The analysis of microfossils found in ocean sediment cores is illuminating the environmental conditions that prevailed at high latitudes during a critical period of Earth history.
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 separation of Eurasia and Greenland due to shifting tectonic plates led to the partial or complete submergence of former land barriers such as the Vring Plateau of the Norwegian continental margin. For the first time, waters could exchange between the NorwegianGreenland Sea, the Arctic Ocean and the North Atlantic.
Dr Harding and his former PhD student Dr James Eldrett have reconstructed the environmental conditions over the Vring Plateau over this time period by carefully analysing the fossilised remains of organic debris and cysts of tiny aquatic organisms called dinoflagellates from sediment cores.
"Because different dinoflagellate species are adapted to different surface water conditions, their fossilised remains help us reconstruct past environments," said Dr Harding.
The evidence from the sediments cores suggests the development of shallow marine environments across parts of the Vring Plateau during the early Eocene. However, the presence of fossilised species that lived in fresh or brackish water indicates that northerly pa
|Contact: Dr Rory Howlett|
National Oceanography Centre, Southampton (UK)