The relationship between ULF geomagnetic pulsations and ionospheric Doppler oscillations: Model predictions

This paper is a continuation of the work of Sutcliffe and Poole (1989, J. geophys. Res. 94, 13,505) which described the mechanisms which connect ground-based geomagnetic pulsation measurements with simultaneously observed Doppler velocity oscillations (V^*) in the ionosphere. We concentrate on a presentation of model predictions that show the extreme variability of V^* with parameters such as radio sounding frequency, electron concentration profile, magnetoionic mode, geomagnetic field inclination, scale length and pulsation frequency. The potential to use these results in a diagnostic fashion is also discussed.     

Analysis and survival of amino acids in Martian regolith analogs

Abstract— We have investigated the native amino acid composition of two analogs of Martian soil, JSC Mars‐1 and Salten Skov. A Mars simulation chamber has been built and used to expose samples of these analogs to temperature and lighting conditions similar to those found at low latitudes on the Martian surface. The effects of the simulated conditions have been examined using high‐performance liquid chromatography (HPLC). Exposure to energetic ultraviolet (UV) light in vacuum appears to cause a modest increase in the concentration of certain amino acids within the materials, which is interpreted as resulting from the degradation of microorganisms. The influence of low temperatures shows that the accretion of condensed water on the soils leads to the destruction of amino acids, supporting the idea that reactive chemical processes involving H₂O are at work within the Martian soil. We discuss the influence of UV radiation, low temperatures, and gaseous CO₂ on the intrinsic amino acid composition of Martian soil analogs and describe, with the help of a simple model, how these studies fit within the framework of life detection on Mars and the practical tasks of choosing and using Martian regolith analogs in planetary research.     

Age and paragenesis of mineralisation at Coronation Hill uranium deposit,Northern Territory,Australia

Coronation Hill is a U?+?Au?+?platinum group elements deposit in the South Alligator Valley (SAV) field in northern Australia, south of the better known unconformity-style U East Alligator Rivers (EAR) field. The SAV field differs from the EAR by having a more complex basin-basement architecture. A volcanically active fault trough (Jawoyn Sub-basin) developed on older basement and then was disrupted by renewed faulting, before being buried beneath regional McArthur Basin sandstones that are also the main hanging wall to the EAR deposits. Primary mineralisation at Coronation Hill formed at 1607?±?26 Ma (rather than 600–900 Ma as previously thought), and so it is likely that the SAV was part of a single west McArthur Basin dilational event. Most ore is hosted in sub-vertical faults and breccias in the competent volcanic cover sequence. This favoured fluid mixing, acid buffering (forming illite) and oxidation of Fe²⁺ and reduced C-rich assemblages as important uranium depositional mechanisms. However, reduction of U in fractured older pyrite (Pb model age of 1833?±?67 Ma) is an important trap in diorite. Some primary ore was remobilised at 675?±?21 Ma to form coarse uraninite?+?Ni-Co pyrite networks containing radiogenic Pb. Coronation Hill is polymetallic, and in this respect resembles the ‘egress’-style U deposits in the Athabascan Basin (Canada). However, these are all cover-hosted. A hypothesis for further testing is that Coronation Hill is also egress-style, with ores formed by fluids rising through basement-hosted fault networks (U reduction by diorite pyrite and carbonaceous shale), and into veins and breccias in the overlying Jawoyn Sub-basin volcano-sedimentary succession.     

Measurement of tsunamis in the open ocean

Abstract

The spectrum of long waves, which are a background to tsunamis, is analyzed on the basis of records of near‐bottom pressure sensors obtained in the Northwest Pacific during the first and second USA‐USSR expeditions on the investigation of tsunamis in the open ocean (1975 and 1978). Instrumental trends, tidal oscillations, and quasistationary longwave noise were contained in the records. Special filters were used to pick out small waves generated by the seismicity of the ocean bottom. A decrease of noise level from 10² cm (including tides) to 10°¹ cm could be reached. The level of long‐wave noise is found to depend on the instrument's location. Minimal disturbances in the records were observed at stations situated on the edge of the continental slope. The influence of cyclones passing over the instrument's site is deduced. It shows an increase in noise level on Nyquist frequency (0.5 min°¹), which possibly is caused by the action of swell generated by the cyclone. Seismicity of the region under investigation for the second expedition (August‐October 1978) is described, and the recurrence of tsunamis is estimated, including microtsunamis. Taking into account this analysis, records were filtered and sections corresponding to probable arrivals of tsunamis from most strong earthquakes were selected. The anomalous disturbance of ocean level with a height of about 0.5 cm was found. Presumably, it was generated by an earthquake with magnitude M = 6.     

Salt Spray Induces Osmotic Adjustment and Tissue Rigidity in Smooth Cordgrass, <Emphasis Type="Italic">Spartina alterniflora</Emphasis> (Loisel.)

Salt spray is one of many abiotic factors that can influence plant productivity and species composition in coastal ecosystems. However, little is known about how marsh plants respond physiologically to the accumulation of sea aerosols on foliar tissues. In this study, experimental microcosms maintained in controlled greenhouse conditions were used to evaluate how low- (1.7 mg dm⁻² day⁻¹, weekly averages) and high- (8.6 mg dm⁻² day⁻¹) salt-spray loads would influence plant–water relations in Spartina alterniflora (Loisel.). While no differences in plant performance (e.g., changes in biomass and leaf area) were observed between the treatments and control plants, a number of physiological modifications attributed to salt spray were observed. In general, salt-treated plants underwent significant decreases in water potential (Ψ) and osmotic potential (Ψ _π) and increases in leaf conductance (g) and bulk modulus of elasticity (ε). It is likely that these physiological responses were used to generate lower Ψ while maintaining osmotic and water homeostasis. That is, by decreasing Ψ _π and increasing g and ε, more efficient water flow through the soil–plant–atmosphere continuum can be achieved, thus generating lower Ψ without promoting loss of turgor.     

