The composition of dust in Jupiter-family comets inferred from infrared spectroscopy

We review the composition of Jupiter-family comet (JFC) dust as inferred from infrared spectroscopy. We find that JFCs have silicate emission features with fluxes roughly 20-25% over the dust continuum (emission strength 1.20-1.25), similar to the weakest silicate features in Oort Cloud (OC) comets. We discuss the grain properties that alter the silicate emission feature (composition, size, and structure/shape), and emphasize that thermal emission from the comet nucleus can have significant influence on the derived silicate emission strength. Recent evidence suggests that grain porosity is the is different between JFCs and OC comets, but more observations and models of silicates in JFCs are needed to determine if a consistent set of grain parameters can explain their weak silicate emission features. Models of 8 m telescope and Spitzer Space Telescope observations have shown that JFCs have crystalline silicates with abundances similar to or less than those found in OC comets, although the crystalline silicate mineralogy of comets 9P/Tempel and C/1995 O1 (Hale-Bopp) differ from each other in Mg and Fe content. The heterogeneity of comet nuclei can also be assessed with mid-infrared spectroscopy, and we review the evidence for heterogeneous dust properties in the nucleus of comet 9P/Tempel. Models of dust formation, mixing in the solar nebula, and comet formation must be able to explain the observed range of Mg and Fe content and the heterogeneity of comet 9P/Tempel, although more work is needed in order to understand to what extent do comets 9P/Tempel and Hale-Bopp represent comets as a whole.     

Comparison of two-dimensional flood propagation models: SRH-2D and Hydro_AS-2D

This article presents a comparison between two two-dimensional finite volume flood propagation models: SRH-2D and Hydro_AS-2D. The models are compared using an experimental dam-break test case provided by Soares-Frazão (J Hydraul Res, 2007. doi: 10.1080/00221686.2007.9521829). Four progressively refined meshes are used, and both models react adequately to mesh and time step refinement. Hydro_AS-2D shows some unphysical oscillations with the finest mesh and a certain loss of accuracy. For that test case, Hydro_AS-2D is more accurate for all meshes and generally faster than SRH-2D. Hydro_AS-2D reacts well to automatic calibration with PEST, whereas SRH-2D has some difficulties in retrieving the suggested Manning’s roughness coefficient.     

Boreal peatland margins as repository sites of long-term natural disturbances of balsam fir/spruce forests

A multidisciplinary, high-resolution paleoecological study (Lepidoptera and plant remains, macroscopic charcoal, pollen) was conducted on a 4000-yr peat monolith extracted from the margin of an ombrotrophic peatland on Anticosti Island (Gulf of St. Lawrence, eastern Canada) to reconstruct the long-term natural disturbances (insect outbreaks, forest fires) of a balsam fir/spruce forest. We hypothesized that an activity of insect defoliators (spruce budworm, hemlock looper) was the main disturbance factor of conifer forests during the Late Holocene. The earliest remains of spruce budworm and hemlock looper were found ca. 3220 and 2350 cal yr BP, respectively. Peaks of insect head capsules occurred from ca. 1640 to ca. 625 cal yr BP. Low balsam fir pollen concentrations during this period suggest a lengthy episode ( 1000 yr) of high insect activity, resulting in extensive fir dieback and mortality. The long-term dynamics of the pristine balsam fir/spruce forests were mainly governed by the activity of insect defoliators. The limited extent and possibly the low occurrence of forest fires in the maritime environment of Anticosti Island allowed the development of mature coniferous stands propitious for insect infestations. Insect head capsules appeared to be a useful and effective tool for establishing insect presence and activity during the Holocene.     

Evaluation of fluidized bed asbestos segregator to determine erionite in soil

Three sets of soil samples were collected by the National Institute for Occupational Safety and Health and one set by South Dakota School of Mines & Technology from in and around the Slim Buttes Land Unit of the Sioux Ranger District of the Custer–Gallatin National Forest in the northwest of South Dakota. The rocks forming the Slim Buttes are sedimentary clays, sands and gravels including re-worked volcanic ash-falls in which the zeolite mineral erionite has crystallized during diagenesis in a fibrous form or morphology similar to that of asbestos. The samples were prepared using the fluidized bed asbestos segregator (FBAS) and analyzed by phase contrast microscopy (PCM) or transmission electron microscopy to detect the presence of mineral fibers. FBAS–PCM results compared to semi-quantitative polarized light microscopy (PLM) and X-ray diffraction analysis indicated a recovery of approximately 1% and a linear relationship that likely can be extrapolated to concentrations well below the 1% detection limit of PLM. There were small variations between a PCM count of 10 fibers to a count of 100 fibers (or a maximum of 200 microscopic fields of view), which indicates the possibility of rapid turnaround of results. Although the four sets of samples examined in this work were collected by slightly different techniques, some tentative conclusions can be drawn about the distribution of erionite in soils. Erionite was detected in almost every soil sample, even those taken several miles from the outcrop, but without any distribution indicating recent transportation from the current volcaniclastic sediment outcrops. Removal of more extensive volcaniclastic sediments through erosion may have resulted in remnant material in soils, including erionite crystals, but this possibility requires further study. Although we have demonstrated that erionite in soils can be detected through FBAS–PCM, we have not attempted to correlate those results with human inhalation exposure through activity-based sampling, and thus, any risk inherent in working these soils is unknown.     

