Mission – The aim of our research is to measure, understand and predict phytoplankton responses to multiple stressors, e.g. Ocean Acidification and warming, by focusing on one of the most sensitive areas on Earth, the subarctic and Arctic Oceans. Covering molecular to ecological processes, we seek to identify those limitations and trade-offs in physiological pathways, which are key for determining the competitive abilities of species. By investigating not only the nature (i.e. process-understanding) but also the diversity (i.e. inter- and intraspecific plasticity) in response patterns we obtain information about the resilience of species and groups, which increases our abilities to predict floristic and functional shifts.

Algae bloom in the Barents Sea, Photo: ESA

Phytoplankton - Phytoplankton are responsible for about half of the global primary production. Hence, they produce every second oxygen molecule we breathe, and by providing the carbon and energy for higher trophic levels, they also sustain and shape most marine ecosystems. Phytoplankton can be distinguished into functional types, which differ in how they alter elemental cycles. The export of carbon and other elements to deep waters and sediments is especially effective for species reaching high abundances of so-called blooms (see satellite image). Any changes in phytoplankton productivity and species composition will thus have far-reaching implications for marine ecosystems and global climate.

Anticipated alterations due to Global Change (Photo: Alfred-Wegener-Institut)

Global Change - The rise in atmospheric CO2 levels, which is predicted to reach up to 1000 µatm within this century, will result in profound alterations of the marine environment (see figure). Firstly, as a greenhouse gas, rising CO2 causes ocean warming: average temperatures of the surface waters have already increased by 0.7°C and may rise by an additional 3°C until the end of this century, with some regions like the Arctic Ocean changing fastest (IPCC 2007). The warming and the concomitant freshening due to ice melts increase the stratification of the surface ocean, which not only reduces the nutrient supply from deeper waters but also alters the light regime phytoplankton encounter in the shallower upper mixed layer. However, there is a secondary problem arising 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'. Since the industrial revolution, the mean pH of the surface ocean has decreased by about 0.1 pH units and is expected to further decline by 0.3 units until the end of this century, which represents a ~150% increase in acidity. To sum up, several environmental parameters will be altered simultaneously, and all of these are major drivers controlling phytoplankton productivity and species composition.