Research Portfolio

The Ocean Biogeochemistry group at MPI-M (2022; photos by B. Dialo)

Selected Research Accomplishments

My working group is jointly affiliated at Universität Hamburg, Helmholtz-Zentrum Hereon, and Max Planck Institute for Meteorology. With these joint forces, the focus of my research is on the oceanic cycles of carbon, nitrogen and oxygen, and the group’s philosophy has been to address these cycles as an interactive component of the Earth system (Ilyina, 2022). In particular, we investigate the variability and predictability of processes regulating the ocean carbon sink and carbon-climate feedbacks. These research topics are studied in concert with variability and changes in Earth's climate and ocean physics in past, present, and future in the framework of the Earth system model. The group continues to focus on the functioning of the biological pump, evolution of the oxygen minimum zones and related transformations in the marine nitrogen cycle. 

One of the ongoing efforts has been on advancing the HAMOCC (Hamburg Ocean Carbon Cycle) model - the main working tool of the group - including incorporation of new processes to fill gaps in our understanding of the ocean carbon sink under chaning climate and extensive evaluation of model performance. This is taking place within the Earth system models MPI-ESM and currently within the ICON (ICOsahedral Non-hydrostatic) framework configurations for longer time scales, as well as with the scope of addressing meso- and submeso-scale processes in ocean biogeochemistry.

The group is networking on many aspects of the oceanic biogeochemical cycles within numerous research projects.

Below is an incomplete list of our recent research accomplishments (still under construction).

For more information, please visit Modeling the carbon cycle in the Earth system.

Predictability of carbon sinks:

Predicting near-term variations in atmospheric CO2 growth, ocean and land carbon sinks (components of the global carbon budget) under changing emissions remains a major challenge requiring ESMs with interactive carbon cycle. We built such a prediction system based on MPI-ESM. Next to an improved reconstruction of the observed evolution of carbon sinks and atmospheric CO2 over the reanalysis period due to assimilation of observational products, we established a predictive skill of up to 5 years for the air–sea and 2 years for the air–land CO2 fluxes and atmospheric CO2 growth rate, respectively (Li et al., 2023). In a first benchmarking study of ESM-based prediction systems enhanced with land and ocean carbon cycle components Ilyina et al. (2021) showed that these predictive horizons appear robust across a number of prediction systems assessed. This furthermore implies that predictive skills of land and ocean C sinks are similar between models driven by CO2 emissions and concentrations, albeit the latter lack predictive atmospheric CO2 capacity. Moreover, in an idealized perfect model framework, we showed that initialization of ocean biogeochemical variables on top of the physics, seem to not substantially add predictive capacity (Spring et al., 2021). Such ESMs with interactive carbon cycle using data assimilation establish themselves as new tools filling the gap between stand-alone models (with inconsistencies due to prescribed forcings) and ESMs (with unresolved timing of climate modes).

Schematic illustration of an initialized by observations prediction system based on an Earth system model (from Hongmei Li et al., 2023).

New processes in HAMOCC filling gaps in our understanding of the ocean carbon feedbacks under changing climate:

The group focuses on missing or insufficiently represented processes in HAMOCC regulating ocean biogeochemical feedbacks in the Earth system under changing climate. By adding riverine inputs of carbon and nutrients into the ocean and representing the fate of terrestrially-derived organic carbon (Lacroix et al., 2021), we revealed that pronounced human-induced perturbation of the ocean primary production are driven by counteracting effects of increased terrestrial inputs of nutrients and increased upper ocean thermal stratification. This has not be shown in previous global model simulations.

Within the BMBF project PalMod, Liu et al. (2021) extended HAMOCC by developing a new comprehensive parameterization of 13C accounting for changes due to biological processes and the 13C air-sea gas exchange. The good agreement between model results and observations for present-day 13C distributions and their evolution over the last century provided the ground, for the first time, to quantify the ocean 13C Suess effect and interpret some earlier unexplained uncertainties in observational 13C products.

Poster Gallery