At sea level, the mean barometric pressure forces mercury 29.92 inches up the test tube,
which is expressed as 29.92 inHg (inches of mercury) or 'One Atmosphere' (i.e. barometric baseline).
During an average cold-front (clockwise high-pressure cell) the barometric pressure climbs to around 30.32 inHg,
a mean rise of 1-1/3% above normal. During an average warm-front (counterclockwise low-pressure cell)
the barometric pressure will fall to around 29.52 inHg, a mean drop of 1-1/3% below normal.
Water has a much higher specific gravity than air. At a depth of 34 feet, water exerts the same pressure per sq. in.
as our entire atmosphere, which is estimated to be around 100 miles high. So the total pressure at a depth
of 34 ft is 29.4 lb psi or 'Two Atmospheres'. Due to water's high specific gravity, when a fish moves just 5.4 inches
downward in the water column, the increase in pressure on the fish is equivalent to the pressure change
during an average high-pressure system (cold front). Conversely, when the same fish swims 5.4 inches
higher in the water column, the drop in pressure is equivalent to an average low-pressure system (warm front).
(You might want to do your own calculations: 1-foot column of water = 0.433 lb / sq. in. <> 1-foot cube of water = 62.35 lb)
Deep-sea fishing gives us the most graphic portrayal of water pressure as compared to barometric pressure.
When fish are winched from water depths over 100 ft (as I often have), there is no Catch-and-Release.
Due the dramatic drop in pressure, when the fish reaches topside its eyes are bulging out of its head
and its bladder is turned inside out and protruding from the fish's mouth.
Roger