Debris Flux Research Articles

Enhanced deep-water circulation facilitated rare earth elements enrichment in pelagic sediments from the northwestern Pacific Ocean

The lack of knowledge about the enrichment mechanism of rare earth elements and yttrium (REY) in deep-sea sediments is impeding the development of theories and exploration strategies for pelagic REY-rich sediments. Ocean circulation variability seems to be crucial in enriching REY in pelagic sediments, which, however, has not been extensively studied. Here, we examined the Pb-Nd isotopic signals of bottom water recorded by the authigenic ferromanganese oxyhydroxide fractions, as well as the Mn/Al and Mn/Ti ratios of bulk samples from a well-dated sediment core in the northwestern Pacific Ocean. These proxies consistently indicate that enhanced deep-water circulation occurred in the study area at ∼11.5–9.5 Ma, which was most likely to be caused by changes in the flow path of bottom currents. The age of this distinct event consists with the forming age of highly REY-rich sediments. We propose that enhanced deep-water circulation in seamount areas could increase the flux of micronodules and fish debris into the pelagic sediments, facilitating the scavenging of REY from seawater. Our findings establish a connection between enhanced deep-water circulation and the enrichment of REY in pelagic sediments.

A 3.3‐Million‐Year Record of Antarctic Iceberg Rafted Debris and Ice Sheet Evolution Quantified by Machine Learning

AbstractOver the last 3.3 million years, the Antarctic Ice Sheet (AIS) has undergone phases of ice sheet growth and decay, impacting sea level and climate globally. Presently, the largely marine‐terminating AIS loses mass primarily by iceberg calving and basal melt of ice shelves. Quantifying past rates and timing of AIS melt is vital to understanding future cryosphere and sea level changes. One proxy for past ice sheet instabilities is iceberg rafted debris (IRD) fluxes. However, traditional methods of IRD quantification are labor‐intensive. Here, we present a new method of identifying IRD grains in sediment core X‐ray images using a convolutional neural network machine learning algorithm. We present a 3.3‐million‐year record of AIS IRD melt events using sediment cores from International Ocean Discovery Program Sites U1536, U1537, and U1538 in the Southern Ocean's “Iceberg Alley.” We identify two increases in the IRD fluxes throughout this period, at ∼1.8 and 0.43 Ma. We propose that after 1.8 Ma, the AIS expanded and transitioned from a primarily terrestrial‐terminating to a primarily marine‐terminating ice sheet. Therefore, after 1.8 Ma, glacial terminations and AIS iceberg discharge are associated with variations in global ice volume, presumably through the mechanism of sea level and, therefore, grounding line change. The second AIS regime change occurs during the Mid‐Brunhes Event (∼0.43 Ma). After this time, there are heightened and continuous IRD fluxes at each glacial termination, indicating increased AIS size and instability after this time.

Ballistic Limit Equation Derivation for Thin Tape Tethers

Electromagnetic tethers of hundreds or thousands of meters have been proposed for maneuvring spacecraft in Low Earth Orbit, and in particular, for post-mission disposals. The debate on tether survivability to debris impact is still influencing further advances in the implementation of such technology because of the large area they expose to the debris environment; thin tape geometries have been proposed instead of round ones to increase the survivability to hypervelocity impacts. In this context, this paper introduces a new Ballistic Limit Equation (BLE) for thin tape tethers, derived from experimental results, numerical simulations, and literature data. The resulting equation is non-monotonic with respect to impact angle, presenting a minimum depending on the debris velocity and size; for high obliquities, the debris fragmentation triggered by shock waves propagating into the material reduces the damage. This feature allows to set a minimum particle diameter for risk assessment, excluding a significant part of the debris flux. The proposed BLE confirms the performance of thin tape tethers, with respect to round wires, due to their better ballistic response as well as their reduced cross-section at high-obliquity impacts.

