Production of n-alkyl lipids in living plants and implications for the geologic past

Leaf waxes (i.e., n-alkyl lipids or n-alkanes) are land-plant biomarkers widely used to reconstruct changes in climate and the carbon isotopic composition of the atmosphere. There is little information available, however, on how the production of leaf waxes by different kinds of plants might influence the abundance and isotopic composition of n-alkanes in sedimentary archives. This lack of information increases uncertainty in interpreting n-alkyl lipid abundance and δ¹³C signals in ancient settings. We provide here n-alkyl abundance distributions and carbon isotope fractionation data for deciduous and evergreen angiosperm and gymnosperm leaves from 46 tree species, representing 24 families. n-Alkane abundances are significantly higher in angiosperms than gymnosperms; many of the gymnosperm species investigated did not produce any n-alkanes. On average, deciduous angiosperms produce 200 times more n-alkanes than deciduous gymnosperms. Although differences between angiosperms and gymnosperms dominate the variance in n-alkane abundance, leaf life-span is also important, with higher n-alkane abundances in longer-lived leaves. n-Alkanol abundances covary with n-alkanes, but n-alkanoic acids have similar abundances across all plant groups. Isotopic fractionation between leaf tissue and individual alkanes (ε_lipid) varies by as much as 10‰ among different chain lengths. Overall, ε_lipid values are slightly lower (−4.5‰) for angiosperm than for gymnosperm (−2.5‰) n-alkanes. Angiosperms commonly express slightly higher Δ_leaf (photosynthetic discrimination) relative to gymnosperms under similar growth conditions. As a result, angiosperm n-alkanes are expected to be generally 3-5‰ more depleted in ¹³C relative to gymnosperm alkanes for the same locality. Differences in n-alkane production indicate the biomarker record will largely (but not exclusively) reflect angiosperms if both groups were present, and also that evergreen plants will likely be overrepresented compared with deciduous ones. We apply our modern lipid abundance patterns and ε_lipid results to constrain the magnitude of the carbon isotope excursion (CIE) at the onset of the Paleocene-Eocene Thermal Maximum (55.8 Ma). When Bighorn Basin (WY) sediment n-alkanes are interpreted in context of floral changes and modern n-alkane production estimates for angiosperms and gymnosperms, the CIE is greater in magnitude (−5.6‰) by ∼1‰ compared to previous estimates that do not take into account n-alkane production.     

A comparison of two models to predict soil moisture from remote sensing data of RADARSAT II

This study investigates the performance of empirical and semiempirical models to predict soil moisture from the data of RADARSAT II synthetic aperture radar (SAR) for the Yarmouk basin in Jordan. Data of SAR were obtained for May and June 2010 and were processed to obtain backscatter (σ ^o ) data for the study area. Results showed significant correlations between soil moisture content (m _v ) and horizontally polarized σ ^o , with coefficient of determination (R ²) of 0.64. The root mean square error for the SAR volumetric soil moisture content was 0.09 and 0.06 m³/m³ for the empirical and semiempirical regression models, respectively. Both models had different clustering patterns in the soil moisture maps in the study area. The spatial agreement between maps of soil moisture was in the range of 55 to 65 % when the maps were reclassified based on intervals of 5 % m _v for both models. In terms of soil moisture interval, both models showed that most of soil moisture changes between the two images (dates) were in the range of ±5 %. Some high differences in ?m _v were observed between the two models. These were mainly attributed to the non-inverted pixels in the soil moisture maps produced by the semiempirical model. Therefore, this model may be applied for a limited range of soil moisture prediction. The use of regression model could predict a wider range for soil moisture when compared with the semiempirical model. However, more work might be needed to improve the empirical model before scaling it up to the whole study area.     

Nonsingular vectorial reformulation of the short-period corrections in Kozai’s oblateness solution

We present fully three-dimensional equations to describe the rotations of a body made of a deformable mantle and a fluid core. The model in its essence is similar to that used by INPOP19a (Integration Planétaire de l’Observatoire de Paris) Fienga et al. (INPOP19a planetary ephemerides. Notes Scientifiques et Techniques de l’Institut de Mécanique Céleste, vol 109, 2019), and by JPL (Jet Propulsion Laboratory) (Park et al. The JPL Planetary and Lunar Ephemerides DE440 and DE441. Astron J 161(3):105, 2021. doi:10.3847/1538-3881/abd414), to represent the Moon. The intended advantages of our model are: straightforward use of any linear-viscoelastic model for the rheology of the mantle; easy numerical implementation in time-domain (no time lags are necessary); all parameters, including those related to the “permanent deformation”, have a physical interpretation. The paper also contains: (1) A physical model to explain the usual lack of hydrostaticity of the mantle (permanent deformation). (2) Formulas for free librations of bodies in and out-of spin-orbit resonance that are valid for any linear viscoelastic rheology of the mantle. (3) Formulas for the offset between the mantle and the idealised rigid-body motion (Peale’s Cassini states). (4) Applications to the librations of Moon, Earth, and Mercury that are used for model validation.

