Over the past few millennia, human activity has been one of the most unpredictable factors influencing environmental transformations. Human activities related to agriculture and land use are the primary forces driving the creation of new landscapes. Conversely, the influence of other factors on landscape transformation remains incompletely understood. In particular, forests have been exploited not only for timber but also for various wood-related products, including charcoal, potash, and tar. We consider that charcoal production, besides food production, which increased linearly with population growth, was a kind of turning point in human pressure on the forest environment. Particularly in the Middle Ages, when the demand for products such as glass, iron, and potash grew very rapidly, the production of these products required a higher temperature than that obtained by burning wood. However, the extent and impact of these activities on a spatial scale has not been fully recognized. Charcoal held significant economic and energy value in the pre-industrial era, evidenced by mapping over 600,000 remnants of charcoal hearths in Central Europe. Over time, the demand for energy escalated, leading to the widespread use of coal in the late 18th and early 19th centuries. Our aim is to provide a comprehensive understanding of the functioning of charcoal hearths and their role in shaping landscapes. To achieve this, we have combined research methods from biogeography, remote sensing, dendroecology, paleoecology, soil science, botany, onomastics, and art history. This interdisciplinary approach aims to capture not only the natural outcomes but also the social and economic consequences of charcoal production. Our paleoecological findings reveal an intermediate disturbance linked to the operation of charcoal hearths, influencing both short-term and long-term changes in ecosystems with a cascading effect. The production of charcoal has far-reaching consequences, exerting a substantial impact on vegetation composition, soil properties, microclimate, the water cycle, and ultimately leading to erosion, thereby affecting adjoining ecosystems. This research addresses the growing interest in the legacy of charcoal hearths in historical human activities and their pivotal role in shaping landscape transformations during the pre-industrial era.

The study is the result of research project No. 2018/31/B/ST10/02498 funded by the Polish National Science Centre.

How to cite: Słowiński, M., Szewczyk, K., Jonczak, J., Halaś, A., Mroczkowska, A., Łuców, D., Słowińska, S., Tyszkowski, S., Kowalska, A., Kołaczkowska, E., Swoboda, P., Chojnacka, A., Gumińska-Nowak, B., Kramkowski, M., Kardasz, C., Barbarino, V., Noryśkiewicz, A. M., Kruczkowska, B., Brykała, D., and Związek, T.: Human impacts on the environment in the preindustrial forest landscapes in Central Europe - an overview, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12672, https://doi.org/10.5194/egusphere-egu24-12672, 2024.

Radiocarbon may serve as a powerful dating tool in palaeoceanography, but its accuracy is severely limited by the need to calibrate radiocarbon dates to calendar ages. A key problem is that marine radiocarbon dates must be corrected for past offsets from either the contemporary atmosphere (i.e. ‘reservoir age’ offsets) or a modelled estimate of the global average surface ocean (i.e. delta-R offsets). This presents a challenge because the spatial distribution of reservoir ages and delta-R offsets can vary significantly, particularly over periods of major marine hydrographic and/or carbon cycle change such as the last deglaciation. Modern reservoir age/delta-R estimates therefore have limited applicability.  The construction of regional marine calibration curves could provide a solution to this challenge, if coherent regions could be defined. Here, we use unsupervised machine learning techniques to define distinct regions of the surface ocean that exhibit coherent behaviour in terms of their radiocarbon age offsets from the contemporary atmosphere (R-ages). We investigate the performance of different clustering algorithms applied to outputs from different numerical models. Comparisons between the cluster assignments across model runs confirm some robust regional patterns that likely arise from constraints imposed by large-scale ocean and atmospheric physics. At the coarsest scale, regions of coherent R-age variability are associated with the major ocean basins. By further dividing basin-scale shape-based clusters into amplitude-based subclusters, we recover regional associations that cohere with known modern oceanographic processes, such as increased high latitude R-ages, or the propagation of R-age anomalies from the Southern Ocean to the Eastern Equatorial Pacific. We show that the medoids for these regional sub-clusters provide significantly better approximations of simulated local R-age variability than constant offsets from the global surface average. The proposed clusters are also found to be broadly consistent with existing reservoir age reconstructions that span the last ~30 ka. We therefore propose that machine learning provides a promising approach to the problem of defining regions for which marine radiocarbon calibration curves may eventually be generated.