Feasibility of using CubeSats and small detectors for in-situ space debris and cosmic dust flux measurement

Impacts on spacecraft by mm-sized debris in Earth orbit can have severe consequences including loss of a spacecraft and generation of more debris. This hazard and potential mitigation are discussed herein, and the risk of an impact (the product of flux and damage) is found vs. size. Reduction of the future flux of mm-sized debris by de-orbiting life-expired space vehicles, only reduces, not eliminates, this hazard. It is thus vital that the flux of mm-sized objects in orbit is well defined, but this requires on-orbit determination. To provide statistically meaningful debris flux data, large detection areas are traditionally required. CubeSats could host debris detectors, but only have small surface areas, and the data from many would be required. Accordingly, flux data from historic small space exposed surfaces are compared herein to MASTER flux model predictions, with good agreement for exposure times of just a few years, demonstrating a viable method to determine the debris flux. The cost of a network of CubeSat mounted impact detectors is also estimated found, and, for fleets of order 100 CubeSats, is comparable to the traditional single large satellite mounted instrument.

Early Oligocene record of an “iceberg alley” in the Weddell Sea from quartz sand microtextural analysis at ODP Site 696

Abstract The greenhouse to icehouse transition at the Eocene-Oligocene boundary (34 Ma) marked the appearance of continental-scale glaciation in Antarctica. The material recovered from Ocean Drilling Program Site 696 is the only record spanning this major climatic shift in the Weddell Sea region. Using scanning electron microscopy, quartz microtextures in 13 samples across the Eocene-Oligocene transition were analyzed to understand the degree of glacial modification and the transportation history of the >150 µm material. The quartz grains were visually grouped, characterized, and interpreted by grain outline, relief, and surface microtextures. Glacial textures are present throughout the entire interval (34.4–33.2 Ma), with the proportion of iceberg-rafted grains in each sample decreasing into the early Oligocene (33.6 Ma), accompanied by an increase in the frequency of eolian and sea-ice-rafted grains. Mass accumulation rates reveal that the flux of iceberg-rafted debris increased coincident with the flux of eolian and sea-ice-rafted grains following 33.6 Ma, suggesting a strong coupling between land-ice development and high-latitude atmospheric processes. When compared with other Antarctic climate proxy data sets, the intensification of ice rafting at Site 696 occurred after ice-sheet inception in East Antarctica. The prominent influx of terrigenous material after 33.6 Ma points to strengthened glacial conditions accompanied by major changes in the environment of the Weddell Sea region, supporting the idea of a high-latitude role in climate perturbations, in agreement with interpretations of other global proxies.

Cosmic dust impacts on the Hubble Space Telescope.

Exposure of the Hubble Space Telescope to space in low Earth orbit resulted in numerous hypervelocity impacts by cosmic dust (micrometeoroids) and anthropogenic particles (orbital debris) on the solar arrays and the radiator shield of the Wide Field and Planetary Camera 2, both subsequently returned to Earth. Solar cells preserve residues from smaller cosmic dust (and orbital debris) but give less reliable information from larger particles. Here, we present images and analyses from electron, ion and X-ray fluorescence microscopes for larger impact features (millimetre- to centimetre-scale) on the radiator shield. Validated by laboratory experiments, these allow interpretation of composition, probable origin and likely dimensions of the larger impactors. The majority (~90%) of impacts by grains greater than 50 μm in size were made by micrometeoroids, dominated by magnesium- and iron-rich silicates and iron sulfides, metallic iron-nickel and chromium-rich spinel similar to that in ordinary chondrite meteorites of asteroid origin. Our re-evaluation of the largest impact features shows substantially fewer large orbital debris impacts than reported by earlier authors. Mismatch to the NASA ORDEM and ESA MASTER models of particle populations in orbit may be partly due to model overestimation of orbital debris flux and underestimation of larger micrometeoroid numbers. This article is part of the theme issue 'Dust in the Solar System and beyond'.

Genotoxic and neurotoxic potential of intracellular nanoplastics: A review.

