Studying the response of Antarctic ice sheets to past warming episodes is essential to understand how they may respond to the present warming climate, as their melting and collapse can contribute to global sea level rise. Detailed records of past ocean temperatures close to the continent are rare, but clues to how ice sheets and sea ice responded to global conditions in the past can be found in funny places — even in the remains of animals that once lived there. A study led by the University of Maine used the presence (and eventual lack thereof) of elephant seals to illustrate how the area transformed in a warm period in the recent past.
A team of researchers led by Brenda Hall, professor at the University of Maine School of Earth and Climate Science, and Climate Change Institute, studied the remains of the southern elephant seal at sites along the Victoria Land Coast of the Ross Embayment, which borders both the West and East Antarctic ice sheets.
Today, the Victoria Land Coast is largely free of elephant seals and even penguins in many places because of shelves of permanent sea ice frozen to its beaches. Besides, modern elephant seals are based largely on subantarctic islands north of the Ross Sea. Past UMaine research, however, uncovered elephant seal remains in the beaches suggesting the species flourished in the area during warm periods of the Holocene. They theorized that the seals were able to occupy the beaches in a period of warmth before extensive sea ice pushed them off of the present-day coast.
For this study, the scientists gathered the mummified and skeletal remains of elephant seals, as well as their molted skin, buried under rocks and snow banks along the Victoria Land Coast, ultimately recovering 305 samples, which they radiocarbon dated and tested for ancient DNA
“Southern elephant seals today tend to haul out in much warmer areas than the Ross Sea,” Hall says. “We were able to use the presence of their molted skin and hair, as well as some bones and mummies desiccated by the polar wind, to show that these seals had once made the Ross Sea their home.”
The results from the molted skin, bones and other remains showed that southern elephant seals not only once occupied the Ross Sea, but were present on the Victoria Land Coast from about 7,000 and 500 years ago. The presence of the seals at this time indicated that there was a reduced amount of ice covering the sea during this time of the Holocene, which coincides with other records of ocean temperatures and circulation in the Ross Sea.
“Our work shows that for much of the Holocene, the Ross Sea was less icy and presumably warmer than it is today and this warmth may have driven retreat of the West Antarctic Ice Sheet from the Ross Sea during the last 8000 years and future warming could continue to push ice retreat,” Hall says. “However, ocean temperature may not be the entire story.”
More research is needed, but the scientists also found a few elephant seals that dated to a much older period just before the last glacial maximum, which suggests that warm water may have existed during the buildup of the ice sheet in the Ross Sea. If the presence of warm ocean temperatures immediately prior to and perhaps even during build-up to the Last Glacial Maximum ice position could be confirmed, it would suggest that factors other than a drop in ocean temperatures, such as lowered sea level, might have been critical in causing ice-sheet advance in the Ross Embayment.
The study was published online Feb. 7, and will be in the March 2023 edition of the journal Quaternary Science Reviews.