Why did glacial cycles intensify a million years ago?
Researchers find clues on the bed of the Atlantic Ocean

Date:
November 8, 2021
Source:
Earth Institute at Columbia University
Summary:
A study says the Mid-Pleistocene Transition may have been linked
to previous erosion of continental soils that subsequently allowed
glaciers to stick to the underlying hard bedrock more efficiently.



FULL STORY ========================================================================== Something big happened to the planet about a million years ago. There was
a major shift in the response of Earth's climate system to variations
in our orbit around the Sun. The shift is called the Mid-Pleistocene Transition.

Before the MPT, cycles between glacial (colder) and interglacial
(warmer) periods happened every 41,000 years. After the MPT, glacial
periods became more intense -- intense enough to form ice sheets in
the Northern Hemisphere that lasted 100,000 years. This gave Earth the
regular ice-age cycles that have persisted into human time.


========================================================================== Scientists have long puzzled over what triggered this. A likely reason
would be a phenomenon called Milankovitch cycles -- cyclic changes in
Earth's orbit and orientation toward the Sun that affect the amount of
energy that Earth absorbs.

This, scientists agree, has been the main natural driver of alternating
warm and cold periods for millions of years. However, research has shown
that the Milankovitch cycles did not undergo any kind of big change a
million years ago, so something else likely was at work.

Coinciding with the MPT, a large system of ocean currents that helps
move heat around the globe experienced a severe weakening. That system,
which sends heat north through the Atlantic Ocean, is the Atlantic
Meridional Overturning Circulation (AMOC). Was this slowdown related
to the shift in glacial periods? If so, how and why? These have been
open questions. A new paper published today in the journal Proceedings
of the National Academy of Sciences proposes an answer.

The researchers analyzed cores of deep-sea sediments taken in the
south and north Atlantic, where ancient deep waters passed by and left
chemical clues.

"What we found is the North Atlantic, right before this crash, was acting
very differently than the rest of the basin," said lead author Maayan
Yehudai, who did the work as a PhD. student at Columbia University's Lamont-Doherty Earth Observatory.

Prior to that oceanic circulation crash, ice sheets in the Northern
Hemisphere began to stick to their bedrock more effectively. This caused glaciers to grow thicker than they had before. This in turn led to a
greater global cooling than before, and disrupted the Atlantic heat
conveyor belt. This led to both stronger ice ages and the ice-age cycle
shift, says Yehudai.

The research supports a long-debated hypothesis that the gradual
removal of accumulated slippery continental soils during previous ice
ages allowed ice sheets to cling more tightly to the older, harder
crystalline bedrock underneath, and grew thicker and more stable. The
findings indicate that this growth and stabilization just before the
weakening of the AMOC shaped the global climate.

"Our research addresses one of the biggest questions about the largest
climate change we had since the onset of the ice ages," said Yehudai. "It
was one of the most substantial climate transitions and we don't fully understand it. Our discovery pins the origin of this change to the
Northern Hemisphere and the ice sheets that evolved there as driving
this shift towards the climate patterns we observe today. This is a very important step toward understanding what caused it and where it came
from. It highlights the importance of the North Atlantic region and ocean circulation for present and future climate change." The research was
led also by Yehudai's advisor, Lamont geochemist Steven Goldstein, along
with Lamont graduate student Joohee Kim. Other collaborators included
Karla Knudson, Louise Bolge and Alberto Malinverno of Lamont-Doherty;
Leo Pena and Maria Jaume-Segui of the University of Barcelona; and
Torsten Bickert of the University of Bremen. Yehudai is now at the Max
Planck Institute for Chemistry.

========================================================================== Story Source: Materials provided by
Earth_Institute_at_Columbia_University. Original written by Marie DeNoia Aronsohn. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Maayan Yehudai, Joohee Kim, Leopoldo D. Pena, Maria Jaume-Segui',
Karla
P. Knudson, Louise Bolge, Alberto Malinverno, Torsten Bickert,
Steven L.

Goldstein. Evidence for a Northern Hemispheric trigger of the
100,000- y glacial cyclicity. Proceedings of the National Academy of
Sciences, 2021; 118 (46): e2020260118 DOI: 10.1073/pnas.2020260118 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/11/211108161424.htm

--- up 9 weeks, 4 days, 9 hours, 25 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)