bluuebunny/crossref_metadata_2025 huggingface dataset:
The kinetoplastid-infecting Bodo saltans virus (BsV), a window into the most abundant giant viruses in the sea
Authors: Deeg Christoph M , Chow Cheryl-Emiliane T , Suttle Curtis A
Published: March 2018

Giant viruses are ecologically important players in aquatic ecosystems that have challenged concepts of what constitutes a virus. Herein, we present the giant Bodo saltans virus (BsV), the first characterized representative of the most abundant group of giant viruses in ocean metagenomes, and the first isolate of a klosneuvirus, a subgroup of the Mimiviridae proposed from metagenomic data. BsV infects an ecologically important microzooplankton, the kinetoplastid Bodo saltans. Its 1.39 Mb genome encodes 1227 predicted ORFs, including a complex replication machinery. Yet, much of its translational apparatus has been lost, including all tRNAs. Essential genes are invaded by homing endonuclease-encoding self-splicing introns that may defend against competing viruses. Putative anti-host factors show extensive gene duplication via a genomic accordion indicating an ongoing evolutionary arms race and highlighting the rapid evolution and genomic plasticity that has led to genome gigantism and the enigma that is giant viruses.
NOTCH activity differentially affects alternative cell fate acquisition and maintenance
Authors: Cheung Leonard , Le Tissier Paul , Goldsmith Sam GJ , Treier Mathias , Lovell-Badge Robin , Rizzoti Karine
Published: March 2018

The pituitary is an essential endocrine gland regulating multiple processes. Regeneration of endocrine cells is of therapeutic interest and recent studies are promising, but mechanisms of endocrine cell fate acquisition need to be better characterised. The NOTCH pathway is important during pituitary development. Here, we further characterise its role in the murine pituitary, revealing differential sensitivity within and between lineages. In progenitors, NOTCH activation blocks cell fate acquisition, with time-dependant modulation. In differentiating cells, response to activation is blunted in the POU1F1 lineage, with apparently normal cell fate specification, while POMC cells remain sensitive. Absence of apparent defects in Pou1f1-Cre; Rbpjfl/fl mice further suggests no direct role for NOTCH signalling in POU1F1 cell fate acquisition. In contrast, in the POMC lineage, NICD expression induces a regression towards a progenitor-like state, suggesting that the NOTCH pathway specifically blocks POMC cell differentiation. These results have implications for pituitary development, plasticity and regeneration. Activation of NOTCH signalling in different cell lineages of the embryonic murine pituitary uncovers an unexpected differential sensitivity, and this consequently reveals new aspects of endocrine lineages development and plasticity.
Endogenous opioids in the nucleus accumbens promote approach to high-fat food in the absence of caloric need
Authors: Caref Kevin , Nicola Saleem M
Published: March 2018

When relatively sated, people (and rodents) are still easily tempted to consume calorie-dense foods, particularly those containing fat and sugar. Consumption of such foods while calorically replete likely contributes to obesity. The nucleus accumbens (NAc) opioid system has long been viewed as a critical substrate for this behavior, mainly via contributions to the neural control of consumption and palatability. Here, we test the hypothesis that endogenous NAc opioids also promote appetitive approach to calorie-dense food in states of relatively high satiety. We simultaneously recorded NAc neuronal firing and infused a µ-opioid receptor antagonist into the NAc while rats performed a cued approach task in which appetitive and consummatory phases were well separated. The results reveal elements of a neural mechanism by which NAc opioids promote approach to high-fat food despite the lack of caloric need, demonstrating a potential means by which the brain is biased towards overconsumption of palatable food.
Dendritic spikes in hippocampal granule cells are necessary for long-term potentiation at the perforant path synapse
Authors: Kim Sooyun , Kim Yoonsub , Lee Suk-Ho , Ho Won-Kyung
Published: March 2018

Long-term potentiation (LTP) of synaptic responses is essential for hippocampal memory function. Perforant-path (PP) synapses on hippocampal granule cells (GCs) contribute to the formation of associative memories, which are considered the cellular correlates of memory engrams. However, the mechanisms of LTP at these synapses are not well understood. Due to sparse firing activity and the voltage attenuation in their dendrites, it remains unclear how associative LTP at distal synapses occurs. Here, we show that NMDA receptor-dependent LTP can be induced at PP-GC synapses without backpropagating action potentials (bAPs) in acute rat brain slices. Dendritic recordings reveal substantial attenuation of bAPs as well as local dendritic Na+ spike generation during PP-GC input. Inhibition of dendritic Na+ spikes impairs LTP induction at PP-GC synapse. These data suggest that dendritic spikes may constitute a key cellular mechanism for memory formation in the dentate gyrus.
Indexing labeled sequences
Authors: Rocher Tatiana , Giraud Mathieu , Salson Mikaël
Published: March 2018

Background

Labels are a way to add some information on a text, such as functional annotations such as genes on a DNA sequences. V(D)J recombinations are DNA recombinations involving two or three short genes in lymphocytes. Sequencing this short region (500 bp or less) produces labeled sequences and brings insight in the lymphocyte repertoire for onco-hematology or immunology studies.

Methods

We present two indexes for a text with non-overlapping labels. They store the text in a Burrows–Wheeler transform (BWT) and a compressed label sequence in a Wavelet Tree. The label sequence is taken in the order of the text (TL-index) or in the order of the BWT (TLBW-index). Both indexes need a space related to the entropy of the labeled text.

