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Greenland Ice Cores tell tales on the Eemian Period and beyondDorthe Dahl-JensenDorthe Dahl-Jensen (CV, PDF) The deep NGRIP ice core from North Greenland (75N, 42W) is 3090m deep and reaches 125.000 years back in time. The climate record has an extremely high resolution with annual layers of the order of 1 cm right down to the base because basal melt reduces the thinning of the basal layers. The lowest 60 m of the ice core contains ice from the last interglacial period, the Eemian period (OIS-5e) and it is seen from the stable isotopes that the period was 5 K warmer in Greenland than in our present interglacial period and very stable. The transition to glacial conditions occurred gradually over several thousand years. The NGRIP ice core contains the first undisturbed record of the Eemian period from the North Atlantic region. The NGRIP results thus contribute to a snap shot of the climate during the Eemian period where it is also known that the global sea level was 4-5 m higher than at present. To evaluate the area and volume of the Greenland Ice Sheet during the Eemian period, it is worth noting that we find Eemian ice in the Dye3 ice core in South Greenland, in the central Greenland Ice cores GRIP and GISP2, in NGRIP and in the little 350m thick ice cap, Renland, on the east coast of Greenland. Additional information on the evolution of the Greenland Ice Sheet is found by observing the internal radio echo sounding layers in the ice along the main ice divide on which most of the deep ice core sites are located. A time dependent ice flow model along the divide is used to follow the paths of the ice containing the Eemian ice now found near the base at the boreholes. The model is constrained to match the dated ice from the boreholes and the internal RES layers can follow these layers between the boreholes further constraining the model. It can be concluded that the there was an significant ice sheet covering Greenland during the warm Eemian period and that the reduction of the Greenland ice sheet at most contributed with a sea level rise of 1-2 m of the observed 5 m. Finally studies of DNA from the basal ice from the DYE-3 ice core in south Greenland reveals that Boreal forest covered South Greenland before it was ice covered. Dating of the basal material indicates that the biological material found in the DYE-3 ice core is older than 400.000 years supporting the above conclusion that ice covered south Greenland during the Eemian period. |
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