Sediment cores from ocean floor could contain 23-million-year-old
climate change clues

Date:
February 17, 2022
Source:
Texas A&M University
Summary:
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 new study.



FULL STORY ========================================================================== 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 the Department of Oceanography at
Texas A&M, and doctoral student Bumsoo Kim have had their work published
in the current issue ofNature Geoscience.

The oceanographers examined cores -- sediment samples from deep parts
of the ocean floor -- from the Oligocene-Miocene era, roughly 23 million
years ago, from areas near Tasmania and Antarctica in the Pacific sector
of the Southern 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. Past releases of methane are believed to be related to
huge earth events, such as 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." However, Kim and
Zhang are now able to document past methane release by using markers
that consume methane. These "methane-eating" substances are preserved
in sediments for tens of millions of years, the researchers said. They
could provide direct evidence of methane release from different places
in the Southern Ocean.

"We saw that a methane release occurred during a peak glaciation about
23 million years ago," Zhang said.

Glaciation is the formation, movement and recession of glaciers, and the process mostly commonly occurs in Antarctica and Greenland. When large
ice sheets form, they draw in a tremendous amount of water that could
lower the sea-level by tens to hundreds of feet.

Zhang added that the methane gas release and its after-effects led
to ocean acidification and hypoxia (a lack of oxygen in the water),
something that has been observed after the Deepwater Horizon incident in
2010, when large amounts of methane were released in 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 and Texas Sea Grant.

========================================================================== Story Source: Materials provided by Texas_A&M_University. Original
written by Keith Randall.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Bumsoo Kim, Yi Ge Zhang. Methane hydrate dissociation across the
Oligocene-Miocene boundary. Nature Geoscience, 2022; DOI:
10.1038/s41561- 022-00895-5 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220217131912.htm

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