Observational Evidence Research Articles

Consumer Product Chemical Mixtures and Oxylipin-Mediated Inflammation and Oxidative Stress during Early Pregnancy: Findings from a Large US Pregnancy Cohort.

Consumer product chemicals pose an environmental risk to public health. Exposure during pregnancy to consumer product chemicals, particularly phthalates and phenols, may increase the susceptibility to pregnancy disorders by dysregulating inflammation and oxidative stress. However, existing studies rely on downstream and nonmodifiable markers of these processes. Oxylipins are oxidized lipids that act as key upstream drivers of inflammation and oxidative stress. Importantly, oxylipins are responsive to therapeutic interventions and thus potentially modifiable. Using recent advances in lipidomics and statistical approaches to address both individual chemical biomarkers and their mixtures, we determined associations between early pregnancy biomarkers of consumer product chemical exposure and oxylipins in a large prospective cohort. Overall, our results revealed associations among oxylipins produced across several biosynthetic pathways, suggesting a pattern indicative of dysregulated inflammation and elevated levels of oxidative stress. Phthalate metabolites were the primary drivers of associations, particularly for metabolites of low molecular weight phthalates, often used in personal care products. However, we found similar associations for a biomarker of a phthalate replacement that is increasingly used in consumer products. Our study provides observational evidence of specific physiological pathways that may be dysregulated by exposure to consumer product chemicals, including legacy phthalates and phthalate replacements.

Discovery of ionized circumstellar gas emission around the long-period Cepheid l Carinae with ALMA

Cepheid circumstellar emissions have previously been detected using both infrared (IR) excess and IR interferometric observations at a few stellar radii. These studies have shown that these circumstellar emission can be produced by ionized gas, however, there is no direct observational evidence to confirm this hypothesis. In this letter, we explore the continuum emission and a spectrum of the bright and long-period Cepheid ell Car (P=35.56,day) at millimeter-wavelengths to detect possible effects of ionized gas emission. We used ALMA observations of ell Car in two spectral setups in Band 6 (near 212 and 253,GHz, respectively) and compared the measured flux density to what would be expected for the stellar continuum. We also derived the spectral index and probed the presence of radio recombination lines (RRLs). We report statistically significant emission of about 3.5$,mJy in the two spectral ranges, which is about 2.5 times the stellar continuum emission. For the first time, we have also been able to derive the spectral index of the flux density, (S_ν ∝ ν^α$), α=+1.26±0.44 (∼3σ error), which is characteristic of partially optically thick, ionized gas emission. Additionally, we discovered an emission line from a RRL of hydrogen H29α centered on the stellar rest velocity, smaller in spatial extent than about 0 (lesssim 100,AU), with a symmetric profile with a width at half power of 55.3±7.5 (1σ error). These findings confirm the presence of ionized gas emission near ell Car. The millimeter emission detected from ell Car can be attributed to ionized gas emission from the Cepheid's chromosphere. Further radio interferometric observations are necessary to confirm the occurrence of these ionized gas envelopes around Cepheids of different pulsation periods.

Observational and experimental evidence that rapid mass loss is consistent with the flight efficiency hypothesis and not caused by reproductive effort in three passerine species

Abstract Breeding birds often lose mass abruptly around the time that their eggs hatch, but the reasons why and the demographic significance of mass loss are contentious. Energy expenditure during offspring provisioning is one long‐standing explanation that fits with life‐history theory (energetic cost hypothesis). Mass loss may also reflect time constraints that limit foraging and self‐maintenance while warming (i.e. brooding) young (time constraint hypothesis). Alternatively, mass loss may be an adaptive strategy to provide benefits through decreased energetic flight costs while foraging and provisioning young (flight efficiency hypothesis). To test these hypotheses, we measured mass loss across the nesting cycle for three passerine species using an automated weighing system and quantified reproductive effort by filming nests. We also experimentally manipulated reproductive effort using a nest heating experiment to test effects on mass loss. Counter to the energetic cost hypothesis, female mass loss did not match changing parental provisioning effort across the reproductive cycle; mass loss in all three species started about 5 days before eggs hatched and finished well before nestling provisioning effort was greatest. The nest heating experiment reduced female and male provisioning rates but did not influence mass loss in either sex, also rejecting the energetic cost hypothesis. Counter to the time constraint hypothesis, more time spent brooding was associated with less mass loss. Path analysis supported the flight efficiency hypothesis for females, where mass loss was not related to energetic costs or time constraints and was positively associated with fledging more and heavier young, as well as a greater proportion of young. Mass loss also did not influence the chance of double‐brooding or survival to the next breeding season. Males lost mass steadily over the nesting cycle, but our results did not strongly support one hypothesis. Ultimately, results supported mass loss providing adaptive benefits for females, while rejecting reproductive cost hypotheses often expected under life‐history theory. Read the free Plain Language Summary for this article on the Journal blog.

