreation, and underwater warfare with submarines. It is hostile to humans in many ways and often inaccessible, and therefore relatively little explored.
Extent
Three quarters of the planet
Oceans and seas
An ocean is a body of
Saline water covers approximately 361,000,000 km2 (139,000,000 sq mi) and is customarily divided into several principal oceans and smaller seas, with the ocean covering approximately 71% of Earth's surface and 90% of the Earth's biosphere.[5] The ocean contains 97% of Earth's water, and oceanographers have stated that less than 5% of the World Ocean has been explored.[5] The total volume is approximately 1.35 billion cubic kilometers (320 million cu mi) with an average depth of nearly 3,700 meters (12,100 ft).[6][7][8]
Lakes, ponds, and rivers
A lake is an area filled with water, localized in a
A pond is an area filled with water, either natural or artificial, that is smaller than a
A river is a natural flowing
Subterranean water
An aquifer is an underground layer of
Aquifers may be classified as porous or karst, where a porous aquifer contains the water in the spaces between the grains of a loose sediment or rock (typically sand or sandstone), while a karst aquifer contains water mainly in relatively large voids in relatively impermeable rock, such as limestone or dolomite.[14]
Water filled
Artificial bodies of water
A reservoir is, most commonly, an enlarged natural or artificial lake, pond or impoundment created using a
Physical characteristics
Water is a
Density
The
The unusual density curve and lower density of ice than of water is vital to life—if water were most dense at the freezing point, then in winter the very cold water at the surface of lakes and other water bodies would sink, the lake could freeze from the bottom up, and all life in them would be killed.[17] Furthermore, given that water is a good thermal insulator (due to its heat capacity), some frozen lakes might not completely thaw in summer.[17] The layer of ice that floats on top insulates the water below.[18] Water at about 4 °C (39 °F) also sinks to the bottom, thus keeping the temperature of the water at the bottom constant (see diagram).[17]
The density of sea water depends on the dissolved salt content as well as the temperature. Ice still floats in the oceans, otherwise they would freeze from the bottom up. The salt content lowers the freezing point by about 1.9 °C and lowers the temperature of the density maximum of water to the fresh water freezing point at 0 °C.[19] This is why, in ocean water, the downward convection of colder water is not blocked by an expansion of water as it becomes colder near the freezing point. The oceans' cold water near the freezing point continues to sink. So creatures that live at the bottom of cold oceans like the Arctic Ocean generally live in water 4 °C colder than at the bottom of frozen-over fresh water lakes and rivers.
As the surface of sea water begins to freeze (at −1.9 °C for salinity 3.5%) the ice that forms is essentially salt-free, with about the same density as freshwater ice.[19] This ice floats on the surface, and the salt that is "frozen out" adds to the salinity and density of the sea water just below it, in a process known as brine rejection. This denser salt water sinks by convection. This produces essentially freshwater ice at −1.9 °C on the surface.[19] On a large scale, the process of brine rejection and sinking cold salty water results in ocean currents forming to transport such water away from the Poles, leading to a global system of currents called the thermohaline circulation.
Pressure
The density of water causes ambient pressures that increase dramatically with depth. The atmospheric pressure at the surface is 14.7 pounds per square inch or around 100 kPa. A comparable hydrostatic pressure occurs at a depth of only 10 metres (33 ft) (9.8 metres (32 ft) for sea water). Thus, at about 10 m below the surface, the water exerts twice the pressure (2 atmospheres or 200 kPa) as air at surface level.
Buoyancy
Any object immersed in water is subjected to a buoyant force that counters the force of gravity, appearing to make the object less heavy. If the overall density of the object exceeds the density of water, the object sinks. If the overall density is less than the density of water, the object rises until it floats on the surface.
Penetration of light
With increasing depth underwater,
The euphotic depth is the depth at which light intensity falls to 1% of the value at the surface. This depth is dependent upon water clarity, being only a few metres underwater in a turbid estuary, but may reach up to 200 metres in the open ocean. At the euphotic depth, plants (such as phytoplankton) have no net energy gain from photosynthesis and thus cannot grow.
Temperature
There are three layers of ocean temperature: the surface layer, the thermocline, and the deep ocean. The average temperature of surface layer is about 17 °C. About 90% of ocean's water is below the thermocline in the deep ocean, where most of the water is below 4 °C.[20]
There are temperature anomalies at active volcanic sites and hydrothermal vents, where deep-water temperatures can significantly exceed 100 °C.
