Resolving climate change in the period 15–23 ka in Greenland ice cores: a new application of spectral trend analysis

Northern Hemisphere climate history through and following the Last Glacial Maximum is recorded in detail in ice cores from Greenland. However, the period between Greenland Interstadials 1 and 2 (15–23 ka), i.e. the period of deglaciation following the last major glaciation, has been difficult to resolve in great detail. We here offer a new subdivision of this in the NGRIP, GRIP and GISP2 ice cores, by newly introducing spectral trend analysis to the study of climate-related data series from ice cores. This analysis reveals patterns of change and discontinuity in the waveform properties of a data series, relating to the environmental (including climatic) history of accumulation of the rock or ice record. The application allows high-resolution correlation between the ice cores, and a greatly improved subdivision of the study interval. Nine climatic phases are recognized, within which more identifiable events can also be correlated between the three locations.     

MIL 03443, a dunite from asteroid 4 Vesta: Evidence for its classification and cumulate origin

Abstract– The absence of dunite (>90 vol% olivine) in the howardite, eucrite, and diogenite (HED) meteorite suite, when viewed with respect to spectroscopic and petrologic evidence for olivine on Vesta, is problematic. Herein, we present petrologic, geochemical, and isotopic evidence confirming that Miller Range (MIL) 03443, containing 91 vol% olivine, should be classified with the HED clan rather than with mesosiderites. Similarities in olivine and pyroxene FeO/MnO ratios, mineral compositions, and unusual mineral inclusions between MIL 03443 and the diogenites support their formation on a common parent body. This hypothesis is bolstered by oxygen isotopic and bulk geochemical data. Beyond evidence for its reclassification, we present observations and interpretations that MIL 03443 is probably a crustal cumulate rock like the diogenites, rather than a sample of the Vestan mantle.     

Bounce Rock—A shergottite‐like basalt encountered at Meridiani Planum,Mars

Abstract– The Opportunity rover of the Mars Exploration Rover mission encountered an isolated rock fragment with textural, mineralogical, and chemical properties similar to basaltic shergottites. This finding was confirmed by all rover instruments, and a comprehensive study of these results is reported here. Spectra from the miniature thermal emission spectrometer and the Panoramic Camera reveal a pyroxene‐rich mineralogy, which is also evident in Mössbauer spectra and in normative mineralogy derived from bulk chemistry measured by the alpha particle X‐ray spectrometer. The correspondence of Bounce Rock’s chemical composition with the composition of certain basaltic shergottites, especially Elephant Moraine (EET) 79001 lithology B and Queen Alexandra Range (QUE) 94201, is very close, with only Cl, Fe, and Ti exhibiting deviations. Chemical analyses further demonstrate characteristics typical of Mars such as the Fe/Mn ratio and P concentrations. Possible shock features support the idea that Bounce Rock was ejected from an impact crater, most likely in the Meridiani Planum region. Bopolu crater, 19.3 km in diameter, located 75 km to the southwest could be the source crater. To date, no other rocks of this composition have been encountered by any of the rovers on Mars. The finding of Bounce Rock by the Opportunity rover provides further direct evidence for an origin of basaltic shergottite meteorites from Mars.     

Petrologic insights from the spectra of the unbrecciated eucrites: Implications for Vesta and basaltic asteroids

Abstract– We investigate the relationship between the petrology and visible–near infrared spectra of the unbrecciated eucrites and synthetic pyroxene–plagioclase mixtures to determine how spectra obtained by the Dawn mission could distinguish between several models that have been suggested for the petrogenesis of Vesta’s crust (e.g., partial melting and magma ocean). Here, we study the spectra of petrologically characterized unbrecciated eucrites to establish spectral observables, which can be used to yield mineral abundances and compositions consistent with petrologic observations. No information about plagioclase could be extracted from the eucrite spectra. In contrast, pyroxene dominates the spectra of the eucrites and absorption band modeling provides a good estimate of the relative proportions of low‐ and high‐Ca pyroxene present. Cr is a compatible element in eucrite pyroxene and is enriched in samples from primitive melts. An absorption at 0.6 μm resulting from Cr³⁺ in the pyroxene structure can be used to distinguish these primitive eucrites. The spectral differences present among the eucrites may allow Dawn to distinguish between the two main competing models proposed for the petrogenesis of Vesta (magma ocean and partial melting). These models predict different crustal structures and scales of heterogeneity, which can be observed spectrally. The formation of eucrite Allan Hills (ALH) A81001, which is primitive (Cr‐rich) and relatively unmetamorphosed, is hard to explain in the magma ocean model. It could only have been formed as a quench crust. If the magma ocean model is correct, then ALHA81001‐like material should be abundant on the surface of Vesta and the Vestoids.     

