Understanding the roles of human land use and climate in shaping past fire regimes is key to predicting future landscape fires and informing effective management decisions. This is especially true for southeast Australia, which has some of the most flammable vegetation on the planet and faces the ongoing impacts of mega wildfires. There is also an ongoing debate on the need for a cultural approach to fire management. Using the Bass Strait Islands as a case study, this talk explores vegetation, fire regimes, Aboriginal land use, and climate change during the Holocene. It provides insights into how the interplay between cultural burning practices and climate influenced fire regimes and shaped the landscape, which has implications for effective future fire management in the region.
How to cite: Adeleye, M.: The impact of cultural burning and climate change on landscape fires, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13287, https://doi.org/10.5194/egusphere-egu25-13287, 2025.
Australia has long been recognized as one of the world’s fire hotspots, but the Black Summer of 2019-2020, when 97,000 km2 were scorched across southeastern Australia, and the larger fires of northern Australia’s savanna and desert in 2023, may indicate a shift toward a higher level of fire activity. Placing these events in context requires developing precisely-dated, high resolution records of bushfire through periods with different climate and land use mean states. We reconstructed bushfire activity for the period 1110-2009 CE using polycyclic aromatic hydrocarbons (PAH) in three precisely-dated, fast-growing, and partially overlapping aragonite stalagmites from cave KNI-51, located in the central Australian tropical savanna. PAH molecular weights are tied to combustion temperature (i.e., low molecular weights form in lower temperature fires), and thus our record preserves evidence of both the timing and intensity of bushfire over the majority of the last millennium.
Comparisons of burn scar satellite imagery with temporal changes in PAH abundances in recently deposited stalagmite suggest that airfall (smoke and ash) from fires within a 5 km radius is primarily responsible for transmitting PAH to the land surface over the cave, a finding supported by our recent controlled burn and irrigation experiment. The rapid growth rate of KNI-51 stalagmites (1-2 mm yr-1), coupled with the extremely thin soils above the cave, appear to allow for transmission and preservation of multi-annual paleofire signals.
To investigate the effects of external forcing on bushfire activity over the last millennium, we applied linear mixed-effect regression to the PAH data, and also included monsoon rainfall (using oxygen isotope ratios from the same stalagmites), annual surface air temperature (using output from the CESM-Last Millennium Ensemble), antecedent fire (using the same stalagmite PAH record), and timing with respect to the arrival of European pastoralists (EP) and their cattle in the 1880s.
The model reveals significant differences prior to and following the arrival of EP. Most notably, prior to the arrival of EP, rainfall was significantly correlated with low and medium intensity fires, but not high intensity ones. After the arrival of EP, the correlation between rainfall and fire activity decreased markedly, and showed no statistically significant correlation to any fire intensity. Similarly, prior to the arrival of EP, antecedent fire activity (determined as the sum of PAH within the previous 5 years) was correlated with all levels of fire intensity, but after EP arrival, only high intensity fires are correlated with such antecedent burning. Our findings thus suggest that fire activity following the arrival of EP in the eastern Kimberley has been distinct from any other extended period of the last nine centuries.
How to cite: Denniston, R., Ondei, S., Argiriadis, E., Rowe, E., Bowman, D., Cugley, J., Woods, D., Kershaw, R., Lee, M., Schuchart, V., Carter, T., and Allen, K.: Pyrogenic Compounds in Tropical Australian Stalagmites Record Changes in Bushfire-Climate Relationships Coincident with the Arrival of European Pastoralists, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1823, https://doi.org/10.5194/egusphere-egu25-1823, 2025.
Tropical alpine environments are some of the most sensitive areas in the world to climate change. The effects of climate change are already apparent in African montane environments as glaciers have significantly retreated and recent droughts, fires, and floods have impacted local communities and ecosystems. The short duration of observational records limits our ability to test whether these disturbances result from natural climate variability or human activity. We used lake sediment cores spanning the last 12 ka from the Rwenzori Mountains, Uganda-D.R.C., to test relationships between fire regimes, vegetation, and climate at two distinct elevations. At mid-elevations, fire activity is suppressed during the warm, wet African Humid Period, but increases with drying and cooling over the late Holocene. At 2 ka, fire abruptly increases triggering a sudden shift to a grass dominated ecosystem, most likely as a result of human ignitions associated with the Iron Age in Africa. At high elevations, despite recent large-scale destructive fires, there is no evidence for local fire over the last 12 ka until the 21st century, implying that fire is novel disturbance in the afroalpine zone. Our results show humans, rather than climate, are a major driver of afromontane fire likely through their control on ignition and as result, changes in fire regimes can cause dramatic ecosystem transformation. Thus, the creation of management plans for these unique ecosystems which focus on prevention of human ignitions are critical for these unique ecosystems, especially in the context of future climate change.
How to cite: Mason, A., Pereboom, E., Russell, J., Ivory, S., Vachula, R., Garelick, S., and Nakileza, B.: Afromontane Fire is a Novel, Transformative, and Human-driven Disturbance, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2651, https://doi.org/10.5194/egusphere-egu25-2651, 2025.
