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Methane gas bubbles rising above the ocean floor
Justin Kim
Sediment cores taken from the Southern Ocean dating back 23 million years are providing insight into how ancient methane escaping from the seafloor could have led to regional or global climate and environmental changes, according to a study from two Texas A&M University researchers.
Yige Zhang,Assistant professor in Department of Oceanography at Texas A&M, and doctoral student Bumsoo Kim have had their work published in the current issue of Nature Geoscience.
The oceanographers examined cores – sediment samples from deep parts of the ocean floor – from the Oligocene-MioceneAround 23 million years ago, the era was in areas near Tasmania and Antarctica, the Pacific sector of South Ocean. There are billions of tons of carbon stored beneath the ocean floor as gas hydrates – ice-like crystals composed of water and natural gas. Methane releases in the past are thought to be linked to major earth events like global warming and subsequent climate shifts.
“For a long time, people thought that methane released from the ocean floor could go into the atmosphere and directly contribute to the greenhouse effect, leading to rapid warming and even mass extinctions,” Zhang said. “But this idea is no longer popular in the last decade or so because we lack direct evidence of methane release in Earth’s history. Also, modern observations show that even when methane gases are released, they rarely make it to the atmosphere.”
Kim and Zhang now have the ability to document past methane emissions using markers that eat methane. These “methane-eating” substances are preserved in sediments for tens of millions of years, the researchers said. They could be used to provide evidence of methane being released from different locations in the Southern Ocean.
“We saw that a methane release occurred during a peak glaciation about 23 million years ago,” Zhang said.
Glaciation refers to the movement, formation, and receding of glaciers. It is most common in Antarctica and Greenland. Large ice sheets can draw in huge amounts of water, which could cause sea level to drop by tens or hundreds of feet.
Zhang stated that methane gas releases and their after-effects caused ocean acidification and hypoxia, which is a lack of oxygen in water. This phenomenon was observed after the incident. Deepwater Horizonincident in 2010, when large quantities of methane were released into the Gulf of Mexico.
“One implication of our study is that if gas hydrates start to decompose in the future due to ocean warming, places like the Gulf of Mexico could suffer severely from ocean acidification and expansion of the low oxygen ‘dead zones’,” Kim said.
The project was funded by Texas A&M’s T3 grants Texas Sea Grant.