Results

These indexes allow efficient text–label queries to count and find labeled patterns. The TLBW-index has an overhead on simple label queries but is very efficient on combined pattern–label queries. We implemented the indexes in C++ and compared them against a baseline solution on pseudo-random as well as on V(D)J labeled texts.

Discussion

New indexes such as the ones we proposed improve the way we index and query labeled texts as, for instance, lymphocyte repertoire for hematological and immunological studies.
Description of a Zostera marina catalase gene involved in responses to temperature stress
Authors: Zang Yu , Liu Jiao , Tang Xue Xi , Zhou Bin
Published: March 2018

Catalase (CAT) is an antioxidant enzyme that plays a significant role in cellular protection against oxidative damage by degradation of hydrogen peroxide to oxygen and water. In the present study, the complete CAT cDNA sequence of Zostera marina was identified through expressed sequence tags (EST) analysis and the rapid amplification of cDNA ends (RACE) technique. The nucleotide sequence of ZmCAT cDNA consisted of 1,816 bp with a 1,434 bp open reading frame (ORF), encoding a polypeptide of 477 amino acid residues, which possessed significant homology to other known plant CATs. The molecular mass of the predicted protein was 55.3 kDa with an estimated isoelectric point of 6.40. Phylogenetic analysis showed that ZmCAT was closely related to CAT from gramineous species. In response to temperature stress, H2O2 and MDA contents in Z. marina increased significantly with cold stress (<10 °C) and heat stress (>25 °C). ZmCAT expression was significantly upregulated at temperatures from 5 to 10 °C and then gradually downregulated, reaching its lowest expression at 30 °C. Recombinant ZmCAT protein exhibited strong antioxidant activity over a wide temperature range, with the highest rZmCAT activity observed at 25 °C and a higher relative activity retained even with heat stress. All these results indicated that ZmCAT was a member of the plant CAT family and involved in minimizing oxidative damage effects in Z. marina under temperature stress.
PME‐1 is regulated by USP36 in ERK and Akt signaling pathways
Authors: Kim Soo‐Yeon , Choi Jihye , Lee Da‐Hye , Park Jun‐Hyeok , Hwang Young‐Jae , Baek Kwang‐Hyun
Published: March 2018

Deubiquitinating enzymes (DUBs) play an important role in the ubiquitin‐proteasome system (UPS) by eliminating ubiquitins from substrates and inhibiting proteasomal degradation. Protein phosphatase methylesterase 1 (PME‐1) inactivates protein phosphatase 2A (PP2A) and enhances the ERK and Akt signaling pathways, which increase cell proliferation and malignant cell transformation. In this study, we demonstrate that USP36 regulates PME‐1 through its deubiquitinating enzyme activity. USP36 increases PME‐1 stability, and depletion of USP36 decreases the PME‐1 expression level. Furthermore, we demonstrate that USP36 promotes the ERK and Akt signaling pathways. In summary, it is suggested that USP36 regulates PME‐1 as a DUB and participates in the ERK and Akt signaling pathways.
Structural and enzymatic analyses of Anabaena heterocyst‐specific alkaline invertase InvB
Authors: Xie Jin , Hu Hai‐Xi , Cai Kun , Xia Ling‐Yun , Yang Feng , Jiang Yong‐Liang , Chen Yuxing , Zhou Cong‐Zhao
Published: March 2018

Anabaena sp. PCC 7120 encodes two alkaline/neutral invertases, namely InvA and InvB. Following our recently reported InvA structure, here we report the crystal structure of the heterocyst‐specific InvB. Despite sharing an overall structure similar to InvA, InvB possesses a much higher catalytic activity. Structural comparisons of the catalytic pockets reveal that Arg430 of InvB adopts a different conformation, which may facilitate the deprotonation of the catalytic residue Glu415. We propose that the higher activity may be responsible for the vital role of InvB in heterocyst development and nitrogen fixation. Furthermore, phylogenetic analysis combined with activity assays also suggests the role of this highly conserved arginine in plants and cyanobacteria, as well as some proteobacteria living in highly extreme environments.
Tectonic Implications of Detrital Zircon Ages From Lesser Himalayan Mesozoic‐Cenozoic Strata, Pakistan
Authors: Qasim Muhammad , Ding Lin , Khan Muhammad Asif , Jadoon Ishtiaq A. K. , Haneef Muhammad , Baral Upendra , Cai Fulong , Wang Houqi , Yue Yahui
Published: March 2018

