Outer Ridge Research Articles

An additively manufactured dual circularly polarized open‐ended waveguide antenna using outer ridges with wideband characteristic

AbstractThis paper presents a novel additively manufactured wideband dual circularly polarized (CP) open‐ended waveguide (OEW) antenna, which adopts a pair of wedge‐shaped outer ridges acting as a circular polarizer. Study found that compared to the con‐ ventional designs that employ internal polarization converting structures, such outer ridges are capable of achieving wider axial ratio bandwidth (ARBW) and better reflection coefficients. On each ridge, two rectangular slots are designed to suppress the higher order mode caused by the increased waveguide size, and further expanding the ARBW. The proposed antenna is fed by two differential ports. By switching the feeding ports, the CP states can be altered to either right‐handed CP (RHCP) or left‐handed CP (LHCP). In terms of configuration, the proposed antenna has a simple one‐piece structure and is fabricated by using dielec‐ tric 3‐D printing technology. To form the waveguide walls, its partial surfaces are coated by copper films through electroplat‐ ing. The proposed antenna features easy fabrication and light weight. Experimental results show that the proposed antenna has an impedance bandwidth of larger than 47.6% (8–13 GHz) with reflection coefficients lower than −15 dB, while the 3‐dB ARBW is 37.7% from 8.4 to 12.3 GHz.

Deeper and stronger North Atlantic Gyre during the Last Glacial Maximum

Subtropical gyre (STG) depth and strength are controlled by wind stress curl and surface buoyancy forcing1,2. Modern hydrographic data reveal that the STG extends to a depth of about 1 km in the Northwest Atlantic, with its maximum depth defined by the base of the subtropical thermocline. Despite the likelihood of greater wind stress curl and surface buoyancy loss during the Last Glacial Maximum (LGM)3, previous work suggests minimal change in the depth of the glacial STG4. Here we show a sharp glacial water mass boundary between 33° N and 36° N extending down to between 2.0 and 2.5 km—approximately 1 km deeper than today. Our findings arise from benthic foraminiferal δ18O profiles from sediment cores in two depth transects at Cape Hatteras (36–39° N) and Blake Outer Ridge (29–34° N) in the Northwest Atlantic. This result suggests that the STG, including the Gulf Stream, was deeper and stronger during the LGM than at present, which we attribute to increased glacial wind stress curl, as supported by climate model simulations, as well as greater glacial production of denser subtropical mode waters (STMWs). Our data suggest (1) that subtropical waters probably contributed to the geochemical signature of what is conventionally identified as Glacial North Atlantic Intermediate Water (GNAIW)5–7 and (2) the STG helped sustain continued buoyancy loss, water mass conversion and northwards meridional heat transport (MHT) in the glacial North Atlantic.

Coastal Evolution of Satingpra Peninsula, Songkhla Province: Implications for Understanding Songkla Lagoon Formation

Songkhla Lagoon has been studied for decades, but there is no clear evidence of its origin. As a barrier to the lagoon, the Satingpra Peninsula plays a crucial role in understanding its formation. Eleven sediment samples from sand ridges and tidal flats on the Satingpra Peninsular were collected and analysed for granulometry and geochronology. Both coarse-grained and fine-grained quartz-rich fractions were utilised to prepare samples of aliquots. The optically stimulated luminescence (OSL) dating was performed using the single-aliquot regenerative dose method for a determined (deposited) age. In addition, previous research, geological surveys and geochronological data were combined to explain their formation in this region. The OSL ages in the present study indicated that the late Holocene regression occurred between 0.36 and 3.27 ka (ka stands for 1,000 years). Integrated with previous studies, recorded ages dating back to the mid-Holocene sea level rise (ca. 6.5 ka) and the subsequent late-Holocene decline, indicate that both the old lagoon and middle beach ridge exhibit a sand ridge formation that runs parallel to the shoreline, extending from the south to the north. The middle sand, in this study, formed from about 3.02 to 1.5 ka ago resulting in the lagoon being isolated from the sea during that time. The lagoonal tide led the deposition as the present tidal flat from 3.3 to 1.7 ka. About 2.19 ka ago, the inner and middle ridges formed due to wind-driven processes influenced by a dry climate. This was followed by a continued sea level regression, leading to the formation of the outer ridge around 1.5 ka ago when the sea level was 1.4 m below the present sea level. However, it’s essential to consider this sea level data in relation to the tectonic and human-induced land motions in the surrounding area. HIGHLIGHTS OSL ages, based on average dose model at the Northern Satingpra Peninsula were 1.04 - 3.27 ka. The old sand ridges of the Satingpra Peninsula prograde northward after mid Holocene sea level highstand. Paleo sea level based on wind-wave sediments contact was 1.4 m lower than present day at 1.46 ka. GRAPHICAL ABSTRACT

