Hydrostatic pressure in the marine environment increases linearly with depth, and organisms at 1000 m experience pressures 100 times greater than those at sea surface level. Previous work has examined the effects of pressure on neuron and nervous system activity in some organisms, as well as the various biochemical adaptations of deep-water species. However, the effects of pressure on other biological tissues are not well understood. In this study, we took the shallow-water jellyfish Aurelia aurita and exposed it to pressures of up to 30 MPa (equivalent to 3000 m depth). We observed behavioral and kinematic changes that are likely due to mechanical effects of hydrostatic pressure on the swimming muscles and bell mesoglea. The pulsation rate of the bell was found to correlate with hydrostatic pressure, although the effect was small relative to the variability between individuals (R2=0.124). Both the maximum contraction and relaxation rates of the bell were found to be significantly reduced at high pressure (30 MPa) relative to near-surface pressure (<1 MPa). The changes in pulse frequency and relaxation rate were both fully and immediately reversed upon release of pressure, but the change to contraction rate was not. Since bell contraction is controlled by muscle fibers and relaxation is controlled by elastic fibers in the mesoglea, the differential effects on contraction versus relaxation suggest that different tissues are affected differently by pressure. This opens the way for future work on how individual organisms can adapt to different environments.

diving and similar applications. A diving depth gauge is a pressure gauge that displays the equivalent depth below the free surface in water. The relationship A depth gauge is an instrument for measuring depth below a vertical datum or other reference surface. They include depth gauges for underwater diving and similar applications. A diving depth gauge is a pressure gauge that displays the equivalent depth below the free surface in water. The relationship between depth and pressure is linear and accurate enough for most practical purposes, and for many The Bourdon tube depth gauge consists of a curved tube made of elastic metal, known as a Bourdon tube. Water pressure on the tube may be on the inside or the outside depending on the design. When the pressure increases, the tube stretches, and when it decreases the tube recovers to the original curvature. This movement is transferred to a pointer by a system of gears or levers, and the pointer may have an auxiliary trailing pointer which is pushed along but does not automatically return with the main pointer, which can mark the maximum depth reached.… A depth gauge is an instrument for measuring depth below a vertical datum or other reference surface. They include depth gauges for underwater diving and similar applications. A diving depth gauge is a pressure gauge that displays the equivalent depth below the free surface in water. The relationship between depth and pressure is linear and accurate enough for most practical purposes, and for many purposes, such as diving, it is actually the pressure that is important. It is a piece of diving equipment used by underwater divers, submarines and submersibles. Most modern diving depth gauges have an electronic mechanism and digital display. Earlier types used a mechanical mechanism and analogue display. Digital depth gauges used by divers commonly also include a timer showing the interval of time that the diver has been submerged. Some show the diver's rate of ascent and descent, which can be is useful for avoiding barotrauma. This combination instrument is also known as a bottom timer. An electronic depth gauge is an essential component of a dive computer. As the gauge only measures water pressure, there is an inherent inaccuracy in the depth displayed by gauges that are used in both fresh water and seawater due to the difference in the densities of fresh water and seawater due to salinity and temperature variations. A depth gauge that measures the pressure of air bubbling out of an open ended hose to the diver is called a pneumofathometer. They are usually calibrated in metres of seawater or feet of seawater. Other types of depth gauge use a physical probe to measure the vertical distance from the reference surface to the bottom or other relevant point, such as a dipstick, sounding pole or sounding line, or use light or sound emitted from a known distance from the surface and reflected by the bottom to calculate depth based on elapsed time of travel. This includes echo sounding and lidar. A level sensor is related technology which measures offset of actual surface from a reference surface, bur does not directly measure depth. The Bourdon tube depth gauge consists of a curved tube made of elastic metal, known as a Bourdon tube. Water pressure on the tube may be on the inside or the outside depending on the design. When the pressure increases, the tube stretches, and when it decreases the tube recovers to the original curvature. This movement is transferred to a pointer by a system of gears or levers, and the pointer may have an auxiliary trailing pointer which is pushed along but does not automatically return with the main pointer, which can mark the maximum depth reached. Accuracy can be good. When carried by the diver, these gauges measure the pressure difference directly between the ambient water and the sealed internal air space of the gauge, and therefore can be influenced by temperature changes. In a membrane depth gauge, the water presses onto a metal canister with a flexible end, which is deflected proportionally to external pressure. Deflection of the membrane is amplified by a lever and gear mechanism and transferred to an indicator pointer like in an aneroid barometer. The pointer may push a trailing pointer which does not return by itself, and indicates the maximum. This type of gauge can be quite accurate when corrected for temperature variations. A pneumofathometer is a depth gauge which indicates the depth of a surface supplied diver by measuring the pressure of air supplied to the diver. Originally there were pressure gaues mounted on the hand cranked diver's air pump used to provide breathing air to a diver wearing standard diving dress, with a free-flow air supply, in which there was not much back-pressure other than the hydrostatic pressure of depth. As non-return valves were added to the system for safety, they increased back pressure, which also increased when demand helmets were introduced, so an additional small diameter hose was added to the diver's umbilical which has no added restrictions and when a low flow rate of gas is passed through it to produce bubbles at the diver, it gives an accurate, reliable and rugged system for measuring diver depth, which is still used as the standard depth monitoring equipment for surface supplied divers. The pneumofathometer gauges are mounted on the diver's breathing gas supply panel, and are activated by a valve. The "pneumo line", as it is generally called by divers, can be used as an emergency breathing air Dive computers have an integrated depth gauge, with digitized output which is used in the calculation of the current decompression status of the diver. The dive depth is displayed along with other values on the display and recorded by the computer for continuous simulation of the decompression model. Most dive computers contain a piezoresistive pressure sensor. Rarely, capacitive or inductive pressure sensors are used.

