Project

Discipline

cold seep; molecular biology; microbiology; brine; next generation sequencing; global change; organic geochemistry; marine; biomarker; biogeochemistry; aerobic oxidation of methane (MOx)

Lead
Mikrobielles Leben in Methan-dominierten marinen Ökosystemen
Lay summary
In tiefen Sedimentschichten der Kontinentalränder sind grosse Mengen des gefährlichen Treibhausgases Methan gespeichert. Dieses Gas kann entlang von geologischen Schwächezonen in Oberflächensedimente bzw. in die Wassersäule und letztendlich in die Atmosphäre transportiert werden, wo es weiter den globalen Klimawandel antreibt. Jedoch wird ein Grossteil des Methans von unterschiedlichen Mikroorganismen in Sedimenten und der Wassersäule “gefressen”, so dass der Ozean eine vergleichsweise geringe Menge an Methan in die Atmosphäre entlässt. Diese Mikroorganismen wirken also wie ein Filter, der Methan zurückhält. Dies könnte sich jedoch in Zukunft ändern: Bedingt durch den globalen Klimawandel wird die Temperatur der Ozeane steigen, was wiederum zu einem verstärkten Methantransport in oberflächennahe Sedimente führen wird. Um abschätzen zu können, wie wichtig die Ozeane in Zukunft als Methanquelle werden könnten, muss allerdings der mikrobielle Methanfilter genauer untersucht werden. Zur Zeit wissen wir sehr wenig über die Effizienz dieses Filters und welche Umweltbedingungen zu einer Selektion bestimmter Mikroorganismen führt, die direkt oder indirekt am Methanabbau beteiligt sind. Im Rahmen des Projektes “Microbes and biogeochemical processes associated to methane oxidation at deep sea brines and highly active cold seep systems” soll genau diese Wissenslücke geschlossen werden. In den letzten Jahren haben wir in verschiedene Ozeanen mehrere Typen von Methan-reichen Ökosystemen beprobt (hochaktive “Cold Seeps” und methanreiche Salzlakenbecken in der Tiefsee) und werden nun die Aktivität, Identität und Häufigkeit der mikrobiellen Gemeinschaften mit Hilfe von biogeochemischen und genetischen Methoden untersuchen. Ziel des Projektes ist es herauszufinden, welche Umweltbedingungen bestimmte methanoxidierende und andere wichtige Mikroorganismen begünstigen und wie sich Umweltfaktoren auf die Effektivität des mikrobiellen Methanfilters auswirken.

Direct link to Lay Summary

Last update: 18.12.2014

Active participation

Communication	Title	Media	Place	Year

Number	Title	Start	Funding scheme

With this proposal, I seek funding for a 1-year extension of the PhD project “Microbial methane consumption in contrasting ocean environments: effects of elevated seepage and geochemical boundary conditions” (SNF DACH Project 200021L_138057. Apr. 2012 - Mar. 2015). The initial aims of of the project were to investigate (i) the marine CH4 filter in view of elevated CH4 fluxes in the future and (ii) to asses the scope for water column CH4 oxidation with respect to magnitude, identity of key organisms and controlling environmental factors. As model systems, we chose several seep systems (natural and man made) in order to cover a range of environmental factor (e.g. seep activity, water depth, age of the seep system) and biogeochemical boundary conditions (eg. redox and salinity gradients and water column hypoxia/anoxia). Methane oxidation was measured with the aid of radio-tracer based ex situ incubations and the identity and abundance of microbial communities was estimated with fluorescence in situ hybridisation (FISH) and lipid biomarker assays. Microbial activity/abundance date were then compared to the spatiotemporal distribution of physicochemical parameters (eg. methane concentration, temperature, salinity and advection patterns). During the first two years of the project, we were able to collect a comprehensive data set, which allowed us to identify several environmental factors controlling water column aerobic methane oxidation (MOx) in marine systems. Our investigations at the cold seeps at the West Spitsbergen Continental Margin showed that currents are a very importing factor controlling the abundance of methanotrophs and thus the capacity for water column MOx. Furthermore, at the ‘Blowout’, a man made cold seep in the North Sea, we found that water column stratification leads to trapping of the uprising methane at the pycnocline where the higher substrate availability supports elevated rates of MOx. Similarly, we could show that seasonal hypoxia/anoxia in the Eckernförde Bay (E-Bay) resulted in elevated bottom water methane concentrations but that MOx under hypoxic conditions at the redoxcline efficiently consumed the uprising methane. Finally, the anoxic, sulfide-rich brine in the deep sea basin ‘Kryos‘ contains high concentrations of methane and sulfate, which makes the anaerobic oxidation of methane thermodynamically feasible. While sulfate reduction was elevated, we could not detect any anaerobic mode of methane oxidation in the brine. Instead, MOx was elevated at the brine sea water interface at sub-micromolar oxygen concentrations. Here, I propose additional analyses of samples that were collected during the first two years of the project to complement the already exiting data sets. (i) At the Svalbard Seeps, we collected several thousand year old methane derived authigenic carbonates. The occurrence of sub-fossilised membrane lipids of anaerobic and aerobic methanotrophs stored in the carbonate matrix can be used to reconstruct seepage in the past, which provides further insight into the temporal dynamics of gas hydrate dissociation at this system. (ii) At the Blowout, methane oxidation rates in the crater were orders of magnitude higher in comparison to the overlying water column, possibly because the vigorous gas ebullition from the sea floor leads to the resuspension of sediments and sediment-associated MOx communities. To further test this hypothesis, I propose to compare the sediment and water column associated MOx community by using FISH and genetic techniques (i.e. next generation sequencing: Roche-454 or Illumina). (iii) For the time series measurements from the E-Bay, we found temporal mismatches between the build up of methane and MOx activity, which could be related to a lag time of MOx community development. In order to evaluate this, I propose to measure the MOx community size by using FISH. Finally, in the Kryos brine-seawater interface, we found unusual and 13C-enriched fatty acid, which may possibly originate from e-Proteobacteria mediating sulfide oxidation. As we could not collect samples for FISH at Kryos, I suggest to conduct NGS to gain insights into the identity and abundance of key microbes at this biogeochemical hot spot.