Radar observations of auroral zone flows during a multiple-onset substorm

We present an analysis of ground magnetic field, ionospheric flow, geosynchronous particle, and interplanetary data during a multiple-onset substorm on 12 April 1988. Our principal results concern the modulations of the ionospheric flow which occur during the impulsive electrojet activations associated with each onset. During the first hour of the disturbance these take place every \sim12.5 min and involve the formation of a new intense westward current filament in the premidnight sector, just poleward of the preexisting extended current system driven by the large-scale flow. These filaments are \sim1 h MLT wide (\sim600 km), and initially expand poleward to a width of \sim300 km before contracting equatorward and coalescing with the preexisting current, generally leaving the latter enhanced in magnitude and/or expanded in latitude. Within the impulsive electrojets the flow is found to be suppressed to values 50–100 m s⁻¹ or less during the first few minutes, before surging equatorward at 0.5-1.0 km s⁻¹ during the phase of rapid coalescence. The implication is that the precipitation-induced Hall conductivity within the impulsive electrojet initially rises to exceed \sim100 mho, before decaying over a few minutes. This value compares with Hall conductivities of \sim20 mho in the quasi-steady current regions, and a few mho or less in the regions poleward of the electrojets and in the preonset ionosphere. Preliminary evidence has also been found that the flow surges propagate from midnight to the morning sector where they are associated with arrested equatorward motion or poleward contractions of the current system. These observations are discussed in terms of present theoretical paradigms of the global behaviour of fields and flows which occur during substorms.     

An example of fingerprint detection of greenhouse climate change

As an example of the technique of fingerprint detection of greenhouse climate change, a multivariate signal or fingerprint of the enhanced greenhouse effect is defined using the zonal mean atmospheric temperature change as a function of height and latitude between equilibrium climate model simulations with control and doubled CO₂ concentrations. This signal is compared with observed atmospheric temperature variations over the period 1963 to 1988 from radiosonde-based global analyses. There is a significant increase of this greenhouse signal in the observational data over this period.These results must be treated with caution. Upper air data are available for a short period only, possibly too short to be able to resolve any real greenhouse climate change. The greenhouse fingerprint used in this study may not be unique to the enhanced greenhouse effect and may be due to other forcing mechanisms. However, it is shown that the patterns of atmospheric temperature change associated with uniform global increases of sea surface temperature, with El NinoSouthern Oscillation events and with decreases of stratospheric ozone concentrations individually are different from the greenhouse fingerprint used here.     

Analysis of high-voltage,high-resolution images of lattice defects in experimentally-deformed dolomite

Deformation-induced stacking defects in dolomite have been characterised following examination at the cation sublattice level using high-resolution electron microscopy at 500kV. Slip on c (≡{0001}) is observed to produce stacking faults, often de-localised laterally, which are terminated by partial dislocations with Burgers vectors of the form 1/3 [1 \(\overline 1 \) 00]: a model for the faulted dolomite lattice has been constructed which agrees with the image appearance. Slip on f (≡{10 \(\overline 1 \) 2}) produces long planar faults which are established as not being stacking faults, in the normal sense, since there appear to be no offsets of the cation sublattice across the faults, nor any general indication of any terminating partial dislocations: it is proposed that the contrast arises from rotational disorder in CO₃ groups which has resulted from the prior passage of partial dislocations during deformation.     

Acquisition and processing of data for isotope-ratio-monitoring mass spectrometry

Methods are described for continuous monitoring of signals required for precise analyses of 13C, 18O, and 15N in gas streams containing varying quantities of CO2 and N2. The quantitative resolution (i.e. maximum performance in the absence of random errors) of these methods is adequate for determination of isotope ratios with an uncertainty of one part in 10(5); the precision actually obtained is often better than one part in 10(4). This report describes data-processing operations including definition of beginning and ending points of chromatographic peaks and quantitation of background levels, allowance for effects of chromatographic separation of isotopically substituted species, integration of signals related to specific masses, correction for effects of mass discrimination, recognition of drifts in mass spectrometer performance, and calculation of isotopic delta values. Characteristics of a system allowing off-line revision of parameters used in data reduction are described and an algorithm for identification of background levels in complex chromatograms is outlined. Effects of imperfect chromatographic resolution are demonstrated and discussed and an approach to deconvolution of signals from coeluting substances described.     

