Protracted storage of CR chondrules in a region of the disk transparent to galactic cosmic rays

Renazzo‐type carbonaceous (CR) chondrites are accretionary breccias that formed last. As such they are ideal samples to study precompaction exposures to cosmic rays. Here, we present noble gas data for 24 chondrules and 3 dark inclusion samples (DIs) from Shi?r 033 (CR2). The meteorite was selected based on the absence of implanted solar wind noble gases and an anomalous oxygen isotopic composition of the DIs; the oxygen isotopes match those in CV3 and CO3 chondrites. Our samples contain variable mixtures of galactic cosmic ray (GCR)‐produced cosmogenic noble gases and trapped noble gases of presolar origin. Remarkably, all chondrules have cosmogenic ³He and ²¹Ne concentrations up to 4.3 and 7.1 times higher than the DIs, respectively. We derived an average ³He‐²¹Ne cosmic ray exposure (CRE) age for Shi?r 033 of 2.03 ± 0.20 Ma (2 SD) and excesses in cosmogenic ³He and ²¹Ne in chondrules (relative to the DIs) in the range (in 10^?8 cm³STP/g) 3.99–7.76 and 0.94–1.71, respectively. Assuming present‐day GCR flux density, the excesses translate into average precompaction ³He‐²¹Ne CRE ages of 3.1–27.3 Ma depending on the exposure geometry. The data can be interpreted assuming a protracted storage of a single chondrule generation prior to the final assembly of the Shi?r 033 parent body in a region of the disk transparent to GCRs.     

Neon produced by solar cosmic rays in ordinary chondrites

Solar‐cosmic‐ray‐produced Ne (SCR‐Ne), in the form of low cosmogenic ²¹Ne/²²Ne ratios (²¹Ne/²²Ne_cos <0.8), is more likely to be found in rare meteorite classes, like Martian meteorites, than in ordinary chondrites. This may be the result of a sampling bias: SCR‐Ne is better preserved in meteorites with small preatmospheric radii and these specimens are often only studied if they belong to unusual or rare classes. We measured He and Ne isotopic concentrations and nuclear tracks in 25 small unpaired ordinary chondrites from Oman. Most chondrites have been intensively heated during atmospheric entry as evidenced by the disturbed track records, the low ³He/²¹Ne ratios, the low ⁴He concentrations, and the high peak release temperatures. Concentration depth profiles indicate significant degassing; however, the Ne isotopes are mainly undisturbed. Remarkably, six chondrites have low ²¹Ne/²²Ne_cos in the range 0.711–0.805. Using a new physical model for the calculation of SCR production rates, we show that four of the chondrites contain up to ~20% of SCR‐Ne; they are analyzed in terms of preatmospheric sizes, cosmic ray exposure ages, mass ablation losses, and orbits. We conclude that SCR‐Ne is preserved, regardless of the meteorite class, in specimens with small preatmospheric radii. Sampling bias explains the predominance of SCR‐Ne in rare meteorites, although we cannot exclude that SCR‐Ne is more common in Martian meteorites than it is in small ordinary chondrites.     

Mesoscale physical processes and zooplankton transport-retention in the northern Norwegian shelf region

Northern Norwegian shelf regions are highly productive, supporting fisheries rich in commercially important species such as cod, herring and capelin. It has been long recognized that the mesoscale jets, meanders and eddies associated with interactions between the North Atlantic Current, Norwegian Coastal Current and regional bottom topographic features such as troughs, banks and shelfbreaks play important roles in transporting and retaining zooplankton. To investigate zooplankton distributions and their correspondence with the physical fields, three large-scale surveys with mesoscale resolutions on physical and biological fields were conducted in northern Norwegian shelf regions between latitudes 68°15′N and 70°15′N in springs of 2000–2002. Survey results provide insights into the relationships between zooplankton distributions and the physical features such as fronts, the Norwegian Coastal Current and eddies related to topographic features. The physical and biological data are integrated and analyzed focusing on water types, estimation of geostrophic currents from direct current measurements, along-shelf transport of zooplankton, and retention of zooplankton by the mesoscale meander–eddy over a typical bank area on the shelf. The estimated mean transport in the upper 100 m on the shelf in the survey region is approximately 6.4×10³ tonnes wet weight day⁻¹ northward. High zooplankton abundances were found over both Malangsgrunnen and Sveinsgrunnen banks. The specific accumulation rate from northward–southward transport in the upper 100 m over Malangsgrunnen was approximately 0.08 day⁻¹, while variable currents with an offshore gradient of zooplankton abundance over Sveinsgrunnen implies an offshore dispersion of coastal-originated zooplankton cohort.     

