Jack Humby

The Beyond EPICA oldest ice is a unique climate archive, continuously reaching back to possibly 1.5 Ma. The continuity of the signals in the ice core likely allows for developing a continuous timescale, mostly based on orbital tuning with O2/N2 and δ18Oatm. The obtained timescale can then be checked for consistency with marine records, 36Cl/10Be dating and possibly with magnetic tie points from cosmogenic isotopes. Since these consistency checks have caveats, additional absolute age constraints may prove useful.The noble gas radioisotope 81Kr ( t1/2 = 229 ka ) with a dating range from 30 ka to 1.5 Ma can provide robust absolute age constraints in ice cores. Especially due to its gaseous and inert properties, its isotopic ratio is not altered by geochemical processes so that it preserves the pristine age information. 81Kr dating could provide additional absolute age constraints for the Beyond EPICA oldest ice. However, due to the high ice demand for numerous analyses on the core, there is no ice available for 81Kr analysis on discrete ice samples.We present gas extraction from the Continuous Flow Analysis (CFA) of the Beyond EPICA oldest ice for 81Kr dating. The gas has been passively collected from the overflow of the debubbler into multi-layer aluminium-foil bags, which are routinely employed for 81Kr dating of groundwater. From the continuous melting of ~3 m long core, discrete ~100 mL STP gas samples have been extracted, and subsequently analyzed offline for 85Kr and 81Kr. Modern air contamination, likely from diffusion through the gas bags during storage, has been quantified with the anthropogenic 85Kr. The contamination can be avoided by transfer of the sampled gas from bag to metal container after collection. The 81Kr age constraints that could be obtained are consistent with preliminary timescales. The presented gas extraction method is non-invasive and requires minimum equipment, potentially providing a base for usage also in future CFA campaigns.

Particulate mineral dust is a critical part of the Earth’s climate system, modulating radiative balance and providing a crucial source of micronutrients to surface oceans. In ice cores, mineral dust also serves as a key proxy for past atmospheric dynamics - controlling dust mobilization and transport - as well as hydroclimate variability, which affects the atmospheric residence time of dust in addition to emission strength in the source regions. Previous studies, including those from the 800,000-year EPICA Dome C ice core, have demonstrated a close coupling between dust particle number concentrations in ice cores and glacial-interglacial climate variability, with consistently higher dust concentrations during cold glacial periods. The new Beyond EPICA-Oldest Ice Core (BE-OIC: 75º 18’ S, 122º 27’ W) extends the existing ice core particulate dust record back through the Mid-Pleistocene Transition (MPT), providing new constraints on this enigmatic period in Earth’s climate history.We present the first continuous record of particulate mineral dust particle size and particle number distributions from the new BE-OIC, spanning from 700,000 years BP through the Mid-Pleistocene Transition. Physical characteristics of individual dust grains were measured online by the University of Bern during the Continuous Flow Analysis measurement campaign at the British Antarctic Survey using dual Classizer One Single Particle Extinction and Scattering instruments (EOS) and an Abakus laser particle sensor (Klotz GmbH), enabling characterization of particle concentration, dust size but also its refractive index over a wide range of diameters (0.2–10 µm). The latter is crucial as it allows us for the first time to resolve the submicrometer mode in the number size distribution.Consistent with earlier work on the EDC ice core, the new BE-OIC record shows elevated dust concentrations during glacial periods both before, during and post MPT. However, the amplitude of glacial-interglacial variability is reduced relative to the past 800,000 years. In addition, modal particle diameters in the number size distribution are smaller during glacials compared to interglacials, indicating enhanced contributions from long-distance dust transport during the colder climate states. We investigate the processes that lead to dust size and number changes, including how reduced glacial intensity pre-MPT may have impacted dust source regions and the atmospheric lifetimes of dust particles. Together, these observations indicate changes in dust source-to-sink dynamics that have implications for biogeochemical cycles in the Southern Ocean and atmospheric dynamics during the MPT.