Clustered erosional submarine furrows at the Blake Outer Ridge on the U.S. Atlantic margin: implications for spatial variations of the Deep Western Boundary Current velocity

Clustered erosional submarine furrows at the Blake Outer Ridge on the U.S. Atlantic margin: implications for spatial variations of the Deep Western Boundary Current velocity

CLEAN imaging systematics of M87 radio jet

ABSTRACT The spectral index images of the jet in the nearby radio galaxy M87 have previously been shown with Very Long Baseline Interferometric arrays at 2–43 GHz. They exhibit flattening of the spectra at a location of inner (central) spine and towards outer ridges. This could imply optical depth effects, lower energy cut-off, or stratification of the emitting particles energy distribution. In this paper, we employ simulations of multifrequency VLBI observations of M87 radio jet with various model brightness distributions. CLEAN deconvolution errors produce significant features in the observed images. For intensity images, they result in the appearance of the inner ridge line in the intrinsically edge brightened jet models. For spectral index images, they flatten the spectra in a series of stripes along the jet. Another bias encountered in our simulations is steepening of the spectra in a low surface brightness jet regions. These types of the imaging artefacts do not depend on the model considered. We propose a method for the compensation of the systematics using only the observed data.

Mid-late holocene accretional history of low-lying, coral-reef rim islets, South-Marutea Atoll, Tuamotu, central South Pacific: The key role of marine hazard events

South-Marutea Atoll is located in the Gambier Island Group, at the south-eastern end of the Tuamotu Archipelago, French Polynesia, central South Pacific. Understanding the modalities of islet building from low-lying atolls over the mid to late Holocene, in relation to sea-level changes and cycles of marine hazard events, is a prerequisite for better anticipate future geomorphic changes to which the islets will likely be faced in the next decades under global climate warming. Herein is presented the depositional history of two selected atoll islets, based on chronostratigraphic analysis of sedimentary, coral-dominated sequences from six excavations. Identified as Motu Aramu and Motu Vainono, these islets are located respectively in north-north-east and due south of the atoll rim. Additional surficial sampling was conducted on modern ocean-facing shingle ridges, respectively on north-north-west (Motu Oire), west (Motu Aranui) and east (Motu Tekava) rim areas, in order to date the latest ridge-emplacement stages. Oire and Aranui sites, located along the leeward atoll sites, are protected from trade winds, Aramu, Vainono and Tekava are located on the windward sides, directly exposed to northeasterly and southeasterly storm swells respectively. A total of 88 coral clasts were collected to be U/Th dated. The excavated sequences range between 2.50 ​m and 0.90 ​m in thickness, from the outer islet sides lagoonwards. Five lithofacies, including two subfacies, were recognized based on texture and biological composition: a coral boulder-cobble-dominated, a coral pebble-dominated – pebble-supported and sand-supported subfacies – and a foraminifera-rich, sand-dominated and an organic-rich, pebble to sand facies. These facies tend to be distributed from ocean sides landwards according to a decreasing grain-size gradient. A model of atoll-island accretion emerges in relation with changes in frequency and intensity of marine hazard events. The islet foundations consist of conglomerate platforms, locally up to 1.0 ​m thick, deposited from about 5,000 to 1,000 ​calendar year (cal yr) BP. Islets began to accrete from 5,000 ​yr cal BP. While at Motu Vainono, islet building occurred continuously over the last 5,000 years, at Motu Aramu, there is an apparent non-depositional episode, from 4,000 to 2,000 ​yr cal BP, interpreted as caused by a marked decreased in enso-related cyclone activity. The outer shingle ridges in all studied sites were regularly reshaped during the last millennium. During the last 5,000 years, the major accretion-islet episodes occurred irrespective of the course of sea level, indicating that sea-level change was not a driver of islet accretion. Periodical, marine high-energy events clearly appear to be the key controls of islet shaping. Shifts of cyclone source areas further south and increasing cyclone intensity, but lower frequency, due to enhanced enso variability throughout the 21st century, is postulated to expose the Gambier island Group to stronger, but fewer disturbance events when compared to the last millennia.