How to cite: Mârza, A.-C., Menviel, L., and Skinner, L.: Towards the construction of regional marine radiocarbon calibration curves: an unsupervised machine learning approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7498, https://doi.org/10.5194/egusphere-egu24-7498, 2024.

The Laacher See eruption (LSE) deposited a key tephra layer that synchronizes Late Glacial paleoclimate records across Europe, and thus provides the temporal framework to investigate the onset of the Younger Dryas cooling in the North Atlantic region. The absolute timing and climatic consequences of this event remain, however, still debated. Here, we present evidence from a high-resolution speleothem record from Herbstlabyrinth Cave, Central Germany, demonstrating distinct spikes in sulfur, fluorescent organic matter, and ash-leached trace elements assigned to the LSE and dating the event c. 13,047 BP₁₉₅₀, with an uncertainty of about 30–40 years. This age supports the recently published radiocarbon wiggle matching date of 13,006 ± 9 BP₁₉₅₀ (Reinig et al., 2021) and contradicts speculations about potential biases arising from volcanic CO₂ emissions. The near-annually resolved speleothem calcite δ¹⁸O data further allows to assess the timing of the LSE and its impact on the regional climatology. Our findings exclude the LSE as a possible trigger of the Younger Dryas and indicate a regional climatic and environmental impact restricted to c. 20 years after the eruption. This unprecedented combination of stable isotopes, trace elements, annually resolved fluorescence, and radiometric dates for a single record provides independent evidence for the Late Glacial synchroneity of Atlantic-European climate relationships and opens new pathways toward a precise, absolutely dated time marker between European terrestrial and Greenland ice core records prior to the Holocene.

References

Reinig F, Wacker L, Jöris O, et al. (2021) Precise date for the Laacher See eruption synchronizes the Younger Dryas. Nature 595(7865): 66-69.

How to cite: Warken, S. F., Schmitt, A. K., Scholz, D., Hertwig, A., Weber, M., Mertz-Kraus, R., Reinig, F., Esper, J., and Sigl, M.: Speleothem sulfur spike confines timing and impact of late Glacial Laacher See eruption, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12386, https://doi.org/10.5194/egusphere-egu24-12386, 2024.

The ~74 ka Youngest Toba Tuff (YTT) eruption of Mount Toba in Indonesia is considered to be the largest volcanic eruption during the last 2.6 Ma. Its impact on global climate regimes and ecosystems, especially in tropical regions, is important due to possible consequences for the evolution and dispersal of early modern humans. In this study, we utilise the high-quality lake-sediment record from Lake Chala (Tanzania/Kenya), recovered by the ICDP DeepCHALLA project, to reconstruct the climatic and environmental impacts of the YTT in eastern equatorial Africa. Previous work identified a cryptotephra layer that was geochemically correlated to the YTT. In this study, focusing on the section of finely laminated sediments lying directly below and above the YTT layer, we compile high-resolution data from thin-section optical microscopy, geochemistry and fossil diatom assemblages in order to trace changes in climatic, local lake-system and wider environmental conditions immediately before and after the YTT event. Most proxy analyses were conducted at annual or higher temporal resolution, which is rare for late-Pleistocene palaeo-records. Our results reveal changes in regional hydroclimate following the YTT eruption, possibly coupled with volcanically induced changes in the El Niño–Southern Oscillation dynamics. Further, the precise location of the YTT layer within varved Lake Chala sediments provides new information on the season of the YTT eruption.

How to cite: Park, J., Wolff, C., Verschuren, D., Leng, M. J., Lacey, J. H., Van Daele, M., Lane, C. S., Martin-Jones, C., Vidal, C. M., Oppenheimer, C., and Barker, P. A.: Climatic and environmental impacts of the ~74 ka Youngest Toba Tuff volcanic eruption in Indonesia as evidenced from the sediment record of Lake Chala (Tanzania/Kenya), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5356, https://doi.org/10.5194/egusphere-egu24-5356, 2024.

