Is Canadian cloudiness increasing?

Abstract

Cloud amount records for the Canadian mid‐latitudes have been analysed in the context of a “warming world” analogue model that compares records of two 20‐year periods. The cloud amounts increase over practically all these regions while temperatures rise. This historical data set has also been extended temporally to permit analysis of high‐latitude cloudiness trends. These are of particular interest in the “fingerprinting” of CO₂‐induced climatic change. Station records from the Canadian Arctic show distinctive increases in total cloud amount in the last forty years especially in the summer season. This result, unlike the historical analogue analysis, seems to be decoupled from temperature changes.     

Heat health planning: The importance of social and community factors

Extreme heat events frequently have adverse effects on population health. Within every population certain groups and individuals are at a greater risk of heat-related morbidity and mortality than others. While certain physiological characteristics (advanced age, chronic conditions, etc.) are known to increase the risk of illness and/or death during periods of extreme heat, the role of social and community level factors in aggravating or mitigating this risk is poorly understood. This paper reviews the literature on the social and community level factors that affect heat-related morbidity and mortality in order to identify shortfalls in current heat health response plans so that new approaches can be recommended. While social isolation, ethnicity, socioeconomic status, and neighborhood characteristics have all been identified as potential factors affecting the risk of heat-related illness and mortality, these are rarely, if ever, identified as heat health research priorities and are thus often neglected in heat emergency planning. Current research and programming practices are often prioritized from the top down where decisions are made at the federal level and research priorities are determined by national research bodies. This, unfortunately, may not allow enough flexibility to meet the needs of physically, socially and culturally diverse communities. A more socio-ecological approach to heat health research and planning would better allow for the identification of community level vulnerabilities and available resources and would encourage communities to work with regional or national partners to adapt response plans accordingly. The development of future plans should involve more partnerships at the community level so that social and community level factors that are currently overlooked may be included in heat health response strategies.     

Self-organised criticality and fluid-rock interactions in the brittle field

The concept of self-organised criticality (SOC) has recently been suggested as a paradigm for the long-term behaviour of earthquakes, even though many of the currently-proposed models require some tuning of the state variables or local conservation rules to produce the universally-observed Gutenberg-Richter frequency-magnitude distribution witha b value near 1. For example, a systematic negative correlation is predicted between modelb values and the degree of conservation of local force after the slip of a single element in an elastic spring/block/frictional slider model. A similar relation is described here for a cellular automaton model with constitutive laws based on fracture mechanics. Such systems, although critical phenomena in the sense of producing order on all scales, are clearly not universal, and may not in general even be true examples of SOC. Nevertheless they adequately reproduce both the observed power-law (fractal or multifractal) scaling and its reported short-term fluctuation.We also present experimental and field evidence for similar systematic variations inb value with the degree of force conservation (expressed in terms of a normalised crack extension force) during subcritical crack growth involving the physical and chemical influence of pore fluids during a single cycle of failure both in tension and compression. We find that the level of conservation is strongly influenced by fluid-rock interaction under stress, allowing energy partition into processes such as: physico-chemical stress corrosion reactions; the dissolution and precipitation of mineral species on crack surfaces; and the purely mechnical phenomenon of dilatant hardening. All of these are known to occur in the Earth on a local scale, but few have been explicitly included in automaton models of seismicity. The implication is that over long time periods pore fluids may exert a strong physical and chemical influence on the universal state of SOC which the system evolves in a complex interplay of local feedback mechanisms keeping the system near criticality, perhaps most strikingly due to the valve action of faults. In the short term, crustal fluids might nevertheless be responsible for systematic local fluctuations about this average state.     

