082 Deep Freezes: Drilling for Earth's Climate Archive

What this episode covers

Given that the coldest ever land temperature was recorded in Antarctica (−89.2°C at Russia’s Vostok Station in 1983), it can be hard to imagine Antarctica as a warm, temperate paradise. But Antarctica hasn’t always been an icy land locked in the grip of a massive ice sheet. In fact, Antarctica was once almost as warm as Melbourne is today. Researchers have estimated that 40-50 million years ago, temperatures in Antarctica reached up to 17°C. Scientists have also found fossils showing that Antarctica was once covered with verdant green forests and inhabited by dinosaurs! Ice sheets have one particularly special property. They allow us to go back in time and to sample accumulation, air temperature and air chemistry from another time. Ice core records allow us to generate continuous reconstructions of past climate, going back at least 800,000 years. By looking at past concentrations of greenhouse gasses in layers in ice cores, scientists can calculate how modern amounts of carbon dioxide and methane compare to those of the past, and, essentially, compare past concentrations of greenhouse gasses to temperature. The large Greenland and Antarctic ice sheets have huge, high plateaux where snow accumulates in an ordered fashion. Slow ice flow at the center of these ice sheets (near the ice divide) means that the stratigraphy of the snow and ice is preserved. Drilling a vertical hole through this ice involves a serious effort involving many scientists and technicians and usually involves a static field camp for a prolonged period of time. Shallow ice cores (100-200 m long) are easier to collect and can cover up to a few hundred years of accumulation, depending on accumulation rates. Deeper cores require more equipment, and the borehole must be filled with drill fluid to keep it open. The drilling fluid used is normally a petroleum-derived liquid like kerosene. It must have a suitable freezing point and viscosity. Collecting the deepest ice cores (up to 3000 m) requires a (semi)permanent scientific camp and a long, multi-year campaign. Ice cores from Greenland and Antarctica are mainstays of modern climate science. Traditionally, scientists drill in places where ice layers accumulate year after year, undisturbed by glacial flows. The long layer cake records from deep sites in the center of Antarctica reveal how greenhouse gases have surged and ebbed across hundreds of thousands of years. But because heat from the bedrock below can melt the deepest, oldest ice, the approach has not yielded ice any older than 800,000 years, from a core drilled at Antarctica’s Dome C in 2004. Scientists from Princeton University retracted an ice core drilled in Antarctica that has yielded 2.7-million-year-old ice, an astonishing find 1.7 million years older than the previous record-holder. Bubbles in the ice contain greenhouse gases from Earth’s atmosphere at a time when the planet’s cycles of glacial advance and retreat were just beginning, potentially offering clues to what triggered the ice ages. That information alone makes the value of the sample incredible. [U794u53qxugp27yz581iEvyq2brib2or8wot34d]