Underwater environment

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**Underwater Environment Extent:**
– Three quarters of Earth’s surface covered by water
– Abyssal plain depths range from 4,000 to 5,500 meters
– Challenger Deep in Mariana Trench reaches 10,924 meters
– Ocean covers 71% of Earth’s surface
– Less than 5% of the World Ocean explored
– Oceans include Pacific, Atlantic, Indian, Southern, and Arctic
– Saline water covers 361,000,000 sqmi
– Oceans contain 97% of Earth’s water
– Average ocean depth is nearly 3,700 meters

**Water Bodies and Ecosystems:**
– Lakes are filled with water in a basin surrounded by land
– Rivers flow under gravity into oceans, lakes, or the ground
– Ponds are smaller than lakes and may be natural or man-made
– Aquifers are underground water-bearing layers
– Reservoirs store water using dams or locks
– Canals are artificial waterways with low-speed current flow
– Aquatic ecosystems include marine and freshwater ecosystems
– Marine ecosystems cover over 70% of Earth’s surface
– Freshwater ecosystems include lakes, rivers, springs, bogs, and wetlands

**Physical Properties of Water:**
– Water density is about 1 gram per cubic centimeter
– Density of ice is 9% less than liquid water
– Water expands above 4°C as temperature increases
– Density of sea water depends on salt content and temperature
– Sunlight absorption increases with depth underwater
– Ocean has surface layer, thermocline, and deep ocean
– Water conducts heat 25 times more efficiently than air
– Sound is transmitted 4.3 times faster in water than in air

**Ecosystem Characteristics and Human Interaction:**
– Limited ambient lighting due to water absorption
– Nutrients for plants are dissolved in the water
– Light conditions vary based on depth and ecosystem
– Underwater activities include diving, research, and warfare
– High ambient pressure impacts gas-filled spaces in the body
– Hazards in Underwater Environments: asphyxia, barotrauma, hypothermia, decompression sickness

**Technological Aspects and Resources:**
– Underwater Vehicles: powered by electric motors, equipped with cameras and lights
– Autonomous Underwater Vehicles (AUVs) operate without operator input
– Various diving weighting systems exist
– Resources and References: Princeton University, NOAA, Encyclopedia Britannica, USGS Water Science School
– Miscellaneous: Lakes and ponds are freshwater bodies, aquifers are underground water reservoirs, information sources like NOAA and educational standards for diving & hyperbaric medicine.

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.

Great Barrier Reef, Australia

Liquid water has been present on Earth for most of the history of the planet. The underwater environment is thought to be the place of the origin of life on Earth, and it remains the ecological region most critical to the support of life and the natural habitat of the majority of living organisms. Several branches of science are dedicated to the study of this environment or specific parts or aspects of it.

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.

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