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.     

Wave refraction–diffraction effect in the wind wave model WWM

Based on the extended mild-slope equation, the wind wave model (WWM; Hsu et al., 2005) is modified to account for wave refraction, diffraction and reflection for wind waves propagating over a rapidly varying seabed in the presence of current. The combined effect of the higher-order bottom effect terms is incorporated into the wave action balance equation through the correction of the wavenumber and propagation velocities using a refraction–diffraction correction parameter. The relative importance of additional terms including higher-order bottom components, the wave–bottom interaction source term and wave–current interaction that influence the refraction–diffraction correction parameter is discussed. The applicability of the proposed model to calculate a wave transformation over an elliptic shoal, a series of parallel submerged breakwater induced Bragg scattering and wave–current interaction is evaluated. Numerical results show that the present model provides better predictions of the wave amplitude as compared with the phase-decoupled model of Holthuijsen et al. (2003).     

Emission metrics under the 2 °C climate stabilization target

In multi-gas climate policies such as the Kyoto Protocol one has to decide how to compare the emissions of different greenhouse gases. The choice of metric could have significant implications for mitigation priorities considered under the prospective negotiations for climate mitigation agreements. Several metrics have been proposed for this task with the Global Warming Potential (GWP) being the most common. However, these metrics have not been systematically compared to each other in the context of the 2 °C climate stabilization target. Based on a single unified modeling framework, we demonstrate that metric values span a wide range, depending on the metric structure and the treatment of the time dimension. Our finding confirms the basic salient point that metrics designed to represent different aspects of the climate and socio-economic system behave differently. Our result also reflects a complex interface between science and policy surrounding metrics. Thus, it is important to select or design a metric suitable for climate stabilization based on an interaction among practitioners, policymakers, and scientists.     

The Cosmic Foreground Explorer (COFE): A balloon-borne microwave polarimeter to characterize polarized foregrounds

The COsmic Foreground Explorer (COFE) is a balloon-borne microwave polarimeter designed to measure the low-frequency and low-ℓ characteristics of dominant diffuse polarized foregrounds. Short duration balloon flights from the Northern and Southern Hemispheres will allow the telescope to cover up to 80% of the sky with an expected sensitivity per pixel better than 100 μK/deg² from 10 GHz to 20 GHz. This is an important effort toward characterizing the polarized foregrounds for future CMB experiments, in particular the ones that aim to detect primordial gravity wave signatures in the CMB polarization angular power spectrum.     

Cold curation of pristine astromaterials: Insights from the Tagish Lake meteorite

The curation and handling of volatile‐bearing astromaterials is of prime importance in current and future plans for sample return missions to targets containing organic compounds, ices, or other volatile components. We report on the specific curation constraints required for the preservation of the Tagish Lake meteorite, a C2 ungrouped chondrite that contains significant concentrations of organic matter, including compounds of prebiotic interest or volatile in character, and which was recovered from a frozen lake surface a few days after its fall. Here, we review the circumstances of the meteorite's handling, its complement of intrinsic and contaminant organic compounds, and an unusual reaction between some of the specimens and the Al foil in which they were enclosed. From our results, we derive the requirements for curation of the meteorite, and describe a specialized facility that enables its curation and handling. The Subzero Facility for Curation of Astromaterials consists of a purified Ar glove box enclosed within a freezer chamber, and enables investigations relevant to curation of samples at or below ?10 °C. We provide several recommendations based on insights obtained from the commissioning and initial use of the facility that are relevant to collection of freshly fallen meteorites, curation of volatile‐bearing meteorites and other astromaterials, and planning and implementation of curation plans for future sample return missions to volatile‐bearing targets.     

