EGU21-3073
https://doi.org/10.5194/egusphere-egu21-3073
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Variations of ocean biogeochemistry in a transient deglacial simulation with MPI-ESM

Bo Liu, Katharina D. Six, Tatiana Ilyina, and Thomas Extier
Bo Liu et al.
  • Max Planck Institute for Meteorology, The Ocean in the Earth System, Hamburg, Germany (bo.liu@mpimet.mpg.de)

Variations in ocean-atmosphere carbon exchange, in response to varying physical and biogeochemical ocean states, is one of the major causes of the glacial-interglacial atmospheric CO2 changes. Most of the existing modelling studies use time-slice simulations with Earth System Models to quantify the proposed mechanisms, such as the impact of a weakened Southern Ocean westerlies and a massive discharge of freshwater from ice sheet melting on the deglacial atmospheric CO2 rise. We present the variations of ocean biogeochemistry in a transient deglaciation (21 – 10 kB.P.) simulation using the Max Planck Institute Earth System Model. We force the model with reconstructions of atmospheric greenhouse gas concentrations, orbital parameters, ice sheet and dust deposition. In line with the physical ocean component, we account for the automatic adjustment of all marine biogeochemical tracers in response to changing bathymetry and coastlines that relate to deglacial melt water discharge and isostatic adjustment. We include a new representation of the stable carbon isotope (13C) in the ocean biogeochemical component to evaluate the simulation against δ13C records from sediment cores.

The model reproduces several proposed oceanic CO2 outgassing mechanisms. First, the net primary production (NPP) in the North Atlantic Ocean dramatically decrease (by 40 – 80%) during the first melt water pulse (15 – 14 kB.P.) which is caused by the weakening in the strength of the Atlantic Meridional Overturning Circulation from 21 to 3 Sv. However, globally the oceanic NPP only slightly decreases by 8% as oceanic NPP in the South Hemisphere increases during the same period. Second, during the melt water pulse in the Southern Ocean the ventilation of intermediate waters, which has high DIC content and low alkalinity concentration, is slightly enhanced. Third, the surface alkalinity decreases due to dilution and due to episodic shifts between CaCO3 production and opal production by phytoplankton. Lastly, CO2 solubility decreases with increasing deglacial sea surface temperature. The increase of surface pCO2 caused by the above mechanisms is, however, smaller than that of the prescribed atmospheric CO2. Thus, the ocean is a weak carbon sink in this deglacial simulation.

How to cite: Liu, B., Six, K. D., Ilyina, T., and Extier, T.: Variations of ocean biogeochemistry in a transient deglacial simulation with MPI-ESM, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3073, https://doi.org/10.5194/egusphere-egu21-3073, 2021.

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