The Late Pleistocene MIS5 - MIS4 transition (ca. 80-70 ka) is globally known to correspond to a major cooling event accompanied by a large decline in eustatic sea level. This transition must have radically changed coastal landscapes worldwide, affecting basin shape, salinity regimes, river courses, as well as biota. Most existing records are from either local lacustrine, ice core or distal oceanic records, while dated and continuous records from coastal environments are lacking. Within the southern North Sea Basin a unique record of coupled terrestrial-marine signals exists in the deposits of the Brown Bank Formation, covering the MIS5-MIS4 transition. Here, we target the Brown Bank Formation to produce a new integrated palaeoenvironment and -climate framework for the MIS5-4 transition and show biotic and abiotic environmental response to rapid cooling in a coastal area.

Multi-proxy records of lipid biomarkers, pollen, mollusk and diatom assemblages for the MIS5-4 transition in the center of the southern North Sea are combined with seismic facies determinations. The Brown Bank Formation consists of multiple facies representing multiple depositional phases around the MIS5-4 transition, and provides insights into the cooling of the terrestrial and shallow marine environments. On land, the vegetation changed from boreal forests to more open, grassland vegetation, combined with an increase in soil erosion. At the same time the shallow marine environment of the southern North Sea experienced subarctic to arctic marine conditions with a high input of soil material. These continued cool marine conditions have not been described earlier for this region and show that sea level remained high and lagged local cooling, as inferred from lipid-biomarker palaeothermometry. Assuming that this lag between sea-level and temperature change is common during cooling events, it is a potential mechanism creating sediment preservation windows during the onset of glacial intervals in shallow marine environments. Preserved records like the one presented here are valuable because they capture both the unique changes in cold marine environments, as well as informative terrestrial signals that are rarely preserved onshore.

How to cite: Waajen, I., Donders, T., Busschers, F., Wesselingh, F., Wagner-Cremer, F., Peterse, F., van Heteren, S., and Plets, R.: A unique preservation window capturing coastal-marine landscape evolution across the MIS5-4 cooling event (Late Pleistocene, North Sea Basin), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8147, https://doi.org/10.5194/egusphere-egu24-8147, 2024.

During the last glacial period changes in the strength of ocean convection in the high-northern latitudes contributed to abrupt global climate changes known as Dansgaard–Oeschger (DO) cycles. However, the lack of high-resolution empirical evidence has yet precluded inferring the physical coupling between ocean and atmosphere. We examined Nordic Sea (NS) circulation changes by reconstructing radiocarbon ventilation ages across four DO cycles in a marine sediment core hinging on a precise multi-tephra-based synchronization to Greenland ice cores. Our results show that open ocean convection in the NS resumed ahead of the abrupt air-temperature increases recorded in ice cores by ∼400 years (95% range: 50-660 years). Thus, implying an active role of ocean dynamics where abrupt warming transitions are likely a nonlinear response to more gradual resumption of NS convection.

How to cite: Simon, M., Muschitiello, F., Sadatzki, H., Berben, S., Friedrich, T., Blindheim, D.-I., Wacker, L., Jansen, E., and Dokken, T.: Nordic Sea convection led abrupt North Atlantic warm events during Dansgaard-Oeschger cycles, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12639, https://doi.org/10.5194/egusphere-egu24-12639, 2024.

The termination of the Holocene Humid Period between 6-5 kyrs ago is relatively well-documented in Africa. By contrast, outside of Africa the spatial extent of this termination, the rate of change (gradual vs. abrupt) and the timing of this termination remain obscure. To assess whether such a termination occurred in Asia and to characterize the spatial and temporal evolution of this termination, we constructed lake-level histories of five closed-basin lakes, four of which are located along a north-south transect in East Asia (Lakes Khukh, Dali, Daihai and Chenghai from 50^ᵒN to 25^ᵒN) and the fifth is the Dead Sea in western Asia (33^ᵒN). A closed-basin lake has no outlet, and therefore its size varies as a function of precipitation and evaporation. Distinct shoreline deposits form at the lake’s margin and are physical relict imprints of past lake-levels. These lake-level histories provide a powerful, first order, quantitative record of past water availability. For each lake, we developed a detailed lake-area history based on numerous radiocarbon, Optical Stimulated Luminescence and U/Th disequilibrium ages.

