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Andresen C.S.,Geological Survey of Denmark | Straneo F.,Woods Hole Oceanographic Institution | Ribergaard M.H.,Danish Meterological Institute | Bjork A.A.,Center for GeoGenetics | And 7 more authors.
Nature Geoscience | Year: 2012

During the early 2000s the Greenland Ice Sheet experienced the largest ice-mass loss of the instrumental record, largely as a result of the acceleration, thinning and retreat of large outlet glaciers in West and southeast Greenland. The quasi-simultaneous change in the glciers suggests a common climate forcing. Increasing air and ocean temperatures have been indicated as potential triggers. Here, we present a record of calving activity of Helheim Glacier, East Greenland, that extends back to about AD1890, based on an analysis of sedimentary deposits from Sermilik Fjord, where Helheim Glacier terminates. Specifically, we use the annual deposition of sand grains as a proxy for iceberg discharge. Our record reveals large fluctuations in calving rates, but the present high rate was reproduced only in the 1930s. A comparison with climate indices indicates that high calving activity coincides with a relatively strong influence of Atlantic water and a lower influence of polar water on the shelf off Greenland, as well as with warm summers and the negative phase of the North Atlantic Oscillation. Our analysis provides evidence that Helheim Glacier responds to short-term fluctuations of large-scale oceanic and atmospheric conditions, on timescales of 3- 10 years. Source

Andresen C.S.,Geological Survey of Denmark | Sicre M.-A.,French National Center for Scientific Research | Straneo F.,Woods Hole Oceanographic Institution | Sutherland D.A.,University of Oregon | And 4 more authors.
Continental Shelf Research | Year: 2013

Sediment core ER07 from Sermilik Fjord by Helheim Glacier in Southeast Greenland was analyzed for alkenones to document sea surface temperature (SST) changes over the past 100 years. The alkenone SST values, ranging from 8 to 12. °C, contrasts with colder values (0-4. °C) obtained from recent hydrographic surveys inside the fjord. We suggest that advection of allochtonous alkenones produced in the warm Irminger Current waters circulating on the shelf likely accounts for this difference. The temperature range of the alkenone-derived record is similar to in situ observations of 8-11. °C on the shelf just outside Sermilik Fjord, and its variability over the past 100 years resembles the constructed variability over the shelf using remote instrumental data. This suggests that oceanographic changes on the adjacent shelf are linked to regional changes of the Irminger Current and the East Greenland Current. The subsurface water heat content has previously been suggested as an important control on Greenland outlet glacier stability and underlined by an episode of warm subsurface waters ~1940 concurrent with markedly increased calving and retreat of Helheim Glacier. Our results therefore suggest that alkenone-derived SST time series from high-sedimentation rate glacial fjords may provide a new approach for reconstruction of past changes of shelf water properties and variability around Greenland. © 2013 Elsevier Ltd. Source

Nielsen J.K.,Danish Meterological Institute | Maus C.,TU Ilmenau | Rzesanke D.,Karlsruhe Institute of Technology | Leisner T.,Karlsruhe Institute of Technology
Atmospheric Chemistry and Physics | Year: 2011

Atmospheric liquid and solid water particles are stabilized if they are coated with either negative or positive electric charge. The surface charge causes an increase of the partial pressure of water vapour close to the surface of each particle, effectively allowing the particles to remain in their condensed phase even if the environmental relative humidity drops below unity. The theory, briefly presented in this paper, predicts a zero parameter relation between surface charge density and water vapour pressure. This relation was tested in a series of Electrodynamic Balance experiments. The measurements were performed by stabilizing charged droplets of pure water near an ice-surface. We observed a divergence in radius as the temperature approached the freezing point from below. We find that the measurements confirm the theory within the experimental uncertainty. In some cases this generally overlooked effect may have impact on cloud processes and on results produced by Electrodynamic Balance experiments. © 2011 Author(s). Source

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