Reef Chemistry Question of the Day #247 Organic vs Inorganic Carbon

[Randy Holmes-Farley]

Reef Chemistry Question of the Day #247

In the ocean, is there typically more inorganic carbon or organic carbon?

For purposes of the question, we consider the following to be the sources.

Inorganic carbon: carbonic acid, carbon dioxide, bicarbonate, carbonate

Organic carbon: nearly all other forms of carbon, including small dissolved organics such as acetate and ethanol, large dissolved biomaterials such as proteins, and particulate organic matter, including whole bacteria, viruses, etc.

A. There is more inorganic carbon
B. There is more organic carbon
C. The values are close enough that the answer varies by location
D. I can't tell because there is a walrus poop in my sample, interfering with testing

 

[JimWelsh]

Isn't answer D just a specialized and more specific case of answer C?

 

[cgdcinc]

I think there are more DIC in the ocean than DOC. So A. I think I remember that the values also depend on depth as well.
These questions are always cool and make me feel really dumb most of the time!!! Lol! I’m glad you do them though.

 

[Randy Holmes-Farley]

Isn't answer D just a specialized and more specific case of answer C?

Perhaps, but the question does say "typically", so unless there are a lot of walrus poops around, it might be considered atyptical to draw a water sample from the ocean and get one.

To make it clear for folks, lets assume that to elect answer C, that would require at least 1% of the ocean to have answer A correct and at least 1% to have answer B correct.

 

[scardall]

I select Answer "B"

 

[rkpetersen]

A, far more, about 5ox as much. Vast amounts of carbon as dissolved CO2 and carbonates, particularly in the deep ocean where much carbon enters but considerably less leaves. Also, most organic carbon is rapidly mineralized to inorganic carbon when organisms die if not consumed by other creatures. This discrepancy will only increase as high atmospheric CO2 levels force more and more inorganic carbon into the ocean (this is in disequilibrium primarily due to anthropogenic sources like fossil fuel burning, and won't equilibrate in our lifetime). We can also expect organic carbon content of the ocean to decrease as its ability to sustain life decreases.

 

[siggy]

A

 

[SDReefer]

I'm going to guess A, more dissolved inorganic carbon due to the sheer amount of diffusion of gases between the ocean and the air, and vice versa.

 

[jml1149]

A

 

[MnFish1]

Reef Chemistry Question of the Day #247

In the ocean, is there typically more inorganic carbon or organic carbon?

For purposes of the question, we consider the following to be the sources.

Inorganic carbon: carbonic acid, carbon dioxide, bicarbonate, carbonate

Organic carbon: nearly all other forms of carbon, including small dissolved organics such as acetate and ethanol, large dissolved biomaterials such as proteins, and particulate organic matter, including whole bacteria, viruses, etc.

A. There is more inorganic carbon
B. There is more organic carbon
C. The values are close enough that the answer varies by location
D. I can't tell because there is a walrus poop in my sample, interfering with testing

The balance of dissolved inorganic carbon (DIC) : dissolved organic carbon (DOC) : particle organic carbon is about 2000:38:1.

So - A but there may be walrus poop in the sample as well.

 

[SaltEverywhere]

Are we talking by weight or numerically? I am guessing that a whale weighs more than a molecule of CO2. I also presume the ocean contains a lot of whales, as well as perhaps some fish, and they might outweigh the total mass of the inorganic compounds which would make the answer B. But I expect there are more moles of inorganic carbon than there are moles of whales, so the answer in that case would be would be A. Disclaimer: No research or experiments were performed in deriving this answer, science did not influence my reasoning in any way, and no walruses were harmed in the making of my reply

 

[MnFish1]

Are we talking by weight or numerically? I am guessing that a whale weighs more than a molecule of CO2. I also presume the ocean contains a lot of whales, as well as perhaps some fish, and they might outweigh the total mass of the inorganic compounds which would make the answer B. But I expect there are more moles of inorganic carbon than there are moles of whales, so the answer in that case would be would be A. Disclaimer: No research or experiments were performed in deriving this answer, science did not influence my reasoning in any way, and no walruses were harmed in the making of my reply

You're ignoring this part of the question:

"For purposes of the question, we consider the following to be the sources. Inorganic carbon: carbonic acid, carbon dioxide, bicarbonate, carbonate Organic carbon: nearly all other forms of carbon, including small dissolved organics such as acetate and ethanol, large dissolved biomaterials such as proteins, and particulate organic matter, including whole bacteria, viruses, etc."

