Melting Patterns Research Articles

Turbulent melting characteristics of hybrid nano-enhanced molten salt phase change material in rectangular enclosure

The turbulent melting characteristics of hybrid nano-enhanced phase change material (HNEPCM) in a three-dimensional rectangular enclosure has been numerically investigated. The lower and upper walls are partially heated and cooled using constant surface temperature boundary condition and the other surfaces are specified with adiabatic boundary condition. The rectangular enclosure is filled with molten salt phase change material (PCM) of potassium nitrate (KNO3) with melting temperature of 334 °C. The transient melting rates of PCM are investigated by dispersing hybrid mono-dispersed spherical nanoparticles of Aluminum oxide (Al2O3) combined with Silicon dioxide (SiO2), Titanium dioxide (TiO2) and Multi-walled carbon nanotubes (MWCNT). The Rayleigh number (Ra) and particle volume fraction (ϕ) are varied in the range of 106≤Ra≤1010 and 2%≤ϕ≤5%. The turbulent phase change process of PCM is modeled using enthalpy–porosity approach with Lam–Bremhorst k−ϵ turbulence model. The three-dimensional governing equations are discretized using Finite difference technique and computations are carried out using Fortran 90 in-house code. The stronger thermal buoyancy force accelerates the melting rate and the melting pattern indicates the accumulation of large quantity of molten metal in the upper regions of the rectangular enclosure. The average melting velocity and turbulent kinetic energy of pure KNO3 PCM is increased by 51.17% and 77.84% by the addition of Al2O3−MWCNT hybrid nanoparticles. The impact of hybrid nanoparticles on the melting rate and thermal performance of PCM is significant in higher Rayleigh number flows than transitional flows. The present results are validated and are in close agreement with the benchmark experimental results.

Revisiting subglacial hydrology as an origin for Mars' valley networks

Although the nature of the early Martian climate is a matter of considerable debate, the presence of valley networks (VN) provides unambiguous evidence for the presence of liquid water on Mars' surface. A subaerial fluvial origin of VN is at odds with the expected phase instability of near-surface water in the cold, dry Late Noachian climate. Furthermore, many geomorphic properties of VN (e.g., deep U-shaped valleys with constant widths; longitudinal profile reversals) are inconsistent with surface water flow. Conversely, subglacial channels exhibit many of these characteristics and could have persisted beneath ice sheets even in a cold climate. Here we model basal melting beneath a Late Noachian Icy Highlands ice sheet and map subglacial hydrological flow paths to investigate the distribution and geomorphometry of subglacial channels. We show that subglacial processes produce enough melt water to carve Mars' VN; that predicted channel distribution is consistent with observations; and corroborate reversed channel gradient measurements of VN consistent with subglacial formation mechanisms. We suggest that, given a sufficient historical global water inventory and Late Noachian geothermal heat flux, subglacial hydrology may have played a significant role in the surface modification of Mars.Plain language summary. Thousands of valley networks on Mars appear to have been carved by flowing water, and exhibit branching characteristics akin to river networks on Earth. Their origins, however, remain enigmatic for two primary reasons. First, ancient Mars was potentially cold, dry, and unable to support liquid water on its surface. Second, many physical characteristics of the valleys are inconsistent with features formed by precipitation and runoff. On Earth, water flowing beneath ice sheets produces channels with similar characteristics to Mars' valley networks. Here we model the deposition and evolution of Martian ice sheets and show that melting at the ice sheet base is likely even under cold and dry surface conditions. The volume, regional distribution, and flow patterns of melt are consistent with the volume and dynamics needed to carve the observed valley networks. A subglacial origin for Mars' valley networks accounts for their formation in a cold, dry climate and produces valley characteristics that match observations.

