Reef Chemistry Puzzle #14 Ignored by most

[Randy Holmes-Farley]

Reef Chemistry Puzzle 14

1. Most marine organisms ignore me.
2. Cyanobacteria sometimes don’t ignore me.
3. I like colder seawater
4. In 35 ppt seawater at 25 deg C, there is about 10.4 ppm of me present

What am I?

Good luck!

Previous Reef Chemistry Puzzle:

Reef Chemistry Puzzle #13 I'm shrinking....

Reef Chemistry Puzzle 13 As I move through the water of a reef aquarium, I am smaller when I am near the bottom. What am I? Good luck! Previous Reef Chemistry Puzzle: https://www.reef2reef.com/threads/reef-chemistry-puzzle-12-water.1027279/ .

www.reef2reef.com

 

[danimal1211]

Silicates?

 

[jda]

Other than people's sanity when cyano appears, guessing nitrogen gas since it is the only weird thing that I can think of that is unique to cyano.

 

[dennis romano]

Going with nitrogen too because of the cyano and colder seawater clues.

 

[Tony Thompson]

N2

 

[danimal1211]

Well at 10.4 ppm it would have to be a major element in SW. I amend my guess to strontium

 

[drolmaeye]

Dissolved oxygen?

ETA: I see this may be too close to the previous answer, and a table for dissolved oxygen at 35 ppt and 25 C showed about 6.8 ppm, so . . . I will be curious what the answer is.

 

[RelaxingWithTheReef]

Going on a limb - Carbonate Ion

 

[Nano_Man]

Yes Randy same one you’re thinking

 

[taricha]

gonna guess diatomic nitrogen.

 

[danimal1211]

When do we get the answer

 

[Randy Holmes-Farley]

Now.

And the answer is...

1. Most marine organisms ignore me.
2. Cyanobacteria sometimes don’t ignore me.
3. I like colder seawater
4. In 35 ppt seawater at 25 deg C, there is about 10.4 ppm of me present

What am I?

Nitrogen, N2.

Solubility of N2 from air is higher in colder water, and at normal pressure and temperature, there is about 10-11 ppm in seawater.

Unlike most marine organisms, that ignore N2, some types of cyanobacteria can take in N2 and "fix" it. That is, they can use it as a source of nitrogen for biomolecules.

What is Seawater? by Randy Holmes-Farley - Reefkeeping.com

Dissolved Atmospheric Gases
Any gas present in the atmosphere will be present in seawater. Many of these are unimportant to reef aquarists, but two are of critical importance: oxygen and carbon dioxide. Aside from carbon dioxide, all of the gases have lower solubility in seawater as the temperature and salinity are raised. Table 4 shows the concentration of the most common gases in seawater at 25°C.

Oxygen is generally most highly concentrated near the ocean's surface. In the top 50 meters or so, oxygen's concentration is controlled largely by exchange with the atmosphere, and is usually close to equilibrium with the air. Between 50 and 100 meters, the O2 level often rises due to photosynthesis. Below about 100 meters in the open ocean the oxygen level drops steadily for the next 1000 meters or so due to biological processes that consume it. It then sometimes rises again in the deeper oceans as oxygen there is replenished by sinking cold ocean water that is rich in oxygen. The importance of dissolved oxygen in seawater and reef aquaria has been discussed in a series of previous articles:

The Need to Breathe in Reef Tanks: Is it a Given Right?

http://www.reefkeeping.com/issues/2005-06/eb/index.php

The Need to Breathe, Part 2: Experimental Tanks

http://www.reefkeeping.com/issues/2005-07/eb/index.php

The Need to Breathe, Part 3: Real Tanks and Real Importance

http://reefkeeping.com/issues/2005-08/eb/index.php

Table 4. Atmospheric gases in seawater at 25 deg C when in equilibrium with air.​
Gas	Concentration​
Carbon dioxide (as HCO3- and CO3--)	100 ppm of CO2​
Nitrogen (N2)	10.7 ppm​
Oxygen (O2)	6.6 ppm​
Argon (Ar)	0.40 ppm​
Neon (Ne)	0.13 ppb​
Helium (He)	0.0066 ppb​
Krypton (Kr)	0.185 ppb​
Xenon (Xe)	0.038 ppb​