Plastic waste comprises polymers of different chemicals that disintegrate into nanoplastic particles (NPLs) of 1-100-nm size, thereby littering the environment and posing a threat to wildlife and human health. Research on NPL contamination has up to now focused on the ecotoxicology effects of the pollution rather than the health risks. This review aimed to speculate about the possible properties of carcinogenic and neurotoxic NPL as pollutants. Given their low-dimensional size and high surface size ratio, NPLs can easily penetrate biological membranes to cause functional and structural damage in cells. Once inside the cell, NPLs can interrupt the autophagy flux of cellular debris, alter proteostasis, provoke mitochondrial dysfunctions, and induce endoplasmic reticulum stress. Harmful metabolic and biological processes induced by NPLs include oxidative stress (OS), ROS generation, and pro-inflammatory reactions. Depending on the cell cycle status, NPLs may direct DNA damage, tumorigenesis, and lately carcinogenesis in tissues with high self-renewal capabilities like epithelia. In cells able to live the longest like neurons, NPLs could trigger neurodegeneration by promoting toxic proteinaceous aggregates, OS, and chronic inflammation. NPL genotoxicity and neurotoxicity are discussed based on the gathered evidence, when available, within the context of the intracellular uptake of these newcomer nanoparticles. In summary, this review explains how the risk evaluation of NPL pollution for human health may benefit from accurately monitoring NPL toxicokinetics and toxicodynamics at the intracellular resolution level.

Space debris environment engineering model 2019: Algorithms improvement and comparison with ORDEM 3.1 and MASTER-8

As an essential tool for realistic description of the current or future debris environment, the Space Debris Environment Engineering Model (SDEEM) has been developed to provide support for risk assessment of spacecraft. In contrast with SDEEM2015, SDEEM2019, the latest version, extends the orbital range from the Low Earth Orbit (LEO) to Geosynchronous Orbit (GEO) for the years 1958–2050. In this paper, improved modeling algorithms used by SDEEM2019 in propagating simulation, spatial density distribution, and spacecraft flux evaluation are presented. The debris fluxes of SDEEM2019 are compared with those of three typical models, i.e., SDEEM2015, Orbital Debris Engineering Model 3.1 (ORDEM 3.1), and Meteoroid and Space Debris Terrestrial Environment Reference (MASTER-8), in terms of two assessment modes. Three orbital cases, including the Geostationary Transfer Orbit (GTO), Sun-Synchronous Orbit (SSO) and International Space Station (ISS) orbit, are selected for the spacecraft assessment mode, and the LEO region is selected for the spatial density assessment mode. The analysis indicates that compared with previous algorithms, the variable step-size orbital propagating algorithm based on semi-major axis control is more precise, the spatial density algorithm based on the second zonal harmonic of the non-spherical Earth gravity (J2) is more applicable, and the result of the position-centered spacecraft flux algorithm is more convergent. The comparison shows that SDEEM2019 and MASTER-8 have consistent trends due to similar modeling processes, while the differences between SDEEM2019 and ORDEM 3.1 are mainly caused by different modeling approaches for uncatalogued debris.

The mechanism of organic matter accumulation in the archipelago marine sediments: Insights from the Middle Devonian Givetian mudstone with low TOC in the Youjiang Basin, South China