Understanding monsoon controls on the energy and mass balance of glaciers in the Central and Eastern Himalaya

Abstract. The Indian and East Asian summer monsoons shape the melt and accumulation patterns of glaciers in High Mountain Asia in complex ways due to the interaction of persistent cloud cover, large temperature ranges, high atmospheric water content and high precipitation rates. Glacier energy- and mass-balance modelling using in situ measurements offers insights into the ways in which surface processes are shaped by climatic regimes. In this study, we use a full energy- and mass-balance model and seven on-glacier automatic weather station datasets from different parts of the Central and Eastern Himalaya to investigate how monsoon conditions influence the glacier surface energy and mass balance. In particular, we look at how debris-covered and debris-free glaciers respond differently to monsoonal conditions. The radiation budget primarily controls the melt of clean-ice glaciers, but turbulent fluxes play an important role in modulating the melt energy on debris-covered glaciers. The sensible heat flux decreases during core monsoon, but the latent heat flux cools the surface due to evaporation of liquid water. This interplay of radiative and turbulent fluxes causes debris-covered glacier melt rates to stay almost constant through the different phases of the monsoon. Ice melt under thin debris, on the other hand, is amplified by both the dark surface and the turbulent fluxes, which intensify melt during monsoon through surface heating and condensation. Pre-monsoon snow cover can considerably delay melt onset and have a strong impact on the seasonal mass balance. Intermittent monsoon snow cover lowers the melt rates at high elevation. This work is fundamental to the understanding of the present and future Himalayan cryosphere and water budget, while informing and motivating further glacier- and catchment-scale research using process-based models.

Development of a novel high resolution melting assay for identification and differentiation of all known 19 serovars of Actinobacillus pleuropneumoniae.

Actinobacillus pleuropneumoniae is the etiological agent of porcine pleuropneumonia, a respiratory infectious disease responsible for global economic losses in the pig industry. From a monitoring perspective as well as due to the different courses of disease associated with the various serovars, it is essential to distinguish them in different herds or countries. In this study, we developed a novel high resolution melting (HRM) assay based on reference strains for each of the 19 known serovars and additional 15 clinical A. pleuropneumoniae isolates. The novel HRM comprises the species‐specific APP‐HRM1 and two serovar‐specific HRM assays (APP‐HRM2 and APP‐HRM3). APP‐HRM1 allowed polymerase chain reaction (PCR) amplification of apxIV resulting in an A. pleuropneumoniae specific melting curve, while nadV specific primers differentiated biovar 2 from biovar 1 isolates. Using APP‐HRM2 and APP‐HRM3, 13 A. pleuropneumoniae serovars can be determined by inspecting the assigned melting temperature. In contrast, serovar 3 and 14, serovar 9 and 11, and serovar 5 and 15 have partly overlapping melting temperatures and thus represent a challenge to accurately distinguish them. Consequently, to unambiguously ensure the correct assignment of the serovar, it is recommended to perform the serotyping HRM assay using a positive control for each serovar. This rapid and user‐friendly assay showed high sensitivity with 1.25 fg–125 pg of input DNA and a specificity of 100% to identify A. pleuropneumoniae. Characteristic melting patterns of amplicons might allow detecting new serovars. The novel HRM assay has the potential to be implemented in diagnostic laboratories for better surveillance of this pathogen.

North Atlantic Footprint of Summer Greenland Ice Sheet Melting on Interannual to Interdecadal Time Scales: A Greenland Blocking Perspective

AbstractRecent rapid melting of the summer Greenland ice sheet (GrIS) and its impact on Earth’s climate has attracted much attention. In this paper, we establish a connection between the melting of GrIS and the variability of summer sea surface temperature (SST) anomalies over the North Atlantic on interannual to interdecadal time scales through changes in subseasonal Greenland blocking (GB). It is found that the latitude and width of GB are important for the spatial patterns of the GrIS melting. The melting of the GrIS on interdecadal time scales is most prominent for the positive Atlantic multidecadal oscillation phase (AMO+) because the high-latitude GB and its large width, long lifetime, and slow decay are favored. However, the North Atlantic mid-high latitude warm–cold–warm (cold–warm–cold) tripole, referred to as the NAT+(NAT−) pattern, on interannual time scales tends to strengthen (weaken) the role of AMO+in the GrIS melting, especially on the northern or northeastern periphery of Greenland, by promoting (inhibiting) high-latitude GB and increasing (decreasing) its width. It is further revealed that AMO+(NAT+) favors the persistence and width of GB mainly through producing weak summer zonal winds and a small summer meridional potential vorticity gradient (PVy) in the North Atlantic mid-high latitudes at 55°–70°N (55°–65°N) compared to the role of negative AMO (NAT−). The event frequency and zonal width of GB events and their poleward shift are favored by the combination of NAT+with AMO+. In contrast, the combination of NAT−and AMO+tends to suppress reduced summer zonal winds and PVy, thus inhibiting the event frequency of GB events and their poleward shift and zonal width.Significance StatementRapid melting of the summer Greenland ice sheet (GrIS) has been observed to frequently occur, especially after the year 2000, leading to a rise in sea level and other effects on Earth’s climate. The physical cause of the rapid melting of the GrIS is an important area of research. We establish a connection between the summer melting of the GrIS and different sea surface temperature (SST) modes in the North Atlantic via changes in Greenland blocking. Although the positive Atlantic multidecadal oscillation (AMO+) phase favors the overall melting of GrIS, the phase of the North Atlantic tripole (NAT) SST pattern modulates the strength and location of the GrIS melting. The positive NAT phase (NAT+) with a warm–cold–warm tripole structure in the North Atlantic mid-high latitudes and AMO+combine to result in a strong warm SST anomaly in the high latitudes of the North Atlantic north of 60°N, which promotes the melting of GrIS on the western, northern, and northeastern peripheries of Greenland via high-latitude Greenland blocking with an increased zonal width. The combination of the negative NAT phase (NAT−) with a cold–warm–cold tripole structure and AMO+tends to suppress this effect. Thus, our results provide a new understanding of why the melting of GrIS shows a strong variability in strength and region.

