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231.
Archaeal lipids record paleosalinity in hypersaline systems 总被引:2,自引:0,他引:2
We present an ecologically based biomarker method for estimating past salinity, especially in hypersaline conditions. The relative amounts of acyclic diether and tetraether membrane lipids synthesized by Archaea correlate with salinity from 0–250 practical salinity units (psu) in modern settings. We examined the preservation of this lipid biomarker–salinity relationship in ancient sedimentary organic matter using samples from two sequences of marls and diatomites deposited just prior to the Messinian Salinity Crisis. Salinity estimates were consistent with expected absolute salinity, as well as the amplitude of variations leading up to the Messinian Salinity Crisis. This lipid biomarker approach to salinity reconstruction complements existing paleosalinity proxies because (i) Archaea survive and thrive over a broad salinity range, well beyond that of haptophyte algae and other plankton which form the microfossil record and (ii) it provides fine salinity resolution for the wide range broadly defined as hypersaline. With the proxy, there is the potential to provide novel insights into salinity variation within desiccating basins in climatically sensitive seas (e.g. Dead Sea, Permian Delaware Basin), evolution of brines, timing of onset of hypersaline conditions and evaporite deposition. 相似文献
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233.
Louise Alexander Joshua F. Snape Ian A. Crawford Katherine H. Joy Hilary Downes 《Meteoritics & planetary science》2014,49(7):1288-1304
New data from a petrological and geochemical examination of 12 coarse basaltic fines from the Apollo 12 soil sample 12023,155 provide evidence of additional geochemical diversity at the landing site. In addition to the bulk chemical composition, major, minor, and trace element analyses of mineral phases are employed to ascertain how these samples relate to the Apollo 12 lithological basalt groups, thereby overcoming the problems of representativeness of small samples. All of the samples studied are low‐Ti basalts (0.9–5.7 wt% TiO2), and many fall into the established olivine, pigeonite, and ilmenite classification of Apollo 12 basaltic suites. There are five exceptions: sample 12023,155_1A is mineralogically and compositionally distinct from other Apollo 12 basalt types, with low pigeonite REE concentrations and low Ni (41–55 ppm) and Mn (2400–2556 ppm) concentrations in olivine. Sample 12023,155_11A is also unique, with Fe‐rich mineral compositions and low bulk Mg# (=100 × atomic Mg/[Mg+Fe]) of 21.6. Sample 12023,155_7A has different plagioclase chemistry and crystallization trends as well as a wider range of olivine Mg# (34–55) compared with other Apollo 12 basalts, and shows greater similarities to Apollo 14 high‐Al basalts. Two other samples (12023,155_4A, and _5A) are similar to the Apollo 12 feldspathic basalt 12038, providing additional evidence that feldspathic basalts represent a lava flow proximal to the Apollo 12 site rather than material introduced by impacts. We suggest that at least one parent magma, and possibly as many as four separate parent magmas, are required in addition to the previously identified olivine, pigeonite, and ilmenite basaltic suites to account for the observed chemical diversity of basalts found in this study. 相似文献
234.
James Edmonds Patrick Luckow Katherine Calvin Marshall Wise Jim Dooley Page Kyle Son H. Kim Pralit Patel Leon Clarke 《Climatic change》2013,118(1):29-43
Combining bioenergy and carbon dioxide (CO2) capture and storage (CCS) technologies (BECCS) has the potential to remove CO2 from the atmosphere while producing useful energy. BECCS has played a central role in scenarios that reduce climate forcing to low levels such as 2.6 Wm?2. In this paper we consider whether BECCS is essential to limiting radiative forcing (RF) to 2.6 Wm?2 by 2100 using the Global Change Assessment Model, a closely coupled model of biogeophysical and human Earth systems. We show that BECCS can potentially reduce the cost of limiting RF to 2.6 Wm?2 by 2100 but that a variety of technology combinations that do not include BECCS can also achieve this goal, under appropriate emissions mitigation policies. We note that with appropriate supporting land-use policies terrestrial sequestration could deliver carbon storage ranging from 200 to 700 PgCO2-equiavalent over the 21st century. We explore substantial delays in participation by some geopolitical regions. We find that the value of BECCS is substantially higher under delay and that delay results in higher transient RF and climate change. However, when major regions postponed mitigation indefinitely, it was impossible to return RF to 2.6 Wm?2 by 2100. Neither finite land resources nor finite potential geologic storage capacity represented a meaningful technical limit on the ability of BECCS to contribute to emissions mitigation in the numerical experiments reported in this paper. 相似文献
235.
