question: Why is getting to the bottom of the ocean so exponentially difficult?
comment: The deeper you go, the heavier the water above you is. So the pressure at these depths is extreme. Building a craft to withstand still remains a challenge.
passages: However, the voyage to the ocean bottom is still a challenging experience. Scientists are working to find ways to study this extreme environment from the shipboard. With more sophisticated use of fiber optics, satellites, and remote-control robots, scientists one day may explore the deep sea from a computer screen on the deck rather than out of a porthole.
  
  Section::::Milestones of deep sea exploration.
  
  The extreme conditions in the deep sea require elaborate methods and technologies, which has been the main reason why its exploration has a comparatively short history.
   The high water pressure at this depth makes designing and operating exploratory craft difficult. The first descent by any vehicle was by the manned bathyscaphe "Trieste" in 1960. This was followed by the unmanned ROVs "Kaikō" in 1995 and "Nereus" in 2009. In March 2012 a manned solo descent was made by film director James Cameron in the deep-submergence vehicle "Deepsea Challenger". Between 28 April and 4 May 2019, the "DSV Limiting Factor" completed four manned dives to the bottom of Challenger Deep.
  
  Section::::History of depth mapping from the surface.
   Section::::Introduction.
  
  Section::::Introduction.:Of the importance of measuring ocean currents.
  
  The underwater world is still mostly unknown. The main reason for it is the difficulty to gather information in situ, to experiment, and even to reach certain places. But the ocean nonetheless is of a crucial importance for scientists, as it covers about 71% of the planet.
   The deep trenches or fissures that plunge down thousands of meters below the ocean floor (for example, the midoceanic trenches such as the Mariana Trench in the Pacific) are almost unexplored. Previously, only the bathyscaphe "Trieste", the remote control submarine "Kaikō" and the "Nereus" have been able to descend to these depths. However, as of March 25, 2012 one vehicle, the "Deepsea Challenger" was able to penetrate to a depth of 10,898.4 meters (35,756 ft).
  
  Section::::Ecosystem.
   Section::::Monitoring.:Technological development.
   BULLET::::- Currents and tidal flows can transport nutrients to underwater environments increasing the variety and density of life at a site. Currents can also be dangerous to divers as they can carry the diver being away from the surface support or the planned exit point. Currents that flow over large obstructions can cause strong local vertical currents and turbulence that are dangerous because they may cause the diver to lose buoyancy control risking barotrauma, or impact against the bottom terrain.
  
  Section::::Regions where recreational diving is a major tourist industry.
  
  BULLET::::- Great Barrier Reef of Australia
   The complexity, medical problems and physiological limits, such as those imposed by high pressure nervous syndrome, the accompanying high costs of professional saturation diving to extreme depths and the development of deep water atmospheric diving suits and remotely operated underwater vehicles in offshore oilfield drilling and production effectively ended the need for ever deeper, non-atmospheric manned intervention in the ocean. These practical factors make watch depth ratings of more than marketing curiosities.
  
  Section::::Experimental Sea-Dweller DEEPSEA CHALLENGE watch.
   Many of these problems are avoided by the use of surface supplied breathing gas, closed diving bells, and saturation diving, at the cost of logistical complexity, reduced maneuverability of the diver and greater expense.
  
  Section::::Dealing with depth.
  
  Both equipment and procedures can be adapted to deal with the problems of greater depth. Usually the two are combined, as the procedures must be adapted to suit the equipment, and in some cases the equipment is needed to facilitate the procedures.
  
  Section::::Dealing with depth.:Equipment adaptations for deeper diving.
   Although a number of human activities are conducted underwater—such as research, underwater diving for work or recreation, and underwater warfare with submarines, the underwater environment is hostile to humans in many ways and therefore little explored.
  