Thermal conductivity
Water
Acoustic properties
Sound is transmitted about 4.3 times faster in water (1,484 m/s in fresh water) than in air (343 m/s). The human brain can determine the direction of sound in air by detecting small differences in the time it takes for sound waves in air to reach each of the two ears. For these reasons, divers find it difficult to determine the direction of sound underwater. Some animals have adapted to this difference and many use sound to navigate underwater.
Ecosystems
An
Marine ecosystems are the largest of
Freshwater ecosystems include
Aquatic ecosystems are characterised by the limitation on ambient lighting due to absorption by the water itself and by dissolved and suspended matter in the water column, and by the support provided by buoyancy. Nutrients usable by plants are dissolved in the water, making them easily available. However, the interaction of light absorption by water, matter and living organisms themselves leads to very different light and light spectrum conditions depending on the respective ecosystem and its water depth. This affects photosynthesis and the ecology of plants and phytoplankton.[27] Outside the euphotic zone, photosynthesis cannot occur and life must use other sources of energy than sunlight.
Humans
Although a number of
An immediate obstacle to human activity under water is that human lungs cannot naturally function in this environment. Unlike the gills of fish, human lungs are adapted to the exchange of gases at atmospheric pressure. Any penetration into the underwater environment for more than a few minutes requires artificial aids to maintain life.
For solid and liquid tissues like bone, muscle and blood, the high ambient pressure is not much of a problem; but it is a problem for any gas-filled spaces like the
With a few exceptions, the underwater environment tends to cool the unprotected human body. This heat loss will generally lead to hypothermia eventually.
Hazards
There are several classes of hazards to humans inherent to the underwater environment.
- Absence of breathable gas, which can cause asphyxia, specifically by drowning.
- Ambient pressures which could cause barotrauma, or toxic effects of breathing gas components at raised partial pressures.
- Ambient temperatures which may lead to hypothermia, or in unusual cases, to hyperthermia, due to high rates of heat exchange.
- Solution of inert breathing gas components may lead to decompression sickness if decompression is too rapid.
- Entrainment of diver by moving water in currents and waves can cause injury by impacting the diver against hard objects or moving them to inappropriate depths.
- Dangerous aquatic organisms of various sorts.
Ambient pressure diving
In ambient pressure diving, the diver is directly exposed to the pressure of the surrounding water. The ambient pressure diver may dive on breath-hold, or use breathing apparatus for scuba diving or surface-supplied diving, and the saturation diving technique reduces the risk of decompression sickness (DCS) after long-duration deep dives. Immersion in water and exposure to cold water and high pressure have physiological effects on the diver which limit the depths and duration possible in ambient pressure diving. Breath-hold endurance is a severe limitation, and breathing at high ambient pressure adds further complications, both directly and indirectly. Technological solutions have been developed which can greatly extend depth and duration of human ambient pressure dives, and allow useful work to be done underwater.[28]
Atmospheric pressure diving
A diver can be isolated from the ambient pressure by using an atmospheric diving suit (ADS), which is a small one-person articulated
Submersibles and submarines
A submersible is a small
Remotely operated or autonomous vehicles
Remotely operated underwater vehicles and autonomous underwater vehicles are part of a larger group of undersea systems known as unmanned underwater vehicles. ROVs are unoccupied, usually highly maneuverable, and operated by a crew either aboard a vessel/floating platform or on proximate land. They are linked to a host ship by a neutrally buoyant tether, or a load-carrying umbilical cable is used along with a tether management system (TMS). The umbilical cable contains a group of electrical conductors and fiber optics that carry electric power, video, and data signals between the operator and the TMS. Where used, the TMS then relays the signals and power for the ROV down the tether cable. Once at the ROV, the electric power is distributed between the components of the ROV. In high-power applications, most of the electric power drives a high-power electric motor which drives a hydraulic pump for propulsion and to power equipment. Most ROVs are equipped with at least a video camera and lights. Additional equipment is commonly added to expand the vehicle's capabilities. Autonomous underwater vehicles (AUVs) are robots that travel underwater without requiring input from an operator. Underwater gliders are a subclass of AUVs.[31]
Sciences
- Hydrology – Science of the movement, distribution, and quality of water on Earth and other planets
- Hydrography – Applied science of measurement and description of physical features of bodies of water
- Limnology – Science of inland aquatic ecosystems
- Marine biology – Scientific study of organisms that live in the ocean
- Marine chemistry – Chemistry of oceans and seas
- Marine ecology– The study of the interactions between organisms and environment in the sea
- Marine geology – Study of the history and structure of the ocean floor
- Oceanography – Study of physical, chemical, and biological processes in the ocean
- Potamology – Study of rivers
- Underwater archaeology – Archaeological techniques practiced at underwater sites
See also
- Timeline of diving technology – Chronological list of notable events in the history of underwater diving equipment
- Underwater acoustics – Study of the propagation of sound in water
- Underwater photography – Genre of photography
- Underwater vision – The ability to see objects underwater
- Science of underwater diving – Scientific concepts that are closely associated with underwater diving
- UNESCO Convention on the Protection of the Underwater Cultural Heritage– Treaty adopted on 2 November 2001
References
- ^ "WordNet Search — ocean". Princeton University. Retrieved February 21, 2012.
