Northwest Africa 5790: A previously unsampled portion of the upper part of the nakhlite pile

We present a geochemical study of recently discovered Martian meteorite Northwest Africa (NWA) 5790 and use our results to constrain its origin and relationship with the other nakhlites. This nakhlite is a clinopyroxene cumulate composed of phenocrysts of augite, olivine, and rare oxides surrounded by a mesostasis composed of vitrophyric glass, feldspars, oxides, phosphates, and fine‐grained olivines and augite. Petrography, and major and trace element compositions of the phases present are consistent with derivation of NWA 5790 from a parental magma common to all the nakhlites. Olivine cores grew from a distinct, incompatible‐element enriched magma and are surrounded by rims containing augite inclusions that grew from the nakhlite parental liquid, supporting previous arguments for xenocrystic olivine cores in nakhlites. Rare earth element microdistributions suggest derivation of NWA 5790 augites from an evolved, relatively oxidized magma, produced by augite fractionation from the common nakhlite parental liquid. Augite grain shapes and CSD patterns are consistent with rapid cooling and derivation near the top of the nakhlite cumulate pile, but patterns are distinct from other nakhlites thought to have formed near the stratigraphic top. The high mesostasis abundance (~44 vol%) indicates solidification near the top of the nakhlite pile close to locations suggested for nakhlites NWA 817 and Miller Range (MIL) 03346. However, the geochemical and petrographic characteristics of these three samples do not permit their placement in a simple stratigraphic order as would occur in a single lava flow. This lack of simple ordering suggests that the nakhlite lava flow split into multiple sections as would occur during breakouts from a single lava flow. Finally we note that NWA 5790 is unique among currently available nakhlites in having phenocryst abundances low enough to allow it to flow.     

Forced oscillation measurements of seismic wave attenuation and stiffness moduli dispersion in glycerine-saturated Berea sandstone

Fluid pressure diffusion occurring on the microscopic scale is believed to be a significant source of intrinsic attenuation of mechanical waves propagating through fully saturated porous rocks. The so-called squirt flow arises from compressibility heterogeneities in the microstructure of the rocks. To study squirt flow experimentally at seismic frequencies the forced oscillation method is the most adequate, but such studies are still scarce. Here we present the results of forced hydrostatic and axial oscillation experiments on dry and glycerine-saturated Berea sandstone, from which we determine the dynamic stiffness moduli and attenuation at micro-seismic and seismic frequencies (0.004–30 Hz). We observe frequency-dependent attenuation and the associated moduli dispersion in response to the drained–undrained transition (∼0.1 Hz) and squirt flow (>3 Hz), which are in fairly good agreement with the results of the corresponding analytical solutions. The comparison with very similar experiments performed also on Berea sandstone in addition shows that squirt flow can potentially be a source of wave attenuation across a wide range of frequencies because of its sensitivity to small variations in the rock microstructure, especially in the aspect ratio of micro-cracks or grain contacts.     

Microplastic Contamination in Karst Groundwater Systems

Groundwater in karst aquifers constitutes about 25% of drinking water sources globally. Karst aquifers are open systems, susceptible to contamination by surface-borne pollutants. In this study, springs and wells from two karst aquifers in Illinois, USA, were found to contain microplastics and other anthropogenic contaminants. All microplastics were fibers, with a maximum concentration of 15.2 particles/L. The presence of microplastic was consistent with other parameters, including phosphate, chloride and triclosan, suggesting septic effluent as a source. More studies are needed on microplastic sources, abundance, and impacts on karst ecosystems.     

长江中游地区暴雨过程的500 hPa信号场特征

文中用500 hPa信号场研究了长江中游地区暴雨发生的气候异常环境,并提出用信号场合成图的检验方法来分析暴雨规律.结果表明,暴雨过程与无雨过程在500 hPa信号场中异常信号显著区的出现及分布形势有明显不同.分析14次暴雨过程的合成图,发现在发生暴雨过程第1天,正异常区常常出现在贝加尔湖附近地区(40°～50°N,80°～100°E)和中国华南地区(20°～25°N,100°～130°E),负异常区出现在中国长江中游北部地区.暴雨过程出现的主要特征是在110°E附近,形成南北向的"+-+"分布形势和波列.     

Evolution of new regional development interventions in New Zealand: An analysis of the first year of the Provincial Growth Fund

Regional development has evolved in response to shifting local and global priorities. These shifts have transformed both the way we think about regions, their role and how that shapes the outcomes and benefits that might occur from engaging in regional development. Key debates centre around the ability (or desirability) of regional development interventions to unsettle path dependence and “lock‐in” created by past approaches and to create opportunities for alternative development futures and to provide choices between sectoral‐based investments to support economic activity in contrast to a more place‐based approach to regional development. This paper overviews the dynamic nature of regional development to offer reasons for its recent resurgence by highlighting the key debates about the purpose and function of regions and what regional development can or should do. We then discuss the New Zealand context specifically and use the first year of Provincial Growth Fund investments to reflect on how the processes, objectives and goals reflect particular interpretations of the meaning and purpose of regional development. We conclude that a strong adherence to a growth imperative has the potential to reinforce path dependencies at the expense of alternative development pathways.     

