[EB66]

We're talking about oxygen production. Not carbon sequestration.

Regarding sequestration: the carbon goes into the trunk, branches, roots and leaves of the tree. Leaves fall off the tree, rot and become soil. The tree eventually dies, rots and becomes soil.

Some carbon will be given off by various decomposition processes, but the overall net effect is by far a carbon sink.

[nearbuy]

> We're talking about oxygen production. Not carbon sequestration.

BurningFrog said the carbon from CO2 goes into plants. Since plant matter isn't accumulating, carbon can't be accumulating, and therefore oxygen can't either. You replied, "This is just plain wrong".

So you're saying the part that is sequestered goes into the soil. That means some significant fraction of the 20 billion tonnes of carbon the Amazon photosynthesizes each year is turning in to soil. You're claiming the amount of soil increases by this amount each year, correct?

[EB66]

> That means some significant fraction of the 20 billion tonnes of carbon the Amazon photosynthesizes each year is turning in to soil.

Correct. That fraction is obviously reduced when the forest is burned.

[nearbuy]

Then why is the soil layer in the Amazon only about a meter deep after millions of years of carbon sequestration? The rainforest photosynthesizes about 3 kg of carbon per square meter per year.

[EB66]

The soil is not only a meter deep. In most places it's several meters deep and it's that deep despite constant heavy rains and erosion.

The soil does not need to be millions of meters deep in order for the forest to be both a net carbon sink and net positive oxygen producer -- it can slowly acrue over time.

And even if biological respiration processes in the forest began to equal carbon sequestration processes -- the forest would still be a massive carbon sink over its lifetime given the massive quantites of plant matter and soil present.

[nearbuy]

It's about a meter deep on average, but it's such a moot point to quibble over because it's too low by a factor of about 100,000. If it were 100 meters deep, we'd still have to answer the same question.

Yes, the rainforest has been a massive carbon sink over its 30+ million year lifetime - because of the carbon it sequestered while it was first growing and expanding.

Yes, it could be producing very, very tiny amounts amounts of oxygen each year so that the rise in soil level isn't noticeable. If the rainforest was still slowly sequestering carbon in soil at a rate of about 1 meter of soil depth per 30 million years, then you're talking about it sequestering about 0.00005% of the carbon it captures through photosynthesis. If you're calling the article "completely wrong" over that, I'm not sure what to say.

And it's not just the yearly rate of oxygen production that must be negligible. The total oxygen produced over the Amazon's lifetime is negligible. As the article points out, if you burned the entire Amazon rainforest, releasing all the sequestered carbon, it would only decrease atmospheric oxygen from about 20.95% to 20.93%.

[baq]

Bacteria and fungus eat the rest? Consider the Azolla event where dead plant material sank into very salty and oxygen poor water, which left several meters of carbon on the bottom of the polar ocean after 800k years.

[nearbuy]

If fungus or aerobic bacteria eat it, then the Amazon doesn't produce surplus oxygen from it. Eating involves recombining the carbon with oxygen into CO2.

The biomass of the Amazon is not, for the most part, sinking into very salty water.

[Ericson2314]

I assume the Amazon and it's tributaries wash most of it away.

[nearbuy]

Most of the soil is kilometers away from the nearest tributary. And it wouldn't explain why it washes away everything except for the last 1 meter of soil. Or why the organic matter wouldn't re-enter the food chain once it reached the ocean, thereby recapturing the oxygen.

If 3kg of carbon sequestration per year per square meter were accumulating as soil, and the rainforest has existed at least 30 million years, the soil would be over 2,000,000 meters deep (with rich organic soil being about 9% carbon). If even 1% of the carbon captured through photosynthesis was sequestered in soil, we should still have much, much deeper soil.