Ice Core Research Articles

Ultra-efficient and thermally-controlled atmospheric structure deicing strategy based on the Peltier effect

Snow and ice coverage pose significant threats to the safe and stable operation of energy equipment. To address the challenges of high power consumption and thermal damage to materials resulting from prolonged use of thermal ice melting technology, this study developed and tested a low-power, thermally controlled de-icing system. The system employs thermoelectric material as the heating element to minimize power consumption and prevent thermal damage to the substrate material. Compared to traditional thermal elements, it offers advantages such as single-sided heat production, a high thermal performance coefficient, and a rapid temperature rise rate. Investigating the effects of temperature difference and current on the heat production coefficient of the system and conducts comparative experiments on the thermal response of different heating elements in low-temperature environments. Furthermore, to further reduce power consumption and minimize unnecessary sensible heat within the ice layer, the thermal control system is designed to maintain the interface temperature between 3 and 5 ℃. This approach selectively melts the interface ice layer to form a water film, facilitating ice layer removal through gravity and centrifugal force. The de-icing energy density achieved with this method is only 10.31 J/cm2, resulting in a 32.167 % reduction in power consumption compared to continuous heating. For the flat plate heating structure, the study explores the physical mechanism of interface temperature control by establishing the relationship between temperature and current through a thermal circuit model. The calculated results closely align with experimental findings, with the maximum error not exceeding 15 %.

Human activity over natural inputs determines the bacterial community in an ice core from the Muztag ata glacier

Human activity over natural inputs determines the bacterial community in an ice core from the Muztag ata glacier

Insights Into Changing Interglacial Conditions in Subarctic Canada From MIS 11 Through MIS 5e From Seasonally Resolved Speleothem Records

AbstractHigh‐resolution records from past interglacial climates help constrain future responses to global warming, yet are rare. Here, we produce seasonally resolved climate records from subarctic‐Canada using micron‐scale measurements of oxygen isotopes (δ18O) in speleothems with apparent annual growth bands from three interglacial periods—Marine Isotope Stages (MIS) 11, 9, and 5e. We find 3‰ lower δ18O values during MIS 11 than MIS 5e, despite MIS 11 likely being warmer. We explore controls on high‐latitude speleothem δ18O and suggest low MIS 11 δ18O values reflect greater contribution of cold‐season precipitation to dripwater from longer annual ground thaw durations. Other potential influences include changes in precipitation source and/or increased fraction of cold‐season precipitation from diminished sea ice in MIS 11. Our study highlights the potential for high‐latitude speleothems to yield detailed isotopic records of Northern Hemisphere interglacial climates beyond the reach of Greenland ice cores and offers a framework for interpreting them.

Decadal-to-centennial increases of volcanic aerosols from Iceland challenge the concept of a Medieval Quiet Period

AbstractExisting global volcanic radiative aerosol forcing estimates portray the period 700 to 1000 as volcanically quiescent, void of major volcanic eruptions. However, this disagrees with proximal Icelandic geological records and regional Greenland ice-core records of sulfate. Here, we use cryptotephra analyses, high-resolution sulfur isotope analyses, and glaciochemical volcanic tracers on an array of Greenland ice cores to characterise volcanic activity and climatically important sulfuric aerosols across the period 700 to 1000. We identify a prolonged episode of volcanic sulfur dioxide emissions (751–940) dominated by Icelandic volcanism, that we term the Icelandic Active Period. This period commences with the Hrafnkatla episode (751–763), which coincided with strong winter cooling anomalies across Europe. This study reveals an important contribution of prolonged volcanic sulfate emissions to the pre-industrial atmospheric aerosol burden, currently not considered in existing forcing estimates, and highlights the need for further research to disentangle their associated climate feedbacks.