Comprehensive assessment of integrated rice-crayfish farming system as a new paradigm to air-water-food nexus sustainability

Integrated rice-crayfish farming (IRCF) is becoming a popular agricultural production mode and has expanded rapidly in China. However, serious concerns over the ecologically and environmentally friendly development of IRCF are still growing. Despite its importance, there is no comprehensive assessment study of IRCF to evaluate if it is a green and sustainable development in agricultural sector. To address such concerns, the life cycle assessment method at the endpoint level and water footprint were employed to elucidate the potential environmental risk caused by the fast development of IRCF. Furthermore, the economic assessment was also carried out using cost-benefit analysis. The results showed that, IRCF systems have higher impacts in the human health damage category compared to rice monoculture (RM) systems. This was attributed to the higher direct field emissions such as methane emission and high-water consumption in IRCF. However, IRCF had lower environmental impacts in the ecosystem damage category than RM, primarily due to decreased fertilizer inputs. Water footprint was the primary concern in IRCF, with 379% higher water consumption than RM. The expansion of IRCF can affect food security for the following two reasons: i) Outer ridge and ditch that are built around rice fields decrease rice planting area and hence total production, ii) Crayfish occupy rice fields in winter and the following spring, so winter-season crops such as winter wheat cannot be grown in IRCF fields. Economic assessment approved that the gross profit is the main motivation for farmers to shift from RM to IRCF, where 297% higher economic benefit can be achieved. Our results indicated that IRCF expansion improved farmers’ income but came with potentially environmental and food security risks. Therefore, strict measures and rational land use planning should be implemented for the sustainable development of IRCF.

ASSESSMENT OF CHANGES IN THE AREA OF GLACIERS IN THE NORTHERN PART OF THE ZHETYSU ALATAU BASED ON REMOTE SENSING DATA

The changes of glaciers in the basins of the Aksu-Bien and Lepsy-Baskan rivers in the northern part of the Zhetysu Alatau were studied for the periods 1956-2001, 2001-2012 and 2012-16, based on the analysis of Landsat TM/ETM+ and OLI data. In 2001, 245 glaciers with a total area of 197.2 km2 were discovered, by 2016 they had decreased to 232 glaciers with a total area of 165.5 km2, which is 31.7 km2 less, that is, 1% per year for 15 years. The rate of glacier reduction was also analyzed based on their differences in size, height and aspect of slopes, as well as other topographic parameters in five basins (Bien, Aksu, Sarkan, Baskan, Leps), where the reduction of glaciers varied from 14.9% to 17.5%. Such a high rate of reduction is probably related to the general trend temperature increases due to the fact that small glaciers are located at a relatively low altitude of the outer ridges of the Zhetysu Alatau. However, according to the results of our research, as well as the works of other authors who have studied this territory, the rate of reduction of the area of glaciers in the northern part of the Zhetysu Alatau is lower compared to other territories. We came to the conclusion that the glaciated areas of the Aksu-Bien and Lepsy-Baskan river basins are located in the most favorable conditions for glaciation – which is confirmed by the larger average sizes of glaciers that are higher than in other basins – and as a result showed a lower rate of reduction than other glaciated areas of the Zhetysu Alatau from 1956 to 2016.

