Sampling schemes for quality estimation of a flowing material

Four sampling schemes dealing with sampling of a continuous material flowing past the sampling point during a fixed time interval (0,T) are studied. Two of the schemes are the ones used in standard practice while the other two are the ones proposed as being possible sampling schemes to be coupled with a metal analyser developed by the CSIRO Division of Mineral Physics.Specific comparisons of the sampling schemes are made for a mathematical model of the functions describing a continuous stream based on simple and realistic assumptions. Discussion is provided on the advantages and disadvantages of the two new sampling schemes proposed for use with the analyser.     

Geochemistry of basalts drilled in the North Atlantic by IPOD Leg 49: Implications for mantle heterogeneity

IPOD Leg 49 recovered basalts from 9 holes at 7 sites along 3 transects across the Mid-Atlantic Ridge: 63°N (Reykjanes), 45°N and 36°N (FAMOUS area). This has provided further information on the nature of mantle heterogeneity in the North Atlantic by enabling studies to be made of the variation of basalt composition with depth and with time near critical areas (Iceland and the Azores) where deep mantle plumes are thought to exist. Over 150 samples have been analysed for up to 40 major and trace elements and the results used to place constraints on the petrogenesis of the erupted basalts and hence on the geochemical nature of their source regions.It is apparent that few of the recovered basalts have the geochemical characteristics of typical “depleted” midocean ridge basalts (MORB). An unusually wide range of basalt compositions may be erupted at a single site: the range of rare earth patterns within the short section cored at Site 413, for instance, encompasses the total variation of REE patterns previously reported from the FAMOUS area. Nevertheless it is possible to account for most of the compositional variation at a single site by partial melting processes (including dynamic melting) and fractional crystallization. Partial melting mechanisms seem to be the dominant processes relating basalt compositions, particularly at 36°N and 45°N, suggesting that long-lived sub-axial magma chambers may not be a consistent feature of the slow-spreading Mid-Atlantic Ridge.Comparisons of basalts erupted at the same ridge segment for periods of the order of 35 m.y. (now lying along the same mantle flow line) do show some significant inter-site differences in Rb/Sr, Ce/Yb,⁸⁷Sr/⁸⁶Sr, etc., which cannot be accounted for by fractionation mechanisms and which must reflect heterogeneities in the mantle source. However when hygromagmatophile (HYG) trace element levels and ratios are considered, it is the constancy or consistency of these HYG ratios which is the more remarkable, implying that the mantle source feeding a particular ridge segment was uniform with respect to these elements for periods of the order of 35 m.y. and probably since the opening of the Atlantic. Yet these HYG element ratios at 63°N are very different from those at 45°N and 36°N and significantly different from the values at 22°N and in “MORB”.The observed variations are difficult to reconcile with current concepts of mantle plumes and binary mixing models. The mantle is certainly heterogeneous, but there is not simply an “enriched” and a “depleted” source, but rather a range of sources heterogeneous on different scales for different elements — to an extent and volume depending on previous depletion/enrichment events. HYG element ratios offer the best method of defining compositionally different mantle segments since they are little modified by the fractionation processes associated with basalt generation.     

Mercury in plankton from a polluted Norwegian Fjord

Plankton of mixed composition has been collected from Sorfjørden and Hardangerfjørden, on the west coast of Norway and analysed for total mercury by flameless atomic absorption. Different methods of decomposing the samples prior to analysis were tested, showing no significant variations in the recovery of mercury. The high levels of mercury (0.52-25.21 ppm dry weight) are apparently associated with a source of industrial pollution. Indications of higher mercury concentrations in phytoplankton than in zooplankton were noticed and suggest a lack of food chain amplification within the lower trophic levels.     

Photogrammetric and laser altimetric reconstruction of water levels for extreme flood event analysis

This paper assesses the feasibility of estimating water levels using digital photogrammetry. A common problem during an extreme flood event is that automated water level recorders do not record the highest water levels, as a result of instrument malfunctioning. This paper explores two possible solutions to this problem based upon data acquired using synoptic remote sensing methods. The first method requires: (a) high-resolution elevation data (for example, in the form of a digital elevation model for the floodplain); and (b) information on the planimetric position of the maximum flood extent, such as from debris lines (known as wrack lines) visible on aerial imagery flown after the event. The planimetric data can then be used to segment the topographic data in order to identify water level elevations. The second method uses a digitial photogrammetric approach and is suitable where no topographic data are available, but aerial imagery is available, flown after the event. Provided this imagery is of the right scale, digital photogrammetric analysis may be used to identify the elevations of wrack lines visible on the imagery. In this paper, the second of these options is compared with the first. The research shows that desktop photogrammetric methods, using 1:4500 scale imagery, can yield water level estimates that are precise to ±0·147 m, on the basis of check data obtained from lidar data. This is a worst possible estimate of the acquired precision given uncertainties in the lidar data. When compared with the first option, based upon segmenting lidar data using flood outlines, the photogrammetric approach was found to be preferable given both the quality of the lidar and uncertainties over how to segment it.     

Crustal assimilation in basalt and jotunite: Constraints from layered intrusions

Massive continental volcanism and/or bolide impacts are considered by many authors to have caused three major mass extinction events during the last 300 million years: the end-Permian, end-Cretaceous and end-Triassic extinctions. However, re-evaluation of the frequency of bolide impacts and plume-related flood basalt provinces indicates that both types of event occur much more frequently than mass extinctions, and so, in isolation, may not be responsible for the largest extinctions. Furthermore, the kill mechanisms associated with either flood basalts or impacts do not appear to be sufficiently powerful to cause worldwide collapse of ecosystems leading to the largest mass extinctions. Contemporaneous flood basalts and bolide impact may be prerequisites for the largest mass extinctions. We present a statistical analysis of the probability of coincidence between volcanism and impact, and show that three random coincidences of these events in the last 300 m.y. are likely. No causal relationship between impact and volcanism is necessary. The lesser mass extinctions, on the other hand, may not require juxtaposition of two such catastrophic events; such coincidences occurring on more than three occasions during the last 300 m.y. become increasingly unlikely.     

