Environment Counts | The Eemian Grail: Greenland ice core records for the last interglacial may help us understand present day sea level rise
Author: Geoff Zeiss – Published At: 2012-09-01 02:40 – (1310 Reads)
There is a gap in all ice-core records in Greenland corresponding to the last interglacial, called the Eemian, which extended from 130,000 to 114,000 years ago. Greenland temperatures were about 3-5Â°C warmer higher than at present during the Eemian, making the Eemian a possible useful analogue to the future climate, which is projected to warm by 2-4Â°C. Model calculations have suggested that the volume of the Greenland ice sheet might have been 30â€“60% smaller than the present-day volume. However, to date the ice core record from Greenland ice drilling programs have not been able to retrieve a complete, undisturbed ice core record for the Eemian. By August 2011 a new drilling project NEEM had retrieved 2.5 km of ice cores including 150 m of ice from the Eemian period. Unfortunately the layer sequence was found to be broken and the hope of finding an undisturbed layer sequence of Eemian ice was not fulfilled. However, the NEEM experimental observations together with airborne radar surveys may allow us to better estimate the extent and depth of the the Greenland ice sheet during the Eemian and its contribution to the rise in sea levels, which could give an indication of what we might expect in the next 100 years as the climate warms. North Greenland Eemian Ice Drilling (NEEM) 2012
The Eemian was the last interglacial period prior to the current Holocene interglacial. Greenland temperatures were about 3-5Â°C warmer higher than at present during the Eemian, making the Eemian a useful analogue to the future climate, which is projected to warm by 2-4Â°C per century.
However, to date the ice core record from Greenland ice drilling programs have not been able to retrieve a complete, undisturbed ice core record for the Eemian. None of the the ice core records from previous drilling programs (Camp Century, DYE-3, GRIP, GRIP2, or NGRIP) contains complete and undisturbed layers from the Eemian, because the layers have either melted or have been disturbed by ice flow close to the bedrock.
The Greenland Ice Sheet Project Two (GISP2,) hit bedrock in July 1993, and recovered an ice core 3053.44 meters in depth.
The Greenland Ice Core Project (GRIP) project retrieved a 3000m long ice core drilled through the Greenland ice sheet at its highest point, Summit in 1989 to 1992. In both GISP2 and GRIP, analysis of the ice cores revealed that layers corresponding to the Eemian had been disturbed by ice flow close to the bedrock.
The lack of undisturbed Eemian ice in the summit area of the Greenland ice sheet as shown by the GISP2 and GRIP projects motivated a search for a new drill site where deep layers were undisturbed. From radio echo sounding measurements a site to the north and west of Summit was selected for the North GReenland Ice core Project(NGRIP)
The NGRIP project began in 1996 and extended until 2004 when bedrock was reached. Disappointingly, due to unforeseen melting at the bedrock only the most recent part of the Eemian was able to be retrieved. The earlier Eemian ice had melted away, apparently from geothermal heating.
To summarize Eemian ice is present but highly garbled in the Summit (GISP2 and GRIP) cores, and incomplete due to basal melting in the NGRIP core.
The goal of retrieving a complete Eemian ice core profile from Greenland prompted the search for a new site with undisturbed deep layers and without significant basal melting. The North EEMian (NEEM) project started in 2007, when tracked vehicles brought equipment from the previous drill site, NGRIP, to the NEEM drill site. The majority of the ice core drilling took place during the summers of 2009-2011.
By August 2011 ice cores had been retrieved for the 2.5 km thick ice sheet. Most importantly, the NEEM ice core contains more that 150 m of ice from the Eemian period and more than 100 m of ice from the previous ice age below the Eemian layer.
Unfortunately, detailed measurements show that the layer sequence above and below the Eemian ice is broken. The hope of finding an undisturbed layer sequence of Eemian ice in the NEEM ice core was not fulfilled.
However, it is hoped that the NEEM ice core, along with the other ice cores (Camp Century, DYE-3, GRIP, GRIP2, or NGRIP), will aid in the interpretation of airborne radar measurements to determine the extent and thickness of the Greenland ice sheet during the Eemian. This could provide a basis for estimating what the Greenland Ice Sheet contributed to the rise in sea levels during the previous interglacial and will suggest what we might expect in sea level rise in the next 100 years as the Earth’s temperature rises to the level experienced during the Eemian.