Fire regimes have distinct global controls, and how burnt area, wildfire size and wildfire intensity independently respond to changes in climate, vegetation, and human activity remains challenging to quantify. Here, we use robust empirical models of burnt area, fire size and a measure of intensity to explore the global sensitivity of fire regimes to changes in climate, atmospheric CO2 and human activity under contrasting climate states, specifically at the end of the century under two climate change mitigation scenarios and at the Last Glacial Maximum. Our simulations show a global shift in wildfire patterns by 2100 CE under both low- and high-mitigation scenarios with reduced burnt area in tropical regions but larger and more intense wildfires in extra-tropical regions. Under low mitigation, increases in burnt area worldwide overwhelm the current human-driven declining trend, with fire size and intensity increasingly limited by dryness and vegetation fragmentation. Under different future conditions burnt area continues to increase due to changes fuel availability and dryness, fire intensity is increasingly limited by fuel build-up, and fire size by fuel continuity. These trends differ from those shown in simulations at the last Glacial Maximum, which show decreased burnt area, alongside increased fire size and intensity compared to present, consistent with sedimentary charcoal evidence. The decoupling between different fire properties occurs because of the different temporal and spatial scales on which the controls of burnt area, fire size and fire intensity operate. Under future conditions, the effect of a warming climate and increasing atmospheric CO2 amplify each other, whereas in cold climate with low atmospheric CO2, they dampen each other. These findings have immediate implications for the improvement of process-based fire models, which currently do not take the distinctions between these fire properties into account. They also suggest that the current observed patterns of fire regimes today may not hold constant under changing conditions.
How to cite: Haas, O., Prentice, C., and P. Harrison, S.: Assessing the sensitivity of fire regimes to climate, atmospheric CO2 and human activity under past and future conditions , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1704, https://doi.org/10.5194/egusphere-egu25-1704, 2025.
Pollen records are the most widespread archive for past climate and vegetation changes, offering valuable insights into Earth’s environmental history. These records provide a unique opportunity to evaluate Earth System Models. In recent years, the availability of quantitative plant cover reconstructions on a continental scale has increased, exemplified by the consistent dataset of REVEALS-based reconstructions provided by Schild et al. (2024) for the entire Northern Hemisphere.
We use this data set for comparison with the changes in tree cover simulated by the Max Planck Institute Earth System Model (MPI-ESM) for the last 20,000 years. While the overall agreement between model and data is promising, there are significant regional discrepancies. Notable differences emerge in boreal regions such as Alaska/Western Canada and Siberia, where the model predicts a delayed and weaker tree cover increase during the deglaciation. Conversely, in temperate forest-steppe transition zones, the model shows an earlier and stronger tree cover expansion, balancing out the Northern Hemispheric mean change.
However, systematic biases complicate the interpretation of this comparison. For instance, the model tends to simulate excessively cold conditions in boreal latitudes, while the reconstructions likely overestimate tree cover in these regions. As a result, the agreement in vegetation history remains uncertain leaving the comparison of absolute values between reconstructions and model results questionable. An EOF analysis highlights common modes of vegetation changes over the last 20,000 years in MPI-ESM and reconstructions, deepening our understanding despite these uncertainties.
References: Schild, L., Ewald, P., Li, C., Hébert, R., Laepple, T., and Herzschuh, U.: LegacyVegetation 1.0: Global reconstruction of vegetation composition and forest cover from pollen archives of the last 50 ka, Earth Syst. Sci. Data Discuss. [preprint], https://doi.org/10.5194/essd-2023-486, in review, 2024
How to cite: Dallmeyer, A., Schild, L., Claussen, M., Kleinen, T., and Herzschuh, U.: Challenges and insights in comparing simulated tree cover changes over the last 20,000 years with reconstructions for the Northern Hemisphere, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8759, https://doi.org/10.5194/egusphere-egu25-8759, 2025.
The Plio-Pleistocene transition (1.5–3 million years ago) was marked by a significant drop in the atmospheric CO2 level by approximately 140 ppm, driving global cooling and amplifying glacial-interglacial cycles [1,2]. While glaciation-induced continental erosion and terrestrially derived organic carbon (OC) burial are typical factors considered key drivers, these processes do not fully explain the causal mechanism in driving the CO2 drawdown without including regions near mid- and low-latitudes [3]. The ecosystem responses to wildfires and post-fire storms can help elucidate these changes. Here, we investigate the impact of wildfires on OC burial rates at regional and global scales from 4 to 1.5 Ma. Regionally, we reconstructed wildfire activity across South Asia using stable nitrogen isotopes of fixed ammonium in clay minerals and pyrogenic carbon abundances. Our study focused on sedimentary records from the Kashmir Siwalik sedimentary succession and the Nicobar Fan sediments from IODP Expedition 362, Site U1480, which provide insights into processes associated with the Andaman-Nicobar accretionary prism and the Indo-Myanmar ranges. The findings reveal a significant intensification of wildfire activity during the Plio-Pleistocene transition (1.5–3.0 Ma), accompanied by a 2.9- and 2.4-fold increase in continental erosion rates and organic carbon burial flux compared to the early Pliocene (3.0–4.0 Ma). We compiled a comprehensive wildfire dataset on a global scale, integrating 20 proxy records from continental and marine sediments. By combining sediment OC content and Mass Accumulation Rate data from 23 ODP/IODP sites worldwide, we quantified the global rate of OC burial. Our findings reveal a dramatic 4.8-fold increase in wildfire activity and a 1.5-fold rise in global OC burial rates, from 2.29 ± 0.48 Mt C per year during the early Pliocene to 3.52 ± 0.80 Mt C per year at the Plio-Pleistocene transition. These results highlight the significant role of fire-driven processes in atmospheric CO2 drawdown, a mechanism that previous studies have largely overlooked.
