Abstract. The Arctic is at the forefront of global warming. More frequent and intense rain-on-snow events during winter are altering the annual snowpack with its environmental proxy records, so that Svalbard glaciers are not only rapidly losing mass but are endangered as climate archives. In this study, we aim to visualise and better constrain the influence of near-surface melt caused by small-scale rain-on-snow events on stable water isotope signatures in seasonal snow in the vicinity of Ny-Ålesund in Svalbard. To this end, we first introduce a simple in-situ melt tracer experiment approach and subsequently present new insights into structural imprint and stable water isotope alteration gained during field experiments near Ny-Ålesund in March 2023. We document diverse features resulting from meltwater infiltration, including unprecedented observations of internal layering within melt lenses, and discuss the importance of snow temperature and stratigraphy for percolation behaviour, ranging from preferential to matrix flow in the non-ripe snowpack. Comparisons of δ18O and δ2H signatures before and after each experiment further reveal that percolation-induced stable water isotope changes are localized, i.e. confined to melt structures, so that sub-annual stable water isotope information can be retrieved from unaffected profile parts where annual accumulation is sufficient.

Connecting the West Antarctic Ice Sheet to the southern Antarctic Peninsula, northern Ellsworth Land is a region of enigmatic glacial history now experiencing significant cryospheric change. Large portions of the Bellingshausen-Sea-draining basins have experienced extreme ice thinning and grounding-line change over the satellite observation period. However, the Holocene glacial history of northern Ellsworth Land, which would help to frame the contemporary changes being observed, is poorly constrained. High-resolution ice cores are crucial for reconstructing this past ice-sheet change. We identify a new deep ice-core drilling site at the triple-ice divide point between the Amundsen, Bellingshausen, and Weddell seas (74 degrees 34(')37('') S, 86 degrees 54(')16('') W) that could be utilised to address this knowledge gap. Using a transient ice-thinning model, constrained by shallow-ice-core data and dated englacial radar stratigraphy, we estimate records of accumulation and ice thinning, and derive preliminary age-depth scales for the proposed coring site. Inclusion of dated radar stratigraphy in the model improves our constraints on the long-term climate history, and highlights that these data are not compatible with a steady-state assumption. We also show that there has been a significant change in the accumulation rate regime and/or ice thickness throughout the Holocene. A deep ice core at this site would provide a climate record up to similar to 30 ka with a resolution of 0.58 ka m(-1) at 60 m above the ice-bed interface. An analysis of the model sensitivity to basal melting shows that a record beyond the onset of the Holocene could still be recovered under high basal-melt-rate scenarios. We thus conclude that an ice core at this site would yield a valuable high-resolution climate record and provide precise constraints to reconstruct climatic changes and glacial retreat during the Holocene, to help resolve the onset of the extensive dynamic thinning observed today.

Ice shelves are heterogeneous composites of firn, meteoric ice, refrozen melt and brine-saturated ice. The properties and distribution of these elements control ice shelf response to stress and susceptibility to fracturing. Here, we quantify how surface-melt and brine infiltration modify the Mode I fracture toughness (K-Ic) of meteoric ice on the Brunt Ice Shelf (BIS), Antarctica. During the 2023/2024 austral summer, we recovered a 37 m core sequence from meteoric infill ice near Halley VI, where radar mapping shows continuous brine horizons at <^> 37 m depth and line scans indicate that the upper 37 m contain <^> 7 % refrozen melt. We combined density, salinity, temperature and grain size measurements with semi-circular three-point bending tests on samples representing (i) meteoric ice, (ii) melt-modified meteoric ice, and (iii) brine-infiltrated meteoric ice. Our results show melt-modified samples are consistently tougher than melt-free meteoric ice, with K-Ic increases up to <^> 40%. This is despite their larger grain size, indicating densification dominates over grain-size effects. In contrast, brine-saturated meteoric ice exhibits markedly lower K-Ic, by 14 %-34 % relative to density-matched, brine-free meteoric ice, consistent with chemical weakening and lower freezing temperatures. Our results demonstrate that as K-Ic varies strongly with density, salinity and depth, a spatially and temporally constant toughness value is unlikely to reproduce calving behaviour accurately. Implementing spatially and vertically variable K-Ic values, and understanding how ice shelf structure and composition evolves over time, is essential to improve predictions of rift propagation and calving.

