Marine primary production and the biological carbon pump
One research objective of the team is to improve our understanding and representation of ecosystem responses to a changing marine environment. By simulating the most important “functional types” of plankton, that form the base of the marine food web, we are able to reproduce major global patterns of the marine ecosystem and its role in the biogeochemical cycles. We investigate how environmental factors control planktonic communities which allows us, in turn, to better project possible shifts in a context of climate change. This is of prior importance because any change in the planktonic communities and/or productivity can have large consequences for: (1) the marine foodweb, especially in the fragile polar ecosystems; and (2) the so-called “Biological Carbon Pump”, a collection of biologically-mediated processes that convey carbon to the deep ocean.
Biomass concentrations of the phytoplankton functional groups in the biogeochemistry model REcoM (mean over the upper 150m of the watercolumn; from Seifert et al., 2022).
Organic matter cycling between primary producers, zooplankton, and sinking particles in the ocean biogeochemistry model REcoM (modified from Karakuş et al. 2021).
Modelling of iron in seawater and feedbacks with phytoplankton physiology and elemental cycles
We make use of the increase in process-based understanding of iron biogeochemistry and phytoplankton physiology to improve the description of the iron cycle in biogeochemical models, its role for phytoplankton physiological adaptations, and the ensuing consequences for elemental fluxes e.g., of silicon and iron.
Iron is present in the ocean in a number of different chemical and physical forms, and this so-called speciation strongly affects the solubility of iron and biological availability.
The models are by necessity global, but the focus of analysis lies on the more than 30% of the surface ocean that are permanently or periodically iron-limited, especially the Southern Ocean.
Illustration of two feedback loops between the iron cycle and biological production that are mediated through the production of organic iron-binding ligands. One feedback is destabilizing (blue), the other stabilizing (red) between the iron cycle and primary production (Völker and Ye, 2022).
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Uptake and cycling of anthropogenic carbon in the ocean
We simulate the changing ocean carbon uptake in response to humans’ perturbation of atmospheric CO2 levels and climate. The increase of the ocean carbon sink over the recent decades is caused by rising atmospheric CO2 levels. The effect of climate change is currently much smaller, but the ocean sink would have been about 5% higher without climate change in the recent years (Friedlingstein et al., 2022).
We simulate the recent past in ocean stand-alone simulations, which also contribute to the Global Carbon Budget and the Regional Carbon Cycle Assessment and Processes project phase 2 (RECCAP2). See GCB subpage for more information on the ocean sink estimate in the Global Carbon Budget.
As part of the MarEsys-Projekts, we have implemented the ocean carbon cycle into the AWI-Earth System Model, and simulate the historical and future ocean anthropogenic carbon uptake under low and high emission scenarios.
A focus of the group is on deep and bottom water formation, e.g. precursors of Antarctic Bottom Water (Nissen et al., 2022). We also investigate the efficiency of ocean-based negative emissions scenarios.
Historical and potential future glocal ocean carbon sink modeled with our earth system model AWI-ESM-1-REcoM2.
Carbon cycle during glacial times
Changes in the marine carbon cycle and storage have a strong impact on atmospheric CO2 levels and are a central topic of paleoclimate research. Using both fully coupled ESM and ocean-only simulations, we examine the role of single drivers (e.g. temperature, ocean circulation, sea ice extension and dust deposition) or their combinations in regulating the oceanic carbon pump during interglacial and glacial periods. Here we work closely together with the Paleoclimate Dynamics and Glaciology Section and use our ESM results to participate in model comparisons with other German institutes.
Anomaly of dissolved inorganic carbon (DIC, mmol/m3) and salinity (psu) between simulations for the pre-industrial and last glacial maximum climate (LGM minus PI, time slice ocean-only simulations; from Du et al., 2022).