References:
[1] Hönisch et al., 2023. Science, 382(6675), p.eadi5177.
[2] Hansen et al., 2013. Philos. Trans. R. Soc. A Math. Phys. Eng. Sci. 371(2001), p.20120294.
[3] Herman et al., 2013. Nature, 504(7480), pp.423-426.
How to cite: Sakthivel, T., Ghosh, P., Ali, S., and Munazir Chauhan, M.: Plio-Pleistocene CO2 drawdown related to wildfire-induced terrestrial organic carbon burial, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-504, https://doi.org/10.5194/egusphere-egu25-504, 2025.
To unravel which processes are responsible for changes in atmospheric CO2 the carbon isotopes are useful helpers widely applied in the past. This study helps to better understand long-term changes in 13C, which has also consequences for the interpretation of atmospheric δ13CO2 measured together with CO2 in ice cores.
The 13C cycle of the Plio-Pleistocene, as recorded in δ13C of benthic foraminifera, has power in periodicities related to the long eccentricity cycle of 405-kyr that is missing in corresponding climate records (e.g. δ18O). Using a global carbon cycle model I show that the long eccentricity cycle in δ13C might have been caused by variations in the isotopic signature of geological sources, namely of the weathered carbonate rock (δ13Crock) or of volcanically released CO2 (δ13Cv). This closure of the 13C cycle in these peridicities also explains the offset in atmospheric δ13CO2 seen between the penultimate and the last glacial maximum. The necessary isotopic signatures in δ13Crock or δ13Cv which align my simulations with reconstructions of the 13C cycle on orbital timscales have most power in the obliquity band (41-kyr) suggesting that land ice dynamics are the ultimate cause for these suggested variations. Since the Asian monsoon as reconstructed from speleothems has also an obliquity-related component it is possible that these proposed changes in weathering are indeed, at least partly, connected to the monsoon as previously suggested. Alternatively, the suggested impact of land ice or sea level on volcanic activity might also be influential for the 13C cycle. This indirect influence of ice sheets on the long eccentricity cycle in δ13C implies that these processes might not have been responsible for the 405-kyr periodicity found in ice-free times of the pre-Pliocene parts of the Cenozoic.
See preprint (https://doi.org/10.5194/cp-2024-63) for details.
How to cite: Köhler, P.: Closing the Plio-Pleistocene 13C cycle in the 405-kyr periodicity by isotopic signatures of geological sources , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5934, https://doi.org/10.5194/egusphere-egu25-5934, 2025.
Changes in the marine biological carbon pump during glacial times have been supposed to contribute to the glacial CO2 drawdown. One particular hypothesis that received attention during last two decades is the Silicic Acid Leakage Hypothesis (SALH), which proposed the Si leakage during glacial times from the Southern Ocean (SO) was transported towards lower latitudes and then contributed to enhanced biological productivity there and thus to global cooling by lowering atmospheric pCO2.
Thanks to the flexible stoichiometry (C:N:Si:Chl ratios) implemented in the biogeochemistry model REcoM (used with AWIESM2), we are able to study Si leakage based on changes in diatom physiology and its effect on nutrient supply to low-latitude surface waters. Our simulations show a significant increase of Si:N ratios in surface seawater in the SO and southern-sourced mode waters at Last Glacial Maximum (LGM) when compared to pre-industrial, confirming the first part of SALH. However, due to stronger stratification and weaker upwelling during LGM, these Si-enriched waters cannot be transported to the low-latitude surface to induce higher diatom growth, arguing against the second part of SALH but in agreement with reconstructions of marine opal accumulation rates. Instead, the simulation of the beginning of the glacial termination reveals that Si leakage during deglaciation drives a low-latitude productivity increase, supporting the more recent Silicic Acid Ventilation Hypothesis (SAVH). The effect of increased biological carbon uptake is more than compensated by intense CO2 outgassing through stronger ventilation, resulting in a rapid CO2 rise during deglaciation.
How to cite: Ye, Y., Köhler, P., Butzin, M., and Völker, C.: Silicic acid leakage during Last Glacial Maximum and glacial termination, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12616, https://doi.org/10.5194/egusphere-egu25-12616, 2025.
