Sunday, May 3, 2015

The Pressure Effects....

Today' weather forecast: "Big high pressure (1033 mb) near North Is, NZ to drift slowly to the E with little change in strength during the next 2-3 days. This high may begin to weaken slowly during the middle of... Appears worst conditions may develop during Mon and continue..."

Pressure also has a big impact in the deep ocean. The bottom of the ocean is an inhospitable place. It is dark, cold, and under extreme pressures. Imagine you are swimming in a pool that is ten feet deep, or just about three meters. You dive to the bottom to pick up a pool toy or a penny and your ears pop. You feel the pressure on your body and on your head. Now imagine increasing that pressure over 100 times. With every ten meters of seawater, add one atmosphere of pressure. Now imagine traveling to 1000m, or 100x10m. Since we already exist at 1bar of pressure, the total pressure would be about 101bar.
Jason can dive to depths of 6000 meters. The ROV is specially reinforced to deal with the extreme pressures at depth so that it doesn’t implode, or compress explosively. The areas we work in the Lau Basin are at depths of 1700 to 2600m, but the pressures are no less damaging. 

Styrofoam cups and heads before their descent to our deep-sea research sites.
To demonstrate the pressures at depth, we sent down several Styrofoam heads that Allie, Joy, Francis and Piper illustrated, and cups that middle school teachers attending a science (STEM) workshop at the University of Nevada illustrated.   The cups and heads dropped to depths between 1900m and 2400m. Simply dropping to the bottom of the ocean allowed the pressures of nearly 200bars, or around 2500 pounds per square inch, to do its work.
The cups, once a full 10oz and over 3 inches tall, shrank down to around 2 to 3oz and around 2 inches tall. We stuffed wads of paper inside to allow them to keep their shape, but that did not necessarily ensure they were perfectly round at the end. Instead, they crumpled as the pressure increased, crushing them on one side or another depending on which way they were oriented. 

The extreme left scale bar was 1 inch. This illustrates nicely how much the cup shrunk!

Styrofoam is made of foam called polystyrene, which is full of air pockets. When put under pressure the air is squeezed out, but the foam retains its shape. This is why Styrofoam makes such a good example of pressure at depth – it does not warp the material past recognition, but it shrinks to a size that seems unrealistic to our 1bar atmosphere. 

 This extreme pressure at deep-sea vents also allows the very hot hydrothermal fluid to remain in a liquid state in most cases, except when the temperature is so high the fluid will boil as we saw in the Mariner blog post.  Many of the deep-sea invertebrates; snails, mussels, shrimp, crabs, do not have gas-filled organelles, such as humans or other land-dwellers, which would be compressed under pressure, and so these creatures are not nearly as affected by pressure as we are.

the normal head
the shrunken head
The bacteria we bring up to our lab are not necessarily barophiles (piezophiles), or pressure-loving, but they do thrive under those conditions nonetheless. Even the fluid samples we bring up show evidence of pressure – there are no bubbles emerging from the vents, but when we remove the fluid from its pressure-tight sampler (the IGT see "hot water" post), it may erupt with bubbles as the gases escape the solution.

Much of the deep ocean is as yet unexplored. And how pressure affects life in this deep ocean biosphere will no doubt lead to a new understanding of the extent of life on Earth.

Contributed Morgan Haldeman, Nick Rhoades and John Kelley.  

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