Ocean acidification and atmospheric carbon

[Darkmisc]

Hi everyone

The following graph shows levels of CO2 in the oceans increasing with atmospheric CO2.

https://ocean.si.edu/conservation/acidification/ocean-acidification-graph

Given that global temperatures should rise with CO2, is it theoretically possible for the oceans warm to the point where their ability to hold CO2 decreases? That is, there is a point after which the ocean will become less acidic as atmospheric CO2 increases (not that this will help anything).Thanks

 

[256bits]

Hi everyone

The following graph shows levels of CO2 in the oceans increasing with atmospheric CO2.

https://ocean.si.edu/conservation/acidification/ocean-acidification-graph

Given that global temperatures should rise with CO2, is it theoretically possible for the oceans warm to the point where their ability to hold CO2 decreases? That is, there is a point after which the ocean will become less acidic as atmospheric CO2 increases (not that this will help anything).Thanks

Hi Darlmisc.
Is that a graph representing surface sea water only, or representative of whole ocean concentration?
How much time does it take for the ocean's waters to mix? days, years, centuries?

 

[Darkmisc]

I'm afraid I don't know any more than what's in the description under the graph.

I hadn't even thought about whether the deep ocean is affected by acidification (and warming). Would the question make sense if it were just confined to the surface water? I'm picturing a scenario similar to how soft drinks go flat at room temperature. Would this happen to the ocean? Or would high concentrations of atmospheric CO2 mean that overall, the pH continues to drop?

 

[256bits]

I'm afraid I don't know any more than what's in the description under the graph.

I hadn't even thought about whether the deep ocean is affected by acidification (and warming). Would the question make sense if it were just confined to the surface water? I'm picturing a scenario similar to how soft drinks go flat at room temperature. Would this happen to the ocean? Or would high concentrations of atmospheric CO2 mean that overall, the pH continues to drop?

Also good questions.
I just noticed that the graph is data from off the coast of Hawaii.
Surface water changes in CO2 content and acidification, and as you mentioned temperature change, would affect the flora and fauna living in the shallow depths - what's a shallow depth - I couldn't find the extent to which they measured.
Ocean mixing has to happen as I would think that the oxygen down deep below has to be from the atmosphere/sea interface and brought down, as would also CO2. I do wonder as to the amount of stratification per depth of the items mentioned.
there has to be some sort of timetable for ocean mixing whether brought about more locally by storms such as hurricanes or typhoons, or more generally by the currents generated by the interaction colder pole seawater with warmer equatorial.
It seems to be an interesting subject to be in.

 

[256bits]

In regards to mixing, there is this,
https://www.theguardian.com/science...cient-greek-discovered-at-bottom-of-black-sea
or, a PF post,
https://www.physicsforums.com/threads/oldest-ship-wreck-found-in-black-sea.958439/#post-6077735

The guardian states,

... shipwreck at the bottom of the Black Sea where it appears to have lain undisturbed for more than 2,400 years.

The 23-metre (75ft) vessel, thought to be ancient Greek, was discovered with its mast, rudders and rowing benches all present and correct just over a mile below the surface. A lack of oxygen at that depth preserved it, the researchers said.
...

Although the Black Sea is not the oceans, is the mixing with depth of the oceans and Black Sea comparable in nature?
Would CO2 follow the same stratification?
Some questions for the peoples at the Smithsonian might want to follow up on at their site to give a clearer picture of what is going on in addition to their explanation of the interaction of the atmosphere and the water interface, and expand that as to how does the whole ocean can/will act as a CO2 sink - ie or is it surface water only..

 

[Darkmisc]

Cheers. Thanks

 

[Bandersnatch]

There's a Wiki article on 'solubility pump' that might be worth looking into. Specifically, the references for the section on anthropogenic changes.

 

[BillTre]

Although the Black Sea is not the oceans, is the mixing with depth of the oceans and Black Sea comparable in nature?
Would CO2 follow the same stratification?

The Black Sea is unusual in its lack of mixing between top and bottom layers.
Some attribute this to a heavier saltier layer under the fresher water which is continuously entering the sea from rivers.