     

Microstructural constraints on the mechanisms of the transformation to reidite in naturally shocked zircon

Zircon (ZrSiO₄) is used to study impact structures because it responds to shock loading and unloading in unique, crystallographically controlled manners. One such phenomenon is the transformation of zircon to the high-pressure polymorph, reidite. This study quantifies the geometric and crystallographic orientation relationships between these two phases using naturally shocked zircon grains. Reidite has been characterized in 32 shocked zircon grains (shocked to stages II and III) using a combination of electron backscatter diffraction (EBSD) and focused ion beam cross-sectional imaging techniques. The zircon-bearing clasts were obtained from within suevite breccia from the Nördlingen 1973 borehole, close to the center of the 14.4 Ma Ries impact crater, in Bavaria, Germany. We have determined that multiple sets (up to 4) of reidite lamellae can form in a variety of non-rational habit planes within the parent zircon. However, EBSD mapping demonstrates that all occurrences of lamellar reidite have a consistent interphase misorientation relationship with the host zircon that is characterized by an approximate alignment of a {100}_zircon with a {112}_reidite and alignment of a {112}_zircon with a conjugate {112}_reidite. Given the tetragonal symmetry of zircon and reidite, we predict that there are eight possible variants of this interphase relationship for reidite transformation within a single zircon grain. Furthermore, laser Raman mapping of one reidite-bearing grain shows that moderate metamictization can inhibit reidite formation, thereby highlighting that the transformation is controlled by zircon crystallinity. In addition to lamellar reidite, submicrometer-scale granules of reidite were observed in one zircon. The majority of reidite granules have a topotaxial alignment that is similar to the lamellar reidite, with some additional orientation dispersion. We confirm that lamellar reidite likely forms via a deviatoric transformation mechanism in highly crystalline zircon, whereas granular reidite forms via a reconstructive transformation from low-crystallinity ZrSiO₄ within the reidite stability field. The results of this study further refine the formation mechanisms and conditions of reidite transformation in naturally shocked zircon.     

Infrastructure hazard resilience trends: an analysis of 25 years of research

Hazard research has made significant strides over the last several decades, answering critical questions surrounding vulnerability and recovery. Recently, resilience has come to the forefront of scholarly debates and practitioner strategies, yet there remain challenges implementing resilience in practice, the result of a complex web of research that spread across numerous fields of study. As a result, there is a need to analyze and reflect on the current state of resilience literature. We reviewed 241 journal articles from the Web of Science and Engineering Village databases from 1990 to 2015 to analyze research trends in geographic location of studies, methods employed, units of analysis, and resilience dimensions studied, as well as correlations between each of these categories. The majority of the studies analyzed were conducted in North America, used quantitative methods, focused on infrastructure and community units of analysis, and studied governance, infrastructure, and economic dimensions of resilience. This analysis points to the need to: (1) conduct studies in developing country contexts, where resilience is particularly important; (2) employ mixed-methods for additional depth to quantitative studies; (3) connect units of analysis, such as infrastructure and community; and (4) expand on the measurement and study of environmental and social dimensions of resilience.     

Race,Space, and Struggles for Mobility: Transportation Impacts on African Americans in Oakland and the East Bay

Abstract

A long history of overt discrimination left an enduring racialized imprint upon the geography of the East Bay. While the benefits of a metropolitan decentralization of jobs, housing, and public investment fell to Whites, discrimination in employment and housing trapped African Americans in urban neighborhoods burdened by infrastructure encroachment and divestment. By circa 1970, overt discrimination succumbed to new, racially neutral, legal, and administrative forms, including regional planning processes. Using an environmental racism framework, we show that these new forms reproduced the existing racialized geography by means of new inequalities in representation and transportation service provision. These new regional transportation policies, like those challenged by a 2005 civil rights lawsuit, favored the mobility needs of more affluent suburbanites over those of African American East Bay bus riders. These policies, layered onto an existing racialized geography, reinforced existing inequalities by failing to address racial barriers to opportunity in the built environment. [Key words: transportation, race, segregation, Oakland]     

Water policy,trust and governance in the Murray-Darling Basin

Concerns for river health in the Murray-Darling Basin (MDB) area and shifting priorities for water use have led to a significant process of water reform over the last decade. The MDB area, also known as the food bowl of Australia, produces much of the country's food and is home to a significant portion of the population. A long-term drought, historical over-allocation of water for irrigation and climate variability have led to mounting concerns about the long-term viability of the rivers. While the reform process has resulted in the Commonwealth government taking control of the rivers from the States, it has also been influenced by changes in governments and consequent shifts in water allocation priorities from a privileging of agriculture to a broader approach encompassing economic, environmental and social concerns. This had led to uncertainty for the people and communities in the Basin and some confusion between the various layers of governance structures. This paper presents the results of exploratory research conducted with key, high-level stakeholders involved in water reform to examine their perceptions of the evolving water policy process. Despite agreement amongst stakeholders that returning water to the environment to ensure river health is critical, our research reveals significant tensions between stakeholders concerning the evolving process, particularly centred on the potential social outcomes and fairness and equity. This suggests the need for more integrated and transparent governance structures, attention to levels of trust between partners and a common vision that incorporates environmental, economic and social goals.     

On the Measurement of PANs by Gas Chromatography and Electron Capture Detection

A fast, automated, gas chromatographic system for the airborne measurement of PAN and a series of its homologues is described and its performance is evaluated. Response factors for PAN, PPN, APAN, PiBN, and MPAN have been determined and are discussed with regard to ECD response and to potential losses in the analytical system. Calibration methods used for these tasks are described and compared. The results from this work should help investigators who are employing the widely used GC/ECD method for the measurement of peroxyacyl nitrates to evaluate peaks of PAN homologues that cannot be calibrated for by using the reported response factors.     

The chemical composition of fogs and intercepted clouds in the United States

Over the past decade, the chemical compositions of fogs and intercepted clouds have been investigated at more than a dozen locations across the United States. Sampling sites have been located in the northeast, southeast, Rocky Mountain, and west coast regions of the US. They include both pristine and heavily polluted locations. Frontal/orographic clouds (warm and supercooled), intercepted coastal stratiform clouds, and radiation fogs have all been examined. Sample pH values range from below 3 to above 7. Major ions also exhibit a wide concentration range, with clouds at some locations exhibiting high sea salt concentrations, while composition at other locations is dominated by ammonium and sulfate or nitrate.