Abstract Southern Hemisphere westerly winds are important drivers of Antarctic and sub‐Antarctic environmental change. Short observational wind records prevent us from fully understanding the scope of their variability. Proxy records provide valuable tools to extend environmental records. Here we present a novel wind study based on the use of windblown diatoms preserved in layers from the first firn core drilled in the sub‐Antarctic Bouvet Island. The firn core diatom record is comprised of high‐concentrations of pristine and locally sourced Southern Ocean marine taxa. This record is the first to characterize the diatom diversity and abundance actively entrained by winds in the sub‐Antarctic region. Correlation analyses reveal interannual diatom abundance variability is primarily driven by wind strength changes in the core of the westerly wind belt. These results validate using the Bouvet Island diatom record as a proxy for reconstructing past atmospheric circulation variability over the Atlantic sector of the westerly wind belt.

The Geological Time Scale provides a global framework for correlating major Earth system changes over geological history. The Anthropocene term is widely used to describe transformative human impacts on the environment but lacks a formal Geological Time Scale definition, and hence is applied and interpreted inconsistently. In this Perspective, we summarize multi-proxy evidence from 12 globally distributed stratigraphic records to show that mid-twentieth century Earth system changes are abrupt, globally synchronous, and stratigraphically distinct, providing a basis for precisely defining the Anthropocene as a series and epoch. Accelerated fossil fuel combustion, industrial pollution and biosphere transformation have caused extensive climate, environmental and ecosystem disruptions that are recorded in stratigraphic successions. Atmospheric carbon dioxide and methane concentrations at 51% and 157% above Holocene levels have driven global temperatures to 1.5 °C above pre-industrial levels, marking a substantial departure from earlier relatively stable climatic conditions. A sharp global plutonium increase in 1952, related to above-ground thermonuclear detonations, provides the most suitable primary marker for establishing the Anthropocene’s base, supported by an array of proxies, many unique to the Anthropocene. Formal recognition of the Anthropocene on the Geological Time Scale would communicate the scale and abruptness of human-driven Earth system change, distinct from the less pronounced human impacts during the Holocene. The Anthropocene is widely used without fixed definition. This Perspective argues for its base to be defined in 1952 by a sharp plutonium upturn coinciding with changes in multiple proxies, providing a globally correlatable horizon reflecting substantial human-driven Earth system disruption.

Rising global temperatures and accelerated melting cause glaciers across the globe to shrink, thereby hampering our ability to reconstruct past climate from ice cores across the globe. In this context, melt-induced alterations of chemical signals in ice cores are an increasing issue not only for researchers working on mid- and low-latitude glaciers but in coastal Antarctica, Greenland, and other (sub-)polar sites, too.Aiming to contribute to a more comprehensive understanding of ice cores as environmental archives when affected by melt, Moser et al. (2023) have recently conducted an in-depth review of the existing literature regarding external drivers of melt events, physics of melt layer formation and behaviour during snow metamorphism, identification and quantification of melt, structural characteristics of melt features, effects of melting on records of chemical impurities, stable water isotopic signatures, and gas record, as well as applications of melt layers as environmental proxies. By briefly walking through formation, manifestation and potential interpretation of refrozen melt sections, we here provide an overview of those aspects of near-surface melting, which are important for ice-core record interpretation more widely.Against this backdrop of existing research and gaps of knowledge, we present the setup and first results of percolation tracer experiments conducted during a field campaign near Ny-Ålesund, Svalbard, in March-April 2023. Showing the alteration of snowpack structure and chemistry through liquid water in-situ, the experiments have provided new insights into (1) meltwater flow and refreezing processes in the vicinity of Ny-Ålesund, and (2) the informational value of stable water isotope records before and after rain-on-snow induced melt events. Finally, we compare these in-situ observations to high-resolution structural scans of melt features in ice cores to explore further conclusions, which help to improve our understanding of melt-affected ice cores. Moser, D. E., Thomas, E. R., Nehrbass-Ahles, C., Eichler, A., & Wolff, E. (2023). Melt-Affected Ice Cores for (Sub-)Polar Research in a Warming World. EGUsphere Preprint. https://doi.org/10.5194/egusphere-2023-1939

