Researchers find clues on the bed of the Atlantic OceanPeer-Reviewed Publication
EARTH INSTITUTE AT COLUMBIA UNIVERSITY
CREDIT: KEVIN KRAJICK/EARTH INSTITUTE
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.
* * * * * * * *
Scientist contacts:
Maayan Yehudai my2430@columbia.edu
Steven Goldstein steveg@ldeo.columbia.edu
JOURNAL
Proceedings of the National Academy of Sciences
METHOD OF RESEARCH
Data/statistical analysis
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
Evidence for a Northern Hemisphere trigger of the 100,000-year glacial cyclicity
ARTICLE PUBLICATION DATE
8-Nov-2021
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The oceans got colder and colder, since Antartica got isolated and Panama closed. This was the change. There wasn’t enough energy in the oceans to do interglacials every 41,000 years. Now 100,000 years the oceans are now super cold, then warming the surface and stratifying “locking” heat in the oceans but with a cold deep oceans. When the “conveyor” starts up again with insane amounts of energy stored and cold waters go to the bottom of the ocean pushing up warm waters for a few thousand years until it runs out again and back to the cycle as the deep oceans fill up again. Dansgaard–Oeschger events are where there isn’t enough stored energy but for a few decades of warm waters. One can see it in Antarctic waters. https://journals.ametsoc.org/view/journals/clim/aop/jcliD200049/jcliD200049.xml
The thinning mixed layer says, it’s going to get colder.
https://scitechdaily.com/thinning-surface-layer-of-ocean-leaves-waters-more-susceptible-to-extreme-warming-events/
The paper that assertions changes in ice sheet friction …. Is a major factor in climate change…. Is conceptually lost.
Explain the temperature changes in the last 20,000 years first. Climate ‘science’ has spent the last 20 years pushing a prediction of warming which cannot explain the temperature change in the last 20,000 years including the Younger Dryas abrupt climate change at 11,900 years ago.
The recent warming has been discovered to have been caused by a reduction in cloud cover and an increase in short wave radiation not an increase in long wave radiation. That finding disproves CAGW.
The warming which we just experienced (in the same regions of the planet) has happened before. See this graph for the temperature on the Greenland Ice sheet for the last 11,000 years.
There have been 9 Dansgaard–Oeschger (D-O events also called Bond events) during this interglacial period.
http://www.climate4you.com/images/GISP2%20TemperatureSince10700%20BP%20with%20CO2%20from%20EPICA%20DomeC.gif
The cyclic D-O warming periods occur in both interglacial period and the glacial period. D-O periods always end with an abrupt drop in temperature.
Does the Current Global Warming Signal Reflect a Recurrent Natural Cycle.
http://wattsupwiththat.files.wordpress.com/2012/09/davis-and-taylor-wuwt-submission.pdf
“Public media in the U.S., including National Public Radio (NPR), were quick to recognize the significance of this discovery. The past natural warming events reported by Mulvaney et al. are similar in amplitude and duration to the present global warming signal, and yet the past warmings occurred before the industrial revolution and therefore were not caused by anthropogenic greenhouse gases.”
http://www.agu.org/pubs/crossref/2003/2003GL017115.shtml
Timing of abrupt climate change: A precise clock by Stefan Rahmstorf
Many paleoclimatic data reveal a approx. 1,500 year cyclicity of unknown origin. A crucial question is how stable and regular this cycle is. An analysis of the GISP2 ice core record from Greenland reveals that abrupt climate events appear to be paced by a 1,470-year cycle with a period that is probably stable to within a few percent; with 95% confidence the period is maintained to better than 12% over at least 23 cycles. This highly precise clock points to an origin outside the Earth system (William: Solar changes (more complicated than just a change in the solar magnetic fields/sunspots) cause the warming and cooling); oscillatory modes within the Earth system can be expected to be far more irregular in period.
The multi-precession cycles of glaciation began after the Panama Isthmus was formed around 2Mya. That disconnected the North Atlantic from the Pacific. I expect that would be a significant factor in ocean currents.
Well, why leave out the influence of the Sun? Occasionally, our central star has a sneezing session, frequently coinciding with a Coronal Mass Ejection (CME), as happened in 2006 and doesn’t crank up its furnace to “normal”, whatever that is. There is nothing in that article that takes such things into account.
I don’t understand why no one takes our central star into account about such things. Not enough solar heat to do more than make a few breezes blow might very well account for prolonged cold periods, while increased solar activity may account for increased warming periods.
There’s other stuff, too, but that’s the gist of it.
Scrape off the soil, and you have an extremely inhomogeneous bedrock. Some perhaps easier to glide across than soil, some rather difficult. Polished granite would make up a fair bit of it….watch a curling match to see how polished granite slides over ice.
A very poorly supported assumption.
It’s a hypothesis. In the absence of actual observational data about the adhesion of ice to different substrates, that’s all it is.
Why did the cycle change? Because the earth got colder. I’d have thought that was obvious.
The most obvious place to look first is the obliquity cycle of 41,000 years and the eccentricity cycle of 100,000 years. Something caused the latter to dominate over the former.
