Flux Variability Research Articles

Insights into the subdaily variations in methane, nitrous oxide and carbon dioxide fluxes from upland tropical tree stems.

Recent studies have shown that stem fluxes, although highly variable among trees, can alter the strength of the methane (CH4) sink or nitrous oxide (N2O) source in some forests, but the patterns and magnitudes of these fluxes remain unclear. This study investigated the drivers of subdaily and seasonal variations in stem and soil CH4, N2O and carbon dioxide (CO2) fluxes. CH4, N2O and CO2 fluxes were measured continuously for 19 months in individual stems of two tree species, Eperua falcata (Aubl.) and Lecythis poiteaui (O. Berg), and surrounding soils using an automated chamber system in an upland tropical forest. Subdaily variations in these fluxes were related to environmental and stem physiological (sap flow and stem diameter variations) measurements under contrasting soil water conditions. The results showed that physiological and climatic drivers only partially explained the subdaily flux variations. Stem CH4 and CO2 emissions and N2O uptake varied with soil water content, time of day and between individuals. Stem fluxes decoupled from soil fluxes. Our study contributes to understanding the regulation of stem greenhouse gas fluxes. It suggests that additional variables (e.g. internal gas concentrations, wood-colonising microorganisms, wood density and anatomy) may account for the remaining unexplained variability in stem fluxes, highlighting the need for further studies.

Spatiotemporal variability of air-sea CO2 fluxes in response to El Niño-related marine heatwaves in the tropical Pacific Ocean.

The tropical Pacific is the largest oceanic source of carbon dioxide (CO2) emissions, where persistent marine heatwaves (MHWs) frequently occur. During persistent MHW events which are associated with strong El Niño events, CO2 outgassing is notably reduced, however, its detailed spatiotemporal response to MHWs has not been fully characterized. In this study, we showed a high degree of consistency between CO2 source regions in the central and eastern tropical Pacific Ocean and the occurrence regions with average annual MHW days exceeding 45 days (co-occurring area covers 80% of the area where MHWs occur). The spatiotemporal variability of the air-sea CO2 flux on interannual and longer timescales can be reconstructed from annual MHW days and occurrence frequency, respectively, in the central and eastern Pacific Ocean of the co-occurring region. In this region, El Niño-related MHWs reduce the air-sea CO2 flux density up to 0.4-0.8 molC/m2/yr per 100 MHW days, corresponding to a reduction of CO2 emissions by approximately 0.1 PgC per 100 MHW days. This is a 10%-40% reduction in CO2 emissions during MHW periods, with the strongest impact (30%-40% CO2 emission reduction) in the equatorial Pacific (5°S-5°N) of the central and eastern Pacific Ocean. In contrast, air-sea CO2 flux variations in coastal eastern upwelling region of the co-occurring region are mainly subjected to seasonal mixed layer variations, and thus not notably affected by El Niño-related MHWs on interannual timescales. By establishing the reproducibility between MHWs and air-sea CO2 flux variations, our results pave a way for detailed future spatiotemporal evolutions of MHW-induced changes in air-sea CO2 flux in the tropical Pacific Ocean.

Origin and intra-annual variability of vertical microplastic fluxes in Fram Strait, Arctic Ocean.

Microplastic (MP) pollution has reached the remotest areas of the globe, including the polar regions. In the Arctic Ocean, MPs have been detected in ice, snow, water, sediment, and biota, but their temporal dynamics remain poorly understood. To better understand the transport pathways and drivers of MP pollution in this fragile environment, this study aims to assess MPs (≥ 11μm) in sediment trap samples collected at the HAUSGARTEN observatory (Fram Strait) from September 2019 to July 2021. MP fluxes determined by μ-Fourier transform infrared (FTIR) imaging ranged from 0 to 2.9 MP m-2 d-1, peaking in April 2020 and April 2021, with all detected MPs being <300μm in size. There was no strong correlation between MPs and any of the recorded biogeochemical and physical variables, as each MP flux event was associated with different variables such as biogenic matter, sea ice concentration, or origin. By providing time series data over 21months, this study provides a baseline for future MP flux assessments in Fram Strait, Arctic.