Nd isotopes demonstrate the role of contamination in the formation of coexisting quartz and nepheline syenites at the Abu Khruq Complex,Egypt

The petrogenesis of Abu Khruq, an 89 Ma alkaline ring complex of eastern Egypt which is composed of alkali gabbros and both silica over- and undersaturated syenites, has been investigated. Major and trace element relationships and Nd and Sr isotope data are consistent with formation of the gabbros from an alkaline mafic magma that experienced extensive fractionation, and all syenites from a felsic derivative of this melt. The parental magma had an ⁸⁷Sr/⁸⁶Sr of 0.7030 and an ¹⁴³Nd/¹⁴⁴Nd of 0.512750 (_Nd = +4.4) indicating derivation from a depeleted mantle source. The initial ¹⁴³Nd/¹⁴⁴Nd ratios are: 0.512721 to 0.512748 for the gabbros, 0.512739 to 0.512750 for the alkali syenites and trachytes, 0.512717 to 0.512755 for the nepheline syenites, and, 0.512706 to 0.512732 for the quartz syenites. In contrast, analyzed Precambrian granites from eastern Egypt have generally lower ¹⁴³Nd/¹⁴⁴Nd ratios (ranging from 0.51247 to 0.51261 or _Nd = -0.8 to 1.7, for 89Ma); their Nd model ages range from 775 to 935 Ma and suggest there was no significant input of pre-Pan-African crust in their formation. Among Abu Khruq rocks, ¹⁴³Nd/¹⁴⁴Nd ratios indicate that the quartz syenites formed by open-system, crustal contamination processes whereas the nepheline syenites experienced little or no contamination. Modeling shows that contamination occurred at various stages, affecting both mafic and more evolved compositions with input of about 20% crustal Nd for the most contaminated samples. The degree of contamination is related to the silica saturation of the quartz syenites. Simplified modeling of magma evolution within Petrogeny's Residua System demonstrates the ability of AFC processes to cause a critically undersaturated magma to evolve across the feldspar join and produce oversaturated rocks. The oversaturated syenites at Abu Khruq were produced in this manner whereas the nepheline syenites formed by fractionation without similarly large degrees of contamination. The results have broad implications for the formation of subvolcanic complexes in continental settings beyond the important production of silica oversaturated compositions from crustal interaction. They underscore the importance of crustal interactions in the formation of the various lithologies. Such interactions occur at various stages in the evolution of the magmas and, as such, are not strictly coupled with fractional crystallization. While previous study of Abu Khruq has demonstrated extensive hydrothermal alteration of O and Sr isotopes, the present work shows that the Nd isotope ratios were not significantly affected and thus reflect magmatic signatures. This feature combined with relatively small corrections for initial ratios emphasizes the utility of Nd isotopes for petrogenetic studies.     

Primary Ca-rich carbonatite magma and carbonate-silicate-sulphide liquid immiscibility in the upper mantle

A primary carbonate phase with Ca/(Ca+Mg) in the range 0.85–0.95 has been identified in a metasomatized, depleted harzburgite nodule from Montana Clara Island, Canary Islands; textural relations show that this carbonate represents a quenched liquid. Although magnesian carbonate melts have been described from upper mantle peridotites, this is the first reported occurrence of a primary magma within peridotite nodules which has the composition of calciocarbonatite, by far the most common carbonatite type occurring in crustal complexes. The carbonate in the Montana Clara harzburgite host is restricted to wehrlitic alteration zones and is intimately associated with a second generation of minerals, mainly olivine, clinopyroxene and spinel, with glass of syenitic composition, and with Fe−Cu-rich sulphides. The metasomatic assemblage was formed by reaction of a sodiumbearing dolomitic melt, derived from a somewhat deeper level in the upper mantle, with the harzburgite mineral assemblage at a pressure of 15 kbars, or lower. As a result of the reaction the residual carbonatite melt became more enriched in calcium. The calciocarbonatite and sulphide phases almost invariably form globules in the silicate glass, indicating the existence of three immiscible liquids under upper mantle conditions. Several alkaline complexes contain carbonatites occurring with syenitic rock types and its seems feasible that the formation of such close associations might have been influenced by processes of liquid immiscibility which took place under upper mantle conditions. Editorial responsibility: I. Parsons     