Analysis of phase change material inside horizontally oriented heat storage unit: A numerical and experimental approach

The present work investigates the heat transfer performance of a horizontal energy storage unit both by numerical and experimental approaches. To augment the heat transfer, high heat conducting Graphene Nanoplatelets (GNP) are added to PCM and its effect on heat transfer characteristics has been investigated. Numerical results of charging-discharging performance are evaluated in terms of contours of temperature and liquid fraction for plain PCM and composite PCM with 1–4% GNP (by mass) addition. The numerically predicted results considering HTF inlet temperatures ranging 750–90 °C and mass flow rate 1.8 lit/min are compared and verified with experimental results. The results reveal that melting pattern of paraffin wax in horizontal unit is not same in upper half and lower half of unit. It is inferred that melting rate increases with increase in inlet temperature of HTF. It is observed that addition of GNP (up to 3% by mass) to PCM helps reduce the charging & discharging duration, improves overall system performance.

CpSSR and High-Resolution Melting Analysis (HRM) for Pinus pseudostrobus Lindl. Variety Genotyping and Discrimination

The unambiguous identification of varieties within the Pseudostrobus complex is a key step to facilitate tree selection and monitoring in the wild as well as in plantations. Molecular tools provide a powerful approach for species delimitation; however, the use of DNA barcodes in this group has met limited success due to widespread haplotype sharing from lineage sorting, hybridization and introgression. Here, we evaluate the utility of real-time PCR coupled with high-resolution melting (HRM) to discriminate among Pinus pseudostrobus Lindl. var. pseudostrobus, apulcensis and oaxacana, from wild populations in central and southern Mexico, using chloroplast DNA sequence variants located within the clpP, ycf2, trnL(UAA)–trnT(UGU) and trnI(CAU)–trnF(GAA) loci. The markers ycf2/trnL(UAA)–trnT(UGU) produced clear melting patterns that separated the varieties pseudostrobus and oaxacana from type var. apulcensis, whereas clpP discriminated over 60% of var. oaxacana individuals. This assay underlines the usefulness of these less-used DNA regions as potential biological markers and exhibits the effect of geography on allele distribution and the likely presence of hybrids among the species and varieties.

Mantle melting, lithospheric strength and transform fault stability: Insights from the North Atlantic

