The Eurasian Arctic During the Last Ice Age
A vast ice sheet once covered the Barents Sea. Its sudden disappearance 100 centuries ago provides a lesson about western Antarctica today
In the 1970s, long before global warming had become much of a public concern, an Ohio State University glaciologist named John Mercer made a disturbing observation. He pointed out that the geography of western Antarctica is strikingly similar to the Eurasian Arctic: Both of these polar regions contain a large continental shelf no more than a few hundred meters deep. The major difference is that western Antarctica has a 2.5-kilometer-thick ice sheet resting on it, whereas the Eurasian Arctic is now comparatively free of grounded ice. Mercer argued that if global warming continued, there was a real threat that the immense ice sheet covering western Antarctica could disintegrate, adding enough water to the ocean to raise sea level by six meters, which would inundate coastlines throughout the world.
Mercer understood the task his observation demanded: To gauge whether the west Antarctic ice sheet is truly in danger of breaking up, scientists must look for clues at the other side of the Earth, in the geological remnants of the former ice sheets that covered northern Eurasia. Many earth scientists took heed and applied their specialties to the investigation, and their work soon began to reveal the glacial history of the Eurasian Arctic. By the mid-1980s, however, the interpretation of the geological observations varied enormously. Whereas some saw evidence for a massive, 3.5-kilometer-thick ice sheet over the whole of northern Europe and Siberia at the height of the last ice age (known to geologists as the Last Glacial Maximum, or LGM), others disputed this appraisal, preferring to believe that there was virtually no ice at all on the seafloor to the north of the Norwegian and Russian mainlands. Contradictory views sparred in the literature. The problem was partly that the geological record in the Arctic can be difficult to read and thus open to misinterpretation. Another obstacle was the paucity of reliable observations from this remote and inhospitable region.
To resolve the issue, the European Science Foundation mounted back-to-back research programs to gather new geological evidence in the vicinity of the former ice sheets in the Eurasian Arctic. These efforts involved more than 50 scientists from seven European countries, including the four of us. The first, dubbed PONAM (for POlar North Atlantic Margins) concentrated on the western side of the Barents Sea. During the follow-up program, named QUEEN (QUaternary Environments of the Eurasian North), the focus shifted east to the Russian Arctic. These efforts provided a great deal of information about the status of northern Eurasia in the Ice-Age world. To grasp the full significance of the results, however, requires that one gain at least a broad understanding of glaciological processes. So here we take a moment to review the basics of how glaciers operate.