Katherine E. McGowan W. Thomas Vestrand Jamie A. Kennea Silvia Zane Mark Cropper France A. Córdova 《Astrophysics and Space Science》2007,308(1-4):309-316
We present X-ray data of the middle-aged radio pulsar PSR B0355+54. The XMM-Newton and Chandra observations show not only
emission from the pulsar itself, but also compact diffuse emission extending ∼50″ in the opposite direction to the pulsar’s
proper motion. Our analysis also indicates the presence of fainter diffuse emission extending ∼5′ from the point source. The
morphology of the diffuse component is similar to the ram-pressure confined pulsar wind nebulae detected for other sources.
We find that the compact diffuse component is well-fitted with a power-law, with an index that is consistent with the values
found for other pulsar wind nebulae. The core emission from the pulsar can be characterized with a thermal plus power-law
fit, with the thermal emission most likely originating in a hot polar cap. 相似文献
236.
M. C. Erlund A. C. Fabian Katherine M. Blundell A. Celotti C. S. Crawford 《Monthly notices of the Royal Astronomical Society》2006,371(1):29-37
We present Chandra observations of two relatively high redshift FR II radio galaxies, 3C 432 and 3C 191 ( z = 1.785 and 1.956, respectively), both of which show extended X-ray emission along the axis of the radio jet or lobe. This X-ray emission is most likely to be due to inverse-Compton scattering of cosmic microwave background (CMB) photons. Under this assumption, we estimate the minimum energy contained in the particles responsible. This can be extrapolated to determine a rough estimate of the total energy. We also present new, deep radio observations of 3C 294, which confirm some association between radio and X-ray emission along the north-east–south-west radio axis and also that radio emission is not detected over the rest of the extent of the diffuse X-ray emission. This together with the offset between the peaks of the X-ray and radio emissions may indicate that the jet axis in this source is precessing. 相似文献
237.
Christian R. Kaiser J. L. Sokoloski Katherine F. Gunn Catherine Brocksopp 《Astrophysics and Space Science》2005,300(1-3):283-288
The large mechanical luminosity of the jets of GRS 1915+105 should give rise to luminous emission regions, similar to those
observed in radio galaxies, where the jets interact with the gas surrounding the source. However, no radio synchrotron emission
of the expected morphology has been found. Here we present the results of a study suggesting that radio bremsstrahlung from
the compressed and heated ISM in front of the jets should be detectable, while the synchrotron lobes may be too faint. We
identify these jet impact sites with two well-known IRAS regions. This identification suggests a distance of GRS 1915+105
of 6.5± 1.6 kpc, significantly closer than the usually assumed distance of 11–12 kpc. We discuss the implications of this
reduced distance estimate. The non-detection of the synchrotron radio lobes implies a significant fraction of non-radiating
particles, possibly protons, in the jets. The apparent motion of small-scale jet components is not superluminal, so if superluminal
motion is required for an object to be termed a microquasar, GRS 1915+105 actually does not qualify. The mass of the black
hole in the system is increased to 21± 9 M⊙, while the mechanical luminosity of the jets is reduced to 14% of the Eddington luminosity. 相似文献
238.
239.
Paulin Gabriel Legorreta Mickelson Katherine A. Contreras Trevor A. Gallin William Jacobacci Kara E. Bursik Marcus 《Landslides》2022,19(4):901-912
Landslides - Geomorphological analysis of landslide processes in mountainous terrains with difficult access has benefited from virtual representation of topography through the use of... 相似文献
240.