The offset ridge-transform structure of ocean basins is one of the most prominent expressions of plate tectonics. Yet why this configuration is favored over a continuous divergent boundary has remained unresolved. We examine this issue using mantle Bouguer anomalies (MBAs) from contrasting ridge systems in the North Atlantic. The Reykjanes Ridge north of the Bight transform fault has no transform offsets and is characterized by rapidly propagating melting centers along a linear axis and a continuous MBA low. To the south, the adjoining Mid-Atlantic Ridge has typical ridge segments each underlain by a discrete MBA “bulls-eye” low and offset by transform and non-transform discontinuities. We hypothesize that the pattern of mantle melting, as reflected in the MBAs, creates chemical and rheologic variations in the residual mantle that either favor or hinder transform fault formation. Within ridge segments, mantle melting efficiently extracts water producing dry and strong residual mantle. At segment ends, low extents of melting and inefficient melt extraction preserve damp and weak mantle. On the linear Reykjanes Ridge continuous melting and rapidly propagating melting centers create continuous strong mantle with possibly weak rheologic variations at high angles to the opening direction, not favoring transform faults. In contrast, stable segmented mantle melting on the Mid-Atlantic Ridge forms bands of strong and weak residual mantle aligned in the spreading direction, the latter creating favorable locations for shear deformation and transform faults. Our hypothesis also explains the lack of transform faults at Earth's endmember spreading rates. At ultra-slow ridges, overall melting is limited and irregular and melt extraction is inefficient. At ultra-fast ridges, mantle melting is pervasive and melt extraction is efficient. In both cases, organized spreading-parallel compositional rheological variations do not form and transform faults are not favored. Our model implies that beyond cooling and strengthening with age, the pattern of mantle melting shapes the rheological structure of oceanic lithosphere and the geometry of plate tectonics.

Influence of geometry on columnar to equiaxed transition during electron beam powder bed fusion of IN718

Correlation between spot-melt scan parameters (linear spot-density aka areal energy density), build geometry, and solidification microstructure evolution (columnar vs equiaxed) in a powder bed fusion technology is investigated. It is shown that to maintain the equiaxed solidification microstructure evolution in electron beam powder bed additive manufacturing (AM), the areal energy density per layer needs to be scaled with respect to the 2D cross-sectional area of the layer being melted. Samples with two different cross-sectional areas (40 × 40 mm and 20 × 20 mm) have been fabricated with varying areal energy densities. For a given square cross-section (20 × 20 mm), increasing the areal energy density (4.8 MJ/sq.m to 14.7 MJ/sq.m) transitioned the solidification microstructure from columnar to equiaxed. The observed microstructure data (Electron Back Scattered Diffraction - EBSD) is quantified by calculating the principal component (PC) score using a spatial statistics methodology. The sample with equiaxed grains is found to have a low PC score while the sample with columnar grain had a high PC score. A semi-analytical model is used to simulate the heat transfer and the local solidification conditions as a function of processing parameters (linear spot-density). The result from the heat transfer model is correlated with previously quantified microstructure data. Space-Time analysis of the melt pattern is done and correlated with the observed microstructure. In addition, from the findings, appropriate parameters have been used to additively manufacture a turbine blade with site-specific or hybrid solidification microstructure (traditional fabrication possible via a patented method of localized cold working and heat treatment).

A 10-year record of Arctic summer sea ice freeboard from CryoSat-2

Satellite observations of pan-Arctic sea ice thickness have so far been constrained to winter months. For radar altimeters, conventional methods cannot differentiate leads from meltwater ponds that accumulate at the ice surface in summer months, which is a critical step in the ice thickness calculation. Here, we use over 350 optical and synthetic aperture radar (SAR) images from the summer months to train a 1D convolution neural network for separating CryoSat-2 radar altimeter returns from sea ice floes and leads with an accuracy >80%. This enables us to generate the first pan-Arctic measurements of sea ice radar freeboard for May–September between 2011 and 2020. Results indicate that the freeboard distributions in May and September compare closely to those from a conventional ‘winter’ processor in April and October, respectively. The freeboards capture expected patterns of sea ice melt over the Arctic summer, matching well to ice draft observations from the Beaufort Gyre Exploration Program (BGEP) moorings. However, compared to airborne laser scanner freeboards from Operation IceBridge and airborne EM ice thickness surveys from the Alfred Wegener Institute (AWI) IceBird program, CryoSat-2 freeboards are underestimated by 0.02–0.2 m, and ice thickness is underestimated by 0.28–1.0 m, with the largest differences being over thicker multi-year sea ice. To create the first pan-Arctic summer sea ice thickness dataset we must address primary sources of uncertainty in the conversion from radar freeboard to ice thickness.