Fifty years of firn evolution on Grigoriev ice cap, Tien Shan, Kyrgyzstan

Abstract. Grigoriev ice cap, located in the Tien Shan mountains of Kyrgyzstan, has a rich history of firn and ice core drilling starting as early as 1962. Here we extend the exceptional record and describe an 18 m firn core, drilled in February 2018 on the summit of Grigoriev ice cap, at 4600 m a.s.l. The core has been analyzed for firn stratigraphy, major ions, black carbon, water stable isotope ratios and total β activity. We find that the core covers 46±3 years and overlaps by 2 to 3 decades with legacy cores. A good agreement is found in major ion concentrations for the overlapping period. Concentrations of black carbon and major ions are reduced since the early 2000s, indicating the onset of meltwater runoff. Nevertheless, general concentration trends of these species are consistent with observations and Central Asian ice core records, since emissions were highest during periods when melt influence was negligible. The record of water stable isotopes does not reflect the strong increase of air temperatures during the last decades, implying that water stable isotope ratios ceased to be proxies of temperature variations at this site. Apart from runoff evidence, however, the firn's thermal regime appears remarkably unchanged. Firn temperatures in 2018 were the highest on record (∼-1.6 °C at ∼17 m depth). However, temperatures in 2023 are again similar to the early 2000s at ∼-2.5 °C. Furthermore, we find little change in net accumulation since the 1980s. We hypothesize (i) that firn temperatures are stabilized by the removal of latent heat through lateral meltwater runoff, and (ii) that mass loss by runoff is compensated by an increase in accumulation. Data from a nearby weather station support the latter hypothesis.

Statistical appraisal of geothermal heat flow observations in the Arctic

Abstract. Geothermal heat flow is an important boundary condition for ice sheets, affecting, for example, basal melt rates, but for ice-covered regions, we only have sparse heat flow observations with partly high uncertainty of up to 30 m W m−2. In this study, we first investigate the agreement between such pointwise heat flow observations and solid Earth models, applying a 1D steady-state approach to perform a statistical analysis for the entire Arctic region. We find that most of the continental heat flow observations have a high reliability and agreement to solid Earth models, except a few data points, such as, for example, the NGRIP (North Greenland Ice Core Project) point in central Greenland. For further testing, we perform a conditional simulation with focus on Greenland in which the local characteristics of heat flow structures can be considered. Simple kriging shows that including or excluding the less reliable NGRIP point has a large influence on the surrounding heat flow. The geostatistical analysis with the conditional simulation supports the assumption that NGRIP might not only be problematic for representing a regional feature but likely is an outlier. Basal melt estimates show that such a local spot of high heat flow results in local high basal melt rates but leads to less variation than existing geophysical models.

Using Icepack to reproduce ice mass balance buoy observations in landfast ice: improvements from the mushy-layer thermodynamics

Abstract. Icepack (v1.1.0) – the column thermodynamics model of the Community Ice CodE (CICE) version 6 – is used to assess how changing the thermodynamics from the Bitz and Lipscomb (1999) physics (hereafter BL99) to the mushy-layer physics impacts the model performance in reproducing in situ landfast ice observations from two ice mass balance (IMB) buoys co-deployed in the landfast ice close to Nain (Labrador) in February 2017. To this end, a new automated surface retrieval algorithm is used to determine the in situ ice thickness, snow depth, basal ice congelation and snow-ice formation from the measured vertical temperature profiles. Icepack simulations are run to reproduce these observations using each thermodynamics scheme, with a particular interest in how the different physics influence the representation of snow-ice formation and ice congelation. Results show that the BL99 parameterization represents well the ice congelation but underrepresents the snow-ice contribution to the ice mass balance. In particular, defining snow-ice formation based on the hydrostatic balance alone does not reproduce the negative freeboards observed for several days in the IMB observations, resulting in an earlier snow-flooding onset, a positive ice thickness bias and reduced snow depth variations. We find that the mushy-layer thermodynamics with default parameters significantly degrades the model performance, overestimating both the congelation growth and snow-ice formation. The simulated thermodynamics response to flooding, however, better represents the observations, and the best results are obtained when allowing for negative freeboards in the mushy-layer physics. We find that the mushy-layer thermodynamics produces a larger variability in congelation rates at the ice bottom interface, alternating between periods of exceedingly fast growth and periods of unrealistic basal melt. This pattern is related to persistent brine dilution in the lowest ice layer by the congelation and brine drainage parameterizations. We also show that the mushy-layer congelation parameterization produces significant frazil formation, which is not expected in a landfast ice context. This behavior is attributed to the congelation parameterization not fully accounting for the conductive heat flux imbalance at the ice–ocean boundary. We propose a modification of the mushy-layer congelation scheme that largely reduces the frazil formation and allows for better tuning of the congelation rates to match the observations. Our results demonstrate that the mushy-layer physics and its parameters can be tuned to closely match the in situ observations, although more observations are needed to better constrain them.

