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Abstract. Gas isotope thermometry using the isotopes of molecular nitrogen and argonhas been used extensively to reconstruct past surface temperature changefrom Greenland ice cores. The gas isotope ratios δ15N andδ40Ar in the ice core are each set by the amount ofgravitational and thermal fractionation in the firn. The gravitationalcomponent of fractionation is proportional to the firn thickness, and thethermal component is proportional to the temperature difference between thetop and bottom of the firn column, which can be related to surfacetemperature change. Compared to Greenland, Antarctic climate change istypically more gradual and smaller in magnitude, which results in smallerthermal fractionation signals that are harder to detect. This has hamperedapplication of gas isotope thermometry to Antarctic ice cores. Here, we present an analytical method for measuring δ15N andδ40Ar with a precision of 0.002 ‰ per atomicmass unit, a two-fold improvement on previous work. This allows us toreconstruct changes in firn thickness and temperature difference at the SouthPole between 30 and 5 kyr BP. We find that variability in firn thickness iscontrolled in part by changes in snow accumulation rate, which is, in turn,influenced strongly by the along-flowline topography upstream of the icecore site. Variability in our firn temperature difference record cannot beexplained by annual-mean processes. We therefore propose that the ice coregas isotopes contain a seasonal bias due to rectification of seasonalsignals in the upper firn. The strength of the rectification also appears tobe linked to fluctuations in the upstream topography. As further evidencefor the existence of rectification, we present new data from the Dome Fujiice core that are also consistent with a seasonal bias throughout theHolocene. Our findings have important implications for the interpretation of ice coregas records. For example, we show that the effects of upstream topography onice core records can be significant at flank sites like the South Pole – theyare responsible for some of the largest signals in our record. Presumablyupstream signals impact other flank-flow ice cores such as EDML, Vostok, andEGRIP similarly. Additionally, future work is required to confirm theexistence of seasonal rectification in polar firn, to determine how spatiallyand temporally widespread rectifier effects are, and to incorporate therelevant physics into firn air models.

Water-stable isotopes in polar ice cores are a widely used temperature proxy in paleoclimate reconstruction, yet calibration remains challenging in East Antarctica. Here, we reconstruct the magnitude and spatial pattern of Last Glacial Maximum surface cooling in Antarctica using borehole thermometry and firn properties in seven ice cores. West Antarctic sites cooled ~10°C relative to the preindustrial period. East Antarctic sites show a range from ~4° to ~7°C cooling, which is consistent with the results of global climate models when the effects of topographic changes indicated with ice core air-content data are included, but less than those indicated with the use of water-stable isotopes calibrated against modern spatial gradients. An altered Antarctic temperature inversion during the glacial reconciles our estimates with water-isotope observations.

Abstract. The variations of δO2/N2 and δAr/N2 in the Dome Fuji ice core were measured from 112 m (bubbly ice) to 2001 m (clathrate hydrate ice). Our method, combined with the low storage temperature of the samples (−50 ∘C), successfully excludes post-coring gas-loss fractionation signals from our data. From the bubbly ice to the middle of the bubble–clathrate transition zone (BCTZ) (112–800 m) and below the BCTZ (>1200 m), the δO2/N2 and δAr/N2 data exhibit orbital-scale variations similar to local summer insolation. The data in the lower BCTZ (800–1200 m) have large scatter, which may be caused by millimeter-scale inhomogeneity of air composition combined with finite sample lengths. The insolation signal originally recorded at the bubble close-off remains through the BCTZ, and the insolation signal may be reconstructed by analyzing long ice samples (more than 50 cm for the Dome Fuji core). In the clathrate hydrate zone, the scatter around the orbital-scale variability decreases with depth, indicating diffusive smoothing of δO2/N2 and δAr/N2. A simple gas diffusion model was used to reproduce the smoothing and thus constrain their permeation coefficients. The relationship between δAr/N2 and δO2/N2 is markedly different for the datasets representing bubble close-off (slope ∼ 0.5), bubble–clathrate hydrate transformation (∼1), and post-coring gas loss (∼0.2), suggesting that the contributions of the mass-independent and mass-dependent fractionation processes are different for those cases. The method and data presented here may be useful for improving the orbital dating of deep ice cores over the multiple glacial cycles and further studying non-insolation-driven signals (e.g., atmospheric composition) of these gases.

