Climate patterns originating in the tropics, particularly in the Pacific and Indian oceans, help determine how much snow falls each year on the West Antarctic Ice Sheet, according to a study published by researchers at the University of Utah.

The study, based on 25 ice cores spanning 1900 to 1999, found that the ice sheet’s eastern sector gained snow over the 20th century while its western sector lost it, with the two regions responding differently to the same distant weather systems.

“Our biggest takeaway was the influence of the tropics on snowfall in Antarctica. Rossby waves can affect temperature, winds and precipitation across the globe,” said Ella Hunter, a graduate student in atmospheric sciences at the University of Utah and first author of the paper, published in the Journal of Geophysical Research: Atmospheres on May 16, according to the University of Utah.

Tropical convection tied to phenomena such as El Niño and the Madden-Julian Oscillation generates storms that send atmospheric ripples known as Rossby waves, named for meteorologist Carl-Gustaf Rossby, toward the South Pole, altering wind patterns and storm tracks over Antarctica, Hunter said.

“Tropical convection or heating in the tropics from sea surface temperatures can create storms that propagate these Rossby waves. And they are really effective at transporting heat and moisture down to the Antarctic ice sheet.”

Two ice sheets in one

The West Antarctic Ice Sheet covers 760,000 square miles with an average thickness of 3,400 feet, and would raise global sea levels by more than 15 feet if it melted entirely, according to the University of Utah. The published study states the ice sheet’s volume equates to 5.3 meters of potential global sea-level rise.

Researchers found the eastern part of the ice sheet received about 350 millimeters of water equivalent in snow per year on average, twice the roughly 175 millimeters recorded in the west. Over the century studied, surface mass balance in the east increased at a rate of 0.224 millimeters of water equivalent per year, while it decreased in the west by 0.087 millimeters per year, Hunter said.

Snowfall was higher in parts of West Antarctica associated with high atmospheric pressure, a pattern that initially puzzled Courtenay Strong, a professor of atmospheric sciences at the University of Utah who led the research team, until Hunter traced the mechanism through different levels of the atmosphere.

“Ella did some really helpful detective work by looking at different levels in the atmosphere. She found the pattern at the bottom, essentially showing storm systems headed toward the region end up getting deflected inland by that ridge of high pressure. That’s what brings higher snowfall to that part of West Antarctica.”

Ice cores as weather stations

The cores used in the study, each 5 centimeters in diameter, were drawn from the top 50 meters of the ice sheet using a portable drill, then cut into 1-meter sections for analysis, according to Summer Rupper, a geography professor at the university’s School of Environment, Society & Sustainability who extracted some of the cores during field trips to Antarctica in 2010 and 2011 and is a co-author of the study.

Rupper said conventional weather stations cannot survive Antarctica’s conditions, making the shallow cores a substitute record of the region’s recent climate.

“You can’t keep weather stations maintained. They just get buried by snow. They get blown over. We think about the deep cores, but these shallow cores are essentially filling the gaps of weather stations. Without them, we wouldn’t have any knowledge of the weather of that system.”

Rupper said the study’s approach of combining multiple cores let researchers examine year-to-year swings in snowfall rather than only long-term trends. “What’s unique about this study is leveraging all these cores together to look more carefully at the drivers of the variability, not just the trends. We tend to focus on the trends, but variability matters a lot for ice sheet stability,” she said.

The research, funded by the National Science Foundation with additional support from the U.S. Department of Energy’s Biological and Environmental Research program, the National Oceanic and Atmospheric Administration’s Climate Program Office and its Physical Sciences Laboratory, also included University of Utah graduate students Christopher Mitchell and Joey Kruger and former postdoctoral researcher Husile Bai, now an assistant professor at Vanderbilt University.