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Abstract The Last Interglacial (LIG: 130,000–115,000 years ago) was a period of warmer global mean temperatures and higher and more variable sea levels than the Holocene (11,700–0 years ago). Therefore, a better understanding of Antarctic ice-sheet dynamics during this interval would provide valuable insights for projecting sea-level change in future warming scenarios. Here we present a high-resolution record constraining ice-sheet changes in the Wilkes Subglacial Basin (WSB) of East Antarctica during the LIG, based on analysis of sediment provenance and an ice melt proxy in a marine sediment core retrieved from the Wilkes Land margin. Our sedimentary records, together with existing ice-core records, reveal dynamic fluctuations of the ice sheet in the WSB, with thinning, melting, and potentially retreat leading to ice loss during both early and late stages of the LIG. We suggest that such changes along the East Antarctic Ice Sheet margin may have contributed to fluctuating global sea levels during the LIG.

Regional sea-level highstand triggered rapid Holocene upstream thinning of the East Antarctic Ice Sheet in Dronning Maud Land, suggest ice sheet and crustal rebound model simulations constrained by cosmogenic nuclide chronometry.

Abstract Oxidative potential is an important property of particulate matter (PM) that has been regarded as a more health‐relevant metric than PM mass. We investigated the oxidative potential of size‐segregated PM and effects of Asian dust events in Fukuoka, western Japan. Aerosol particles with diameters smaller and larger than 2.5 μm (fine and coarse particles, respectively) were collected continually from 16 March through 26 May 2016. The oxidative potential was analyzed using dithiothreitol (DTT) assay; chemical components of PM were also found. Air‐volume normalized oxidative potential quantified by DTT assay (DTTv) was significantly higher during Asian dust events than during nondust‐event days. The mean DTTv of fine and coarse particles during Asian dust events were, respectively, 1.5 and 2.7 times higher than that during nonevent days. DTTv of fine particles was highly correlated with elements dominated by anthropogenic combustion sources and with the elements emitted from multiple sources including mineral dust and combustion sources. DTTv of coarse particles strongly correlated with the mineral dust derived elements, suggesting concentration of mineral dust particles as an important controlling factor especially for the oxidative potential of the coarse particles. We estimated the contributions of water‐soluble transition metals to the oxidative potential of PM. Water‐soluble transition metals (mainly Cu and Mn) can explain only approximately 37% and 60% of the measured oxidative potential of fine and coarse particles, respectively, suggesting substantial contributions of aerosol components other than water‐soluble transition metals such as quinones and insoluble minerals.

The Antarctic temperature record displays a puzzling asynchrony with changes in CO2 through glacial cycles. Here, the authors show that a 720,000-year Antarctic temperature record is affected by variations in obliquity-induced local insolation that are associated with phase modulation of eccentricity cycle.

To better understand how sea salt reacts in surface snow of Antarctica, we collected and identified non-volatile particles in surface snow along a traverse in East Antarctica. Samples were obtained during summer 2012/2013 from coastal to inland regions within 69°S to 80°S and 39°E to 45°E, a total distance exceeding 800 km. The spatial resolution of samples is about one sample per latitude between 1500 and 3800 m altitude. Here, we obtain the atomic ratios of Na, S and Cl, and calculate the masses of sodium sulphate and sodium chloride. The results show that, even in the coast snow sample (69°S), sea salt is highly modified by acid (HNO3 or H2SO4). The fraction of sea salt that reacts with acid increases in the region from 70°S to 74°S below 3000 m a.s.l., where some NaCl remains. At the higher altitudes (above 3300 m a.s.l.) in the inland region (74°S to 80°S), the reaction uses almost all of the available NaCl.

