Sensitivity of phytoplankton to climate change: Direct and interactive effects of CO2 on primary production and community composition

• Main Author: Seifert, Miriam
• Other Authors: Hauck, Judith, Vogt, Meike
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Universität Bremen 2022
• Subjects: biogeochemical modelling; ocean acidification; multiple driver; meta-analysis; phytoplankton; coccolithophores; 570; 570 Life sciences; biology; ddc:570; Ocean acidification
• Online Access: https://media.suub.uni-bremen.de/handle/elib/5813; https://doi.org/10.26092/elib/1436; https://nbn-resolving.org/urn:nbn:de:gbv:46-elib58132

Marine phytoplankton constitutes about half of the primary production on Earth. It forms the base of the marine food web and is a pivotal player in the marine biological carbon pump. The primary environmental drivers that control phytoplankton growth are temperature, nutrient availability, light, and the concentration of inorganic carbon species. Ongoing climate change modifies these drivers, leading to a warming, high-CO2 ocean with altered nutrient availabilities and light regimes. Changes in phytoplankton productivity and community composition resulting from these newly emerging environmental states in the ocean have important implications for the marine ecosystem and carbon cycling. Biogeochemical ocean models are used to investigate how marine primary production may be affected by future climate change under different emission scenarios. Phytoplankton growth rates in models are typically determined by functions describing growth dependencies on temperature, light, and nutrients. However, a large body of laboratory studies on phytoplankton responses to environmental drivers reveals two points that are usually not considered in current biogeochemical models. Firstly, phytoplankton growth can be considerably modified by the state of the carbonate system. Changes in inorganic carbon species concentrations can be either growth-enhancing (CO2(aq) and bicarbonate are substrates for photosynthesis), or growth-dampening (increasing CO2(aq) levels lead to a shift in the carbonate equilibria and result in a pH decrease, a process which is called ocean acidification). Functions describing this growth dependence of phytoplankton on the carbonate system have not been implemented in large-scale ocean biogeochemical models so far. Secondly, growth responses towards one driver can be modified if the level of another driver is changing. Functions including these so-called interactive driver effects partly exist in models (e.g. the response to varying light levels may depend on the nutrient limitation term). However, the ...