  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.
   The deep sea is one of the less explored areas on Earth. Pressures even in the mesopelagic become too great for traditional exploration methods, demanding alternative approaches for deep sea research. Baited camera stations, small manned submersibles and ROVs (remotely operated vehicles) are three methods utilized to explore the ocean's depths. Because of the difficulty and cost of exploring this zone, current knowledge is limited. Pressure increases at approximately one atmosphere for every 10 meters meaning that some areas of the deep sea can reach pressures of above 1,000 atmospheres. This not only makes great depths very difficult to reach without mechanical aids, but also provides a significant difficulty when attempting to study any organisms that may live in these areas as their cell chemistry will be adapted to such vast pressures.
   The field of ocean acidification and the impact of anthropogenic carbon dioxide emission has seen similar growth and most of the cited articles in this field have relied to a significant extent on data collected during scuba diving operations.
   Section::::Technology.
   Amongst technical divers, there are divers who participate in ultra-deep diving on scuba below . This practice requires high levels of training, experience, discipline, fitness and surface support. Only thirty-five persons are known to have ever dived below a depth of on self-contained breathing apparatus recreationally. The Holy Grail of deep scuba diving was the mark, first achieved by John Bennett in 2001, and has only been achieved seven times since.
   Human error is inevitable and everyone makes mistakes at some time. The consequences of these errors are varied and depend on many factors. Most errors are minor and do not cause significant harm, but others can have catastrophic consequences. Examples of human error leading to accidents are available in vast numbers, as it is the direct cause of 60% to 80% of all accidents.
   The development of subsea oil and gas fields requires specialized equipment. The equipment must be reliable enough to safeguard the environment and make the exploitation of the subsea hydrocarbons economically feasible. The deployment of such equipment requires specialized and expensive vessels, which need to be equipped with diving equipment for relatively shallow equipment work (i.e. a few hundred feet water depth maximum) and robotic equipment for deeper water depths. Any requirement to repair or intervene with installed subsea equipment is thus normally very expensive. This type of expense can result in economic failure of the subsea development.
   Section::::Undersea missions.
   Even in areas where the bottom sediments are ancient, bottom trawling, by reintroducing the sediment into the water column, can create harmful algae blooms. More suspended solids are introduced into the oceans from bottom trawling than any other man-made source.
  
  Section::::Environmental damage.:Deep sea damage.
  
  The UN Secretary General reported in 2006 that 95 percent of damage to seamount ecosystems worldwide is caused by deep sea bottom trawling. A study published in "Current Biology" suggests a cutoff of 600 meters is a point which ecological damage increases significantly.
  
  Section::::Environmental damage.:Current restrictions.
  
  Today, some countries regulate bottom trawling within their jurisdictions:
   Section::::Similar efforts.
  
  As of February 2012, several other vehicles are under development to reach the same depths. The groups developing them include:
  
  BULLET::::- Triton Submarines, a Florida-based company that designs and manufactures private submarines, whose vehicle, "Triton 36000/3", will carry a crew of three to the seabed in 120 minutes.
  
  BULLET::::- Virgin Oceanic, sponsored by Richard Branson's Virgin Group, is developing a submersible designed by Graham Hawkes, "DeepFlight Challenger", with which the solo pilot will take 140 minutes to reach the seabed.
   Unmanned remotely operated vehicles (ROV's) allow performance of a variety of tasks at almost any depths for extended periods, but there are still many essential underwater tasks which can only be performed or are most effectively performed by a diver. A diver is still the most versatile underwater tool, but also the most unpredictable, and his own behaviour may threaten his safety.
   An underwater habitat has to meet the needs of human physiology and provide suitable environmental conditions, and the one which is most critical is breathing air of suitable quality. Others concern the physical environment (pressure, temperature, light, humidity), the chemical environment (drinking water, food, waste products, toxins) and the biological environment (hazardous sea creatures, microorganisms, marine fungi). Much of the science covering underwater habitats and their technology designed to meet human requirements is shared with diving, diving bells, submersible vehicles and submarines, and spacecraft.
   Section::::Hazards and risk.:Extremely limited visibility.
   BULLET::::- exploration: The underwater environment is relatively unexplored, it is not difficult to find places where no-one has gone before or if they have, no-one has recorded the fact or described or surveyed the site, even quite close to heavily populated areas. The marine ecosystems are largely undescribed, and there are many undiscovered species yet to be found and described. There are shipwrecks and flooded caves to challenge the adventurous and foolhardy.
  
  Section::::Scope.:Specialties.
  
  There are many diving activities, and equipment and environmental specialties which require training additional to that provided by the entry level courses:
  
  Activities:
   However, maintaining an underwater habitat is much more expensive and logistically difficult than diving from the surface. It also restricts the diving to a much more limited area.
  
  Section::::Technical classification and description.
  
  Section::::Technical classification and description.:Pressure modes.
  
  Underwater habitats are designed to operate in two fundamental modes.
   According to Marie Söderqvist, CEO of the analysis company United Minds and author of the book "Status – vägen till lycka" (Eng. "Status – the road to happiness"), sinking is not just a protest against the ban on spraying champagne: "One gives the finger to everything – bans, global justice, saving the planet and equality."
  
  Section::::Spread and media attention.
   As one descends, in addition to the normal atmospheric pressure at the surface, the water exerts increasing hydrostatic pressure of approximately 1 bar (14.7 pounds per square inch) for every 10 m (33 feet) of depth. The pressure of the inhaled breath must balance the surrounding or ambient pressure to allow inflation of the lungs. It becomes virtually impossible to breathe air at normal atmospheric pressure through a tube below three feet under the water.
  