The mid-Pleistocene transition (MPT) is arguably the most enigmatic long-term climate shift of the Quaternary and is characterized by increasingly severe glacial conditions about 1.2 to 0.6 million years ago. Although the MPT was suggested to be linked with a continuous lowering of glacial atmospheric CO2 (CO2,atm) levels, the processes underlying this CO2,atm decline are incompletely understood. Here we compare two new benthic foraminiferal (Cibicidoides/Cibicides sp.) δ13C records reflecting Circumpolar Deep Water (CDW), from central South Pacific International Ocean Discovery Program Site U1541 (54.2°S, 125.4°W, 3606 m water depth) and Southeast Atlantic Ocean Drilling Program Site 1094 (53.2°S, 05.1°E, 2807 m water depth), with similar records from the global ocean to identify possible reorganizations in the oceanic respired carbon pool over the past 2 million years that may explain CO2,atm changes across the MPT. We show a good agreement between lower CDW δ13C signatures in the central South Pacific and in the Southeast Atlantic, and a wide-spread glacial decline in CDW δ13C signatures across five Southern Ocean sites during the MPT. This points at a contribution from reduced glacial CDW ventilation and increased glacial respired carbon storage in the Southern Ocean to the glacial CO2,atm decline across the MPT. We also highlight an Atlantic-Pacific Southern Ocean-wide increase in the magnitude of deglacial CDW δ13C shifts during the MPT, which coincides with an amplitude increase in glacial-interglacial Antarctic Circumpolar Current flow strength variations (Lamy et al., 2024). This highlights that not only an increased Southern Ocean respired carbon storage might have driven CO2,atm variations across the MPT but also more efficient outgassing of that carbon during deglacial phases post-MPT. We will address potential linkages of glacial respired carbon storage and deglacial outgassing to changes in Antarctic ice sheet dynamics and southern hemisphere westerlies across the MPT.
References:
Lamy, F., Winckler, G., Arz, H., Farmer, J., Gottschalk, J., Lembke-Jene, L., Middleton, J.L., et al., 2024. Five million years of Antarctic Circumpolar Current strength variability. Nature 627, 789–796. doi: 10.1038/s41586-024-07143-3
How to cite: Gottschalk, J., Hasenfratz, A. P., Middleton, J. L., Farmer, J. R., Michel, E., Basak, C., Hanley, J. E., Knudson, C. A., Jaccard, S. L., Lamy, F., and Winckler, G.: Southern Ocean contribution to glacial atmospheric CO2 decline across the mid-Pleistocene transition, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8406, https://doi.org/10.5194/egusphere-egu25-8406, 2025.
The Southern Ocean (SO) is believed to play a pivotal role in modulating atmospheric CO2 concentrations, both across glacial/interglacial cycles and during abrupt climate shifts. Previous studies using coarse-resolution Earth system models have suggested that stronger southern hemisphere westerly winds enhance the upwelling of deep waters, which in turn increases CO2 outgassing. However, mesoscale processes have a significant impact on Southern Ocean circulation. To better capture these dynamics, we assess the effects of changes in the position and strength of the southern hemisphere westerlies through a series of numerical simulations using the eddy-rich and eddy-permitting ocean, sea-ice, and carbon cycle model, ACCESS-OM2. Our results show that a 10% increase in southern hemispheric westerly wind stress leads to a 0.13 GtC/yr increase in Southern Ocean CO2 outgassing. We also find that a poleward shift of the SH westerlies enhances CO2 outgassing, with a sensitivity of 0.08 GtC/yr for a 5-degree poleward shift.
We further compare the impact and timescale of the Southern Ocean carbon cycle changes driven by dynamic wind variations with those resulting from changes in Antarctic Bottom Water transport and iron fertilisation.
How to cite: Menviel, L., Spence, P., Kiss, A., Chamberlain, M., Hayashida, H., Waugh, D., England, M., Saini, H., and Meissner, K.: Impact of Southern Ocean processes on atmospheric CO2 concentration, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13359, https://doi.org/10.5194/egusphere-egu25-13359, 2025.
The advent of large, open-access databases such as Neotoma has revolutionized the field of paleoecology, providing unprecedented opportunities to conduct large-scale analyses of past environmental change. These databases allow for the integration of thousands of fossil pollen records, enabling a more comprehensive understanding of spatial and temporal variability across ecosystems. By combining these data with advanced numerical methods and/or other proxies, we can refine our understanding of how past climatic changes influenced biodiversity. This integrated approach holds the potential to push paleoecology into exciting new directions, with implications for forecasting future climate and biodiversity changes.
Our work explores innovative uses of fossil pollen datasets, particularly large-scale compilations of Late Quaternary records, to investigate long-term vegetation dynamics and climate change. We apply novel spatio-temporal techniques to gain new insights into biodiversity change. This approach has enabled us to uncover global patterns of vegetation change and deepen our understanding of climate-vegetation interactions (Mottl et al. 2021a). By quantifying rates of ecological change (Mottl et al. 2021b), we demonstrated that vegetation rates of change began accelerating globally between three to four thousand years ago, and that recent rates of change now are even higher than those associated with the end of the last ice age. Our follow-up comparative study comparing our results with other proxies across the Amazon, provided a much-needed interdisciplinary framework to examine past environmental conditions in this region (Albert et al. 2023), showing that rates of change in both geological and paleoecological records are exceptionally high over recent geological times.