Ice core reconstructions of atmospheric methane (CH4) and its stable carbon isotope ratio (δ13CH4) provide important constraints for understanding the links between human activity, methane and climate. However, uncertainties in existing δ13CH4 records since the preindustrial (~1850 CE), reconstructed from measurements of polar firn air and a small number of high-accumulation ice core sites, limit the precise determination of the timing and rate of recent changes in source/sink evolution. To re-assess methane dynamics over the last two centuries, we present continuous multi-core records of atmospheric CH4 and carbon monoxide (CO) between 1824 and 1994 CE reconstructed from high snow accumulation Antarctic sites and supplement these data with new bubble ice measurements of δ13CH4 spanning 50-years from 1938 to 1988 CE at a < 5-year resolution. Across the 50-year record, atmospheric CH4 mixing ratios increase by > 580 ppb and each δ13CH4 measurement therefore requires a considerable correction for diffusive fractionation resulting from a sustained growth in the overlying atmospheric methane burden during firn transport. An overlap with direct atmospheric observations is used to validate corrections for this phenomenon. Source/sink dynamics necessary to drive the simultaneous temporal trends observed in CH4, CO and δ13CH4 since 1850 CE are then inferred using a 6-troposphere, multi-tracer box model. Isotopic corrections, their implications and subsequent modelling results will be discussed.

Arctic and subarctic regions are warming at an alarming rate, with consequences for permafrost degradation, greenhouse gas emission, ecosystem destabilization, and infrastructure deterioration. Despite high latitude sensitivity to modern climate change, a substantial gap remains in our understanding of high latitude environmental response to past episodes of climatic change. Peat soils, common across the high latitudes, provide a valuable archive for paleoclimate reconstruction to address this knowledge gap. Many such records exist across interior Alaska and have high potential as paleoclimate archives.Here we develop a multi-proxy paleoclimate record from a peat bog soil (Terric Hemistel) in the Delta River Valley of interior Alaska to explore mechanisms of peatland initiation and evolution. We aim to develop a comprehensive record related to the formation and evolution of this peat bog and test the hypothesis that increased moisture availability and water perching within the soil, rather than warmer temperatures, initiated peatland development. We evaluate key physical and chemical properties of organic and mineral soil materials from pedon descriptions and samples collected by horizon with depths defined according to organic matter content, bulk density, pH, carbon (C), nitrogen (N), and the carbon to nitrogen (C/N) ratio. We use radiocarbon dates to build an age-depth model and analyze stable isotopic signatures (δ13C) of bulk material for moisture and habitat changes, while also evaluating compound-specific isotopic trends (δ13C, δD) of plant waxes to track hydrological fluctuations. Finally, we perform analyses of bacterial branched glycerol dialkyl glycerol tetraethers (brGDGTs) to enable temperature reconstruction.Our preliminary chronological framework demonstrates the initiation of the peat bog during the Middle Holocene (ca. 6800 cal yr BP) with a consistent growth rate of ~0.15 mm/yr. At the landscape scale, there is relative stability indicated by pedogenesis through the Holocene, but at the pedon scale there is a shift from concurrent aeolian deposition and mineral soil development to accumulation of organics. This shift in predominant parent material is likely due to a changing moisture regime, inferred to be the result of feedbacks between increased summer precipitation and increased soil water holding capacity. We hypothesize that brGDGTs will show relatively flat temperatures through the Holocene, following other work in the area, while C/N ratios and stable isotope data will indicate pronounced changes in moisture. This multi-proxy approach will help improve models of peatland formation and resolve debate over the response of peatlands to varying climatic conditions (e.g., drier vs. wetter). Such work is particularly important for contextualizing peatland development under ongoing and future climate change.

