Written by Sean Beckwith, PhD student
ST. PETERSBURG, FL – Since she was an undergraduate, Amelia Shevenell has been interested in how ocean and atmospheric temperatures influence Antarctica’s ice sheets in the distant and not-so-distant past.
For at least 34 million years, Antarctica has been partially or completely covered in ice. Plate tectonics positioned Antarctica over the pole more than 65 million years ago, and drove India, Australia, and South America northward during the breakup of the supercontinent, Gondwana. This tectonic break-up formed the Southern Ocean, which encircles Antarctica. The Antarctic Circumpolar Current now mostly isolates Antarctica from heat derived from lower latitudes, but not completely. South of the Polar Front, warm nutrient-rich waters formed in northern latitudes upwell, bringing heat to Antarctica’s ice sheets. Both modern and geologic observations indicate to Dr. Shevenell that oceanic and atmospheric warming influences Antarctica’s ice sheet stability.
NSF funded research aboard the US ice-breaker R/V Nathaniel B. Palmer in 2014 is yielding new information on the role of ocean and atmospheric temperatures on East Antarctica’s ice sheet evolution.
By studying the marine geologic record close to Antarctica’s ice sheets, researchers seek to understand the mechanisms by which glaciers retreat when climates were as warm or warmer than present. During the 2014 expedition to the Sabrina Coast, East Antarctica, Shevenell and her collaborators discovered that the East Antarctic Ice Sheet is more sensitive to climate changes than previously thought. This is important because global sea level would rise 53 meters (174 feet) if the East Antarctic Ice Sheet melted completely. More realistically, ice melt from the most sensitive regions of East Antarctica could raise global sea levels ~19 meters (~60 feet). Glaciers along the Sabrina Coast are presently retreating and could contribute 3–5 meters (9–16.5 feet) of global sea level rise in a warming world.
Shevenell, USF graduate students, and collaborators collected evidence that ice expanded to the Sabrina Coast in the early-to-middle Eocene, much earlier than is traditionally accepted. They discovered deep channels carved into sediments and evidence for least 11 glacial advances and retreats across the continental shelf. These results indicate variability of regional glaciers may have been enhanced by large amounts of meltwater during the Oligocene and Miocene, geologic times when climate was warmer and atmospheric CO2 higher than at present. About seven million years ago as global climates cooled, regional glaciers expanded, stabilized, and were not influenced by meltwater. These results indicate that the East Antarctic Ice Sheet has long responded to climate variability. If meltwater increases as with continued warming, Antarctica’s ice sheets might respond more dynamically than expected.
In early 2018, Dr. Shevenell will return to Antarctica aboard the International Ocean Discovery Program (IODP) drillship, the JOIDES Resolution. Dr. Shevenell and her USF CMS Ph.D. student, Imogen Browne, will work with an international team of scientists to drill sites in the Ross Sea, which will enhance understanding of Antarctica’s ice sheet evolution over the past 20 million years. This cruise is particularly exciting because Dr. Shevenell has worked for over a decade on proposing and planning this Expedition.
As researchers explore Antarctica, more data is generated that can be plugged into ice and climate models to improve our collective understanding of ice sheet response to ongoing warming. Model improvements will ultimately enable scientists to make accurate estimates of regional sea level rise, which are critical to policy makers, particularly those in low-lying regions, such as Tampa Bay.