Local ice caps in Finderup Land,North Greenland,survived the Holocene Thermal Maximum     

Nicolaj K. Larsen  Laura B. Levy  Astrid Strunk  Anne Sofie Sndergaard  Jesper Olsen  Torben L. Lauridsen 《Boreas: An International Journal of Quaternary Research》2019,48(3):551-562

Local glaciers and ice caps (GICs) comprise only ~5.4% of the total ice volume, but account for ~14–20% of the current ice loss in Greenland. The glacial history of GICs is not well constrained, however, and little is known about how they reacted to Holocene climate changes. Specifically, in North Greenland, there is limited knowledge about past GIC fluctuations and whether they survived the Holocene Thermal Maximum (HTM, ~8 to 5 ka). In this study, we use proglacial lake records to constrain the ice‐marginal fluctuations of three local ice caps in North Greenland including Flade Isblink, the largest ice cap in Greenland. Additionally, we have radiocarbon dated reworked marine molluscs in Little Ice Age (LIA) moraines adjacent to the Flade Isblink, which reveal when the ice cap was smaller than present. We found that outlet glaciers from Flade Isblink retreated inland of their present extent from ~9.4 to 0.2 cal. ka BP. The proglacial lake records, however, demonstrate that the lakes continued to receive glacial meltwater throughout the entire Holocene. This implies that GICs in Finderup Land survived the HTM. Our results are consistent with other observations from North Greenland but differ from locations in southern Greenland where all records show that the local ice caps at low and intermediate elevations disappeared completely during the HTM. We explain the north–south gradient in glacier response as a result of sensitivity to increased temperature and precipitation. While the increased temperatures during the HTM led to a complete melting of GICs in southern Greenland, GICs remained in North Greenland probably because the melting was counterbalanced by increased precipitation due to a reduction in Arctic sea‐ice extent and/or increased poleward moisture transport.  相似文献   

The brecciated texture of polymict eucrites: Petrographic investigations of unequilibrated meteorites from the Antarctic Yamato collection     

Christian Vollmer  Stella Rombeck  Julia Roszjar  Adam R. Sarafian  Stephan Klemme 《Meteoritics & planetary science》2020,55(3):558-574

We report on the petrography and mineralogy of five Yamato polymict eucrites to better constrain the formation and alteration of crustal material on differentiated asteroids. Each sample consists of different lithic clasts that altogether form four dominant textures and therefore appear to originate from closely related petrological areas within Vesta′s crust. The textures range from subophitic to brecciated, porphyritic, and quench‐textured, that differ from section to section. Comparison with literature data for these samples is therefore difficult, which stresses that polymict eucrites are extremely complex in their petrography and investigation of only one thick section may not be representative for the host rock. We also show that sample Y‐793548 consists of more than one lithic unit and must therefore be classified as polymict instead of monomict. The variety and nature of lithic textures in the investigated Yamato meteorites indicate shock events, intense post‐magmatic thermal annealing, and secondary alteration. These postmagmatic features occur in different intensities, varying from clast to clast or among coexisting mineral fragments on a small, local scale. Several clasts within the eucrites studied have been modified by late‐stage alteration processes that caused deposition of Fe‐rich olivine and Fe enrichment along cracks crosscutting pyroxene crystals. However, formation of these secondary phases seems to be independent of the degree of thermal metamorphism observed within every type of clast, which would support a late‐stage metasomatism model for their formation.  相似文献   

Late Pliocene sand ridges at the western margin of the Barents Sea—do they monitor Late Pliocene glaciations?     

Stig-Morten Knutsen  Kjell-Bjrnar Larsen 《Global and Planetary Change》1996,12(1-4)

Seismic data combined with core analysis of the northwesternmost exploration well on the Norwegian continental margin, well 7316/5-1, has been used to map and discuss the genesis of three well-defined sand ridges. The sand ridges have a NE-SW to N-S orientation and are of Late Pliocene age. The dimensions of the ridges are: height 40 m, length 2–4 km and width 0.5–1 km.In relation to the glaciation models of the Barents Sea, the position of well 7316/5-1, and especially information from a core that penetrated one of the sand ridges, provide important information. The ridges are not, in themselves, diagnostic for grounded glaciers at the margin of the Barents Sea shelf during the Late Pliocene, although the presence of pebbles in a cored section of the ridges may represent ice-dropped material. Whether the possible influx of glaciogenic material is related to local or regional glaciations on the Barents Shelf remains to be evaluated.  相似文献   

A multi-phase chemo-dynamical SPH code for galaxy evolution. Testing the code     

Peter Berczik  Gerhard Hensler  Christian Theis  Rainer Spurzem 《Astrophysics and Space Science》2003,284(2):865-868

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Scanning electron microscopy,cathodoluminescence, and Raman spectroscopy of experimentally shock‐metamorphosed quartzite     

Arnold Gucsik  Christian Koeberl  Franz Brandsttter  Eugen Libowitzky  Wolf Uwe Reimold 《Meteoritics & planetary science》2003,38(8):1187-1197