Despite the fact that the mean values of total organic carbon (TOC) content in the Luofu Formation are relatively low, at or below 1.0 wt%, it still has the potential to be a veritable source rock. To elucidate the influences of various paleogeographic factors on sedimentary environments, 25 samples from Well A on the slope and 32 samples from Well B in the basin centre were selected for study. The samples were analyzed by thin section microscopy and field emission-scanning electron microscopy, along with X-ray diffraction and geochemical analyses (TOC content, sulfur content, organic petrography, inorganic carbon isotope and major and trace elements) in order to understand variations in and controls on the mineralogy, lithofacies, depositional environments, as well as the organic matter accumulation mechanism. The results of our study indicate that mudstone of the Luofu Formation was deposited into 4 lithofacies groups, namely as the siliceous lithofacies, mixed lithofacies, argillaceous lithofacies and calcareous lithofacies. The siliceous lithofacies mudstone was developed in the deep-water columns, while the mixed lithofacies mudstone was deposited on shallow-water columns. The organic matter accumulation model of the Luofu Formation can be further divided into the following four stages, each with its own unique characteristics: (1) The organic matter accumulation was caused by the relatively high productivity and dysoxic basin bottom water columns; (2) The organo-mineral complexes may promote the organic matter accumulation to some extent; (3) The organic matter enrichment was facilitated by the dysoxic/anoxic conditions and relatively high productivity from the basin to the slope; (4) The organic matter was preserved at shortened exposure duration of oxic conditions on the slope. The correlations between various geochemical indicators (redox, paleoproductivity and terrestrial debris flux) and TOC content suggest that oxic water columns and low productivity are the main reasons for the widespread mudstone with low TOC. The organic-rich mudstone, as the target stratigraphic section for exploration, may be deposited in the basin bottom water columns away from upwelling and close to hydrothermal activity in stage 3.

Enhanced subglacial discharge from Antarctica during meltwater pulse 1A

Subglacial discharge from the Antarctic Ice Sheet (AIS) likely played a crucial role in the loss of the ice sheet and the subsequent rise in sea level during the last deglaciation. However, no direct proxy is currently available to document subglacial discharge from the AIS, which leaves significant gaps in our understanding of the complex interactions between subglacial discharge and ice-sheet stability. Here we present deep-sea coral 234U/238U records from the Drake Passage in the Southern Ocean to track subglacial discharge from the AIS. Our findings reveal distinctively higher seawater 234U/238U values from 15,400 to 14,000 years ago, corresponding to the period of the highest iceberg-rafted debris flux and the occurrence of the meltwater pulse 1A event. This correlation suggests a causal link between enhanced subglacial discharge, synchronous retreat of the AIS, and the rapid rise in sea levels. The enhanced subglacial discharge and subsequent AIS retreat appear to have been preconditioned by a stronger and warmer Circumpolar Deep Water, thus underscoring the critical role of oceanic heat in driving major ice-sheet retreat.

A method for calculating lateral surface area of bistatic radar beam overlap

It has been shown that bistatic radars using radio telescopes as receivers can be used to increase the sensitivity of orbital debris measurements over traditional terrestrial monostatic radar. A method to calculate the lateral surface area of a bistatic radar is needed to evaluate the efficacy of a proposed bistatic radar configuration for orbital debris measurements. For over three decades, models of the orbital debris (OD) environment in low Earth orbit (LEO) have been developed to assess the risk posed by OD to spacecraft. While terrestrial radar measures debris 3 mm and larger and in situ measurements provide data for debris smaller than 1 mm, no good data sources exist for debris between 1 mm and 3 mm in size. This results in large variations between competing OD models. It also happens to be the size regime which poses the highest mission-ending risk to spacecraft. It is, therefore, of interest to investigate potential new data sources for this under-sampled size regime. There are many radars and radio telescopes that could be combined to create sensitive bistatic radars that could potentially bridge the size gap. In addition to sensitivity, it is necessary to predict the expected count rate of a candidate sensor to evaluate its performance. NASA’s Orbital Debris Engineering Model (ORDEM) can be used to predict the flux of debris passing through the line of sight of a radar or telescope. This flux is related to a count rate through the calculation of the lateral surface area of the sensor. While this can be done easily for monostatic radars, a method for calculating the lateral surface area of a bistatic radar is needed. This new method of calculation has been developed and is described. The new method maps the radar beam overlap in 3D space, calculating the area of the complex surface formed by the gain product of the two antennas. Comparisons of the monostatic and new bistatic lateral surface area calculation methods for the monostatic case are presented. Results of a sample lateral surface area calculation for a bistatic radar observation configuration currently employed by NASA are shown. Finally, a guide for total error as a function of baseline and target altitude is established.