We carried U‐Pb‐Hf geochronology of the clastic sequence covering upper Mesozoic‐Cenozoic period. The upper Mesozoic sequence is overlain unconformably by the Cenozoic strata, marking regional K‐T boundary, which is mapped as angular unconformity. This angular relationship may strongly indicate a compressional orogenic event that occurred during the Late Cretaceous. Late Cretaceous Kohistan‐Karakoram collision and ophiolite emplacement may account for the development of this compression along the northern Indian margin. The U‐Pb‐Hf isotopic analyses of the upper Mesozoic and lower Cenozoic sequence (Hangu Formation and Lower Patala Formation) are similar to the Tethyan and Lesser Himalayan signatures, which indicate the Indian‐plate provenance. The two younger Cretaceous grains recorded in the Hangu Formation might be derived from the Indian‐plate volcanic rocks and/or Tethyan Himalayan volcanic rocks. The absence of ophiolitic age component in the precollision sequence may indicate that these ophiolites are not exposed until final India‐Eurasia collision. The major shift in provenance is recorded in the upper part of the Patala Formation, where the presence of disconformity and the appearance of <100 Ma detrital zircons indicate the contribution of Eurasian source (i.e., Kohistan‐Ladakh arc; KLA), which is further supported by the ɛHf(t) signatures. Upsection, the contribution from Eurasian source increased in the Early Middle Eocene Kuldana Formation. Therefore, we suggest that the provenance mixing close to Paleocene‐Eocene boundary indicates that the India‐Eurasia collision in the north Pakistan occurred at ∼56–55 Ma and subsequent exhumation increased the contribution of the northern (Eurasian) provenance in the upsection.
Numerical Models of Pore Pressure and Stress Changes Along Basement Faults Due to Wastewater Injection: Applications to the 2014 Milan, Kansas Earthquake
Authors: Hearn Elizabeth H. , Koltermann Christine , Rubinstein Justin L.
Published: March 2018

We have developed groundwater flow models to explore the possible relationship between wastewater injection and the 12 November 2014 Mw 4.8 Milan, Kansas earthquake. We calculate pore pressure increases in the uppermost crust using a suite of models in which hydraulic properties of the Arbuckle Formation and the Milan earthquake fault zone, the Milan earthquake hypocenter depth, and fault zone geometry are varied. Given pre‐earthquake injection volumes and reasonable hydrogeologic properties, significantly increasing pore pressure at the Milan hypocenter requires that most flow occur through a conductive channel (i.e., the lower Arbuckle and the fault zone) rather than a conductive 3‐D volume. For a range of reasonable lower Arbuckle and fault zone hydraulic parameters, the modeled pore pressure increase at the Milan hypocenter exceeds a minimum triggering threshold of 0.01 MPa at the time of the earthquake. Critical factors include injection into the base of the Arbuckle Formation and proximity of the injection point to a narrow fault damage zone or conductive fracture in the pre‐Cambrian basement with a hydraulic diffusivity of about 3–30 m2/s. The maximum pore pressure increase we obtain at the Milan hypocenter before the earthquake is 0.06 MPa. This suggests that the Milan earthquake occurred on a fault segment that was critically stressed prior to significant wastewater injection in the area. Given continued wastewater injection into the upper Arbuckle in the Milan region, assessment of the middle Arbuckle as a hydraulic barrier remains an important research priority.
Diverse Eruptive Activity Revealed by Acoustic and Electromagnetic Observations of the 14 July 2013 Intense Vulcanian Eruption of Tungurahua Volcano, Ecuador
Authors: Anderson J. F. , Johnson J. B. , Steele A. L. , Ruiz M. C. , Brand B. D.
Published: March 2018

During the powerful July 2013 eruption of Tungurahua volcano, Ecuador, we recorded exceptionally high amplitude, long‐period infrasound (1,600‐Pa peak‐to‐peak amplitude, 5.5‐s period) on sensors within 2 km of the vent alongside electromagnetic signals from volcanic lightning serendipitously captured as interference. This explosion was one of Tungurahua's most powerful vulcanian eruptions since recent activity began in 1999, and its acoustic wave is among the most powerful volcanic infrasound ever recorded anywhere. We use these data to quantify erupted volume from the main explosion and to classify postexplosive degassing into distinct emission styles. Additionally, we demonstrate a highly effective method of recording lightning‐related electromagnetic signals alongside infrasound. Detailed chronologies of powerful vulcanian eruptions are rare; this study demonstrates that diverse eruptive processes can occur in such eruptions and that near‐vent infrasound and electromagnetic data can elucidate them.
An Auroral Boundary‐Oriented Model of Subauroral Polarization Streams (SAPS)
Authors: Landry R. G. , Anderson P. C.
Published: March 2018

An empirical model of subauroral polarization stream (SAPS) electric fields has been developed using measurements of ion drifts and particle precipitation made by the Defense Meteorological Satellite Program from 1987 to 2012 and Dynamics Explorer 2 as functions of magnetic local time (MLT), magnetic latitude, the auroral electrojet index (AE), hemisphere, and day of year. Over 500,000 subauroral passes are used. This model is oriented in degree magnetic latitude equatorward of the aurora and takes median values instead of the mean to avoid the contribution of low occurrence frequency subauroral ion drifts so that the model is representative of the much more common, latitudinally broad, low‐amplitude SAPS field. The SAPS model is in broad agreement with previous statistical efforts in the variation of the SAPS field with MLT and magnetic activity level, although the median field is weaker. Furthermore, we find that the median SAPS field is roughly conjugate in both hemispheres for all seasons, with a maximum in SAPS amplitude and width found for 1800–2000 MLT. The SAPS amplitude is found to vary seasonally only from about 1800–2000 MLT, maximizing in both hemispheres during equinox months. Because this feature exists despite controlling for the AE index, it is suggested that this is due to a seasonal variation in the flux tube averaged ionospheric conductance at MLT sectors where it is more likely that one flux tube footprint is in darkness while the other is in daylight.
Direct Evidence for Throat Aurora Being the Ionospheric Signature of Magnetopause Transient and Reflecting Localized Magnetopause Indentations
Authors: Han De‐Sheng , Liu J.‐J. , Chen X.‐C. , Xu T. , Li B. , Hu Z.‐J. , Hu H.‐Q. , Yang H.‐G. , Fuselier S. A. , Pollock C. J.
Published: March 2018