Mineralogy and phase chemistry of Mount St. Helens tephra sets W and Y as keys to their identification

Voluminous and widespread tephras were produced frequently during the last 36,000 yr of volcanic activity at Mount St. Helens. Numerous tephra sets have been defined by D. R. Mullineaux, J. H. Hyde, and M. Rubin (1975, U.S. Geological Survey Journal of Research, 3, 329–335) on the basis of field relations, FeMg phenocryst assemblage, and ¹⁴C chronology and are valuable marker beds for regional stratigraphic studies. In this study modal abundances and mineral compositions were determined (via petrographic and electron microprobe techniques) for numerous samples of individual layers within tephra sets W and Y to evaluate the degree of compositional variability within and between tephra layers and criteria by which to distinguish among Mount St. Helens and other Pacific Northwest tephras. Although individual layers within a set (e.g., We, Wn) cannot be distinguished from each other on the basis of mineralogic characteristics examined, mineral compositions allow distinction among layers W and Y and other Pacific Northwest tephras (e.g., Mazama, Glacier Peak). FeTi oxide compositions and T-f_O2 estimates derived using coexisting magnetite-ilmenite are especially useful due to the compositional homogeneity of these minerals both within and between samples of a given unit over a wide geographic area. The silicates show more compositional variability than the oxides, but $\text{iO}{}_2\text{Al}{}_2\text{O}{}_3$ contents in hornblende and Fe/Mg ratios in hypersthene aid in distinguishing among Pacific Northwest tephras.     

Age of New Zealand Pleistocene substages by fission-track dating of glass shards from tephra horizons

Eleven tephras and two pumice-rich horizons interbedded in Pleistocene marine sediments of the Wanganui Basin have been dated using the fission-track method on glass shards. Ages of the lower boundaries of New Zealand Pleistocene marine Substages are 0.45 m.y. (Putikian), 1.06 m.y. (Okehuan), 1.55 m.y. (Marahauan). On the basis of sedimentation rates an estimation of 1.86 m.y. is obtained for the Plio-Pleistocene boundary (Hautawan).     

Effects of climate on numbers of northern prairie wetlands

The amount of water held in individual wetland basins depends not only on local climate patterns but also on groundwater flow regime, soil permeability, and basin size. Most wetland basins in the northern prairies hold water in some years and are dry in others. To assess the potential effect of climate change on the number of wetland basins holding water in a given year, one must first determine how much of the variability in number of wet basins is accounted for by climatic variables. I used multiple linear regression to examine the relationship between climate variables and percentage of wet basins throughout the Prairie Pothole Region of Canada and the United States. The region was divided into three areas: parkland, Canadian grassland, and United States grassland (i.e., North Dakota and South Dakota). The models - which included variables for spring and fall temperature, yearly precipitation, the previous year's count of wet basins, and for grassland areas, the previous fall precipitation - accounted for 63 to 65% of the variation in the number of wet basins. I then explored the sensitivities of the models to changes in temperature and precipitation, as might be associated with increased greenhouse gas concentrations. Parkland wetlands are shown to be much more vulnerable to increased temperatures than are wetlands in either Canadian or United States grasslands. Sensitivity to increased precipitation did not vary geographically. These results have implications for waterfowl and other wildlife populations that depend on availability of wetlands in the parklands for breeding or during periods of drought in the southern grasslands.The U.S. Government right to retain a non-exclusive, royalty-free license in and to any copyright is acknowledged.     

Temperature trends and interannual variability in the Strait of Georgia,British Columbia

A continuous 36 year long record of semi-monthly temperature profiles from the central Strait of Georgia, British Columbia is used to examine low frequency variability and trends through the water column. Decomposition of temperature anomalies into empirical orthogonal functions shows that the dominant mode accounts for 78% of the variance, while the principal component associated with this mode (PC1) is dominated by fluctuations on interannual time scales. To relate the variability within the Strait to that occurring over the northeast Pacific, PC1 is compared with anomalies in local air temperature, sea surface temperatures off the west coast of Vancouver Island, and upper ocean temperatures along Line-P. These comparisons suggest that much of the interannual variability observed in the Strait of Georgia occurs in response to large-scale atmospheric forcing over the northeast Pacific. However, following tropical El Niño events there are significant anomalies associated with processes occurring along the coastal oceanic wave guide. The strongest event in the entire record, the remarkable negative temperature anomaly of winter 1978/1979, appears to be associated with a deep water intrusion that was forced locally.     

The short period magnetic variable HD 133029

It is shown that the magnetic measurements of HD 133029 exhibit a correlation of magnetic intensity with exposure length. Due to this effect a re-examination of the star's period was undertaken, resulting in a new period of 0.168 days. The significance of such a short period is discussed. It is argued that this short variation cannot be due to an oblique rotator.