The Global Structure of the Milky Way’s Stellar Halo Based on the Orbits of Local Metal-poor Stars

Abstract We analyze the global structure of the Milky Way (MW)'s stellar halo, including its dominant subcomponent, Gaia-Sausage-Enceladus (GSE). The method for reconstructing the global distribution of this old stellar component is to employ the superposition of the orbits covering the large MW’s space, where each of the orbit-weighting factors is assigned following the probability that the star is located at its currently observed position. The selected local, metal-poor sample with [Fe/H] <−1, using Gaia Early Data Release 3 and Sloan Digital Sky Survey Data Release 16, shows that the global shape of the halo is systematically rounder at all radii in more metal-poor ranges, such that an axial ratio, q, is nearly 1 for [Fe/H] <−2.2 and ∼0.7 for −1.4 < [Fe/H] < −1.0. It is also found that a halo in the relatively metal-rich range of [Fe/H] >−1.8 actually shows a boxy/peanut-like shape, suggesting a major merger event. The distribution of azimuthal velocities shows a disk-like flattened structure at −1.4 < [Fe/H] < −1.0, which is thought to be the metal-weak thick disk. For the subsample of stars showing GSE-like kinematics, at [Fe/H] >−1.8, its global density distribution has an axis ratio of 0.9, which is more spherical than the general halo sample, and an outer ridge at r ~ 20 kpc. This spherical shape is consistent with the features of accreted halo components, and the ridge suggests that the orbit of GSE’s progenitor had an apocenter of ∼20 kpc. Implications for the formation of the stellar halo are also presented.

The origin of the potassium‐rich annular zones at the Bosumtwi impact structure, Ghana, investigated by field study, radiometric analysis, and first cosmogenic nuclide data

AbstractThe 10.5‐km‐diameter, 1 Ma Bosumtwi impact structure in Ghana is one of the youngest, large impact structures known on Earth. The preservation of the morphology of its ejecta deposits, with an annular moat and outer ridge resembling those of rampart impact craters on Mars, makes Bosumtwi a remarkable impact structure on the African continent. An airborne radiometric survey of the southwestern part of Ghana reveals enigmatic circular feature enriched in potassium, coinciding with the crater rim and an outer ejecta ridge at Bosumtwi. The goal of this study is to investigate possible origins of these features, by impact processes (shock metamorphic effects, impact‐induced hydrothermal systems) or postimpact surficial processes (erosion, weathering). The origin of these features is discussed here based on field observations, ground‐based radiometric measurements, and first cosmogenic nuclide analyses (10Be). The data indicate that the rim and outer ridge were eroded more rapidly than the rest of the impact structure. Accordingly, the downward advance of the weathering fronts in the annular moat, after ejecta emplacement, are responsible for leaching of K from the lateritic residual observed at the surface. The Bosumtwi impact structure is, therefore, a valuable natural laboratory to investigate the factors controlling erosion and weathering processes in the Ashanti belt since impact 1 Ma ago. Simulations of vertical profiles of 10Be concentration further constrain local variations of the erosion rate. In light of this study, circular K anomalies in radiometric surveys might be indicative of potential impact structures in tropical regions.

How to grow your cable bacteria: Establishment of a stable single-strain culture in sediment and proposal of Candidatus Electronema aureum GS

Cable bacteria are multicellular filamentous bacteria within the Desulfobulbaceae that couple the oxidation of sulfide to the reduction of oxygen over centimeter distances via long distance electron transport (LDET). So far, none of the freshwater or marine cable bacteria species have been isolated into pure culture. Here we describe a method for establishing a stable single-strain cable bacterium culture in partially sterilized sediment. By repeated transfers of a single cable bacterium filament from freshwater pond sediment into autoclaved sediment, we obtained strain GS, identified by its 16S rRNA gene as a member of Ca. Electronema. This strain was further propagated by transferring sediment clumps, and has now been stable within its semi-natural microbial community for several years. Its metagenome-assembled genome was 93% complete, had a size of 2.76 Mbp, and a DNA G + C content of 52%. Average Nucleotide Identity (ANI) and Average Amino Acid Identity (AAI) suggest the affiliation of strain GS to Ca. Electronema as a novel species. Cell size, number of outer ridges, and detection of LDET in the GS culture are likewise consistent with Ca. Electronema. Based on these combined features, we therefore describe strain GS as a new cable bacterium species of the candidate genus Electronema, for which we propose the name Candidatus Electronema aureum sp.nov. Although not a pure culture, this stable single-strain culture will be useful for physiological and omics-based studies; similar approaches with single-cell or single-filament transfers into natural medium may also aid the characterization of other difficult-to-culture microbes.