We present an optimised impurities continuous-flow analysis (CFA) method specifically developed to analyse the Beyond EPICA Oldest Ice Core (BE-OIC; >700 ky bp). Hosted at the British Antarctic Survey (BAS1) and operated collaboratively with our BE-OI partners2-12, the new CFA method was designed to operate at a melt rate of 1.5 cm min-1. The system included the continuous analyses of trace elements (triple quadrupole inductively-coupled plasma mass spectrometry, Agilent 8900 ICP-QQQ-MS/MS & inductively-coupled plasma optical emission spectroscopy, Agilent 5900 ICP-OES; BAS1); major anions (Cl-, SO42-, NO3- and MSA, Dionex fast ion chromatography, FIC; BAS1); NH4+ (fluorometry; BAS1); electrolytic conductivity (Dionex CDM-1 & Amber Science ECM 3201; BAS1); insoluble particulate size distribution (Abakus Klotz laser diffraction spectrometry, and EOS Single Particle Extinction Scattering, SPES2; U. Bern2); and stable water isotopes (δ18O, δ2H; Picarro cavity ring-down spectrometry, CRDS; U. Bern2, BE-OI Isotope Consortium7-10,12). For the first time, we present sections of BE-OIC chemistry data, focusing on trace elements (ICP-QQQ-MS & ICP-OES) and major anions (FIC). In addition, the CFA campaign provided discrete liquid samples for single-particle trace elemental analysis (U. Bern2), organic analysis (U. Cambridge3, Ca’ Foscari U. Venice9&CNR-ISP10), δ34S (U. St. Andrews5), diatoms (BAS1), halogens (Ca’ Foscari U. Venice9 & CNR-ISP10), and tephra (BAS1, U. St. Andrews5 & Swansea U.6). Furthermore, discrete gas samples were collected for 81Kr dating (Heidelberg U.11).

The Skytrain Ice Rise ice core adds to the handful of climate records from Antarctica that cover the whole of the last glacial period (here, we consider ~100-10 ka bp). By our count 7 records have been published covering the entire period and a further 6 cover a substantial part of it. Using the synchroneity of signals across the continent (for example in components of dust and in methane) we can tie the records together temporally. The precision of such ties is good enough to allow comparison of the timing and shape of particular events across the continent.Many of the differences between sites will derive from local changes of elevation that certainly occur at ice rise sites. We first will discuss the glacial water isotope record from Skytrain Ice Rise (in comparison to other sites) in this context. This will supplement the work we have already done on the Holocene and the last interglacial period using the Skytrain Ice Rise core.However we primarily focus on a number of events such as the Antarctic Cold Reversal and some of the large Antarctic Isotopic Maxima (eg AIM 12). We will present records from the different sectors of Antarctica. We will investigate whether any sectors of Antarctica led in such events, and determine the relative amplitude of such events around the continent. This information will offer diagnostic tests to ideas about the causes and process of millennial scale variability across the glacial period.

Fracture-induced ice shelf instability is a critical contributor to uncertainties in sea level projections, which are central to global flood mitigation planning. While the occurrence of ice fracturing at critical stress thresholds is well-documented, the mechanisms governing fracture timing, rate, and orientation remain poorly understood, particularly across ice shelves with varying ice properties and provenance. Observations on the Brunt Ice Shelf reveal unique fracture behaviours, where rifts deviate from their stress-predicted pathways to avoid blocks of meteoric ice, and preferentially fracture through thinner marine ice. The speed of propagation is also influenced by these differences in ice type. To improve our understanding of these fracture dynamics, a 37 m firn core through thin, marine-based ice was collected in 2024 on the Brunt Ice Shelf. This core provides a high-resolution record of precipitation and climate changes over the past 40 years, with saline layers at the base. Biogenic species within the core trace variations in summer sea ice extent and proximity to open water, including the A-81 calving in 2023, while an increasing prevalence of melt layers highlights a rise in surface melt. By integrating fracture toughness measurements from layers with varying melt and accumulation conditions, we demonstrate how climatic and environmental shifts could influence ice shelf susceptibility to fracture propagation.

Recent work demonstrates that the Skytrain ice core, retrieved from the Weddell Sea Embayment in West Antarctica, can inform us about the (in-)stability of the Ronne-Filcher Ice Shelf and the West Antarctic Ice Sheet in past warm periods. Here we switch our focus to the Last Glacial period at Skytrain and describe our “Calcium Conundrum”, which may be linked to ice sheet dynamics. The Skytrain calcium record diverges from those of other Antarctic ice cores across several distinct time intervals. The increased Ca at Skytrain is not accompanied by a corresponding increase in other terrigenous elements such as Al. We hypothesize that the elevated Ca intervals result from additional input of relatively local dust, unique to Skytrain. To test this, we present new geochemical measurements on the soluble phase and fully digested dust particles from a ‘regular Ca’ interval (20–31 ka) and an ‘excess Ca’ interval (42–49 ka). Trace element data confirm elevated Ca levels during the excess Ca interval, associated also with a significant Ba increase relative to Al. However, terrigenous elements associated with silicate minerals exhibit no significant difference between the two intervals when normalised to Al. Radiogenic Sr and Nd isotopes of the regular Ca interval fall within range of South American source areas, typical for Antarctica during the Last Glacial Period. In contrast, 87Sr/86Sr and eNd values for the excess Ca interval are significantly different from those of the regular Ca interval. Using a collation of Sr and Nd isotope data of potential source regions, complemented by new measurements on rocks from the nearby Ellsworth Mountains, we assess the possibility that the recurring excess Ca signal during the Last Glacial fingerprints a dynamic ice sheet in the Weddell Sea Embayment that intermittently exposed nearby nunataks to physical erosion and dust transport. Additionally, we report the first (to our knowledge) Ca isotope measurements on ice cores in an effort to further fingerprint the source of the excess Ca.

