AMHERST, Mass. – A new study of past conditions on the East Antarctic Ice Sheet suggests the region may again add to significant worldwide sea level rise with continued global warming, say geologist Reed Scherer and colleagues at Northern Illinois University. Their research used state-of-the-art climate and ice sheet models developed by Robert DeConto at the University of Massachusetts Amherst and David Pollard at Penn State.
In the current issue of Nature Communications, Scherer, DeConto and colleagues report that they have discovered new evidence that helps to settle a decades-long disagreement among climate scientists about the stability of the East Antarctic Ice Sheet during the Pliocene, three million years ago, and what the presence of diatoms and algae fossils at high altitude today says about past climate conditions there.
After microscopic marine fossils called diatoms were discovered about 30 years agoat high altitudes in the Transarctic Mountains on the edge of the world’s largest ice sheet, some climate researchers said this showed that the ice sheet retreated and sea level rose at least once in the Pliocene. They said that higher seas allowed marine algae and diatoms to accumulate in central Antarctica, eventually to be pushed up into the mountains by a regrowing ice sheet. Others said the diatoms were more likely transported from the seacoast by strong winds.
The new investigation suggests both views offer partial answers to the question. Scherer, DeConto and colleagues found that the diatoms were likely blown into the mountains by strong winds that occurred at the same time significant ice sheet melting was taking place. The retreating ice first exposed deep basins on the edges of the continent, and as the marine basins rose above sea-level to become land, thousands of years after the ice retreated, diatoms once deposited on the sea-floor became exposed to strong Antarctic winds blowing in the direction of the mountains.
The authors believe theirs is the first published study to relate the fossil data directly to the ice sheet’s size in that epoch. DeConto, who last month received the Tinker-Muse Prize, a top international honor in Antarctic research, says the findings support the idea that parts of the East Antarctic Ice Sheet, a significant factor in sea-level risebecause it holds most of the world’s fresh water, are vulnerable to retreat and partial collapse with relatively modest future warming.
For this work supported by the National Science Foundation, the researchers used ice sheet and climate models and found the ice sheet experienced a series of retreats and re-advances during Pliocene warm periods. While these retreats were not as dramatic as some had predicted, Scherer’s team reports they were significant enough to open bays in the sea with good conditions for plankton diatoms to flourish. The retreats also removed the weight of ice, allowing land and once-submerged diatoms to rise above sea level over time. Wind then picked up the diatoms and deposited them across the Transantarctic Mountains.
Many scientists consider that climate conditions during the Pliocene warm periods and sea-level rise may be an indicator of what could be in store for Earth in coming decades as the climate warms. Scherer says, “During certain intervals of Pliocene warmth, the sea level could have been as much as 75 feet higher than it is now.”
He adds, “This latest work, together with other recent ice sheet modeling studies by DeConto and Pollard, clearly demonstrates the sensitivity of modern ice sheets to warming. No model is ever perfect, but these scientists use sophisticated physics and the latest data to produce atmospheric and ice models that are truly state-of-the-art, providing a picture of the past and glimpse into our future.”
For the future, Scherer points out, “The question is always how quickly could sea levels rise, and we’re probably looking at several hundred years into the future before reaching a peak high that matches the Pliocene, but the problem of progressive sea-level rise is already upon us. The DeConto-Pollard models assume we continue to burn fossil fuels at the current pace. If we make improvements for the better, ice sheet reduction could be significantly delayed. We’d still have a problem, but we could keep the sea-level rise small and slow.”