Around 55 million years ago at the beginning of the Eocene epoch, the Earth's poles are believed to have been free of ice. But by the early Oligocene around 25 million years later, ice sheets covered Antarctica and continental ice had developed on Greenland.
"This change from greenhouse to icehouse conditions resulted from decreasing greenhouse gas concentrations and changes in Earth's orbit," said Dr Ian Harding of the University of Southampton's School of Ocean and Earth Science (SOES) at the National Oceanography Centre, Southampton (NOCS): "However, the opening or closing of various marine gateways and shifts in ocean currents may also have influenced regional climate in polar high-latitudes."
The evidence from the sediments cores suggests the development of shallow marine environments across parts of the Vøring Plateau during the early Eocene. However, the presence of fossilized species that lived in fresh or brackish water indicates that northerly parts of the plateau as well as the crest of the Vøring Escarpment were still above water.
In the late Eocene sediments (around 44 million years old) only marine plankton species were found, indicating that the entire Vøring Plateau had by then subsided and become submerged. This demonstrates that marine connections were established between the various Nordic sea basins much earlier than had previously been thought. These surface water connections may have promoted the increased surface water productivity evidenced by the abundance of planktonic fossils preserved in the sediment cores of this age.
"Increased productivity would have drawn carbon dioxide down from the atmosphere," said Dr Harding: "Because carbon dioxide is a greenhouse gas, this may have contributed to declining global temperatures and led to the early development of continental ice on Greenland in the latest Eocene."
Citation: Eldrett, J. S.&Harding, I. C. 'Palynological analyses of Eocene to
Oligocene sediments from DSDP Site 338, Outer Vøring Plateau', Marine Micropaleontology, 2009, 73, 226-240