My guess is that even if it included whales inorganic would win

 

[SaltEverywhere]

You're ignoring this part of the question:

"For purposes of the question, we consider the following to be the sources. Inorganic carbon: carbonic acid, carbon dioxide, bicarbonate, carbonate Organic carbon: nearly all other forms of carbon, including small dissolved organics such as acetate and ethanol, large dissolved biomaterials such as proteins, and particulate organic matter, including whole bacteria, viruses, etc."

My guess is that even if it included whales inorganic would win

I was including whales as part of particulate organic organisms such as bacteria and viruses, but mostly I filed them under “etc”

 

[MnFish1]

I was including whales as part of particulate organic organisms such as bacteria and viruses, but mostly I filed them under “etc”

YEAH. a big particle lol. - my guess is even counting the fish/mammals the inorganic still wins lol

 

[SDReefer]

What's the answer @Randy Holmes-Farley ? This is a good question!!

 

[Randy Holmes-Farley]

Are we talking by weight or numerically? I am guessing that a whale weighs more than a molecule of CO2. I also presume the ocean contains a lot of whales, as well as perhaps some fish, and they might outweigh the total mass of the inorganic compounds which would make the answer B. But I expect there are more moles of inorganic carbon than there are moles of whales, so the answer in that case would be would be A. Disclaimer: No research or experiments were performed in deriving this answer, science did not influence my reasoning in any way, and no walruses were harmed in the making of my reply

I'm counting carbon atoms (weight or number), not moles of something they may be a part of.

let's have some math fun...


There are a lot of carbon atoms in each big whale (assume 300,000 pounds, guess 10% carbon (might be a low estimate due to blubber having a lot of carbon ), so maybe a million moles, or 7 x 10^29 carbon atoms, and quite a few whales (roughly one million, but most aren't that big). So 10^6 x 7 x 10^29 = 7 x 10^35 carbon atoms in whales.

There are also a lot of bicarbonate ions in seawater, with just one carbon atom each. A liter of seawater might contain 2 millimoles of bicarbonate, or 10^21 bicarbonate ions. Total volume of the ocean is about 1.3 billion cubic kilometers. There are 10^12 liters in a cubic kilometer, so that's 1.3 x 10^21 liters. Thus the carbon due to bicarbonate ion is about 1.3 x 10^42.

So there's very roughly 1.3 x 10^42/7 x 10^35 = ~2 million times as much carbon in bicarbonate as in whales.

 

[Randy Holmes-Farley]

Hope I did the math right.

 

[Randy Holmes-Farley]

FWIW, wikipedia has a nice summary of biomass and carbon:

https://en.wikipedia.org/wiki/Biomass_(ecology)

In general, I don't want to calculate it out for every organism, so let's intend the question to relate to something that is actually going to be in a real water sample you might take, so no tuna, whales, or walrus present.

I'm also not sure how one would deal with benthic bacteria, which are only "somewhat" in the water, but according to wikipedia may contain a lot of carbon.

 

[JimWelsh]

Hope I did the math right.

Almost.

so maybe a million moles, or 7 x 10^29 carbon atoms

2 millimoles of bicarbonate, or 10^21 bicarbonate ions

Avogadro's number is 6.022 * 10^23, so these should be "6 x 10^29" and "1.2 x 10^21" respectively. That means that the 1.3 should be multiplied by the 1.2 to become 1.6, and then the division at the end returns 1.6 x 10^42/6 x 10^35 = 2.6 million, which would round to 3 million instead of just 2 million.

 

[Randy Holmes-Farley]

Close enough for whale work.