10. december 2008

‘The Modern Age’ is defined by Danish ice core research

Denmark is now the holder of the international standard reference, which precisely defines when the ice age ends and the modern age begins. The answer lies in the ice cores from the NorthGRIP drilling in Greenland. Researchers from the Niels Bohr Institute at the University of Copenhagen have analysed these ice cores and found that there was an abrupt climate change from the ice age to the modern age. This means that the ice age did not, as believed until now, end around 11.000 years ago – no, it ended 11.711 years ago.

How long is a meter? – how much does a kilo weight? – how long is a second? Yes, if it was not for a standard size for the units of measurement, it could vary a great deal depending on who measured or weighed something. That is why international standard sizes have been implemented, which all measuring instruments in the world should be calibrated to. For example, the standard for a kilogram is in Paris.

The yardstick of the age
But there are other standards, which require international agreement. The earth’s geological ages are important to map life and events in the earth’s history. The geological ages are the ‘yardstick of the age’, which is defined by the transition from one state of the planet to another.

The transition can be seen in geological deposits – for example the transition from the Cretaceous Period, where the dinosaurs die out – to the Tertiary Period, where the mammals gain ground. This happened very suddenly 65 million years ago and this is seen very clearly in deposits, where the layers change from being chalk stratum to stratum of clay. A place where this can be seen clearly is in Morocco and it is there that the international standard is fixed, but we also see it in Denmark at Stevns Cliff.

The transition from the ice age to the modern has however lacked a clearly defined date. It took a long process over several thousand years to warm up the earth and melt the kilometre thick ice caps that covered large parts of the northern hemisphere. So when precisely did the cold ice age end and the warm modern age begin?

Archive of the climate of the past
Usually, one finds the answer in geological deposits, where sediments and traces of the biological life change. But suddenly one found the answer in a completely different place – in the ice cores from the NorthGRIP drilling in Greenland.

The three kilometre thick ice cap is like an archive of the climate of the past. The ice is formed by snow that year after year remains and is gradually compressed into ice and the annual layers of ice are analysed at a very high resolution for a number of substances, which each in their own way tell something about the climate.

“Our new, extremely detailed data from the examination of the ice cores shows that in the transition from the ice age to our current warm interglacial period the climate shift is so sudden that it is if a button was pressed”, explains ice core researcher Jørgen Peder Steffensen, Centre for Ice and Climate at the Niels Bohr Institute at the University of Copenhagen.

Jørgen Peder Steffensen is one of the experts in an international forum of geologists and ice core researchers who study the annual layers in sediments in the seabed, deposits on land and in the earth’s thick ice caps in order to map and coordinate the layers.

Also in the group is Professor Mike Walker from Lampeter University in Wales, UK and Jørgen Peder Steffensen tells that when Mike Walker saw the results from the ice cores he exclaimed, “This is just the type of date we geologists need for a clear definition of the transition from the Pleistocene (meaning past) to the Holocene (meaning present)”.

Mike Walker was then responsible for getting the ice cores from Greenland recognised as the international standard for fixing the date for the end of the ice age and the beginning of our current warm modern age, which geologically is called the Holocene. The final decision has now been made in the International Commission on Stratigraphy, which has approved the ice cores from Greenland.

“It is the first time an ice core has been used as an international standard reference for a geological age and it is a great recognition of our extremely detailed scientific data”, explains Jørgen Peder Steffensen.

The official layer, which marks the start of the warm modern age, the Holocene, lies in the ice core from NorthGRIP at a depth of 1492,45 meters. This layer consists of snow, which according to the dating fell 11.703 years before the year 2000.

Watch the program in KU videoportal, NBI NEWS: GOLDEN SPIKE IN ICE CORE

Publikation: Episodes Vol 31. N0.2 Juni 2008. Af Mike Walker et al.

Ratification from International Commission on Stratigraphy:

Geological timetabel with 'golden nails':

Link: https://www.iceandclimate.nbi.ku.dk/publications/papers/