The West Antarctic Ice Sheet: ancient origins and present-day relevance

Drilling a bedrock core in West Antarctica. Credit: David Sugden.

One century after the excruciating expedition of endurance led by Sir Ernest Shackleton across the entire Antarctic continent, a new era of heroic Antarctic exploration may have dawned. A team of researchers from the University of Edinburgh and Northumbria University  have ventured to West Antarctica to complete a new study. The group set out to examine the geological and topographical history of the ice sheet perforated by the remote Ellsworth Mountain range: no easy task, considering that temperatures typically average around -30°C.

The focus was to determine the age of the ‘trimline’ – the highest edge cut by past glaciers – in order to establish the circumstances of the ice sheet’s origins and how it has changed over millions of years. The team employed various techniques in order to date the exposed rock area, including ground penetrating radar, a ground-based sonar system for measuring depth; and cosmogenic nuclide analysis, used to date rocks via rare isotopes formed after rock’s exposure to cosmic rays. After scouring the mountainous region for two-metre rock core samples, which were taken via a backpack-mounted drill, analysis revealed the past fluctuations in glacial cover.

The trimline of the Ellsworth Mountain range was dated to approximately 14 million years ago, even though the last glacial maximum (LGM) – the last period of time when Earth’s ice sheets were at their greatest extension – also covered the rock around 24,500 BCE. This means that the great Western Ice Sheet may have expanded in the middle of the Miocene era (between 23 and 5 million years ago). The Antarctic environment at that point would be comparable to the current climates of Greenland or Patagonia, some 20-23°C warmer than today. Based on the findings of this study, lead scientist, Professor David Sugden of the University of Edinburgh’s School of GeoSciences, theorises that this trimline may also represent the greatest period of expansion for the West Antactic Ice Sheet, at a time when beetle species and plant life thrived in the mountains. However, since this great expansion, the study found that the ice sheet has remained fairly stable, because the old rock formations are so well preserved.

Pinnacles and spires on the Ellsworth Mountains, West Antarctica. Credit: George Denton.

This central region of the West Antarctic Ice Sheet does not appear to be at significant risk of shifting in climate or ecology any time soon. Although this may sound like good news, the same may not be said for the ice sheets surrounding the Antarctic coast, around which levels of sea ice were seen to be at a new record low earlier this year. These concerns fall in line with previous observations made by Professor Sugden and his team of the potential loss of peripheral ice sheet during interglacial periods.These observations were supported by marine ecological evidence: most notably, similarities of octopus and other invertebrate species between the Ross Sea (of the Pacific Ocean) and Wedell Sea (of the Atlantic Ocean).  “I’m  very concerned that we may be beyond the tipping-point,” Professor Sugden confirmed. “A sea level rise of up to 3.5 metres in the next two centuries may be inevitable”.

In discussing the importance of the findings of this study, Professor Sugden said: “These findings help us understand how the Antarctic Ice Sheet has evolved, and to fine-tune our models and predict its future. The preservation of old rock surfaces is testimony to the stability of at least the central parts of the Antarctic Ice Sheet – but we are still very concerned over other parts of Antarctica amid climate change.” To predict the effects of such change upon global sea levels, climate and ecology on the continent, sophisticated modelling techniques are employed. However, scientific models are only as accurate as their creators are informed, and are required to work under certain assumptions. This study has generated vital data to inform these simulations to better predict future ice sheet behaviour and the accompanying consequences.

 

This article was written by Jack Kellard and edited by Bonnie Nicholson.

One thought on “The West Antarctic Ice Sheet: ancient origins and present-day relevance

  1. Jack

    Corrigendum: I would like to make clear that the article above does not suggest that Shackleton’s expedition of 1917 was successful, and in fact they were beleaguered for many months after the loss of their ship to the ice in 1915.

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