ALBERT

Description: Thick sulfate evaporite accumulations are absent from Proterozoic strata between ca. 2000 and ca. 1000 Ma, and detailed sedimentologic, stratigraphic, and geochemical data for the oldest Neoproterozoic thick marine sulfate evaporite successions are largely lacking. The middle Neoproterozoic Ten Stone Formation (Little Dal Group, Northwest Territories, Canada) consists of ~500 m of pelagic lagoonal gypsite and anhydritite (rocks consisting of the minerals gypsum and anhydrite) deposited shortly before the ca. 811 Ma Bitter Springs carbon isotope anomaly in an intracratonic basin that developed prior to breakup of Rodinia. The thickness of regional stratigraphic subdivisions of this formation, defined by subtle silt- and carbonate-bearing intervals, indicates a minor terrigenous source in the southeast and a silled connection to the open ocean in the northwest. Deposition of the Ten Stone Formation began with abrupt, tectonically triggered subsidence and restriction, and ended equally abruptly, as shown by stratigraphic contacts across which lithofacies corresponding to strikingly different paleoenvironments change sharply, with no evidence for hiatus or erosion. Stratigraphic cyclicity in the evaporite succession is minimal owing to isolation of bottom-hugging, dense lagoonal brine from overlying waters. Deposition of the Ten Stone Formation in a basin that experienced intermittent, basin-scale tectonic adjustments, as recorded by details of its stratigraphy, supports the interpretation that the Mackenzie Mountains Supergroup accumulated in an extensional, tectonically active intracratonic basin whose structure resembled a lower-plate extensional system. The absence of halite from the Ten Stone Formation contrasts with its abundance in the stratigraphically lower, gypsum-free Dodo Creek Formation, suggesting that deposition of the lower to middle Little Dal Group spanned a major oxygenation event, during which the sequence of evaporite mineral precipitation from seawater changed from halite-first to sulfate-first in response to rapid accumulation of atmospheric oxygen and concomitant increase in the global marine sulfate reservoir. The limited range of sulfur isotope values in a new data set spanning hundreds of meters of gypsite indicates a strongly and persistently oxidizing mid-Neoproterozoic atmosphere, an abundance of sulfate in seawater, and marine oxygenation extending below storm wave base. The mineralogy, sedimentology, stratigraphy, and geochemistry of the Ten Stone Formation are virtually indistinguishable from those of thick, Phanerozoic "deep-water" (below wave-base) evaporite successions, and indicate that the tectonic, climatic, and geochemical conditions required for deposition of thick successions of marine sulfate evaporites were well established prior to ca. 811 Ma. Thick sulfate evaporite successions in equivalent stratigraphic positions just below the Bitter Springs carbon isotope excursion elsewhere in Laurentia, as well as on the Congo craton, and in South Australia attest to the global impact of the rapidly increased seawater sulfate reservoir prior to Rodinia’s breakup. High relative burial rates of organic matter prevailed before the breakup of Rodinia and led to oxygenation of the atmosphere-ocean system, growth of the seawater sulfate reservoir, and, in association with a warm and arid climate, deposition for the first time in Earth’s history of thick sulfate evaporites in the middle Neoproterozoic, ~100 m.y. before the first Cryogenian glacial episode. The Neoproterozoic Oxygenation Event may have taken place in several steps, the first of which preceded the Bitter Springs anomaly.

Description: Life on Earth is thought to have coevolved with the chemistry of the oceans and atmosphere, and the shift from an anoxic to an oxic world across the Archean-Proterozoic boundary represents a fundamental step in this process. In order to understand the relative influence of biological and geological factors on this transition, we must constrain key variables in seawater chemistry before the Great Oxidation Event (ca. 2500 Ma). We present a multielement (C-S-Fe-Mo) biogeochemical study of ca. 2662 Ma shales from the Hamersley Province in Western Australia. Our data reveal a sustained episode of Fe-limited pyrite formation under an anoxic and sulfidic (euxinic) water column. This is the oldest known occurrence of euxinia in Earth's history and challenges the paradigm of persistently Fe-rich Archean oceans. Bulk trace metal chemistry and preservation of strong mass-independent S isotope fractionations in sedimentary pyrites indicate that ocean euxinia was possible prior to oxidative weathering, suggesting that sulfidic waters may have been common throughout the Archean Eon. C-S-Fe systematics suggest that oxygenic photosynthesis was the primary source of organic carbon in the basin, and the absence of Mo enrichments highlights a potential link between inefficient nitrogen fixation and the delayed arrival of the Great Oxidation Event.

