Simultaneous stable isotope analysis of methane and nitrous oxide on ice core samples

Methane and nitrous oxide are important greenhouse gases which show a strong increase in atmospheric mixing ratios since pre-industrial time as well as large variations during past climate changes. The understanding of their biogeochemical cycles can be improved using stable isotope analysis. However, high-precision isotope measurements on air trapped in ice cores are challenging because of the high susceptibility to contamination and fractionation. Here, we present a dry extraction system for combined CH4 and N2O stable isotope analysis from ice core air, using an ice grating device. The system allows simultaneous analysis of δD(CH4) or δ13C(CH4), together with δ15N(N2O), δ18O(N2O) and δ15N(NO+ fragment) on a single ice core sample, using two isotope mass spectrometry systems. The optimum quantity of ice for analysis is about 600 g with typical "Holocene" mixing ratios for CH4 and N2O. In this case, the reproducibility (1σ ) is 2.1‰ for δD(CH4), 0.18‰ for δ13C(CH4), 0.51‰ for δ15N(N2O), 0.69‰ for δ18O(N2O) and 1.12‰ for δ15N(NO+ fragment). For smaller amounts of ice the standard deviation increases, particularly for N2O isotopologues. For both gases, small-scale intercalibrations using air and/or ice samples have been carried out in collaboration with other institutes that are currently involved in isotope measurements of ice core air. Significant differences are shown between the calibration scales, but those offsets are consistent and can therefore be corrected for.

[Assessment of proliferation: core biopsy or resection specimen? Discrepancies in breast cancer with low and high proliferation]

The assessment of the proliferation fraction is becoming more and more important; however, there is no consensus concerning optimal validation. Depending on the institute the proliferation fraction is determined either from a core biopsy (SB) or resection specimen (OP).

Validity and responsiveness of the Core Outcome Measures Index (COMI) for the neck

Patient-orientated outcome questionnaires are essential to evaluate treatment success. To compare different treatments, hospitals, and surgeons, standardised questionnaires are required. The present study examined the validity and responsiveness of the Core Outcome Measurement Index for neck pain (COMI-neck), a short, multidimensional outcome instrument.

Duration of Greenland Stadial 22 and ice-gas Δage from counting of annual layers in Greenland NGRIP ice core

High-resolution measurements of chemical impurities and methane concentrations in Greenland ice core samples from the early glacial period allow the extension of annual-layer counted chronologies and the improvement of gas age-ice age difference (Δage) essential to the synchronization of ice core records. We report high-resolution measurements of a 50 m section of the NorthGRIP ice core and corresponding annual layer thicknesses in order to constrain the duration of the Greenland Stadial 22 (GS-22) between Greenland Interstadials (GIs) 21 and 22, for which inconsistent durations and ages have been reported from Greenland and Antarctic ice core records as well as European speleothems. Depending on the chronology used, GS-22 occurred between approximately 89 (end of GI-22) and 83 kyr b2k (onset of GI-21). From annual layer counting, we find that GS-22 lasted between 2696 and 3092 years and was followed by a GI-21 pre-cursor event lasting between 331 and 369 yr. Our layer-based counting agrees with the duration of stadial 22 as determined from the NALPS speleothem record (3250 ± 526 yr) but not with that of the GICC05modelext chronology (2620 yr) or an alternative chronology based on gas-marker synchronization to EPICA Dronning Maud Land ice core. These results show that GICC05modelext overestimates accumulation and/or underestimates thinning in this early part of the last glacial period. We also revise the possible ranges of NorthGRIP Δdepth (5.49 to 5.85 m) and Δage (498 to 601 yr) at the warming onset of GI-21 as well as the Δage range at the onset of the GI-21 precursor warming (523 to 654 yr), observing that temperature (represented by the δ15N proxy) increases before CH4 concentration by no more than a few decades.

Radiocarbon analysis in an Alpine ice core: Record of anthropogenic and biogenic contributions to carbonaceous Radiocarbon analysis in an Alpine ice core: Record of anthropogenic and biogenic contributions to carbonaceous aerosols in the past (1650-1940)

Long-term concentration records of carbonaceous particles (CP) are of increasing interest in climate research due to their not yet completely understood effects on climate. Nevertheless, only poor data on their concentrations and sources before the 20th century are available. We present a first long-term record of organic carbon (OC) and elemental carbon (EC) concentrations – the two main fractions of CP – along with the corresponding fraction of modern carbon (fM) derived from radiocarbon (14C) analysis in ice. This allows a distinction and quantification of natural (biogenic) and anthropogenic (fossil) sources in the past. CP were extracted from an ice archive, with resulting carbon quantities in the microgram range. Analysis of 14C by accelerator mass spectrometry (AMS) was therefore highly demanding. We analysed 33 samples of 0.4 to 1 kg ice from a 150.5 m long ice core retrieved at Fiescherhorn glacier in December 2002 (46°33'3.2" N, 08°04'0.4" E; 3900 m a.s.l.). Samples were taken from bedrock up to the firn/ice transition, covering the time period 1650–1940 and thus the transition from the pre-industrial to the industrial era. Before ~1850, OC was approaching a purely biogenic origin with a mean concentration of 24 μg kg−1 and a standard deviation of 7 μg kg−1. In 1940, OC concentration was about a factor of 3 higher than this biogenic background, almost half of it originating from anthropogenic sources, i.e. from combustion of fossil fuels. The biogenic EC concentration was nearly constant over the examined time period with 6 μg kg−1 and a standard deviation of 1 μg kg−1. In 1940, the additional anthropogenic input of atmospheric EC was about 50 μg kg−1.

Differential patterns of multisensory interactions in core and belt areas of human auditory cortex

The auditory cortex is anatomically segregated into a central core and a peripheral belt region, which exhibit differences in preference to bandpassed noise and in temporal patterns of response to acoustic stimuli. While it has been shown that visual stimuli can modify response magnitude in auditory cortex, little is known about differential patterns of multisensory interactions in core and belt. Here, we used functional magnetic resonance imaging and examined the influence of a short visual stimulus presented prior to acoustic stimulation on the spatial pattern of blood oxygen level-dependent signal response in auditory cortex. Consistent with crossmodal inhibition, the light produced a suppression of signal response in a cortical region corresponding to the core. In the surrounding areas corresponding to the belt regions, however, we found an inverse modulation with an increasing signal in centrifugal direction. Our data suggest that crossmodal effects are differentially modulated according to the hierarchical core-belt organization of auditory cortex.