British Antarctic Survey

The rapid expansion of glacial lakes in high-mountain regions, both in number and area, increases the risk of Glacial Lake Outburst Floods (GLOFs) to downstream communities. Optical remote sensing is essential for regional monitoring, as these lakes are frequently widespread and often inaccessible. However, clear image acquisition in mountainous areas is regularly hindered by shadowing, seasonal snow, and cloud cover. In the Himalayas, more frequent imaging is necessary to accurately inventory lakes during the short, snow-free periods. The HJ-2A/B satellites deployed by China now provide daily revisits at 16 m resolution, enabling comprehensive, high-quality mapping of glacial lakes. This study introduces a novel framework that uses a deep-learning U-Net model to detect lakes in HJ-2 imagery automatically and assesses its efficacy for monitoring lake changes in the China–Nepal section of the Central Himalayas (CNCH). Our findings indicate that the frequent imaging capabilities of HJ-2 permit annual lake mapping within a specific 1-mon period, achieving an accuracy and sensitivity to area changes exceeding 99%, with the ability to detect changes as small as 0.004 km 2 . In our case study, we identify 2738 lakes in 2022 and 2739 lakes in 2023, with respective areas of 256.51 ± 14.41 km 2 and 260.89 ± 14.59 km 2 . Despite certain limitations in geometric and radiometric calibration, this study establishes that HJ-2 imagery is highly effective for consistent, frequent monitoring of glacial lake changes and GLOF risks compared to previous satellite imagery.

Ice cores provide the only direct archive of past atmospheric greenhouse gases (GHG). However, physical and chemical processes occurring before, during, and after bubble enclosure can alter the atmospheric signal recorded in ice. In particular, gas diffusion within the bubble-clathrate transition zone (BCTZ) has been shown to generate centimeter-scale, non-atmospheric variability, which we refer to as the “Lüthi effect” (Lüthi et al., 2010). Below the BCTZ, diffusive smoothing dampens these non-atmospheric signals but also atmospheric variability. While the Lüthi effect and diffusive smoothing have been documented for CO2 and the δO2/N2 ratio, their impact on N2O and CH4 remains poorly constrained. In addition, chemical reactions within the ice can alter atmospheric signals, particularly for N2O, which has been shown to be produced in situ by nitrate reduction in dust-rich Antarctic ice during glacial periods.Here we investigate diffusion and in situ production processes potentially affecting CO2, CH4, and N2O by analyzing five samples from the BCTZ of the Talos Dome ice core (TALDICE). GHG concentrations were measured at centimeter-scale resolution using a novel laser sublimation extraction system coupled to a quantum cascade laser absorption spectrometer (Mächler et al., 2023). δO2/N2 ratios were analyzed by isotope ratio mass spectrometry following the recapture of the same samples after GHG measurements with the laser spectrometer.Our results show for the first time that N2O and CH4 are also affected by the Lüthi effect in the BCTZ. The strong 1:1 correlation between CO2 and N2O variability suggests similar diffusion coefficients for these gases. These findings provide new constraints on N2O diffusion, relevant for modeling diffusive smoothing in deep and old ice such as the recently drilled Beyond EPICA ice core. Consistent with previous studies, our results indicate that the N2O record in TALDICE is not significantly affected by the aforementioned in situ production during glacial periods. The atmospheric N2O signal can therefore be retrieved when measurements are either spatially averaged to smooth the centimeter-scale variability induced by the Lüthi effect, obtained above the BCTZ, or taken well below the BCTZ where diffusive smoothing has attenuated this variability.ReferencesLüthi, D., Bereiter, B., Stauffer, B., Winkler, R., Schwander, J., Kindler, P., Leuenberger, M., Kipfstuhl, S., Capron, E., Landais, A., Fischer, H., and Stocker, T. F.: CO2 and O2/N2 variations in and just below the bubble–clathrate transformation zone of Antarctic ice cores, Earth and Planetary Science Letters, 297, 226–233, https://doi.org/10.1016/j.epsl.2010.06.023, 2010.Mächler, L., Baggenstos, D., Krauss, F., Schmitt, J., Bereiter, B., Walther, R., Reinhard, C., Tuzson, B., Emmenegger, L., and Fischer, H.: Laser-induced sublimation extraction for centimeter-resolution multi-species greenhouse gas analysis on ice cores, Atmos. Meas. Tech., 16, 355–372, https://doi.org/10.5194/amt-16-355-2023, 2023.