The Optimal Deployment Strategy of Mega-Constellation Based on Markov Decision Process

LEO satellite mega-constellation projects have been proposed by many countries or commercial organizations in recent years. With more than 2000 satellites launched by SpaceX to configure the Starlink system, the orbital resources are more constrained given the existence of spacecrafts and countless orbital debris. Due to this, the operating environment is full of uncertainty and information symmetry is absent for designers and stakeholders during the process of project deployment. The flux model of space debris on orbit has been built for assessing the LEO operation environment. Based on the orbital debris flux model, the collision probability can be calculated, which is an important variable of the state space. Given the condition that tge number of satellites decreases due to collision between satellites and debris, the Markov decision model has been built for optimal deployment strategy and decision-making. In order to assure that the mega-constellation system could provide services when satellites have failed, additional satellites need to be launched. The optimal deployment is the decision to launch a moderate number of satellites to maximize the benefit and minimize the cost. Assuming that at least 30 satellites need to be operated, 4 deployment scenarios are considered and the optimal deployment strategies can be obtained.

Characteristics and fluxes of plastic debris based on socio-economic data for Patos Lagoon-a choked coastal Lagoon in South Brazil.

Patos Lagoon, located in southern Brazil, is the world's largest choked coastal lagoon. Studies have revealed that plastic pollution affects lagoons; however, to date, they have only focused on a few limited regions of the lagoon. Top-down quantification methods based on socio-economic data from 2010 to 2017 were used to measure the amount of plastic reaching Patos Lagoon, thus broadening the perspective of plastic pollution in this area. According to the findings, Patos Lagoon's hydrographic regions produced an average of 4.54 Mton of plastic during the studied period. 1.86 Mton was consumed on average. High- and low-density polyethylene (HDPE and LDPE, respectively), polypropylene (PP), and polyvinyl chloride (PVC) were the main resins produced. Food-related activities were the largest consumer of plastic (17.98%), indicating a higher amount of single-use plastics being used in the basin. The preforms for plastic bottles, bags, and packaging were the most commonly manufactured plastic utensils. An estimated 8 to 14% of all plastics used to end up as mismanaged waste in the Patos Lagoon hydrographic basin. This resulted in 1.73 and 10.72 Kton, or 0.5 and 3.2g/per person/per day, of plastic waste flowing into the waters of Patos Lagoon throughout the study period. These findings can help focus on management efforts by providing managers and policymakers with information for better plastic pollution mitigation in this environment.

Identification of polystyrene nanoplastics from natural organic matter in complex environmental matrices by pyrolysis-gas chromatography-mass spectrometry.

Due to the flux of plastic debris entering the environment, it becomes urgent to document and monitor their degradation pathways at different scales. At the colloidal scale, the systematic hetero-association of nanoplastics with the natural organic matter complexifies the ability to detect plastic signatures in the particle collected in the various environments. The current techniques used for microplastics could not discriminate the polymers at the nanoscale from the natural macromolecules, as the plastic mass in the aggregate is within the same order. Only a few methods are available concerning nanoplastics identification in complex matrices, with the coupling of pyrolysis with gas chromatography and mass spectrometry (Py-GC-MS) as one of the most promising due to its mass-based detection. However, natural organic matter in environmental samples interferes with similar pyrolysis products. These interferences are even more critical for polystyrene polymers as this plastic presents no dominant pyrolysis markers, such as polypropylene, that could be identified at trace concentrations. Here, we investigate the ability to detect and quantify polystyrene nanoplastics in a rich phase of natural organic matter proposed based on the relative ratio of pyrolyzates. The use of specific degradation products (styrene dimer and styrene trimer) and the toluene/styrene ratio (RT/S) are explored for these two axes. While the size of the polystyrene nanoplastics biased the pyrolyzates of styrene dimer and trimer, the RT/S was correlated with the nanoplastics mass fraction in the presence of natural organic matter. An empirical model is proposed to evaluate the relative quantity of polystyrene nanoplastics in relevant environmental matrices. The model was applied to real contaminated soil by plastic debris and literature data to demonstrate its potential.