The role of deformation-assisted by water influx on partial melting of a granite protolith, and its role in the evolution of southwestern São Francisco Craton margin, Brazil

The Areado Granite-Migmatite Unit is part of the basement from the Southern Brasilia Orogen at southwestern São Francisco Craton margin, outcropping between Alfenas and Areado regions, Minas Gerais State, Brazil. This unit is composed of garnet meta-syenogranite, hornblende-garnet metatexite, and stromatic diatexite with different degrees of partial melting. This study characterizes the garnet meta-syenogranite, its migmatitic counterparts and investigates the different patterns of deformation and partial melting involved to produce the observed migmatites within the unit. The connection between the garnet meta-syenogranite, hornblende-garnet metatexite, and biotite diatexite is inferred from field observations and assemblage of accessory minerals. Petrography associated with modal analysis, structural data, quartz c-axis analysis, zircon U–Pb (LA-MC-ICP-MS and SHRIMP) dating, as well as trace elements chemical analysis in quartz and titanite to determine metamorphic, partial melting, and deformation evolution were used as tools in this investigation. The garnet meta-syenogranite has a crystallization age of 2069.8 ± 5 Ma. Lower intercepts from zircon indicate a metamorphic and partial melting age between 671 ± 58 and 657 ± 40 Ma. Melt crystallization ages are inferred between 622 ± 7 Ma and 604 ± 6 Ma. Different rates of partial melt are structurally connected, being higher at the base of the unit, and are related with contrasting amounts of water influx and deformation. The deformation during metamorphism/partial melting was the main cause of the differential aspect of the produced rocks. Quartz c-axis thermometer yielded deformation temperatures of 765–935 °C and other pulses occurred between 590 and 715 °C, both between 11 and 15 kbar. Those values match the Zr-in-titanite thermobarometer data, which is 670–710 °C for low-temperature titanite and 785–815 °C for high-temperature crystals. These data indicate that the protolith was generated at a Rhyacian late magmatic stage of the Mineiro Belt and passed by a Neoproterozoic deformational-metamorphic event of high temperature.

Melting and energy storage characteristics of macro-encapsulated PCM-metal foam system

In this study a novel encapsulated phase change material (PCM)-metal foam hybrid system is proposed for energy storage applications. The idea is to improve the melting rate of PCM in encapsulated PCM systems with the introduction of metal foam structures inside the capsules. The main objective of the work is to develop a numerical model which can simulate the melting of PCM in this hybrid system due to the flow of heat transfer fluid (HTF) around the capsule with the resolution of the metal foam geometry at the pore-scale level. The developed model couples geometry creation, phase change and fluid flow models. The foam geometry is created using overlapping circular pores with random location, radii, and overlap. The phase change model is developed by modifying the enthalpy method to incorporate the presence of four phases – HTF, metal, solid PCM, and liquid PCM. This is coupled with an implicit flow solver within a finite volume framework. An in-depth analysis of a base case is conducted by fixing different geometrical parameters such as capsule size, porosity, pore size distribution and shell thickness. The results of the base case are then compared in subsequent parametric studies, by varying one geometrical parameter at a time. The parametric studies reveal that the structure of the metal foam plays an important role in determining the melting pattern and the energy storage characteristics because of its net-like large inner surface area. It is found that the melting time is reduced for lower capsule size, lower porosity, and higher shell thickness. The average pore size and range are crucial in determining the rate of melting.

Tectonic discontinuity, partial melting and exhumation in the Garhwal Himalaya (Northwest India): Constrains from spatial and temporal pressure-temperature conditions along the Bhagirathi valley