homogeneous—excepting so far as density increases with pressure or is influenced by the increase of heat with depth —an adjustment would be established by It is conceded also that the matter composing the earth at a depth of a few miles below the surface is so highly heated that it would become plastic or even highly fluid if the pressure under which it exists were removed. The best conception we can frame of the general physical condition of the earth is, that it consists of a more or less spherical mass, which is highly heated and in a potentially plastic condition within, and&#32; &#8203; that inclosing this inner sphere is a comparatively thin shell of solid rocks—the passage from the hot and potentially plastic interior to the cold and rigid outer shell being gradual, one merging with the other by insensible gradations. Deep erosion of subtuberant mountains should reveal a central area of igneous rock surrounded by a belt of metamorphosed rocks which on its outer border, in case the injection occurred in ordinary sedimentary strata, should pass into unaltered sand-stone, shale, etc. In such an instance a radial section should reveal a gradation from igneous rock through metamorphosed rocks to unaltered sedimentary beds. The breadth of the central core of igneous rock would vary with the size of the intrusion, and, down to a certain limit at least, with the depth of the plane of erosion. The hypothesis, however, that the sea is the&#32; &#8203; source of the water which, converted into steam, takes such a conspicuous part in volcanic eruption is open to several objections. In almost all land areas the rocks below the surface are saturated with water, the source of which is mainly rain. Excepting that the pressure of the sea on its floor tends to force water into the rocks beneath, there does not seem any good reason for concluding that the earth's crust where covered by the sea is more highly charged with water than the portions beneath land areas. In support of this conclusion it may be pointed out that volcanoes of recent date occur in the Great Basin, hundreds of miles distant from the Pacific. The Great Basin is a region of faults, and as much a belt of weakness in the earth's crust as if it had chanced to be situated near the sea. Owing to the increase of pressure with depth, it is evident that cavities in rocks in which any considerable bodies of water can be stored must become less and less frequent as the distance below the surface increases. As has been shown by Van Hise, at a depth in excess of about thirty thousand feet what may be termed appreciable cavities can not exist. Rocks under pressure become compact, so that deeply seated rocks must be less porous than similar material near the surface. These considerations lead to the conclusion that water-charged portions of the earth's crust How molten lava becomes charged with water can only be conjectured. It is well known that many liquids, especially when highly heated and under heavy pressure, will absorb gases. In a similar way we may conceive that liquid or plastic rock, on coming in contact with water, will absorb the steam produced. When molten lava rising in the conduit of a volcano passes through water-charged rocks and nears the surface, pressure is relieved and the occluded steam escapes. This escape is either quiet or explosive, dependent on the nature of the magma in which the steam is dissolved. Under certain conditions the plastic material rising in a fissure may expand between layers of stratified rock so as to form laccolites, subtuberant mountains, etc. If a break extends entirely through the crust, molten material forced into it may reach the surface. As the molten lava rises in such a break, it passes through rocks that are more and more highly water-charged, the water is vaporized, or perhaps its elements are dissociated, and the vapors and gases formed are absorbed by the fluid rock. As the lava comes to the surface the steam and gases absorbed under great pressure escape and furnish some of the most striking phenomena of volcanic eruptions. Under the vast pressure that exists at a depth of several miles it is impossible to comprehend how fissures can exist, but the plastic material beneath is under pressure of a similar order of magnitude, tending to force it out through any opening that may be formed. This objection is based on the assumption that the highly heated material forming the earth's interior is homogeneous. It has been argued that, if the material within the surface shell was not homogeneous—excepting so far as density increases with pressure or is influenced by the increase of heat with depth—an adjustment would be established by the flow of matter from one locality to another. In reply, it may be said, however, that this conclusion is inconsistent with the idea of a solid but potentially plastic inner sphere. From the point of view assumed in this essay, it appears that what may be termed a local flow of the matter comprising the earth's interior would not occur unless there was a local relief or a local increase of pressure. The idea that the earth as a whole is a rigid body is in harmony with the conclusions of eminent physicists and astronomers, while the assumption of local plasticity due to local relief of pressure is consistent with the observed movements of elevation and depression familiar to geologists. In such an occurrence the main explosion would probably be preceded by a breaking of the rocks and possibly subterranean explosions which would bring temporary relief of pressure. The behavior of many dormant volcanoes and the earthquakes that frequently accompany a renewal of their activity might thus be explained. When igneous intrusions enter the water-charged portion of the earth's crust but do not reach the surface, steam is also generated, and may assist such intruded magmas in opening passages for themselves and in elevating the domes that are raised above them.

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