The Eemian interglacial period occurred between 130,000 and 115,000 years ago. Previous attempts to extract an ice core from this time period have been unsuccessful, but scientists in Greenland have recently been successful. The North Greenland Eemian Ice Drilling (NEEM) team, extracted an ice core from the Northern Greenland ice sheet and were able to analyze atmospheric changes during this time using air bubbles frozen in the ice. Using stable water isotopes, the data reveal that surface temperatures at NEEM peaked at 8 ± 4°C above the mean of the past millennium during the Eemian interglacial period, followed by gradual cooling (Dahl-Jenson et al. 2013). The scientists also found that between 128,000 and 122,000 years ago the thickness of the ice decreased by 400 ± 250 meters, reaching surface elevations of 130 ±300 meters below present levels. Furthermore, melting and movement patterns of ice before the Eemian interglacial period indicate that significant melting and refreezing events occurred during these years.¾Olivia Jacobs
Neem Community Members, 2013. Eemian interglacial reconstructed from a Greenland
folded ice core. Nature 493, 489–494.
At the North Greenland Eemian Ice Drilling (NEEM) site, Dahl-Jenson et al.extracted a 2,540-meter ice core from the Greenland glacier between 2008 and 2012. Using this ice core, they were able to extract air bubbles trapped inside and analyze them based on their isotopic properties. The scientists also used a radio echo sounding (RES) imaging technique to map previous flow patterns and surface temperatures of the Greenland ice sheet to get a more complete picture of temperatures and glacial melt during the Eemian interglacial period.
Data from the ice core showed significant spikes in the levels of CH4, d15N, d18Oatm, and N2O, and a drop in the d18Oicelevels between depths of 2,370 and 2,418 meters. These changing levels of atmospheric isotopes correspond to the time of the Eemian interglacial period, and are furthermore all associated with global temperature rise. The largest spike in CH4 occurred 128,000 years ago, which indicates that temperatures peaked around this time. Also at these depths, the air content levels in the ice increased significantly, which points to melting and refreezing events near the surface of the glacier. Using these data, the scientists calculated a surface temperature change of +7.5 ± 1.8°C at the depositional site compared to the previous millennium.
The RES data also reveal significant folding patterns during the Eemian interglacial period, which agrees with the NEEM ice core’s data from the time period. The radar’s images show continuous and undisturbed internal layers to depths of 2,200 meters in the NEEM region. Below 2,200 meters, however, significant folding and overturning patterns due to glacial movement occurred in the ice, making it fuzzy and more difficult to interpret. The NEEM data verify these findings, as they appear to be too disturbed at depths below 2,450 meters to reconstruct temperature data. Also, the RES images show that Eemian ice contains much larger crystals than glacial ice, which is another indicator of warming and refreezing during this time period.
Dahl-Jenson et al. concluded that over the course of 6,000 years, between 128,000 years ago and 122,000 years ago, surface elevation decreased from 210 ± 350 above to 130 ± 300 meters below present surface elevations. When adjusted for isostatic rebound, the overall change in glacial elevation was calculated to be 400 ± 350 meters. The Eemian interglacial period saw a sea level change of 4–8 meters, and the NEEM data predict a contribution to sea level change of about two meters from the Greenland ice sheet. This indicates that Antarctica must have contributed significantly to global sea level change during this time period.
Recent observations made in 2012 indicate strong patterns of melt at the NEEM site and parallel many changes found in the ice core from the Eemian interglacial period. Few melt layers were found before 1995 but they have increased significantly since then, and in July 2012 a large heat wave caused surface melt over 97% of the Greenland ice sheet. The 2010–12 annual surface temperatures have been recorded as 1–2°C above the 1950–80 average, and Dahl-Jenson et al. estimated a temperature change of 8 ±4°C warmer than the average of the recent millennium during the Eemian interglacial period. While this is a much greater change than what is currently being observed, similar melt patterns to those of the Eemian period have been detected and surface melt is likely to become more common in the future.