When handling such large, heterogeneous datasets (e.g., fossil pollen compilations) for advancing paleoecological research, reproducibility is essential. The integration of open-access databases like Neotoma into research workflows must be accompanied by rigorous, transparent procedures for data sourcing, cleaning, filtering, and analysis. The establishment of reproducible workflows ensures that the entire process, from dataset compilation to final analysis, is transparent, reliable, and accessible for future researchers. In all our work, we emphasize the importance of standardized data preparation and validation steps, using our newly developed FOSSILPOL workflow (Flantua et al. 2023; FOSSILPOL website). This not only facilitates the synthesis of complex datasets but also fosters interdisciplinary collaboration. By ensuring that the analysis of paleoecological data is fully reproducible, we can reduce biases, improve the quality of results, and build a robust foundation for further interdisciplinary climate and biodiversity studies.
REFERENCES
Albert, J. S. et al. (2023). Human impacts outpace natural processes in the Amazon. Science, 379(6630), eabo5003.
Flantua et al. (2023). A guide to the processing and standardization of global palaeoecological data for large‐scale syntheses using fossil pollen. Global Ecology and Biogeography, 32(8), 1377–1394.
Fossilpol website: https://hope-uib-bio.github.io/FOSSILPOL-website/index.html
Mottl et al. (2021a). Global acceleration in rates of vegetation change over the past 18,000 years. Science, 372(6544), 860–864.
Mottl et al (2021b). Rate-of-change analysis in paleoecology revisited: A new approach. Review of Palaeobotany and Palynology, 293, 104483.
How to cite: Flantua, S., Mottl, O., and Felde, V.: Advancing understanding of past environmental dynamics: Reproducible analytical workflows with large-scale fossil pollen compilations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17582, https://doi.org/10.5194/egusphere-egu25-17582, 2025.
Ongoing climate change is increasing vegetation flammability, intensifying fire activity in the boreal forests of eastern North America. This situation suggests a potential tipping point in fire regimes, raising critical questions about their impact on the biodiversity and structure of these ecosystems. To gain a deeper understanding of landscape dynamics and ongoing environmental changes, it is essential to understand how this climate, vegetation and fire linkages operate across various temporal and spatial scales. By integrating paleo-datasets (charcoal, pollen, chironomids, and testate amoebae) with model simulations of vapor pressure deficit (VPD) and plant-available soil water (ASW) over the past 8,000 years, we show that drier spring conditions over the last 3,000 years led to fewer but larger and more severe fire episodes, peaking within the last 250 years. This shift in fire regimes promoted an increase in fire-adapted conifer species, particularly Pinus banksiana, across the landscape. These findings challenge previous projections of increased dominance by thermophilous species under climate change scenarios and instead suggest an expansion of pyrophilous vegetation. Such ecological transitions are set to drive significant environmental and socio-economic consequences.
How to cite: Girardin, M., Ali, A. A., Gaboriau, D., Lesven, J., Remy, C., Danneyrolles, V., Asselin, H., Boucher, E., Arseneault, D., Gennaretti, F., Grondin, P., Garneau, M., Magnan, G., Gauthier, S., Fréchette, B., and Bergeron, Y.: Increasing spring dryness accelerates transitions toward pyrogenic vegetation in eastern boreal North America, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2611, https://doi.org/10.5194/egusphere-egu25-2611, 2025.
Wildfires are among the main disturbances affecting Mediterranean ecosystems. These extreme events significantly impact erosion dynamics over long periods and can affect environmental systems by causing excessive sediment transfers downstream. Traditional methods for studying soil erosion in post-wildfire contexts generally focus on short temporal scales, such as months or a few years after wildfire events.
However, this temporal framework does not allow to capture the dynamics, trajectory, and resilience of erosion processes over a longer time scale (e.g. 20 years). In this context, the study of sedimentary archives provides a powerful resource for reconstructing the resilience of ecosystems to such disturbances.
This study is based on the analysis of sediment cores collected in a small reservoir draining the Peguière headwater catchment (Var, 0.18 km², south-east France), which was completely affected by a historic wildfire in 2003. These sediment cores were dated using natural and artificial radionuclides (210Pbxs, 137Cs), and their physical and chemical properties were characterized using a range of techniques, including high-resolution geochemical elemental analysis (XRF), tomography scanning, and the characterization of organic matter properties.
Initial results show that this wildfire caused significant changes in geochemical properties of sediment. Certain elements, especially manganese, became more abundant during the post-fire period, which was also observed for radionuclides such as 137Cs. The post-fire period was also characterized by a change in the properties of organic matter and an acceleration of sediment inputs into the reservoir.
