EGU2020-10433
https://doi.org/10.5194/egusphere-egu2020-10433
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Variations of the Carbonate Counter Pump in the Southern Ocean during the Mid-Brunhes event and their contribution to the global biospheric productivity

Margaux Brandon1,2, Stéphanie Duchamp-Alphonse1, Amaëlle Landais2, Elisabeth Michel2, Gulay Isguder2, and Thomas Extier2
Margaux Brandon et al.
  • 1GEOPS, Université Paris-Saclay, CNRS, 91405 Orsay Cedex, France (margaux.brandon@u-psud.fr)
  • 2Laboratoire des Sciences du Climat et de l’Environnement, LSCE/IPSL, CEA-CNRS-UVSQ, Université Paris-Saclay, 91191 Gif-sur-Yvette, France

During the last 800,000 years, atmospheric CO2 concentrations have varied with an amplitude of more than 100 ppm, with the fastest increases registered during deglaciations. The mechanisms behind the increases of CO2 are still discussed since several parameters are involved. Biological productivity on land and in the ocean played a major role in the variations of atmospheric CO2. Particularly, productivity variations in the Southern Ocean along deglaciations are key because changes in the efficiency of the Soft Tissue Pump (STP) and the Carbonate Counter Pump (CCP) in the Subantarctic Zone significantly impact the exchanges between ocean and atmospheric reservoirs. As calcifying organisms, coccolithophores and planktonic foraminifera represent the major producers of CaCO3 and are therefore good tools to reconstruct past variations of CCP.

Among the last 9 deglaciations, Termination V registers the strongest global productivity (20% higher) compared to the other 8 interglacial periods. Associated with the Mid-Brunhes event, it is followed by the warm MIS 11, the longest interglacial (~ 30 ka). MIS 11 also registers a strong carbonate production in the ocean, most probably favoured by the low eccentricity during this period. Studying the variations of the CCP during this specific period of time is therefore important to better understand its relation with biospheric productivity changes and its impact on atmospheric CO2.

Here we present micropaleontological (coccoliths and foraminifera) and geochemical (CaCO3) data from marine core MD04-2718, located in the Indian sector of the Southern Ocean (48°53 S; 65°57 E) throughout Termination V and MIS 11, that we compared with other productivity data from the Southern Ocean as well as reconstruction of global biospheric productivity data (Δ17O of O2).

 Results show that coccolith and foraminifera abundances and masses increase during Termination V and MIS 11. The good correlation between variations of CaCO3 in the sediment and calcite mass from coccoliths and foraminifera shells proves that exported CaCO3 is essentially of planktonic origin and reveals that CCP significantly increases over this period.

We suggest that the strengthening of CCP through the increase in production and export of calcite associated to coccolith and foraminifera in the Southern Ocean may have contributed to increase the atmospheric CO2 during Termination V and MIS 11, while the strong biological productivity registered during this period would have permitted to maintain the CO2 level relatively low

How to cite: Brandon, M., Duchamp-Alphonse, S., Landais, A., Michel, E., Isguder, G., and Extier, T.: Variations of the Carbonate Counter Pump in the Southern Ocean during the Mid-Brunhes event and their contribution to the global biospheric productivity, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10433, https://doi.org/10.5194/egusphere-egu2020-10433, 2020

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Presentation version 1 – uploaded on 05 May 2020
  • CC1: Effect on atmospheric CO2, Alexander Haumann, 15 May 2020

    Thank you for this very nice display, Margaux! Very clear presentation and great results!

    I had another question on the CCP effect during MIS11, but maybe it is a difficult one to answer. I am trying to understand how big this effect could be in terms of atmospheric CO2. Do you have an estimate of how much the atmospheric CO2 would increase during MIS11 due to this process (rough order of magnitude)? And if not, is there a way to estimate this, maybe by implementing your results in a box model?

    • AC1: Reply to CC1, Margaux Brandon, 18 May 2020

      Thank you for your comment Alexander!

      Unfortunately, I don’t have any estimates of atmospheric CO2 based on our results.

      As the carbonate accumulation measured in the sediment does not reflect the total carbonate production at the surface ocean, we need to estimate the coccolith and foraminifera carbonate production at the ocean surface

       

      Saavedra-Pellitero et al., 2017 (doi:10.1002/2017PA003156) calculated an estimation of the carbonate accumulation rate on the seafloor for the whole Southern Ocean for MIS 11 based on coccolith carbonate accumulation rates in the Pacific sector. Using estimates of a Carbon cycle box model, they found that such an increase in Carbonate Counter Pump caused by coccolith carbonate production would cause an 8 ppm increase in atmospheric CO2.

      This estimates takes into account carbonate production from coccolith but not from foraminifera, that also have a role in the Carbonate Counter Pump. Therefore, the 8 ppm may be underestimated but at least it gives an idea of the impact of such increase in carbonate production.

       

      So, to answer your question, we may be able to have a broad estimate of the impact of Carbonate Counter Pump increase during MIS 11 using our results and a carbon cycle box model. But it would be very interesting to have such estimate based on many data from the Southern Ocean and from lower latitudes, knowing that in these low-latitudes regions, there is a strong increase in coral reef expansion, also playing a role in the Carbonate Counter pump!

       

      I hope it is clear enough and it answers your question!

       

      Best regards,

      Margaux