33.10 Barometer How High Is That?

[bfishn]

Good catch. Wiki reports the (previous?) world record high as 32.06", set in Mongolia in 2001.

[Iclass]

I... don't think so. When they get the simple stuff wrong, one has to wonder about the rest;

"Here’s how it works. In simple terms, barometric pressure—or atmospheric pressure—is the weight of the air pressing down upon us."

Atmospheric pressure . Once below the surface, pressure is distributed equally in all directions.

Which is the reason a low pressure would make it easier for plankton to move about...

[bfishn]

I'm afraid it doesn't work like that. If pressure affected the ability of an object to move through water, our submarines would be in big trouble.

While underwater pressure at any given point is equal from all directions (not just pushing down), it increases with depth at a rate of 0.43psi per foot.

Standard atmosphere measures 29.92 inches of mercury column, which is equal to 14.696 psi. The actual pressure depends on the altitude and local weather conditions, which on the earth surface has ranged from measured extremes of 25.7 to 32 inHg. The typical frontal variations we experience are more in the range of 1-2 inHg, or 0.5 to 1 psi.

Due to atmospheric pressure, water pressure is already about 14.7 psia just under the surface. A fish (or plankton) at 10 feet deep is subject to about 19 psi, and at 34 feet deep undergoes 2 atmospheres, or about 29 psi.

When you look back at our typical 0.5 to 1 psi frontal pressure changes, it becomes obvious that the pressure change a fish (or plankton) undergoes from a storm front is actually less than they feel with a mere change of 3 feet in depth, something most fish (and plankton) do all day with no apparrent ill effects or changes in behavior.

If, as you suggest, a rising barometer forced fish or plankton to go deep, you can see that action would actually result in even further increases in pressure.

[Iclass]

You seem very knowledgeable about this subject, but I have a question about the comparison of plankton to submarines...

I would think a subs ability to alter its buoyancy, also a fish swim bladder, would have a big impact on how the pressure affects it? I would also think the ability of a sub or fish propelling itself thru the water would be a little more efficient than plankton as well. Are these factors not considered when talking about pressure? I know my car seems to run easier at higher altitudes where there's less air pressure...

[bfishn]

I think you're confusing pressure with density. Air can be considered a fluid for some purposes, but not all properties are shared with water. For instance, air can be compressed, in which case an increase in pressure results in an increase in density per volume. Water on the other hand, can't be compressed, so pressure and density are independant properties. In water, the density is controlled by temperature (and chemistry), with the most dense water being that at 39 degrees F. (why ice floats).

While water pressure has no bearing on the ability of an object to move through it, density does, albeit to a fairly small degree.

"Plankton" is far too broad a category to cover means and mechanics of locomotion in a post. In general, all plankton is at the mercy of current. Density is a factor in movement. Some zooplankton are heavier than water and must "swim" constantly so as not to sink to the bottom (if you can call wiggling your cilia swimming).

[Iclass]

So if air can be compressed, the opposite is true as well? Like the spreading out of air in water...I truly believe we are on some level of saying the same things, I'm just not communicating very well thru text. simply put air pressure low or high affects the distribution of many species of plankton throughout the water column.

[bfishn]

No, I'm saying that temporary, short-term atmospheric pressure changes (like we see with a storm front) have no effect on the movement of plankton. dtrs5kprs’ references state that long term (like that of climate change) high pressure (might) affect the total biomass of plankton in an area, but that’s a different matter entirely.

Once you can get beyond thinking that pressure only pushes downward, I think you'll grasp what I'm trying to say.

[Iclass]

Ahh, I understand the confusion now... Didn't mean to infer that pressure only pushed downward. But according to many scientists in the world of aquaculture, the changes in atmospheric pressure does affect the movements of plankton.

[bfishn]

Could you post a link please?

[Iclass]

Don't have a link, so let's put it like this

A change in barometric pressure changes the buoyancy of plankton...