Eccentricity has two main periodicities: one cycle with an average of ~100,000 years and a longer cycle with a periodicity of ~413,000 years.
The most important cycle is obliquity, ie 41,000 years.
Doesn’t the record show when eccentricity is lowest in the 413,000 year periodicity cycle it causes an interglacial period that is much longer. We are at that cycle point now.
NB : Read the posts by “John Tillman” above (the first response to the very first post here) and “Ulric Lyons” below before reacting to this one.
I think it’s more a case of something (gradual long-term cooling passing some “threshold” ?) resulting in the 100kyr cycle starting to modulate whether a particular phase of the 41kyr cycle would “trigger” a glacial-to-interglacial transition … or not.
I had to dig out the “Global Benthic / SPECMAP” data from my “spreadsheets from my previous, broken, laptop archive” to check it against the EPICA (Dome-C) dataset, but my vague memory of the most recent interglacials having 80kyr / 120kyr spacing rather than “the regular [100kyr] ice-age cycles that have persisted into human time” mentioned at the start of the ATL article appears to be correct.
geology and continental drift and all this is really interesting
don’t remember seeing any of this in the climate models
all to interested in the flawed Rawleigh CO2 experiments of the late 1800
Al Gore already solved this. CO2 fluctuates on a 100 kya, so ice must fluctuate on a 100 kya. Why are we spending money to study settled science?
Because of everyone’s favourite reason.
Here’s mine – a long term trend of deepening glaciation. Glacial-interglacial flicker between attractors is a sign of transition to glaciation that could in future become deep and of the quasi “snowball earth” variety.
Obliquity is the dominant Milankovitch driver. From 3-1 million years ago obliquity alone started interglacials. This one every ~40k years. But at the “mid Pleistocene revolution” or MPR this ceased to be the case and from then on interglacials required the combined maximal warming peak of all three cycles, eccentricity and precession as well as obliquity. Thus one every 100k years.
The next transition will be to permanent deep glaciation unbroken by interglacials. Antarctica is leading the world toward glacial inception now:
https://notrickszone.com/2021/11/09/temperature-bottom-falling-out-antarcticas-coldest-half-year-since-measurements-began-60-years-ago/
Except that the soil bed-load would have been frozen with ice and behaved similarly to clean ice, as can be seen in the shear moraines in ice tunnels in Greenland.
Also, the interglacials are long enough to develop new soils between glaciations!
Another thing to consider is that thicker ice generally increases the probability of the basal ice/frozen ground-moraine to actually melt from pressure and geothermal heat. The melted ice decreases friction in the same manner as ice skates work.
Lastly, it isn’t just planar contact friction that retards the movement of continental glaciers. In rugged terrain, such as the Canadian glaciers encountered crossing New England, barriers such as individual mountains can divert the glacial paths around or over the obstacles. In the case of deep valleys oblique to the flow of ice, forward movement can be stopped until the ice is thick enough to over-top the mountain(s) containing the valley. Then the ice shears over the obstacle instead of moving over the ground. There are places in New England where soil and grus are preserved in pressure shadows, and striations indicate a chaotic, turbulent movement at the base. Similarly, it was recently reported that soil and entrained vegetation was discovered in the Greenland core drilling done by CRREL in the 1960s.
I think they should have had a glaciologist on the team!
A glacier very close to the equator formed as the Himalayas rose, lifted by the subduction of the Indian tectonic plate under the Eurasian Plate:
The role of terrestrial plants in limiting atmospheric CO2 decline over the past 24 million years, Nature 460, 85-88 (2 July 2009) doi:10.1038/nature08133 Letter, concludes that grasslands are the result of the CO2 suffocation of trees. Plate tectonics were responsible for CO2-depleting mineral formation, especially, the uplift of the Himalayas. CO2 levels dropped to 200-250 ppm from 1000-1500 ppm as forests starved for CO2, gave way to prairies. https://www.readcube.com/articles/10.1038/nature08133 (emphasis added)
Inter-glacial frequency over the last 1.2 million years is still essentially constrained by obliquity cycles, so the question is why did the new sequence start skipping peaks in obliquity, or skipping two from the Eemian to the Holocene. And why did it get both colder and warmer than around 2 million years ago.
One explanation is that global temperatures track the advance and recession of the Karakoram and Himalayan glaciers near the equator. When temperatures rise, more snowfall precipitates over the region, adding to the size of the glaciers, presumably, thus increasing earth’s albedo (ceteris paribus, holding other things constant). The mountain ranges constantly surge, 1 cm per year, thus the glaciers have advanced over the 5 million year period.
I want to know more about this: ”
In 2015, a team led by John Higgins, a Princeton geochemist, excavated the record-setting core.
At first, the oldest ice seemed to contain startling levels of CO2, several times the 407 parts per million (ppm) we see today, says Yuzhen Yan, the Princeton geochemist who led the new study. Further analysis, however, revealed the bubbles had been contaminated by CO2 percolating from beneath the ice, likely released by microbes. That meant the team had to toss out data from many of the oldest samples—a reflection of their conscientiousness, says Bärbel Hönisch, a geochemist at Columbia University.”