Dynamic massive star formation: Radio flux variability in UCHII regions

Theoretical models of early accretion during the formation process of massive stars have predicted that regions exhibit radio variability on timescales of decades. However, large-scale searches for such temporal variations with sufficient sensitivity have not yet been carried out. Our aim is to identify regions with variable radio wavelength fluxes and to investigate the properties of the identified objects, especially those with the highest level of variability. We compared the peak flux densities of 86 ultracompact regions measured by the GLOSTAR and CORNISH surveys and identified variables that show flux variations higher than 30% over the ∼8 yr timespan between these surveys. We found a sample of 38 variable regions, which is the largest sample identified to date. The overall occurrence of variability is 44±5%, suggesting that variation in regions is significantly more common than prediction. The variable regions are found to be younger than nonvariable regions, all of them meeting the size criterion of hypercompact (HC) regions. We studied the seven regions that show the highest variability (the ``Top7'') with variations &gt; 100%. The Top7 variable regions are optically thick at 4--8 GHz and compact, suggesting they are in a very early evolutionary stage of or regions. There is a significant correlation between variability and the spectral index of the radio emission. No dependence is observed between the variations and the properties of the sources' natal clumps traced by submillimeter continuum emission from dust, although variable regions are found in clumps at an earlier evolutionary stage.

Predictions to Increase Lasso Peptide Production in the Heterologous Host Streptomyces coelicolor M1152.

Production of specialized metabolites are restricted to the metabolic capabilities of the organisms. Genome-scale models (GEM)s are useful to study the whole metabolism and to find metabolic engineering targets to increase the yield of a target compound. In this work we use a modified model of Streptomyces coelicolor M145 to simulate the production of lagmysin A (LP4) and the novel lagmysin B (LP2) lasso peptide, in the heterologous host Streptomyces coelicolor M1152. Overexpression targets were identified using the flux scanning based on enforced objective flux (FSEOF) algorithm and flux variability analysis (FVA), considering growth in minimum and in complex medium. Thirteen reactions were found as candidate metabolic engineering targets for both lasso peptides considering both settings. We propose the overexpression of enzymes of the glycolysis pathway (GAPD, PGK, PGM and ENO) and leucine biosynthesis (IPPS, IPPMIb, IPPMIa, IPMD and OMCDC) to enhance the production of either lagmysin A or B.

Variability of methane content and fluxes in the rybinsk reservoir based on field observations in different seasons of the year

The formation of methane fluxes in the Rybinsk reservoir and the variability of its content in water were investigated during several field campaigns on the reservoir in different seasons. The Rybinsk reservoir is a very large, relatively shallow, low-flow, mesotrophic-eutrophic, morphologically complex basin-valley type reservoir with perennial flow regulation, created on the Upper Volga in 1941. In total, water and air sampling was carried out at 71 stations to determine methane concentration, which was combined with measurements of water column characteristics . As a result, a network of reference stations was established, where regular measurements are made, as well as additional stations in the water area and river estuaries. For control purposes, water samples were taken at the hydroelectric power plant units and downstream of the Sheksninskaya HPP dam, placed within the Rybinsk city. In general, the Rybinsk reservoir is characterised by relatively low methane concentrations - at most stations the average content of dissolved CH4 in water does not exceed 20 µl/l. The lowest concentrations were observed during the winter period. Methane fluxes from the surface of the Rybinsk reservoir vary from 4 to 718 mgC-CH4 m-2 day-1. Specific fluxes in summer period are larger than those measured in autumn, also in summer the spatial variability of the measured fluxes is more significant. Flux values depend on reservoir stratification, oxygen content in water, organic matter in bottom sediments and other factors. Methane degassing through the dam is significantly less than the fluxes from the surface.