Description: Abstract Antarctic sea ice shows a large degree of regional variability, which is partly driven by severe weather events. Here we bring a new perspective on synoptic sea ice changes by presenting the first in situ observations of an explosive extratropical cyclone crossing the winter Antarctic marginal ice zone (MIZ) in the South Atlantic. This is complemented by the analysis of subsequent cyclones and highlights the rapid variations that ice‐landing cyclones cause on sea ice: Midlatitude warm oceanic air is advected onto the ice, and storm waves generated close to the ice edge contribute to the maintenance of an unconsolidated surface through which waves propagate far into the ice. MIZ features may thus extend further poleward in the Southern Ocean than currently estimated. A concentration‐based MIZ definition is inadequate, since it fails to describe a sea ice configuration which is deeply rearranged by synoptic weather.

Description: We created six new tree-ring chronologies in northern Utah, which were used with pre-existing chronologies from Utah and western Wyoming to reconstruct mean annual flow for the Logan River, the largest tributary of the regionally important Bear River. Two reconstruction models were developed, a ‘Local’ model that incorporated two Rocky Mountain juniper chronologies located within the basin, and a ‘Regional’ model that also included limber pine and pinyon pine chronologies from a larger area. The Local model explained 48.2% of the variability in the instrumental record and the juniper chronologies better captured streamflow variability than Douglas-fir collected within the Logan basin. Incorporating chronologies from the northern and southern margins of the transition zone of the western precipitation dipole increased the skill of the Regional model (r2 = 0.581). We suggest the increased Regional model skill indicates that both nodes of the western precipitation dipole influence northern Utah climate. The importance of Rocky Mountain juniper in both reconstructions of streamflow for this region suggests that future work should target these trees where more traditionally desirable species are not present. The reconstructions provide the first extended record of streamflow in northern Utah. Pre-instrumental streamflows (1605-1921) exhibited considerable variability when compared to the instrumental period (1922-2005). Our findings confirm that the inherent uncertainty in contemporary water management and planning in the region is due to hydroclimatic variability that has persisted for at least the last four centuries.

Description: The first systematic study of the BaO–B 2 O 3 system and barium orthoborate Ba 3 B 2 O 6 (3BaO·B 2 O 3 ) was reported in 1949. Thereafter, the system was repeatedly refined but the structure of Ba 3 B 2 O 6 compound has not been adequately studied yet. In our study we have, for the first time, obtained the crystalline samples of Ba 3 B 2 O 6 . The solved structure ( Pbam , a = 13.5923(4) Å, b = 13.6702(4) Å, c = 14.8894(3) Å) belongs to the class of ‘anti-zeolite’ borates with a pseudotetragonal [ Ba 12 (BO 3 ) 6 ] 6+ cation pattern which contains channels along the c axis filled with anionic clusters. The Ba 3 B 2 O 6 compound may be regarded as a fluorine-free end-member of the Ba 3 (BO 3 ) 2– x F 3 x solid solution. The BaO–B 2 O 3 phase diagram presented in our study is based on our research and literature data. This article is protected by copyright. All rights reserved.

Description: To address the problem of indoor fungal growth, understanding the influence of moisture conditions on the fungal colonization process is crucial. This paper explores the influence of past moisture conditions on current processes. Specifically, it studies the growth and water sorption of conidia of Penicillium rubens formed at lower water activities (ranging from 0.86 to 0.99). For the first time, dynamic vapor sorption (DVS) is applied as a tool to quantify the water sorption of conidia as a function of the water activity at conidiation. Furthermore, growth experiments on agar and gypsum substrates are reported that relate hyphal growth rates of the mycelium from pretreated conidia to the water activity at conidiation. No effect of the conidiation water activity on mycelial growth rates is found on either gypsum or agar. It is found, however, that conidia formed at lower activities have a higher dry weight and attract more water from humid air. It is shown that both phenomena can be explained by conidia from lower activities carrying higher amounts of compatible solutes, glycerol in particular. The enhanced sorption observed in this study might constitute a mechanism through which solute reserves contribute to survival during the early steps of fungal colonization. The sorption behavior of conidia of Penicillium rubens that were formed under harsh moisture conditions was studied using a dynamic vapor sorption apparatus. It is found that conidia formed at low water activity will attract many times their own volume in water from humid air. From analysis of the sorption isotherms, it is deduced that this enhanced sorption behavior must be caused by large amounts of intra- and extracellular glycerol that was stored during sporulation.