The complex construction history of Poverty Point’s timber circles and concentric ridges

ABSTRACT The Poverty Point World Heritage Site (ca. 1700–1100 BC) is one of the world’s unique fisher-hunter-gatherer sites. Magnetic gradient surveys of ca. 25 ha together with magnetic susceptibility studies, coring, targeted excavations, and stratigraphic investigations have yielded important new discoveries about aspects of the construction history of the site’s monumental concentric ridges and massive plaza. Thirty-six timber circles with diameters ranging up to 62 m are located in and near the plaza. The closely spaced posts and circle clusters suggest extensive rebuilding. Ridge construction components have been identified through the presence of distinctive linear magnetic anomalies. The components provide evidence for ridge single and multistage construction, repairs, and possible deconstruction. The innermost two ridges are inferred to be the earliest, as they exhibit evidence for longer, more complex construction histories than the outer ridges. We now see that Poverty Point’s construction history is both more complex and more accessible than previously thought.

Description of two new species of Bassozetus (Ophidiiformes: Ophidiidae) and a redescription of Bassozetus robustus Smith and Radcliffe 1913

Two new deepwater assfish species, Bassozetus trachibranchus and Bassozetus squamosus, are described from the 29 western Atlantic and four western Indian and western South Pacific specimens, respectively. In addition, a redescription of Bassozetus robustus Smith and Radcliffe in Radcliffe 1913, with which both of the above two new species have been previously confused, is provided on the basis of 14 specimens and its distributional range is revised to the western Pacific Ocean. The three species are separable from the 13 known congeners by the following combination of characters: dorsal-fin rays (116–126), anal-fin rays (95–103), oblique scale rows (30–47), pelvic-fin length (14.3–21.7% SL), a single well-developed median bashibranchial tooth patch, and one or two deep indentations on the sagitta dorsal margin, plus long gill rakers (10–14 in B. robustus) and head, predorsal and prepelvic lengths (20.5–22.8% SL, 19.4–21.1% SL and 15.3–18.1% SL, respectively, in B. robustus). Additionally, B. trachibranchus, B. squamosus and B. robustus are distinguishable from each other as follows: oblique scale rows (39–45 in B. trachibranchus, 44–47 in B. squamosus, and 30–36 in B. robustus), eye diameter to head length ratio (greater in B. squamosus than in similarly sized specimens of the other species), pelvic fin length/distance between pelvic and anal fins ratio (smaller in B. robustus than in similarly sized specimens of the other species), and 2nd to 4th lower limb morphology (many small tooth patches arranged along the outer ridges in B. trachibranchus, absent or a few only in the other species).

Influence of structure and pore pressure of plate interface on tectonic tremor in the Nankai subduction zone, Japan

Episodes of tectonic tremor are observed in the Nankai accretionary prism close to the trough axis; however, their non-impulsive signals and the distortion of seismic signals in the accretionary prism make it challenging to accurately estimate their locations. Reliable tremor locations would help to characterize geological conditions favourable for tremor generation and could offer insights into the up-dip limit of coseismic ruptures. Here we report a new approach to pinpoint tremor locations based on seismic phase polarization. The estimated epicentres of tremor distribution mostly coincide with low-velocity shear zone or thick underthrust sediments where high pore pressures are inferred, and the distribution of tremor appears to be controlled by characteristics of the shear zone. A tremor episode occurred a couple days after the off-Mie earthquake clearly shows migration at a velocity similar to that of very low frequency earthquakes. Migration of tremor initiated around the outer ridge where the estimated pore pressure is greatest. The spatio-temporal tremor distribution indicates that pore pressure relaxation could trigger the tremor migration. The occurrence of tremor thus may indicate a weak shallow plate interface that is prone to slip following large earthquakes. Based on the information of tremor migration, the permeability along the fault can be estimated as 3.7×10−12 m2.

