Reef Chemistry Question of the Day #72 Altitude 1: oxygen

Randy Holmes-Farley

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Reef Chemistry Question of the Day #72

While most of us live close enough to sea level that there is little impact of altitude on our reefs, some of us live at high enough altitude that certain processes are impacted.

One of the most readily understood processes is the reduced availability of oxygen at high altitude.

One way to possibly counteract the reduced oxygen levels at high altitude is to keep the aquarium at cooler temperatures to allow more oxygen to dissolve into the water.

Compared to a reef aquarium at sea level and at 25 deg C (77 deg F), what temperature would you need to keep the reef at to exactly offset the reduced oxygen level at 5,000 feet above sea level? 10,000 feet?

A. 23 deg C (73 deg F) at 5,000 feet and 21 deg C (70 deg F) at 10,000 feet
B. 21 deg C (70 deg F) at 5,000 feet and 17 deg C (63 deg F) at 10,000 feet
C. 19 deg C (66 deg F) at 5,000 feet and 13 deg C (55 deg F) at 10,000 feet
D. 16 deg C (61 deg F) at 5,000 feet and 7 deg C (45 deg F) at 10,000 feet

Please consider only the change in oxygen levels due to temperature and altitude, not any change that may result from changes to the metabolic processes of the creatures as a function of temperature.

Good luck!





























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buzzword

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Lived at 5280' until 2 years ago. Never had a problem with tank at 79-80* SPS, clams it all did well.
It is not that there is less oxygen at altitude it is the pressure difference that creates less available O2 percentage. Correct me if I am wrong.
 
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Randy Holmes-Farley

Randy Holmes-Farley

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Lived at 5280' until 2 years ago. Never had a problem with tank at 79-80* SPS, clams it all did well.
It is not that there is less oxygen at altitude it is the pressure difference that creates less available O2 percentage. Correct me if I am wrong.

There is less O2 overall due to the pressure being lower and the percentage of O2 being about the same in that lower pressure.

So, do you have a pick of an answer? :)
 

Cory

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Purely a guess but B.
 
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Randy Holmes-Farley

Randy Holmes-Farley

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And the answer is...D. 16 deg C (61 deg F) at 5,000 feet and 7 deg C (45 deg F) at 10,000 feet

Clearly, reducing the temperature is not a good way to make up for the reduced O2 present at higher altitude.

You can use an online calculator to determine the reduction in pressure with altitude. For example:

http://www.altitude.org/air_pressure.php

If we enter 5,000 feet, we see the pressure is reduced to 0.84 times the seawater level. At 10,000 feet, the pressure is 0.70 times the seawater level. The oxygen tracks exactly with the pressure, so it is reduced to 0.84 and 0.70 times normal at these altitudes.

IMO, that's fairly significant at 10,000 feet.

Colder water holds more O2, and we can look that value up in tables or in books.

For example:
http://www.engineeringtoolbox.com/oxygen-solubility-water-d_841.html

oxygen-solubility-water.png


From such tables, we can see that it takes dropping the temperature to 16 degrees C to increase the O2 solubility to 1/0.84 (=1.19) times the level at 25 degrees C, and all the way to 4 degrees C to offset the 10,000 foot (0.7; 1/0.7 = 1.4) drop in O2.



 

leptang

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The highest ive backpacked was up to 12,365 ft. Oh it was hard to breath, my hands turned blue. I couldn't imagine anyone who would want to keep a reef tank alive at that altitude.
 

leptang

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The highest ive backpacked was up to 12,365 ft. Oh it was hard to breath, my hands turned blue. I couldn't imagine anyone who would want to keep a reef tank alive at that altitude.
 

MnFish1

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At sea level the dissolved O2 at 25 is 8.26 mg.l.
at 5000 feet the dissolved O2 at 25 is 6.83 mg/l. at 16 deg its 8.17
at 10000 feet the dissolved 02 at 25 is 5.6 mg/l at 45 deg is 8.27
So D is the answer
 

rkpetersen

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I solved it before looking at the rest of the thread and realizing that this is a necropost from three years ago! I did get the right answer though, D. I didn't have that specific table but solved it a different way.

At 5000 ft altitude, effective partial pressure of oxygen is 17.3%, or 82.8% of sea level. Assuming the dissolved oxygen saturation level in seawater parallels this decrease, at 5000 feet it should be 6.8 ppm (O2 sat at 77 degrees, sea level, 1.026 sg) x 82.8% = 5.63 ppm. O2 carrying capacity of seawater increases by roughly 0.07 ppm for every degree Fahrenheit decrease in temperature. So, (6.8-5.6)/.07 = 17 degree temperature drop to get the O2 level back up, or 60 degrees F. For 10,000 ft, same calculation gives 46 degrees F. Only answer that fits is D.
 
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Randy Holmes-Farley

Randy Holmes-Farley

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Isn't this close to What we are discussing?

Yes, lower air density lowers O2 and raises pH (by lowering CO2).

I thought you were implicating an air density increase due to cold air temps to cause a pH rise. It would cause a fall in pH.
 
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Randy Holmes-Farley

Randy Holmes-Farley

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I was referring to "close " about the temp, you have shown a larger variance, w elevation? Just asking?

Sorry, I’m not sure what you are saying, [emoji3]
 

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