These post-fire processes affect the reservoir water quality and highlight the consequences of fire damage on long-term soil stabilization, plant cover and regeneration.
These retrospective and multi-proxy approaches provide a comprehensive understanding of the resilience of post-fire erosion dynamics. Understanding these processes over extended timescales will improve landscape management and the implementation of environmental protection measures to fight against the detrimental effects of wildfire on the degradation of soil and water resources.
How to cite: Ducruet, R., Evrard, O., and Foucher, A.: Reconstruction of Post-Wildfire Soil Erosion Using Lake Archives (1975-2024): a French Mediterranean case study, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10783, https://doi.org/10.5194/egusphere-egu25-10783, 2025.
Understanding the long-term interactions among vegetation, fire, and climate is critical for interpreting ecosystem responses to climatic perturbations. Project Prometheus investigates Holocene paleofire dynamics, vegetation shifts, and climate variability in the Mediterranean, using speleothem records from caves in Italy (Alps, Apennines, Sardinia) and the Balkans. By integrating multiple proxies, including polycyclic aromatic hydrocarbons (PAHs) as fire markers and n-alkanes as a proxy for vegetation composition and terrigenous input, this project aims to provide insights into the environmental drivers of fire activity from millennial to sub-centennial timescales, thus creating a high resolution fire history for the Mediterranean region.
Speleothems offer a novel paleoenvironmental archive, and we apply an advanced hydrocarbon extraction protocol adapted from a study on Australian stalagmites1. This method, which includes slow acid dissolution in a clean-room setting to minimize contamination and maximize compound yields, has significantly improved the detection limits and expanded the range of PAHs identified2. Uranium-thorium (U-Th) dating ensures a precise chronological framework, enabling robust correlation between fire, vegetation, and climate proxies.
Here we present results from the initial phase of the project, analyizing a dozen archives from Italy, Greece, and Northern Macedonia, at low resolution (millennial- and sub-millennial-scale). Preliminary results, will provide a first indication of technique effectiveness, archive quality, and regional historical variations (if any) in paleofire regimes. Comparative studies with paleofire data from lake sediments in Italy, where shifts in fire regimes have been previously documented, as well as with modern fire data derived from registries and satellite observations, will help contextualizing our findings within broader regional fire histories.
This research advances our understanding of vegetation-wildfire-climate interactions in the Mediterranean by contributing high-resolution, multi-proxy reconstructions from an understudied archive. By linking past fire and vegetation responses to climatic variability, it provides critical context for assessing future ecosystem resilience and informing land management policies under changing climate conditions.
How to cite: Ardenghi, N., Columbu, A., Denniston, R., Zanchetta, G., Isola, I., and Argiriadis, E.: Reconstructing Holocene Vegetation, Fire, and Climate Interactions in the Mediterranean Using Speleothem Archives, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20051, https://doi.org/10.5194/egusphere-egu25-20051, 2025.
In recent years, there have been considerable improvements in reconstructing past environments. However, the majority of studies focuses either on the Holocene period (ca. 12 ka BP until present) or the Last Glacial Maximum (LGM, ca. 21 ka BP). Since going further back in time encompasses additional challenges, we aim to assess the capabilities and robustness of methods that are currently in use to reconstruct the paleovegetation during the late Last Glacial period (ca. 60–20 ka BP). We compare four different methods of reconstructing past vegetation cover in Europe during the Last Glacial and highlight the strengths and limitations of each method: 1) The classical biomisation approach using fossil pollen data that assigns taxa into plant functional types (PFTs) and PFTs into biomes based on ecological traits and climatic preferences. 2) The REVEALS (Regional Vegetation Abundance from Large Sites) algorithm, which utilizes fossil pollen data in conjunction with taxon-specific parameters (e.g., relative pollen productivity) to estimate the regional plant cover. 3) The dominant biomes derived from the Biome4 global vegetation model using bioclimatic variables from a global climate model output (HadAMH3 and HadCM3). 4) A dedicated vegetation model that statistically reconstructs land-cover from the output of a global climate model (HadAMH3 and HadCM3) using the present climate-vegetation relationship and a CO2 correction factor. Our results show that all methods reconstruct a glacial vegetation dominated by open landscapes (e.g., tundra and steppes) and coniferous forests to various degrees. The existence of transient local patches of mixed and temperate forests is consistent with the general interpretation of glacial landscapes in Europe in the literature. However, regional and chronological discrepancies as well methodological challenges render it difficult to decipher which method most closely represents the actual paleovegetation. Nonetheless, exhausting qualitative and quantitative comparisons across different methods using different approaches allow us to limit the ecological range of the potential vegetation. Such a better comprehension of glacial environments has major implications for our understanding of human (Neanderthals and anatomically modern humans) and faunal population dynamics of in Europe, particularly in response to climatic transitions.
How to cite: Kern, O. A., Schlüter, P., Maier, A., and Vercauteren, N.: Evaluating proxy-based vegetation reconstructions against model-based approaches: A case study from Europe during the late Last Glacial period, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5787, https://doi.org/10.5194/egusphere-egu25-5787, 2025.