Magnetopause transients, observing as brief entries into the magnetosheath by satellites, are commonly observed in the vicinity of the magnetopause and have been explained by several possible mechanisms. However, satellite observations alone are insufficient to determine the dynamics and context of transients. Throat auroras are characterized as north‐south aligned discrete auroral forms extending from the equatorward edge of the discrete auroral oval that are only observed near dayside convection throat region and have been suggested as the ionospheric signature of localized magnetopause indentations. Using coordinated observations from the Magnetospheric Multiscale Mission (MMS) and ground‐based all‐sky imagers, we show apparent one‐to‐one correspondences between transients observed by MMS near the subsolar magnetopause and throat auroras observed on the ground. The correspondence is valid not only for typical throat aurora with larger spatial scale but also for these with tiny scales. We even notice that the transient durations observed by satellite are approximately proportional to the width (east‐west extension) of the throat aurora. These results provide direct evidence that throat auroras are ground signatures for the magnetopause transients. With the aid of auroral observations, we suggest that these transients reflect localized magnetopause indentations but are not produced by motion of the entire magnetopause. We also found that most transients observed here are associated with earthward flow enhancements, which indicates that high‐speed jets in the magnetosheath could be a driver for producing these transients.
Detailed Regression Model of Plasma Sheet By
Authors: Petrukovich A. A. , Lukin A. S.
Published: March 2018

In a statistical model plasma sheet By primarily depends on interplanetary magnetic field (IMF)
and geodipole tilt τ. With 11 years of Geotail measurements we investigate a role of several other parameters with a linear regression model. Optimal averaging window of IMF input, maximizing correlation and regression coefficients, is found to be 2.25 hr. Influence of IMF
and local Bz on IMF penetration (regression with regard to
) and the deviations from the predefined warp deformation are at the level 5–10% relative to the primary model coefficients. The IMF penetration beyond 25 RE is somewhat larger for northward IMF, while closer to the Earth it becomes somewhat larger for southward IMF. These smaller effects turned out to be rather uneven across the tail, making reliable quantification and physical interpretation not always possible. The major reasons of difficulties are uneven coverage and internal correlations in the input space (
–τ–
) due to combination of spacecraft orbit and neutral sheet dynamics, effects of coordinate transformations, etc. In particular, origins of extremely large IMF
penetration (order of 30–50% above the average one) for some years and tail locations remain not fully clear. A larger multispacecraft data set covering all seasons in all spatial zones is necessary to further advance in this study.
Rarefaction of the Very Slow (<350 km/s) Solar Wind in Cycle 24 Compared With Cycle 23
Authors: Tokumaru Munetoshi , Shimoyama Tomoya , Fujiki Ken'ichi , Hakamada Kazuyuki
Published: March 2018

We investigate long‐term variation of the very slow solar wind (VSSW), whose speed is less than 350 km/s, during the period between 1997 and 2015, that is, Cycles 23 and 24, using interplanetary scintillation measurements, which enable determination of the global distribution of the flow speed and the electron density fluctuation level ΔNe. We find that the occurrence rate of VSSW increases in the maximum phase of the solar cycle, and it was mostly associated with high ΔNe in Cycle 23. However, the VSSW is found to be more associated with low ΔNe in Cycle 24. This fact is consistent with an increased occurrence of the low‐density VSSW observed in situ in Cycle 24. These facts, which are considered to be a manifestation of weak solar activity in this cycle, suggest that the VSSW has become significantly rarefied in recent years. We identify the source region of the VSSW on the photosphere using a potential field analysis and examine the magnetic field properties of the VSSW source. We find that the low‐ΔNe VSSW is associated with a smaller expansion factor and possibly a slightly weaker photospheric field strength than the high‐ΔNe VSSW. The results obtained here may suggest that more open magnetic field areas producing the VSSW in Cycle 24 are formed in the quiet Sun region, which is associated with a lower mass flux supply into the corona, than those in Cycle 23.
Energy Balance From a Mantle Pseudotachylyte, Balmuccia, Italy
Authors: Ferrand Thomas P. , Labrousse Loïc , Eloy Grégoire , Fabbri Olivier , Hilairet Nadège , Schubnel Alexandre
Published: March 2018