On the relationship between excursions and paleomagnetic secular variation – Records from MIS 5, North Atlantic Ocean

We have recovered four new records of the paleomagnetic field variability within Marine Isotope Stage 5 (MIS 5: 71–130 ka) from deep-sea sediment cores of the Bahama Outer Ridge, western North Atlantic Ocean. These cores contain reproducible evidence of the Blake Event and are located within 300 km of cores used by Smith and Foster (1969) to define the Blake Event. Our new paleomagnetic records have both reproducible directions and relative paleointensities, but they should be considered only medium-resolution records because they were recovered from sediments with bulk accumulation rates of only ~6 cm/kyr. Paleomagnetic interpretations of the records are complicated by the fact that the Blake Event occurs partially within two narrow zones of bacterial magnetite. Our rock magnetic and paleomagnetic studies suggest that the bacterial magnetite has not contributed significantly to the directional or relative paleointensity results. Our records indicate that the Blake event occurred ~119–126,000 years BP, within MIS5e (114–130,000 years BP). The Blake Event is a local magnetic field reversal (Class II excursion) with directions flipping quickly to reversed-polarity directions, hovering statically for at least 6000 years, and then flipping quickly back to normal polarity directions. The core dynamo source for the Blake Event must have a strong axisymmetric and global-scale character to produce such a true local polarity reversal. We have carried out detailed short-interval (3 ka and 9 ka) statistical analysis of the PSV (after removal of true excursional directions) from three of our records to assess the pattern of PSV through MIS 5 and associated with the Blake Event. Reproducible statistical results among the three records suggest significant deviations away from long-term average on time scales greater than 3 ka and 9 ka. The overall angular dispersions are generally low (~10°) except for two narrow intervals (~25°). The high dispersion intervals are associated with the lowest paleointensity intervals and excursions.

Overpressured Underthrust Sediment in the Nankai Trough Forearc Inferred From Transdimensional Inversion of High‐Frequency Teleseismic Waveforms

AbstractActive‐source seismic surveys have resolved the fine‐scale P‐wave velocity (Vp) of the subsurface structure in subduction forearcs. In contrast, the S‐wave velocity (Vs) structure is poorly resolved despite its usefulness in understanding rock properties. This study estimates Vp and Vs structures of the Nankai Trough forearc, by applying transdimensional inversion to high‐frequency teleseismic waveforms. As a result, a thin (∼1 km) low‐velocity zone (LVZ) is evident at ∼6 km depth beneath the sea level, which is located ~3 km seaward from the outer ridge. Based on its high Vp/Vs ratio (∼2.5) and comparison to an existing seismic reflection profile, we conclude that this LVZ reflects a high pore pressure zone at the upper portion of the underthrust sediment. We infer that this overpressured underthrust sediment hosts slow earthquake activities and that accompanied strain release helps impede coseismic rupture propagation further updip.

Last glacial maximum deglaciation of the Southern Velebit Mt. (Croatia): insights from cosmogenic 36Cl dating of Rujanska Kosa

Although several types of glacial landforms and deposits were described from different parts of the Croatian Dinarides, up to date there are no quantitative glacial chronological data. Here we present the first cosmogenic 36Cl glacial chronology from the Southern Velebit Mt. from a moraine complex known as the Rujanska Kosa. We sampled four limestone boulders and used 20 mm ka−1 erosion corrected ages, as the study area is composed of well-karstified carbonate deposits and located in one of the highest precipitation regions of Europe. The inner Rujanska Kosa ridge yielded an age of 20.7 ± 2.2 ka for the retreat of glaciers in that part of Velebit Mt. A slightly older age was measured from the outer ridge on the left-lateral part of the Rujanska Kosa, which dates back to 22.7 ± 2.7 ka ago. Whilst the ages between inner and outer ridges overlap within error, we can place an age difference between the two moraines to be between 0 and 6.9 ka, supported by the geomorphic evidence that the latter is older. Although we could not perform any geomorphological work higher up in the Rujno paleo-ice field due to the remnant minefields, our results may indicate a Late Pleistocene (i.e. la st glacial maximum) retreat of ice from the Southern Velebit Mt. Despite the small number of valid samples, acquired age data on glacial landforms in Southern Velebit Mt. are in accordance with ages from several other Mediterranean mountain ranges.