We sought to improve the analytical methods employed when operating a laser particle counter and to evaluate the influence of the storage processes on dust concentrations in polar snow and ice samples. We corrected the particle size ranges and threshold voltage using the new calibration curve, confirmed the analytical precision and dust concentrations of blank of wipers using in a clean room, and managed any variations in the laser sensor's sensitivity by measuring standard particles. The 15 ml glass screw bottles without packing (liner of cap of bottles) yielded the lowest dust concentration of the blank among two types of bottles and nine types of packing for dust analysis. Storage of samples of the Dome Fuji ice core (Antarctica) in a refrigerator for 1 year resulted in just a 4% decrease in dust concentration, which is within the analytical precision of the laser particle counter. Storage in a freezer resulted in an increase in dust concentrations and a decrease in the ratio of large particles more than 0.98 μm in particle diameter in the samples, suggesting a change in dust particle size during storage and an influence by the materials of the storage bottles. The addition of dispersants to the Antarctic snow samples is not clearly suitable when analyzing dust concentrations after sample storage by refrigeration or freezing．

We investigated the decontamination procedures used on polar deep ice cores before chemical analyses such as measurements of the concentrations of iron species and dust (microparticles). We optimized cutting and melting protocols for decontamination using chemically ultraclean polyethylene bags and simulated ice samples made from ultrapure water. For dust and ion species including acetate, which represented a high level of contamination, we were able to decrease contamination to below several μg l^ for ion concentrations and below 10000 particles ml^ for the dust concentration. These concentration levels of ion species and dust are assumed to be present in the Dome Fuji ice core during interglacial periods. Decontamination of the ice core was achieved by cutting away approximately 3 mm of the outside of a sample and by melting away approximately 30% of a sample's weight. Furthermore, we also report the preparation protocols for chemical analyses of the 2nd Dome Fuji ice core, including measurements of ion and dust concentrations, pH, electric conductivity (EC), and stable isotope ratios of water (δD and δO), based on the results of the investigation of the decontamination procedures.

The roles and impacts of black carbon (BC), an important aerosol species affecting Earth's radiation budget, are not well understood owing to lack of accurate long-term observations. To study the temporal changes in BC since the pre-industrial period, we analysed BC in an ice core drilled in northwest Greenland. Using an improved technique for BC measurement and a continuous flow analysis system, we obtained accurate and high temporal resolution records of BC particle size and mass/number concentrations for the past 350 years. Number and mass concentrations, which both started to increase in the 1870s associated with inflow of anthropogenically derived BC, reached their maxima in the 1910s-1920s and then subsequently decreased. On the basis of backward trajectory analyses, we found that North America was the dominant source region of the anthropogenic BC in the ice core. The increase in anthropogenic BC shifted the annual concentration peaks of BC from summer to winter-early spring. After BC concentrations diminished to pre-industrial levels, the annual peak concentration of BC returned to the summer. We found that anthropogenic BC particles were larger than biomass burning BC particles. By separating the BC in winter and summer, we reconstructed the temporal variations in BC that originated from biomass burning, including the period with large anthropogenic input. The BC that originated from biomass burning showed no trend of increase until the early 2000s. Finally, possible albedo reductions due to BC are discussed. Our new data provide key information for validating aerosol and climate models, thereby supporting improved projections 31 of future climate and environment. [ABSTRACT FROM AUTHOR]

Ice cores can provide long-term records of black carbon (BC), an important aerosol species closely linked to the climate and environment. However, previous studies of ice cores only analysed BC particles with diameter of <600-850 nm, which could have led to underestimation of BC mass concentrations. Information on the size distribution of BC particles is very limited, and there are no Arctic ice core records of the temporal variation in BC size distribution. In this study, we applied a recently developed improved technique to analyse the BC concentration in an ice core drilled at the SIGMA-D site in northwest Greenland. The improved technique, which uses a modified Single-Particle Soot Photometer and a high-efficiency nebulizer, widens the measurable range of BC particle size. For high-resolution continuous analyses of ice cores, we developed a continuous flow analysis (CFA) system (resolution: 10-40 mm). Coupling of the improved BC measurement technique with the CFA system allows accurate high-resolution measurements of the size distribution and concentration of BC particles with diameter between 70 nm and 4 µm, with minimal particle losses. Using this technique, we reconstructed the size distributions and the number and mass concentrations of BC particles during the past 350 years. On the basis of the size distributions, we assessed the underestimation of BC mass concentrations measured using the conventional method. For the period 2003-2013, the underestimation of the average mass concentration would have been 12%-17% for the SIGMA-D core. [ABSTRACT FROM AUTHOR]