Calc-alkaline and alkaline miocene and calc-alkaline recent volcanism in the Southernmost Patagonian Cordillera, Chile

In the southernmost Patagonian Cordillera (south of Lat. 54°45′) previously unrecorded calc-alkaline dacites and andesites, and adjacent alkali-basalts, were dated at 21 and 18 Ma (K-Ar), respectively. In the same area post-glacial low-K calc-alkaline andesites, identified at Isla Cook, represent the southernmost Recent volcanism recorded so far in South America, about 400 km south of Monte Burney, previously known as the southernmost Recent volcano. The association of contemporaneous calc-alkaline and alkali volcanics suggests a subduction-related environment for the Miocene volcanism, and the Recent calc-alkaline volcanics indicate that currently there is a small component of subduction of the Antarctic Plate beneath the South American part of the Scotia Plate.     

Seagrass Organic Carbon Stocks Show Minimal Variation Over Short Time Scales in a Heterogeneous Subtropical Seascape

Blue carbon initiatives require accurate monitoring of carbon stocks. We examined sources of variability in seagrass organic carbon (C_org) stocks, contrasting spatial with short temporal scales. Seagrass morphology and sediment C_org stocks were measured from biomass and shallow sediment cores collected in Moreton Bay, Australia. Samples were collected between 2012 and 2013, from a total of 77 sites that spanned a gradient of water turbidity. Environmental measures of water quality between 2000 and 2013 revealed strong seasonal fluctuations from summer to winter, yet seagrass biomass exhibited no temporal variation. There was no temporal variability in C_org stocks, other than below ground biomass stocks were slightly higher in June 2013. Seagrass locations were grouped into riverine, coastal, and seagrass loss locations and short temporal variability of C_org stocks was analysed within these categories to provide clearer insights into temporal patterns. Above ground C_org stocks were similar between coastal and riverine meadows. Below ground C_org stocks were highest in coastal meadows, followed by riverine meadows. Sediment C_org stocks within riverine meadows were much higher than at coastal meadows and areas of seagrass loss, with no difference in sediment C_org stocks between these last two categories. Riverine seagrass meadows, of higher turbidity, had greater total C_org stocks than meadows in offshore areas irrespective of time. We suggest that C_org stock assessment should prioritise sampling over spatial gradients, but repeated monitoring over short time scales is less likely to be warranted if environmental conditions remain stable.     

The one-point PDF of the initial conditions of our local Universe from the IRAS PSC redshift catalogue

The algorithm ztrace of Monaco & Efstathiou is applied to the IRAS PSCz catalogue to reconstruct the initial conditions of our local Universe with a resolution down to ~5  h ¹ Mpc. The one-point probability distribution function (PDF) of the reconstructed initial conditions is consistent with the assumptions that: (i) IRAS galaxies trace mass on scales of ~5  h ¹ Mpc and (ii) the statistics of the primordial density fluctuations are Gaussian. We use simulated PSCz catalogues, constructed from N -body simulations with Gaussian initial conditions, to show that local non-linear bias can cause the recovered initial PDF (assuming no bias) to be non-Gaussian. However, for plausible bias models, the distortions of the recovered PDF would be difficult to detect using the volume finely sampled by the PSCz catalogue. So, for Gaussian initial conditions, a range of bias models remain compatible with our PSCz reconstruction results.     

A modelling study of the effect of cloud saturation and particle growth rates on charge transfer in thunderstorm electrification

Numerical studies have been made of the importance of cloud saturation to the sign of charge transfer during graupel/ice crystal interactions in thunderstorms. Previous laboratory studies led to the idea that the diffusional growth rates of the interacting ice surfaces may influence the sign of the charge transferred during brief collisional contact. The ice crystals grow by vapour diffusion in a supersaturated environment while the graupel surface grows by diffusion under low accretion rate conditions, but will sublimate when heated sufficiently by riming. The graupel surface is also influenced, even under net sublimation conditions, by the vapour released to it from droplets freezing on its surface. In a cloud, the diffusional growth rates are also affected by ventilation when the supercooled droplets and their local environment flow past the riming surface.The diffusional growth rates of ice crystals and riming graupel particles are calculated for various cloud saturation ratios, then the sign of electric charge transferred during crystal/graupel collisions is determined according to the concept of the relative vapour diffusional growth rates, according to Baker et al., 1987 [Baker, B., Baker, M.B., Jayaratne, E.J., Latham, J., Saunders, C.P.R., 1987. The influence of diffusional growth rates on the charge transfer accompanying rebounding collisions between ice crystals and soft hailstones. Quart. J. Roy. Met. Soc. 113, 1193–1215]. It is found necessary, in order to account for the observation of positive charging of riming graupel at high accretion rates, to modify the assumptions of Baker et al. in order to increase the flux of vapour to the graupel surface. The variable growth parameters available may be adjusted to represent the environmental saturation conditions in various laboratory experiments, including the mixing of clouds from regions having different growth conditions, and are used to determine charge sign sensitivity to cloud saturation ratio, temperature and accretion as measured by the cloud effective liquid water content.