The pattern and timing of tectonic discontinuity and partial melting in the Garhwal Himalaya, resulting from the India–Asia collision, are crucial factors for understanding the evolution of the Himalayan orogen, but these parameters remain poorly constrained. Middle- to high-grade metamorphic rocks from the Main Central Thrust (MCT) zone and the High Himalaya Crystalline Sequence (HHCS) along the Bhagirathi valley in northwest India have been investigated in this study. The primary mineral assemblage of the gneisses and migmatites in the HHCS is garnet + biotite + white mica + quartz + kyanite + rutile ± ilmenite ± sillimanite. The metamorphic grade at thermal peak rapidly increases upwards across the MCT from garnet schists (515–550 °C, 8–9 kbar) in the footwall to garnet-bearing migmatite (705–735 °C, 10–13 kbar) in the hanging wall. The P–T condition decreased upwards in kyanite gneiss of the lower HHCS (690 °C, 8.3 kbar), yielding a high field pressure gradient near the MCT. The prominent metamorphic discontinuity could have been caused by the southward extrusion of the HHCS along with the MCT. The base of the HHCS experienced high-grade metamorphism at 38–25 Ma, mainly at 31.9 ± 0.5 Ma. The new data, combined with previous studies, suggest that the prominent metamorphic discontinuity is characterized by the different periods of peak metamorphism and the overprint in the hanging wall (Eocene–Oligocene metamorphism and Early Miocene overprint) and footwall (Early Miocene metamorphism and Late Miocene to Pliocene overprint) of the MCT. The second metamorphic discontinuity occurred near the migmatite zone in the lower-middle HHCS, which experienced the anatexis (690–740 °C, 7–9 kbar) at 37–25 Ma, mainly at 33.9 ± 1.2 Ma. The Bhagirathi HHCS experienced a regional Barrovian-type Eohimalayan metamorphism associated with fluid-present melting of muscovite + plagioclase + quartz + H2O → melt ± kyanite at 34–32 Ma without a strong Miocene overprint. The period of partial melting is significantly older than the intrusion of ca. 22 Ma Early Miocene Gangotri leucogranites at the top of the HHCS. Protracted periods of crystallization (38–22 Ma) indicate a long duration of more than ca. 15 Myr of anatexis, from initiation of migmatization to pluton formation in the Bhagirathi HHCS. The protracted fluid-present melting and subsequent rapid exhumation in the Bhagirathi HHCS could be associated with heterogeneous extrusion forming the tectonic discontinuity in the lower-middle HHCS. The metamorphic grade decreased towards the upper HHCS (620 °C, 6.5 kbar) across the Jhala Normal Fault where occurs in the right-way-up sequence. On the other hand, in the central Himalaya, the thrusting occurred between upper HHCS and lower-middle HHCS in the inverted metamorphic sequence. The Early Miocene migmatites in the footwall of the significant tectonic discontinuity are dominant, and diachronous extrusion accompanied with the fluid-absent melting reactions is the common mechanism to exhume the HHCS, unlike the heterogeneous extrusion in the northwest Himalaya.

The implications of permafrost thaw and land cover change on snow water equivalent accumulation, melt and runoff in discontinuous permafrost peatlands

AbstractIn the discontinuous permafrost zone of the Northwest Territories (NWT), Canada, snow covers the ground surface for half the year. Snowmelt constitutes a primary source of moisture supply for the short growing season and strongly influences stream hydrographs. Permafrost thaw has changed the landscape by increasing the proportional coverage of permafrost‐free wetlands at the expense of permafrost‐cored peat plateau forests. The biophysical characteristics of each feature affect snow water equivalent (SWE) accumulation and melt rates. In headwater streams in the southern Dehcho region of the NWT, snowmelt runoff has significantly increased over the past 50 years, despite no significant change in annual SWE. At the Fort Simpson A climate station, we found that SWE measurements made by Environment and Climate Change Canada using a Nipher precipitation gauge were more accurate than the Adjusted and Homogenized Canadian Climate Dataset which was derived from snow depth measurements. Here, we: (a) provide 13 years of snow survey data to demonstrate differences in end‐of‐season SWE between wetlands and plateau forests; (b) provide ablation stake and radiation measurements to document differences in snow melt patterns among wetlands, plateau forests, and upland forests; and (c) evaluate the potential impact of permafrost‐thaw induced wetland expansion on SWE accumulation, melt, and runoff. We found that plateaus retain significantly (p < 0.01) more SWE than wetlands. However, the differences are too small (123 mm and 111 mm, respectively) to cause any substantial change in basin SWE. During the snowmelt period in 2015, wetlands were the first feature to become snow‐free in mid‐April, followed by plateau forests (7 days after wetlands) and upland forests (18 days after wetlands). A transition to a higher percentage cover of wetlands may lead to more rapid snowmelt and provide a more hydrologically‐connected landscape, a plausible mechanism driving the observed increase in spring freshet runoff.