Dietary Acid Load and Human Health: A Systematic Review and Meta-analysis of Observational Studies.

Dietary acid load (DAL) plays an important role in different aspects of human health. The aim of this meta-analysis was to systematically synthesize the observational evidence reporting on the associations between the DAL (represented by a potential renal acid load [PRAL] and net endogenous acid production [NEAP]) and a range of health outcomes. A systematic search of Medline (via PubMed), EMBASE, Scopus, and Web of Science was performed to identify eligible studies. Study screening and risk-of-bias assessment were conducted by 2 independent reviewers. The credibility of each outcome was graded based on predefined criteria: pooled effect size with corresponding 95% CI, 95% prediction interval, heterogeneity, small-study effect, and excess significance bias. In total, 118 observational studies (case-control [n = 22], cross-sectional [n = 65], and cohort [n = 31]) on 38 outcomes were included, incorporating a total population of 1 014 081 participants. Overall, 21/37 and 20/38 of the outcomes reported statistically significant effect sizes for PRAL and NEAP, respectively. The credibility of the evidence for PRAL was rated convincing (class I) for type 2 diabetes (T2D), and as highly suggestive evidence (class II) for overall cancer and systolic blood pressure. By assessing the credibility of the evidence for NEAP, T2D and overall cancer presented convincing evidence (class I) and breast cancer presented highly suggestive evidence (class II). The remaining outcomes presented class III (suggestive) or lower evidence (weak or no association). The higher acid-forming potential of diet was associated with a higher risk of T2D and overall cancer. Since this meta-analysis included observational studies and some of the associations were graded as weak, caution should be exercised in interpreting these associations. Further cohort studies are required with consideration of other factors that can cause biases. PROSPERO registration no. CRD42022336050.

Interactions between Dust Aerosols and the Ultra-high Atmospheric Boundary Layer: Case study of vertical observation over the Taklimakan Desert, China

A deep atmospheric boundary layer (ABL) with a height of up to 4,000–6,000 m can develop over the Taklimakan Desert (TD). Nevertheless, the deep ABL in the TD was only studied for clean days. To date, the observational evidence concerning the interaction between the ultra-high ABL and dust aerosols over the TD remains scarce. In May 2022, we conducted the inaugural observational particle-sounding experiment in the TD, selecting representative cases of light and heavy dust days. The results captured a distinctive stratified structure of the daytime ABL induced by dust aerosols characterized by an ultra-thick residual layer (RL) in the afternoon. On heavy dust days, the daytime ABL was divided into convective boundary layer (CBL), capping inversion layer (CIL), RL and residual capping inversion layer (RCIL). Dust aerosols exerted a warming effect in the atmosphere reaching a maximum of about 1.0 K/day at the top of the dust aerosol layer and causing a temperature inversion. A CIL about 1,000 m occurred between the CBL and the RL, which acted as a barrier, restraining CBL development and hindering dust aerosol transport. Furthermore, a deeper stable boundary layer on heavy dust days at night was observed. A unique vertical structure of nocturnal dust aerosol concentrations peaks of 477μg/m3 was also observed in the deep RL at 1800-2600 m. The radiation effects of dust aerosols strengthened and weakened the stability of the RL above and below the dust layer, respectively. The study provided vertical observational evidence of the impact of dust aerosols on the deep ABL structure, thus contributing to a more profound comprehension of aerosol–radiation interactions over the desert arid region.

