question: How does deep ocean pressure compare to that in space?
comment: In space, there is no atmosphere. To liken the two, I draw upon the wisdom of Matt Groening. “We’re so deep, it’s the equivalent of over 150 atmospheres of pressure! How much can this vessel withstand?” “Well, it’s a spaceship, so I’m guessing between 0 and 1.”
passages: Vacuum is measured in units of pressure, typically as a subtraction relative to ambient atmospheric pressure on Earth. But the amount of relative measurable vacuum varies with local conditions. On the surface of Jupiter, where ground level atmospheric pressure is much higher than on Earth, much higher relative vacuum readings would be possible. On the surface of the moon with almost no atmosphere, it would be extremely difficult to create a measurable vacuum relative to the local environment.
   Similarly, much higher than normal relative vacuum readings are possible deep in the Earth's ocean. A submarine maintaining an internal pressure of 1 atmosphere submerged to a depth of 10 atmospheres (98 metres; a 9.8 metre column of seawater has the equivalent weight of 1 atm) is effectively a vacuum chamber keeping out the crushing exterior water pressures, though the 1 atm inside the submarine would not normally be considered a vacuum.
   An example of Mars analog comparison mission is HI-SEAS of the 2010s. Other Mars analog studies include Mars Desert Research Station and Arctic Mars Analog Svalbard Expedition
  
  BULLET::::- Australia Mars Analog Research Station
  
  BULLET::::- Flashline Mars Arctic Research Station
  
  BULLET::::- MARS-500
  
  BULLET::::- Concordia Station
  
  The ISS has also been described as a predecessor to Mars expedition, and in relation to a Mars habitat the study importance and nature of operation a closed system was noted.
  
  At about 28 miles (45 km, 150 thousand feet ) Earth altitude the pressure starts to be equivalent to Mars surface pressure.
   One atmosphere is approximately equal to 33 feet of sea water or 14.7 psi, which gives 4.9/11 or about 0.445 psi per foot. Atmospheric pressure may be considered constant at sea level, and minor fluctuations caused by the weather are usually ignored. Pressures measured in fsw and msw are gauge pressure, relative to the surface pressure of 1 atm absolute, except when a pressure difference is measured between the locks of a hyperbaric chamber, which is also generally measured in fsw and msw.
   The concept is not limited to environments frequented by people. Almost any place in the universe will have an ambient pressure, from the hard vacuum of deep space to the interior of an exploding supernova. At extremely small scales the concept of pressure becomes irrelevant, and it is undefined at a gravitational singularity.
  
  Section::::Units of pressure.
   BULLET::::- Deep space is generally much more empty than any artificial vacuum. It may or may not meet the definition of high vacuum above, depending on what region of space and astronomical bodies are being considered. For example, the MFP of interplanetary space is smaller than the size of the Solar System, but larger than small planets and moons. As a result, solar winds exhibit continuum flow on the scale of the Solar System, but must be considered a bombardment of particles with respect to the Earth and Moon.
   Section::::Some examples.:Ocean example.
  
  If the density of a gas is persistent, then it isn't really behaving like a gas. Instead it is behaving like an incompressible fluid, or liquid, and this situation looks more like an ocean. Assuming density is constant, then a graph of pressure vs altitude will have a retained slope, since the weight of the ocean over head is directly proportional to its depth.
  
  Section::::Some examples.:Isothermal-barotropic approximation and scale height.
   For an isothermal atmosphere, formula_5 or about 63% of the total mass of the atmosphere exists between the planet's surface and one scale height. (The total air mass below a certain altitude is calculated by integrating over the density function.)
  
  For the ocean example there was a sharp transition in density at the top or "surface" of the ocean. However, for atmospheres made of gas there is no equivalent sharp transition or edge. Gas atmospheres simply get less and less dense until they're so thin that they're space.
  
  Section::::Some examples.:The U.S. Standard Atmosphere.
   Carbon dioxide partial pressure (pCO2)
  
  Section::::Ocean climate variables.:Ocean subsurface.
  
