PHYTOCHANGE - New approaches to assess the responses of phytoplankton to Global Change
Despite their microscopic size phytoplankton are responsible for about half of the global primary production. This diverse group of organisms drives the biogeochemical cycles of important elements, exporting massive amounts of carbon to deep waters and sediments. Phytoplankton therefore strongly influence the partitioning of gases between ocean and atmosphere, especially when occurring in high abundances of so called blooms (see satellite image). With respect to their specific effects on biogeochemical cycling phytoplankton can be distinguished into different groups. Diatoms play a major role in determining the vertical fluxes of silicate and organic carbon, coccolithophores affect the carbon cycle through the production of calcium carbonate, and diazotrophs (N2-fixing cyanobacteria) influence marine productivity by altering the availability of reactive nitrogen. Dinoflagellates are an important group with complex interactions in the foodweb, also owing to their ability to produce toxins.
Human-induced climate change will result in significant alterations in the marine environment within the next 100 years and beyond (see figure). Several future scenarios predict an increase from currently 380 to 750 µatm CO2 for the year 2100 (IPCC scenario IS92a). As the ocean takes up CO2 the dissolved inorganic carbon concentration increases and the pH of seawater decreases. This acidification of the surface ocean is expected to intensify and, by the end of this century, pH levels will have dropped by 0.4 units relative to pre-industrial values. In addition, rising temperatures will impact surface ocean stratification, which in turn will affect the surface water light regime and nutrient input from deeper layers. Phytoplankton will be affected by these environmental changes in many ways, altering the complex balance of biogeochemical cycles and climate feedback mechanisms.
The overall aim of our research group is to quantify as well as to understand marine phytoplankton responses to the projected changes. Working on different phytoplankton groups and specific oceanic regions complementary issues are addressed. To develop a process-based understanding of observed responses, a combination of mass-spectrometric and fluorimetric techniques is applied.
Community shifts and productivity changes in the Southern Ocean
The future of pelagic calcification
The future of oceanic nitrogen fixation
Competitive interactions of dinoflagellates under ocean acidification