Observations of Wind-Direction Variability in the Nocturnal Boundary Layer

Large sudden wind-direction shifts and submeso variability under nocturnal conditions are examined using a micrometeorological network of stations in north-western Victoria, Australia. The network was located in an area with mostly homogeneous and flat terrain. We have investigated the main characteristics of the horizontal propagation of events causing the wind-direction shift and not addressed in previous studies. The submeso motions at the study site exhibit behaviour typical of flat terrain, such as the lower relative mesovelocity scale and smaller cross-wind variances than that for complex terrain. The distribution of wind-direction shifts shows that there is a small but persistent preference for counter-clockwise rotation, occurring for 55% of the time. Large wind-direction shifts tend to be associated with a sharp decrease in air temperature (74% of the time), which is associated with rising motion of cold air, followed by an increase in turbulent mixing. The horizontal propagation of events was analyzed using the cross-correlation function method. There is no preferred mean wind direction associated with the events nor is there any relationship between the mean wind and propagation directions. The latter indicates that the events are most likely not local flow perturbations advected by the mean flow but are rather features of generally unknown origin. This needs to be taken into account when developing parametrizations of the stable boundary layer in numerical models.     

Ecological periodic tables for benthic macrofaunal usage of estuarine habitats in the US Pacific Northwest

This study shows that spatially and temporally recurring benthic macrofauna-habitat patterns validate the ecological relevance of habitat types to benthic macrofauna and suggest they can serve as elements in ecological periodic tables of benthic macrofaunal usage. We discovered patterns across nine habitat types (intertidal eelgrass [Zostera marina], dwarf eelgrass [Zostera japonica], oyster [Crassostrea gigas] ground culture, burrowing mud shrimp [Upogebia pugettensis], burrowing ghost shrimp [Neotrypaea californiensis], shell, sand, mud, and subtidal) on a variety of benthic macrofaunal community state variables in Grays Harbor, Washington, USA and compared them to those in Willapa Bay, Washington, USA. There were nominal differences in benthic macrofaunal Bray-Curtis similarity between all the habitats investigated except eelgrass and oyster in both estuaries. Across-habitat patterns on mean benthic macrofaunal species richness, abundance, biomass, abundance of deposit, suspension and facultative feeders, a dominance and a diversity index for the five habitats common to both studies were the same on a rank measurement scale: eelgrass ≈ oyster > mud shrimp > ghost shrimp ≈ subtidal. The patterns for most of the habitats and benthic macrofaunal measures were the same on a ratio measurement scale.     

Comparison and relative quality assessment of the GLC2000, GLOBCOVER,MODIS and ECOCLIMAP land cover data sets at the African continental scale

Land cover dynamics at the African continental scale is of great importance for global change studies. Actually, four satellite-derived land cover maps of Africa now available, e.g. ECOCLIMAP, GLC2000, MODIS and GLOBCOVER, are based on images acquired in the 2000s. This study aims at stressing the compliances and the discrepancies between these four land cover classifications systems. Each of them used different mapping initiatives and relies on different mapping standards, which supports the present investigation. In order to do a relative comparison of the four maps, a preamble was to reconcile their thematic legends into more aggregated categories after a projection into the same spatial resolution. Results show that the agreement between the four land cover products is between 56 and 69%. While all these land cover datasets show a reasonable agreement in terms of surface types and spatial distribution patterns, mapping of heterogeneous landscapes in the four products is not very successful. Land cover products based on remote sensing imagery can indeed significantly be improved by using smarter algorithms, better timing of image acquisition, improved class definitions. Either will help to improve the accuracy of future land cover maps at the African continental scale. Data producers may use the areas of spatial agreement for training area selection while users might need to verify the information in the areas of disagreement using additional data sources.     

