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901.
902.
We investigate the sensitivity of a coarse resolution coupled climate model to the representation of the overflows over the Greenland–Scotland ridge. This class of models suffers from a poor representation of the water mass exchange between the Nordic Seas and the North Atlantic, a crucial part of the large-scale oceanic circulation. We revisit the explicit representation of the overflows using a parameterisation by hydraulic constraints and compare it with the enhancement of the overflow transport by artificially deepened passages over the Greenland–Scotland ridge, a common practice in coarse resolution models. Both configurations increase deep water formation in the Nordic Seas and represent the large-scale dynamics of the Atlantic realistically in contrast to a third model version with realistic sill depths but without the explicit overflow transport. The comparison of the hydrography suggests that for the unperturbed equilibrium the Nordic Seas are better represented with the parameterised overflows. As in previous studies, we do not find a stabilising effect of the overflow parameterisation on the Atlantic meridional overturning circulation but merely on the overflow transport. As a consequence the surface air temperature in the Nordic Seas is less sensitive to anomalous surface fresh water forcing.Special attention is paid to changes in the subpolar gyre circulation. We find it sensitive to the overflow transport and the density of these water masses through baroclinic adjustments. The analysis of the governing equations confirms the presence of positive feedbacks inherent to the subpolar gyre and allows us to isolate the influence of the overflows on its dynamics. 相似文献
903.
904.
Andrea Patzer Dominik C. Hezel Verena Bendel Andreas Pack 《Meteoritics & planetary science》2018,53(7):1391-1412
We performed a LA-ICP-MS study of refractory lithophile trace elements in 32 individual objects selected from a single section of the reduced CV3 chondrite Leoville. Ingredients sampled include ferromagnesian type I and II chondrules, Al-rich chondrules (ARCs), calcium-aluminum-rich inclusions (CAIs), a single amoeboid olivine aggregate (AOA), and matrix. The majority of rare earth element (REE) signatures identified are either of the category “group II” or they are relatively flat, i.e., more or less unfractionated. Data derived for bulk Leoville exhibit characteristics of the group II pattern. The bulk REE inventory is essentially governed by those of CAIs (group II), ARCs (flat or group II), type I chondrules (about 90% flat, 10% group II), and matrix (group II). Leoville matrix also shows a superimposed positive Eu anomaly. The excess in Eu is possibly due to terrestrial weathering. The group II pattern, however, testifies to volatility-controlled fractional condensation from a residual gas of solar composition at still relatively high temperature. In principle, this signature (group II) is omnipresent in all types of constituents, suggesting that the original REE carrier of all components was CAI-like dust. In addition, single-element anomalies occasionally superimposing the group II signature reveal specific changes in redox conditions. We also determined the bulk chemical composition of all objects studied. For Mg/Si, Mg/Fe, and Al/Ca, Leoville's main ingredients—type I chondrules and matrix—display a complementary relationship. Both components probably formed successively in the same source region. 相似文献
905.
As part of an assessment of crystalline rock as a potential host for a nuclear waste repository, water samples were collected from more than 50 locations from the crystalline basement where it is under sedimentary cover in Northern Switzerland and where it is at the surface in the Black Forest. These samples describe the changing chemistry of water in an extended flow system from dilute recharge waters far from chemical equilibrium with its host rock to saline waters at temperatures of 50 to 100°C with residence times far in excess of 105 a that have reached chemical equilibrium with their host rock.This unique set of samples allows an analysis of the chemical evolution of granitic waters from surficial waters far from equilibrium to almost equilibrated waters. Mobile ions, rare gases and isotopic data are used to estimate the extent of reaction between waters and their host rock. The evolution of controlled elements is interpreted as a function of this extent of reaction. Silica contents correspond to approximate equilibrium even in the recharge waters. The relative concentrations of Ca and especially Mg are significantly lower in the borehole waters than in recharge waters indicating a trend towards equilibrium. The Na/K ratios correspond to equilibrium only in the most evolved, older, waters which are shown to be at full equilibrium. 相似文献
906.
