Shallow Circulations: Relevance and Strategies for Satellite Observation

Shallow circulations are central to many tropical cloud systems. We investigate the potential of existing and upcoming data to document these circulations. Different methods to observe or constrain atmospheric circulations rely on satellite-borne instruments. Direct observations of the wind are currently possible at the ocean surface or using tracer patterns. Satellite-borne wind lidar will soon be available, with a much better coverage and accuracy. Meanwhile, circulations can be constrained using satellite observations of atmospheric diabatic heating. We evaluate the commonalities and discrepancies of these estimates together with reanalysis in systems that include shallow circulations. It appears that existing datasets are in qualitative agreement, but that they still differ too much to provide robust evaluation criteria for general circulation models. This state of affairs highlights the potential of satellite-borne wind lidar and of further work on current satellite retrievals.     

Thermal evolution of the central Halls Creek Orogen,northern Australia

The Halls Creek Orogen in northern Australia records the Palaeoproterozoic collision of the Kimberley Craton with the North Australian Craton. Integrated structural, metamorphic and geochronological studies of the Tickalara Metamorphics show that this involved a protracted episode of high‐temperature, low‐pressure metamorphism associated with intense and prolonged mafic and felsic intrusive activity in the interval ca 1850–1820 Ma. Tectonothermal development of the region commenced with an inferred mantle perturbation event, probably at ca 1880 Ma. This resulted in the generation of mafic magmas in the upper mantle or lower crust, while upper crustal extension preceded the rapid deposition of the Tickalara sedimentary protoliths. An older age limit for these rocks is provided by a psammopelitic gneiss from the Tickalara Metamorphics, which yield a ²⁰⁷Pb/²⁰⁶Pb SHRIMP age of 1867 ± 4 Ma for the youngest detrital zircon suite. Voluminous layered mafic intrusives were emplaced in the middle crust at ca 1860–1855 Ma, prior to the attainment of lower granulite facies peak metamorphic conditions in the middle crust. Locally preserved layer‐parallel D₁ foliations that were developed during prograde metamorphism were pervasively overprinted by the dominant regional S₂ gneissosity coincident with peak metamorphism. Overgrowths on zircons record a metamorphic ²⁰⁷Pb/²⁰⁶Pb age of 1845 ± 4 Ma. The S₂ fabric is folded around tight folds and cut by ductile shear zones associated with D₃ (ca 1830 Ma), and all pre‐existing structures are folded around large‐scale, open F₄ folds (ca 1820 Ma). Construction of a temperature‐time path for the mid‐crustal section exposed in the central Halls Creek Orogen, based on detailed SHRIMP zircon data, key field relationships and petrological evidence, suggests the existence of one protracted thermal event (>400–500°C for 25–30 million years) encompassing two deformation phases. Protoliths to the Tickalara Metamorphics were relatively cold (～350°C) when intruded by the Fletcher Creek Granite at ca 1850 Ma, but were subsequently heated rapidly to 700–800°C during peak metamorphism at ca 1845 Ma. Repeated injection of mafic magmas caused multiple remelting of the metasedimentary wall rocks, with mappable increases in leucosome volume that show a strong spatial relationship to these intrusives. This mafic igneous activity prolonged the elevated geotherm and ensured that the rocks remained very hot (≥650°C) for at least 10 million years. The Mabel Downs Tonalite was emplaced during amphibolite facies metamorphism, with intrusion commencing at ca 1835 Ma. Its compositional heterogeneity, and the presence of mutual cross‐cutting relations between ductile shear zones and multiple injections of mingled magma suggest that it was emplaced syn‐D₃. Broad‐scale folding attributable to F₄ was accompanied by widespread intrusion of granitoids, and F₄ fold limbs are truncated by large, mostly brittle retrograde S₄ shear zones.     

Aerobic degradation of organic carbon inferred from dinoflagellate cyst decomposition in Southern Ocean sediments

Organic carbon (OC) burial is an important process influencing atmospheric CO₂ concentration and global climate change; therefore it is essential to obtain information on the factors determining its preservation. The Southern Ocean (SO) is believed to play an important role in sequestering CO₂ from the atmosphere via burial of OC. Here we investigate the degradation of organic-walled dinoflagellate cysts (dinocysts) in two short cores from the SO to obtain information on the factors influencing OC preservation. On the basis of the calculated degradation index kt, we conclude that both cores are affected by species-selective aerobic degradation of dinocysts. Further, we calculate a degradation constant k using oxygen exposure time derived from the ages of our cores. The constant k displays a strong relationship with pore-water O₂, suggesting that decomposition of OC is dependent on both the bottom- and pore-water O₂ concentrations.     