Abstract. Air in polar ice cores provides unique information on past climatic and atmospheric changes. We developed a new method combining wet extraction, gaschromatography and mass spectrometry for high-precision, simultaneous measurements of eight air components (CH4, N2O andCO2 concentrations; δ15N, δ18O, δO2∕N2 and δAr∕N2; and total aircontent) from an ice-core sample of ∼ 60 g. The ice sample is evacuated for ∼ 2 h and melted under vacuum, and thereleased air is continuously transferred into a sample tube at 10 K within 10 min. The air is homogenized in the sample tubeovernight at room temperature and split into two aliquots for mass spectrometric and gas chromatographic measurements. Care is taken to minimize(1) contamination of greenhouse gases by using a long evacuation time, (2) consumption of oxygen during sample storage by a passivation treatment onsample tubes, and (3) fractionation of isotopic ratios with a long homogenization time for splitting. Precision is assessed by analyzing standardgases with artificial ice and duplicate measurements of the Dome Fuji and NEEM ice cores. The overall reproducibility (1 SD) of duplicate ice-coreanalyses are 3.2 ppb, 2.2 ppb and 2.9 ppm for CH4, N2O and CO2 concentrations;0.006 ‰, 0.011 ‰, 0.09 ‰ and 0.12 ‰ for δ15N, δ18O, δO2∕N2and δAr∕N2; and 0.63 mLSTP kg−1 for total air content, respectively. Our new method successfully combines thehigh-precision, small-sample and multiple-species measurements, with a wide range of applications for ice-core paleoenvironmental studies.

Abstract. Air in polar ice cores provides various information on past climatic and atmospheric changes. We developed a new method combining wet extraction, gas chromatography and mass spectrometry, for high-precision, simultaneous measurements of eight air components (CH4, N2O and CO2 concentrations, δ15N, δ18O, δO2/N2, δAr/N2 and total air content) from an ice core sample of ~60 g. The ice sample is evacuated for ~2 hours and melted under vacuum, and the released air is continuously transferred into a sample tube at 10 K within 10 minutes. The air is homogenized in the sample tube overnight at room temperature, and split into two aliquots for mass spectrometric and gas chromatographic measurements. Cares are taken to minimize contamination of greenhouse gases with long evacuation time, consumption of oxygen during sample storage by passivation treatment on sample tubes, and fractionation of isotopic ratios with long homogenization time for splitting. Precisions are assessed by analysing standard gases with artificial ice, and by duplicate measurements of the Dome Fuji and NEEM ice cores. The overall reproducibility (one standard deviation) from duplicate ice-core analyses are 3.2 ppb, 2.2 ppb and 3.1 ppm for CH4, N2O and CO2 concentrations, 0.006, 0.010, 0.09 and 0.12 ‰ for δ15N, δ18O, δO2/N2 and δAr/N2, and 0.67 mlSTP kg-1 for total air content, respectively. Our new method successfully combines the high-precision, small-sample and multiple-species measurements, with a wide range of applications for ice-core paleoenvironmental studies.

We describe a 13-year-old boy with piso-hamate coalition confirmed by X-ray. Computed tomography (CT) and magnetic resonance imaging (MRI) revealed type 1 coalition according to the classification of DeVilliers Minnaar. Piso-hamate coalition is rare, and suspicions should be raised in instances of chronic ulnar-sided wrist pain, particularly in individuals with a history of elevated hand usage, especially amongst athletes engaging in intensive hand grip activities. Surgical resection of the synchondrosis site between the pisiform and the hamate is an efficacious intervention that can mitigate pain. Level of Evidence: Level V (Therapeutic) [ABSTRACT FROM AUTHOR]

The global ocean constitutes the largest heat buffer in the global climate system, but little is known about its past changes. The isotopic and elemental ratios of heavy noble gases (krypton and xenon), together with argon and nitrogen in trapped air from ice cores, can be used to reconstruct past mean ocean temperatures (MOTs). Here we introduce two successively developed methods to measure these parameters with a sufficient precision to provide new constraints on past changes in MOT.The air from an 800-g ice sample - containing roughly 80 mL STP air - is extracted and processed to be analyzed on two independent dual-inlet isotope ratio mass spectrometers. The primary isotope ratios (δ15 N, δ40 Ar and δ86 Kr values) are obtained with precisions in the range of 1 per meg (0.001‰) per mass unit. The three elemental ratio values δKr/N2 , δXe/N2 and δXe/Kr are obtained using sequential (non-simultaneous) peak-jumping, reaching precisions in the range of 0.1-0.3‰.The latest version of the method achieves a 30% to 50% better precision on the elemental ratios and a twofold better sample throughput than the previous one. The method development uncovered an unexpected source of artefactual gas fractionation in a closed system that is caused by adiabatic cooling and warming of gases (termed adiabatic fractionation) - a potential source of measurement artifacts in other methods.The precisions of the three elemental ratios δKr/N2 , δXe/N2 and δXe/Kr - which all contain the same MOT information - suggest smaller uncertainties for reconstructed MOTs (±0.3-0.1°C) than previous studies have attained. Due to different sensitivities of the noble gases to changes in MOT, δXe/N2 provides the best constraints on the MOT under the given precisions followed by δXe/Kr, and δKr/N2 ; however, using all of them helps to detect methodological artifacts and issues with ice quality.

