In glacial periods of the Pleistocene during the last 1.5 million years, icebergs from Antarctica drifted significantly further north than they do today – in some cases close to the southern tip of Africa. This allowed larger amounts of frozen freshwater to reach far into the Atlantic. A recent study by Cardiff University, jointly with experts from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) in Bremerhaven, has shown that this transport of freshwater into the Atlantic may have altered the stratification of the deep water masses, with major consequences for large-scale ocean circulation and the climate at the time.
Core-sample analysis sheds new light on icebergs
As the team describes in an article recently published in Nature, these findings are, on the one hand, based on an extensive analysis of core samples from the deep sea in the southern Atlantic, conducted by a team led by Cardiff University; and on the other, on iceberg simulations run at the AWI. “Using a special ship, sediment cores were drilled at various locations - and then investigated layer by layer,” explains Jens Gruetzner from the AWI, who participated in the eight-week expedition. Core samples from the waters surrounding the Antarctic frequently contain material that originated from the Antarctic continent. The huge glaciers grind away at the bedrock as they gradually slide from the mainland. When the glacier tongues finally reach the ocean, they become thinner towards the tip, increase in flow speed and icebergs break off. These icebergs drift away, carrying the enclosed material – referred to as ice-rafted debris - with them. When an iceberg melts during its journey, the ice-rafted debris sinks and is deposited on the seafloor.