Observational evidence of the Kuroshio meander and its propagation in the East China Sea

Observational evidence of the Kuroshio meander and its propagation in the East China Sea

Plasma proteomic evidence for increased β-amyloid pathology after SARS-CoV-2 infection.

Previous studies have suggested that systemic viral infections may increase risks of dementia. Whether this holds true for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus infections is unknown. Determining this is important for anticipating the potential future incidence of dementia. To begin to do this, we measured plasma biomarkers linked to Alzheimer's disease pathology in the UK Biobank before and after serology-confirmed SARS-CoV-2 infections. SARS-CoV-2 infection was associated with biomarkers associated with β-amyloid pathology: reduced plasma Aβ42:Aβ40 ratio and, in more vulnerable participants, lower plasma Aβ42 and higher plasma pTau-181. The plasma biomarker changes were greater in participants who had been hospitalized with COVID-19 or had reported hypertension previously. We showed that the changes in biomarkers were linked to brain structural imaging patterns associated with Alzheimer's disease, lower cognitive test scores and poorer overall health evaluations. Our data from this post hoc case-control matched study thus provide observational biomarker evidence that SARS-CoV-2 infection can be associated with greater brain β-amyloid pathology in older adults. While these results do not establish causality, they suggest that SARS-CoV-2 (and possibly other systemic inflammatory diseases) may increase the risk of future Alzheimer's disease.

The Association Between Temporomandibular Disorders and Tinnitus: Evidence and Therapeutic Perspectives from a Systematic Review

Background/Objectives: Tinnitus, often described as a ringing in the ears, affects a significant portion of the population, varying in perception and severity. Methods: This systematic review investigates the correlation between tinnitus and temporomandibular joint disorders (TMDs) within a PRISMA-compliant framework, ensuring methodological transparency and rigor. Using databases, such as PubMed, Scopus, and Web of Science, we analyzed studies from the past decade to evaluate clinical and observational evidence. Results: A significant association between TMD and tinnitus was found, with somatosensory and neuroplastic mechanisms contributing to this relationship. Key therapeutic approaches identified include manual therapy and multidisciplinary treatments, demonstrating potential clinical efficacy. Conclusions: However, the available evidence remains inconsistent, emphasizing the need for further research with standardized methodologies to improve understanding and refine therapeutic strategies. This review provides a foundation for future studies aiming to enhance tinnitus management by addressing underlying TMD-related mechanisms.

Searching for new variable white dwarfs: The discovery of the three new pulsating and three new binary systems

In recent years, approximately 150 low-mass white dwarfs (WDs), typically with masses below $0.4 M_ ⊙ $, have been discovered. Observational evidence indicates that most of these low-mass WDs are in binary systems, supporting binary evolution scenarios as their primary formation pathway. A few extremely low-mass (ELM) WDs in this population have also been found to be pulsationally variable. In this work we present a comprehensive analysis aimed at identifying new variable low-mass WDs. From our candidate selection, 16 objects were identified as being within the ZZ Ceti instability strip. Those objects were observed over multiple nights using high-speed photometry from the SOAR/Goodman and SMARTS-1m telescopes. Our analysis led to the discovery of three new pulsating WDs: one pulsating ELM WD, one low-mass WD, and one ZZ Ceti star. Additionally, we identified three objects in binary systems, two with ellipsoidal variations in their light curves (one of which is likely a pre-ELM star) and a third that shows a reflection effect.

Fast-rotating A- and F-type Stars with Hα Emissions in NGC 3532: Candidate UV-dim Stars?

Abstract Extended main-sequence stars that are dim in the ultraviolet passbands of the Hubble Space Telescope (UV-dim stars) are found in several young and intermediate-age star clusters in the Magellanic Clouds (MCs). The obscuring of the dust in the disks of stars expelled as a result of fast rotation has been suggested to be responsible for the appearance of UV-dim stars and to play an important role in the formation of extended main sequences. In this paper, we report a population of A- and F-type stars that show Hα emission features in their spectra in the young (~340 Myr old) neighboring Galactic star cluster NGC 3532. By fitting the observed absorption profiles, we found that most Hα emitters are fast-rotating stars, indicating that they form decretion disks by fast rotation like Be stars. As A- and F-type stars dominate the extended main-sequence turnoff regions of intermediate-age clusters, their appearance provides observational evidence to support the dust extinction scenario for these clusters, and they might be the counterparts of UV-dim stars that are detected in remote MC star clusters such as NGC 1783.