The Surprising Long‐Term Evolution of the ULXP NGC 7793 P13

ABSTRACTThe ultra‐luminous x‐ray pulsar (ULXP) NGC 7793 P13 has been regularly monitored with XMM‐Newton, NuSTAR, and Swift for the last 8 years. Here, we present the latest results of this monitoring campaign with respect to the pulse period evolution and spectral variability. We find that since the source recovered from an x‐ray low state in 2020–2022 the spin‐up rate has increased significantly compared with before the off‐state, even though the x‐ray luminosity has not shown an equivalent increase. We find that the x‐ray and optical/UV flux are anti‐correlated, and speculate that this variability might be driven by a large accretion disk, precessing at a super‐orbital period of 7–8 years. We study the spectral behavior in the XMM‐Newton and NuSTAR data, and find very little changes in the spectral shape, despite the large flux variability. This spectral consistency provides further indication that the observed flux variability is a geometric effect and not due to intrinsic changes of the accretion rate.

Congo River: Analysis of suspended sediment flux in a multichannel megasystem in Central Africa

Tropical mega rivers play a crucial role in transferring water and sediment to the oceans. The Congo River is the second largest in the world by volume of water, playing a significant role in the export of fresh water and sediment from the continent to the Atlantic Ocean. This paper aims to analyze the variability of the suspended sediment flux of the Congo River between 2005 and 2018. Suspended Sediment Concentration (SSC), water discharge and water level data were used at the Brazzaville station, which represents 97% of the basin area, and precipitation data for the entire basin. Solid discharge, specific sediment yield and denudation rate of the basin were estimated. The estimated water discharge was 41 268 m³.s-1 for the period between 1947 and 2023, with a bimodal river regime with a flood peak in December and a secondary peak in May. The mean annual SSC estimated for the Congo River was 27.20 mg.L-1. A moderate (r = 0.48) and weak (r = -0.26) correlation was observed between SSC and precipitation, and SSC and water level, respectively, possibly influenced by the basin's terrain characteristics. During the year, the Congo River transfers 33.66 × 106 ton.year-1 of sediment to the ocean, has a specific sediment yield of 9.62 ton.km-2.year-1 and a very low denudation rate (3.37 mm.ky-1).

Atmospheric Variability Drives Anomalies in the Bering Sea Air–Sea Heat Exchange

Abstract High latitudes, including the Bering Sea, are experiencing unprecedented rates of change. Long-term Bering Sea warming trends have been identified, and marine heatwaves (MHWs), event-scale elevated sea surface temperature (SST) extremes, have also increased in frequency and longevity in recent years. Recent work has shown that variability in air–sea coupling plays a dominant role in driving Bering Sea upper-ocean thermal variability and that surface forcing has driven an increase in the occurrence of positive ocean temperature anomalies since 2010. In this work, we characterize the drivers of the anomalous surface air–sea heat fluxes in the Bering Sea over the period 2010–22 using ERA5 fields. We show that the surface turbulent heat flux dominates the net surface heat flux variability from September to April and is primarily a result of near-surface air temperature and specific humidity anomalies. The airmass anomalies that account for the majority of the turbulent heat flux variability are a function of wind direction, with southerly (northerly) wind advecting anomalously warm (cool), moist (dry) air over the Bering Sea, resulting in positive (negative) surface turbulent flux anomalies. During the remaining months of the year, anomalies in the surface radiative fluxes account for the majority of the net surface heat flux variability and are a result of anomalous cloud coverage, anomalous lower-tropospheric virtual temperature, and sea ice coverage variability. Our results indicate that atmospheric variability drives much of the Bering Sea upper-ocean temperature variability through the mediation of the surface heat fluxes during the analysis period. Significance Statement A long-term ocean warming trend and a recent increase in marine heatwaves in the Bering Sea have been identified. Previous work showed that anomalies in the exchange of heat between the ocean and the atmosphere were the primary driver of Bering Sea temperature variability, but the processes responsible for the heat exchange anomalies were unknown. In this work, we show that the atmosphere is the primary driver of anomalies in the Bering Sea air–sea heat exchange and therefore plays an important role in altering the thermal state of the Bering Sea. Our results highlight the importance of understanding more about how the ocean and the atmosphere interact at high latitudes and how this relationship will be affected by future climate change.