Low-concentration insoluble microparticles that are preserved in ice cores offer valuable information for reconstructing past environmental changes. However, their low concentrations and limited sample availability present challenges for extraction and recovery while ensuring representativeness of results. The analysis of ice cores using continuous flow analysis systems generates large volumes of excess meltwater as a by-product with the potential to improve the acquisition of targeted low-concentration insoluble microparticle samples. Here, we present Antarctic ice core diatom records, representative of targeted low-concentration insoluble microparticle records, recovered from excess meltwater generated from a continuous flow analysis system. We analyse these records to evaluate the feasibility of using this excess meltwater to generate replicable and representative results. Our results demonstrate that diatom records obtained from a continuous flow analysis system exhibit high recovery percentages and replicability, with minor quantifiable loss and memory effects in the system. Our multi-outlet sampling assessment highlights that the waste lines of the continuous flow analysis system are an optimal source for sampling excess meltwater. Additionally, the analysis of diatom spatial distribution in filters suggest a lower threshold for applying analytical methods which assume targeted microparticles are homogeneously distributed. These results confirm that a continuous flow analysis system can be used to extract targeted low-concentration insoluble microparticles from ice core samples, yielding representative and reproducible results.

The Southern Hemisphere westerly winds (SHWWs) (45-65 degrees S) are important regulators of the Southern Hemisphere climate. The scarcity of observational records at the core of the wind belt hinders our understanding of the environmental impact and long-term variability of the westerly winds. The Cordillera Darwin Icefield (CDI) (54-55 degrees S) is favorably located to capture environmental changes at the current core of the SHWW belt. Here, we present chemical and microparticle records from the first firn core from the CDI. We evaluate regional climate reanalysis data using in situ automatic weather station observations and apply a downscaling approach to study regional-to-local environmental conditions at the firn core site. We use these records to assess the preservation of local-to-regional environmental information in the firn. Our CDI firn core records present minor post-depositional disruptions, preserving the original seasonality of locally sourced impurities. Local surface air temperature and melt estimations suggest the icefield has been progressively exposed to surface melt conditions, but not enough to produce significant melt at the firn core site. Air mass trajectories demonstrate air parcels are directly transported from local marine and terrestrial environments, establishing a route for the transport and deposition of chemical compounds and aerosols to the firn core site. These results highlight the potential of high elevation sites (>2,000 m a.s.l) in the CDI to hold valuable paleoenvironmental records directly from the core of the SHWW belt, records which are currently threatened by increasing surface air temperatures.

In recent decades, the Southern Hemisphere westerly winds have strengthened and migrated south, attributed to greenhouse gas emissions and stratospheric ozone depletion. However, the onset and acceleration of these drivers is coincident with the start of the instrumental record, thus, hindering our ability to determine the significance of the recent trends. Here, we present a novel wind reconstruction based on marine diatoms preserved in an Antarctic Peninsula ice core, providing a unique record to reconstruct westerly winds across the Pacific sector of the Southern Ocean (SO). The annually resolved record provides clear evidence that a southward migration of the Pacific sector westerly wind belt occurred in the 1960s, coupled with a prolonged strengthening trend. The poleward shift and acceleration of the westerly winds across this SO sector is unprecedented in the context of the past 140 years and coincident with the anthropogenically induced increase in greenhouse gases and ozone depletion.