Structure Functions of Rotation Measures Revealing the Origin of Fast Radio Bursts

Abstract Structure function (SF) analysis is a powerful tool for studying plasma turbulence. Theoretically, the SF of Faraday rotation measure (RM) is expected to include a geometric component due to the relative orientation of sight lines through an ordered magnetic field. However, observational evidence for this component remains elusive. Here, we report that the SFs of the binary PSR B1744–24A and the repeating fast radio burst (FRB) 20201124A exhibit both a periodic geometric component, caused by binary orbital motion, and a flat statistical component. The statistical component, induced by stochastic fluctuations in electron density and magnetic field, aligns with RM scatter derived from pulse depolarization. These findings indicate that FRB 20201124A has a binary origin and suggest that the periodic geometric component can serve as a diagnostic tool to identify binary companions.

Persistent GeV Counterpart to the Microquasar GRS 1915+105

Abstract Microquasars are compact binary systems hosting collimated relativistic jets. They have long been proposed as cosmic-ray accelerators, probed via the gamma-ray emission produced by relativistic particles. However, the observational evidence is steadily increasing but limited: there are around 20 microquasars known to date, of which only 3 have so far been firmly detected in the GeV gamma-ray range, always in a flaring or special spectral state. Here we present Fermi-LAT observations of the region around the microquasar GRS 1915+105, which reveal the presence of previously unknown multi-GeV emission consistent with the position of the microquasar. No periodicity or variability is found, indicating a persistent source of gamma rays. The properties of the emission are consistent with a scenario in which protons accelerated in the jets interact with nearby gas and produce gamma rays. We find that if the jet has been operating at an average of 1% of the Eddington limit for 10% of the time that GRS 1915+105 spent in its current mass transfer state, the transfer of 10% of the available power to protons is enough to reach the ∼3 × 1049 erg required to explain the GeV signal. Therefore, our results support a scenario in which microquasars with low-mass stellar companions act as hadronic accelerators, strengthening the idea that microquasars as a class contribute to at least some fraction of the observed cosmic-ray flux.

Quantifying the acceleration of multidecadal global sea surface warming driven by Earth’s energy imbalance

Abstract Global mean sea surface temperature (GMSST) is a fundamental diagnostic of ongoing climate change, yet there is incomplete understanding of multi-decadal changes in warming rate and year-to-year variability. Exploiting satellite observations since 1985 and a statistical model incorporating drivers of variability and change, we identify an increasing rate of rise in GMSST. This accelerating ocean surface warming is physically linked to an upward trend in Earth’s energy imbalance (EEI). We quantify that GMSST has increased by 0.54 ± 0.07 K for each GJ m–2 of accumulated energy, equivalent to 0.17 ± 0.02 K decade‒1 (W m‒2)‒1. Using the statistical model to isolate the trend from interannual variability, the underlying rate of change of GMSST rises in proportion with Earth’s energy accumulation from 0.06 K decade–1 during 1985–89 to 0.27 K decade–1 for 2019–23. While variability associated with the El Niño Southern Oscillation triggered the exceptionally high GMSSTs of 2023 and early 2024, 44% (90% confidence interval: 35%–52%) of the +0.22 K difference in GMSST between the peak of the 2023/24 event and that of the 2015/16 event is unexplained unless the acceleration of the GMSST trend is accounted for. Applying indicative future scenarios of EEI based on recent trends, GMSST increases are likely to be faster than would be expected from linear extrapolation of the past four decades. Our results provide observational evidence that the GMSST increase inferred over the past 40 years will likely be exceeded within the next 20 years. Policy makers and wider society should be aware that the rate of global warming over recent decades is a poor guide to the faster change that is likely over the decades to come, underscoring the urgency of deep reductions in fossil-fuel burning.