In the Balmuccia massif (NW Italy), a pseudotachylyte vein network (N068 trending) in a spinel lherzolite is interpreted as the product of frictional melting during a single Mw > 6 earthquake. The subvertical fault underwent a metric dextral coseismic displacement, raking 60°SW. The average width of the main slip surface is ~ 5 mm. A dense network of thin (20–200 μm) injection and ultramylonite‐like veins decorates the fault walls. In the injection veins, Raman microspectrometry mapping reveals pockets of still preserved amorphous silicate, containing ≈ 1% of structurally bound H2O. In the ultramylonite‐like veins, electron backscattered diffraction mapping reveals that ultrafine (0.2–2 μm) olivine grains exhibit a strong fabric with (010) planes parallel to shearing, consistent with temperatures above 1250°C during deformation and suggesting fast recrystallization from the frictional melt. The veins also exhibit pyroxene and recrystallized spinel, which proves that the earthquake occurred at a minimum depth of 40 km. The energy balance demonstrates that complete fault lubrication must have occurred during coseismic sliding (i.e., dynamic friction coefficient ≪ 0.1). Because of the low viscosity of slightly hydrated ultramafic liquids (≈ 1 Pa·s), we argue that lubrication was only transient, as the melt could rapidly flow into tensile fractures, which led to rapid cooling and promoted strength recovery and sliding arrest. Combined together, our observations suggest that this pseudotachylyte is the frozen record of a deep (>40 km) earthquake of 6 < Mw < 7. Its focal mechanism is deduced from the crystal preferred orientation due to late coseismic creep in ultramylonite‐like veins and deciphered by electron backscattered diffraction.
Characterizing Afterslip and Ground Displacement Rate Increase Following the 2014 Iquique‐Pisagua Mw 8.1 Earthquake, Northern Chile
Authors: Hoffmann Felix , Metzger Sabrina , Moreno Marcos , Deng Zhiguo , Sippl Christian , Ortega‐Culaciati Francisco , Oncken Onno
Published: March 2018

The 2014 Iquique‐Pisagua Mw 8.1 earthquake ruptured only parts of the 1877 Northern Chile‐Southern Peru seismic gap. Here we present a comprehensive analysis of 152 continuous and campaign Global Positioning System time series that captured more than a decade of interseismic loading prior to the event and 2 years of afterslip. In high spatiotemporal resolution, our data document upper plate response not only at the coseismically affected latitudes but also at the adjacent Loa plate segment to the south. Using a combination of elastic and viscoelastic half‐space models of different stages of the seismic cycle, we found that the highly coupled, former seismic gap contains a narrow low coupling zone at 21°S latitude. Just after the 2014 earthquake, this zone acts as a barrier impeding afterslip to continue southward. Possible reasons for this impediment could involve crustal heterogeneities or coupling discontinuities at the plate interface. After 2 years, afterslip cumulates to a maximum of ~89 cm and becomes negligible. Global Positioning System observations south of the inferred seismotectonic barrier reveal a deformation rate increase in the second year after the event. Our slip models suggest that this could be caused by a downdip coupling increase, perhaps bringing the highly coupled southern Loa segment closer to failure. Taken together, our results reveal (1) the interaction between different areas undergoing stress release and stress buildup in a major seismic gap, (2) constraints for the temporal variation of coupling degree in different stages of the seismic cycle, and (3) the influence of large earthquakes at adjacent segments.
Calibrating Dense Spatial Arrays for Amplitude Statics and Orientation Errors
Authors: Langston Charles A.
Published: March 2018

An iterative procedure is designed to calibrate dense arrays of three‐component seismic instruments for station amplitude statics and horizontal component orientation errors. Station amplitude statics refers to differences in sensor and digitizer gains and amplification effects due to local site and installation conditions. Amplitude statics and orientation errors can seriously affect computation of the wavefield gradient tensor that is the basis of seismic strain and rotation computations as well as analysis of wave field attributes through wave gradiometry since wave spatial gradients rely on first‐order differences of the wavefield between sensors in an array. The technique is based on the assumption of a common wave field observed over a small array using teleseismic earthquake observations. In situ calibration of the broad band, 800‐m aperture array at Pinyon Flat, California, achieves relative amplitude precision for vertical components of the array from 0.16% to 0.25% and horizontal components from 0.16% to 0.61%. Relative sensor orientations can be determined to a precision better than 0.35°. Comparison of horizontal strains computed from array observations of a regional M4.9 earthquake and strains from the Gladwin Tensor borehole strain meter at Pinyon Flat shows excellent correspondence over the frequency band of 0.05 to 2 Hz. Agreement of borehole measured strains and seismic array strains for regional/local seismic events gives confidence that a borehole strain meter and single, three‐component, colocated seismometer can be used as a “point array” for deducing wavefield attributes from wave gradiometry.
Seasonal Evolution of Ocean Heat Supply and Freshwater Discharge From a Rapidly Retreating Tidewater Glacier: Jorge Montt, Patagonia
Authors: Moffat Carlos , Tapia Fabian J. , Nittrouer Charles A. , Hallet Bernard , Bown Francisca , Boldt Love Katherine , Iturra Claudio
Published: March 2018

Proglacial fjords are critical conduits for the exchange of heat and freshwater between the ocean and land ice, and their dynamics heavily modulate the rate of retreat of tidewater glaciers. Here the magnitude, spatial structure, and seasonal evolution of the ocean forcing on the proglacial fjord off a rapidly retreating glacier (Jorge Montt, Patagonia) are characterized using data from multiple shipboard surveys from 2010 to 2016, a multiyear mooring array, and a weather station. The melting of the glacier is forced by relatively warm (8–11°C) waters entering the fjord over a shallow (45 m deep) sill ≈20 km from the terminus. This warm subsurface water is renewed every summer from the surface layer of Gulf of Penas., is transported along the 100‐km long Baker Channel, and reaches the proglacial fjord in the late austral summer to early fall, where it remains relatively warm until late austral spring. Analysis of the freshwater fractions in the fjord reveals that the total freshwater content has a strong seasonal signal with maximum fractional values in the summer, mostly explained by the seasonality of subglacial discharge from the glacier. The submarine melting fraction has no strong seasonal signal, but is a first‐order contributor to the freshwater content of the fjord in winter. This seasonal evolution is consistent with idealized theories of meltwater production, and suggests that the seasonal supply of heat is critical to sustain a high mean temperature for melting, but does not directly control the melting rate variability.
Submesoscale Mixing on Initial Dilution of Radionuclides Released From the Fukushima Daiichi Nuclear Power Plant
Authors: Kamidaira Yuki , Uchiyama Yusuke , Kawamura Hideyuki , Kobayashi Takuya , Furuno Akiko
Published: March 2018