Antarctic ice shelves in the Amundsen Sea embayment are vulnerable to rapid disintegration, the dynamics of which depend strongly on the rate of melting of the ice shelf. In particular, melt rates in the grounding zone - where ice transiently makes contact with the bedrock - have proven difficult to measure using remote methods which rely on remote measurements of the ice freeboard and an application of the hydrostatic approximation. Here, we extend existing remote observations of melt rates into the grounding zone by incorporating a model of the elastic flexure of ice shelves. The numerical model is tested against existing analytical models, and then demonstrated on select ice shelves in the Amunsdsen sea embayment. Melt rates are found which are comparable with existing hydrostatic estimates away from the grounding zone, but are more continuous within the region of transient contact with the bedrock.

Extreme weather represents one of the most significant consequences of a warming climate. Improving constraints on how such events may manifest in the future is therefore a key priority, particularly for hazards that lead to severe societal, ecological, and financial impacts, such as heatwaves, extreme rainfall, droughts and their compounding effects.Past interglacial periods provide physically realised instances of warm-climate states that can be used to contextualise ongoing anthropogenic warming and to inform future changes. Each interglacial is characterised by a distinct combination of orbital forcing and greenhouse gas concentrations, ice-sheet configuration, and background climate. Comparing these periods allows the partial isolation of the roles played by different climate drivers and large-scale circulation patterns in shaping the frequency, intensity, variability and spatial distribution of extreme events.Here, we compare extreme weather characteristics across four interglacial periods: the mid-Holocene (6 ka), the Last Interglacial (127 ka), Marine Isotope Stage 11 (408 ka), and Marine Isotope Stage 31 (1072 ka), alongside a pre-industrial control. The analysis is based on preliminary equilibrium time-slice simulations conducted using the HadGEM3-GC5.0 coupled climate model, which also enables an initial assessment of model performance across a range of interglacial climates. We demonstrate how distinct warm-climate conditions have affected polar and global extreme events in the past and discuss the mechanisms underpinning these changes and their relevance for future climates.

Surface melting and runoff account for about half of the current mass loss of the Greenland Ice Sheet. Regional climate models (RCMs) project runoff to increase further over the 21st century, but the magnitude of this trend varies strongly between different models. This variability arises because RCMs rely on simplified representations of the complex firn hydrological system in Greenland’s percolation zone. However, key parameters for parametrizing meltwater retention and runoff processes remain poorly constrained due to a lack of time-resolved, in situ observations of firn liquid water content.We address this gap by demonstrating that the Autonomous phase-sensitive Radio-Echo Sounder (ApRES) can continuously trace the amount of liquid water in the firn. At three automatic weather station sites on the ice sheet (KAN_U, DYE-2 and Camp Century), we acquired hourly ApRES time series between spring 2023 and 2025, covering two melt seasons. By analyzing these observations in combination with a firn model, we quantify rates of lateral meltwater flow. Comparison with runoff simulations from three RCMs shows that all models overestimate local runoff at KAN_U, and that some even predict runoff at DYE-2 (2124 m a.s.l.), where our observations indicate that all meltwater is refrozen. Expanding these observations will support the development of improved representations of Greenland’s firn hydrological system in RCMs and ultimately enhance the accuracy of GrIS mass balance projections.