A macroscopic damage‐plastic constitutive law for modeling quasi‐brittle fracture and ductile behavior of concrete

A new phenomenological macroscopic constitutive model for the numerical simulation of quasi‐brittle fracture and ductile concrete behavior, under general triaxial stress conditions, is presented. The model is particularly addressed to simulate a wide range of confinement stress states, as also, to capture the strong influence of the mean stress value in the concrete failure mechanisms. The model is based on a two‐surface damage‐plastic formulation. The mechanical behavior in different domains of the stress space is separately described by means of a quasi‐brittle or ductile material response:

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Holocene survival of the wild horse in Europe: a matter of open landscape?

The wild horse Equus ferus was one of the most frequent species of the Late Pleistocene large ungulate fauna in Eurasia and played an important role in the subsistence of human groups, especially at the end the Late Glacial. It is frequently assumed that E. ferus became extinct in Europe at the beginning of the Holocene because of the development of woodlands and loss of open habitats. Because of its preference for open habitats and in spite of its adaptability, the appearance or disappearance of the wild horse could therefore be a suitable palaeoecological indicator for the opening of the Holocene primeval woodlands. We revised the dating and reliability of the subfossil record and dated several bones by atomic mass spectrometry ¹⁴C dating. From the beginning of the Holocene (9600 cal a BC) to the end of the Atlantic Period (3750 cal a BC) there are 207 archaeological sites with wild horse records available in Europe. E. ferus survived the Pleistocene Holocene transition in Europe, but the spatiotemporal dynamics of populations fluctuated remarkably in the early and middle Holocene. Small and sparse populations increasingly became extinct during the early Holocene, until between 7100 and 5500 cal a BC the wild horse was almost absent in central parts of the European Lowlands. Particular conditions in natural open patches in the canopy forests, chalklands and floodplains may have maintained the local survival of the horse in some regions of the Lowlands, however. In the Late Atlantic, between 5500 and 3750 cal a BC the range of the wild horse was again extended. It re‐immigrated into central and western Europe, probably as a consequence of increasing landscape opening by Neolithic peoples. The data presented here may be a valuable part of the debate on the degree of openness of the early and middle Holocene landscape. Copyright © 2011 John Wiley & Sons, Ltd.     

Is area affected by flood or stagnant water independently associated with poorer health outcomes in urban slums of Dhaka and adjacent rural areas?

This study investigated the association of flood/stagnant water (FSW) with various health outcomes among respondents living in urban slums of Dhaka and adjacent rural areas. We also assessed the differences of individual-, household- and area-level characteristics between the FSW-affected and non-affected areas. Bangladesh as a whole and slums in the megacity of Dhaka in particular are severely affected by the FSW. Data were collected from 3,207 subjects (aged 10+ years) through baseline surveys conducted in March 2008 and 2009. Twelve big slums in Dhaka and three adjacent villages were selected as study areas. Face-to-face interviews using a multidimensional pre-tested questionnaire were conducted by the trained university graduates. We performed various types of analyses ranging from the simple frequency analysis to the multivariable-adjusted logistic regression modelling. Our empirical findings suggest that slums were more affected by the FSW as compared to the rural areas. People living in the FSW-affected areas were more vulnerable in terms of individual-, household- and area-level characteristics than non-affected people. Age was also significantly associated with various health outcomes. According to multivariable analyses controlled for various factors, the FSW-affected people reported significantly higher likelihoods of health symptoms (namely fever, cold/cough, weakness), communicable diseases (namely diarrhoea and gastric disease) and poor mental well-being as compared to the non-affected people. Only the burden of non-communicable diseases was lower in the FSW-affected areas than the non-affected areas. Our findings lead us to conclude that the FSW-affected area is an independent risk factor for various physical and mental health problems. Urban slums are more affected than rural areas by the FSW. Therefore, we underscore the necessities of well-designed and comprehensive public health interventions focusing on individual, community and higher levels of interventions to reduce the FSW-related health and other consequences among the people living in the FSW-affected areas and urban slums in the rapidly growing city of Dhaka, Bangladesh.     

The contribution of humic substances to the acidity of colored natural waters

An operationally defined carboxyl content of humic substances extracted from rivers, streams, lakes, wetlands, and groundwaters throughout the United States and Canada is reported. Despite the diversity of the samples, only small variations were observed in this humic carboxyl content. The dissociation behavior of two combined fulvic/humic acid extracts was studied and it was found that the dissociation of the humics varied in a predictable manner with pH. Using a carboxyl content of 10 μeq/ mg humic organic carbon, and mass action quotient calculated from sample pH, the ionic balances of three highly colored Nova Scotia rivers were estimated.