This study developed a submesoscale eddy‐resolving oceanic dispersal modeling system comprising a double‐nested oceanic downscaling model and an offline oceanic radionuclide dispersion model. This was used to investigate the influences of submesoscale coherent structures (SCSs) and associated ageostrophic secondary circulations (ASCs) on the three‐dimensional (3‐D) dispersal of dissolved cesium‐137 (137Cs) released from the Fukushima Daiichi Nuclear Power Plant (FNPP1). Extensive model‐data comparison demonstrated that the innermost high‐resolution model, with a lateral grid resolution of 1 km, could successfully reproduce transient mesoscale oceanic structures, the Kuroshio path and stratification, and spatiotemporal variations of 137Cs concentrations. Using an accompanying mesoscale eddy‐resolving model (grid resolution: 10 km) as a guide, we showed that submesoscale dynamics are important for improved representation of both the eddy field and the resultant 3‐D dispersal of 137Cs, with the temporal variability of surface 137Cs near the FNPP1 being equivalent to that in the coarse‐resolution model. According to energy conversion and spectral analyses, SCSs and ASCs occur most intensively on the submesoscale, primarily because of shear instability. However, baroclinic instability serves as a secondary mechanism. SCSs have prominent seasonality, reflected by intensification in the colder months, which is when the FNPP1 accident occurred. Analysis of the vertical flux of 137Cs was performed by decomposition of the variables into eddy, mesoscale, and submesoscale components using frequency and wave number filters. It revealed that 42.7% of the FNPP1‐derived 137Cs was transported downward below the mixed layer by eddies with the major contribution being from ASCs induced by submesoscale eddies.
Wind Stress Mediated Variability of the Filchner Trough Overflow, Weddell Sea
Authors: Daae K. , Darelius E. , Fer I. , Østerhus S. , Ryan S.
Published: March 2018

The Filchner Trough (FT) is a key site for exchange of water masses between the Weddell Sea continental shelf and the deep ocean. Cold and dense Ice Shelf Water (ISW), a precursor for Antarctic Bottom Water, flows north along the FT and overflows the Filchner Sill. Although access of warm water to the Weddell Sea continental shelf is limited due to the presence of the Antarctic Slope Front, southward transport of warm water is facilitated through the FT. We use moored current meters from the Filchner Sill region to show that the monthly scale variability of the ISW overflow is connected to the variability of the alongslope wind stress upstream. Periods with significant correlation between the wind and ISW overflow are characterized by (I) wind directed along the continental slope, (II) high ISW overflow speed, and (III) high variability in the 16–64 day period band for wind and current. We propose that a recirculation of the slope current, associated with the Antarctic Slope Front, may occur in the FT during periods of strong wind forcing, and that such recirculation could explain the correlation between the wind stress and the ISW overflow. We further show that an increased wind stress along the continental slope leads to increased current speed within the slope current and the Antarctic Coastal Current, with possible implications for the on‐shore heat transport.
Climate Change Projected to Exacerbate Impacts of Coastal Eutrophication in the Northern Gulf of Mexico
Authors: Laurent Arnaud , Fennel Katja , Ko Dong S. , Lehrter John
Published: March 2018

The continental shelf in the northern Gulf of Mexico experiences expansive seasonal hypoxic conditions and eutrophication‐driven acidification in bottom waters. Rising surface ocean temperatures, freshwater and nutrient inputs, and atmospheric CO2 will further exacerbate these conditions. Using a high‐resolution, regional circulation‐biogeochemical model, we simulated the spatiotemporal dynamics of oxygen and inorganic carbon in the northern Gulf of Mexico under present and a projected future (2100) climate state. Results indicate a modest expansion of the hypoxic zone, but more severe hypoxia and greater exposure to prolonged hypoxic conditions. The main drivers underlying these changes are a reduction in oxygen solubility (accounting for 60–74% of the change) and increased stratification (accounting for less than 40%). pH is projected to decrease across the shelf with lowest values in hypoxic waters where aragonite saturation will approach the saturation limit. In the model simulations, acidification is primarily driven by atmospheric and offshore CO2 levels, while the enhancement in stratification only accounts for 7% or less of the total change in pH. Decreased buffering capacity and increased stratification in the future will enhance respiration‐induced acidification (i.e., a decrease in bottom water pH by respired CO2), which will amplify the climate‐induced acidification. According to the model, the magnitude of future changes varies significantly from year to year. The largest effects are simulated in years with large freshwater discharge and upwelling‐favorable winds.
Controls Over Sediment Flux Along Soil‐Mantled Hillslopes: Insights From Granular Dynamics Simulations
Authors: BenDror Eran , Goren Liran
Published: March 2018