The Stubenberg meteorite—An LL6 chondrite fragmental breccia recovered soon after precise prediction of the strewn field
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Addi Bischoff Jean‐Alix Barrat Kerstin Bauer Christoph Burkhardt Henner Busemann Samuel Ebert Michael Gonsior Janina Hakenmüller Jakub Haloda Dennis Harries Dieter Heinlein Harald Hiesinger Rupert Hochleitner Viktor Hoffmann Melanie Kaliwoda Matthias Laubenstein Colin Maden Matthias M. M. Meier Andreas Morlok Andreas Pack Alexander Ruf Philippe Schmitt‐Kopplin Maria Schönbächler Robert C. J. Steele Pavel Spurný Karl Wimmer 《Meteoritics & planetary science》2017,52(8):1683-1703
907.
Investigating the shock histories of lunar meteorites Miller Range 090034, 090070, and 090075 using petrography,geochemistry, and micro‐FTIR spectroscopy
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Dayl J. P. Martin John F. Pernet‐Fisher Katherine H. Joy Roy A. Wogelius Andreas Morlok Harald Hiesinger 《Meteoritics & planetary science》2017,52(6):1103-1124
Fourier transform infrared (FTIR) spectroscopy and cathodoluminescence (CL) imaging techniques, combined with electron microprobe analyses, have been used to determine the physical state of feldspathic phases that have been subject to varying levels of shock in the grouped lunar meteorites Miller Range 090034, 090070, and 090075. Six feldspathic phases have been identified based on spectral, textural, and chemical properties. A specific infrared wavelength band ratio (1064/932 cm?1 equivalent to 9.40/10.73 μm), chosen because it can distinguish between some of the feldspathic phases, can be used to estimate the pressure regimes experienced by these phases. In addition, FTIR spatial mapping capabilities allow for visual comparison of variably shocked phases within the samples. By comparing spectral and compositional data, the origin and shock history of this lunar meteorite group has been determined, with each of the shocked feldspathic phases being related to events in its geological evolution. As such, we highlight that FTIR spectroscopy can be easily employed to identify shocked feldspathic phases in lunar samples; estimate peak shock pressures; and when compared with chemical data, can be used to investigate their shock histories. 相似文献
908.
In search of the Earth‐forming reservoir: Mineralogical,chemical, and isotopic characterizations of the ungrouped achondrite NWA 5363/NWA 5400 and selected chondrites
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Christoph Burkhardt Nicolas Dauphas Haolan Tang Mario Fischer‐Gödde Liping Qin James H. Chen Surya S. Rout Andreas Pack Philipp R. Heck Dimitri A. Papanastassiou 《Meteoritics & planetary science》2017,52(5):807-826
High‐precision isotope data of meteorites show that the long‐standing notion of a “chondritic uniform reservoir” is not always applicable for describing the isotopic composition of the bulk Earth and other planetary bodies. To mitigate the effects of this “isotopic crisis” and to better understand the genetic relations of meteorites and the Earth‐forming reservoir, we performed a comprehensive petrographic, elemental, and multi‐isotopic (O, Ca, Ti, Cr, Ni, Mo, Ru, and W) study of the ungrouped achondrites NWA 5363 and NWA 5400, for both of which terrestrial O isotope signatures were previously reported. Also, we obtained isotope data for the chondrites Pillistfer (EL6), Allegan (H6), and Allende (CV3), and compiled available anomaly data for undifferentiated and differentiated meteorites. The chemical compositions of NWA 5363 and NWA 5400 are strikingly similar, except for fluid mobile elements tracing desert weathering. We show that NWA 5363 and NWA 5400 are paired samples from a primitive achondrite parent‐body and interpret these rocks as restite assemblages after silicate melt extraction and siderophile element addition. Hafnium‐tungsten chronology yields a model age of 2.2 ± 0.8 Myr after CAI, which probably dates both of these events within uncertainty. We confirm the terrestrial O isotope signature of NWA 5363/NWA 5400; however, the discovery of nucleosynthetic anomalies in Ca, Ti, Cr, Mo, and Ru reveals that the NWA5363/NWA 5400 parent‐body is not the “missing link” that could explain the composition of the Earth by the mixing of known meteorites. Until this “missing link” or a direct sample of the terrestrial reservoir is identified, guidelines are provided of how to use chondrites for estimating the isotopic composition of the bulk Earth. 相似文献
909.