The Mid-Pleistocene Transition (MPT; 1.25 – 0.8 Myr) marks a transition from the “41-kyr world”, in which the Earth alternated between cold and warm periods about every 41,000 years, to the “100-kyr world” in which the Earth remained predominantly under glacial conditions but was punctuated every 80,000 to 120,000 years by interglacial periods. Variations in orbital forcing, the “pacemaker of the ice ages”, are stable across the MPT and thus cannot be invoked as a driver of this transition. Thus, most hypotheses call upon a forcing that drives a secular change, a feedback in the Earth system that changes/emerges, or a combination of the two.One hypothesis for the MPT suggests that a long-term decline in (glacial) atmospheric CO2 levels led to a cooling, facilitating the formation of extensive ice sheets in North America and a sea-level drop of approximately 70 m (Bintanja & van de Wal, 2008). Accordingly, decreasing atmospheric CO2 concentration may have played a central role in driving this global cooling. Despite recent advances in marine and ice core CO₂ reconstructions (Nuber et al., 2025; Marks Peterson et al., 2025) the change of greenhouse gas forcing across the MPT remains uncertain for CO2.In order to investigate the role of atmospheric CO2 across the MPT, greenhouse gases and the stable carbon isotopic composition of CO2 (δ13C-CO2) were measured on discrete ice core samples from the Beyond EPICA ice core. For this purpose, a coupled Laser induced sublimation extraction – Quantum Cascade laser Absorption Spectrometer (LISE-QCLAS) was used, allowing the simultaneous and semi-continuous extraction and measurement of CO2, CH4 and N2O as well as δ13C-CO2 on air samples of only 1 – 2 mL, corresponding to 10 – 15 g of ice.This talk will present the first ice core data capable of capturing glacial–interglacial variations in atmospheric CO₂ across the MPT. Additionally, we will present the first unconditionally pristine measurements of δ13C-CO2 during the 41-kyr world. These data will allow us to explore the underlying biogeochemical processes that may be responsible for the new modes of atmospheric CO2 variability we have observed.

Whistler-mode chorus waves are electromagnetic emissions in the Earths’ magnetosphere that play a central role in the dynamics of the outer radiation belt, contributing to both acceleration and loss of relativistic electrons. The efficiency of these processes strongly depend on the wave intensity and the ratio of the electron plasma frequency to the electron gyrofrequency (fpe/fce). Using approximately 24.5 years of THEMIS wave observations, we examine how chorus wave intensity and spatial distribution vary with relative frequency, geomagnetic activity and fpe/fce. The strongest chorus waves are observed during periods of high geomagnetic activity (AE > 200nT). At low relative frequencies (flhr < f < 0.1fce), equatorial chorus is strongest during periods of high fpe/fce, primarily within 5 < L* < 8 and 22-12 MLT. In contrast, at high relative frequencies (0.5fce < f < 0.7fce), equatorial chorus is strongest when fpe/fce is low, between 4 < L* < 6 and 21-09 MLT. At intermediate relative frequencies (0.3fce < f < 0.4fce), chorus intensities are observed in the same region and are largely independent of fpe/fce. We find that off-equatorial chorus emissions are also largely independent of fpe/fce. Results show that the locations of peak chorus intensity are controlled by the availability of resonant source electrons and reduced Landau damping. Our findings identify regions where chorus-driven acceleration of electrons to relativistic energies is expected to be the most significant.