- ^ "ocean, n". Oxford English Dictionary. Retrieved February 5, 2012.
- ^ "ocean". Merriam-Webster. Retrieved February 6, 2012.
- ^ "WordNet Search — sea". Princeton University. Retrieved February 21, 2012.
- ^ a b "NOAA – National Oceanic and Atmospheric Administration – Ocean". Noaa.gov. Retrieved 2012-11-08.
- ^ Qadri, Syed (2003). "Volume of Earth's Oceans". The Physics Factbook. Retrieved 2007-06-07.
- hdl:1912/3862. Archived from the originalon 6 September 2015. Retrieved 27 September 2012.
- ^ "Volumes of the World's Oceans from ETOPO1". NOAA. Archived from the original on 2015-03-11. Retrieved 2015-03-07.
{{cite web}}
: CS1 maint: bot: original URL status unknown (link) - ^ Purcell, Adam. "Lakes". Basic Biology.
- ^ "Dictionary.com definition". Retrieved 2008-06-25.
- ^ "Definition of POND". www.merriam-webster.com. 21 August 2023.
- ISBN 978-0723233381.
- ^ "GNIS FAQ". United States Geological Survey. Retrieved 26 January 2012.
- ^ "aquifer | Types & Facts". Encyclopedia Britannica. Retrieved 2021-06-28.
- ISBN 9780890514962.
- ^ ISBN 978-0-08-037941-8.
- ^ a b c d e Perlman, Howard. "Water Density". The USGS Water Science School. Retrieved 2016-06-03.
- ISBN 978-1-13-361109-7.
- ^ a b c "Can the ocean freeze?". National Ocean Service. National Oceanic and Atmospheric Administration. Retrieved 2016-06-09.
- ^ "Temperature of Ocean Water". Windows to the Universe. National Earth Science Teachers Association (NESTA).
- ISBN 0-412-74050-8.
- ^ "Oceanic Institute". www.oceanicinstitute.org. Archived from the original on 2019-01-03. Retrieved 2018-12-01.
- ^ "Ocean Habitats and Information". 2017-01-05. Archived from the original on April 1, 2017. Retrieved 2018-12-01.
- ^ "Facts and figures on marine biodiversity | United Nations Educational, Scientific and Cultural Organization". www.unesco.org. Retrieved 2018-12-01.
- ^ Drogin, Bob (August 2, 2009). "Mapping an ocean of species". Los Angeles Times. Retrieved August 18, 2009.
- )
- PMID 35356568.
- ^ Kot, Jacek (2011). Educational and Training Standards for Physicians in Diving and Hyperbaric Medicine (PDF). Kiel, Germany: Joint Educational Subcommittee of the European Committee for Hyperbaric Medicine (ECHM) and the European Diving Technical Committee (EDTC).
- ^ "WASP Specifications" (PDF). Archived from the original (PDF) on 3 March 2014. Retrieved 27 February 2014.
- ^ "Submersible". The Canadian Encyclopedia. 2011. Archived from the original on 2017-12-04. Retrieved 2019-08-09.. The Canadian Encyclopedia. F.J. Chambers 02/07/2006 "Cyrus Albert Birge - the Canadian Encyclopedia". Archived from the original on March 15, 2012. Retrieved 2011-10-20.
{{cite web}}
: CS1 maint: bot: original URL status unknown (link) - ^ "Remotely Operated Vehicle Design and Function". Maritime About. Archived from the original on 1 July 2016. Retrieved 4 June 2016.
Footnotes
- ^ (1-0.95865/1.00000) × 100% = 4.135%