Ingo Leya Jean‐Christophe David Thomas Faestermann Michaela Froehlich Niko Kivel Dominik Koll Gunther Korschinek Sarah McIntyre Silke Merchel Stefan Pavetich Georg Rugel Dorothea Schumann Thomas Smith Anton Wallner 《Meteoritics & planetary science》2020,55(4):818-831
We measured specific activities of the long‐lived cosmogenic radionuclides 60Fe in 28 iron meteorites and 53Mn in 41 iron meteorites. Accelerator mass spectrometry was applied at the 14 MV Heavy Ion Accelerator Facility at ANU Canberra for all samples except for two which were measured at the Maier‐Leibnitz Laboratory, Munich. For the large iron meteorite Twannberg (IIG), we measured six samples for 53Mn. This work doubles the number of existing individual 60Fe data and quadruples the number of iron meteorites studied for 60Fe. We also significantly extended the entire 53Mn database for iron meteorites. The 53Mn data for the iron meteorite Twannberg vary by more than a factor of 30, indicating a significant shielding dependency. In addition, we performed new model calculations for the production of 60Fe and 53Mn in iron meteorites. While the new model is based on the same particle spectra as the earlier model, we no longer use experimental cross sections but instead use cross sections that were calculated using the latest version of the nuclear model code INCL. The new model predictions differ substantially from results obtained with the previous model. Predictions for the 60Fe activity concentrations are about a factor of 2 higher, for 53Mn, they are ~30% lower, compared to the earlier model, which gives now a better agreement with the experimental data. 相似文献
910.
ke V. Rosn Beda A. Hofmann Moritz von Sivers Marc Schumann 《Meteoritics & planetary science》2020,55(1):149-163
Radionuclide activities were measured in the low‐background gamma‐ray spectrometry facility GeMSE in eight meteorite falls (Lost City, Tamdakht, Huaxi, Boumdeid, Xining, Kamargaon, Degtevo, and Ouidiyat Sbaa) and two finds (SaU 606 and Mürtschenstock) to evaluate the use of radionuclides for terrestrial age estimates. Results indicate that these meteorites were all derived from small‐ (r < 25 cm) to medium‐sized (r < 65 cm) meteoroids. Short‐lived 48V (t1/2 = 16.0 d) and 51Cr (t1/2 = 27.7 d) were only detected in Oudiyat Sbaa (EH), while 7Be (t1/2 = 53.1 d) was also detected in Degtevo (H) and Kamargaon (L), in agreement with reported fall dates. The 22Na/26Al activity ratio in Huaxi agrees with the previously reported short cosmic‐ray exposure age of this meteorite while 22Na/26Al in Kamargaon likely records a complex exposure history. Bayesian statistical analysis verifies the detection of very low activities of 44Ti (t1/2 = 60 a) in the relatively large H chondrites (>100 g) Degtevo, Huaxi, Tamdakht, Lost City, and SaU 606. Additionally, large samples from Oudiyat Sbaa (EH) and Kamargaon (L) gave positive detections. For H chondrite target compositions, detected 44Ti(Fe+Ni)/26Al averaged 0.055 ± 0.013. Activities of 22Na and 54Mn in SaU 606 show that this meteorite fell between July and September 2012, making SaU 606 the second recent fall from Oman identified using gamma‐ray spectrometry. The upper activity limit of 22Na in the Mürtschenstock meteorite shows that it fell prior to 1999 and is not related to a bolide observation in 2015. Mürtschenstock shows 137Cs ~10× higher than previously determined in Oman meteorites, likely due to Chernobyl fallout. 相似文献