High-resolution precipitation and temperature downscaling for glacier models

The spatial resolution gap between global or regional climate models and the requirements for local impact studies motivates the need for climate downscaling. For impact studies that involve glacier modelling, the sparsity or complete absence of climate monitoring activities within the regions of interest presents a substantial additional challenge. Downscaling methods for this application must be independent of climate observations and cannot rely on tuning to station data. We present new, computationally-efficient methods for downscaling precipitation and temperature to the high spatial resolutions required to force mountain glacier models. Our precipitation downscaling is based on an existing linear theory for orographic precipitation, which we modify for large study regions by including moist air tracking. Temperature is downscaled using an interpolation scheme that reconstructs the vertical temperature structure to estimate surface temperatures from upper air data. Both methods are able to produce output on km to sub-km spatial resolution, yet do not require tuning to station measurements. By comparing our downscaled precipitation (1 km resolution) and temperature (200 m resolution) fields to station measurements in southern British Columbia, we evaluate their performance regionally and through the annual cycle. Precipitation is improved by as much as 30% (median relative error) over the input reanalysis data and temperature is reconstructed with a mean bias of 0.5°C at locations with high vertical relief. Both methods perform best in mountainous terrain, where glaciers tend to be concentrated.     

Terror in the skies of Russia

It was just another normal day for the residents of the Russian town of Chelyabinsk as they set off for work on Friday 15 February 2013. A rock less than 20 metres wide changed all that. A meteor weighing some 11 000 tonnes hit the Earth's atmosphere above the Ural Mountains with an estimated speed of 18 km/s (65 000 km/h). It exploded over Chelyabinsk with the force of 30 Hiroshima bombs, causing a shockwave to tear through the region and injuring over 1500 people. It was the biggest meteor strike in the last 100 years, and undoubtedly the most archived ever.     

Suspended solid yield from forest harvesting on upland blanket peat

Forest harvesting activities, if not carefully carried out, can disturb the forest soils and can cause significant suspended solid concentration increases in receiving water. This study examined how harvesting, following forestry guidelines, influenced suspended solid concentrations and loads in the receiving water of a blanket peat salmonid catchment. The study site comprised of two forest coupes of 34‐year‐old conifers drained by a first‐order stream. The upper coupe was not felled and acted as a baseline ‘control’ catchment; the downstream coupe was completely harvested in summer 2005 and served as the ‘experimental’ catchment. Good management practices such as the proper use of brash mats and harvesting only in dry weather were implemented to minimize soil surface disturbance and streambank erosion. Stream flow and suspended solid measurements at an upstream station (US) and a downstream station (DS) in the study stream commenced over a year before felling took place. The suspended solid concentrations, yields and release patterns at US and DS were compared before and after harvesting. These showed that post‐guideline harvesting of upland blanket peat forest did not significantly increase the suspended solid concentrations in the receiving water and the aquatic zone need not be adversely affected by soil releases from sites without a buffer strip. Copyright © 2010 John Wiley & Sons, Ltd.     

New insights into Late Pleistocene glacial and postglacial history of northernmost Ungava (Canada) from Pingualuit Crater Lake sediments

The Pingualuit Crater was formed by a meteoritic impact ca. 1.4 million years ago in northernmost Ungava (Canada). Due to its geographical position near the center of successive North American ice sheets and its favorable morphometry, the Pingualuit Crater Lake (water depth = 246 m) promises to yield a unique continuous sedimentary sequence covering several glacial/interglacial cycles in the terrestrial Canadian Arctic. In this paper, we suggest the existence of a subglacial lake at least during the Last Glacial Maximum (LGM) by hydraulic potential modeling using LGM ice-surface elevation and bed topography derived from a digital elevation model. These results support the hypothesis that the bottom sediments of the Crater Lake escaped glacial erosion and may contain a long-term continental sedimentary sequence. We also present the stratigraphy of a 9 m-long core retrieved from the deep basin of the lake as well as a multiproxy reconstruction of its deglacial and postglacial history. The base of the core is formed by very dense diamicton reflecting basal melt-out environments marking the end of subglacial conditions at the coring site. The overlying finely laminated silt are related to the onset of proglacial conditions characterized by extremely low lacustrine productivity. Infra Red Stimulated Luminescence and AMS ¹⁴C dating, as well as biostratigraphic data indicate sediment mixing between recent (e.g. Holocene) and much older (pre- to mid-Wisconsinan) material reworked by glacier activity. This process prevents the precise dating of these sediments that we interpret as being deposited just before the final deglaciation of the lake. Two finer grained and organic-rich intervals reflect the inception of lacustrine productivity resulting from the cessation of glacial meltwater inputs and ice-free periods. The lower organic interval corresponds to the early postglacial period (6850–5750 cal BP) and marks the transition between proglacial and postglacial conditions during the Holocene Thermal Maximum, while the uppermost organic-rich core section represents late Holocene sediments (～4200–600 cal BP). The organic intervals are separated by a basin-scale erosive slide occurring around 4200 cal BP and likely related to 1) a seismic event due to the glacio-isostatic rebound following the last deglaciation or 2) slope instabilities associated with rapid discharge events of the lake.