  BULLET::::- Backscatter
  
  BULLET::::- Carbon Dioxide
  
  BULLET::::- Chlorophyll
  
  BULLET::::- Conductivity
  
  BULLET::::- Density
  
  BULLET::::- Iron
  
  BULLET::::- Irradiance
  
  BULLET::::- Nutrients
  
  BULLET::::- Nitrate
  
  BULLET::::- Methane
  
  BULLET::::- Ocean current
  
  BULLET::::- Single Point
  
  BULLET::::- Water Column
  
  BULLET::::- Ocean tracers
  
  BULLET::::- Oxygen
  
  BULLET::::- Phytoplankton
  
  BULLET::::- Salinity
  
  BULLET::::- Sigma-T
  
  BULLET::::- Sound Velocity
  
  BULLET::::- Temperature
  
  BULLET::::- Turbidity
  
  Section::::Ocean observation sources.
  
  Section::::Ocean observation sources.:Satellite.
  
  There is a composite network of satellites that generate observations. These include:
  
  Section::::Ocean observation sources.:"In situ".
  
  There is a composite network of in situ observations. These include:
  
  Section::::Ocean observation sources.:Subsurface.
   Atmospheric pressure pressing on the surface of a liquid must be taken into account when trying to discover the "total" pressure acting on a liquid. The total pressure of a liquid, then, is "ρgh" plus the pressure of the atmosphere. When this distinction is important, the term "total pressure" is used. Otherwise, discussions of liquid pressure refer to pressure without regard to the normally ever-present atmospheric pressure.
   The average value of surface pressure on Earth is 985 hPa. This is in contrast to mean sea-level pressure, which involves the extrapolation of pressure to sea-level for locations above or below sea-level. The average pressure at mean sea-level (MSL) in the International Standard Atmosphere (ISA) is 1013.25 hPa, or 1 atmosphere (Atm), or 29.92 inches of mercury. 
   Solar heating on the day side and radiative cooling on the night side of a planet can induce pressure difference. Thermal tides, which are the wind circulation and waves driven by such a daily-varying pressure field, can explain a lot of variability of the Martian atmosphere. Compared to Earth's atmosphere, thermal tides have a larger influence on the Martian atmosphere because of the stronger diurnal temperature contrast. The surface pressure measured by Mars rovers showed clear signals of thermal tides, although the variation also depends on the shape of the planet's surface and the amount of suspended dust in the atmosphere. The atmospheric waves can also travel vertically and affect the temperature and water-ice content in the middle atmosphere of Mars.
   "Surface pressure" is the atmospheric pressure at a location on Earth's surface (terrain and oceans). It is directly proportional to the mass of air over that location.
  
  For numerical reasons, atmospheric models such as general circulation models (GCMs) usually predict the nondimensional "logarithm of surface pressure".
   Section::::Mechanical properties.:Pressure and buoyancy.
  
  In a gravitational field, liquids exert pressure on the sides of a container as well as on anything within the liquid itself. This pressure is transmitted in all directions and increases with depth. If a liquid is at rest in a uniform gravitational field, the pressure formula_1 at depth formula_2 is given by 
  
  where:
  
  For a body of water open to the air, formula_7 would be the atmospheric pressure.
   where formula_14 is the Stefan–Boltzmann constant.
  
  Section::::Solar radiation pressure.
  
  Solar radiation pressure is due to the sun's radiation at closer distances, thus especially within the Solar System. While it acts on all objects, its net effect is generally greater on smaller bodies since they have a larger ratio of surface area to mass. All spacecraft experience such a pressure except when they are behind the shadow of a larger orbiting body.
   At about 28 miles (45 km, 150 thousand feet ) Earth altitude the pressure starts to be equivalent to Mars surface pressure. However, the major component of Mars air, CO gas, is denser than Earth air for a given pressure. Perhaps more significantly there is no land at this altitude on earth. The highest point on earth is the summit of Mount Everest at about 5.5 miles (8.8 km, 29 thousand feet), where the pressure is about fifty times greater than on the surface of Mars. The correct atmospheric pressure can be created by a vacuum chamber. NASA's Space Power Facility was used to test the airbag landing systems for the Mars Pathfinder and the Mars Exploration Rovers, Spirit and Opportunity, under simulated Mars atmospheric conditions.
   Since gravity is inversely proportional to the square of the distance, a space station 400 km above the Earth feels almost the same gravitational force as we do on the Earth's surface. The reason a space station does not plummet to the ground is not that it is not subject to gravity, but that it is in a free-fall orbit.
  