Abstract— We studied unshocked and experimentally (at 12, 25, and 28 GPa, with 25, 100, 450, and 750°C pre‐shock temperatures) shock‐metamorphosed Hospital Hill quartzite from South Africa using cathodoluminescence (CL) images and spectroscopy and Raman spectroscopy to document systematic pressure or temperature‐related effects that could be used in shock barometry. In general, CL images of all samples show CL‐bright luminescent patchy areas and bands in otherwise nonluminescent quartz, as well as CL‐dark irregular fractures. Fluid inclusions appear dominant in CL images of the 25 GPa sample shocked at 750°C and of the 28 GPa sample shocked at 450°C. Only the optical image of our 28 GPa sample shocked at 25°C exhibits distinct planar deformation features (PDFs). Cathodoluminescence spectra of unshocked and experimentally shocked samples show broad bands in the near‐ultraviolet range and the visible light range at all shock stages, indicating the presence of defect centers on, e.g., SiO₄ groups. No systematic change in the appearance of the CL images was obvious, but the CL spectra do show changes between the shock stages. The Raman spectra are characteristic for quartz in the unshocked and 12 GPa samples. In the 25 and 28 GPa samples, broad bands indicate the presence of glassy SiO₂, while high‐pressure polymorphs are not detected. Apparently, some of the CL and Raman spectral properties can be used in shock barometry.  相似文献   

Report on the Twelfth United Nations/European Space Agency Workshop on Basic Space Science (Beijing, P.R. China, 24–28 May 2004)     

Willem Wamsteker  Hans J. Haubold 《Astrophysics and Space Science》2006,305(3):325-330

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Mezen Bay—a key area for understanding Weichselian glaciations in northern Russia     

Kurt H. Kjr  Igor N. Demidov  Eiliv Larsen  Andrew Murray  Jan K. Nielsen 《第四纪科学杂志》2003,18(1):73-93

Sediment successions in coastal cliffs around Mezen Bay, southeastern White Sea, record an unusually detailed history of former glaciations, interstadial marine and fluvial events from the Weichselian. A regional glaciation model for the Weichselian is based on new data from the Mezen Bay area and previously published data from adjacent areas. Following the Mikulinian (Eemian) interglacial a shelf‐centred glaciation in the Kara Sea is reflected in proglacial conditions at 100–90 ka. A local ice‐cap over the Timan ridge existed between 75 and 65 ka. Renewed glaciation in the Kara Sea spread southwestwards around 60 ka only, interrupted by a marine inundation, before it advanced to its maximum position at about 55–50 ka. After a prolonged ice‐free period, the Scandinavian ice‐sheet invaded the area from the west and terminated east of Mezen Bay about 17 ka. The previously published evidence of a large ice‐dammed lake in the central Arkhangelsk region, Lake Komi, finds no support in this study. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Recent extreme slope failures in glacial environments: effects of thermal perturbation     

Christian Huggel 《Quaternary Science Reviews》2009,28(11-12):1119-1130

This paper describes recent exceptional slope failures in high-mountain, glacial environments: the 2002 Kolka–Karmadon rock–ice avalanche in the Caucasus, a series of ice–rock avalanches on Iliamna Volcano, Alaska, the 2005 Mt. Steller rock–ice avalanche in Alaska, and ice and rock avalanches at Monte Rosa, Italy in 2005 and 2007. Deposit volumes range from 10⁶ to 10⁸ m³ and include rock, ice and snow. Here we focus on thermal aspects of these failures reflecting the involvement of glacier ice and permafrost at all sites, suggesting that thermal perturbations likely contributed to the slope failures. We use surface and troposphere air temperatures, near-surface rock temperatures, satellite thermal data, and recent 2D and 3D thermal modeling studies to document thermal conditions at the landslide sites. We distinguish between thermal perturbations of volcanic-geothermal and climatic origin, and thermal perturbations related to glacier–permafrost interaction. The data and analysis support the view that recent, current and future climatic change increases the likelihood of large slope failures in steep glacierized and permafrost terrain. However, some important aspects of these settings such as the geology and tectonic environment remain poorly understood, making the identification of future sites of large slope instabilities difficult. In view of the potentially large natural disasters that can be caused by such slope failures, improved data and understanding are needed.  相似文献   

Translating Milankovitch climate forcing into eustatic fluctuations via thermal deep water expansion: a conceptual link     

Michael Schulz  Christian Schäfer-Neth 《地学学报》1997,9(5-6):228-231

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Authors' Reply     

Kaare L. Rasmussen  Hans J. F. Olsen  Raymond Gwozdz  Evgeniy M. Kolesnikov 《Meteoritics & planetary science》2001,36(7):1001-1006

Abstract— Jull et al. propose an alternative interpretation of our depth vs. ¹⁴C data measured on a peat core from the central Tunguska impact site (Rasmussen et al., 1999). We find that the proposed alternative is untenable.  相似文献