From The University of Arizona: “New study solves long-standing mystery of what may have triggered ice age”

From The University of Arizona


Media contact
Daniel Stolte
Science Writer, University Communications

Researcher contacts
Marcus Lofverstrom
Department of Geosciences

Diane Thompson
Department of Geosciences

Sophisticated simulations of climate during the onset of the last glacial period – some 100,000 years ago – may help explain why a massive ice sheet formed in Scandinavia despite its comparatively mild climate.

At the beginning of the last ice, local mountain glaciers grew and formed large ice sheets, like the one seen here in Greenland, that covered much of today’s Canada, Siberia, and Northern Europe. Credit: Annie Spratt/Unsplash.

A new study led by University of Arizona researchers may have solved two mysteries that have long puzzled paleo-climate experts: Where did the ice sheets that rang in the last ice age more than 100000 years ago come from and how could they grow so quickly?

Understanding what drives Earth’s glacial–interglacial cycles – the periodic advance and retreat of ice sheets in the Northern Hemisphere – is no easy feat, and researchers have devoted substantial effort to explaining the expansion and shrinking of large ice masses over thousands of years. The new study, published in the journal Nature Geoscience, proposes an explanation for the rapid expansion of the ice sheets that covered much of the Northern Hemisphere during the most recent ice age, and the findings could also apply to other glacial periods throughout Earth’s history.

About 100000 years ago when mammoths roamed the Earth the Northern Hemisphere climate plummeted into a deep freeze that allowed massive ice sheets to form. Over a period of about 10000 years local mountain glaciers grew and formed large ice sheets covering much of today’s Canada Siberia and northern Europe.

While it has been widely accepted that periodic “wobbling” in the Earth’s orbit around the sun triggered cooling in the Northern Hemisphere summer that caused the onset of widespread glaciation, scientists have struggled to explain the extensive ice sheets covering much of Scandinavia and northern Europe, where temperatures are much more mild.

Unlike the cold Canadian Arctic Archipelago where ice readily forms Scandinavia should have remained largely ice-free due to the North Atlantic Current which brings warm water to the coasts of northwestern Europe. Although the two regions are located along similar latitudes, the Scandinavian summer temperatures are well above freezing, while the temperatures in large parts of the Canadian Arctic remain below freezing through the summer, according to the researchers. Because of this discrepancy, climate models have struggled to account for the extensive glaciers that advanced in northern Europe and marked the beginning of the last ice age, said the study’s lead author, Marcus Lofverstrom.

“The problem is we don’t know where those ice sheets (in Scandinavia) came from and what caused them to expand in such a short amount of time,” said Lofverstrom, an assistant professor of geosciences and head of the UArizona Earth System Dynamics Lab.

To find answers, Lofverstrom helped develop an extremely complex Earth-system model, known as the Community Earth System Model, which allowed his team to realistically recreate the conditions that existed at the beginning of the most recent glacial period. Notably, he expanded the ice-sheet model domain from Greenland to encompass most of the Northern Hemisphere at high spatial detail. Using this updated model configuration, the researchers identified the ocean gateways in the Canadian Arctic Archipelago as a critical linchpin controlling the North Atlantic climate and ultimately determining whether or not ice sheets could grow in Scandinavia.

The simulations revealed that as long as the ocean gateways in the Canadian Arctic Archipelago remain open Earth’s orbital configuration cooled the Northern Hemisphere sufficiently to allow ice sheets to build up in Northern Canada and Siberia, but not in Scandinavia.

In a second experiment the researchers simulated a previously unexplored scenario in which marine ice sheets obstructed the waterways in the Canadian Arctic Archipelago. In that experiment, the comparatively fresh Arctic and North Pacific water – typically routed through the Canadian Arctic Archipelago – was diverted east of Greenland, where deep water masses typically form. This diversion led to a freshening and weakening of the North Atlantic deep circulation, sea ice expansion, and cooler conditions in Scandinavia.

“Using both climate model simulations and marine sediment analysis, we show that ice forming in northern Canada can obstruct ocean gateways and divert water transport from the Arctic into the North Atlantic,” Lofverstrom said, “and that in turn leads to a weakened ocean circulation and cold conditions off the coast of Scandinavia, which is sufficient to start growing ice in that region.”

“These findings are supported by marine sediment records from the North Atlantic, which show evidence of glaciers in northern Canada several thousand years before the European side,” said Diane Thompson, assistant professor in the UArizona Department of Geosciences. “The sediment records also show compelling evidence of a weakened deep ocean circulation before the glaciers form in Scandinavia, similar to our modeling results.”