Reconstruction of warm-season temperatures in central Europe during the past 60 000 years from lacustrine branched glycerol dialkyl glycerol tetraethers (brGDGTs)

Abstract. Millennial-scale climate variations during the last glacial period, such as Dansgaard–Oeschger (DO) cycles and Heinrich events, have been extensively studied using ice core and marine proxy records. However, there is a limited understanding of the magnitude of these temperature fluctuations in continental regions, and questions remain about the seasonal signal of these climate events. This study presents a 60 000-year-long temperature reconstruction based on branched glycerol dialkyl glycerol tetraethers (brGDGTs) extracted from lake sediments from the Eifel Volcanic Field, Germany. brGDGTs are bacterial membrane-spanning lipids that are known to have a strong relationship with temperature, making them suitable for temperature reconstructions. We test several temperature calibration models on modern samples taken from soils and multiple maar lakes. We find a negative bias in brGDGT-based temperature estimates associated with water depth and anoxic conditions that can be corrected for by accounting for a brGDGT isomer that is only produced in anoxic conditions. The corrected temperature reconstruction correlates with proxy and climate model estimates of temperature spanning the same time period, validating the calibration approach we selected. However, millennial-scale variability is significantly dampened in the brGDGT record, and in contrast to other Northern Hemisphere climate records, during several Heinrich stadials, temperatures actually increase. We demonstrate that these apparent discrepancies can be explained by the unique seasonal response of the brGDGT paleothermometer to temperatures of months above freezing (TMAF). Our data support the view that warm-season temperatures in Europe varied minimally during the last glacial period and that abrupt millennial-scale events were defined by colder, longer winters. Our continuous high-resolution temperature reconstruction provides important information about the magnitude of seasonal climate variability during the last glacial period that can be used to test climate models and inform studies of paleoecological change.

Friction coefficient of sliding isolators in icing conditions

This paper investigates the variation in static friction coefficient of a double curved surface slider (DCSS) due to low temperature exposure. In the experimental campaign, a full-scale DCSS was subjected to displacement controlled cyclic motions after exposure to different temperatures (20, 0 and −20 °C) for different levels of exposure times (3, 12 and 24 hrs). Tests were repeated for several normal stresses (40, 60 and 80 MPa) and maximum loading velocities (250, 500 and 750 mm/s). Force-displacement curves obtained from the tests were used to calculate static friction coefficients. It is revealed that exposure of DCSS to low temperature leads to formation of an ice layer on the sliding surface. The corresponding sliding is no more a function of properties representative of dry-dry friction, but the ice layer behaves as a lubricant. Thus, static friction coefficient decreases in case of an ice layer on the sliding surface.

Underlying mechanisms governing on distribution and stratification of DOM during seasonal freeze-thaw cycles

During the freeze-thaw cycles of ice-covered lakes, DOM undergoes a series of transformations including enrichment, dispersion, and filtration. However, the mechanisms and influence factors on lake pollution processes remain unclear. Therefore, this study investigates the distribution of DOM components and elucidate the role of ice-layer sieving its mechanisms within ice-water-sediments. Study identifies significant variations in the characteristics of DOM, protein-like substances tend to migrate towards the ice layer, while humic-like substances predominantly remain in water. This selective distribution is primarily influenced by the physical and chemical properties of DOM during the freezing process. The ice layer acts as a sieve, allowing smaller molecules such as protein-like substances to pass through more easily, while larger molecules like humic-like substances are retained in the water. Additionally, Temperature plays a pivotal role in affecting the contents of DOM. As the temperature decreases, the solubility of DOM decreases, leading to its precipitation and enrichment in sediments. Conversely, an increase in temperature can facilitate the release of DOM from sediments into the water. Furthermore, high content of total dissolved solids can affect the solubility and stability of DOM, potentially leading to changes in its composition and distribution. These insights provide a deeper understanding of the complex interplay between thermal processes and chemical dynamics within ice-covered aquatic environments. They offered valuable insights into the behavior of organic pollutants in frozen lake systems. The findings have potential implications for environmental management strategies aimed at mitigating the effects of climate.