High‐Arctic climate conditions for the last 7000 years inferred from multi‐proxy analysis of the Bliss Lake record,North Greenland

The Arctic is more vulnerable to climate change than are mid latitudes. Therefore, palaeolimnological studies from the High Arctic are important in providing insights into the dynamics of the climate system. Here we present a multi‐proxy study from one of the world's northernmost lakes: Bliss Lake, Peary Land, Greenland. The early Holocene (10 850–10 480 cal. a BP) is characterized by increased erosion and gradually more marine conditions. Full marine conditions developed from 10 480 cal. a BP until the lake was isolated at 7220 cal. a BP. From its marine isolation at 7220 cal. a BP Bliss Lake becomes a lacustrine environment. Evidence from geochemical proxies (δ¹³C and total organic carbon) suggests that warmer conditions prevailed between 7220 and 6500 cal. a BP, corresponding to the Holocene thermal maximum, and from 3300 until 910 cal. a BP. From 850 to 500 cal. a BP colder climate conditions persisted. The transition from warmer to colder climate conditions taking place around 850 cal. a BP may be associated with the transition from the Medieval Warm Period to the Little Ice Age. Copyright © 2011 John Wiley & Sons, Ltd.     

Transition enthalpies and entropies of high pressure zinc metasilicates and zinc metagermanates

The enthalpies of transition at T= 298 K between zinc metasilicate assemblages, measured by molten oxide solution calorimetry, are:

The triple multimineral barrier for hazardous waste encapsulation

According to the present state of science and technology, the ultimate disposal of critical substances such as chemotoxic wastes, metal slurries, radioactive substances, etc., as well as houshold waste, necessitates enclosure within a multi-barrier system. The geology of the disposal site plays an important role. The site itself defines the geological barrier which has to fulfill at least two requirements: namely low permeability and retention, respectively retardation qualities. These can be achieved to a certain degree either by clay minerals, zeolites or an artificial product such as active coal. In order to increase the imperviousness and retardation potentials of e.g. clayey geological barriers, technical barriers have to be added. One of them and the most important is the mineralogic barrier. It consists of clay dominated layers and according to the multimineral barrier concept the different layers have to meet different functions.     

Evaluation and application of dialysis porewater samplers for microbiological studies at sediment-water interfaces

The equilibrium diffusion technique has become a valuable tool for ecological and biogeochemical studies in aquatic environments. In sediment ecosystems, changes in concentration of microbial metabolites with increasing depth can be determined dependably and reproducibly with this technique. Since the permeation characteristics of the membranes employed are crucial, selecting the proper membrane requires knowledge about its behavior under conditions which prevail in the natural environment. Thirteen polymer sheets were evaluated comparing permeation terms for biogeochemically relevant solutes, biodegradability, and mechanical strength. Cellulose-based dialysis membranes are most satisfactory when employed in low temperature anoxic environments. For this membrane, correction terms were calculated to account for diffusion losses during retrieval and sampling. Optimal incubation times can now be predicted from experimentally determined permeation coefficients for several porewater solutes. Dialysis porewater samplers (DPS) have been successfully applied during more than 100 independent experiments for the collection of interstitial water from surface sediments. DPS were used for water depths as deep as 290 meters.     

Mantle fragments in the Scandinavian caledonides

Mantle fragments of ultramafic composition are widespread in the Scandinavian Caledonides (SC). Lenses and boudins of Alpine-type peridotites in the Scandinavian Caledonides represent parts of dismembered ophiolite sequences and fragments of sub-continental upper mantle. Metaperidotites of nappes in internal positions are generally isofacial with the metamorphic envelope, usually Caledonian metasediments but in places also Precambrian metagranitoids forming the basement cores of the nappes. Caledonian metamorphism strongly modified the texture and mineralogy of the peridotites and resulted in a systematic metamorphic pattern which is consistent with the pattern observed in the envelope.

Metaperidotites of the external massifs display at least a two-stage metamorphic history: an early Caledonian high-pressure high-temperature phase related to early crustal stacking and a late Caledonian regional metamorphic overprint which produced a regular Barrovian-type metamorphic pattern of in-situ metamorphism.

Metaperidotites from nappes in intermediate positions (Iapetus Ocean ophiolites and ultramafic rocks from island arc environments) show strongly diverging histories. Metaperidotites from internal ophiolites (oceanic ophiolites, Köli) lack any evidence of subduction metamorphism, are serpentinized to various degrees, show abundant primary mantle relic mineralogies and the Caledonian metamorphic overprint is low. Metaperidotites from external (island arc) ophiolites and other associations (Seve) often show relic high-pressure metamorphism related to the Finnmarkian phase of the Caledonian orogeny. The Seve metaperidotites are occasionally associated with eclogites and show a weak overprint of late Caledonian regional metamorphism. Alpine-type peridotites are absent in the foreland of the Baltic Shield and in the innermost nappes (Lofoten).

The metamorphic characteristics and evolution recorded by the metaperidotites in the Scandinavian Caledonides allow a general reconstruction of the dynamics of collision belt formation.