High-resolution aerosol concentration data from the Greenland NorthGRIP and NEEM deep ice cores

Records of chemical impurities from ice cores enable us to reconstruct the past deposition of aerosols onto polar ice sheets and alpine glaciers. Through this they allow us to gain insight into changes of the source, transport and deposition processes that ultimately determine the deposition flux at the coring location. However, the low concentrations of the aerosol species in the ice and the resulting high risk of contamination pose a formidable analytical challenge, especially if long, continuous and highly resolved records are needed. Continuous flow analysis, CFA, the continuous melting, decontamination and analysis of ice-core samples has mostly overcome this issue and has quickly become the de facto standard to obtain high-resolution aerosol records from ice cores after its inception at the University of Bern in the mid-1990s. Here, we present continuous records of calcium (Ca2+), sodium (Na+), ammonium (NH+4), nitrate (NO-3) and electrolytic conductivity at 1 mm depth resolution from the NGRIP (North Greenland Ice Core Project) and NEEM (North Greenland Eemian Ice Drilling) ice cores produced by the Bern Continuous Flow Analysis group in the years 2000 to 2011 (Erhardt et al., 2021). Both of the records were previously used in a number of studies but were never published in full 1 mm resolution. Alongside the 1 mm datasets we provide decadal averages, a detailed description of the methods, relevant references, an assessment of the quality of the data and its usable resolution. Along the way we will also give some historical context on the development of the Bern CFA system. The data is available in full 1 mm and 10-year-averaged resolution on PANGAEA (https://doi.org/10.1594/PANGAEA.935838, Erhardt et al., 2021

The effect of age and unilateral leg immobilisation for 2 weeks on substrate ulilisation during moderate-intensity exercise in human skeletal muscle

Age and inactivity have been associated with intramuscular triglyceride (IMTG) accumulation. Here, we attempt to disentangle these factors by studying the effect of 2 weeks of unilateral leg immobilization on substrate utilization across the legs during moderate-intensity exercise in young (n = 17; 23 ± 1 years old) and older men (n = 15; 68 ± 1 years old), while the contralateral leg served as the control. After immobilization, the participants performed two-legged isolated knee-extensor exercise at 20±1W(_50% maximalwork capacity) for 45 min with catheters inserted in the brachial artery and both femoral veins.Biopsy samples obtained from vastus lateralis muscles of both legs before and after exercise were used for analysis of substrates, protein content and enzyme activities. During exercise, leg substrate utilization (respiratoryquotient) did not differ between groups or legs. Leg fatty acid uptake was greater in older than in young men, and although young men demonstrated net leg glycerol release during exercise, older men showed net glycerol uptake. At baseline, IMTG, muscle pyruvate dehydrogenase complex activity and the protein content of adipose triglyceride lipase, acetyl-CoA carboxylase 2 and AMP-activated protein kinase (AMPK)γ3 were higher in young than in older men. Furthermore, adipose triglyceride lipase, plasma membrane-associated fatty acid binding protein and AMPKγ3 subunit protein contents were lower and IMTG was higher in the immobilized than the contralateral leg in young and older men. Thus, immobilization and age did not affect substrate choice (respiratory quotient) during moderate exercise, but the whole-leg and molecular differences in fatty acid mobilization could explain the age- and immobilization-induced IMTG accumulation

Lithium in Greenland ice cores measured by ion chromatography

Abstract: Ion chromatography is a widely used technique to analyse ice cores for ions like Na+, NH4+, K+, Mg++, Ca++, F-, MSA-, Cl-, NO3- and SO4-- that are present in polar ice cores at ppb level. By using sample preconcentration and an optimised separation technique we have been able to detect Li+ in ice core samples in concentrations as low as 0.0001 meq·kg-1 or 0.7 ppt by ion chromatography. During routine analysis of ions in ice cores, the lithium content has been evaluated and recorded. The IC technique used in these measurements and some exemplary IC data from the GRIP (Greenland Ice Core Project) and the NGRIP (North Greenland Ice Core Project) ice cores will be presented. By these data we introduce Li+ concentration as a new parameter in the analysis of ice cores.Like other ions Li+ reflects climatic changes and shows seasonal cycles. On the basis of the geochemistry of lithium we suggest that Li+ measured in the Greenland ice cores is derived from mineral dust. However data from the NGRIP ice core that represents the 8.2 ka BP Holocene cold event show a strong Li+ signal that does not correlate with any other ionic component measured. This means that the lithium content in ice cores is a signal with its own pattern, which is not yet understood

Seasonal variability in ice crystal properties at NorthGRIP. A case study around 301 m depth

The aim of this case study is to quantify the seasonal variability in crystal properties, and to discuss the reason for the variability. A continuous 1.10 m long vertical thin section profile covering approximately five annual cycles has been obtained from the NorthGRIP ice core at around 301 m depth. The crystal outline and the c-axis orientation of more than 13k crystals in the profile have been measured on a new Australian automated ice crystal analyzer. In 2.5 cm resolution we observe a strong seasonal variability in crystal areas of more than 30 % deviation from the average value of 6.7 mm2. Each year, a band of smaller crystals is observed in ice deposited during springtime. The area distribution function is found to be close to a log normal distribution. The crystal areas are compared to the concentration of chemical impurities in the ice; at a 5 cm resolution, the best correlation is found with the concentration of Ca2+. Our results show no seasonal variability of the average c-axis orientation of ice crystals