Wilhelms, Frank

[["dc.bibliographiccitation.artnumber","20150347"],["dc.bibliographiccitation.issue","2086"],["dc.bibliographiccitation.journal","PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES"],["dc.bibliographiccitation.volume","375"],["dc.contributor.author","Weikusat, Ilka"],["dc.contributor.author","Jansen, Daniela"],["dc.contributor.author","Binder, Tobias"],["dc.contributor.author","Eichler, Jan"],["dc.contributor.author","Faria, Sergio H."],["dc.contributor.author","Wilhelms, Frank"],["dc.contributor.author","Kipfstuhl, Sepp"],["dc.contributor.author","Sheldon, Simon G."],["dc.contributor.author","Miller, Heinrich"],["dc.contributor.author","Dahl-Jensen, Dorthe"],["dc.contributor.author","Kleiner, Thomas"],["dc.date.accessioned","2018-11-07T10:27:30Z"],["dc.date.available","2018-11-07T10:27:30Z"],["dc.date.issued","2017"],["dc.description.abstract","Microstructures from deep ice cores reflect the dynamic conditions of the drill location as well as the thermodynamic history of the drill site and catchment area in great detail. Ice core parameters (crystal lattice-preferred orientation (LPO), grain size, grain shape), mesostructures (visual stratigraphy) as well as borehole deformation were measured in a deep ice core drilled at Kohnen Station, Dronning Maud Land (DML), Antarctica. These observations are used to characterize the local dynamic setting and its rheological as well as microstructural effects at the EDML ice core drilling site (European Project for Ice Coring in Antarctica in DML). The results suggest a division of the core into five distinct sections, interpreted as the effects of changing deformation boundary conditions from triaxial deformation with horizontal extension to bedrock-parallel shear. Region 1 (uppermost approx. 450m depth) with still small macroscopic strain is dominated by compression of bubbles and strong strain and recrystallization localization. Region 2 (approx. 450-1700m depth) shows a girdle-type LPO with the girdle plane being perpendicular to grain elongations, which indicates triaxial deformation with dominating horizontal extension. In this region (approx. 1000m depth), the first subtle traces of shear deformation are observed in the shape-preferred orientation (SPO) by inclination of the grain elongation. Region 3 (approx. 1700-2030m depth) represents a transitional regime between triaxial deformation and dominance of shear, which becomes apparent in the progression of the girdle to a single maximum LPO and increasing obliqueness of grain elongations. The fully developed single maximum LPO in region 4 (approx. 2030-2385m depth) is an indicator of shear dominance. Region 5 (below approx. 2385m depth) is marked by signs of strong shear, such as strong SPO values of grain elongation and strong kink folding of visual layers. The details of structural observations are compared with results from a numerical ice sheet model (PISM, isotropic) for comparison of strain rate trends predicted from the large-scale geometry of the ice sheet and borehole logging data. This comparison confirms the segmentation into these depth regions and in turn provides a wider view of the ice sheet. This article is part of the themed issue 'Microdynamics of ice'."],["dc.identifier.doi","10.1098/rsta.2015.0347"],["dc.identifier.isi","000391840100005"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/14306"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/43241"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","PUB_WoS_Import"],["dc.publisher","Royal Soc"],["dc.relation.issn","1471-2962"],["dc.relation.issn","1364-503X"],["dc.rights","CC BY 4.0"],["dc.rights.uri","https://creativecommons.org/licenses/by/4.0/"],["dc.title","Physical analysis of an Antarctic ice core-towards an integration of micro- and macrodynamics of polar ice"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.journal","Frontiers in Earth Science"],["dc.bibliographiccitation.volume","4"],["dc.contributor.author","Karlsson, Nanna B."],["dc.contributor.author","Eisen, Olaf"],["dc.contributor.author","Dahl-Jensen, Dorthe"],["dc.contributor.author","Freitag, Johannes"],["dc.contributor.author","Kipfstuhl, Sepp"],["dc.contributor.author","Lewis, Cameron"],["dc.contributor.author","Nielsen, Lisbeth T."],["dc.contributor.author","Paden, John D."],["dc.contributor.author","Winter, Anna"],["dc.contributor.author","Wilhelms, Frank"],["dc.date.accessioned","2020-12-10T18:44:21Z"],["dc.date.available","2020-12-10T18:44:21Z"],["dc.date.issued","2016"],["dc.description.abstract","Radar-detected internal layering contains information on past accumulation rates and patterns. In this study, we assume that the radar layers are isochrones, and use the layer stratigraphy in combination with ice-core measurements and numerical methods to retrieve accumulation information for the northern part of central Greenland. Measurements of the dielectric properties of an ice core from the NEEM (North Greenland Eemian Ice Drilling) site, allow for correlation of the radar layers with volcanic horizons to obtain an accurate age of the layers. We obtain 100 a averaged accumulation patterns for the period 1311–2011 for a 300 by 350 km area encompassing the two ice-core