Results of statistical analysis of primary components concentrations in bulk chemical composition of ordinary chondrite groups

We used two different methods of statistical analysis—cluster analysis and principal component analysis—to analyze the concentrations of principal chemical components (Si, Mg, Ca, Fe, Ni) and Co in ordinary chondrites. The analysis is based predominantly on published data (metadata). In total, chemical composition data from 646 ordinary chondrites were used in the statistical analysis. The aim of this analysis was to establish whether it would be possible or not to distinguish H, L, and LL chondrites based on the concentrations of major elements and Co in their bulk chemical compositions. It was also important to determine what conclusions such an analysis could enable to draw about matter differentiation in the formation environments of primordial parent bodies of particular ordinary chondrite groups (H, L, and LL). Another aim of the statistical analysis was to determine whether the distribution of Fe and Ni (with Co admixtures) is independent of petrographic types within particular groups of chondrites. This is of crucial importance for determining the distribution of FeNi(Co) ore occurrences in potential extraterrestrial deposits on modern asteroids—the sources of ordinary chondrites. The obtained results of statistical analyses confirmed that a clear-cut distinction between particular groups of ordinary chondrites is only possible for group H, while distinguishing L chondrites from LL chondrites is not always obvious. The results of the statistical analyses relating to the question of the possible existence of several primordial parent bodies (formation environments) of each group of ordinary chondrites are consistent with the results of contemporary astronomical spectroscopy research. What is particularly interesting is obtaining indications of the existence of common formation environments of the matter of L and LL chondrites, possibly on a few primordial parent bodies. The statistical analyses indicate that there is no correlation between the concentration of principal chemical components and the petrographic type of ordinary chondrites. This proves homogenous distributions of these elements within the parent bodies of each group of ordinary chondrites. Hence, the distribution of these elements in individual present-day asteroids is also homogenous.     

Limnological conditions in a subarctic lake (northern Québec, Canada) during the late Holocene: analyses based on fossil diatoms

A fossil diatom record covering the past 3000 cal. years BP wasanalyzed from a small lake in northwestern Québec near the northernlimit of present-day tree-line. Fragilaria virescens var.exigua Grunow in Van Heurck was the dominant speciesthroughout the core with abundances ranging between 13–35% of thetotal valve count. There was a replacement of alkaliphilous taxa byacidophilous taxa beginning ca. 1300 cal. yr ago, probably reflectinglong-term, natural acidification processes. A diatom-based transfer functionwas used to provide quantitative estimates of variations in lakewater dissolvedorganic carbon (DOC). These inferred values showed that DOC concentrations haveremained stable over the past 3000 years (mean ± S.D. = 5 ± 0.43 mg C l^–1), suggesting relatively constant allochthonouscarbon inputs and underwater light conditions during the late Holocene. Thereconstructed DOC data were compared to the palynological record from the samelake. Our study indicates that, in contrast to paleolimnological records fromlakes in central and western Canada, climatic variations and associatedvegetational shifts have been too subtle to cause pronounced variations in DOCin this northern Québec site.     

Coordinated Observations of Comet Hale–Bopp between 32 and 860 GHz

Earth, Moon, and Planets - The concept of simultaneous multifrequency continuum observations, successfully tested on Comet Hyakutake, was applied to Comet Hale-Bopp, using the Heinrich Hertz...     

Recovery of Injected Freshwater from a Brackish Aquifer with a Multiwell System

Herein we propose a multiple injection and recovery well system strategically operated for freshwater storage in a brackish aquifer. With the system we call aquifer storage transfer and recovery (ASTR) by using four injection and two production wells, we are capable of achieving both high recovery efficiency of injected freshwater and attenuation of contaminants through adequately long residence times and travel distances within the aquifer. The usual aquifer storage and recovery (ASR) scheme, in which a single well is used for injection and recovery, does not warrant consistent treatment of injected water due to the shorter minimum residence times and travel distances. We tested the design and operation of the system over 3 years in a layered heterogeneous limestone aquifer in Salisbury, South Australia. We demonstrate how a combination of detailed aquifer characterization and solute transport modeling can be used to maintain acceptable salinity of recovered water for its intended use along with natural treatment of recharge water. ASTR can be used to reduce treatment costs and take advantage of aquifers with impaired water quality that might locally not be otherwise beneficially used.     