The redox potential of soil as an additional factor describing the variability of methane fluxes from a wetland during dry conditions: a case study for Biebrza National Park, Poland

The redox potential of soil as an additional factor describing the variability of methane fluxes from a wetland during dry conditions: a case study for Biebrza National Park, Poland

Evaluation of the Maximum Evaporation and the Priestley‐Taylor Models for Inland Waterbodies

AbstractThe Priestley‐Taylor (PT) model is a classic model of potential evaporation of terrestrial and marine surfaces. It is now recognized that the Bowen ratio (β) implicit in the PT model is too sensitive to temperature. The model also requires the surface net radiation (Rn) as input even though Rn is not an independent external forcing. The maximum evaporation model (MEM) proposed by Yang and Roderick (2019, https://doi.org/10.1002/qj.3481) is a potential candidate for replacing the PT model. Past studies have evaluated the MEM for land ecosystems and for the global ocean. This study represents the first evaluation of the MEM for inland waterbodies. Results are based on eddy‐covariance observation at a large lake and at a small fishpond. Although there were complex error structures and error compensation patterns among its intermediate variables, the MEM was able to reproduce the observed monthly (R2 &gt; 0.95) and interannual variability (R2 &gt; 0.78) in the lake latent heat flux. A key assumption of the MEM, that the incoming and outgoing longwave radiation is coupled, was a reasonable approximation at both the monthly and the annual time scale for the large lake and at the monthly time scale for the small fishpond. This assumption allows the MEM to treat Rn as an intermediate variable instead of a prescribed forcing. These results support the MEM as an alternative to the PT model at locations where Rn measurements are not available. In situations where Rn data is available, a revised PT model with reduced β temperature sensitivity is recommended.

Multiband Optical Variability of the Blazar 3C 454.3 on Diverse Timescales

Due to its peculiar and highly variable nature, the blazar 3C 454.3 has been extensively monitored by the WEBT team. Here, we present for the first time these long-term optical flux and color variability results using data acquired in B, V, R, and I bands over a time span of about two decades. We include data from WEBT collaborators and public archives such as SMARTS, Steward Observatory, and Zwicky Transient Facility. The data are binned and segmented to study the source over this long term when more regular sampling was available. During our study, the long-term spectral variability reveals a redder-when-brighter trend, which, however, stabilizes at a particular brightness cutoff of ∼14.5 mag in the I band, after which it saturates and evolves into a complex state. This trend indicates increasing dominance of jet emission over accretion disk (AD) emission until jet emission completely dominates. Plots of the variation in spectral index (following F ν ∝ ν −α ) reveal a bimodal distribution using a one-day binning. These correlate with two extreme phases of 3C 454.3, an outburst or high-flux state and a quiescent or low-flux state, which are respectively jet- and AD-dominated. We have also conducted intraday variability studies of nine light curves and found that six of them are variable. Discrete correlation function analysis between different pairs of optical wave bands peaks at zero lags, indicating cospatial emission in different optical bands.