An in-depth examination of rheology within the deep sections of polar ice sheets is essential for enhancing our understanding of glacial flow. In this study, we investigate the crystalline textural properties of the 3035-m-long Antarctic deep ice core, with a particular emphasis on its lowermost 20%. We examine the crystal orientation fabric (COF) and compare it with various other properties from the ice core. In the uppermost approximately 80% thickness zone (UP80%), the clustering strength of single pole COF steadily increased, reaching its possible maximum at the bottom of the UP80%. Below 1800 m in the UP80%, layers with more or fewer dusty impurities exhibit slower or faster growth of cluster strength. This situation continued until 2650 m. In the remaining lowermost approximately 20% thickness zone (LO20%), the trend of the COF clustering strength changed around 2650 m and exhibited substantial fluctuations below this depth. In more impurity-rich layers, stronger clustering is maintained. In impurity-poor layers, relaxation of the COF clustering occurred due to the emergence of new crystal grains with c-axis orientation distinctly offset from the existing cluster, and dynamic recrystallization related to this emergence. The less impure layers show apparent features of bulging and migrating grain boundaries. We argue that the substantial deformational regime of polar ice sheets involves dislocation creep in both UP80% and LO20%, with dynamic recrystallization playing a critical role in the LO20%, particularly in impurity-poor layers, to recover a potential of COF available for the continuation of dislocation-creep-based deformation. Furthermore, we observe that layers and cluster axes of COF rotate meridionally due to rigid-body rotation caused by simple shear strain above subglacial slopes. These features provide vital clues for the development of the 3D structure of polar ice sheets in the deeper part, leading to inhomogeneous deformation between layers in various thickness scales, and the formation of folds, faults and mixing depending on the layers. [ABSTRACT FROM AUTHOR]

Here we present the high-resolution CFA data from the top 479m of the East Greenland Ice coring Project (EGRIP) ice core covering the past 3.8 thousand years. The data consists of 1mm-depth-resolution profiles of calcium, sodium, ammonium, nitrate and electrolytic conductivity as well as decadal averages of these profiles. Alongside the data we provide a description of the measurement setup, procedures, the relevant references for the specific methods as well as an assessment of the precision of the measurements, the sample to depth assignment and the depth and temporal resolution of the data set. The nominally 1-mmdata represents an oversampling of the record as the true resolution is limited by the analytical setup to approximately 1 cm. The error of absolute depth assignment of the data may be on the order of 1 cm, however relative depth offsets between the records of the individual species is only on the order of 1mm. The presented data has sub-annual resolution over the entire depth range and has already formed part of the data for an annually layer-counted time scale for the EGRIP ice core used to improve and revise the multi-core Greenland ice-core chronology (GICC05) to a new version, GICC21 (Sinnl et al., 2021). The data is available in full 1-mm resolution and decadal averages on PANGAEA (https://doi.org/10.1594/PANGAEA.945293 (Erhardt et al., 2022b)). [ABSTRACT FROM AUTHOR]

We reconstructed surface mass balance (SMB) around Dome Fuji, Antarctica, over the last 5000 years using the data from 15 shallow ice cores and 7 snow pits. The depth-age relationships for the ice cores were determined by synchronizing them with a layer-counted ice core from West Antarctica (WAIS Divide ice core) using volcanic signals. The reconstructed SMB records for the last 4000 years show spatial patterns that may be affected by their locations relative to the ice divides around Dome Fuji, proximity to the ocean, and wind direction. The SMB records from the individual ice cores and snow pits were stacked to reconstruct the SMB history in the Dome Fuji area. The stacked record exhibits a long-term decreasing trend at - 0.037±0.005 kg m-2 per century over the last 5000 years in the preindustrial period. The decreasing trend may be the result of long-term surface cooling over East Antarctica and the Southern Ocean, and sea-ice expansion in the water vapor source areas. The multidecadal to centennial variations of the Dome Fuji SMB after detrending the record shows four distinct periods during the last millennium: mostly negative period before 1300 C.E., slightly positive for 1300-1450 C.E., slightly negative for 1450-1850 C.E. with a weak maximum around 1600 C.E., and strong increase after 1850 C.E. These variations are consistent with those of previously reconstructed SMB records in the East Antarctic plateau. The low accumulation rate periods tend to coincide with the combination of strong volcanic forcings and solar minima for the last 1000 years, but the correspondence is not clear for the older periods, possibly because of the lack of coincidence of volcanic and solar forcings, or the deterioration of the SMB record due to smaller number of stacked cores. [ABSTRACT FROM AUTHOR]