Quantifying heterogeneous monsoonal melt on a debris-covered glacier in Nepal Himalaya using repeat uncrewed aerial system (UAS) photogrammetry

AbstractThe ablation zones of debris-covered glaciers in Himalaya exhibit heterogeneous processes and melt patterns. Although sub-debris melt is measured at ablation stakes, the high variability of debris thickness necessitates distributed melt measurements at the glacier scale. Focusing on Annapurna III Glacier, we used uncrewed aerial system (UAS) photogrammetry to estimate total volume loss and slope-perpendicular glacier melt between May and November 2019 using flow-corrected point clouds. Results indicated the average elevation change was −1.10 ± 0.19 m, while the mean melt was −0.87 m w.e., equating to a mean melt rate of −0.47 cm w.e. d−1. However, the spatial pattern was highly variable due to complex local processes necessitating future study over short intervals. The evaluation of specific areas showed the interplay of debris thickness variability, subseasonal debris redistribution, supraglacial channel reconfiguration and the imprint of relict ice cliffs in leading to contemporary melt rates. Ice cliffs had higher melt distances (mean −3.9 ± 0.19 m) compared to non-cliff areas (mean −0.75 ± 0.19 m) and were the predominant control on the spatial patterns of seasonal melt rates. Crucially, the definition of ice cliff areas from thinning data has a profound impact on derived melt rates and melt enhancement. Our study demonstrates the possibility and utility of deriving fully-distributed slope-perpendicular melt measurements.

Interrelationships of Sea Surface Salinity, Chlorophyll-α Concentration, and Sea Surface Temperature near the Antarctic Ice Edge

AbstractSatellite data can now provide a coherent picture of sea surface salinity (SSS), chlorophyll-α concentration (Chlα), sea surface temperature (SST), and sea ice cover across the Southern Ocean. The availability of these data at the basin scale enables novel insight into the physical and biological processes in an area that has historically been difficult to gather in situ data from. The analysis shows large regional and interannual variability of these parameters but also strong coherence across the Southern Ocean. The covariability of the parameters near the marginal ice zone shows a generally negative relationship between SSS and Chlα (r = −0.87). This may in part be attributed to the large seasonality of the variables, but analysis of data within the spring period (from November to December) shows similarly high correlation (r = −0.81). This is the first time that a large-scale robust connection between low salinity and high phytoplankton concentration during ice melt period has been quantified. Chlorophyll-α concentration is also well correlated with SST (r = 0.79) providing a potential indicator of the strength of the temperature limitation on primary productivity in the region. The observed correlation also varied regionally due to differences in ice melt patterns during spring and summer. Overall, this study provides new insights into the physical characteristics of the Southern Ocean as observed from space. In a continually warming and freshening Southern Ocean, the relationships observed here provide a key data source for testing ocean biogeochemical models and assessing the effect of sea ice–ocean processes on primary production.

Comparing Greenland Ice Sheet Melt Variability From Different Satellite Passive Microwave Remote Sensing Products Over a Common 5-year Record

Satellite microwave brightness temperature (Tb) observations over the Greenland Ice Sheet permit determination of melted/frozen snow conditions at spatial and temporal scales that are uniquely suited for climate model validation and metrics of ice sheet change. Strong microwave sensitivity to the presence of liquid water in the snowpack is clear. Yet, a host of unique microwave-derived melt products covering the ice sheet are available, each based on different methodology, and with unknown inter-product agreement. Here, we compared five different published microwave melt products over a common 5-year (2003–2007) record to establish compatibility between products and agreement with in situ observations from a network of on-ice weather stations (AWS) spanning the ice sheet. A sixth product, leveraging both Tb seasonal trends and diurnal variability, was also introduced and included in the comparison. We found variable agreement between products and observations, with melt estimates based on microwave emissions modeling and the newly presented Adaptive Threshold (ADT) algorithm showing the best performance for AWS sites with more than 1-day average annual melt period (e.g., 68.9% of ADT melt days consistent with AWS observations; 31.1% of ADT frozen days contrasting with AWS observed melt). Spatial patterns of melting also varied between products. The different products showed substantial spread in melt occurrence even for products with the best AWS agreement. Product differences were generally larger under higher melt conditions; whereby, the fraction of the ice sheet experiencing ≥25 days of melting each year ranged from 4 to 25% for different products. While long-term satellite records have consistently shown increasing decadal trends in melt extent, our results imply that the melt frequency at any given location, particularly in the ice sheet interior where melting is less prevalent, is still subject to significant uncertainty.