Ice-Core Micro-CT Image Segmentation with Dual Stream Spectrum Deconvolution Neural Network and Gaussian Mixture Model

Polar ice sheets, or ice cores, are among the most well-known natural archives that might provide crucial historical details about our planet's previous environment. An important factor in establishing the fundamental characteristics of ice, likes pore close-off, albedo, melt events, is the ice-core microstructure. To engulf these complications Ice-Core Micro-CT Image Segmentation with Dual Stream Spectrum Deconvolution Neural Network and Gaussian Mixture Model (ICMCTS-WSOA-DSSDNN-GMM)is proposed. Initially, micro scale CT images are collect from Alfred Wegener Institute ice-core storage as input. Then,data’s are given to pre-processing. In pre-processing, it enhance image brightness, remove salt pepper noise, crop outer ring (carbon fiber casing) to have only ice particles in image utilizing Federated Neural Collaborative Filtering (FNCF).The pre-processing output is given to segmentation. Here, micro scale CT image is utilized for segmenting high-resolution scans using Gaussian Mixture Model (GMM). After that, the segmented images are given to Dual Stream Spectrum Deconvolution Neural Network optimized with Water Strider Optimization Algorithm for classifying micro scale CT images as sintered snow, compacted firn and bubbly ice. The proposed ICMCTS-WSOA-DSSDNN-GMM method is executed in python. The performance of ICMCTS-WSOA-DSSDNN-GMM approach attains 16.24%, 17.90% and 27.7% high accuracy, 14.04%, 25.51% and 19.31% higher precision and 14.36%, 12.65%, 14.51% higher recall analyzed with existing techniques likes Ice-Core Micro-CT Image Segmentation With Deep Learning and Gaussian Mixture Method (ICMCTS-U-net-GMM), Computer Aided Detection of COVID 19 from CT Images Depend on Gaussian Mixture Method with Kernel Support Vector Machines Classifer (ICMCTS-KNN-GMM) and the Gmmseg: Gaussian mixture based generative semantic segmentation methods(ICMCTS-FCN-GMM) respectively.

Assessing transient changes in the ocean carbon cycle during the last deglaciation through carbon isotope modeling

Abstract. Atmospheric carbon dioxide concentration (pCO2) has increased by approximately 80 ppm from the Last Glacial Maximum (LGM) to the early Holocene. The change in this atmospheric greenhouse gas is recognized as a climate system response to gradual change in insolation. Previous modeling studies suggested that the deglacial increase in atmospheric pCO2 is primarily attributed to the release of CO2 from the ocean. Additionally, it has been suggested that abrupt change in the Atlantic meridional overturning circulation (AMOC) and associated interhemispheric climate changes are involved in the release of CO2. However, understanding remains limited regarding oceanic circulation changes and the factors responsible for changes in chemical tracers in the ocean during the last deglaciation and their impact on atmospheric pCO2. In this study, we investigate the evolution of the ocean carbon cycle during the last deglaciation (21 to 11 ka BP) using three-dimensional ocean fields from the transient simulation of the MIROC 4m climate model, which exhibits abrupt AMOC changes similar to those observed in reconstructions. We investigate the reliability of simulated changes in the ocean carbon cycle by comparing the simulated carbon isotope ratios with sediment core data, and we examine potential biases and overlooked or underestimated processes in the model. Qualitatively, the modeled changes in atmospheric pCO2 are consistent with ice core records. For example, during Heinrich Stadial 1 (HS1), atmospheric pCO2 increases by 10.2 ppm, followed by a reduction of 7.0 ppm during the Bølling–Allerød (BA) period and then by an increase of 6.8 ppm during the Younger Dryas (YD) period. However, the model underestimates the changes in atmospheric pCO2 during these events compared to values derived from ice core data. Radiocarbon and stable isotope signatures (Δ14C and δ13C) indicate that the model underestimates both the activated deep-ocean ventilation and reduced efficiency of biological carbon export in the Southern Ocean and the active ventilation in the North Pacific Intermediate Water (NPIW) during HS1. The relatively small changes in simulated atmospheric pCO2 during HS1 might be attributable to these underestimations of ocean circulation variation. The changes in Δ14C associated with strengthening and weakening of the AMOC during the BA and YD periods are generally consistent with values derived from sediment core records. However, although the data indicate continuous increase in δ13C in the deep ocean throughout the YD period, the model shows the opposite trend. It suggests that the model either simulates excessive weakening of the AMOC during the YD period or has limited representation of geochemical processes, including marine ecosystem response and terrestrial carbon storage. Decomposing the factors behind the changes in ocean pCO2 reveals that variations in temperature and alkalinity have the greatest impact on change in atmospheric pCO2. Compensation for the effects of temperature and alkalinity suggests that the AMOC changes and the associated bipolar climate changes contribute to the decrease in atmospheric pCO2 during the BA and the increase in atmospheric pCO2 during the YD period.