Sub‐annual moraine formation at an active temperate Icelandic glacier

AbstractThis 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

Newly formed and remodeled human bone exhibits differences in the mineralization process

During human skeletal growth, bone is formed via different processes. Two of them are: new bone formation by depositing bone at the periosteal (outer) surface and bone remodeling corresponding to a local renewal of tissue. Since in remodeling formation is preceded by resorption, we hypothesize that modeling and remodeling could require radically different transport paths for ionic precursors of mineralization. While remodeling may recycle locally resorbed mineral, modeling implies the transport over large distances to the site of bone apposition. Therefore, we searched for potential differences of size, arrangement and chemical composition of mineral particles just below surfaces of modeling and remodeling sites in femur midshaft cross-sections from healthy children. These bone sites were mapped using scanning synchrotron X-ray scattering, Raman microspectroscopy, energy dispersive X-ray analysis and quantitative backscattered electron microscopy.The results show clear differences in mineral particle size and composition between the sites, which cannot be explained by a change in the rate of mineral apposition or accumulation. At periosteal modeling sites, mineral crystals are distinctly larger, display higher crystallinity and exhibit a lower calcium to phosphorus ratio and elevated Na and Mg content. The latter may originate from Mg used for phase stabilization of mineral precursors and therefore indicate different time periods for mineral transport. We conclude that the mineralization process is distinctively different between modeling and remodeling sites due to varying requirements for the transport distance and, therefore, the stability of non-crystalline ionic precursors, resulting in distinct compositions of the deposited mineral phase. Statement of SignificanceIn growing children new bone is formed either due to apposition of bone tissue e.g. at the outer ridge of long bones to allow growth in thickness (bone modeling), or in cavities inside the mineralized matrix when replacing tissue (bone remodeling). We demonstrate that mineral crystal shape and composition are not the same between these two sites, which is indicative of differences in mineralization precursors. We suggest that this may be due to a longer mineral transport distance to sites of new bone formation as compared to remodeling where mineral can be locally recycled.

Similar Glacial‐Interglacial δ15N Variations in Two MIS 13–10 Sediment Sequences in the Western North Atlantic Ocean: Changes in Nitrogen Sources, Denitrification, or Diagenesis?

AbstractWe have determined total organic carbon‐mass accumulation rates (TOC‐MARs) and δ15N values in Marine Isotope Stages (MIS) 13–10 sediments from two oligotrophic parts of the western North Atlantic Ocean—Ocean Drilling Program (ODP) Site 1063 on the Bermuda Rise and Site 1058 on the Blake Outer Ridge. Both TOC‐MARs and δ15N values vary significantly in these depositional records. TOC‐MARs are highest in sediments deposited at Site 1063 during MIS 12 and MIS 10, implying marine productivity or TOC preservation increased at this location during glacial stages, and low TOC‐MARs during most of MIS 11 in Site 1063 sediment imply low rates during this warm interval. In contrast to the Site 1063 record, productivity or preservation appears to have been greater at Site 1058 during parts of the MIS 11 interglacial than during the glacial intervals. Unlike the TOC‐MAR records, δ15N values at both locations exhibit similar glacial‐interglacial alternations. Values peak during substage 11.3 and gradually decrease toward the terminations of MIS 12 and MIS 10. The similarity of the δ15N patterns at these two sites implies that nitrogen cycling at these locations is largely independent of changes in local surface production of organic matter, and the higher δ15N values are unlikely to result from denitrification. Instead, the δ15N alternations likely result from glacial‐interglacial alternations between higher rates of sediment delivery to these western North Atlantic locations during glacial periods that favored TOC preservation and lower rates during interglacials that allowed more TOC degradation and associated diagenetic alteration of its nitrogen isotopic composition, leading to higher sediment δ15N values.