Role of QBO and MJO in Sudden Stratospheric Warmings: A Case Study

The impact of the quasi-biennial oscillation (QBO) and Madden–Julian oscillation (MJO) on the dynamics of major sudden stratospheric warmings (SSWs) observed in the winters of 2018, 2019, and 2021 is investigated. Using data from the MERRA-2 reanalysis, we analyze the daily mean variability of critical atmospheric parameters at the 10 hPa level, including zonal mean polar cap temperature, zonal mean zonal wind, and the amplitudes of planetary waves 1 and 2. The results reveal dramatic increases in polar cap temperature and significant wind reversals during the SSW events, particularly in 2018. The analysis of planetary wave (PW) amplitudes demonstrates intensified wave activity coinciding with the onset of SSWs, underscoring the pivotal role of PWs in these stratospheric disruptions. Further examination of outgoing long-wave radiation (OLR) anomalies highlights the influence of QBO phases on tropical convection patterns. During westerly QBO (w-QBO) phases, enhanced convective activity is observed in the western Pacific, whereas the easterly QBO (e-QBO) phase shifts convection patterns to the maritime continent and central Pacific. This modulation by QBO phases influences the MJO’s role during SSWs, affecting tropical and extra-tropical weather patterns. The day-altitude variability of upward heat flux reveals distinct spatiotemporal patterns, with pronounced warming in the polar regions and mixed heat flux patterns in low latitudes. The differences observed between the SSWs of 2017–2018 and 2018–2019 are likely related to the varying QBO phases, emphasizing the complexity of heat flux dynamics during these events. The northern annular mode (NAM) index analysis shows varied responses to SSWs, with stronger negative anomalies observed during the e-QBO phase compared to the w-QBO phases. This variability highlights the significant role of the QBO in shaping the stratospheric and tropospheric responses to SSWs, impacting surface weather patterns and the persistence of stratospheric anomalies. Overall, the study demonstrates the intricate interactions between stratospheric dynamics, QBO, and MJO during major SSW events, providing insights into the broader implications of these atmospheric phenomena on global weather patterns.

On the use of lithogenic tracer measurements in aerosols to constrain dust deposition fluxes to the ocean southeast of Australia

Abstract. Australia contributes a significant amount of dust-borne nutrients (including iron) to the Southern Ocean, which can stimulate marine primary productivity. A quantitative assessment of the variability in dust fluxes from Australia to the surrounding ocean is therefore important for investigating the impact of atmospheric deposition on the Southern Ocean's carbon cycle. In this study, lithogenic trace metals (aluminium, iron, thorium, and titanium) contained in aerosols collected between 2016 and 2021 from kunanyi / Mount Wellington in lutruwita / Tasmania (Australia) were used to estimate dust deposition fluxes. Lithogenic fluxes were calculated using each tracer individually, as well as an average using all four tracers. This latter approach enabled an assessment of the uncertainty associated with flux calculations using only individual tracers. Elemental ratios confirmed the lithogenic nature of each tracer in aerosols when compared with both Australian soil samples and the average Earth's upper continental crust. Lithogenic flux estimates showed annual dust deposition maxima during the austral summer, following the Australian dust storm season, and annual minimum deposition flux over winter. The data provided here will help to constrain model estimates of Southern Hemisphere atmospheric deposition fluxes and their subsequent impact on global ocean biogeochemical cycles.

Heterologous Biosynthesis of Taxifolin in Yarrowia lipolytica: Metabolic Engineering and Genome-Scale Metabolic Modeling.

Taxifolin, also known as dihydroquercetin (DHQ), is a flavonoid recognized for its potent antioxidant properties and a wide range of biological activities, including anti-tumor, antiviral, and immunomodulatory effects. Conventional extraction and chemical synthesis methods for taxifolin are often limited by low yields and associated environmental concerns. In this study, we investigated the heterologous biosynthesis of taxifolin in Yarrowia lipolytica through a combination of metabolic engineering and genome-scale metabolic modeling (GSM), complemented by flux balance analysis (FBA). We engineered Yarrowia lipolytica by introducing key biosynthetic genes and successfully synthesized taxifolin using naringenin (NAR) as a substrate, chosen for its low cost. Fermentation experiments demonstrated an optimal taxifolin yield of 10% at a substrate concentration of 200mg/L naringenin, with a maximum yield of 26.4mg/L taxifolin at 1g/L naringenin. To further enhance production, we applied a marker-free Cre-loxP-based gene integration method, allowing stable genomic integration of key genes, which increased taxifolin yield to 34.9mg/L at 1g/L naringenin. Additionally, intermediate metabolites eriodictyol (ERI) and dihydrokaempferol (DHK) accumulated to concentrations of 89.2mg/L and 21.7mg/L, respectively. Furthermore, we integrated metabolic data into a GSM and applied FBA to optimize the taxifolin biosynthetic pathway. Through Pareto frontier analysis, sensitivity analysis, flux variability analysis, and single gene deletion simulations, we identified key genetic modifications that significantly enhanced taxifolin yield. Overexpression of GND1 and IDP2 increased yields by 94% and 155%, respectively, while knockout of LIP2 led to a 46% increase. Using tri-baffled shake flasks to improve oxygen supply resulted in a 120% yield increase, whereas YPG medium decreased yield by 59%, validating our model's accuracy. To ensure stable and efficient gene expression, we integrated multi-copy constructs into the ribosomal DNA (rDNA) locus of Yarrowia lipolytica, doubling taxifolin production. These results demonstrate the effectiveness of GSM and FBA in addressing bottlenecks in microbial taxifolin biosynthesis and provide a basis for future optimization and large-scale production.