  Section::::Gas giants.
  
  For gas giant planets such as Jupiter, Saturn, Uranus, and Neptune, where the surfaces are deep in the atmosphere and the radius not known, the surface gravity is given at the 1 bar pressure level in the atmosphere. 
   Maintenance of liquid surface water also requires a sufficiently thick atmosphere. Possible origins of terrestrial atmospheres are currently theorised to outgassing, impact degassing and ingassing. Atmospheres are thought to be maintained through similar processes along with biogeochemical cycles and the mitigation of atmospheric escape. In a 2013 study led by Italian astronomer Giovanni Vladilo, it was shown that the size of the circumstellar habitable zone increased with greater atmospheric pressure. Below an atmospheric pressure of about 15 millibars, it was found that habitability could not be maintained because even a small shift in pressure or temperature could render water unable to form as a liquid.
   Section::::Mechanism.
  
  Atmospheric pressure is caused by the gravitational attraction of the planet on the atmospheric gases above the surface, and is a function of the mass of the planet, the radius of the surface, and the amount and composition of the gases and their vertical distribution in the atmosphere. It is modified by the planetary rotation and local effects such as wind velocity, density variations due to temperature and variations in composition.
  
  Section::::Mean sea-level pressure.
   At the bottom of the trench the water column above exerts a pressure of , more than 1,000 times the standard atmospheric pressure at sea level. At this pressure, the density of water is increased by 4.96%, so that 95.27 of any unit of volume of water under the pressure of the Challenger Deep would contain the same mass as 100 of those units at the surface. The temperature at the bottom is .
   At ground level, atmospheric tides can be detected as regular but small oscillations in surface pressure with periods of 24 and 12 hours. Daily pressure maxima occur at 10 a.m. and 10 p.m. local time, while minima occur at 4 a.m. and 4 p.m. local time. The absolute maximum occurs at 10 a.m. while the absolute minimum occurs at 4 p.m. However, at greater heights the amplitudes of the tides can become very large. In the mesosphere (heights of ~ 50 – 100 km) atmospheric tides can reach amplitudes of more than 50 m/s and are often the most significant part of the motion of the atmosphere.
   To find the component of this force normal to the surface, another cosine factor must be applied resulting in a pressure "P" on the surface of:
  
  Note, however, that in order to account for the net effect of solar radiation on a spacecraft for instance, one would need to consider the "total" force (in the direction away from the sun) given by the preceding equation, rather than just the component normal to the surface that we identify as "pressure".
   BULLET::::- U.S. Naval Research Laboratory ocean-floor pressure sensors detected a freak wave caused by Hurricane Ivan in the Gulf of Mexico, 2004. The wave was around high from peak to trough, and around long. Their computer models also indicated that waves may have exceeded in the eyewall.
   At about 150 thousand feet of altitude (28 miles (45 km)) on Earth, the atmospheric pressure starts to be equivalent to the surface of Mars.
  
  See also Effects of high altitude on humans
  
  BULLET::::- Temperature
   BULLET::::- Sea level pressure (SLP) is the pressure at sea level or (when measured at a given elevation on land) the station pressure reduced to sea level assuming an isothermal layer at the station temperature. This is the pressure normally given in weather reports on radio, television, and newspapers or on the Internet. When barometers in the home are set to match the local weather reports, they measure pressure reduced to sea level, not the actual local atmospheric pressure. The reduction to sea level means that the "normal range of fluctuations" in pressure is the same for everyone. The pressures which are considered "high pressure" or "low pressure" do not depend on geographical location. This makes isobars on a weather map meaningful and useful tools.
  