The warming of the Arctic causes increased input of terrestrial dissolved organic matter (tDOM) into the coastal Arctic ecosystems and increased production of phytoplankton derived organic matter (pDOM). Studies have shown that increased DOM input results in both increased bacterial activity and community change. However, it is less clear whether this will affect fjord and marine systems with similar bacterial communities to the same extent and hence influence predictions for the entire Arctic Ocean. In this study, we aim to highlight the effects of the addition of different DOM sources on the activity and structure of marine and fjord bacterial communities in the Arctic. tDOM isolated from Svalbard permafrost soil and pDOM from Diatom exudates was added to water sampled from an Arctic fjord (Isfjorden, Svalbard) and from the Northern Barents Sea (79.8 N and 33.7 E) in August 2019. The samples were incubated for six days and bacterial abundance, activity and community composition measured in regular intervals. While starting communities where similar, responses were very distinct in fjord and marine waters. Bacterial abundance and production increased in both environments over the incubation period, but were 10-fold higher in fjord incubations. This higher productivity was accompanied with a large shift in community composition, mainly driven by the increase of Glaciecola (Gammaproteobacteria). In the marine community, Polaribacter (Flavobacteriia) increased most in abundance. In both environments, the combined addition of pDOM and tDOM gave the strongest response in terms of bacterial abundance and productivity. We show that responses in terms of community composition change and productivity are highly different between fjord and open ocean environments and this highlights the need for further studies to determine the fate of increased DOM input in different Arctic marine ecosystems.

Primary Presenter: Oliver Müller, University of Bergen (oliver.muller@uib.no)

Authors:

Oliver Müller, University of Bergen  (oliver.muller@uib.no)

Gunnar Bratbak, University of Bergen  (Gunnar.Bratbak@uib.no)

Maria Paulsen, Aarhus University  (marialundpaulsen@gmail.com)