Volume diffusion of Ytterbium in YAG: thin-film experiments and combined TEM–RBS analysis

In this study, we address volume diffusion of ytterbium in yttrium aluminum garnet (YAG) using thin-film single crystal diffusion couples. We employ analytical transmission electron microscopy (ATEM) as a tool for combined microstructural and microchemical analysis and compare the results to Rutherford backscattering (RBS) analysis. Given the high spatial resolution of the method, we focus on microstructural changes of the thin-film diffusant source during the diffusion anneal. We evaluate the potential influence of the associated changes in its transport properties on the evolution of concentration profiles in the single crystal substrate. This approach allows us to test the reliability of determination of volume diffusion coefficients from thin-film diffusion experiments. We found that for the chosen experimental setting, the influence of thin-film re-crystallization is small when compared with the experimental uncertainty and good estimates for the volume diffusion coefficients of Yb in YAG can be obtained using standard assumptions. Both Yb-concentration profiles analyzed with ATEM and with RBS give similar results. At 1,450°C and 1 bar, we infer log D _Yb (m²/s) values of −19.37 ± 0.07 (TEM) and −19.84 ± 0.02 (RBS). Although the change in thin-film transport properties associated with successive crystallization during the diffusion anneal does not play a major role for our experimental setup, this effect cannot generally be ignored.     

Impact of improved assimilation of temperature and salinity for coupled model seasonal forecasts

We assess the impact of improved ocean initial conditions for predicting El Niño-Southern Oscillation (ENSO) and Indian Ocean dipole (IOD) using the Bureau of Meteorology’s Predictive Ocean Atmosphere Model for Australia (POAMA) coupled seasonal prediction model for the period 1982–2006. The new ocean initial conditions are provided by an ensemble-based analysis system that assimilates subsurface temperatures and salinity and which is a clear improvement over the previous optimal interpolation system which used static error covariances and was univariate (temperature only). Hindcasts using the new ocean initial conditions have better skill at predicting sea surface temperature (SST) variations associated with ENSO than do the hindcasts initialized with the old ocean analyses. The improvement derives from better prediction of subsurface temperatures and the largest improvements come during ENSO–IOD neutral years. We show that improved prediction of the Niño3.4 SST index derives from improved initial depiction of the thermocline and halocline in the equatorial Pacific but as lead time increases the improved depiction of the initial salinity field in the western Pacific become more important. Improved ocean initial conditions do not translate into improved skill for predicting the IOD but we do see an improvement in the prediction of subsurface temperatures in the Indian Ocean (IO). This result reflects that the coupling between subsurface and surface temperature variations is weaker in the IO than in the Pacific, but coupled model errors may also be limiting predictive skill in the IO.     

Stratigraphic status,age, and paleobathymetry of the Grey shale Member,Dalmiapuram Formation,Cauvery Basin,India

Grey shale Member of the Dalmiapuram Formation, Ariyalur Group, Cauvery Basin, India was studied for its stratigraphic position, age, and paleobathymetry with a re-look into the lithological relationship and foraminifer assemblages in the deepened limestone mine excavations at M/s Dalmia Cements, Dalmiapuram. Twenty grey shale samples from Kovandankurchchi (pit-4) and Kallakkudi mines yielded diversified calcareous, benthic, and rare index planktic foraminifera. The foraminiferal assemblages suggest a latest Albian age and middle neritic depositional conditions. The abundance of kaolinite and smectite clay minerals relate to warm/humid climate which corroborate with rising relative sea level during grey shale deposition. The grey shale occurs in patches within the marl bedded limestone member which exhibits cyclic deposition of limestone and marl. The limestone mine sections demonstrate that the grey shale forms part of basal marl bedded limestone, directly overlying the coral algal limestone. The present study demonstrates that the grey shale outcrops in Dalmiapuram Formation should be placed stratigraphically as part of marl bedded limestone. The member status for grey shale which is current usage stands discounted.