The δD temperature proxy in Antarctic ice cores varies in parallel with CO2 through glacial cycles. However, these variables display a puzzling asynchrony. Well-dated records of Southern Ocean temperature will provide crucial information because the Southern Ocean is likely key in regulating CO2 variations. Here, we perform multiple isotopic analyses on an Antarctic ice core and estimate temperature variations at this site and in the oceanic moisture source over the past 720,000 years, which extend the longest records by 300,000 years. Antarctic temperature is affected by large variations in local insolation that are induced by obliquity. At the obliquity periodicity, the Antarctic and ocean temperatures lag annual mean insolation. Further, the magnitude of the phase lag is minimal during low eccentricity periods, suggesting that secular changes in the global carbon cycle and the ocean circulation modulate the phase relationship among temperatures, CO2 and insolation in the obliquity frequency band. [ABSTRACT FROM AUTHOR]

Sea salts and halogens in aerosols, frost flowers, and brine play an important role in atmospheric chemistry in polar regions. Simultaneous sampling and observations of frost flowers, brine, and aerosol particles were conducted around Siorapaluk in northwestern Greenland during December 2013 to March 2014. Results show that water-soluble frost flower and brine components are sea-salt components (e.g., Na+, Cl−, Mg2+, K+, Ca2+, Br−, and iodine). Concentration factors of sea-salt components of frost flowers and brine relative to seawater were 1.14–3.67. Sea-salt enrichment of Mg2+, K+, Ca2+, and halogens (Cl−, Br−, and iodine) in frost flowers is associated with sea-salt fractionation by precipitation of mirabilite and hydrohalite. High aerosol number concentrations correspond to the occurrence of higher abundance of sea-salt particles in both coarse and fine modes, and blowing snow and strong winds. Aerosol number concentrations, particularly in coarse mode, are increased considerably by release from the sea-ice surface under strong wind conditions. Sulfate depletion by sea-salt fractionation was found to be limited in sea-salt aerosols because of the presence of non-sea-salt (NSS) SO42−. However, coarse and fine sea-salt particles were found to be rich in Mg. Strong Mg enrichment might be more likely to proceed in fine sea-salt particles. Magnesium-rich sea-salt particles might be released from the surface of snow and slush layer (brine) on sea ice and frost flowers. Mirabilite-like and ikaite-like particles were identified only in aerosol samples collected near new sea-ice areas. From the field evidence and results from earlier studies, we propose and describe sea-salt cycles in seasonal sea-ice areas. [ABSTRACT FROM AUTHOR]

Sea-salts and halogens in aerosols, frost flowers and brine play an important role in atmospheric chemistry in polar regions. Simultaneous sampling and observations of frost flowers, brine, and aerosol particles were conducted around Siorapaluk in north-western Greenland during December 2013-March 2014. Results show that water-soluble frost flower and brine constituents were sea salts (e.g., Na+, Cl-, Mg2+, and Br-). Concentration factors of sea-salt constituents of frost flowers and brine relative to seawater were 1.14-3.67. Sea-salt enrichments of Mg2+, K+, Ca2+, and halogens (Cl-, Br-, and I) in frost flowers were associated with sea-salt fractionation by precipitation of mirabilite and hydrohalite. Aerosol number concentrations, particularly in coarse mode, were increased considerably by release from the sea-ice surface under strong wind conditions. Sulphate depletion by sea-salt fractionation was found to be slight in sea-salt aerosols because of heterogeneous SO42- formation on sea-salt particles. However, coarse and fine sea-salt particles were found to be rich in Mg. Strong Mg enrichment might be more likely to proceed in fine sea-salt particles. Mg-rich sea-salt particles might be released from the sea-ice surface and frost flowers. Mirabilite-like and ikaite-like particles were identified only in aerosol samples collected near new sea-ice areas. [ABSTRACT FROM AUTHOR]