A Spatial Variant of the Basic Reproduction Number for the New Orleans Yellow Fever Epidemic of 1878

A spatial variant of the basic reproduction number (R₀), here defined as the number of subsequent deaths attributed to an initial mortality, can be used to identify geographic variation within an epidemic. A spatial R₀ was calculated at the neighborhood level, here defined by a 50‐m buffer surrounding an index case, for mortality data from the 1878 yellow fever epidemic of New Orleans. The highest number of secondary mortalities linked to a neighborhood index case was twelve, with a further eighty‐seven extrapolated morbidity cases. Results also highlight the importance of multideath residences and cultural contacts in neighborhood‐level disease spread.     

Seasonal temperatures for the past ∼400 years reconstructed from diatom and chironomid assemblages in a high-altitude lake (Lej da la Tscheppa,Switzerland)

We analysed a 42 cm long sediment record from Lej da la Tscheppa, a high-altitude lake (2,616 m a.s.l.) in the Upper Engadine valley (Switzerland) for subfossil diatoms, chironomids and pollen. The chronology of the top 21 cm of the record was established using ²¹⁰Pb analysis using a constant-rate-of-supply model, and validated with ¹³⁷Cs measurements and the content of spheroidal carbonaceous particles. A tentative chronology for the lower part of the core was obtained through extrapolation of the sedimentation rates in the uppermost part of the record. Pollen assemblages in the record reflect regional changes in forestation and land-use patterns in the Upper Engadine valley and show no evidence of significant local human activity in the lake’s catchment. Diatom assemblages record a distinct increase in planktonic taxa since the early 19th century, suggesting a decrease in the duration of ice-cover. In contrast, chironomid assemblages remained stable during a large part of the record. We applied an established chironomid-based July air temperature transfer function and a newly developed diatom-based spring air temperature transfer function to reconstruct past seasonal air temperature changes at Lej da la Tscheppa. The reconstructions indicate a diatom-inferred warming trend in spring temperatures during the past ca. 400 years, whereas chironomid-inferred summer temperatures suggest a slight cooling trend. These biota-based reconstructions are in good agreement with the centennial-scale temperature trend in an independent reconstruction of regional temperatures in the Upper Engadine region based on instrumental records and documentary proxy evidence from the Alps. Our results suggest that, in high-altitude lakes, independent chironomid- and diatom-based seasonal temperature reconstruction is possible and can be successfully used to track seasonal temperature trends.     

Influence of Clouds on UV Irradiance at Ground Level and Backscattered Exittance

The influence of various cloud parameters and the interactions with the ground albedo and the solar zenith angle have been studied by means of model simulations. The radiative transfer model suitable for a cloudy atmosphere as well as for a clear atmosphere has been developed on the basis of the Discrete Ordinate Method. This study leads to a general understanding for cloudy atmospheres: in the presence of a uniform cloud, the cloud scattering is dominant to molecular and aerosol scattering, and it is also wavelength-independent; the ratio of transmitted irradiance in a cloudy atmosphere to that in the background clear atmosphere is independent of cloud height and solar zenith angle. That’s to say, the radiation downwelling out of a cloud is quite isotropic; it decreases approximately exponentially with the cloud optical depth at a rate related to the ground albedo; the reflected irradiance at the top of the atmosphere is dependent on cloud optical depth as well as on solar zenith angle, but not on ground albedo for clouds of not very thin optical depth.     

Fluxes of uranium and thorium series isotopes in the Santa Barbara Basin

Samples from the MANOP Santa Barbara Basin sediment trap intercomparison were analyzed for the isotopes of uranium, thorium, radium, lead, and polonium. All of the traps showed approximately the same compositions and isotopic ratios, indicating that they trapped similar materials. The²³⁴Th flux via falling particles was very close to the flux predicted from the production and scavenging rates of²³⁴Th from the water column. The²¹⁰Pb content of the trapped particles and the surface sediments were the same, however, the measured flux of²¹⁰Pb was seven times greater than the predicted flux. Predicted and measured fluxes of²²⁸Th and²¹⁰Po were similarly out of balance. To explain this apparent inconsistency, we suggest (as others have done) that the Santa Barbara Basin is an area where scavenging from the water column is intensified and where sediments deposited initially on the margins may be physically remobilized on a short time scale. These two effects increase the apparent area from which the basin derives the longer-lived isotopes but does not increase significantly the supply of the short-lived²³⁴Th.     

An electron microscopy study of naturally occurring oxidation produced precipitates in iron-bearing olivines

Iron-bearing olivine grains naturally altered by oxidation were examined in the transmission electron microscope to determine the precipitate phases and their crystallographic and morphological relationships to the host. Precipitate complexes heterogeneously nucleated on dislocations were composed of Si-rich, Mg-rich/Si-rich, and Fe-rich regions corresponding to - tridymite, enstatite, and magnetite and/or hematite, respectively. The tridymite and magnetite (hematite) occurred as rod-like interleaved fingers, while the enstatite was more equidimensional. The crystal orientations of the precipitate phases with respect to the host structure, listed in Table 2, were well defined, but, in general, could not be simply related to the close packing of oxygen planes. Iron-rich (001) planar precipitates occasionally nucleated homogeneously in the host as well as heterogeneously on dislocations. Oxygen diffusion does not appear to be the rate-controlling process for precipitate nucleation and growth as precipitation kinetics in fresh olivine oxidized at 900 ° C would indicate an oxygen diffusivity of 10^–8 cm²/sec, a value 10 orders of magnitude faster than determined previously.     

