Wevets I suspect that the problem stems from the different ways that people are using “oxygen produced”. And from reading your post I suspect that you are also using it very loosely. This is going to be a very long reply, but unfortunately this is one of those simple concepts that can get very confusing if it’s not explained fully because it can be very counter-intuitive.
The problem is essentially the difference between gross production and net production. All photosynthetic organisms produce oxygen. That’s not a problem. The problem occurs because all photosynthetic organisms also consume oxygen. That last fact tends to be omitted altogether or skipped over lightly in HS biology classes but it’s essential to answering this question.
Plants produce oxygen as a by product of producing solid, organic food. Once that food is produced it is then burned in exactly the same manner as humans and other heterotrophs burn food. All that us heterotrophs have done is lost the ability to produce organic food form the inorganic, but everything after that is identical in the way that we gain and utilise energy.
Bare with me I am answering your question. Really.
So what we have in a typical plant (plant from here on is convenient shorthand for any photosynethic organism) is a situation where it produces one mole of oxygen and then promptly destroys one mole of oxygen in order to utilise the energy in the food it has just created. The net oxygen production in such a situation of course is zero however it is still perfectly accurate to say that oxygen production is one mole. You are hopefully starting to see where the problems arise. Any individual plant may produce many litres of oxygen every day. But the exact same plant is also very likely to consume precisely the same amount of oxygen leading to no net oxygen production.
There are only two ways that a plant can actually manage a net production of oxygen.
One is if it increases in living biomass. Basically it has to be growing. That’s because oxygen is only produced if the plant produces solid food from gas and it remains in solid form. So a growing tree for example is a net oxygen producer in any given year provided it weighs more in December than it did in January. If a tree weighs the same amount or less then it hasn’t produced any oxygen in this manner. Producing oxygen in this way is pretty hard for unicellular organisms because they have such a rapid turnover. While algae may bloom rapidly on the surface of the ocean it dies just as rapidly and the amount of mass present as living cells remains constant year to year. As a result algae/plankton tend not to produce any net oxygen by biomass increase.
Similarly most forests don’t produce any net oxygen by biomass increase. That’s because seedlings can only grow and add weight after a mature tree has died, and after death the mature tree rapidly rots, and rotting destroys exactly the same amount of oxygen as the tree had managed to create. So once again no net production. But note that this is net production. Gross of oxygen may be huge. The Amazon for example, often touted as ‘the lungs of the Earth’ produces vast amounts of oxygen every year, but only in gross terms. The Amazon is at best oxygen neutral and probably a net oxygen sink. It consumes more oxygen than it creates in any given year.
The second way that plants can be net oxygen producers is if they remove their biomass from the geochemical cycle. Basically it means they, or at least parts of them have to die, and be buried somewhere where they can’t rot. That’s vital because as soon as a plant rots any net oxygen it may have produced in its lifetime is consumed by the decay process.
Some terrestrial plants manage to be net oxygen producers in this way. Perhaps the most spectacular examples would be the forests that became preserved indefinitely as coal. Because they couldn’t decay the oxygen they produced was never destroyed when the material decayed, and so those plants made a net contribution to atmospheric oxygen. A small but still appreciable amount of oxygen production results from material being partially burned and stored in the soil as charcoal. Other material is stored in the soil as extremely chemically stable humus components. Still more results from material being swept into lakes or the seabed and buried in sediments where it can not decay because the pressure and lack of gas exchange preserve it. And some plant material is preserved in peat bogs and so forth. But as you can see it’s actually fairly unusual for land plants to be removed from the oxygen cycle. And as a result land plants don’t make much contribution at all to net oxygen production. They may be massive gross oxygen producers but because the oxygen they produce gets ‘burned’ when they rot after death they don’t contribute at all to any change on oxygen levels in the air.
In contrast marine plants, especially phytoplankton, find it very easy to leave the oxygen cycle. When they die they sink immediately into the oceanic sediments. And in those sediments decay is essentially stopped. As a result plankton tends to be the single largest contributor to net oxygen production. It’s a pretty spectacular contributor to gross oxygen production as well of course but it makes up by far the lion’s share of net production.
So after all that here’s what seem to have been meant by those references of yours:
National Geo is referring strictly to gross production. A figure of around 50% for gross oxygen production is within the ranges I’ve seen published for gross oxygen production, or actually primary production, which is roughly the same thing. IOW 50% of the oxygen that is created in any given year is done by land plants, but that figure makes no mention at all that around 50% of the oxygen that is destroyed each year is destroyed by land plants or organisms feeding on land plants. So the figure doesn’t have any bearing at all on relative contributions to oxygen in the air at all.
Ask a scientist doesn’t make its position very clear at all. I’m assuming they are referring to net production, but the fact that they imply that high figure is due to surface area alone casts that into doubt. Phytoplankton contribute disproportionately because they don’t decay as much a terrestrial plants. It’s not down to surface are much at all.
Oceans online is referring strictly to primary productivity. That is effectively a surrogate for gross production, not net production.
Sorry, but reliable figures this sort of thing just don’t exist. It’s just too damn hard to measure and too variable on every scale. There has been a flurry of activity in this field in the last 10 years or so as a result of people desperately working out carbon budgets due to global warming concerns. For every publication saying one thing there will be another that contradicts it. All that anyone can really do is lump together all the results, throw in a few fudge factors and come up with a reasonable estimation. But depending on which fudge factors are used the results can easily vary by 40%.
Your two links on dissociation don’t work so I really can’t help you. But be aware that measuring the role of dissociation is very hard to do and there’s a lot of debate about its role, so both figures could mean the same thing but just have been calculated in different ways.
<—me
) sites to be even mentioning it, there should be some primary source material on oxygen contributions to the atmosphere from the biosphere.