 

[jim mcnamara]

Meromictic waters do not mix - the term was started for use on lakes that did not run over every year - in contrast to holomictic - ones that do turn over.

https://aslopubs.onlinelibrary.wiley.com/doi/abs/10.4319/lo.1985.30.3.0451
The Black Sea apparently did recently start to mix in 1979, and seems to continue doing so.

The deep in some fjords are meromictic as well. https://link.springer.com/article/10.1007/BF0003162

 

[olivermsun]

It seems quite likely that pCO₂ is measured from surface water.

Ocean mixing has several timescales — the mixed layer at the surface might be well mixed over less than a day; the upper ocean below the mixed layer might be mixed on timescales of months to a few years. The very deep ocean, which is basically never exposed to direct wind forcing (except at key locations), probably would not equilibrate for a millennium or more.

 

[Baluncore]

Given that global temperatures should rise with CO2, is it theoretically possible for the oceans warm to the point where their ability to hold CO2 decreases?

CO₂ in the ocean is in equilibrium with CO₂ in the atmosphere, but with a long time constant. The temperature of the ocean would have to rise very significantly before CO₂ stopped moving from the atmosphere into the ocean. We can expect pH to continue to fall if atmospheric CO₂ continues to rise at the present rate.

There is a worrying pH interaction related to the iron cycle in the ocean. Phytoplankton require two doses of iron one week apart to mature. They then convert CO₂ into O₂ and organic carbon compounds. Later, they are eaten by krill that are in turn eaten by whales, that excrete the two doses of iron needed for the next generation of phytoplankton. If we break that iron cycle we greatly reduce the phytoplankton population replacement and the CO₂ to O₂ transformation.

There is some good news and some bad news. First the good news is you don't need to worry about the solubility of CO₂ in warmer seawater. But the bad news is that the pH limit on krill exoskeleton formation is rapidly approaching and will reach us long before temperature limits the solubility of CO₂ in seawater. It seems we are going to have to trust in the rapid evolution of krill stocks that can build an exoskeleton in progressively more acidic seawater.

This is a good argument for increasing the whale population, and for avoiding the harvest of krill, which is a significantly lower cost option than manufacturing and dumping bio-available iron in the Ocean.

 

[Laroxe]

I think this is in fact a good example of why many of the issues in the understanding of climate change are so contentious. Of course the oceans are not becoming acidic, they are (possibly) becoming less alkali, with the change being estimated to be from a pH of 8.2 at the start of the industrial revolution to the current 8.1 pH.

I thought this paper, even though it is getting on, was a good example of the very real problems in the scientific validation of acidification, I think the methods used to inform this issue are important. There is no doubt that the oceans play a significant role in the carbon cycle, but currently virtually all of the changes seen in ocean chemistry due to anthropomorphic CO2 emissions are dwarfed by the differences seen over various timescales, at different locations and during different weather. Much of the data which is available doesn't seem to provide anything like a reliable global picture. Many more current papers appear to try to ignore these issues, which is unfortunate, and acidification of the oceans seems to have become less of an issue.

The oceans also contain vast amounts of carbonates and is often contained in carbonate rocks which act as a buffer to changes in the pH. These carbonates are in fact an indicator of the role of the oceans in serving as a long term CO2 sink. Over long timescales CO2 is removed from the ocean and laid down as new carbonate rocks.

The capacity of the oceans to store CO2 over various timescales in solution, biologically and geologically appears to be vast but the processes that remove carbon into long term storage take a very long time. The quality of the data we have, hasn't resulted in useful models that allow us to predict the effects of CO2 on the oceans and the ones that have been used have proven to be so inaccurate that they are often used to discredit climate modelling. Unfortunately, the glacial speed (!) of some of the oceanic processes this means that we can predict that the oceans don't provide a solution to the potential problems predicted to occur due to human CO2 emissions.

https://www.nature.com/articles/s41467-018-04922-1

 

[Baluncore]

Of course the oceans are not becoming acidic, they are (possibly) becoming less alkali, with the change being estimated to be from a pH of 8.2 at the start of the industrial revolution to the current 8.1 pH.

The use or misuse of the terminology is simply rhetorical.
It should worry us all, that the pH continues to fall numerically.

A cycle of chain, is only as strong as the weakest link.
The average strength of the links is quite irrelevant.
Once it breaks, it matters not which link in the cycle broke.