The use of bromide and chloride mass ratios to differentiate salt-dissolution and formation brines in shallow groundwaters of the Western Canadian Sedimentary Basin

In the Western Canadian Sedimentary Basin, the petroleum industry handles two geochemically distinctive brines that are traceable in the environment: formation brines extracted along with hydrocarbons from the basin, and salt-dissolution brines, produced by dissolving deep halite formations to create caverns for petroleum product storage. The concentrations of the conservative ions chloride (Cl) and bromide (Br) in many formation brines plot closely to the seawater evaporation trajectory of previous studies. These brines contain Cl/Br mass ratios of around 300, while salt-dissolution brines are relatively Br depleted, having Cl/Br mass ratios in excess of 20,000. An oilfield site in central Alberta had experienced nearby releases of both salt-dissolution and formation brines. Geochemical mixing trends were defined by theoretically mixing samples of local salt-dissolution and formation brine sources with background shallow groundwater. Most site monitoring wells and local surface water samples plotted directly on a salt-dissolution brine dilution trend, while results from four monitoring wells, all located directly downgradient of formation brine spills, suggested the mixing of formation brines into shallow groundwater. This work indicates that there is a large-scale salt-dissolution brine plume beneath the site and reinforces the use of Cl and Br concentrations and mass ratios as environmental tracers.     

Lipids of marine Archaea: Patterns and provenance in the water-column and sediments

We measured archaeal lipid distributions from globally distributed samples of freshwater, marine, and hypersaline suspended particulate matter. Cluster analysis of relative lipid distributions identified four distinct groups, including: (1) marine epipelagic (<100 m) waters, (2) marine mesopelagic (200-1500 m) and upwelling waters, (3) freshwater/estuarine waters, and (4) hypersaline waters. A pronounced difference in lipid composition patterns is the near absence of ring-containing glycerol dialkyl glycerol tetraethers (GDGTs) at high salinity. Different archaeal communities populate marine (mesophilic Crenarchaeota and Euryarchaeota), and hypersaline environments (halophilic Euryarchaeota) and community shifts can regulate differences in lipid patterns between marine and hypersaline waters. We propose that community changes within meosphilic marine Archaea also regulate the lipid patterns distinguishing epipelagic and mesopelagic/upwelling zones. Changes in the relative amounts of crenarchaeol and caldarchaeol and low relative abundances of ringed structures in surface waters differentiate lipids from the epipelagic and mesopelagic/upwelling waters. Patterns of lipids in mesopelagic (and upwelling) waters are similar to those expected of the ammonia-oxidizing Group I Crenarchaeota, with predominance of crenarchaeol and abundant cyclic GDGTs; non-metric multidimensional analysis (NMDS) shows this pattern is associated with high nitrate concentrations. In contrast, limited culture evidence indicates marine Group II Euryarchaeota may be capable of producing mainly caldarchaeol and some, but not all, of the ringed GDGTs and we suggest that these organisms, along with the Crenarchaeota, contribute to lipids in epipelagic marine waters. Calculated TEX₈₆ temperatures in mesopelagic samples (reported here and in published data sets) are always much warmer than measured in situ temperatures. We propose lipids used in the temperature proxy derive from both Euryarchaeaota and Crenarchaeota, and observed values of TEX₈₆ are subject to changes in their ecology as influenced by nutrient fluctuations or other perturbations. Applications of published core-top TEX₈₆-SST correlations require that (1) the surface waters are always composed of similar communities with the same temperature response and (2) that deeper water GDGT production is not transported to the sediments. Our lipid distribution patterns demonstrate both surface-water archaeal community differences (which accompany greater nutrient influxes, shoaling of mesopelagic Crenarchaeota during upwelling periods, and possibly due to an influx of terrestrial Archaea), and changes in organic matter transport through the water column can affect the distribution of lipids recorded in sediments. We therefore suggest that reported temperature shifts in ancient applications indicate TEX₈₆ lipids recorded not only temperature changes, but also changes in archaeal ecology, nutrient concentrations, and possibly oceanographic conditions.     

I/I ratios in surface waters of the English Lake District

Accelerator Mass Spectrometry (AMS) was used to measure ¹²⁹I/¹²⁷I ratios in surface sea, lake, and river water samples collected in 2004 and 2005 from the English Lake District and from SW Scotland, areas which are in relatively close proximity to the Sellafield nuclear fuel reprocessing plant in NW England. The ¹²⁹I/¹²⁷I ratios in surface water collected from the shore of the Irish Sea were in the range 2.8 × 10⁻⁶ to 8.2 × 10⁻⁶. These ratios are one order of magnitude higher than that of seawater collected from the Irish Sea in 1992, correlating with the increase in ¹²⁹I content of the Sellafield liquid effluent discharge over the last decade. The ¹²⁹I/¹²⁷I ratios in lakes in the Lake District were in the range 0.7 × 10⁻⁶ to 6.4 × 10⁻⁶ and decreased exponentially as a function of distance from Sellafield. Consideration of the relative variation of stable I concentrations and ¹²⁹I/¹²⁷I ratios suggests that Sellafield gaseous discharges may be the dominant source of ¹²⁹I to the lakes.