Microbial communities in marine sediments are able to use ancient material as a carbon source. Although they prefer fresh organic material, if there is not enough of it, microbes also use carbon from rocks. Since this bacterial metabolism releases greenhouse gases, this process is an additional source of fossil greenhouse gases. This is the result of a study led by the Alfred Wegener Institute, which has now been published in the journal Nature Geosciences.
![[Translate to English:] Schmelzwasserströme](/fileadmin/_processed_/2/2/csm_20200629_Schmelzwasser_TorbenStichel_a55b311e7b.jpg "Meltwater streams")
Is old organic material (eroded from organic-rich rocks such as coal) that reaches the sea from melting glaciers - as has long been assumed - simply redeposited there? Or can it also be converted there by microbes, for which there have been increasing signs in recent years? A team led by lead author Manual Ruben from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) together with international partner institutions has now investigated these questions in Nature Geoscience. For this purpose, the researchers carried out 14C analyses on organic biomarkers that originate from the membranes of living microbes. These biomarkers were extracted from sediments of the Hornsund, the southernmost large fjord of Spitsbergen. The glaciers flowing into Hornsund have retreated at a dramatic rate over the past decades.
Heterotrophic organisms incorporate the carbon signature that is also found in their food ("you are what you eat"). Therefore, 14C analyses on biomarkers can be used to determine whether these microbes also metabolise ancient organic material. The research team was able to show that the microbial communities in the sediment prefer to convert fresh organic material, which, for example, gets into the sediment when seaweed dies and its remains sink to the bottom. However, if there is not enough of it, they are quite capable of using the old material as a carbon source, which is brought in by ever faster melting glaciers. The microbial communities living in the sediments of Hornsund even feed up to 50 % of their carbon turnover from these fossil organic compounds, which are presumably difficult to degrade. Until now, it was assumed that these compounds are so inert due to previous degradation processes during diagenesis and catagenesis that they can hardly be converted. Against the backdrop of climate change, however, more fossil carbon could escape into the atmosphere as a result of this process.
Participating institutions:
- Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research
- MARUM – Center for Marine Environmental Sciences at Bremen University
- UiT The Arctic University of Norway
- Adam Mickiewicz University in Poznań
Original publication:
Manuel Ruben, Jens Hefter, Florence Schubotz, Walter Geibert, Martin Butzin, Torben Gentz, Hendrik Grotheer, Matthias Forwick, Witold Szczuciński, Gesine Mollenhauer: Fossil organic carbon utilization in marine Arctic fjord sediments; Nature Geosciences (2023). DOI: 10.1038/s41561-023-01198-z