There may be good news about the oceans in a globally warmed world
Study suggests ongoing oxygen loss from the seas due to climate change
may reverse in the future

Date:
June 28, 2023
Source:
Rutgers University
Summary:
An analysis of oxygen levels in Earth's oceans may provide some
rare, good news about the health of the seas in a future, globally
warmed world. A study analyzing ocean sediment shows that ocean
oxygen levels in a key area were higher during the Miocene warm
period, some 16 million years ago when the Earth's temperature
was hotter than it is today.


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FULL STORY ==========================================================================
An analysis of oxygen levels in Earth's oceans may provide some rare,
good news about the health of the seas in a future, globally warmed world.

A Rutgers-led study published in Nature analyzing ocean sediment shows
that ocean oxygen levels in a key area were higher during the Miocene
warm period, some 16 million years ago when the Earth's temperature was
hotter than it is today.

In recent decades, levels of life-sustaining oxygen in the ocean have
been decreasing, raising concerns that oxygen-deficient zones in key
parts of the world oceans will expand, further harming marine life.

Scientists have attributed the trend to climate change-induced rising temperatures, which affect the amount of oxygen that can be absorbed
from the atmosphere.

"Our study shows that the eastern equatorial Pacific, which today is home
to the largest oxygen-deficient zone in the oceans, was well oxygenated
during the Miocene warm period, despite the fact that global temperatures
at that time were higher than at present," said Anya Hess, the lead author
of the study and a Rutgers doctoral student working with Yair Rosenthal,
a Distinguished Professor focused on marine and Earth sciences with the
Rutgers School of Art and Sciences and the School of Environmental and Biological Sciences.

Hess added: "This suggests that current oxygen loss may ultimately
reverse." The fastest rates of oxygen loss in recent decades have
been in oxygen- deficient zones, and they are expected to continue to
expand and become shallower, threatening fisheries by shrinking fish
habitat. However, climate models diverge in their predictions of how
these zones will respond beyond the year 2100, inspiring the team to investigate more.

To test current climate models, researchers chose the mid-Miocene,
when climate conditions were similar to those predicted for the next few centuries in the current era of climate change. Researchers examined ocean sediments deposited during the mid-Miocene in the eastern equatorial
Pacific. The sediments were recovered from the seafloor by scientists
aboard the National Science Foundation-funded research vessel JOIDES
Resolution as part of what is now known as the International Ocean
Discovery Program (IODP).

The researchers isolated the fossilized remains of microorganisms the
size of individual grains of sand that live in the water column called foraminifera.

The scientists analyzed the chemical composition of the foraminifera,
which reflects the chemical profile of the ancient ocean. They discerned
oxygen levels of ancient oceans in a few ways, including using isotopes of nitrogen - - forms of the element that have a different relative atomic
mass -- as detectors. The isotopes are sensitive to a process called denitrification that only occurs at very low oxygen levels. They also
employed a method of analysis that compares levels of iodine and calcium
and gives subtle readings that can differentiate between well-oxygenated conditions and moderately well-oxygenated conditions.

The methods showed the area was well oxygenated during the height of
Miocene warmth, even approaching modern day levels seen in the open-ocean
South Pacific.

"These results were unexpected and suggest that the solubility-driven
loss of oxygen that has occurred in recent decades is not the end of
the story for oxygen's response to climate change," Rosenthal said.

Other authors on the study include Ken Miller, a Distinguished Professor
in the Department of Earth and Planetary Sciences in the Rutgers School
of Arts and Sciences, Alexandra Auderset and Alfredo Martinez-Garcia
of the Max Planck Institute for Chemistry in Germany, Daniel Sigman of Princeton University and Xiaoli Zhou of Tongji University in China.

* RELATED_TOPICS
o Earth_&_Climate
# Environmental_Awareness # Climate # Oceanography #
Global_Warming
o Fossils_&_Ruins
# Early_Climate # Origin_of_Life # Fossils # Early_Mammals
* RELATED_TERMS
o Ocean o Ocean_current o Ozone o Paleoclimatology o
Antarctic_ice_sheet o Greenland_ice_sheet o Climate_model
o Oxygen

========================================================================== Story Source: Materials provided by Rutgers_University. Original written
by Kitta MacPherson.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Anya V. Hess, Alexandra Auderset, Yair Rosenthal, Kenneth G. Miller,
Xiaoli Zhou, Daniel M. Sigman, Alfredo Marti'nez-Garci'a. A well-
oxygenated eastern tropical Pacific during the warm Miocene. Nature,
2023; DOI: 10.1038/s41586-023-06104-6 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/06/230628125214.htm

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