Sodium trisilicate: A new high-pressure silicate structure (Na2Si[Si2O7])

Crystals of sodium trisilicate (Na₂Si₃O₇) have been grown in the presence of melt at 9 GPa, 1200 °C using the MA6/8 superpress at Edmonton, and the X-ray structure determined at room pressure (R=2.0%). Na₂Si₃O₇ is monoclinic with a=8.922(2) Å, b= 4.8490(5) Å, c=11.567(1) Å, β=102.64(1)° (C2/c), D _x = 3.295 g·cm^-3. Silicon occurs in both tetrahedral and octahedral coordination (^[6]Si∶^[4]Si = l∶2). The SiO₄ tetrahedra form a diorthosilicate [Si₂O₇] group and are linked by the isolated SiO₆ octahedra via shared corners into a framework of 6-membered (^[4]Si-^[4]Si-^[6]Si^[4]Si-^[4] Si-^[6]Si) and 4-membered (^[4]Si-^[6]Si-^[4]Sr-^[6]Si) rings: 〈^[6]Si-O〉=1.789 Å, 〈^[4]Si-O〉= 1.625 Å, ^[4]Si-O-^[4]Si=132.9° and the bridging oxygen is overbonded (s = 2.22). Channels parallel to b-axis and [110] accommodate Na in irregular 6-fold coordination: 〈Na-O〉 = 2.511 Å.     

X-ray absorption near-edge spectra of transition metal disulfides FeS2 (pyrite and marcasite), CoS2, NiS2 and CuS2, and their isomorphs FeAsS and CoAsS

Metal K- and L₃-, sulfur K- and arsenic K- and L₃-edge X-ray absorption near-edge spectra of a series of metal disulfides, FeS₂ (both pyrite and marcasite), CoS₂, NiS₂, and CuS₂, and their isomorphs, FeAsS and CoAsS, are presented. The features in this region of these spectra are interpreted using band structure and molecular orbital calculations in terms of the transitions from the 1s or 2p_3/2 state to unoccupied states. The 3d transition metal L₃-edge spectra of these materials show dependence on the degree of multiplet splitting in the final state, and thus offer less information on the electronic ground state. There are substantial differences in the spectra of the isostructural materials, whereas the spectra of the isotopes pyrite and marcasite show several similarities, illustrating the dependence of near-edge region on electronic structure.     

Greenhouse,gaia and global change: a personal view of the pitfalls of interdisciplinary research

Recognition of the possible consequences of global‐scale pollution has spawned research programs loosely termed ‘global change’. These programs are hampered by the problems of academic apartheid first identified by those attempting to examine the Gaia hypothesis. Global change is, in many ways, a synonym for global geography: the study of processes and their consequences at the human/environment interface. Assessment of highly complex systems demands integrative, interdisciplinary research; the search for, and recognition of, negative feedbacks; and, most importantly, the courage to formulate hypotheses which bridge many single disciplines. I illustrate some of the pitfalls of interdisciplinary research with reference to my own research in atmospheric science, by the application of atmospheric science to the study of climatic impacts and consideration of the integration of climatic impacts into global change.     

A fracture-mechanical cellular automaton model of seismicity

We present a cellular automaton model which simulates the process of seismogenesis using rules for evolution which are derived from the field of fracture mechanics, and include an interplay of positive and negative feedbacks. We describe the implementation of this model, and its analysis, in a massively parallel environment using the Connection Machine. Starting from a lattice with a fractal distribution of fracture toughnesses, theb value evolves in a way which closely mimics both the evolutions ofb value observed in the laboratory and derived from earthquake catalogues, reaching a broad and irregular maximum in the period preceding a major event, and declining rapidly during catastrophic failure. We conclude that the processes modelled are a reasonable representation of those occurring in Nature, and that the cellular automaton paradigm is a valuable way of simulating these processes on a large scale in an economical manner.