SCACE – Circum-Antarctic Climate-processes and Ecosystem study
Climate change is most pronounced in the polar regions. Air temperature around the Antarctic Peninsula has increased by about 2.5 °C since the mid 20th Century, five times as much as the global average. With the aim of investigating how physical environmental factors impact the ecosystem of the Circumpolar Current and Southern Ocean, the internationally coordinated Polar Year project SCACE was designed and conducted in multinational cooperation. The objectives of SCACE were to assess the present state of the circum-Antarctic marine ecosystem and to reveal the interplay of processes from atmospheric forcing of the sea surface through water mass properties, currents and transport of nutrients, the build up of biomass by phytoplankton photosynthesis, the dependent higher trophic levels of the food web and eventually to the sedimentation of organic material to the deep sea and the sea floor.
Interaction of these physical, chemical and biological processes determines, whether the Southern Ocean acts as a source or as a sink of atmospheric CO2. If driven solely by physical and chemical processes the Southern Ocean would take the role of a source because cold and CO2 enriched water masses well up from great depth to the surface to release their excess CO2 there to the atmosphere. This physical carbon pump is counteracted by the so-called biological pump, the uptake of CO2 through photosynthesis near the sea surface and the subsequent sedimentation of organic carbon particles. Shifts of the delicate balance between the physical and biological pumps of carbon determine whether the Southern Ocean will attenuate or amplify greenhouse-gas driven changes of climate.
The major German contribution to SCACE was carried out during Polarstern Cruise ANT-XXIV/2 (28th November 2007 – 4th February 2008). Measurements made along the Greenwich Meridian showed clear changes in the species composition of the food web across water mass boundaries, so-called fronts. In the area of the eastern Weddell Gyre a phytoplankton bloom was discovered which had developed in a shallow and stable mixed layer formed as a consequence of the early-summer sea ice melt. This bloom covered an area roughly twice the size of Germany as revealed by satellite images of ocean colour. The data collected will be used inter alia for an estimation of the fluxes of carbon
associated with that bloom. Further studies shall be performed with numerical models to forecast whether long-term changes in sea ice cover related to climate change will have an influence on the function of the Southern Ocean as a source or sink of atmospheric CO2 - beside its influence on sea ice dependent species such as Krill (Euphausia superba), which plays a central role in the Southern Ocean ecosystem.