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Paleoceanography 4: Methane Hydrates, a Molecular Clue

This is Jim Fiorendino, your host for On the Ocean. Scientists follow a trail of biomarkers left by ancient organisms to reconstruct a record of Earth’s climate history. At Texas A&M University, oceanographers are currently hunting for molecular clues in the Tasman Sea using sediment samples collected by the International Ocean Discovery Program.

The Tasman Sea is the body of water located between the east coast of Australia and New Zealand.

Methane hydrates are ice-like substances in which methane gas is trapped; methane is a greenhouse gas, and is composed of three hydrogen atoms bonded to one carbon atom. Some scientists believe there is more methane hydrate in marine sediments than all other forms of fossil fuel combined. Methane is produced by thermogenic processes deep in the earth or through biological activity. Biologically produced methane hydrates can be distinguished from thermogenically produced methane hydrates by studying their carbon isotopes; biologically-produced methane hydrates are depleted in the heavier carbon 13 isotope.

Right: A ball and stick model showing the structure of methane hydrate. A methane molecule is trapped within a cage of water molecules (United States Department of Energy). Left: Burning methane hydrate (United States Geological Survey). https://geology.com/articles/methane-hydrates/

Release of methane hydrates into the world’s oceans and atmosphere could dramatically acidify the oceans and raise global temperatures. Scientists are trying to understand the history of methane hydrate destabilizations, and whether this could have contributed to the major climate shift that occurred during the Cenozoic Era. Release of methane from gas hydrates would mean an all-you-can-eat buffet for microorganisms that eat methane. These methanotrophs produce lipid biomarkers that are preserved in sediments for millions of years, waiting for scientists to discover them and read their ancient record of methane disturbances. To ensure accuracy, records of past methane hydrate release events are compared with a suite of lipid biomarkers, as well as their compound-specific carbon isotopes.

Location of inferred and recovered methane hydrates in the oceans. Image from Council of Canadian Acadamies, based on data from Kvenvolden and Rogers (2005). http://www.globalcarbonproject.org/news/MethaneHydrates.html

This has been On the Ocean, a program made possible by the Department of Oceanography and a production of KAMU-FM on the campus of Texas A&M University in College Station. For more information and links, please go to ocean.tamu.edu and click On the Ocean.

Featured image from: Mikkel Juul Jensen/SPL/Cosmos (left) and Aphelleon/Shutterstock (right)

Script Author: James M. Fiorendino

Contributing Professor: Dr. Yige Zhang

Dr. Yige Zhang