LATE QUATERNARY CHANGES IN PINYON AND JUNIPER DISTRIBUTIONS IN THE WHITE MOUNTAIN REGION OF CALIFORNIA AND NEVADA

Data from packrat middens are used to reconstruct the migration of single-leaf pinyon (Pinus monophylla) and Utah juniper (Juniperus osteosperma) in the White Mountain region of California and Nevada for the last 20,000 years. Today this region is characterized by arid conditions with dry summers. Pinyon woodlands, which are favored by dry summer conditions, are dominant at middle elevations of the White Mountains. The midden record indicates that during the late Pleistocene and early Holocene, juniper was dominant at elevations now occupied by desert shrubs. A late Pleistocene-early Holocene record of desert shrubs was found only in the double rainshadow of the Sierra Nevada and the White Mountains. Pinyon entered the area during the Holocene (ca. 9000 yr B.P.) and subsequently became more important than juniper. During the late Holocene, desert shrubs became established at the lower elevation sites that they now occupy. The late Pleistocene-early Holocene record indicates that there may have been a more zonal upper-level wind flow and associated penetration of Pacific moisture, as indicated by the occurrence of desert shrubs downwind of the north-south-trending mountain ranges. Zonal flow probably became less important during the early Holocene based on the increasing amount of pinyon. The increase in pinyon also may indicate a change from an even seasonal distribution of precipitation to the dry summer conditions presently found in the region. [Key words: biogeography, packrat middens, Great Basin paleoenvironments, Pinus monophylla, Juniperus osteosperma, White Mountains.]     

Grain carriers of isotopic anomalies

The dynamics of grain motion through gas are examined in terms of the injection of isotopically anomalous (compared to solar abundances) material into the early solar nebula. Calculations indicate that the injected grains cannot penetrate to the center of any of a range of reasonable configurations, suggesting the formation of an edge region enriched in injected material. Furthermore, the dynamical behavior of grains in turbulent flows indicates that pockets of grains can have some resistance to turbulent diffusion. The constraints developed here are used to delineate a set of consistent, injected-grain models for the origin of the isotopic anomalies in meteorite inclusions.Invited contribution to the Proceedings of a Workshop onThermodynamics and Kinetics of Dust Formation in the Space Medium held at the Lunar and Planetary Institute, Houston, 6–8 September, 1978.     

Modeling studies of the upper ocean response to a tropical cyclone

A coupled ocean and boundary layer flux numerical modeling system is used to study the upper ocean response to surface heat and momentum fluxes associated with a major hurricane, namely, Hurricane Dennis (July 2005) in the Gulf of Mexico. A suite of experiments is run using this modeling system, constructed by coupling a Navy Coastal Ocean Model simulation of the Gulf of Mexico to an atmospheric flux model. The modeling system is forced by wind fields produced from satellite scatterometer and atmospheric model wind data, and by numerical weather prediction air temperature data. The experiments are initialized from a data assimilative hindcast model run and then forced by surface fluxes with no assimilation for the time during which Hurricane Dennis impacted the region. Four experiments are run to aid in the analysis: one is forced by heat and momentum fluxes, one by only momentum fluxes, one by only heat fluxes, and one with no surface forcing. An equation describing the change in the upper ocean hurricane heat potential due to the storm is developed. Analysis of the model results show that surface heat fluxes are primarily responsible for widespread reduction (0.5°–1.5°C) of sea surface temperature over the inner West Florida Shelf 100–300 km away from the storm center. Momentum fluxes are responsible for stronger surface cooling (2°C) near the center of the storm. The upper ocean heat loss near the storm center of more than 200 MJ/m² is primarily due to the vertical flux of thermal energy between the surface layer and deep ocean. Heat loss to the atmosphere during the storm’s passage is approximately 100–150 MJ/m². The upper ocean cooling is enhanced where the preexisting mixed layer is shallow, e.g., within a cyclonic circulation feature, although the heat flux to the atmosphere in these locations is markedly reduced.     