Description: Constraining oxygen levels in the early Precambrian surface ocean has been a longstanding goal, but efforts have been challenged by the availability of suitable proxies. Here we present a novel approach, iodine geochemistry, which broadens our perspective by providing constraints on shallow, carbonate-dominated marine settings. Iodate ( ) persists exclusively in oxic waters and is the sole iodine species incorporated into carbonate minerals, allowing iodine-to-calcium ratios (I/Ca) in shallow carbonates to be used as a paleoredox indicator. Our data from a series of Mesoarchean through Paleoproterozoic carbonates deposited under shallow-marine conditions reveal a progressive surface ocean oxygenation in the early Paleoproterozoic. These data seem to indicate that a largely anoxic surface ocean extended throughout the Archean until the Great Oxidation Event (GOE) at ca. 2.4 Ga, implying that previous inferences of pre-GOE oxygen production may reflect oxygen oases, transient oxidation events, or oxygen levels below those required for accumulation. The data suggest formation and persistence of and, consequently, surface ocean oxygen concentrations of at least 1 µM during the GOE. Following the initial rise of oxygen, carbonate-associated iodine in globally extensive carbonate units deposited during the Lomagundi positive carbon isotope excursion at ca. 2.22–2.1 Ga suggests a widespread aerobic iodine cycle beyond that operating prior to the event, synchronous with high relative rates of organic carbon burial and apparent expansion of oxidative conditions.

Description: Although initial studies have demonstrated the applicability of Ni isotopes for cosmochemistry and as a potential biosignature, Ni isotope composition of terrestrial igneous and sedimentary rocks, and ore deposits remains poorly known. Our contribution is four-fold: (1) to detail an analytical procedure for Ni isotope determination, (2) to determine the Ni isotope composition of various geological reference materials, (3) to assess the isotope composition of the Bulk Silicate Earth relative to the Ni isotope reference material NIST SRM 986, and (4) to report the range of mass-dependent Ni isotope fractionations in magmatic rocks and ore deposits. After purification through a two-stage chromatography procedure, Ni isotope ratios were measured by MC-ICP-MS and were corrected for instrumental mass bias using a double-spike correction method. Measurement precision (two standard error of the mean) was between 0.02 and 0.04‰ and intermediate measurement precision for NIST SRM 986 was 0.05‰ (2 s ). Igneous and mantle-derived rocks displayed a restricted range of δ 60/58 Ni values between -0.13 and +0.16‰ suggesting an average BSE composition of +0.05‰. Manganese nodules (Nod A1; P1), shale (SDO-1), coal (CLB-1) and a metal-contaminated soil (NIST SRM 2711) showed positive values ranging between +0.14 and +1.06‰, whereas komatiite-hosted Ni-rich sulfides varied from -0.10 to -1.03‰. © 2013 The Authors. Geostandards and Geoanalytical Research © 2013 International Association of Geoanalysts

Description: [1]  Science missions have limited lifetimes, necessitating an efficient investigation of the field site. The efficiency of onboard cameras, critical for planning, is limited by the need to downlink images to Earth for every decision. Recent advances have enabled rovers to take follow-up actions without waiting hours or days for new instructions. We propose using built-in processing by the instrument itself for adaptive data collection, faster reconnaissance, and increased mission science yield. We have developed a machine learning pixel classifier that is sensitive to texture differences in surface materials, enabling more sophisticated onboard classification than was previously possible. This classifier can be implemented in a Field Programmable Gate Array (FPGA) for maximal efficiency and minimal impact on the rest of the system's functions. In this paper, we report on initial results from applying the texture-sensitive classifier to three example analysis tasks using data from the Mars Exploration Rovers.