Retrieving a common accumulation record from Greenland ice cores for the past 1800 years

Abstract. In the accumulation zone of the Greenland ice sheet the annual accumulation rate may be determined through identification of the annual cy-cle in the isotopic climate signal and other parameters that exhibit seasonal vari-ations. On an annual basis the accumulation rate in different Greenland ice cores is highly variable, and the degree of correlation between accumulation series from different ice cores is low. However, when using multi year averages of the dif-ferent accumulation records the correlation increases significantly. A statistical model has been developed to estimate the common climate signal in the differ-ent accumulation records through optimization of the ratio between the variance of the common signal and of the residual. Using this model a common Green-land accumulation record with five years resolution for the past 1800 years has been extracted. The record establishes a climatic record which implies that very dry conditions during the 13th century together with dry and cold spells dur-ing the 14th century may have put extra strain on the Norse population in Green-land and have contributed to their extinction

A first chronology for the East Greenland Ice-core Project (EGRIP) over the Holocene and last glacial termination

This paper provides the first chronology for the deep ice core from the East Greenland Ice-core Project (EGRIP) over the Holocene and the late last glacial period. We rely mainly on volcanic events and common peak patterns recorded by dielectric profiling (DEP) and electrical conductivity measurement (ECM) for the synchronization between the EGRIP, North Greenland Eemian Ice Drilling (NEEM) and North Greenland Ice Core Project (NGRIP) ice cores in Greenland. We transfer the annual-layer-counted Greenland Ice Core Chronology 2005 (GICC05) from the NGRIP core to the EGRIP ice core by means of 381 match points, typically spaced less than 50 years apart. The NEEM ice core has previously been dated in a similar way and is only included to support the match-point identification. We name our EGRIP timescale GICC05-EGRIP-1. Over the uppermost 1383.84 m, we establish a depth–age relationship dating back to 14 967 years b2k (years before the year 2000 CE). Tephra horizons provide an independent validation of our match points. In addition, we compare the ratio of the annual layer thickness between ice cores in between the match points to assess our results in view of the different ice-flow patterns and accumulation regimes of the different periods and geographical regions. For the next years, this initial timescale will be the basis for climatic reconstructions from EGRIP high-resolution proxy data sets, e.g. stable water isotopes, chemical impurity or dust records

GRIP ice core detailed water isotope (δ18O) data

The ice core was drilled during the GRIP project in 1989-1992 at the Summit of the Greenland ice sheet. The length is 3025 m. Present-day accumulation 0.23 m ice/yr. Position 72.57N 37.62W, 3232 m a.s.l.. Data from the top 101.3 m comes from the S3 shallow core, but the two data sets have been fully integrated on a common depth scale. The delta-18O data were all measured immediately after the drilling (1989-90). The delta-18O data uncertainty is 0.1 per mil. All samples are cut in 2.5cm depth resolution and sample depths are for the bottom of each sample. As diffusion in the firn and snow degrade the annual signal, the data are also provided in a deconvoluted version that seeks to correct for this effect. Following the approach of S.J. Johnsen, the deconvolution uses an adaptive cut-off frequency permitting a fixed maximimum amplification (50) of the spectral components in the original data

DYE-3 4B ice core detailed water isotope data

The shallow core 4B was drilled to 174 m 8 km upstream from DYE-3 (DYE-3 main core position: 65.18N, 43.83W). The exact position is not available. The delta-18O data were all measured immediately after the 1983 drilling operation. The delta-18O data uncertainty is 0.1 per mil. The samples are cut to achieve an average resolution of 8 samples per year, i.e. the depth resolution increases with depth (as annual layers thin). All sample depths are for the bottom of each sample

DYE-3 ice core detailed water-isotope data

The detailed water isotope data consists of 2 sections of delta-18O data and 2 sections of delta-D data. The cores was drilled to bedrock 1979-1981 during the GISP program. Position: 65.18N, 43.83W, 2480 m a.s.l.. The delta-18O data were all measured immediately after the drilling (1979-81), while the delta-D data were measured in 2004 specifically for the GICC05 dating effort. The delta-18O data uncertainty is 0.1 per mil, while the delta-D data uncertainty is 0.5 per mil. All sections are cut to achieve an average resolution of 8 samples per year, i.e. the depth resolution increases with depth (as annual layer thicknesses thin). The cutting scale for the d18O data generally produced a higher resolution than intended, while the delta-D cutting scale was adjusted to be more precise in achieving 8 samples per year. All sample depths are given for the bottom of each sample