Zygnematophycean "glacier algae" form extensive blooms on ablating glacier surfaces despite the ultra-oligotrophic conditions apparent. Previous work has postulated that this oligotrophic bloom paradox is due to (i) lower nutrient requirements of glacier algae, (ii) efficient uptake and storage of the nutrients available, and/or (iii) ineffective characterisation of the actual nutrient environment that glacier algae experience. We investigate the latter here by directly sampling the thin (∼2 mm) melt water film in which glacier algal cells reside across three glaciers in Svalbard during the 2023 melt season, comparing to outcomes from more typical bulk ice sampling techniques. Micromelt samples generally contained increased concentrations of ammonium (NH4+), nitrate (NO3-), nitrite (NO2-), and phosphate (PO43-), though trends were not uniform, and concentrations remained well within oligotrophic levels. Several major ion species were significantly increased in micromelt fractions as compared to bulk samples, indicating aeolian deposition and marine aerosol influences on the glacier algal environment. In turn, enhanced micromelt dissolved organic carbon concentrations (DOC) indicated likely DOC delivery by glacier algae to the microbial food web from the onset of bloom formation. Taken together, datasets reveal new fine-scale heterogeneity in the glacier algal meltwater environment.

The extent of grounded ice and buttressing by the Ronne Ice Shelf, which provides resistance to the outflow of ice streams, moderate West Antarctic Ice Sheet stability. During the Last Glacial Maximum, the ice sheet advanced and was grounded near the Weddell Sea continental shelf break. The timing of subsequent ice sheet retreat and the relative roles of ice shelf buttressing and grounding line changes remain unresolved. Here we use an ice core record from grounded ice at Skytrain Ice Rise to constrain the timing and speed of early Holocene ice sheet retreat. Measured δ 18 O and total air content suggest that the surface elevation of Skytrain Ice Rise decreased by about 450 m between 8.2 and 8.0 kyr before 1950 ce (±0.13 kyr). We attribute this elevation change to dynamic thinning due to flow changes induced by the ungrounding of ice in the area. Ice core sodium concentrations suggest that the ice front of this ungrounded ice shelf then retreated about 270 km (±30 km) from 7.7 to 7.3 kyr before 1950 ce . These centennial-scale changes demonstrate how quickly ice mass can be lost from the West Antarctic Ice Sheet due to changes in grounded ice without extensive ice shelf calving. Our findings both support and temporally constrain ice sheet models that exhibit rapid ice loss in the Weddell Sea sector in the early Holocene.

Marine-sourced fatty acids provide a promising new suite of proxies for past sea-ice reconstructions, validated using ice cores from Bouvet Island, Greenland, and Alaska. Despite showing great potential as a sea-ice proxy, the transport, deposition, and preservation of these fatty acids within the ice sheet are poorly understood. Additionally, complementary data of the same suite of fatty acids in the source, the surrounding sea ice, is lacking in number, spatial distribution, and seasonal variety, especially in the Antarctic. This study presents an improved method using high-performance liquid chromatography high-resolution mass spectrometry (HPLC-HRMS) for the determination of marine-sourced fatty acids in ice cores and sea ice. The method presents a new preconcentration step using stir bar sorptive extraction (SBSE) as well as reduced background contamination using a trapping column tandem analytical system in HPLC. The method is suitable to detect and quantify a suite of 10 fatty acids with recoveries above 70% and with limits of detection in the low ppb and subppb levels. A range of fatty acids were detected and quantified in samples from two sub-Antarctic ice cores, taken from Peter first Island and Young Island. The results from these cores displayed a variety of fatty acids present in both ice cores (lauric acid, myristic acid, oleic acid, linoleic acid, palmitoleic acid, heptadecanoic acid, pentadecanoic acid, docosahexaenoic acid, eicosapentaenoic acid, and arachidonic acid) as well as a large difference in concentrations between different fatty acids and between the two ice cores. Additionally, this study presents the first results of fatty acid concentrations in the pancake sea ice collected from the Antarctic Marginal Ice Zone.