Stable isotopes of water reveal differences in plant – soil water relationships across northern environments

We compared stable isotopes of water in plant stem (xylem) water and soil collected over a complete growing season from five well-known long-term study sites in northern/cold regions. These spanned a decreasing temperature gradient from Bruntland Burn (Scotland), Dorset (Canadian Shield), Dry Creek (USA), Krycklan (Sweden), to Wolf Creek (northern Canada). Xylem water was isotopically depleted compared to soil waters, most notably for deuterium. The degree to which potential soil water sources could explain the isotopic composition of xylem water was assessed quantitatively using overlapping polygons to enclose respective data sets when plotted in dual isotope space. At most sites isotopes in xylem water from angiosperms showed a strong overlap with soil water; this was not the case for gymnosperms. In most cases, xylem water composition on a given sampling day could be better explained if soil water composition was considered over longer antecedent periods spanning many months. Xylem water at most sites was usually most dissimilar to soil water in drier summer months, although sites differed in the sequence of change. Open questions remain on why a significant proportion of isotopically depleted water in plant xylem cannot be explained by soil water sources, particularly for gymnosperms. It is recommended that future research focuses on the potential for fractionation to affect water uptake at the soil-root interface, both through effects of exchange between the vapour and liquid phases of soil water and the effects of mycorrhizal interactions. Additionally, in cold regions, evaporation and diffusion of xylem water in winter may be an important process.     

Using isotopes to understand landscape-scale connectivity in a groundwater-dominated,lowland catchment under drought conditions

The Demnitzer Millcreek catchment (DMC), is a 66 km² long-term experimental catchment located 50 km SE of Berlin. Monitoring over the past 30 years has focused on hydrological and biogeochemical changes associated with de-intensification of farming and riparian restoration in the low-lying landscape dominated by rain-fed farming and forestry. However, the hydrological function of the catchment, which is closely linked to nutrient fluxes and highly sensitive to climatic variability, is still poorly understood. In the last 3 years, a prolonged drought period with below-average rainfall and above-average temperatures has resulted in marked hydrological change. This caused low soil moisture storage in the growing season, agricultural yield losses, reduced groundwater recharge, and intermittent streamflows in parts of an increasingly disconnected channel network. This paper focuses on a two-year long isotope study that sought to understand how different parts of the catchment affect ecohydrological partitioning, hydrological connectivity and streamflow generation during drought conditions. The work has shown the critical importance of groundwater storage in sustaining flows, basic in-stream ecosystem services and the dominant influence of vegetation on groundwater recharge. Recharge was much lower and occurred during a shorter window of time in winter under forests compared to grasslands. Conversely, groundwater recharge was locally enhanced by the restoration of riparian wetlands and storage-dependent water losses from the stream to the subsurface. The isotopic variability displayed complex emerging spatio-temporal patterns of stream connectivity and flow duration during droughts that may have implications for in-stream solute transport and future ecohydrological interactions between landscapes and riverscapes. Given climate projections for drier and warmer summers, reduced and increasingly intermittent streamflows are very likely not just in the study region, but in similar lowland areas across Europe. An integrated land and water management strategy will be essential to sustaining catchment ecosystem services in such catchment systems in future.     

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.     

Rising powers: the evolving role of BASIC countries

The exponential growth in global populations, economic activity and resource utilization means it is becoming increasingly difficult to satisfy global demand for a number of fundamental resources, while some key ecosystems services are under stress. The likelihood of future resource scarcities have begun to influence the positions taken within international climate change negotiations by fast-growing developing countries. When Brazil, South Africa, India, and China formed the BASIC group it took many by surprise. The coordination needed to align this heterogeneous group of countries cannot simply be understood in terms of a set of shared interests around climate policy. How the BASIC group emerged and the nature of its cooperation on climate change are examined within the broader context in which these increasingly powerful countries came to join forces. Although traditionally aligned with the G77 group of developing countries, recent strategising as a group of emerging economies reflects their realization that there are insufficient global resources available to follow the same development pathway as industrialized countries. Hence, they must seek alternative growth pathways, which requires establishing common ground while also keeping track of each others' positions on important global issues like climate change.     

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.