Role of microorganisms in the formation of unique iron ore caves

The National Science Foundation (NSF) has awarded $400,00 to three researchers in the Department of Biology and Geoscience at The University of Akron (UA) to continue their groundbreaking research on cave formation. The scientists are studying communities of microorganisms and their role in the formation of unique iron ore caves, which make up only about one percent of caves worldwide.

A majority of caves are found in limestone rock. They are formed by water flowing through the ground which erodes limestone deposits, leaving behind a series of tunnels and caverns. However, banded iron formations, or BIF, are rocks formed from iron deposits in ancient oceans. These iron-rich rocks are extremely resistant to the type of erosion that forms most caves, with surfaces that can be more than a billion years old. Yet, somehow, the BIFs in Brazil contain thousands of caves.

Preliminary research by the team at UA shows these BIF caves have high populations of active microbial communities. The researchers theorize that the microbes use iron within the rock to respire, in a similar way that humans use oxygen. This respiration causes the rust-like iron oxides that make up the cave to become soluble. This theory is supported by the discovery of dissolved iron in water within the cave, as well as evidence that the iron is dissolving behind the walls, causing the cave to collapse in on itself. The team now believes the flow of groundwater simply carries off the iron oxides after microbes do all the work of chewing through the BIF. Over time, this process could be responsible for the voids in the walls of the cave, which eventually meet to form a new cave that is large enough to be entered by humans.

"The identification of cave forming processes in BIF is significant as it dramatically expands the environments in which caves can form," states Dr. Hazel Barton, director of the integrated bioscience program at UA. "These caves provide critical subterranean habitats for many rare and endangered animal species. There is also a strong correlation between the location of these BIF caves and the presence of iron ores of global economic significance, providing the source material for the production of steel."

The team has been studying the caves in Brazil over the course of the last seven years. With continued funding from the NSF, Barton and her associates from UA, Dr. John Senko and Dr. Ira Sasowsky, will again take a group of students to Brazil to study the BIF caves firsthand. There, they will continue to test the hypothesis that the activities of microorganisms are responsible for the formation of BIF caves.

They will test their hypothesis both in the field and in a lab, and models will be used to show how iron is oxidized and swept away. The data gathered will show potential cave forming processes across a range of scales, from microscopic to regional, and will help to determine the role that microbes play in iron cave development.

Provided by University of Akron