Roles of ecological and hydrological processes in the variability of carbon fluxes in a salt marsh of the Yangtze Estuary: Model simulations vs. measurements

Carbon exchange in coastal wetlands is a complex biochemical process regulated by a combination of meteorological, plant-soil, and hydrological factors. In the Yangtze Estuary, a process-based carbon flux model was developed to further elucidate the spatiotemporal dynamics of carbon fluxes of different marsh species and elevations, incorporating the roles of climatic, hydrological, and geographical factors. The model was validated based on measurements of CO2 and CH4 fluxes using the static chamber and eddy covariance methods. The results showed that the model reproduced well the time series of the net ecosystem change (NEE) and CH4 flux from diel to half-month scales. During tidal cycling, the ecosystem CO2 and CH4 fluxes were suppressed under inundation, and the magnitude of suppression was proportional to the water depth. The landform of the tidal flat determined the submerged height and duration, and the hydrological effects on carbon fluxes varied with elevation. The model also reasonably reflected the negative correlation between tidal height and salinity and carbon fluxes during the spring-neap cycle. Sensitivity tests revealed that temperature and tidal height were the two most critical factors affecting the carbon fluxes. Wavelet coherence analysis further indicated that temperature and tidal height explained most of the periodic variations in NEE at the diel scale. Specifically, temperature dominated CH4 emission dynamics in spring and winter, whereas tides replaced temperature as the dominant factor in summer. The temperature also exhibited a stronger coherent intensity at high elevations, whereas the influence of tides was greater in low-lying regions. This study emphasizes the associated effects of climatic, biological, and hydrological factors on the spatiotemporal heterogeneity of carbon fluxes in the coastal marshes. This coupled model is expected to be beneficial for estimating the carbon sequestration capacity in China's coastal salt marshes under global change conditions.

A multi-frequency, multi-epoch radio continuum study of the Arches cluster with the Very Large Array

Context. The Arches cluster, one of the most massive clusters in the Milky Way, is located about 30 pc in projection from the central massive black hole Sagittarius A* at a distance of ≈8 kpc from Earth. With its high mass, young age, and location in the Galaxy’s most extreme star forming environment, the Arches is an extraordinary laboratory for studying massive stars and clusters. Aims. Our objective is to improve our knowledge of the properties of massive stars and the Arches cluster through high-angular-resolution radio continuum studies. Methods. We observed the Arches cluster with the Karl G. Jansky Very Large Array in the C- and X-bands (central frequencies of 6 and 10 GHz respectively) in two epochs at C-band and five epochs at X-band throughout 2016, 2018, and 2022, covering time spans ranging from 22 days to 6 years. We used the A-configuration to achieve the highest possible angular resolution and cross-matched the detected point-sources with stars detected in the infrared, using proper motion catalogues to ensure cluster membership. Results. We report the most extensive radio point-source catalogue of the cluster to date, with a total of 25 radio detections (7 more than the most recent study). We also created the deepest (2.5 μJy in X-band) images of the cluster so far in the 4 to 12 GHz frequency range. Most of our stellar radio sources (12 out of 18) show a positive spectral index, indicating that the dominant emission process is free-free thermal radiation, which probably originates from stellar winds. We find that radio variability is more frequent than what was inferred from previous observations, and affects up to 60% of the sources associated with bright stellar counterparts, with two of them, F18 and F26, showing extreme flux variability. We propose four of our detections (F6, F18, F19, and F26) as primary candidates for colliding-wind binaries (CWBs) based on their consistent flat-to-negative spectral index. We classify F7, F9, F12, F14, and F55 as CWB binary candidates based on their high flux and/or spectral index variability, and X-ray counterparts. Thus, we infer a 14/23 ≈ 61% multiplicity fraction for the radio stars of the Arches cluster when combining our findings with recent infrared radial velocity studies.

