Specific conductivity and hydrogen ions measured on two ice core (NEEM and NGRIP)

A stratigraphy-based chronology for the North Greenland Eemian Ice Drilling (NEEM) ice core has been derived by transferring the annual layer counted Greenland Ice Core Chronology 2005 (GICC05) and its model extension (GICC05modelext) from the NGRIP core to the NEEM core using 787 match points of mainly volcanic origin identified in the electrical conductivity measurement (ECM) and dielectrical profiling (DEP) records. Tephra horizons found in both the NEEM and NGRIP ice cores are used to test the matching based on ECM and DEP and provide five additional horizons used for the timescale transfer. A thinning function reflecting the accumulated strain along the core has been determined using a Dansgaard-Johnsen flow model and an isotope-dependent accumulation rate parameterization. Flow parameters are determined from Monte Carlo analysis constrained by the observed depth-age horizons. In order to construct a chronology for the gas phase, the ice age-gas age difference (Delta age) has been reconstructed using a coupled firn densification-heat diffusion model. Temperature and accumulation inputs to the Delta age model, initially derived from the water isotope proxies, have been adjusted to optimize the fit to timing constraints from d15N of nitrogen and high-resolution methane data during the abrupt onset of Greenland interstadials. The ice and gas chronologies and the corresponding thinning function represent the first chronology for the NEEM core, named GICC05modelext-NEEM-1. Based on both the flow and firn modelling results, the accumulation history for the NEEM site has been reconstructed. Together, the timescale and accumulation reconstruction provide the necessary basis for further analysis of the records from NEEM.

Dome C age scale EDC1 for ice core EDC99

A tentative age scale (EDC1) for the last 45 kyr is established for the new 788 m EPICA Dome C ice core using a simple ice flow model. The age of volcanic eruptions, the end of the Younger Dryas event, and the estimated depth and age of elevated 10Be, about 41 kyr ago were used to calibrate the model parameters. The uncertainty of EDC1 is estimated to ±10 yr for 0 to 700 yr BP, up to ±200 yr back to 10 kyr BP, and up to ±2 kyr back to 41 kyr BP. The age of the air in the bubbles is calculated with a firn densification model. In the Holocene the air is about 2000 yr younger than the ice and about 5500 yr during the last glacial maximum.

Continuous density log of icecore BER11C95_25

A 181 m long ice core was drilled at 79° 36' 51'' S, 45° 43' 28'' W, near the summit of Berkner Island, Antarctica 886 m a.s.l.). Berkner Island is located within the Filchner and Ronne Ice Shelves, and the ice near the summit shows little lateral flow. The density of the ice core was measured every 3 mm along ist length, using attenuation of a gamma-ray beam, which gave an absolute accuracy of 2%. As expected, there is a general density increase with depth, the maximum densities of > 900 kg/m**3 being reached just above 100 m depth. Comparison with electrical conductivity method (ECM) shows density variations with the same wavelength as annual signals, which can be seen in the ECM log (higher acidity during summer). In the shallowest part of the core, the density of winter layers is higher than that of summer layers, a relationship which is reversed at greater depth. We assume that the densification rates for the two types of firn are different. Similar density phenomena were observed on ice cores from Greenland, showing that such phenomena are not a local effect.