The rapid increase of atmospheric carbon dioxide (CO2) and the concurrent decline in Δ14C during the last deglaciation were mainly ascribed to the release of old, 14C-depleted CO2 from an abyssal ocean reservoir, specifically the Southern Ocean, or the deep Pacific Ocean via intermediate waters. In support of this hypothesis, several records from intermediate waters around the globe depict a drop in Δ14C during the deglaciation. However, other records closer to the source regions of intermediate waters do not depict this anomaly and thus, question the hypothesis. Alternative scenarios include the release of 14C-depleted CO2 by hydrothermal vents, volcanoes and pockmarks. An ideal region to test the hypothesized scenarios is the western equatorial Pacific Ocean (WEP), where intermediate waters of southern and northern origin converge.
We present paired planktic and benthic foraminiferal 14C ages from a depth transect (404 – 2210 m) of seven gravity cores from the WEP that cover the past 25 kyrs. Our records do not show any discernible Δ14C anomaly during the Last Glacial Maximum and initial deglaciation making the WEP an unlikely candidate for the release and ventilation of oceanic CO2 to the atmosphere. However, the intermediate-depth records consistently show anomalously low benthic Δ14C values during the final stage of the deglaciation and early Holocene. This Δ14C variability will be discussed in the context of potential sources and mechanisms.
How to cite: Hollstein, M., Kienast, M., Martínez-Méndez, G., Stott, L., Steinke, S., De Pol-Holz, R., Southon, J., and Mohtadi, M.: Radiocarbon ages of western Pacific intermediate waters during the past 25 kyrs: Implications for global carbon cycling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7116, https://doi.org/10.5194/egusphere-egu25-7116, 2025.
Changes in the formation of North Atlantic Deep Water (NADW) and the expansion of southern-sourced waters in the Atlantic Ocean are linked to enhanced marine carbon storage during glacial and stadial periods, explaining late Pleistocene atmospheric CO2 variations. However, the role of deep-water formation in the Nordic Seas, a key NADW source, and its influence on Atlantic overturning remains unclear, especially after the last glacial maximum. In this study, we present high-resolution reconstructions of bottom water [CO32-] from Cibicidoides wuellerstorfi, along with stable isotopes and aragonitic pteropod abundances in marine sediment core PS1243 from the deep Norwegian Sea, to explore past deep-water dynamics and their impact on carbon cycling. Our data suggest continuous formation of dense, well-ventilated deep waters during Marine Isotope Stages 5 and 4, with a deepening of the aragonite compensation depth during the MIS 5b-to-4 transition. MIS 5e indicates resilience of Nordic Seas overturning in spite of a warmer North Atlantic and suggested summer Arctic sea ice reduction. A compilation of Atlantic [CO32-] records suggests that dense waters from the Nordic Seas expanded into the western North Atlantic, reducing its carbon storage capacity during MIS 4 and stadial MIS 5. Our study highlights differences in the sensitivity of Atlantic and Nordic Seas overturning to past climate conditions, with implications for the Atlantic's role in atmospheric CO2 variations.
How to cite: Stobbe, T., Bauch, H., Frick, D., Yu, J., and Gottschalk, J.: Sustained deep-water formation in the Nordic Seas during Marine Isotope Stages 5 and 4 and implications for carbon storage in the North Atlantic, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6454, https://doi.org/10.5194/egusphere-egu25-6454, 2025.
The Pleistocene is characterized by substantial variations in ice volume and pronounced climatic oscillations. Over the last 1 million years, glacial-interglacial climate cycles are marked by increasing amplitude and by a pronounced decrease in pCO₂ levels during glacial intervals. The mechanisms driving this carbon cycle reorganization, and a full quantification of oceanic and sedimentary carbon sinks during glacials, remain unresolved. To address this question, we measure organic and inorganic δ13C, as well as the total organic carbon (TOC) to quantify export productivity and organic carbon burial changes on the NW Shelf of Australia.
Bulk carbonate sediments from IODP Expedition 356 Site U1460 (27°22′S, 112°55′E), collected at a water depth of 214.5 mbsf, are the focus of this study. This site, located on the outer North West Shelf of Australia, is influenced by the competition between the southward flowing oligotrophic Leeuwin Current and the colder norward flowing West Australian Current. During glacial intervals, the West Australian Current is dominant, facilitating enhanced productivity through wind driven upwelling. These dynamics suggest that the region could have acted as a significant organic carbon sink during Late Pleistocene glacials, with high rates of organic carbon accumulation on the western Australian shelf and continental slopes. Here, we present preliminary results from δ¹³C and TOC analyses spanning the last ~600,000 years. These data provide insights into the variability of organic carbon burial and its contribution to the global carbon cycle in the Mid- to Late Pleistocene, advancing our understanding of carbon storage mechanisms in response to climatic shifts.