Together, the experiments suggest that the formation of marine ice in northern Canada may be a necessary precursor to glaciation in Scandinavia, the authors write.

Pushing climate models beyond their traditional application of predicting future climates provides an opportunity to identify previously unknown interactions in the Earth system, such as the complex and sometimes counterintuitive interplay between ice sheets and climate, Lofverstrom said.

“It is possible that the mechanisms we identified here apply to every glacial period, not just the most recent one,” he said. “It may even help explain more short-lived cold periods such as the Younger Dryas cold reversal (12,900 to 11,700 years ago) that punctuated the general warming at the end of the last ice age.”

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As of 2019, the The University of Arizona enrolled 45,918 students in 19 separate colleges/schools, including The University of Arizona College of Medicine in Tucson and Phoenix and the James E. Rogers College of Law, and is affiliated with two academic medical centers (Banner – University Medical Center Tucson and Banner – University Medical Center Phoenix). The University of Arizona is one of three universities governed by the Arizona Board of Regents. The university is part of the Association of American Universities and is the only member from Arizona, and also part of the Universities Research Association . The university is classified among “R1: Doctoral Universities – Very High Research Activity”.

Known as the Arizona Wildcats (often shortened to “Cats”), The University of Arizona’s intercollegiate athletic teams are members of the Pac-12 Conference of the NCAA. The University of Arizona athletes have won national titles in several sports, most notably men’s basketball, baseball, and softball. The official colors of the university and its athletic teams are cardinal red and navy blue.

After the passage of the Morrill Land-Grant Act of 1862, the push for a university in Arizona grew. The Arizona Territory’s “Thieving Thirteenth” Legislature approved The University of Arizona in 1885 and selected the city of Tucson to receive the appropriation to build the university. Tucson hoped to receive the appropriation for the territory’s mental hospital, which carried a $100,000 allocation instead of the $25,000 allotted to the territory’s only university Arizona State University was also chartered in 1885, but it was created as Arizona’s normal school, and not a university). Flooding on the Salt River delayed Tucson’s legislators, and by the time they reached Prescott, back-room deals allocating the most desirable territorial institutions had been made. Tucson was largely disappointed with receiving what was viewed as an inferior prize.

With no parties willing to provide land for the new institution, the citizens of Tucson prepared to return the money to the Territorial Legislature until two gamblers and a saloon keeper decided to donate the land to build the school. Construction of Old Main, the first building on campus, began on October 27, 1887, and classes met for the first time in 1891 with 32 students in Old Main, which is still in use today. Because there were no high schools in Arizona Territory, the university maintained separate preparatory classes for the first 23 years of operation.


The University of Arizona is classified among “R1: Doctoral Universities – Very high research activity”. UArizona is the fourth most awarded public university by National Aeronautics and Space Administration for research. The University of Arizona was awarded over $325 million for its Lunar and Planetary Laboratory (LPL) to lead NASA’s 2007–08 mission to Mars to explore the Martian Arctic, and $800 million for its OSIRIS-REx mission, the first in U.S. history to sample an asteroid.

National Aeronautics Space Agency OSIRIS-REx Spacecraft.

The LPL’s work in the Cassini spacecraft orbit around Saturn is larger than any other university globally.

National Aeronautics and Space Administration/European Space Agency [La Agencia Espacial Europea][Agence spatiale européenne][Europäische Weltraumorganisation](EU)/ASI Italian Space Agency [Agenzia Spaziale Italiana](IT) Cassini Spacecraft.

The University of Arizona laboratory designed and operated the atmospheric radiation investigations and imaging on the probe. The University of Arizona operates the HiRISE camera, a part of the Mars Reconnaissance Orbiter.

U Arizona NASA Mars Reconnaisance HiRISE Camera.

NASA Mars Reconnaissance Orbiter.

While using the HiRISE camera in 2011, University of Arizona alumnus Lujendra Ojha and his team discovered proof of liquid water on the surface of Mars—a discovery confirmed by NASA in 2015. The University of Arizona receives more NASA grants annually than the next nine top NASA/JPL-Caltech-funded universities combined. As of March 2016, The University of Arizona’s Lunar and Planetary Laboratory is actively involved in ten spacecraft missions: Cassini VIMS; Grail; the HiRISE camera orbiting Mars; the Juno mission orbiting Jupiter; Lunar Reconnaissance Orbiter (LRO); Maven, which will explore Mars’ upper atmosphere and interactions with the sun; Solar Probe Plus, a historic mission into the Sun’s atmosphere for the first time; Rosetta’s VIRTIS; WISE; and OSIRIS-REx, the first U.S. sample-return mission to a near-earth asteroid, which launched on September 8, 2016.

