Why did glacial cycles intensify a million years ago? Researchers find clues on the bed of the Atlantic Ocean.
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 on November 8, 2021, 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.”
Reference: “Evidence for a Northern Hemispheric trigger of the 100,000-y glacial cyclicity” by Maayan Yehudai, Joohee Kim, Leopoldo D. Pena, Maria Jaume-Seguí, Karla P. Knudson, Louise Bolge, Alberto Malinverno, Torsten Bickert and Steven L. Goldstein, 8 November 2021, Proceedings of the National Academy of Sciences.
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.
no first hand info , with no real proof, pure speculation with selected data, we know from ice core samples that last ice age was about 10,000 yrs a far cry from 100,000,
“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.”
Orbital mechanics change the amount of solar energy that the Earth receives: The amount it actually absorbs is moderated by atmospheric and geological processes.
“… 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.”
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. 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.
Lastly, it isn’t just planar contact friction that ret*rds 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 at right angles to the flow of ice, forward movement can be stopped until the ice is thick enough to over-top the mountain(s). 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.
I think they should have had a glaciologist on the team!
two reasons why it got colder and glaciers lasted 90,000 years cold as agianst the previous 30,000 years cold
1,000,000 annual years ago
earths magnetic field half as intense as it is now 2021
1821 2021 over the past two hundred years the magnetic field has weakened about 9 percent on a global average but as it at its strongest its been in the last 100,000 years
reason one the infrared heat of the earth surface fled quicker through interstellar space as the magnetic field lines are poor and weak
reason two stratovolcaos disturb the earth cycle and the northern and southern hemipshere atmosphere and lithosphere and hydrosphere and cryrosphere
13,699,000,000 anno universo = 1,000,000 annual years ago antarctica and south sandwich islands beethoven peninsula volcanic field 71 55 s 73 42 w summit 1050 m 3445 feet volcano number 390825 intraplate continental crust > 25 kilometres the beethoven peninsula contains nine nunataks consisting of basaltic lava flows and associated hydroclastites no primary volcanic edifice is preserved and it is not clear whether the exposure represent individual volcanic vents or a volcanic field the youngest dated rocks are less than one million years old
13,699,000,000 anno universo = 1,000,000 annual years ago 1,000,000 or less annual years ago Antarctica Brabant island volcanic field 64 28 s 62 33 w summit 2522 metres elevation 8274 feet volcano number 390826 intraplate continental crust > 25 kilometres isolated exposures of the bahia bouquet formation occur on Brabant island a potassium argon date of less than 1 million years ago was obtained from a rock at the northern end of the island
13,699,000,000 anno universo = 1,000,000 +- 90,000 annual years ago phillippines luzon Corregidor caldera 14 4 n 120 58 e summit 173 metres elevation 568 feet volcano number 273810 subduction zone continental crust > 25 kilometres Corregidor is a largely submarine caldera with a post caldera dacitic lava dome located on the bataan lineament at the mouth of manilla bay Corregidor island forms the northern part of the calderas and Caraballo island lies to the south east part of the caldera rim a radiometric date of 1.0 +- 0.09 million years was obtained
13,699,000,000 anno universo = 1,000,000 +- 90,000 annual years ago united states america Washington goat rock hogback mountain old snowy mountain stratavolcano shield latitude 46 5 n longitude -121 4 w summit 2494 metres elevation 8182 feet volcanic number 321801 subduction zone continental crust > 25 kilometres the deeply eroded goat rocks stratovolcano was active between 2.5 and 0.5 million years ago the andesitic volcano was constructed between about 2.5 and 0.5 ma over older products of a major rhyolitic explosive eruption during the late Pliocene and early Pleistocene the small hogback mountain shield volcano was constructed south of white pass about 1.0 ma the tieton andesitic the earths largest known andesitic lava flow travelled 80 kilometres to the east following extensive erosion mid to late Pleistocene andesites were erupted onto the glaciated cispus river valley
13,699,000,000 anno universo = 1,000,000 annual years japan Honshu daito stratovolcano 38 299 n 140 527 e summit 1366 metres elevation 4482 feet volcano number 283875 subduction zone continental crust > 25 kilometres daito volcano is an andesitic stratovolcano nne of the zao volcanic massif daito dake was active about 1 million years ago
13,698,600,000 anno universo = 1,400,000 1,200,000 1,000,000 annual years ago japan Honshu futamata stratovolcano 37 243 n 139 97 e summit 1544 metres elevation 5066 feet volcano number 283865 calderas lava dome subduction zone continental crust > 25 kilometres
futamata yama is a late Pleistocene about 140,000 or 90,000 years old stratovolcano and lava dome
a thick lava flow extends to the north west it is located within the quaternary tonohetsuri caldera
the oval shaped narioka caldera cuts the western rim of tonohetsuri caldera and the western rim of the older ono caldera these large calderas were formed during eruption of the kumado ashino and nishigo pyroclastic flows about 1.4 1.2 and 1.0 million years ago respectively 1,000,000 magnitude 4
13,699,000,000 anno universo = 1,000,000 700,000 annual years ago Indonesia java gede 5 93 s 106 07 e summit 595 metres elevation 1952 feet volcano number 263810 gede volcano on the north west tip of java is of quaternary age and is located about 280 kilometres from the French the gede salak volcanic complex consists of pyroclastic flows on its western flanks and lava flows on its eastern flanks mount gede is also surrounded by plio quaternary tuffs ranging from 0.07 to 0.1 mn in age suggest that these tufts come from the calderas of the nearby rawa dano volcanic complex but gravity anomalies in the region suggest that neither gede nor its nearby volcanoes could have been responsible for these igimbrites and instead suggest a pre existing caldera in the sundra straight was responsible quaternary gede salak volcanic complex banten area at the junction between Sumatra arc and java arc Indonesia
13,699,000,000 anno universo = 1,000,000 annual years ago turkey etrusk stratovolcano 39 032 n 43 66 e summit 3100 metres elevation 10171 feet volcano number 213023 the Pliocene etrusk volcano is one of the major volcanic centres of eastern Anatolia just north east of lake van there is a 5 kilometre wide horseshoe shaped caldera near the centre of the volcano with the Pleistocene karniyak scoria cone about 11 kilometres away on the south west flank near the lake k ar dating the main volcanic edifice of etrusk was formed between 4.3 and 3.9 ma ending with caldera collapse
Between 1 and 0.43 ma basalts erupted from the south west flank predominantly from a north south extending fissure as well as from the karniyak hill and a maar shaped volcanic centre and
the younger dated trachybasalt from karniyak was 0.36 +- 0.06 ma
“… earths magnetic field half as intense as it is now 2021 …”
Just because two things are correlated over time does not mean that one of them is responsible for changes in the other. See the following link for examples of spurious correlations:
New England is not in Canada. It is part of the United States (to a previous comment).