The ice sheets on the northern and southern ends of the world are separated by almost an entire Earth, yet they are more closely interconnected than previously thought, according to a new study. Researchers from McGill University and other institutions teamed up to examine how the world’s ice sheets influence each other, publishing their findings in Nature.
They studied the past 40,000 years and found that melting Northern Hemisphere ice, which increased global sea levels, was linked to a retreat of the Southern Hemisphere’s Antarctic ice sheet. Their findings, along with future work on the topic, could lead to climate modeling adjustments geared to improving understanding of the planet’s remaining ice sheets. This is an important issue because these melting ice sheets could have a huge impact on sea-level rise, which will affect coastal cities and low-lying regions around the world.
A link between distant icy poles
The new study reports that during the last Ice Age, as temperatures plunged, water in the Northern Hemisphere froze into land ice. With the water locked in frozen form, global sea levels dropped, enabling the Antarctic ice sheet to expand.
That set into motion a self-reinforcing loop. The ice sheet, as snow accumulated on it, gradually spread out under its weight, expanding the sheet’s surface area. With a larger surface area, more snow accumulated, continuing the cycle and building a massive, kilometers-thick continental glacier.
The process reversed itself when temperatures began to warm during the last deglaciation (approximately 20,000 to 9,000 years ago). Ice in the Northern Hemisphere retreated. Much of it melted back into the ocean, raising global sea levels and causing the Antarctic ice sheet to retreat in turn. Warmer temperatures caused increased melting, and edges of the ice sheet calved into the ocean, floating out to sea to melt.
The findings demonstrate just how closely connected the polar ice caps are, despite their geographic distance. “What was surprising to me is how important this effect is,” says geophysicist and climate scientist Natalya Gomez, lead author on the study and an assistant professor at McGill University’s Department of Earth and Planetary Sciences in Montreal.
The findings also underscore the interconnectedness of the world’s natural systems, which is key for better understanding human-caused climate change, she says: “If you make a change to one part of that system, it could have implications for something very far away.”
A record in rocks thousands of years old
To study the ice sheets, Gomez and her fellow researchers used models and studied a variety of geological records to analyze how ice sheets have influenced each other over the past 40,000 years.
One important geological record is called iceberg-rafted debris – rocks carried out to sea by floating Antarctic ice and eventually dropping to the ocean floor, leaving a record in the sediment that can help scientists unravel the mysteries of the past. “It can tell you when the ice sheet was ejecting lots of icebergs, and when it was not ejecting as many icebergs,” Gomez says. “So it’s sort of a record of the timing and activity of the ice sheet itself.”
Such records show that ice loss since the Last Glacial Maximum (the period approximately 26,000 to 20,000 years ago when ice sheets had the greatest mass during that ice age) hasn’t been smooth and steady. Rather, Gomez’s team found “pulses” of accelerated ice loss, which were more dynamic than scientists previously believed. Knowing about these dynamic pulses will be very helpful in terms of future modeling efforts.
Significance of an interconnected planet
Gomez adds that the new findings will help scientists with future modeling efforts. “It really is an important factor in being able to model,” she says. In order to accurately describe the dynamics of the Antarctic ice sheet, she says, scientists will need to “consider what’s happening all the way on the other side of the world.”
“I think this study is a good example of how the Earth, the Earth’s climate, and the Earth’s sea level and ice sheets – and the atmosphere and the oceans – are all an interconnected system,” says William Lipscomb, senior scientist at the National Center for Atmospheric Research, who was not involved in the Gomez study. “And so the response of the ice sheets depends on what happens to all of Earth’s climate, including the atmosphere, and the ocean, and the solid Earth.”