Ice on Greenland ~20 million years earlier than previously thought – 0/2/07
The Earth had glaciers in parts of the northern hemisphere as far back as 38 million years ago, much earlier than was previously thought
That is the conclusion of scientists at the National Oceanography Centre, Southampton (NOCS), reported online by Nature magazine this week.
The research indicates for the first time that there was glacial ice, probably of restricted extent, on Greenland during a time when CO2 levels are thought to have been significantly higher than pre-industrial values: the findings therefore have implications for our understanding of future climate change in an increasingly CO2-rich world. The next task is to investigate ice extent and stability during this geological analogue for the future.
The Earth went through a profound change in climate during the transition between the Eocene and Oligocene periods (around 34 million years ago) when the Antarctic ice sheets expanded to close to their modern size. But the existence of northern polar ice had only previously been demonstrated back to the Miocene period (around 15 million years ago).
The new research provides evidence for an earlier development of northern hemisphere ice, linked to glaciers on East Greenland which are identified as the likely source of `ice-rafted’ debris found in sediments drilled from the Norwegian-Greenland Sea and dated as being between 38 and 30 million years old.
The debris consists of pebbles and mineral grains showing characteristic surface features indicating that they were frozen into glacial ice which subsequently calved as icebergs at the coast. Then, as the icebergs melted, the rock debris was shed into the water column and subsequently incorporated in seafloor sediments. Surface textures and size distributions indicate that the ice-rafted debris was glacial in origin (melted from continental ice) rather than shed from sea ice.
James Eldrett, Ian Harding, Paul Wilson, Emily Butler and Andrew Roberts, all of the University of Southampton’s School of Ocean and Earth Science, which is based at NOCS, used ice-rafted debris (IRD) analysis, photographic, electron microscopic, geochemical and rock magnetic techniques in their research which was partially funded by the Natural Environment Research Council.