Redistribution of uranium and thorium series isotopes during isovolumetric weathering of granite

Previous studies of the distribution of U and Th in parent versus weathered granites have shown both depletion and enrichment of these elements during weathering. In this study, the distribution of U and Th decay series isotopes was determined in a weathering profile of a granitic saprolite, which showed textural preservation indicating isovolumetric weathering. Two types of dissolution methods were used: a whole-rock dissolution and a sodium-citrate dithionite leach to preferentially attack noncrystalline phases of weathering products. Using volume-based activities, 45–70 percent of the total ²³²Th was gradually removed during weathering. Although the whole-rock ${}^{228}\text{Th}{}^{232}\text{Th}$ activity ratios were in equilibrium, there were large excesses of ²²⁸Th in the leachable fraction of both parent rock (${}^{228}\text{Th}{}^{232}\text{Th}\text{= 2.06}$) and partially weathered saprolite (${}^{228}\text{Th}{}^{232}\text{Th}\text{= 3–6.5}$), due to alpha recoil and release of daughter ²²⁸Th to the weathering rind of the mineral grain. For the most weathered sample, 81 percent of the thorium was in the teachable fraction and ${}^{228}\text{Th}{}^{232}\text{Th}\text{= 1}$, indicating that even the more resistant minerals were attacked.The total U activities showed as much variation in the six parent rock samples as in the weathered profile, and ${}^{234}\text{U}{}^{238}\text{U}$ were in equilibrium in both the whole-rock and leachable fractions. ²³⁰Th was deficient relative to ²³⁴U and ²²⁶Ra in both fractions, suggesting recent addition of U and Ra to the entire profile. The large variation in U was not from absorption onto the intermediate weathering products, because only 11–23 percent of the U was in the leachable fraction.     

Experimental study of a jotunite (hypersthene monzodiorite): constraints on the parent magma composition and crystallization conditions (P,T, f O 2) of the Bjerkreim-Sokndal layered intrusion (Norway)

The Bjerkreim-Sokndal layered intrusion is part of the Rogaland anorthosite Province of southern Norway and is made of cumulates of the anorthositemangerite-charnockite suite. This study presents experimental phase equilibrium data for one of the finegrained jotunite (Tjörn locality) occurring along its northwestern lobe. These experimental data show that a jotunitic liquid similar in composition to the Tjörn jotunite, but slightly more magnesian and with a higher plagioclase component is the likely parent of macrocyclic units (MCU)III and IV of the intrusion. The limit of the olivine stability field in the experimentally determined phase diagram as well as comparison of the Al₂O₃ content of low-Ca pyroxenes from experiments and cumulates (1.5%) yields a pressure of emplacement 5 kbar. Experimentally determined Fe-Ti oxide equilibria compared to the order of cumulus arrival in the intrusion show that the oxygen fugacity was close to FMQ (fayalite-magnetite-quartz) during the early crystallization. It subsequently decreased relative to this buffer when magnetite disappeared from the cumulus assemblage and then increased until the reentry of this mineral. Calculated densities of experimental liquids show a density increase with fractionation at 7, 10 and 13 kbar due to the predominance of plagioclase in the crystallizing assemblage. At 5 kbar and 1 atm (FMQ-1), where plagioclase is the liquidus phase, density first increases and then drops when olivine (5 kbar) or olivine+ilmenite (1 atm: FMQ-1) precipitate. At 1 atm and NNO (nickel-nickel oxide), the presence of both magnetite and ilmenite as near liquidus phases induces a density decrease. In the Bjerkreim magma chamber, oxides are early cumulus phases and liquid density is then supposed to have decreased during fractionation. This density path implies that new influxes of magma emplaced in the chamber were both hotter and denser than the resident magma. The density contrast inferred between plagioclase and the parent magma shows that this mineral was not able to sink in the magma, suggesting anin situ crystallization process.     

Magnetic properties of iron-rich oxisols

Four occurrences of highly magnetic soil in Brazil have been analysed with a view to identifying the magnetic minerals and quantifying the soil magnetization. Techniques used include X-ray diffraction, X-ray fluorescence and Mössbauer spectroscopy. This approach leads us to identify several ways that these soils, which have spontaneous magnetization in the range 1_s<35 j/t/kg,="" can="" come="">One soil, which forms on dolerite (19.6 wt% Fe₂O₃), is found to contain fully-oxidized titanomaghemite inherited from the parent rock. This oxide has a canted ferrimagnetic spin structure with _s=36 J/T/kg of sample. The three others, formed on very iron-rich rock (50–90 wt% Fe₂O₃), contain magnetite or maghemite as the magnetic species and in two cases the soil is more magnetic than the parent rock (largely composed of pure hematite).     

Development of unusual rock weathering features in the Cordillera Blanca,Peru

Mylonite textures in granodiorite boulders are responsible for higher rates of surface denudation of host rocks and the progressive development of unusual rock weathering features, termed weathering posts. These textures are characterized by smaller grain sizes, higher biotite content, and a higher biotite axial ratio in host rocks relative to weathering posts. Elemental concentrations do not show a significant difference between weathering posts and the host rocks in which they are found, and this reflects the absence of a weathering residue on the rock surfaces. Chemical weathering loosens the bonds between mineral grains through the expansion of biotite, and the loosened grains fall off or are blown off the boulder surface and continue their chemical alteration in the surrounding soil. The height of weathering posts on late Quaternary moraines increases at a linear rate of ~ 1.45 ± 0.45 cm (1000 yr)^? 1 until post heights reach the diameter of host rocks. Such a rate of boulder denudation, if unrecognized, would generate significant errors (> 20%) in cosmogenic exposure ages for Pleistocene moraines. Given the paucity of boulders with diameters that significantly exceed 1.5 m, the maximum age of utility of weathering posts as a numeric age indicator is ~ 100 ka.