Global attention has been focused on extreme climatic changes. This paper investigates the relationship between different phases of solar activity and extreme precipitation events in Kerala, India. Sunspot number and rainfall data were analysed over 122 years (1901-2022) on an annual scale. A negative correlation was observed in the winter and post-monsoon seasons, while positive correlations were seen in the pre-monsoon and monsoon seasons, all of which were statistically significant. Using cross-wavelet transform, the temporal relationship between sunspot number and rainfall values was investigated, revealing significant cross-power at an 8-12 year scale across all seasons. Wavelet coherence between the two data sets demonstrated significant correlation at the 2-4 and 4-8 year scales throughout the four seasons. The results show that the seasonal rainfall over Kerala is related to solar activity. The solar phases of Solar Cycles 14-24 were determined for all seasons, and the years with excessive and insufficient rainfall were identified. It was observed that the descending phase had an impact on excess rainfall events during the winter and pre-monsoon seasons, while the ascending phase notably affected the monsoon and post-monsoon seasons. The study specifically examined the different magnetic polarities of sunspots in alternating solar cycles, focusing on even and odd cycles. It was found that extreme rainfall events were more frequent during the winter and pre-monsoon seasons in the even cycles, whereas in the odd cycles, they were more prevalent during the monsoon and post-monsoon seasons. These findings are presented for the first time and may offer new perspectives on how different phases affect rainfall. This study suggests a physical link between solar activity and extreme precipitation in Kerala, which could increase predictability.

Records of the volcanic forcing of climate prior to the satellite era depend on scaling the flux of sulfate deposited on polar ice sheets­ using a ‘transfer function’, a number calibrated based on radioactivity in Greenland from thermonuclear testing as well as Antarctic sulfate flux records from the 1991 Pinatubo eruption (e.g. Gao et al., 2007). For high latitude eruptions, this transfer function is based solely on model simulations of sulfate flux to Greenland from the Icelandic Laki eruption in 1783 and the Alaskan Katmai/Novarupta eruption in 1912 (Gao et al., 2007).  Since the initial determination of this transfer function, the number of ice cores containing sulfate from the Pinatubo eruption has increased eight-fold, and sulfur isotope measurements at high resolution over sulfate peaks in the ice has allowed for discrimination between stratospheric sulfate and sulfate transported at lower levels in the atmosphere from different sources (e.g. Burke et al., 2023). Here we revisit the estimation of the transfer function in light of these new data-based constraints from eruptions in the 20th century, and we reassess the uncertainty associated with the application of a single transfer function across volcanic eruptions in the past.   Gao, C., Oman, L., Robock, A. and Stenchikov, G.L., 2007. Atmospheric volcanic loading derived from bipolar ice cores: Accounting for the spatial distribution of volcanic deposition. Journal of Geophysical Research: Atmospheres, 112(D9). Burke, A., Innes, H.M., Crick, L., Anchukaitis, K.J., Byrne, M.P., Hutchison, W., McConnell, J.R., Moore, K.A., Rae, J.W., Sigl, M. and Wilson, R., 2023. High sensitivity of summer temperatures to stratospheric sulfur loading from volcanoes in the Northern Hemisphere. Proceedings of the National Academy of Sciences, 120(47), p.e2221810120.

Peter I Island is situated in the Bellingshausen Sea, a region that has experienced considerable climate change in recent decades. Warming sea surface temperatures and reduced sea ice cover have been accompanied by warming surface air temperature, increased snowfall, and accelerated mass loss over the adjacent ice sheet. Here we present data from the first firn core drilled on Peter I Island, spanning the period 2001-2017 CE. The stable water isotope data capture regional changes in surface air temperature and precipitation (snow accumulation) at the site, which are highly correlated with the surrounding Amundsen-Bellingshausen seas and the adjacent Antarctic Peninsula (r > 0.6, p < 0.05). The firn core data, together with the unique in situ data from an automatic weather station, confirm the high skill of the ERA5 reanalysis in capturing daily mean temperature and inter-annual precipitation variability, even over a small sub-Antarctic island. This study demonstrates the suitability of Peter I Island for future deep-ice-core drilling, with the potential to provide a valuable archive to explore ice-ocean-atmosphere interactions over decadal to centennial timescales for this dynamic region.

