Analyzing Glacial-Interglacial Ocean Biogeochemical States in the MPI-Earth System Model

Abstract:

There is still little consensus about the mechanisms causing the glacial - interglacial variations
in atmospheric CO2 concentrations of around 100 ppm. Some of those mechanisms are
driven by alterations in ocean biogeochemical cycles. Hence, it is crucial to understand ocean
biogeochemistry dynamics during glacial-interglacial transitions. Within the German national
climate modeling initiative PalMod, aiming at simulating a full glacial cycle (135k – today) in
transient mode with a state-of-the-art Earth System Model (ESM), we address the ocean
biogeochemistry cycles using a comprehensive modeling approach. In order to set up the
model we start with ocean only simulations, which are based on the 3-D ocean general
circulation model MPIOM coupled to the ocean biogeochemistry model HAMOCC.
Atmospheric forcing data is derived from a fully coupled LGM simulation including the
atmosphere general circulation model ECHAM6. This setup provides us a sophisticated
representation of the ocean biogeochemistry during the LGM without using any kind of datarestoring,
to be consistent with the biological, chemical and physical dynamics of the model.
We analyze alterations in ocean biogeochemistry during the LGM in comparison to a preindustrial
control climate. We discuss and quantify the changes in ocean biogeochemical
cycles between these two states, as well as possible implications for carbon transfer due to
changes in ocean dynamics. In the next steps we will use the ocean biogeochemistry model as
part of the fully coupled MPI-ESM. Our results aim at improving the understanding of glacial
– interglacial changes in atmospheric CO2, especially in terms of marine carbon sequestration
and release. The presented work contributes to developing comprehensive ESMs, which are
capable of simulating the climate evolution and the variability during the last glacial cycle.