Sediment flux from soil‐mantled hillslopes controls the volume of sediments delivered to rivers, the rate of rock exhumation, and the topographic evolution of hillslopes. Recent studies have inferred a nonlinear relation between hillslope gradient and sediment flux, but the functional forms proposed to date generally lack mechanistic explanations. Furthermore, although environmental disturbances have been invoked as facilitating sediment mobilization on soil‐mantled hillslopes that reside below the angle of repose (the threshold for slope‐driven motion), the way in which disturbances control the flux has received little investigation. Here we develop and employ a discrete element granular dynamics numerical model to study the relations between flux, slope, and disturbance characteristics at the grain scale. The numerical grains are subjected to gravitational body forces, contact forces, and random external perturbation forces, which are used to represent natural disturbances and which are characterized by perturbation magnitude and wavelength. Simulation results reveal an abrupt transition between two regimes. Low and intermediate slopes show granular creep, whereby grain velocity rapidly decays with depth. High slopes, albeit still below the angle of repose, show deep, granular slides, where all available material participates in the sliding motion. These two regimes can be described by two different theories for flow down an inclined plane. The simulations reveal that the external perturbations effectively reduce the angle of repose and that the nonlinearity in the slope‐flux relation emerges from each regime separately and from the transition between them in particular. Simulations further demonstrate a positive correlation of sediment flux with perturbation magnitude and wavelength.
Microbial Community Responses to Modern Environmental and Past Climatic Conditions in Omongwa Pan, Western Kalahari: A Paired 16S rRNA Gene Profiling and Lipid Biomarker Approach
Authors: Genderjahn S. , Alawi M. , Wagner D. , Schüller I. , Wanke A. , Mangelsdorf K.
Published: March 2018

Due to a lack of well‐preserved terrestrial climate archives, paleoclimate studies are sparse in southwestern Africa. Because there are no perennial lacustrine systems in this region, this study relies on a saline pan as an archive for climate information in the western Kalahari (Namibia). Molecular biological and biogeochemical analyses were combined to examine the response of indigenous microbial communities to modern and past climate‐induced environmental conditions. The 16S rRNA gene high‐throughput sequencing was applied to sediment samples from Omongwa pan to characterize the modern microbial diversity. Highest diversity of microorganisms, dominated by the extreme halophilic archaeon Halobacteria and by the bacterial phylum Gemmatimonadetes, was detected in the near‐surface sediments of Omongwa pan. In deeper sections abundance and diversity significantly decreases and Bacillus, known to form spores, become dominant. Lipid biomarkers for living and past microbial life were analyzed to track the influence of climate variation on the abundance of microbial communities from the Last Glacial Maximum to Holocene time. Since water is an inevitable requirement for microbial life, in this dry region the abundance of past microbial biomarkers was evaluated to conclude on periods of increased paleoprecipitation in the past. The data point to a period of increased humidity in the western Kalahari during the Last Glacial to Holocene transition indicating a southward shift of the Intertropical Convergence Zone during this period. Comparison with results from a southwestern Kalahari pan suggests complex displacements of the regional atmospheric systems since the Last Glacial Maximum.
Estimating Convection Parameters in the GFDL CM2.1 Model Using Ensemble Data Assimilation
Authors: Li Shan , Zhang Shaoqing , Liu Zhengyu , Lu Lv , Zhu Jiang , Zhang Xuefeng , Wu Xinrong , Zhao Ming , Vecchi Gabriel A. , Zhang Rong‐Hua , Lin Xiaopei
Published: March 2018

Parametric uncertainty in convection parameterization is one major source of model errors that cause model climate drift. Convection parameter tuning has been widely studied in atmospheric models to help mitigate the problem. However, in a fully coupled general circulation model (CGCM), convection parameters which impact the ocean as well as the climate simulation may have different optimal values. This study explores the possibility of estimating convection parameters with an ensemble coupled data assimilation method in a CGCM. Impacts of the convection parameter estimation on climate analysis and forecast are analyzed. In a twin experiment framework, five convection parameters in the GFDL coupled model CM2.1 are estimated individually and simultaneously under both perfect and imperfect model regimes. Results show that the ensemble data assimilation method can help reduce the bias in convection parameters. With estimated convection parameters, the analyses and forecasts for both the atmosphere and the ocean are generally improved. It is also found that information in low latitudes is relatively more important for estimating convection parameters. This study further suggests that when important parameters in appropriate physical parameterizations are identified, incorporating their estimation into traditional ensemble data assimilation procedure could improve the final analysis and climate prediction.
Numerical Solutions of the Mean‐Value Theorem: New Methods for Downward Continuation of Potential Fields
Authors: Zhang Chong , Lü Qingtian , Yan Jiayong , Qi Guang
Published: March 2018

Downward continuation can enhance small‐scale sources and improve resolution. Nevertheless, the common methods have disadvantages in obtaining optimal results because of divergence and instability. We derive the mean‐value theorem for potential fields, which could be the theoretical basis of some data processing and interpretation. Based on numerical solutions of the mean‐value theorem, we present the convergent and stable downward continuation methods by using the first‐order vertical derivatives and their upward continuation. By applying one of our methods to both the synthetic and real cases, we show that our method is stable, convergent and accurate. Meanwhile, compared with the fast Fourier transform Taylor series method and the integrated second vertical derivative Taylor series method, our process has very little boundary effect and is still stable in noise. We find that the characters of the fading anomalies emerge properly in our downward continuation with respect to the original fields at the lower heights.
Old Continental Crust Underlying Juvenile Oceanic Arc: Evidence From Northern Arabian‐Nubian Shield, Egypt
Authors: Li Xian‐Hua , Abd El‐Rahman Yasser , Abu Anbar Mohamed , Li Jiao , Ling Xiao‐Xiao , Wu Li‐Guang , Masoud Ahmed E.
Published: March 2018