MAJOR ELEMENT COMPOSITIONAL VARIATION WITHIN AND BETWEEN DIFFERENT LATE EOCENE MICROTEKTITE STREWNFIELDS

Major element compositional overlap exists between microspherules of different microtektite layers or strewnfields. For this reason, microspherules of similar composition cannot, a priori, be assumed to belong to the same microtektite event and those of different compositions cannot, a priori, be assumed to result from different events. Nevertheless, despite major element compositional overlap between microspherules of different strewnfields, multivariate factor analysis shows microtektites and related microspherules of three stratigraphically different late Eocene layers to follow recognizably different compositional trends. The microtektite population of the North American strewnfield (Globorotalia cerroazulensis Zone) follows compositionally well defined trends and is characterized by high concentrations of SiO₂, Al₂O₃, and TiO₂. The microspherule population of the slightly older crystal-bearing Globorotalia cerroazulensis Zone microspherule layer is more heterogeneous and characterized by microspherules which are relatively enriched in FeO and MgO and relatively impoverished in SiO₂ and TiO₂. The microspherule population of the oldest microspherule layer in the uppermost Globigerapsis semiinvoluta Zone is highly heterogeneous and characterized by microspherules which are relatively enriched in CaO and impoverished in Al₂O₃ and Na₂O. Individual microspherules of this oldest late Eocene horizon often exhibit major element compositions similar to those of the lower Gl. cerroazulensis Zone layer and occasionally exhibit major element compositions similar to North American layer microtektites. Nevertheless, late Eocene microspherule occurrences can be assigned to appropriate late Eocene microtektite horizons on the basis of major element compositional trends.     

Tree-mycorrhiza symbiosis accelerate mineral weathering: Evidences from nanometer-scale elemental fluxes at the hypha-mineral interface

In soils, mycorrhiza (microscopic fungal hypha) living in symbiosis with plant roots are the biological interface by which plants obtain, from rocks and organic matter, the nutrients necessary for their growth and maintenance. Despite their central role in soils, the mechanism and kinetics of mineral alteration by mycorrhiza are poorly constrained quantitatively. Here, we report in situ quantification of weathering rates from a mineral substrate, (0 0 1) basal plane of biotite, by a surface-bound hypha of Paxillus involutus, grown in association with the root system of a Scots pine, Pinus sylvestris. Four thin-sections were extracted by focused ion beam (FIB) milling along a single hypha grown over the biotite surface. Depth-profile of Si, O, K, Mg, Fe and Al concentrations were performed at the hypha-biotite interface by scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDX). Large removals of K (50-65%), Mg (55-75%), Fe (80-85%) and Al (75-85%) were observed in the topmost 40 nm of biotite underneath the hypha while Si and O are preserved throughout the depth-profile. A quantitative model of alteration at the hypha-scale was developed based on solid-state diffusion fluxes of elements into the hypha and the break-down/mineralogical re-arrangement of biotite. A strong acidification was also observed with hypha bound to the biotite surface reaching pH < 4.6. When consistently compared with the abiotic biotite dissolution, we conclude that the surface-bound mycorrhiza accelerate the biotite alteration kinetics between pH 3.5 and 5.8 to ∼0.04 μmol biotite m⁻² h⁻¹. Our current work reaffirms that fungal mineral alteration is a process that combines our previously documented bio-mechanical forcing with the μm-scale acidification mediated by surface-bound hypha and a subsequent chemical element removal due to the fungal action. As such, our study presents a first kinetic framework for mycorrhizal alteration at the hypha-scale under close-to-natural experimental conditions.     

The Topaz Basin archaeological obsidian source in the transition zone of central Arizona

The Classic Period Migration Project involves the analysis of archaeological sites at Perry Mesa in central Arizona and resulted in the discovery of several small marekanite1 obsidian artifacts that signaled a previously unlocated source. The source was eventually located in the Topaz Basin area of the upper Cienega Creek stream basin, southwest of Camp Verde, Arizona.² While this locality solves the “unknown” sources in the Perry Mesa archaeological assemblage, it has not appeared in the archaeological record of Arizona with any frequency. The glass itself is an excellent medium for tool production, so its near absence in the archaeological record is likely attributable to social/territorial causes as well as limited secondary deposition, and along with other “minor” sources points to the archaeological utility of understanding these smaller sources. © 2009 Wiley Periodicals, Inc.