Computer modeling study reveals history of global ice sheet evolution

Imagine a huge ice sheet covering Canada and spilling over much of the northern United States, like ice spilling down the side of a cake. That was the situation sometime between 19,000 and 26,000 years ago. Ice sheets covered land as far south as present-day Pennsylvania, Ohio, Indiana, Michigan, and Wisconsin.

It’s interesting to imagine, but what matters to us today is what happened to the land when that ice sheet melted. And how will it affect modern-day sea level rise and land subsidence?

PhD candidate Karen Williams undertook computer modeling research to examine how the Earth would change after the ice melted. With her supervisor, Associate Professor D. Sarah Stamps of the Department of Earth Sciences, and collaborators Daniele Melini of the Italian National Institute of Geography, and Giorgio Spada of the Department of Physics and Astronomy at the University of Bologna, Italy. We collaborated and published the results. was recently published in the Journal of Geophysical Research: Solid Earth.

What they found: ups and downs

Williams used computational modeling to assess the impact of the melting of the Laurentide Ice Sheet on the modern vertical movement of land.

She tested various hypotheses about how the melting of ice sheets would affect the Earth, oceans, and gravitational fields. The scientific term for how the solid Earth responds to this melting is “glacial isostatic adjustment.” Then, through “various assumptions,” they simulated how the results depended on the Earth’s internal structure through nearly 130,000 computational simulations.

“A general pattern of downward movement (causing relative sea level rise) is observed in the eastern region of the United States,” the authors said.

The opposite was true in eastern Canada, where upwelling motion caused a relative sea-level decline.

Why does land rise and fall?

When you compare what the models suggest to what’s happening today, you really begin to understand why land sinks.

Williams said that by getting more accurate model estimates of what is contributing to land uplift or subsidence, “natural and/or anthropogenic factors such as excessive groundwater withdrawal in the Gulf of Mexico and Chesapeake” “We can identify areas undergoing localized vertical displacements caused by the source.” Bay. ”

For example, Stamps notes that “some of the most significant differences between the modeled effects of glacier isostatic adjustment and observed values ​​occur in places where known groundwater extraction exists, such as in Houston, Texas. will occur.”

Helping communities plan

The findings will help create maps for researchers to guide decisions about aquifer management, Williams said. Ultimately, this research will be incorporated into a comprehensive U.S. Geological Survey report to help Chesapeake Bay region stakeholders better understand the economic, ecological, and social impacts of sea level rise. .

“Improved estimates of vertical displacement due to glacier isostatic adjustment allow for more accurate predictions of land subsidence and relative sea level change, which may influence the effects of current coastal disasters,” Williams said. It will help us cope.”