The Toba Eruption 74,000 Years ago Strengthened the Indian Winter Monsoon‐Evidence From Coccolithophores

AbstractThe global impact of the Youngest Toba Tuff (YTT) supereruption is still heavily debated, ranging from having little effects on climate to significantly affecting modern human evolution. Climate models and proxy records show that the eruption may have caused cooling of the Asian landmass, thus impacting regional climate such as the Indian monsoon system. However, the immediate effect of the eruption on the Indian monsoon has not been indisputably demonstrated in any proxy record. Here, we present a paleo‐primary productivity (PP) record in core SO130‐289KL from the northeastern Arabian Sea based on the coccolithophore species Florisphaera profunda transfer function. Florisphaera profunda decreased from ∼30% before the YTT eruption to ∼8% right after the YTT eruption, which translates to an increase in PP by ∼65% from a long‐term average of ∼200 gC/m2/yr for about 8–19 years after the eruption. The duration was estimated using a new error‐weighted mean age of the YTT eruption (73.9 ± 0.1 ka, 2σ uncertainties) based on recent age estimates from ice cores, radiometric dating, and speleothem records. The elevated PP is most likely linked to the deepening of the surface ocean mixed layer driven by strengthened northeasterly Indian winter monsoon winds. This hypothesis is supported by stable oxygen isotope records from speleothem and ice cores, which show indications of a strengthening of the Indian winter monsoon during times of increased PP. Our results support previous modeling studies and provide unequivocal evidence from a marine record for an Indian monsoon response to the supereruption.

Quantitative Insights on Impurities in Ice Cores at the Micro‐Scale From Calibrated LA‐ICP‐MS Imaging

AbstractUnderstanding the microscopic variability of impurities in glacier ice on a quantitative level has importance for assessing the preservation of paleoclimatic signals and enables the study of macroscopic deformational as well as dielectric ice properties. Two‐dimensional imaging via laser‐ablation‐inductively‐coupled‐plasma‐mass‐spectrometry (LA‐ICP‐MS) can provide key insight into the localization of impurities in the ice. So far, these findings are mostly qualitative and gaining quantitative insights remains challenging. Recent advances in LA‐ICP‐MS high‐resolution imaging now allow ice grains and grain boundaries to be resolved individually. These resolutions require new adequate quantification strategies and, consequently, accurate calibration with matrix‐matched standards. Here, we present three different quantification methods, which provide a high level of homogeneity at the scale of a few tens of microns and are dedicated to imaging applications of ice cores. One of the proposed methods has a second application, offering laboratory experiments to investigate the displacement of impurities by grain growth, with important future potential to study ice‐impurity interactions. Standards were analyzed to enable absolute quantification of impurities in selected ice core samples. Calibrated LA‐ICP‐MS maps indicate similar spatial distributions of impurities in all samples, while impurity levels vary distinctly: Higher concentrations were detected in glacial periods and Greenland, and lower levels in interglacial periods and samples from central Antarctica. These results are consistent with ranges from complementary meltwater analysis. Further comparison with cm‐scale melting techniques calls for a more sophisticated understanding of the ice chemistry across spatial scales, to which calibrated LA‐ICP‐MS maps now contribute quantitatively.