Comparisons of Energetic Electron Observations Between FIREBIRD‐II CubeSats and POES/MetOp Satellites From 2018 to 2020

AbstractPrecipitation into the atmosphere is one of the main processes by which high energy electrons trapped in Earth's inner magnetosphere are lost from the system. Precipitating electrons can affect the chemical composition of the atmosphere and provide insight into the complex dynamics of the Van Allen radiation belts. This study compares energetic electron precipitation measurements at low‐Earth‐orbit by the Focused Investigations of Relativistic Electron Burst Intensity, Range, and Dynamics (FIREBIRD‐II) CubeSats with NOAA Polar‐orbiting Operational Environmental Satellite (POES) and ESA Meteorological Operational satellite (MetOp) satellites, which are equipped with the Medium‐Energy Proton Electron Detector (MEPED). The analysis considers 51 high quality conjunction events at &gt;300 keV during times of low to moderate geomagnetic activity. The spacecraft capture similar electron flux variability, and FIREBIRD‐II observations fall between POES/MetOp and telescopes, likely a result of FIREBIRD‐II sampling both precipitating and mirrored electrons due to uncertainties in pointing direction. Results demonstrate the value of high‐resolution differential energy observations of electron precipitation by low‐cost CubeSats such as FIREBIRD‐II, especially during periods of low flux.

Benthic foraminiferal population dynamics at the Goban Spur off Southwest Ireland reveal glacial-interglacial bottom water ventilation and organic flux variability over the last 420,000 years

Benthic foraminiferal population dynamics at the Goban Spur off Southwest Ireland reveal glacial-interglacial bottom water ventilation and organic flux variability over the last 420,000 years

New interpretation of the two hard X-ray sources IGR J17503-2636 and IGR J17507-2647

We report on the results of X-ray observations ( INTEGRAL and of two hard X-ray sources, IGR\,J17503-2636 and IGR\,J17507-2647, whose nature is not fully elucidated in the literature. Three observations covered the field of IGR\,J17503-2636, in 2020 and twice in 2023. The analysis of the two observations performed in September 2023, six days apart, did not detect allowing us to pose the most stringent 3sigma upper limit on the source flux to date (sim 9.5times 2-10 keV, flux corrected for absorption). This value implies that the amplitude of the X-ray flux variability exceeds a factor of sim 2100, compared with the discovery outburst in 2018. A candidate X-ray periodicity at 0.335397(3) seconds has been barely detected (significance of $ from with (pulsed fraction of (10 pm 1)&lt;!PCT!&gt;). The new data, put into the context of previous literature, allow us to propose a new classification of IGR\,J17503-2636 as a symbiotic X-ray binary, rather than a candidate supergiant fast X-ray transient. IGR\,J17507-2647 was formerly reported below 10 keV only during Chandra observations performed in 2009. We report here on two observations that serendipitously covered the source field in 2020 and in 2023, finding a stable X-ray emission, both in X-ray flux and spectral shape. The long-term, persistent X-ray emission has also been probed by several short observations and by INTEGRAL data spanning several years. We have detected an iron line in the emission (with centroid energy in the range of 6.3-6.6 keV), never reported before in the IGR\,J17507-2647 spectrum. The source properties favor the identification with a cataclysmic variable. stars: neutron - X-rays: binaries - pulsars: individual: IGR\,J17503-2636, IGR\,J17507-2647, IGR\,J17505-2644