Alpine Antarctica, before the ice

Deep below the icy surface of East Antarctica lies a mountain range with alpine topography carved by ancient glaciers, a landscape frozen in time for millions of years and rife with clues about the origin and evolution of the world’s largest ice sheet.

Many studies hint that Antarctica’s ice sheet began to form about 34 million years ago (SN: 10/11/08, p. 12), but where that ice sheet originated and how it evolved have long been mysteries. Now, scientists who used ice-penetrating radar to survey a 30-by-30–kilometer area in East Antarctica report in the June 4 Nature that they may have discovered the birthplace of the Antarctic ice sheet.

The area surveyed during two field seasons — the Antarctic summers of 2005 and 2007 — sits more than 4 kilometers above sea level and is known as Dome A, says Simon M. Mudd, a geomorphologist at the University of Edinburgh. Buried far beneath that region’s relatively flat surface, however, lies a chain of peaks called the Gamburtsev Mountains. The new data, the first collected in the region since an aircraft-mounted radar probed the ice nearby in the 1970s, provides the first detailed glimpse at the subglacial topography there, Mudd says. “The topography here is less well known than the surface of Mars,” he notes.

The team’s radar data indicate that the region’s ice-smothered terrain is similar to that seen in the European Alps today, Mudd says. Ice in the surveyed region is between about 1,650 meters and 3,150 meters thick, which makes the tallest peak in this stretch of the Gamburtsevs a little more than 2,400 meters tall. Many of the valleys high on those long-buried peaks have nearly semicircular profiles and steep cliffs at the head of the valley — distinctive signs that the valleys were carved by glacial ice, probably around the time Antarctica first began to cool about 34 million years ago. For those glaciers to have flowed, average summer temperatures at those altitudes must have been at least 3° Celsius, Mudd notes.

As Antarctica cooled even further, mountain glaciers grew, swept downslope and coalesced in valleys already previously carved by major rivers and their tributaries. Over 20 million years, the glaciers that originated in this region thickened and spread into a continent-sized ice sheet, which has swaddled Antarctica — and largely preserved its subglacial topography — for the past 14 million years.

Another team of scientists, including Robin E. Bell, a geophysicist at Columbia University’s Lamont-Doherty Earth Observatory in Palisades, N.Y., has been conducting airborne surveys of East Antarctica as part of the Antarctica’s Gamburtsev Province project. The team’s survey covers about 2 million square kilometers, an area larger than the state of Alaska, and has imaged the complete Gamburtsev range. Data indicate that the entire mountain chain has a remarkably rugged, glacier-scarred topography.

In addition to ice-penetrating radar, the team’s aircraft sported equipment that measured magnetic and gravitational anomalies. Such data will provide Bell and her colleagues with information about the mineral composition of the mountains and the arrangement of tectonic plates in the area.

“Soon we’ll be able to tell the full story of how these mountains formed and how the ice sheet developed,” Bell notes.