Melting polar and alpine ice sheets in response to global warming pose ecological and societal risks but will also hamper our ability to reconstruct past climate and atmospheric composition across the globe. Since polar ice caps are crucial environmental archives but highly sensitive to ongoing climate warming, the Arctic and Antarctic research community is increasingly faced with melt-affected ice cores, which are already common in alpine settings of the lower latitudes. Here, we review the characteristics and effects of near-surface melting on ice-core records, focusing on a polar readership and making recommendations for melt-prone study regions. This review first covers melt layer formation, identification and quantification of melt, and structural characteristics of melt features. Subsequently, it discusses effects of melting on records of chemical impurities, i.e. major ions, trace elements, black carbon, and organic species as well as stable water isotopic signatures, gas records, and applications of melt layers as environmental proxies. Melting occurs during positive surface energy balance events, which are shaped by global to local meteorological forcing, regional orography, glacier surface conditions and subsurface characteristics. Meltwater flow ranges from homogeneous wetting to spatially heterogeneous preferential flow paths and is determined by temperature, thermal conductivity and stratigraphy of the snowpack. Melt layers and lenses are the most common consequent features in ice cores and are usually recorded manually or using line scanning. Chemical ice-core proxy records of water-soluble species are generally less preserved than insoluble particles such as black carbon or mineral dust due to their strong elution behaviour during percolation. However, high solubility in ice as observed for ions like F−, Cl−, NH4+ or ultra-trace elements can counteract the high mobility of these species due to burial in the ice interior. Stable water isotope records like δ18O are often preserved but appear smoothed if significant amounts of meltwater are involved. Melt-affected ice cores are further faced with questions about the permeability of the firn column for gas movement, and gas concentrations can be increased through dissolution and in situ production. Noble gas ratios can be useful tools for identifying melt-affected profile sections in deep ice. Despite challenges for ice-core climate reconstruction based on chemical records, melt layers are a proxy of warm temperatures above freezing, which is most sensitive in the dry snow and percolation zone. Bringing together insights from snow physics, firn hydrology, and ice-core proxy research, we aim to foster a more comprehensive understanding of ice cores as climate and environmental archives, provide a reference on how to approach melt-affected records, and raise awareness of the limitations and potential of melt layers in ice cores.

Biogenic volatile organic compounds (BVOCs) contribute to the formation of secondary organic aerosol (SOA) through atmospheric oxidation. Previously detected SOA-markers in northern hemisphere ice cores from Alaska, Greenland, Russia, and Switzerland indicate the transportation of isoprene and monoterpene oxidation products from their forestry sources to these glacial regions. Antarctica is geographically further removed from the BVOC's source, indicating significantly lower SOA-marker concentrations are likely in southern hemisphere ice cores. The aim of this study was to develop a sensitive mass-spectrometric method to detect and quantify low-abundance SOA-markers of isoprene and monoterpenes in ice core samples. Employment of a triple quadrupole HPLC-MS method enabled limit of detections in the range of 0.4-10 ppt for nine terrestrial SOA-markers and a marker of biomass burning, levoglucosan. Quantification was conducted in the multiple reaction monitoring mode with two specific transitions monitored for each target compound. Application of the developed method onto a section of a Jurassic ice core from Antarctica revealed the presence of seven of the target compounds: 2-methylerythritol, 2-methylglyceric acid, cis-pinonic acid, 3-methyl-1,2,3-butanetricarboxylic acid, pinolic acid, cis-norpinonic acid, and pinic acid. Repeatability ranged between 2.2% and 6.2%. This is the first time that such SOA-markers have been discovered and quantified in Antarctic ice.