40Ar/39Ar ages and zircon petrochronology for the rear arc of the Izu-Bonin-Marianas intra-oceanic subduction zone

Long-lived intra-oceanic arcs of Izu-Bonin-Marianas (IBM)-type are built on thick, granodioritic crust formed in the absence of pre-existing continental crust. International Ocean Discovery Program Expedition 350, Site U1437, explored the IBM rear arc to better understand continental crust formation in arcs. Detailed petrochronological (U–Pb geochronology combined with trace elements, oxygen and hafnium isotopes) characterizations of zircon from Site U1437 were carried out, taking care to exclude potential contaminants by (1) comparison of zircon ages with ship-board palaeomagnetic and biostratigraphic ages and ⁴⁰Ar/³⁹Ar geochronology, (2) analysing zircon from drill muds for comparison, (3) selectively carrying out in situ analysis in petrographic thin sections, and (4) minimizing potential laboratory contamination through using pristine equipment during mineral separation. The youngest zircon ages in Site U1437 are consistent with ⁴⁰Ar/³⁹Ar and shipboard ages to a depth of ~1390 m below sea floor (mbsf) where Igneous Unit Ig 1 yielded an ⁴⁰Ar/³⁹Ar age of 12.9 ± 0.3 Ma (all errors 2σ). One single zircon (age 15.4 ± 1.0 Ma) was recovered from the deepest lithostratigraphic unit drilled, Unit VII (1459.80–1806.5 mbsf). Site U1437 zircon trace element compositions are distinct from those of oceanic and continental arc environments and differ from those generated in thick oceanic crust (Iceland-type) where low-δ¹⁸O evolved melts are produced via re-melting of hydrothermally altered mafic rocks. Ti-in-zircon model temperatures are lower than for mid-ocean ridge rocks, in agreement with low zircon saturation temperatures, suggestive of low-temperature, hydrous melt sources. Zircon oxygen (δ¹⁸O = 3.3–6.0‰) and hafnium (εHf = + 10–+16) isotopic compositions indicate asthenospheric mantle sources. Trace element and isotopic differences between zircon from Site U1437 rear-arc rocks and the Hadean detrital zircon population suggest that preserved Hadean zircon crystals were probably generated in an environment different from modern oceanic convergent margins underlain by depleted mantle.     

Late Holocene marine productivity changes in Northern Patagonia-Chile inferred from a multi-proxy analysis of Jacaf channel sediments

A multi-proxy approach based on organic (organic carbon, alkenones, and C/N) and inorganic geochemical proxies (biogenic opal, inorganic carbon, Fe, Ti, and Ca) preserved in the sediments of the Jacaf channel (CF7-PC33; 44°21′S, 72°58′W, 510 m water depth), Chilean fjords, yields evidence of major past productivity fluctuations in accordance with climatic changes over the last ∼1800 years. The downcore record clearly shows two productivity/climate modes. The first period, prior to 900 cal yr BP, is characterized by decreased marine productivity and a reduced continental signal, pointing to diminished precipitation and runoff. In contrast, the second period between ∼750 cal yr BP and the late 1800s (top of core) is illustrated by elevated productivity and an increased continental signal, suggesting higher precipitation and runoff. Both time intervals are separated by a relatively abrupt transition of ∼150 years which roughly coincides with the beginning of the Little Ice Age. The increased content of freshwater diatoms and Chrysophyte cysts that characterize the last 200 years of the latter mode coincides with a significant decrease in the carbonate content of the sediment; together they further indicate increased terrigenous contributions and decreased marine carbonate productivity at the end of the Little Ice Age. The correspondence between our record and other paleoclimate studies carried out in South America and Antarctica demonstrates that the Chilean fjord area of Northern Patagonia is not just sensitive to local climatic variability but also to regional and possibly global variability.     

Model computations of Schumann resonance on Titan

We model the global electromagnetic (Schumann) resonance in the atmosphere of Titan. Parameters of conductivity of the lower ionosphere were implemented taken from existing aeronomic models of Titan's atmosphere. Two exponential conductivity profiles were constructed: one of them suggests favorable conditions for Schumann resonance and the other models considerable attenuation in the ionospheric plasma. Peak frequencies and Q-factors of resonance were computed as well as resonance spectra for the signals arriving from individual vertical lightning discharges and from strokes uniformly distributed over the planet. The models show that detection of Schumann resonance on Titan is feasible, especially in favorable conditions. Possible applications of Schumann resonance in the studies of Titan's lightning activity are outlined.