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Stable water isotope record from block profiles Chli-Titlis_Profile1
No full textStable water isotope record from block profiles Chli-Titlis_Profile
Stable water isotope record from block profiles in the ice tunnel at Chli Titlis glacier, Switzerland
No full textCold glaciers at the highest locations of the European Alps have been investigated by drilling ice cores to retrieve their stratigraphic climate records. Findings like the Oetztal ice man have demonstrated that small ice bodies at summit locations of comparatively lower altitudes may also contain old ice if locally frozen to the underlying bedrock. In this case, constraining the maximum age of their lowermost ice part may help to identify past periods with minimum ice extent in the Alps. However, with recent warming and consequent glacier mass loss, these sites may not preserve their unique climate information for much longer. Designed as a case study for investigating the maximum age of cold-based summit glaciers in the Alps, we utilized here an existing ice cave at Chli Titlis (3030 m), Central Switzerland. The cave offers direct access to the glacier stratigraphy without the logistical effort required in ice core drilling. In addition, a pionieering exploration had already demonstrated stagnant cold ice conditions at Chli Titlis, albeit more than 25 years ago. Our englacial temperature measurements and the analysis of the isotopic and physical properties of ice blocks sampled at three locations within the ice cave show that cold ice still exists fairly unchanged today. State-of-the-art micro-radiocarbon analysis constrains the maximum age of the ice at Chli Titlis to about 5000 years before present. By this means, the approach presented here will contribute to a future systematic investigation of cold-based summit glaciers, also in the Eastern Alps
Stable water isotope measured on CG ice core
No full textThe Colle Gnifetti record represents the stack of four cores (KCH, KCS, KCI and CC)
Stable water isotope measured on CDD ice core
No full textStable water isotope measured on CDD ice cor
Annual means of delta 18O time series Colle Gnifetti ice core CC
No full textAnnual means of delta 18O time series Colle Gnifetti ice core C
Annual means of delta 18O time series Colle Gnifetti ice cores
No full textAmong Alpine ice core drilling sites, the Colle Gnifetti glacier saddle situated in the Monte Rosa summit range is the only one whose net snow accumulation rate is low enough to offer climate records back to some 1000 yr. It is demonstrated that the strong snow erosion at this site particularly hampers the interpretation of stable water isotope records d18O, dD in terms of atmospheric temperature changes. We evaluate the d18O records from four Colle Gnifetti cores for their common variability to extract a composite isotope record that may be compared with the instrumental temperature evidence. Time series analyses over the last 120 yr reveal that the common d18O signal is mainly reflected in the low frequency variability, starting at the decadal scale. Comparing the correspondingly smoothed composite record to the high-elevation temperature time series (specifically adjusted to the seasonality of the net snow accumulation) reveals the following findings: On the decadal scale, the isotope variability correlates with the temperature record at around R=0.65 but is interrupted by three, ca. 10-yr long mismatch periods. The multidecadal isotope signal closely reflects the strong overall 20th century temperature increase, thereby showing an up to three-fold higher isotope temperature sensitivity than commonly assumed. Over the entire instrumental period back to 1760, five more such mismatch periods are embedded in the generally coherent pattern of the d18O and instrumental temperature records (including the strong overestimate of the temperature around 1850 by the isotope temperature proxy). For the early instrumental period (1890-1760) characterized by a comparably weak long-term temperature trend, the isotope signal generally suggests warmer conditions of about 0.4°C compared to instrumental data
Stable water isotope measured on Col du Dôme and Colle Gnifetti ice cores
No full textIn the European Alps, ice core studies have been mainly performed in view of the recent man-made influence on the atmospheric load of aerosol-related species, while respective investigations on the pre-industrial aerosol or on stable water isotope-based climate records remained sparse. We address from a glaciological perspective the specific conditions of Alpine drilling sites and, in particular, the role of depositional noise. Thereby, we refer to two major drilling areas (located in the summit range of Monte Rosa and Mt Blanc massif, respectively) which largely differ in their snow accumulation rate and, hence, in their accessible time scale. A simple scheme considering the seasonality of both, the precipitation-borne signal and the snow erosion-controlled net accumulation rate is presented. It shows that water isotope trends are generally more sensitive to distortion by a seasonality effect than recent snow impurities trends, although the influence of a given seasonal accumulation rate cycle on the mean levels of water isotopes and impurities is similar. These findings are illustrated on the decadal and centennial time scale by the inter- and intra-site variability of major ion and water isotope records. The intra-site comparison includes the discussion of strong water isotope depletions seen some meters above bedrock at low accumulation drilling sites
Seismic data from Colle Gnifetti glacie saddle around borehole KCI, Swiss Alps
No full textTwo seismic surveys were carried out on the high-altitude glacier saddle, Colle Gnifetti, Monte Rosa, Italy/Switzerland. Explosive and vibroseismic sources were tested to explore the best way to generate seismic waves to deduce shallow and intermediate properties (<100 m) of firn and ice. The explosive source (SISSY) excites strong surface and diving waves, degrading data quality for processing; no englacial reflections besides the noisy bed reflector are visible. However, the strong diving waves are analyzed to derive the density distribution of the firn pack, yielding results similar to a nearby ice core. The vibrator source (ElViS), used in both P- and SH-wave modes, produces detectable laterally coherent reflections within the firn and ice column. We compare these with ice-core and radar data. The SH-wave data are particularly useful in providing detailed, high-resolution information on firn and ice stratigraphy. Our analyses demonstrate the potential of seismic methods to determine physical properties of firn and ice, particularly density and potentially also crystal-orientation fabric
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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