How Microbial Life Shapes Lime Formation in the Deep Ocean

Microorganisms are everywhere and have been influencing the Earth’s environment for over 3.5 billion years. Researchers from Germany, Austria and Taiwan have now deciphered the role they play in the formation of lime – for the first time in the deep sea rather than in the laboratory. The basis was a five-meter-long lime core obtained during an expedition. The team of authors has now published their results in the journal Communications Earth & Environment.

Correlation between Microorganisms and Mineral Formation

Microorganisms are usually associated with decomposition and degradation processes, but they also facilitate and accelerate the formation of minerals that would otherwise only form very slowly or not at all. This phenomenon is precisely what interests researchers in geology, geochemistry and materials science, as it can be used for topics in basic and applied research. For example, lime minerals bind carbon dioxide (CO2) from the atmosphere as a solid over long periods of time.

Methane Emissions as a Natural Laboratory

Methane and other hydrocarbons escape from the ocean floor at so-called cold springs; they form the basis for ecosystems independent of sunlight. The basic process is methane oxidation without oxygen, which is carried out jointly by archaea and bacteria. “This metabolic reaction indirectly leads to the formation of lime in sediments near the ocean floor. Marine methane sources are therefore excellent ecosystems for studying microbial processes and their influence on mineral formation,” explains lead author Daniel Smrzka from MARUM – Center for Marine Environmental Sciences and the Department of Geosciences at the University of Bremen.

Understanding Lime Formation Rates

Although the basic process of calcification by microbes at cold springs is understood, the actual formation rate of the rocks is still unclear. “Answers and precise estimates of the formation rates of calc minerals are essential to recognize the relevance of the newly formed rocks in terms of their carbon storage potential,” says Smrzka. In addition, studies neglected the direct influence of microorganisms on the formation rates, although this has long been known. During the SO266 expedition, conducted jointly by Taiwanese and MARUM scientists on the research vessel SONNE into the South China Sea near the coast of Taiwan, methane sources were investigated in an area of ​​over 40,000 square meters. A five-meter-long core of pure lime was recovered using the MARUM-MeBo200 mobile drilling rig. “This core is the longest continuous archive of methane-generated calcification to date, with a maximum age of almost 40,000 years,” emphasizes Smrzka. “This exceptional sample not only provides a unique look into the past dynamics of methane formation in this region, but also new insights into the interplay between microbial activity and calcification in these ecosystems.”

Microbial mats and calcification rates

In general, two different types of cement phases are observed in limestones from methane seeps on the ocean floor. “The exceptional degree of preservation of the rocks and the unusual amount of cement present enabled us for the first time to date several cement phases separately, with the result that the pink cements grew up to 25 times faster than the clear cements. The ability to date these two cement phases side by side and compare their ages provides the first and only quantitative estimates of the influence of microorganisms on rock formation,” says Daniel Smrzka. This means that microbial mats can potentially bind CO2 up to 25 times faster than if the minerals were formed without their influence.

Implications for Mineral Formation and Climate Research

These results confirmed previous experimental studies based on microbial cultivation and mineral formation, but provide quantitative estimates of rock formation over thousands of years for the first time. According to the team of authors, these results are an important step towards better understanding the phenomenon of microbially influenced mineral formation and quantifying it for the first time. In addition, microbial activity influences the formation of minerals in almost all ecosystems and environmental conditions.

The MARUM Research Initiative

The study is part of the research of the Cluster of Excellence “Ocean Floor – Unexplored Interface of the Earth”, which is located at MARUM. The marine carbon cycle at cold springs and the formation of authigenic minerals are among the core topics of the cluster.

MARUM is gaining fundamental scientific knowledge about the role of the ocean and the seabed in the entire Earth system. The dynamics of the ocean and the seabed significantly shape the entire Earth system through interactions of geological, physical, biological and chemical processes. This influences the climate and the global carbon cycle and creates unique biological systems. MARUM stands for basic and open-ended research with responsibility to society, for the benefit of the marine environment and in line with the United Nations’ sustainability goals. It publishes its quality-controlled scientific data and makes it freely accessible. MARUM informs the public about new findings on the marine environment and provides actionable knowledge in dialogue with society. MARUM’s cooperation with companies and industrial partners takes place while maintaining its goal of protecting the marine environment.

Scientific contacts
Dr. Daniel Smrzka
General Geology – Marine Geology
MARUM – Center for Marine Environmental Sciences and Department of Geosciences, University of Bremen
E-mail: dsmrzka@marum.de
Website: https://www.marum.de/

Prof. Dr. Gerhard Bohrmann
General Geology – Marine Geology
MARUM – Center for Marine Environmental Sciences and Department of Geosciences, University of Bremen
E-mail: gbohrmann@marum.de
Website: https://www.marum.de/

Original publication
Daniel Smrzka, Yiting Tseng, Jennifer Zwicker, Andrea Schröder-Ritzrau, Norbert Frank, Anne-Désirée Schmitt, Thomas Pape, Daniel Birgel, Jörn Peckmann, Saulwood Lin, Gerhard Bohrmann
Journal: Communications Earth & Environment
Article Title: Marine carbon burial enhanced by microbial carbonate formation at hydrocarbon seeps
Article Publication Date: 05 January 2025
DOI: 10.1038/s43247-024-01960-0

Source: (IDW)