Phytoplankton ecophysiology
Mission – The aim of our research is to measure, understand and predict the reactions of phytoplankton to various factors such as warming, nutrient deficiency or ocean acidification, by focusing on one of the most sensitive areas on Earth, the subarctic and Arctic Ocean. Thereby, we contribute to the Helmholtz research program "Changing Earth - Sustaining our Future". By covering molecular and ecological processes, we seek to identify the constraints and trade-offs in physiological processes that are critical to species competitiveness. By examining not only the nature (i.e. process understanding) but also the diversity of response patterns (i.e. inter- and intraspecific plasticity), we obtain information on the resilience of species and groups, which improves our ability to predict floristic and functional change.
Phytoplankton - Phytoplankton, unicellular photosynthetic organisms, are responsible for about half of the world's primary production. By providing carbon and energy for higher trophic levels, they maintain and shape marine ecosystems. Phytoplankton can be divided into different functional types, which differ in how they influence global elemental cycles. The export of carbon and other elements to deep water and sediments is particularly effective for species that reach high biomasses in so-called blooms (see satellite image). Any change in the productivity and species composition of phytoplankton will have far-reaching effects on marine ecosystems and the global climate.
Global Change - The rise in atmospheric CO2 levels has led to fundamental alterations of the marine environment (see figure), which will further amplify depending on our emission scenarios. Firstly, as a greenhouse gas, rising CO2 causes ocean warming: temperatures of the surface waters have already increased by 1.1°C on average, while some regions like the Arctic Ocean changing fastest (IPCC 2022). The warming and the concomitant freshening due to ice melts increase the stratification, which not only reduces the nutrient supply from deeper waters but also alters the light regime phytoplankton encounter in the shallower upper mixed layer. Secondly, there is a problem arising directly from CO2: As much of the anthropogenic CO2 is taken up by the ocean, concentrations of CO2 and bicarbonate increase while the concentration of carbonate ions and the pH decrease, also known as 'Ocean Acidification'. Just like warming, also these changes in carbonate chemistry are particularly pronounced in polar regions owing to the higher CO2 solubility at lower water temperatures. To sum up, almost all environmental parameters will be altered simultaneously, all of which are major drivers controlling phytoplankton productivity and species composition.