Sodium-glucose cotransporter 2 inhibitors and outcomes in transthyretin amyloid cardiomyopathy: Systematic review and meta-analysis.

Transthyretin amyloid cardiomyopathy (ATTR-CM) commonly leads to heart failure but has traditionally been an exclusion criterion in randomized clinical trials (RCTs) of sodium-glucose cotransporter 2 inhibitors (SGLT2i); therefore, the effects of these drugs in this population remain undocumented. In light of recent studies, this meta-analysis aimed to investigate the effect of SGLT2i on the prognosis of patients with ATTR-CM. A comprehensive search of Medline, Scopus, and the Cochrane Library was conducted up to November 17, 2024. Study selection, data extraction and quality assessment were carried out independently by two investigators. Associations of SGLT2i with outcomes were pooled using random-effects meta-analyses. A total of five studies (9766 participants, 4 propensity score-matched) were included. The use of SGLT2i was associated with significant reductions in all-cause mortality [hazard ratio (HR) .54, 95% confidence interval (CI) .44-.66], cardiovascular mortality (HR .39, 95% CI .23-.65), major adverse cardiovascular events (HR .71, 95% CI .61-.83), and heart failure hospitalizations (HFHs) (HR .63, 95% CI .52-.77) compared to non-use. The odds of cardiac arrhythmias were significantly lower among SGLT2i users compared to non-users [odds ratio (OR) .73, 95% CI .65-.83]. Specifically, SGLT2i use was associated with significant reductions in the odds of atrial fibrillation (AF) (OR .75, 95% CI .62-.91), ventricular tachycardia (OR .72, 95% CI .59-.88), and sudden cardiac arrest (OR .71, 95% CI .50-.99). The use of SGLT2is may be associated with a more favourable prognosis in patients with ATTR-CM. Adequately powered, long-term RCTs are required to validate the available observational evidence.

Navigating the Nuances Around Extubation Decisions and Observational Evidence.

Navigating the Nuances Around Extubation Decisions and Observational Evidence.

Detection of ubiquitous circumbinary matter in hot subdwarfs formed from common-envelope ejections

ABSTRACT The formation of compact binary systems is largely driven by their evolution through a common envelope (CE) phase, crucial for understanding phenomena such as type Ia supernovae and black hole mergers. Despite their importance, direct observational evidence for CE material has been elusive due to the transient nature of these envelopes. Numerical simulations suggest that some envelope material may persist post-ejection. In this study, we investigate circumstellar material (CSM) surrounding hot subdwarf (sdB) stars, focusing on material ejected during the CE phase of binary evolution. We analyse Ca ii K absorption lines in 727 sdB candidates from the LAMOST-LRS survey, selecting 145 stars with strong absorption features, indicating the presence of CSM. We compare the velocities of the Ca ii K lines with the systemic velocities of sdB binaries, confirming that the material originates from ejected CE material. The results show that the CSM persists long after the CE event, suggesting the formation of a stable, long-lived circumstellar environment around sdB stars. This study enhances our understanding of the role of CSM in post-CE evolution and provides new insights into the physical processes shaping the evolution of sdB binaries.

P1168 Real-world evidence comparison of the effectiveness of ustekinumab with anti-TNF or vedolizumab in ulcerative colitis: 2-year maintenance therapy results from the prospective, observational RUN-UC study