Using the space debris flux to assess the criticality of the environment in low Earth orbit

In this paper we introduce a new index for evaluating the likelihood of accidental collisions leading to the complete destruction of intact objects in a volume of space in low Earth orbit (LEO). The proposed index is therefore not intended to assess the criticality of individual objects or missions, but rather to estimate the global impact of space activities on a given region of space. Moreover, the new index has been designed to be objective, as simple as possible, built from easily accessible data, as well as smoothly reproducible by third parties. Named “volumetric collision rate index”, it has been developed starting from analytical equations expressing the collision rate as a function of the fluxes of intact objects and cataloged debris pieces. The application of reasonable simplifying assumptions and approximations has finally made it possible to define a dimensionless index that explicitly depends only on the spatial densities of intact objects and cataloged debris pieces. It has therefore been applied to the LEO environment, analyzing its evolution from mid-2008 to mid-2020, a crucial period characterized by an impressive change of space activity patterns, with the launch of lots of small satellites and mega-constellations. We also discuss how the index can be further improved, taking into account the maneuverable satellites, which do not contribute to the collision rate, and the increasing number of cubesats, which in many respects are more similar to debris, finally presenting a preliminary analysis in this direction.

Space debris flux on LAPAN satellites during Solar Cycle 25

Solar activity has been known to have impacts on the altitude of low Earth orbit satellites and space debris as well. Consequently, this will affect the flux of debris population around a satellite’s orbit. LAPAN currently has three satellites in low Earth orbit which will still be in operation during Solar Cycle 25 which began in December 2019 and is expected to reach the peak in 2025. It is widely known that even a very small debris can give detrimental effects to those satellites due to their hypervelocity speed. In the present study we report the space debris flux on LAPAN-TUBSAT, LAPAN A2, and LAPAN A3 satellites during the solar cycle. The flux is generated using ORDEM 3.1 released by NASA.

Optical Characterization of DebriSat Fragments in Support of Orbital Debris Environmental Models

The NASA Orbital Debris Program Office (ODPO) develops, maintains, and updates orbital debris environmental models, such as the NASA Orbital Debris Engineering Model (ORDEM), to support satellite designers and operators by estimating the risk from orbital debris impacts on their vehicles in orbit. Updates to ORDEM utilize the most recent validated datasets from radar, optical, and in situ sources to provide estimates of the debris flux as a function of size, material density, impact speed, and direction along a mission orbit. On-going efforts within the NASA ODPO to update the next version of ORDEM include a new parameter that highly affects the damage risk – shape. Shape can be binned by material density and size to better understand the damage assessments on spacecraft. The in situ and laboratory research activities at the NASA ODPO are focused on cataloging and characterizing fragments from a laboratory hypervelocity-impact test using a high-fidelity, mock-up satellite, DebriSat, in controlled and instrumented laboratory conditions. DebriSat is representative of present-day, low Earth orbit satellites, having been constructed with modern spacecraft materials and techniques. The DebriSat fragment ensemble provides a variety of shapes, bulk densities, and dimensions. Fragments down to 2 mm in size are being characterized by their physical and derived properties. A subset of fragments is being analyzed further in NASA’s Optical Measurement Center (OMC) using broadband, bidirectional reflectance measurements to provide insight into the optical-based NASA Size Estimation Model. Additionally, pre-impact spectral measurements on a subset of DebriSat materials were acquired for baseline material characterization. This paper provides an overview of DebriSat, the status of the project, and ongoing fragment characterization efforts within the OMC.

The Interaction between the LEO Satellite Constellation and the Space Debris Environment

The wide application of satellite constellations in the field of space-based global communications and remote sensing has led to a substantial increase in small-satellite launch plans, a sharp increase in the density of space objects in low-Earth orbit (LEO), and a reduction in available orbit and frequency resources. This will further aggravate the trend of deterioration of the space debris environment. Taking the Starlink constellation as an example, this paper describes the influence of the constellation from the environmental debris flux of the satellite, the evaluation of the number of evasion maneuvers, the change of risk level, the success rate of post mission disposal (PMD) and the growth rate of space objects. The simulation results show that the collision risk of the Starlink constellation is related to the orbital parameters, and the higher success rate of post-mission disposal (PMD) can reduce the collision risk of the constellation. The large constellations increases the growth rate of space objects, and even if all the satellites are disposed of after the mission, the impact of constellations on the space environment can not be offset.