The fate of the West Antarctic Ice Sheet (WAIS)¹ is the largest cause of uncertainty in long-term sea-level projections. In the last interglacial (LIG) around 125,000 years ago, data suggest that sea level was several metres higher than today^2–4, and required a significant contribution from Antarctic ice loss, with WAIS usually implicated. Antarctica and the Southern Ocean were warmer than today^5–8, by amounts comparable to those expected by 2100 under moderate to high future warming scenarios. However, direct evidence about the size of WAIS in the LIG is sparse. Here we use sea salt data from an ice core from Skytrain Ice Rise, adjacent to WAIS, to show that, during most of the LIG, the Ronne Ice Shelf was still in place, and close to its current extent. Water isotope data are consistent with a retreat of WAIS⁹, but seem inconsistent with more dramatic model realizations¹⁰ in which both WAIS and the large Antarctic ice shelves were lost. This new constraint calls for a reappraisal of other elements of the LIG sea-level budget. It also weakens the observational basis that motivated model simulations projecting the highest end of projections for future rates of sea-level rise to 2300 and beyond.

Conventional methods of inorganic impurity analysis do not provide high enough depth resolution for many scientific questions in ice core science. In this study, we present a setup of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for high-resolution glacier ice impurity analysis to the sub-millimetre scale. This setup enables ice core chemical impurity analysis to a depth resolution of ∼182 µm while consuming only very small amounts of ice. The system performs simultaneous analysis of sodium, magnesium and aluminium incorporated in the ice matrix. In this case study within the framework of the WACSWAIN (WArm Climate Stability of the West Antarctic Ice Sheet in the last INterglacial) project, our method is applied to a selection of samples from the Skytrain ice core (West Antarctica) over a total length of 6.7 m consisting of about 130 single samples. The main goal of this study is to use the new LA-ICP-MS method to extract meaningful climate signals on a depth resolution level beyond the limits of continuous-flow analysis (CFA). A comparison between low-resolution CFA data and the high-resolution LA-ICP-MS data reveals generally good agreement on the decimetre scale. Stacking of parallel laser measurements together with frequency analysis is used to analyse the high-resolution LA-ICP-MS data at millimetre resolution. Spectral analysis reveals that despite effects of impurity accumulation along ice crystal grain boundaries, periodic concentration changes in the Skytrain ice core on the millimetre scale can be identified in ice from 26.8 ka (kiloyears before present, i.e. 1950 CE). These findings open new possibilities for climate data interpretation with respect to fast changes in the last glacial period and beyond, for example within the Beyond EPICA oldest-ice project.

We present an age model for the 651 m deep ice core from Skytrain Ice Rise, situated inland of the Ronne Ice Shelf, Antarctica. The top 2000 years have previously been dated using age markers interpolated through annual layer counting. Below this, we align the Skytrain core to the AICC2012 age model using tie points in the ice and air phase, and we apply the Paleochrono program to obtain the best fit to the tie points and glaciological constraints. In the gas phase, ties are made using methane and, in critical sections, δ¹⁸O_air; in the ice phase ties are through ¹⁰Be across the Laschamps event and through ice chemistry related to long-range dust transport and deposition. This strategy provides a good outcome to about 108 ka (∼ 605 m). Beyond that there are signs of flow disturbance, with a section of ice probably repeated. Nonetheless values of CH₄ and δ¹⁸O_air confirm that part of the last interglacial (LIG), from about 117–126 ka (617–627 m), is present and in chronological order. Below this there are clear signs of stratigraphic disturbance, with rapid oscillation of values in both the ice and gas phase at the base of the LIG section, below 628 m. Based on methane values, the warmest part of the LIG and the coldest part of the penultimate glacial are missing from our record. Ice below 631 m appears to be of age > 150 ka.