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Ocean acidification and atmospheric carbon

  1. Oct 24, 2018 #1
    Hi everyone

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


    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).

  2. jcsd
  3. Oct 24, 2018 #2


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    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?
  4. Oct 25, 2018 #3
    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?
  5. Oct 25, 2018 #4


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    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.
  6. Oct 25, 2018 #5


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    In regards to mixing, there is this,
    or, a PF post,

    The guardian states,
    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..
  7. Oct 26, 2018 #6
    Cheers. Thanks
  8. Oct 26, 2018 #7


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    There's a Wiki article on 'solubility pump' that might be worth looking into. Specifically, the references for the section on anthropogenic changes.
  9. Oct 26, 2018 #8


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    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.
  10. Oct 26, 2018 #9

    jim mcnamara

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    Staff: Mentor

  11. Oct 29, 2018 #10


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    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.
  12. Nov 9, 2018 #11


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    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.
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