How to cite: V. Del Gaudio, A., M. Bialik, O., Auer, G., and De Vleeschouwer, D.: Quantifying carbon burial on the Northwest Australian shelf: Connections with Late Pleistocene climatic patterns , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8309, https://doi.org/10.5194/egusphere-egu25-8309, 2025.
During the glacial-interglacial transitions of the past 800 000 years (800 ka), commonly referred to as “glacial terminations”, atmospheric CO2 concentrations (pCO2) rose by 50-100 ppm. Biological productivity from the Southern Ocean (SO) significantly impacted these variations through changes in the Biological Carbon Pump strength, which includes the Soft Tissue Pump (STP) i.e., the net downward flux of phytoplanktonic organic carbon, and the Carbonate Counter Pump (CCP) i.e., the export of planktonic calcium carbonates increasing the surface-to-depth alkalinity gradient. Both modulate ocean-atmosphere exchanges as they respectively decrease and increase CO2 concentrations in the surface ocean and hence the atmosphere. Paleoclimate studies focusing on the SO highlight decreasing STP from the Subantarctic as a potential driver of increasing pCO2 during glacial terminations. A few studies have demonstrated the probable impact of CCP on pCO2 over specific glacial terminations (Duchamp-Alphonse et al., 2018; Brandon et al., 2022; Anderson et al., 2024) but very little is known about CCP patterns over the past 800 ka.
This study aims to reconstruct changes in CCP strength over the past 800 ka and assess their impacts on pCO2. Following the exact same strategy as the one developed by Brandon et al., (2022), we performed micropaleontological (coccolith and foraminifera abundances and morphometrics) and geochemical analyses (CaCO3, CaXRF, d13CN. pachyderma, d18ON. pachyderma) on sediment core MD97-2115 (43°10,84S, 171°48,55W), retrieved in the Pacific sector of the Subantarctic Zone. Preliminary results show that the carbonate fine fraction (< 20µm) of the sediment is mainly composed of coccoliths (Emiliania huxleyi and Gephyrocapsa morphotypes; Coccolithus pelagicus; Calcidiscus leptoporus) and might be used as a CCP signal.
Anderson, H. J. et al. Millennial-Scale Carbon Flux Variability in the Subantarctic Pacific During Marine Isotope Stage 3 (57–29 ka). Paleoceanography and Paleoclimatology 39, e2023PA004776 (2024).
Brandon, M. et al. Enhanced Carbonate Counter Pump and upwelling strengths in the Indian sector of the Southern Ocean during MIS 11. Quaternary Science Reviews 287, 107556 (2022).
Duchamp-Alphonse, S. et al. Enhanced ocean-atmosphere carbon partitioning via the carbonate counter pump during the last deglacial. Nature Communications 9, 1–10 (2018).
How to cite: Pige, N., Wang, Y., Duchamp-Alphonse, S., Sépulcre, S., Thuruttath Unnikrishnan, V., Brandon, M., Landais, A., and Michel, E.: Carbonate counter pump strength and its impact on atmospheric pCO2 over the past 800 ka: evidence from Southern Ocean micropaleontological and geochemical data , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12867, https://doi.org/10.5194/egusphere-egu25-12867, 2025.
Posters virtual: Thu, 1 May, 14:00–15:45 | vPoster spot 5
EGU25-15465 | Posters virtual | VPS6
Soil heating under wildfires and prescribed burns and their relevance to archaeological investigationsThu, 01 May, 14:00–15:45 (CEST) | vP5.2
Fires can alter the properties of soil and other material via heat transfer. The identification of soil heating effects in hearths, for example, has long been a cornerstone in archaeological investigations. However, wildfires can also alter soils, and there is a surprising level of uncertainty into what degree soils are heated and to which depth this occurs in wildfires. This can lead to erroneous assumptions regarding the potential impact of wildfires when attributing heat induced changes in the soil, especially when laboratory heating results are extrapolated to field conditions.
To address this research gap, we compiled and examined new and published field data on maximum temperatures and heating durations for mineral soils during wildfires and prescribed burns in forests, shrublands and grasslands around the globe; and compared these to data obtained from laboratory heating experiments.
Most fires heated only the uppermost centimetres of the mineral soil, rarely exceeding 300 °C below 1 cm depth. Their heat pulses were shorter (<500 s) than those often applied in laboratory studies (1800-3600 s). The highest near-surface temperatures occurred in shrubland wildfires, whereas the longest heating durations in forests with deep organic layers and high fuel loads.
While it is clear that smouldering logs, tree trunks and root systems, or slash pile burns can impart intense heating to substantial depths akin to that under hearths, most landscape-scale fires generate short and shallow heat pulses that are unlikely to lead to detectable lasting changes in the mineral soil.
How to cite: Doerr, S., Badia-Villas, D., Bryant, R., Matthew, D., Antonio, G.-G., Jorge, M.-S., Jessica, M., Carmen, S.-G., Cristina, S., Cathelijne, S., and Pete, R.: Soil heating under wildfires and prescribed burns and their relevance to archaeological investigations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15465, https://doi.org/10.5194/egusphere-egu25-15465, 2025.