Little is known about the ocean temperature's long-term response to climate perturbations owing to limited observations and a lack of robust reconstructions. Although most of the anthropogenic heat added to the climate system has been taken up by the ocean up until now, its role in a century and beyond is uncertain. Here, using noble gases trapped in ice cores, we show that the mean global ocean temperature increased by 2.57 ± 0.24 degrees Celsius over the last glacial transition (20,000 to 10,000 years ago). Our reconstruction provides unprecedented precision and temporal resolution for the integrated global ocean, in contrast to the depth-, region-, organism- and season-specific estimates provided by other methods. We find that the mean global ocean temperature is closely correlated with Antarctic temperature and has no lead or lag with atmospheric CO2, thereby confirming the important role of Southern Hemisphere climate in global climate trends. We also reveal an enigmatic 700-year warming during the early Younger Dryas period (about 12,000 years ago) that surpasses estimates of modern ocean heat uptake.

Palaeoclimate variations are an essential component in constraining future projections of climate change as a function of increasing anthropogenic greenhouse gases. The Earth System Sensitivity (ESS) describes the multi-millennial response of Earth (in terms of global mean temperature) to a doubling of CO2 concentrations. A recent study used a correlation of inferred temperatures and radiative forcing from greenhouse gases over the past 800,000 years to estimate the ESS from present day CO2 is about 9°C, and to imply a long-term commitment of 3–7°C even if greenhouse gas levels remain at present-day concentrations. However, we demonstrate that the methodology of ref. does not reliably estimate the ESS in the presence of orbital forcing of ice age cycles and therefore conclude that the inferred present-day committed warming is considerably overestimated. There is a Reply to this Comment by Snyder, C. W. Nature 547, http://dx.doi.org/10.1038/nature22804 (2017).

To better understand the surface properties of the Antarctic ice sheet, we measured the specific surface area (SSA) of surface snow during two round-trip traverses between a coastal base near Syowa Station, located 15 km inland from the nearest coast, and Dome Fuji, located 1066 km inland, in East Antarctica from November 2021 to January 2022. Using a handheld integrating sphere snow grain sizer (HISSGraS), which directly measures the snow surface without sampling, we collected 215 sets of SSA data, with each set comprising measurements from 10 surfaces along a 20 m transect. The measured SSA shows no elevation or temperature dependence between 15 and 500 km from the coast (elevation: 615–3000 m), with a mean and standard deviation of 25 ± 9 m 2 kg -1. Beyond this range, SSA increases toward the interior, reaching 45 ± 11 m 2 kg -1 between 800 and 1066 km from the coast (3600–3800 m). SSA shows significant variability depending on surface morphologies and meteorological events. For example, (i) glazed surfaces formed by an accumulation hiatus in katabatic wind areas show low SSA (19 ± 4 m 2 kg -1), decreasing the mean SSA and increasing SSA variability. (ii) Freshly deposited snow shows high SSA (60–110 m 2 kg -1), but the snow deposition is inhibited by snow drifting at wind speeds above 5 m s -1. Our analyses clarified that temperature-dependent snow metamorphism, snowfall frequency, and wind-driven inhibition of snow deposition play crucial roles in the spatial variation of surface snow SSA in the Antarctic inland. The extensive dataset will enable the validation of satellite-derived and model-simulated SSA variations across Antarctica. [ABSTRACT FROM AUTHOR]

Melt layers are clear indicators of extreme summer warmth on polar ice caps. The visual identification of refrozen meltwater as clear bubble-free layers cannot be used to study some past warm periods, because, in deeper ice, bubbles are lost to clathrate formation. We present here a reliable method to detect melt events, based on the analysis of Kr/Ar and Xe/Ar ratios in ice cores, and apply it to the detection of melt in clathrate ice from the Eemian at NEEM, Greenland. Additionally, melt layers in ice cores can compromise the integrity of the gas record by dissolving soluble gases, or by altering gas transport in the firn, which affects the gas chronology. We find that the easily visible 1 mm thick bubble-free layers in the WAIS Divide ice core do not contain sufficient melt to alter the gas composition in the core, and do not cause artifacts or discontinuities in the gas chronology. The presence of these layers during winter, and the absence of anomalies in soluble gases, suggests that these layers can be formed by processes other than refreezing of meltwater. Consequently, the absence of bubbles in thin crusts is not in itself proof of a melt event.

Future Greenland temperature evolution will affect melting of the ice sheet and associated global sea-level change. Therefore, understanding Greenland temperature variability and its relation to global trends is critical. Here, we reconstruct the last 1,000 years of central Greenland surface temperature from isotopes of N2 and Ar in air bubbles in an ice core. This technique provides constraints on decadal to centennial temperature fluctuations. We found that northern hemisphere temperature and Greenland temperature changed synchronously at periods of ~20 years and 40–100 years. This quasi-periodic multi-decadal temperature fluctuation persisted throughout the last millennium, and is likely to continue into the future.