The Wilkes Subglacial Basin (WSB) is one of the largest tectonic features in East Antarctica as it stretches for almost 1600 km from the Southern Ocean towards South Pole. Significant research has focussed on the tectonic origin of the basin with competing models ranging from Paleozoic, Mesozoic and Cenozoic extensional models to flexural models related to the Cenozoic uplift of the Transantarctic Mountains. Comparatively little effort has however been placed on investigating the cryptic basement of the WSB despite its key location at the transition between the exposures of the Archean-Mesoproterozoic Terre Adelie Craton and the late Neoproterozoic to Ordovician age Ross Orogen.Here we present enhanced aeromagnetic and airborne gravity imaging augmented by satellite magnetic and satellite gravity data and comparisons with formerly adjacent southeastern Australia to redefine key features of the basement in the northern WSB region.We show that a prominent magnetic low located beneath the Western Basins within the WSB is not caused by a ca 3 km thick Cambrian rift basin as previously proposed (Ferraccioli et al., 2009, Tectonophysics) but images instead a linear Archean crustal ribbon extending further north to exposures of Archean rocks in the Terre Adelie craton and in the Gawler Craton. Cambrian sedimentary basins are confirmed further east beneath the northern Central Basins. Prominent magnetic highs along the eastern flank of the WSB and at the edge of the southern Central Basins were previously interpreted to reveal Ross age igneous basement associated with an arc-back arc system. However, the occurrence of longer wavelength satellite magnetic anomalies both in the WSB and at the edge of the Gawler Craton and in the Curnamona Craton in Australia lead us to propose an alternative hypothesis that predicts the occurrence of more extensive Paleo to Mesoproterozoic basement than previously inferred. Furthermore, a prominent linear residual gravity anomaly along the western flank of the WSB is interpreted here as reflecting uplifted mafic lower crust associated with Paleoproterozoic rifting. High amplitude aeromagnetic anomalies may reflect coeval banded iron formations associated at shallower crustal levels with such Paleoproterozoic rifting processes.By comparing gravity signatures over the WSB and southern Australia and by incorporating recent seismic constraints at the transition between the Gawler Craton and the Delamerian Orogen we reassess the extent and architecture of both the Precambrian and Cambrian basement.Overall, our results and models have significant implications for tectonic studies of the basement of the WSB, including better defining the role of inherited tectonics structures on the more recent Paleozoic, Mesozoic to Cenozoic evolution of the WSB. Furthermore, the larger degree of heterogeneity in the crustal basement identified here will help inform next generation models of intracrustal contributions to geothermal heat flow beneath this key sector of the East Antarctic Ice Sheet.

This poster provides an overview of the PROMOTE (Progressing Earth System Modelling for Tipping Point Early Warning Systems) project. One project aim is to develop a version of the UK Earth System Model (UKESM) that is suitable to become the model component of a potential early warning system of Subpolar Gyre or Greenland Ice Sheet tipping. In PROMOTE, we (i) undertake targeted development of UKESM to advance its representation of the Greenland Ice Sheet and North Atlantic Subpolar Gyre, (ii) develop innovative simulation techniques aiming to make the simulation of tipping behaviour in the Subpolar Gyre and Greenland Ice Sheet more controlled and efficient, (iii) use machine-learning and other analysis techniques as well as model simulations to inform the design of observational networks, and (iv) evaluate tipping processes and impacts of tipping in our newly developed model versions. PROMOTE is run by a team of scientists and model developers at 7 UK national research centres and universities during 2025-2030, and is part of the “Forecasting Tipping Points” programme funded by the Advanced Research and Invention Agency (ARIA).

Biomarkers and dinoflagellate cyst assemblages are valuable proxies for reconstructing palaeoceanographic conditions and past ocean-ice interactions in polar regions. However, in the modern Southern Ocean, the sparse and uneven distribution of surface sediment samples of these proxies limits our ability to fully evaluate their oceanic and environmental affinities. This is particularly problematic in the West Antarctic region, where upwelling of Circumpolar Deep Water (CDW) onto the continental shelf influences the dynamics and stability of the West Antarctic and Antarctic Peninsula ice sheets. Because these ice sheets could together, if destabilised, contribute an equivalent of 4.5 m to global sea-level rise, better tools for reconstructing CDW and its interactions with the ice sheets are needed. Here we expand the surface sediment database for this region by analysing dinoflagellate cyst assemblages and organic geochemical biomarkers (isoGDGTs, OH-GDGTs, di-unsaturated highly branched isoprenoids) in a new set of 80+ surface sediment samples. We constrain the relationships between dinoflagellate cyst assemblages and surface oceanographic conditions, IPSO25 and sea ice occurrence, and assess TEX86 and TEX86OH as potential proxies for CDW-influenced (sub)surface ocean temperatures. Our refined transfer functions are then used to generate a new GDGT-based temperature record covering 2.5–0.6 million years from IODP Site U1537 in the Scotia Sea’s “Iceberg Alley”. Together, these expanded proxy calibration datasets and their down-core application contribute new insights into past ocean-ice interactions, knowledge vital for understanding future cryosphere and sea level changes.