Badass gully morphodynamics and sediment generation in Waipaoa Catchment,New Zealand

Large (>0.1 km²) gully–mass movement complexes (badass gullies) are significant contributors to the sediment cascade in New Zealand's steepland East Coast Region catchments. The scale of change taking place in these gully systems allows significant evolution in morphology and sediment dynamics to be tracked at annual to decadal timescales. Here we document changes in two adjacent badass gullies in Waipaoa catchment (Tarndale and Mangatu) to infer sediment generation processes and connectivity using a morphological budgeting approach. A baseline dataset for this study is provided by a LiDAR-derived digital elevation model (DEM) in 2005. We produced new DEMs and orthophoto mosaics using photogrammetry in 2017, 2018, and 2019 to quantify gully morphodynamics and associated volumes of sediment erosion and deposition in both systems as they co-evolved. Results indicate ongoing rapid development of both gully complexes. Severe erosion took place at the gully heads with lowering and migration (up to 25 m vertically and laterally) of the topographic divide separating the two gullies between 2005 and 2019. Over the same period, net lowering of each gully system was ~250 mm year⁻¹. Key sediment-generating processes included surface erosion, deep-seated landslides, and debris flows. Longer term, the overall contribution of sediment from both badass gullies to the Waipaoa catchment has been declining. In the mid-20th century, both gullies yielded in excess of 300 kt year⁻¹. From 2005 to 2019, 80 kt year⁻¹ was yielded from Tarndale and 110 kt year⁻¹ from Mangatu. Our most recent surveys demonstrated considerable variability in sediment yield, ranging from 76 kt year⁻¹ (2017–2018) to 291 kt year⁻¹ (2018–2019). The annual variability observed reflects the complex morphodynamics of discrete hillslopes and tributary fans in these badass gully systems and underlines the importance of integrating decadal and annual surveys when assessing system trajectory. © 2020 John Wiley & Sons, Ltd.     

On the small-scale fractal geometrical structure of a living coral reef barrier

The topographical complexity of coral reefs is of primary importance for a number of hydrodynamical and ecological processes. The present study is based on a series of high-resolution seabottom elevation measurements along the Maupiti Barrier Reef, French Polynesia. Several statistical metrics and spectral analysis are used to characterize the spatial evolution of the coral geometrical structure from the reef crest to the backreef. A consistent fractal-like power law exists in the spectral density of bottom elevation for length scales between 0.1 and 7 m, while at larger scale, the reef structure shows a different pattern. Such a fine characterization of the reef geometrical structure provides key elements to reconstruct the reef history, to improve the representation of reef roughness in hydrodynamical models and to monitor the evolution of coral reef systems in the context of global change. © 2020 John Wiley & Sons, Ltd.     

Sub-annual moraine formation at an active temperate Icelandic glacier

This paper presents detailed geomorphological and sedimentological investigations of small recessional moraines at Fjallsjökull, an active temperate outlet of Öræfajökull, southeast Iceland. The moraines are characterized by striking sawtooth or hairpin planforms, which are locally superimposed, giving rise to a complex spatial pattern. We recognize two distinct populations of moraines, namely a group of relatively prominent moraine ridges (mean height ~1.2 m) and a group of comparatively low-relief moraines (mean height ~0.4 m). These two groups often occur in sets/systems, comprising one pronounced outer ridge and several inset smaller moraines. Using a representative subsample of the moraines, we establish that they form by either (i) submarginal deformation and squeezing of subglacial till or (ii) pushing of extruded tills. Locally, proglacial (glaciofluvial) sediments are also incorporated within the moraines during pushing. For the first time, to our knowledge, we demonstrate categorically that these moraines formed sub-annually using repeat uncrewed aerial vehicle (UAV) imagery. We present a conceptual model for sub-annual moraine formation at Fjallsjökull that proposes the sawtooth moraine sequence comprises (i) sets of small squeeze moraines formed during melt-driven squeeze events and (ii) larger push moraines formed during winter re-advances. We suggest the development of this process-form regime is linked to a combination of elevated temperatures, high surface meltwater fluxes to the bed and emerging basal topography (a depositional overdeepening). These factors result in highly saturated subglacial sediments and high porewater pressures, which induces submarginal deformation and ice-marginal squeezing during the melt season. Strong glacier recession during the summer, driven by elevated temperatures, allows several squeeze moraines to be emplaced. This process-form regime may be characteristic of active temperate glaciers receding into overdeepenings during phases of elevated temperatures, especially where their englacial drainage systems allow efficient transfer of surface meltwater to the glacier bed near the snout margin. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd     

Thermal Remote Sensing of Near Surface Environmental Variables: Application Over the Oklahoma Mesonet

Many recent studies have applied satellite remote sensing data to large‐scale hydrologic and biospheric modeling. It is widely accepted that the thermal infrared observations from the Advanced Very High Resolution Radiometer (AVHRR) have the potential to estimate land surface conditions, such as surface temperature, near surface air temperature, and near surface water vapor. In this study, algorithms to estimate all three variables are presented and applied to an area covering the state of Oklahoma for a six day period in August, 1994. The results were validated using ground observations from the 111 station Oklahoma Mesonet. Validation of the remote sensing algorithms with Mesonet observations produced comparable results to previous validation studies. In addition, the validation process revealed inadequacies in thermal modeling that had not been detected in previous validation studies leading to the development of a new approach to estimate atmospheric water vapor.