Bacteria Plays Role In Formation Of Dolomite

While scientists remain uncertain exactly how the mineral dolomite is formed, an international team of researchers say that they have discovered that the process can be facilitated by bacteria.
According to a recent press release jointly issued Monday by the Cluster of Excellence “The Future Ocean” and GEOMAR | Helmholtz Centre for Ocean Research Kiel, the mineral is primarily formed in extreme ecosystems like lakes and lagoons with high salinity.
The exact process behind dolomite’s creation remains a mystery, though, but now researchers representing the two aforementioned organizations, as well as colleagues from ETH Zurich and the Centro de Astrobiología in Madrid, Spain, believe they have gotten one step closer to understanding the potential causes.
“In simple laboratory experiments with globally distributed marine bacteria which use sulfur compounds instead of oxygen for energy production (sulfaterespiration), the scientists were able to demonstrate the formation of primary dolomite crystals under conditions that prevail today in marine sediments,” the press release said.
“The dolomite precipitates exclusively within a mucus matrix, secreted by the bacteria to form biofilms,” added Dr. Stefan Krause, Geomicrobiologist at GEOMAR | Helmholtz Centre for Ocean Research Kiel. “Different chemical conditions prevail within the biofilm compared to in the surrounding water. In particular, the alteration of the magnesium to calcium ratio plays an important role. These changes allow for the formation of dolomite crystals.”
Their findings have been published in the journal Geology, and additionally, the experts were able to demonstrate that the ratios of different calcium isotopes between ambient water, biofilm, and dolomite crystals were different, GEOMAR’s Dr. Volker Liebetrau explained. Those ratios play an important role in re-creating environmental conditions of the past, and will allow more for exact interpretation of climate indicators stored within rocks.
“Evidence of primary dolomite formation by a process as common as microbial sulphate respiration under conditions that currently prevail in the seabed, provides new insights into the reconstruction of fossil dolomite deposits,” the press release said. However, it asks, “why are large scale deposits from primary dolomite no longer formed at the ocean floor?”
Professor Tina Treude, head of the Working Group at GEOMAR, admits that the team is still puzzled by that question.
“One possibility is that massive primary dolomite can form particularly during times when large quantities of organic matter in the seabed are degraded by sulfate-respiring bacteria,” she explained. “Such conditions exist when the sea water above the seafloor is free of oxygen. In Earth´s history, several such oxygen-free periods have occurred, partly consistent with time periods of intensified dolomite deposition.”

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