19.11.2012: FB2-Seminar

"Aggregation of microbially altered organic matter in the Greenland Sea: Potential effects of sea surface warming and acidification"

Mascha Wurst1, Helge-Ansgar Giebel2, Nicole Händel1, Eva-Maria Nöthig1 & Anja Engel3

1 Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany

2 Institute for Chemistry and Biology of the Marine Environment, University of Oldenburg, Germany

3 Helmholtz Centre for Ocean Research, GEOMAR, Kiel, Germany

Abstract:

Anthropogenic climate change, like sea surface warming and acidification, is starting to impact marine pelagic ecosystems and marine carbon cycling in many different direct and indirect ways. In the surface ocean the cycling of organic matter is regulated by complex interactions of production, remineralization and export processes. Among the remineralization of organic matter, the vertical flux of biogenic carbon is promoted by rapid sedimentation of particles, carrying large fractions of particulate carbon via the biological pump. Aggregation processes in the water column are often initiated by the formation of gel particles, such as transparent exopolymer particles (TEP), from extracellular dissolved organic matter produced by phyto- and bacterioplankton. In order to investigate separated and synergistic effects of sea surface warming and acidification on heterotrophic cycling of dissolved organic carbon (DOC) and subsequently on the aggregation of extracellular organic matter, we conducted a replicated, factorial perturbation experiment with an arctic marine bacterioplankton community onboard RV Polarstern in June/July 2009. Microbiological and biogeochemical analyses indicate a shift in the bacterial community structure, in line with higher degradation rates of organic matter and the formation of TEP. Temperature rather than pH will determine microbial cycling of carbon with implications for the microbial contribution to the biological carbon pump. Sea surface temperature increase will potentially affect microbial cycling of organic matter in the future Arctic Ocean.