The Neoproterozoic Arabian‐Nubian Shield (ANS) is the best preserved and the largest exposed Neoproterozoic juvenile crust on Earth. While the lithology and early Sr and Nd isotopic data demonstrate that the ANS crust is overwhelmingly juvenile, pre‐ANS old zircon crystals have been increasingly recognized in the ANS igneous and sedimentary rocks, casting doubt on the “juvenility” of the ANS crust. In order to understand the origin of the old continental materials in the ANS and its roles in generation of juvenile oceanic arcs, we carry out for the first time an integrated in situ analysis of zircon U‐Pb age and Hf‐O isotopes for greywacke and felsic volcanic cobble samples from the Atud Formation in the Eastern Desert of northwestern part of the ANS. Our data indicate that the Atud Formation was deposited between ca. 720 and 700 Ma, concurrent with the production of oceanic arcs in the ANS. The Atud greywacke was derived from the erosion of a proximal arc terrane that contains numerous old continental crust materials. We identify for the first time a 755‐Ma felsic volcanic cobble from the Atud Formation that is derived from old continental materials during juvenile crust production, suggesting presence of an old continental crust substrate that underlies the ANS. Our work demonstrates that reworking of old continental crust played important roles in generation of oceanic arcs in the northwestern ANS that is likely much less juvenile than previously thought. Thus, the crustal growth rates calculated based on estimates of temporal island arc development need to be revised.
Evidence for Extending Anomalous Miocene Volcanism at the Edge of the East Antarctic Craton
Authors: Licht K. J. , Groth T. , Townsend J. P. , Hennessy A. J. , Hemming S. R. , Flood T. P. , Studinger M.
Published: March 2018

Using field observations followed by petrological, geochemical, geochronological, and geophysical data, we infer the presence of a previously unknown Miocene subglacial volcanic center ~230 km from the South Pole. Evidence of volcanism is from boulders of olivine‐bearing amygdaloidal/vesicular basalt and hyaloclastite deposited in a moraine in the southern Transantarctic Mountains. 40Ar/39Ar ages from five specimens plus U‐Pb ages of detrital zircon from glacial till indicate igneous activity 25–17 Ma. The likely source of the volcanism is a circular −735 nT magnetic anomaly 60 km upflow from the sampling site. Subaqueous textures of the volcanics indicate eruption beneath ice or into water at the margin of an ice mass during the early Miocene. These rocks record the southernmost Cenozoic volcanism in Antarctica and expand the known extent of the oldest lavas associated with West Antarctic Rift system. They may be an expression of lithospheric foundering beneath the southern Transantarctic Mountains.
Toward Global Mapping of Methane With TROPOMI: First Results and Intersatellite Comparison to GOSAT
Authors: Hu Haili , Landgraf Jochen , Detmers Rob , Borsdorff Tobias , Aan de Brugh Joost , Aben Ilse , Butz André , Hasekamp Otto
Published: March 2018

The TROPOspheric Monitoring Instrument (TROPOMI), launched on 13 October 2017, aboard the Sentinel‐5 Precursor satellite, measures reflected sunlight in the ultraviolet, visible, near‐infrared, and shortwave infrared spectral range. It enables daily global mapping of key atmospheric species for monitoring air quality and climate. We present the first methane observations from November and December 2017, using TROPOMI radiance measurements in the shortwave infrared band around 2.3 μm. We compare our results with the methane product obtained from the Greenhouse gases Observing SATellite (GOSAT). Although different spectral ranges and retrieval methods are used, we find excellent agreement between the methane products acquired from the two satellites with a mean difference of 13.6 ppb, standard deviation of 19.6 ppb, and Pearson's correlation coefficient of 0.95. Our preliminary results capture the latitudinal gradient and show expected regional enhancements, for example, in the African Sudd wetlands, with much more detail than has been observed before.
Suppression of the Polar Tongue of Ionization During the 21 August 2017 Solar Eclipse
Authors: Dang Tong , Lei Jiuhou , Wang Wenbin , Burns Alan , Zhang Binzheng , Zhang Shun‐Rong
Published: March 2018

It has long been recognized that during solar eclipses, the ionosphere‐thermosphere system changes greatly within the eclipse shadow, due to the rapid reduction of solar irradiation. However, the concept that a solar eclipse impacts polar ionosphere behavior and dynamics as well as magnetosphere‐ionosphere coupling has not been appreciated. In this study, we investigate the potential impact of the 21 August 2017 solar eclipse on the polar tongue of ionization (TOI) using a high‐resolution, coupled ionosphere‐thermosphere‐electrodynamics model. The reduction of electron densities by the eclipse in the middle latitude TOI source region leads to a suppressed TOI in the polar region. The TOI suppression occurred when the solar eclipse moved into the afternoon sector. The Global Positioning System total electron content observations show similar tendency of polar region total electron content suppression. This study reveals that a solar eclipse occurring at middle latitudes may have significant influences on the polar ionosphere and magnetosphere‐ionosphere coupling.