Abstract Background Observational real-world evidence (RWE) studies on the effectiveness of ustekinumab (UST) in ulcerative colitis (UC) are needed in addition to RCTs, which may not represent everyday clinical practice. For this reason, the prospective, controlled, propensity score (PS)-adjusted RUN-UC study was conducted on UC patients starting a new biologic therapy with a follow-up period of up to 3 years. The aim of the present analysis was to evaluate the effectiveness of 2-year maintenance therapy with UST vs. anti-TNF or vedolizumab (VDZ). Methods Between 2020-2022, 507 UC patients starting a new therapy with UST or other biologics were enrolled in 34 IBD-experienced centres in Germany. After the exclusion of patients with a stoma, small molecules and missing outcomes, the final sample consisted of 483 patients. Clinical remission (CR) (pMayo ≤ 1 plus a bleeding subscore=0) and steroid-free remission (CR and no systemic use of steroids or oral budesonide) were considered as outcomes. PS adjustment with inverse probability of treatment weighting (IPTW) was implemented to reduce confounders' effect. Results A total of 483 UC-patients [153 UST (bio-naïve: 13), 165 anti-TNF (ADA: 30.3%, IFX: 61.8%, GOL: 7.9%) (bio-naïve: 114) and 165 VDZ (bio-naïve: 106)] were included in the analysis. The PS-adjustment reduced systemic differences in the baseline parameters (UST/anti-TNF/VDZ: 43.1/46.1/50.9% males, 23.5/24.2/20.6% EIMs), in particular, the "bio-experienced" characteristic was also equalised, between the groups. Treatment persistence over 24 months showed differences between UST (68.6%), VDZ (73.3%) and anti-TNF (58.8%) (p=0.012), but this was only statistically significant for VDZ vs anti-TNF (p=0.005) but not for UST vs VDZ (p> 0.05) and UST vs anti-TNF (p>0.05) (Figure 1). The PS-weighted 24-month effectiveness (n=367) of UST (mITT analysis) in terms of clinical remission and steroid-free remission (Table 1) differed between the following groups (CR: UST 33.3%, anti-TNF 30.2%, VDZ 48.0%) compared to VDZ (p=0.031), but not compared to anti-TNF (UST vs anti-TNF p>0.05 and anti-TNF vs VDZ p=0.005). A sub-analysis evaluating steroid-free remission in bio-experienced patients after one prior anti-TNF treatment showed no statistical difference. was (UST 41.5%, anti-TNF 20.0% and VDZ 43.8%; p=0.130). Conclusion In this prospective RUN-UC study with PS-weighted groups, UST, anti-TNF and VDZ showed a more variable 24-month effectiveness, favouring VDZ over UST and anti-TNF. However, in a subgroup of bio-experienced patients with only one anti-TNF before baseline, steroid-free remission was numerically but not statistically higher with UST and VDZ than with anti-TNF.

Montelukast Use and the Risk of Neuropsychiatric Adverse Events in Children

Spontaneous reports have indicated that montelukast increases the risk of neuropsychiatric adverse events, and the US Food and Drug Administration added a boxed warning about these risks in 2020. However, the potential mechanism is not well understood, and the observational evidence is scarce, particularly in children. To assess the potential association between the use of montelukast and the risk of neuropsychiatric adverse events in children and adolescents. This nationwide register-based cohort study used data from Sweden from January 1, 2007, to November 30, 2021. Participants included children aged 6 to 17 years who used montelukast and long-acting β-agonists (LABA). Data analysis was performed from December 2023 to April 2024. Montelukast vs LABA. The primary outcome, any neuropsychiatric adverse event, was a composite of secondary outcomes, including anxiety; depression; sleep-related disorders; suicide and suicidal actions; disrupted control of activity, attention, and behavior; and confusion and psychotic-like symptoms. Outcomes were defined on the basis of diagnosis codes and dispensings of prescription drugs for specific neuropsychiatric symptoms. Patients were followed up from drug initiation to discontinuation, and treatment and censoring weights were used to adjust for potential confounding on baseline and selection bias from informative censoring. Pooled logistic regression was used to estimate hazard ratios (HRs). The final cohort included 74 291 children (mean [SD] age, 12.3 [3.3] years; 35 446 female [47.7%]); 26 462 used montelukast and 47 829 used LABA. During a mean (SD) follow-up of 5.8 (3.2) months, 310 neuropsychiatric adverse events in the montelukast patients and 566 events in the LABA patients were identified. In the weighted cohort, the incidence rates of neuropsychiatric adverse events were 2.39 per 100 patient-years among the montelukast users and 2.41 per 100 patient-years among the LABA users. This translated to a weighted HR of 0.99 (95% CI, 0.84-1.16). No substantial differences were observed between the montelukast and LABA patients when analyzing the risk of specific neuropsychiatric adverse events: the HRs were 0.79 (95% CI, 0.54-1.14) for anxiety; 1.16 (95% CI, 0.70-1.95) for depression; 0.93 (95% CI, 0.76-1.13) for sleep-related disorders; 1.31 (95% CI, 0.64-2.69) for suicide and suicidal actions; 1.27 (95% CI, 0.84-1.90) for disrupted control of activity, attention, and behavior; and 0.51 (95% CI, 0.05-5.53) for confusion and psychotic-like symptoms. The risk of the primary outcome was consistent over subgroups and a range of sensitivity analyses. In this large study of children and adolescents based on data from routine clinical practice, there was no association between use of montelukast and the risk of neuropsychiatric adverse events. In aggregation with other robust observational studies, these results can inform the management of asthma and allergic rhinitis in this patient group.

