From: ScienceDaily
Published October 23, 2013 06:08 AM

How life in ocean sediments responds to climate change

Traces of past microbial life in sediments off the coast of Peru document how the microbial ecosystem under the seafloor has responded to climate change over hundreds of thousands of years. For more than a decade scientists at the Max Planck Institute for Marine Microbiology and their colleagues at MARUM and the University of Aarhus have investigated microbial life from this habitat. This "Deep Biosphere," reaching several hundred metres below the seafloor, is exclusively inhabited by microbes and is generally considered as stable.

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Nevertheless, only little is known about how this system developed over millennia and how this microbial life influences the cycling of carbon in the oceans. In a new study appearing in the Proceedings of the National Academy of Sciences (PNAS) Dr. Sergio Contreras, a palaeoceanographer, and his Bremen colleagues use a careful examination of drill-cores from the continental shelf of Peru to actually show how surprisingly dynamic this deeply buried ecosystem can be.

Below the sea floor, consortia of two different domains of microorganisms (archaea and bacteria) tap the energy of methane, which they oxidize by using sulfate. This process is known as the anaerobic oxidation of methane (AOM) and has been intensively studied by Bremen researchers. Methane, also produced by archaea, emerges from deeper layers of the sediment, while sulfate diffuses slowly from the water column into the sediment. Both reactants meet at the so-called methane oxidation front. Only at this front are concentrations of sulfate and methane high enough for the microbial turnover to take place, and here the AOM process leaves behind mineral and biological fossil signatures. For example, archaeol, a constituent of the archaeal cell membrane, is an extremely stable molecule that is preserved over thousands to millions of years. Minerals such as barite (barium sulfate) and dolomite (magnesium calcium carbonate) also precipitate at this methane oxidation front due to microbial activity.

Sea floor image via Shutterstock.

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