DEDALO: Device for Enhanced Dust Analyses with Light Obscuration sensors

Instruments based on light obscuration sensors are widely used for measuring the size distribution of insoluble sub-visible particles in liquid suspensions, being fast and suitable for in situ and real-time measurements. Such instruments are typically calibrated by means of reference polystyrene spherical particles with a specific refractive index, which unavoidably leads to systematic errors when determining the size of particles of different materials. In this paper, we propose a reliable and consistent method to overcome this limitation by setting the refractive index value according to the sample, thus achieving an improved particle size distribution (PSD) measurement. An ad hoc, ready-to-use, open source code with a graphical interface able to drive an in-line instrument and obtain a real-time correction to the PSD has been developed. The method has been extensively validated with several oil emulsions characterized by different refractive index values and the results have been compared with an independent optical method. As an example of application, we have adopted this approach for the analysis of dust suspended in meltwater of an ice core from a glacier in the Aosta Valley (Italy). We believe that our approach will strongly improve the accuracy in characterizing liquid suspensions and reduce discrepancies between data obtained with different methods. The code has been made publicly available at: https://instrumentaloptics.fisica.unimi.it/dedalo/ and on the GitHub page of the corresponding author (https://github.com/LucaTeruzzi/DEDALO).

Research on the Cold Storage Characteristics of Ice Storage Photovoltaic Cold Storage

The ice-on-coil storage tank is one of the core devices in the latent heat cold storage system. The main objective of this study is to couple the solar photovoltaic cold storage with Cold Thermal Energy Storage technology. The internal ice-melting coil energy storage system used the water as a heat transfer fluid for adopting a day and night cold storage control strategy. The experiments were conducted for several days under the conditions of photovoltaic-driven cold storage with and without load for a continuous cold storage. The reasons for the occurrence of ice layers during ice accumulation and melting, as well as the operational economy of the system were analyzed. Moreover, the characteristics of the cold storage tank were summarized. Consequently, when the external ice thickness of the coil was within the range of 27 to 32mm, the ice storage rate reached 35.82% and achieved the optimal refrigeration efficiency in both the coil and the cold storage. The daily ice production in the cold storage tank decreased by an average of 22.06% during continuous operation with load compared to the unloaded operation. However, the daily refrigeration capacity increased by 45.774%. In addition, when cold thermal energy storage was coupled with solar photovoltaic technology, the refrigeration capacity decreased by 7.15% compared to using Cold Thermal Energy Storage technology alone, which resulting in an annual electricity cost saving of 30.20%.

Thickness of the Seasonal Deposits at the Martian North Polar Region From Shadow Variations of Fallen Ice Blocks

AbstractThe seasonal deposition and sublimation of CO2 constitute a major element in the Martian volatile cycle. Here, we propose to use the shadow variations of the ice blocks at the foot of the steep scarps of the North Polar Layered Deposits (NPLD) to infer the vertical evolution of the seasonal deposits. We conduct an experiment at a steep scarp centered at (85.0°N, 151.5°E). We assume that no snowfall remains on top of the selected ice blocks, the frost ice layer is homogeneous around the ice blocks and their surroundings, and no significant moating is present. We show that the average thickness of the seasonal deposits due to snowfalls in Mars Year 31 is 0.97 ± 0.13 m at Ls = 350.7° in late winter. The large depth measured makes us wonder if snowfalls are more frequent and violent than previously thought. Meanwhile, we show that the average frost thickness in Mars Year 31 reaches 0.64 ± 0.18 m at Ls = 350.7° in late winter. Combined, the total thickness of the seasonal cover in Mars Year 31 reaches 1.63 ± 0.22 m at Ls = 350.7° in late winter, continuously decreases to 0.45 ± 0.06 m at Ls = 42.8° in middle spring and 0.06 ± 0.05 m at Ls = 69.6° in late spring. These estimates are up to 0.8 m lower than the existing Mars Orbiter Laser Altimeter results during the spring. Meanwhile, we observe that snow in the very early spring of Mars Year 36 can be 0.36 ± 0.13 m thicker than that in Mars Year 31. This study demonstrates the dynamics of the Martian climate and emphasizes the importance of its long‐term monitoring.

