Abstract
AbstractWe investigate the relative importance of ecosystem complexity and phytoplankton light absorption for climate studies. While the complexity of Earth System models (ESMs) with respect to marine biota has increased over the past years, the relative importance of biological processes in driving climate‐relevant mechanisms such as the biological carbon pump and phytoplankton light absorption is still unknown. The climate effects of these mechanisms have been studied separately, but not together. To shed light on the role of biologically mediated feedbacks, we performed different model experiments with the EcoGENIE ESM. The model experiments have been conducted with and without phytoplankton light absorption and with two or 12 plankton functional types. For a robust comparison, all simulations are tuned to have the same primary production. Our model experiments show that phytoplankton light absorption changes ocean physics and biogeochemistry. Higher sea surface temperature decreases the solubility of CO2 which in turn increases the atmospheric CO2 concentration, and finally the atmospheric temperature rises by 0.45°C. An increase in ecosystem complexity increases the export production of particulate organic carbon but decreases the amount of dissolved organic matter. These changes in the marine carbon cycling, however, hardly reduces the atmospheric CO2 concentrations and slightly decreases the atmospheric temperature by 0.034°C. Overall we show that phytoplankton light absorption has a higher impact on the carbon cycle and on the climate system than a more detailed representation of the marine biota.
Highlights
We investigate the relative importance of ecosystem complexity and phytoplankton light absorption for climate studies
Using an Earth system model (ESM), we focus on two climate-relevant feedbacks, the biological pump and the phytoplankton light absorption feedback to study their relative importance for the climate system
The absorption of the solar radiation can occur in all the layers of the ocean and in the uppermost layer as in the standard setup used by Ward absorption impacts directly sea surface temperature, biogeochemical properties and atmospheric CO2 concentration, leading indirectly to changes in chlorophyll biomass and global atmospheric temperature
Summary
Using an Earth system model (ESM), we focus on two climate-relevant feedbacks, the biological pump and the phytoplankton light absorption feedback to study their relative importance for the climate system. Manizza et al (2005) used an Ocean General Circulation Model (OGCM) to show that phytoplankton light absorption intensifies the seasonal cycle of temperature, mixed layer depth, and ice cover by roughly 10%, leading to an increase in phytoplankton biomass and to an amplification of the initial physical perturbations. These feedbacks depend on the spatial and seasonal scale (Oschlies, 2004). We have modified the model by implementing phytoplankton light absorption
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