Geological features and resource potential of deep-sea mud highly enriched in rare-earth elements in the Central Pacific Basin and the Penrhyn Basin

Deep-sea mud enriched in rare-earth elements and yttrium (REY-rich mud) has been recognized as a new resource for REY and scandium (Sc). Recently, highly REY-rich mud with more than 2,000 ppm of REY was found in the western North Pacific Ocean. The high REY content was attributed to enhanced deposition of fish debris, which acts as a host for REY, resulting from fish proliferation caused by topographically induced upwelling of nutrients. To investigate the spatial extent of the highly REY-rich mud, we conducted mineralogical and chemical analyses on selected sediment cores collected near topographic highs in the Central Pacific Ocean. The maximum REY content of the study cores was 4,489 ppm. The correlation between REY contents and abundance of fish debris indicated that the presence of large amounts of fish debris was responsible for the REY enrichment. The results of the mineralogical analysis suggested that there are three layers of REY-rich mud on the basis of the presence/absence of zeolite group minerals in the study cores. The first layer with phillipsite formed as a result of fish proliferation due to interactions between water currents and topography in the latest Eocene to early Oligocene. The layers with clinoptilolite probably formed as the result of an increased depositional flux of fish debris in the equatorial high-surface-productivity area in the middle Eocene. The layer without zeolite group minerals likely formed in relation to increased fish debris production caused by increased biological activity and high ecosystem efficiency together with slow sedimentation of other components in the South Pacific Gyre. Calculation of the resource amount in a 1-km2 area around the study sites, based on mining to the depth where the average grade is maximum when mined from the surface, revealed that the highly REY-rich mud could provide 1.4% of the global annual mine production of REY and 0.8–1.3 times the global annual supply of Sc. This finding suggests that REY-rich mud in the Central Pacific Ocean is a prospective REE resource.

Modeling the feedbacks between surface ablation and morphological variations on debris-covered Baltoro Glacier in the central Karakoram

Recent studies show that many debris-covered glaciers exhibit high-magnitude differential thinning despite the presence of supraglacial debris. Existing studies have not adequately explored the variability in surface ablation, morphology, and related feedback mechanisms that incorporate topographically controlled surface irradiance and debris transport. In this study, we address these issues using a radiation-driven surface ablation model that more fully characterizes ablation dynamics by accounting for temporally-linked radiative forcing, surface geomorphological evolution and gravitational debris flux. Simulation results based on Baltoro Glacier in the central Karakoram indicate the following: 1) A debris-covered glacier can exhibit high spatial variability in surface ablation due to heterogeneous debris thickness and debris transport. A bare-ice glacier given similar initial conditions, has higher overall ablation but exhibits much less variability. 2) The topographic influence on surface ablation is non-negligible because glacier-surface topography controls irradiance and gravitational debris flux. The overall ablation on a debris-covered glacier tends to increase in response to high-frequency topographic variations due to the larger area with thin debris cover. In contrast, a bare-ice glacier exhibits decreased overall ablation in response to high-frequency topographic variations due to its high sensitivity to topographic shading. 3) Gravity-driven surface debris flux plays an important role in local debris thickness redistribution, which regulates ablation rates over the ablation season. 4) Surface ablation dynamics on a debris-covered glacier is regulated by active system couplings and feedbacks between surface morphology, melt and debris transport. Consequently, certain locations on a debris-covered glacier may be more sensitive to radiative forcing than previously thought. Simulation results suggest that nonlinear feedback responses may permit debris-covered glacier subsystems to be very sensitive to radiative forcing, thereby causing significant morphological changes to the glacier surface.