Adopting a hot film to measure thickness of an ice layer under sweeping wind

Ice can easily form on low-temperature surfaces. To prevent damage caused by undesirable ice, the presence of ice on a surface together with the ice thickness must be determined. This investigation proposed to measure the thickness of an ice layer under sweeping wind using a hot film and two thermocouples. On the basis of the steady temperature gradient in the ice layer and the solved ice-layer surface temperature from the main stream, the ice layer thickness was obtained. The model required the heat flux through the ice layer and the measured steady temperature rise at the ice surface adjacent to the heater. The ice thickness determined by the proposed method was compared with that measured with a microcalliper. In addition, CFD was used to generate temperature data to evaluate the proposed method for the ice layer blown by high-speed winds. The results demonstrated that the proposed method could accurately measure the thickness of the ice layer under wind blowing at 5–300 m/s. The relative discrepancy in the inferred ice thickness with the microcalliper-measured thickness was <10%, and the accuracy of the method increased with the wind speed.

Pliocene CO2 rise due to sea-level fall as a mechanism for the delayed ice age

Global sea level fell progressively during the Pliocene in response to the growth of ice sheets at high northern latitudes. However, not until ∼2.7 Ma did the climate system actually generate and maintain major ice sheets in the Northern Hemisphere. A decline in atmospheric CO2 levels (pCO2) is thought to be responsible for the Pleistocene ice ages. However, the link between pCO2 and Pliocene glaciations, or their delay, is not well understood, mainly because the magnitude of pCO2 remains uncertain beyond the maximum age of ice cores (∼0.8 Ma). Here, we develop a carbonate clumped isotope (∆47) geothermometer specifically for pedogenic carbonate in Chinese loess, which we use to reconstruct temperatures in northern China, and pCO2, for the past 7.24 Ma. The palaeotemperature results show an oscillatory cooling trend over time in the East Asian monsoon region, in good agreement with coeval tropical sea surface temperature records. The pCO2 reconstruction using the pedogenic carbonate palaeobarometer reveals low values (150–325 ppmv) during the intervals of 7.24–4.3 Ma and 2.6–0 Ma. In contrast, there is a three-step rise in pCO2 up to 535 ppmv from 4.3 to 2.6 Ma, coincident with an oscillatory decrease in sea level and in benthic δ13C. We suggest that the Pliocene CO2 rise was causally related to the sea-level fall and associated organic carbon oxidation on exposed continental shelves, thereby delaying the onset of the ice age. This implies a negative feedback mechanism induced by long-term cooling since the Late Miocene, which may have delayed the onset of the ice age but did not prevent it.

A link between the size and composition of comets

ABSTRACT All cometary nuclei that formed in the early Solar System incorporated radionuclides and therefore were subject to internal radiogenic heating. Previous work predicts that if comets have a pebble-pile structure internal temperature build-up is enhanced due to very low thermal conductivity, leading to internal differentiation. An internal thermal gradient causes widespread sublimation and migration of either ice condensates, or gases released from amorphous ice hosts during their crystallization. Overall, the models predict that the degree of differentiation and re-distribution of volatile species to a shallower near-surface layer depends primarily on nucleus size. Hence, we hypothesize that cometary activity should reveal a correlation between the abundance of volatile species and the size of the nucleus. To explore this hypothesis, we have conducted a thorough literature search for measurements of the composition and size of cometary nuclei, compiling these into a unified data base. We report a statistically significant correlation between the measured abundance of CO/H2O and the size of cometary nuclei. We further recover the measured slope of abundance as a function of size, using a theoretical model based on our previous thermophysical models, invoking re-entrapment of outward migrating high volatility gases in the near-surface pristine amorphous ice layers. This model replicates the observed trend and supports the theory of internal differentiation of cometary nuclei by early radiogenic heating. We make our data base available for future studies, and we advocate for collection of more measurements to allow more precise and statistically significant analyses to be conducted in the future.