Wave erosion, frontal bending, and calving at Ross Ice Shelf

Abstract. Ice shelf calving constitutes roughly half of the total mass loss from the Antarctic ice sheet. Although much attention is paid to calving of giant tabular icebergs, these events are relatively rare. Here, we investigate the role of frontal melting and stresses at the ice shelf front in driving bending and calving on the scale of ∼100 m, perpendicular to the ice edge. We focus in particular on how buoyant underwater “feet” that protrude beyond the above-water ice cliff may cause tensile stresses at the base of the ice. Indirect and anecdotal observations of such feet at the Ross Ice Shelf front suggest that the resulting bending may be widespread and can trigger calving. We consider satellite observations together with an elastic beam model and a parameterization of wave erosion to better understand the dynamics at the ice shelf front. Our results suggest that on average frontal ablation rather consistently accounts for 20±5 m yr−1 of ice loss at Ross Ice Shelf, likely mostly due to wave erosion and smaller-scale, 𝒪(100 m), foot-induced calving. This constitutes only ∼2 % of the total frontal mass loss (since near-front ice velocities are ∼1000 m yr−1). Observational evidence suggests that sporadic larger events can skew this rate (we document one foot-induced calving event of size ∼1 km). Stresses from foot-induced bending are likely not sufficient to initiate crevassing but rather act to propagate existing crevasses. In addition, our results support recent findings by Buck (2024) that additional bending moments, likely due to temperature gradients in the ice, may play a role in driving frontal deflections. The highly variable environment, irregularity of pre-existing crevasse spacing, and complex rheology of the ice continue to pose challenges in better constraining the drivers behind the observed deformations and resulting calving rates.

Irradiation origin and stability of CO on trans-Neptunian objects. Laboratory constraints and observational evidence from JWST/DiSCo-TNOs

The James Webb Space Telescope large program DiSCo-TNOs has recently shown that CO_2 ice is ubiquitous on 54 medium-size trans-Neptunian objects (TNOs). TNO surfaces are found to define three main spectral and thus compositional groups that are likely linked to their position before planetary migration. CO ice is observed on the spectral type that is richest in CO_2 and on the type that is richer in CH_3OH and organics. Considerations on the thermal evolution of TNOs predicted the depletion of hypervolatiles such as CO from their surface layers, however. We investigate a potential irradiation origin of CO as well as its stability by studying the distribution of CO in two TNO compositional types and compared it with irradiation experiments. We studied the 4.68 μm band of CO and the 2.70 μm band of CO_2 to probe the relation between the two molecules in 33 TNOs. We performed ion irradiation experiments on CO_2 and CH_3OH ices at 45 and 60 K with 30 keV H^+. We compared the laboratory spectra to TNO observations by focusing on the band areas and positions. We find that the two types of surfaces in which CO is detected are very distinct in terms of their relative abundances and chemical environment. CO that is observed on surfaces that are rich in CO_2 are consistent with being produced by CO_2 irradiation, specifically, at 45 K. On objects that are rich in CH_3OH and complex organics, CO is more likely formed by irradiation of CH_3OH. As the CO band areas are only partly related with temperature, the chemical environment plays a major role in the CO retention. We find that the CO that is observed on TNO surfaces is compatible with being a secondary molecule that is entirely formed by late irradiation processes. Its abundance and stability is mostly controlled by the matrix from which it formed.