NASA – GRAIL Flying in Formation (Artist’s Concept). Credit: NASA.
National Aeronautics Space Agency Juno at Jupiter.

NASA/Lunar Reconnaissance Orbiter.


NASA Parker Solar Probe Plus named to honor Pioneering Physicist Eugene Parker. The Johns Hopkins University Applied Physics Lab.
National Aeronautics and Space Administration Wise/NEOWISE Telescope.

The University of Arizona students have been selected as Truman, Rhodes, Goldwater, and Fulbright Scholars. According to The Chronicle of Higher Education, UArizona is among the top 25 producers of Fulbright awards in the U.S.

The University of Arizona is a member of the Association of Universities for Research in Astronomy , a consortium of institutions pursuing research in astronomy. The association operates observatories and telescopes, notably Kitt Peak National Observatory just outside Tucson.

National Science Foundation NOIRLab National Optical Astronomy Observatory Kitt Peak National Observatory on Kitt Peak of the Quinlan Mountains in the Arizona-Sonoran Desert on the Tohono O’odham Nation, 88 kilometers (55 mi) west-southwest of Tucson, Arizona, Altitude 2,096 m (6,877 ft). annotated.

Led by Roger Angel, researchers in the Steward Observatory Mirror Lab at The University of Arizona are working in concert to build the world’s most advanced telescope. Known as the Giant Magellan Telescope (CL), it will produce images 10 times sharper than those from the Earth-orbiting Hubble Telescope.

GMT Giant Magellan Telescope(CL) 21 meters, to be at the Carnegie Institution for Science’s NOIRLab NOAO Las Campanas Observatory(CL), some 115 km (71 mi) north-northeast of La Serena, Chile, over 2,500 m (8,200 ft) high.

The telescope is set to be completed in 2021. GMT will ultimately cost $1 billion. Researchers from at least nine institutions are working to secure the funding for the project. The telescope will include seven 18-ton mirrors capable of providing clear images of volcanoes and riverbeds on Mars and mountains on the moon at a rate 40 times faster than the world’s current large telescopes. The mirrors of the Giant Magellan Telescope will be built at The University of Arizona and transported to a permanent mountaintop site in the Chilean Andes where the telescope will be constructed.

Reaching Mars in March 2006, the Mars Reconnaissance Orbiter contained the HiRISE camera, with Principal Investigator Alfred McEwen as the lead on the project. This National Aeronautics and Space Agency mission to Mars carrying the UArizona-designed camera is capturing the highest-resolution images of the planet ever seen. The journey of the orbiter was 300 million miles. In August 2007, The University of Arizona, under the charge of Scientist Peter Smith, led the Phoenix Mars Mission, the first mission completely controlled by a university. Reaching the planet’s surface in May 2008, the mission’s purpose was to improve knowledge of the Martian Arctic. The Arizona Radio Observatory , a part of The University of Arizona Department of Astronomy Steward Observatory , operates the Submillimeter Telescope on Mount Graham.

University of Arizona Radio Observatory at NOAO Kitt Peak National Observatory, AZ USA, U Arizona Department of Astronomy and Steward Observatory at altitude 2,096 m (6,877 ft).

Kitt Peak National Observatory in the Arizona-Sonoran Desert 88 kilometers 55 mi west-southwest of Tucson, Arizona in the Quinlan Mountains of the Tohono O’odham Nation, altitude 2,096 m (6,877 ft)

The National Science Foundation funded the iPlant Collaborative in 2008 with a $50 million grant. In 2013, iPlant Collaborative received a $50 million renewal grant. Rebranded in late 2015 as “CyVerse”, the collaborative cloud-based data management platform is moving beyond life sciences to provide cloud-computing access across all scientific disciplines.

In June 2011, the university announced it would assume full ownership of the Biosphere 2 scientific research facility in Oracle, Arizona, north of Tucson, effective July 1. Biosphere 2 was constructed by private developers (funded mainly by Texas businessman and philanthropist Ed Bass) with its first closed system experiment commencing in 1991. The university had been the official management partner of the facility for research purposes since 2007.

U Arizona mirror lab-Where else in the world can you find an astronomical observatory mirror lab under a football stadium?

University of Arizona’s Biosphere 2, located in the Sonoran desert. An entire ecosystem under a glass dome? Visit our campus, just once, and you’ll quickly understand why The University of Arizona is a university unlike any other.

University of Arizona Landscape Evolution Observatory at Biosphere 2.