Study Offers New Insights into Deep History of Mid-Miocene Antarctic Ice Sheet

In March 2021, the average concentration of atmospheric carbon dioxide (CO₂) increased to around 418 ppm, a level not observed on Earth for several million.

Researchers have been analyzing the deep history to predict how the future might be.

A new study by researchers from the University of Massachusetts Amherst integrates ice sheet, climate and vegetation model simulations with a range of various geologic and climatic scenarios to offer the clearest insights thus far into the deep past of the Antarctic ice sheet and what could be the future of the planet.

The Antarctic ice sheet has gained specific attention from the scientific community since it is “a lynchpin in the earth’s climate system, affecting everything from oceanic circulation to climate,” stated Anna Ruth Halberstadt, a PhD candidate in geosciences and the lead author of the study, which was recently published in the Earth and Planetary Science Letters journal.

The ice sheet comprises enough frozen water to elevate current sea levels by 57 m.

But it has been hard to re-build the mid-Miocene Antarctic climate precisely. Although scientists can run models, without the help of geologic data to verify the models against, it is hard to select which simulation is right. On the other hand, they can infer from geologic data, but these data points provide only local snapshots, not a broader climatic context.

We need both models and geologic data to know anything at all. Without knowing the elevation it’s difficult to interpret the geologic record.

Anna Ruth Halberstadt, Study Lead Author and PhD Candidate in Geosciences, University of Massachusetts Amherst

One last complicating factor exists: geology. The Transantarctic Mountains divides Antarctica into two, and any evident picture of Antarctica’s deep past should be able to explain the slow uplift of the mountain range of the continent.

Halberstadt together with her collaborators, including scientists from both the United Kingdom and New Zealand, developed a special method that involves combining an ice sheet model with a climate model while simulating the kinds of vegetation that would grow under every climatic model scenario.

The research team made use of the historical geologic datasets that contained well-known paleoclimatic data points like glacial proximity, vegetation, and past temperature to benchmark their modeled climates.

Then, they employed their measured model runs to find which CO₂ and tectonic model scenarios met the known geologic constraints. Lastly, Halberstadt and her collaborators extrapolated continent-wide glacial conditions.

Supported by the NSF, the researchers re-built a thick but reduced ice sheet under the warmest mid-Miocene environmental conditions. In this model, the margins of Antarctica’s ice sheet had retreated considerably, but higher precipitation resulted in a thickening of the interior regions of the ice sheet.

The researchers’ modeling indicates that ice over Antarctica’s Wilkes Basin region advanced at the time of glacial periods and retreated during interglacials. The Wilkes Basin is the region that is believed to be especially sensitive to future warming and might contribute to sea-level rise in the future.

Antarctica’s paleoclimate is fundamental to understanding the future.

Anna Ruth Halberstadt, Study Lead Author and PhD Candidate in Geosciences, University of Massachusetts Amherst

Journal Reference:

Halberstadt, A. R. W., et al. (2021) CO₂ and tectonic controls on Antarctic climate and ice-sheet evolution in the mid-Miocene. Earth and Planetary Science Letters. doi.org/10.1016/j.epsl.2021.116908.