Fluid inclusion analysis techniques are used by geologists to gather information on the pressure, volume, and temperature conditions during the crystallization of the mineral (here ice) containing the inclusion.
There are three assumptions that usually made in dealing with fluid inclusions:
• The composition of the trapped fluid has not changed since inclusion formation
• The density of the trapped fluid has not changed since inclusion formation
• The volume of the inclusion has not changed since inclusion formation
Natural fluid inclusions will contain multiple chemical components (impurities) and may contain multiple phases (gas, liquids, precipitated crystals).
The analysis of fluid inclusions (say to determine the pressure of formation) therefore involves measuring the composition and density and then applying the appropriate equation of state calculations to calculate unknowns.
Fluid inclusion measurements and analysis are not simple to perform. I would not think you can say whether the pressure is higher or lower than the formation pressure without doing a complete analysis.
The analysis of air bubbles in ice are important for the study of the past composition of the atmosphere and climate change.
Suppose the pressure at the Earth's surface is $P$.
Consider an air column of cross-sectional area $A$.
The upward force on the column is $F_{\text{up}}=PA$.
Denote the weight of the column as $W$.
By definition of "weight", the downward force on the column is $F_{\text{down}}=W$.
Suppose the pressure is too low, such that $F_{\text{up}}<F_{\text{down}}.$
The column of air will then fall downward.
As it does, it more air molecules are arriving at the surface of the Earth, increasing the density of air and therefore also increasing the pressure.
Since the pressure increases, so does $F_{\text{up}}$.
This will continue until $F_{\text{up}} = F_{\text{down}}$, at which time the system is in equilibrium and stays the same.
In other words, the pressure is such as to balance the weight of the column because that's the only situation which won't immediately change.
Best Answer
When they say blood pressure is 100 mmHg, that really means 100 mmHg higher than atmospheric pressure. It's a gauge pressure, not an absolute pressure. The corresponding absolute pressure would be about (760 + 100) mmHg.
Originally posted by Georg in a comment