sites: NEEM and NGRIP (North Greenland Ice Core Project). Our results show a clear trend of high accumulation rates west of the ice divide and low accumulation rates east of the ice divide. At the NEEM site, this accumulation pattern persists throughout our study period with only minor temporal variations in the accumulation rate. In contrast, the accumulation rate shows more pronounced temporal variations (based on our centennial averages) from 170 km south of the NEEM site to the NGRIP site. We attribute this variation to shifts in the location of the high–low accumulation boundary away from the ice divide."],["dc.identifier.doi","10.3389/feart.2016.00097"],["dc.identifier.eissn","2296-6463"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/78421"],["dc.language.iso","en"],["dc.notes.intern","DOI Import GROB-354"],["dc.publisher","Frontiers Media S.A."],["dc.relation.eissn","2296-6463"],["dc.rights","http://creativecommons.org/licenses/by/4.0/"],["dc.title","Accumulation Rates during 1311–2011 CE in North-Central Greenland Derived from Air-Borne Radar Data"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","749"],["dc.bibliographiccitation.issue","2"],["dc.bibliographiccitation.journal","CLIMATE OF THE PAST"],["dc.bibliographiccitation.lastpage","766"],["dc.bibliographiccitation.volume","9"],["dc.contributor.author","Svensson, Anders"],["dc.contributor.author","Bigler, M."],["dc.contributor.author","Blunier, T."],["dc.contributor.author","Clausen, H. B."],["dc.contributor.author","Dahl-Jensen, Dorthe"],["dc.contributor.author","Fischer, H."],["dc.contributor.author","Fujita, S."],["dc.contributor.author","Goto-Azuma, K."],["dc.contributor.author","Johnsen, S. J."],["dc.contributor.author","Kawamura, Kensuke"],["dc.contributor.author","Kipfstuhl, Sepp"],["dc.contributor.author","Kohno, M."],["dc.contributor.author","Parrenin, F."],["dc.contributor.author","Popp, T."],["dc.contributor.author","Rasmussen, Steve"],["dc.contributor.author","Schwander, J."],["dc.contributor.author","Seierstad, I."],["dc.contributor.author","Severi, M."],["dc.contributor.author","Steffensen, J. P."],["dc.contributor.author","Udisti, Roberto"],["dc.contributor.author","Uemura, R."],["dc.contributor.author","Vallelonga, P."],["dc.contributor.author","Vinther, B. M."],["dc.contributor.author","Wegner, A."],["dc.contributor.author","Wilhelms, Frank"],["dc.contributor.author","Winstrup, M."],["dc.date.accessioned","2018-11-07T09:30:07Z"],["dc.date.available","2018-11-07T09:30:07Z"],["dc.date.issued","2013"],["dc.description.abstract","The Toba eruption that occurred some 74 ka ago in Sumatra, Indonesia, is among the largest volcanic events on Earth over the last 2 million years. Tephra from this eruption has been spread over vast areas in Asia, where it constitutes a major time marker close to the Marine Isotope Stage 4/5 boundary. As yet, no tephra associated with Toba has been identified in Greenland or Antarctic ice cores. Based on new accurate dating of Toba tephra and on accurately dated European stalagmites, the Toba event is known to occur between the onsets of Greenland interstadials (GI) 19 and 20. Furthermore, the existing linking of Greenland and Antarctic ice cores by gas records and by the bipolar seesaw hypothesis suggests that the Antarctic counterpart is situated between Antarctic Isotope Maxima (AIM) 19 and 20. In this work we suggest a direct synchronization of Greenland (NGRIP) and Antarctic (EDML) ice cores at the Toba eruption based on matching of a pattern of bipolar volcanic spikes. Annual layer counting between volcanic spikes in both cores allows for a unique match. We first demonstrate this bipolar matching technique at the already synchronized Laschamp geomagnetic excursion (41 ka BP) before we apply it to the suggested Toba interval. The Toba synchronization pattern covers some 2000 yr in GI-20 and AIM19/20 and includes nine acidity peaks that are recognized in both ice cores. The suggested bipolar Toba synchronization has decadal precision. It thus allows a determination of the exact phasing of inter-hemispheric climate in a time interval of poorly constrained ice core records, and it allows for a discussion of the climatic impact of the Toba eruption in a global perspective. The bipolar linking gives no support for a long-term global cooling caused by the Toba eruption as Antarctica experiences a major warming shortly after the event. Furthermore, our bipolar match provides a way to place palaeo-environmental records other than ice cores into a precise climatic context."],["dc.identifier.doi","10.5194/cp-9-749-2013"],["dc.identifier.isi","000317009700016"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/10609"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/31225"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Copernicus Gesellschaft Mbh"],["dc.relation.issn","1814-9332"],["dc.relation.issn","1814-9324"],["dc.relation.orgunit","Fakultät für Geowissenschaften und Geographie"],["dc.rights","CC BY 3.0"],["dc.rights.uri","https://creativecommons.org/licenses/by/3.0/"],["dc.title","Direct linking of Greenland and Antarctic ice cores at the Toba eruption (74 ka BP)"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]