ESTIMATING CONTRIBUTION OF WATER FLOW COMPONENTS TO KAMENG RIVER BASIN USING HYDROLOGICAL MODELLING

Abstract. The Himalayas, also known as third pole of the Earth feed some of the major rivers of the world viz. Ganga, Indus, Brahmaputra etc. The accurate assessment of water resources in eastern Himalayas is very important for respective policy makers. The detailed assessment of water resources and hydrological cycle component are very critical for attaining United Nations sustainable development goals (SDGs) such as affordable and clean energy, clean water and sanitation and building resilient infrastructure This study focuses on Kameng river basin, estimating the melt water & its contribution to the total discharge of the river. A 3-layer VIC model coupled with energy balance algorithm is used to estimate the patterns of melt and discharge profile in the region. Net contribution of melt water to the river were estimated to be about 18% during peak melt season in upper catchments. With advancement in technology, acquiring meteorological data via remote sensing has become more accurate & of high resolution. This data is one of the major inputs of the model. With accurate forecasting of these parameters, multipurpose hydropower projects in these regions can plan well in advance thus playing a major role in Integrated Water Resource Management. In current study the coefficient of determination & Nash-Sutcliffe efficiency were calculated to be 0.82 & 0.71 respectively. With increasing population in the region, any substantial change in the streamflow will have consequences unknown as of now, thus making this study a necessity & need of hour.

Buoyancy of post‐fertilised Dissostichus mawsoni eggs and implications for early life history

AbstractGametes from gravid Antarctic toothfish (Dissostichus mawsoni) were combined in vitro and buoyancy measurements were made on fertilised eggs during early development. Eggs were strongly positively buoyant, indicating that they would ascend quickly in the water column and reside near or in association with the underside of sea ice, which covers most of the spawning habitat during winter. An association with sea ice may provide: protection from the turbulence of ice‐free surface waters, a mechanism that modifies the velocity of advection by surface currents, and a habitat with a concentrated planktonic food source during spring months. An association with sea ice would also create spatial differences in egg advection patterns for eggs produced spanning a large geographic area. The effects of climate change on sea ice formation and melting patterns, or fishery‐induced changes in the spatial density of adults could then influence juvenile advection patterns and influence survival.

Reconstruction of primary alkaline magma composition from mineral archives: Decipher mantle metasomatism by carbonated sediment

Alkaline magmas play a key in understanding crust-mantle interaction and deep carbon recycling. Here, petrography and in situ mineral analyses of evolved alkaline rocks from the North China Craton are reported to decipher mantle metasomatism by recycled carbonated sediments via reconstruction of primary magma composition. The alkaline rocks are nepheline syenites for which new, consistent zircon and titanite UPb ages of ~235 Ma are presented. The rocks are highly evolved (SiO2 = 58.1–60.0 wt%) with negative anomalies for Sr, Ba, Ti, P and Eu, and relative depletion of MREE, indicating fractional crystallization of feldspar, apatite, titanite and amphibole. Core-rim variation of 87Sr/86Sr (0.7052–0.7092) of late-crystallized low Mg# clinopyroxene and feldspar are attributed to crustal assimilation.The origin of primary alkaline magma is recorded in early high Mg# (70–84) clinopyroxenes with weak Eu anomalies (Eu/Eu* = 0.94–1.29), suggesting that they crystallized from a little-differentiated mantle-derived magma (Mg# > 60). Their variable 87Sr/86Sr ratios (0.7031–0.7060) correlate positively with Sr/Y and (La/Yb)N and negatively with Ti/Eu ratios, but are not correlated with Mg# or Eu/Eu*. Moreover, the REE patterns of melt equilibrated with high 87Sr/86Sr clinopyroxene is similar to coeval alkaline rocks from adjacent areas. These features indicate that the primary alkaline magma was derived from the mixing of depleted mantle and enriched mantle metasomatized by carbonatite melts from subducted crustal materials. Low zircon εHf(t) values (−1.4 to −2.8) imply that the subducted crustal material was carbonated sediments. Calcite and CO2 inclusions occur in early-crystallized olivine, clinopyroxene and zircon, and amphibole and fluorapatite both reveal a volatile-rich (H2O, F and CO2) alkaline magma derived from mantle enriched by carbonate metasomatism. The mineral archives of alkaline rocks not only record mantle metasomatism by recycled carbonated sediments, but also fractional crystallization and assimilation during magma evolution.