A first chronology for the North Greenland Eemian Ice Drilling (NEEM) ice core

摘要

A stratigraphy-based chronology for the North Greenland Eemian Ice Drilling(NEEM) ice core has been derived by transferring the annual layer countedGreenland Ice Core Chronology 2005 (GICC05) and its model extension(GICC05modelext) from the NGRIP core to the NEEM core using 787 match pointsof mainly volcanic origin identified in the electrical conductivitymeasurement (ECM) and dielectrical profiling (DEP) records. Tephra horizonsfound in both the NEEM and NGRIP ice cores are used to test the matchingbased on ECM and DEP and provide five additional horizons used for the timescale transfer.A thinning function reflecting the accumulated strain along the core hasbeen determined using a Dansgaard–Johnsen flow model and anisotope-dependent accumulation rate parameterization. Flow parameters aredetermined from Monte Carlo analysis constrained by the observed depth-agehorizons.In order to construct a chronology for the gas phase, the ice age–gas agedifference (Δage) has been reconstructed using a coupled firndensification-heat diffusion model. Temperature and accumulation inputs tothe Δage model, initially derived from the water isotope proxies, havebeen adjusted to optimize the fit to timing constraints from δ15Nof nitrogen and high-resolution methane data during the abrupt onset ofGreenland interstadials.The ice and gas chronologies and the corresponding thinning functionrepresent the first chronology for the NEEM core, namedGICC05modelext-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 basisfor further analysis of the records from NEEM.