Understanding the temporal variation of cosmic radiation and solar activity during the Holocene is essential for studies of the solar-terrestrial relationship. Cosmic-ray produced radionuclides, such as 10 Be and 14 C which are stored in polar ice cores and tree rings, offer the unique opportunity to reconstruct the history of cosmic radiation and solar activity over many millennia. Although records from different archives basically agree, they also show some deviations during certain periods. So far most reconstructions were based on only one single radionuclide record, which makes detection and correction of these deviations impossible. Here we combine different 10 Be ice core records from Greenland and Antarctica with the global 14 C tree ring record using principal component analysis. This approach is only possible due to a new high-resolution 10 Be record from Dronning Maud Land obtained within the European Project for Ice Coring in Antarctica in Antarctica. The new cosmic radiation record enables us to derive total solar irradiance, which is then used as a proxy of solar activity to identify the solar imprint in an Asian climate record. Though generally the agreement between solar forcing and Asian climate is good, there are also periods without any coherence, pointing to other forcings like volcanoes and greenhouse gases and their corresponding feedbacks. The newly derived records have the potential to improve our understanding of the solar dynamics and to quantify the solar influence on climate.

Abstract.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 DansgaardJohnsen 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 ( age) has been reconstructed using a coupled firn densification-heat diffusion model. Temperature and accumulation inputs to the age model, initially derived from the water isotope proxies, have been adjusted to optimize the fit to timing constraints from δ 15 N 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.

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Abstract. The concept of a positive feedback between ice flow and enhanced melt rates in a warmer climate fuelled the debate regarding the temporal and spatial controls on seasonal ice acceleration. Here we combine melt, basal water pressure and ice velocity data. Using 20 years of data covering the whole ablation area, we show that there is not a strong positive correlation between annual ice velocities and melt rates. Annual velocities even slightly decreased with increasing melt. Results also indicate that melt variations are most important for velocity variations in the upper ablation zone up to the equilibrium line altitude. During the extreme melt in 2012, a large velocity response near the equilibrium line was observed, highlighting the possibility of meltwater to have an impact even high on the ice sheet. This may lead to an increase of the annual ice velocity in the region above S9 and requires further monitoring.

[1] High-resolution density profiles of 16 firn cores from Greenland and Antarctica are investigated in order to improve our understanding of the densification of layered polar firn. A vertical resolution of 1-5 mm enables us to study the detailed densification processes and the evolution of the layering and the resulting variability in density with increasing depth. The densification of layered firn is important for the process of air enclosure in ice and is connected with the observed formation of a nondiffusive zone. Our findings show the following. (1) Mean density profiles, obtained from high-resolution measurements, only partly show clear transitions in densification rate at densities of 550, 730, or 820-840 kg/m 3 , as they are commonly used in literature. (2) The density variability, induced by the layering, shows a similar pattern at all sites: high variabilities at the surface, a rapid drop to a relative minimum in variability at mean density of 600-650 kg/m 3 , followed by a second relative maximum. (3) This leads to increased variability at densities of the firn-ice transition for most of the sites. (4) The variability at the surface decreases with increasing mean annual temperature and accumulation rate, whereas the variability at the firn-ice transition increases. We can exclude a change in local climate conditions as an explanation for the density variability since the firn cores in this study cover a broad range in mean annual temperature, accumulation rate, and age. Overall, high-resolution density profiles deliver a more complex picture of compaction of polar firn as a layered granular medium than has been obtained from mean density profiles in the past.