All five lakes show that substantial changes in lake-level (up to 60 m) and surface area (of up to six times that of modern area) occurred throughout the Holocene. The results indicate that in East Asia wet conditions were initiated during the Bølling-Allerød and weakened and dried during the Younger-Dryas. The onset of the Holocene Humid Period, at 11.5 kyrs, was rapid, with the lakes rising to their high-stands within a half millennium. In western Asia, the lake-level rise most likely occurred later, at ~10 kyrs. During the Holocene Humid Period the lakes were significantly larger than the modern lakes. The wet conditions in northeast Asia and western Asia prevailed until 6 kyrs, when the lakes dried out abruptly, within a few decades, and have not been restored to their pre-6 kyrs sizes since. In South China, the rapid drying occurred earlier, at ca. 8 kyrs. All five lakes show a substantial dry period between 6 – 4 kyrs. In northeast Asia the dry conditions prevail until today. However, in both South China and western Asia the lakes rose at 3 kyrs and remained mostly high until recently.

Our findings from the five Asian closed-basin lakes show that during the early Holocene, Asia was scattered with lakes that were much larger than today and that an abrupt onset and abrupt termination of the Holocene humid period occurred across Asia. We use the lake-level histories to quantify regional water availability, to discuss the migration of rain-belts in Asia, speleothem oxygen isotopes and pollen records, and the ability of transient climate models to capture the magnitude, extent and rapidness of these wet conditions and hydroclimatic transitions.

How to cite: Goldsmith, Y., Xu, H., Ts, N., Torfstein1, A., Stein, M., and Enzel, Y.: Abrupt onset and termination of the Holocene Humid Period across Asia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5613, https://doi.org/10.5194/egusphere-egu24-5613, 2024.

Pingo remnants are the deep lakes that formed by melting of ice lenses during permafrost degradation at the end of the Last Glacial, and they are particularly abundant in the northern Netherlands. Most of these isolated circular depressions have a diameter of 100-200 meters and are filled with a 5-10 meters thick sequence of lake and peat deposits, making them valuable archives of climate and environmental change. These natural sediment- and pollen-traps record not only the rapid changes during the Last Glacial-Interglacial Transition but also reveal the Holocene forest development as well as traces of human impact in the surrounding landscape.

In this study, we report on the study of a continuous organic fill of nearly 18 meters in Nieuwe Veen, which may be the deepest pingo remnant in NW Europe. The pingo remnant fill is composed of a sequence of partly sand laminated lake and peat deposits containing fine and coarse detrital gyttjas, calcium- and iron-carbonate gyttjas and wood, sedge and moss peats with abundant macrofossils. A series of radiocarbon dates on selected terrestrial macrofossils provides a solid age model for the complete sequence starting 14,700 calendar years ago, coinciding with the first warming of the Late-Glacial Interstadial, corresponding to the onset of Greenland Interstadial 1 (GI-1). The results from 5-10 cm resolution palynological analyses reveal a complete picture of vegetation development while loss on ignition measurements at cm-resolution show the openness of the vegetation cover associated to colder periods as well as phases of human forest clearance.

A phase of particular interest is the cold Younger Dryas stadial corresponding to Greenland Stadial 1 (GS-1), which is represented by a more than 10 meters thick layer of sandy gyttjas. This allows for a reconstruction of environmental change in unprecedented detail with a resolution of potentially 1 cm/yr. The onset of the Younger Dryas stadial is abrupt and clearly visible in the core, as well as in the botanical and lithological proxies. There appear to be at least three distinct phases during the Younger Dryas stadial interval, especially reflected in the aquatic flora and lithological proxies, indicating shifting conditions in (hydro-)climate.

At the onset of the Holocene, also clearly visible, sand influx in the basin decreased rapidly due to an increasing vegetation cover in the surrounding landscape indicated by the botanical proxies. The lake system eventually changes into a fen and bog. In the Early Holocene, carbonate rich lake deposits indicate the influence of groundwater seepage. During the infilling, the source of the water changes towards atmospheric water, as evidenced by more oligotrophic species in the palynological record. Phases of forest opening related to human impact appear remarkably late in the record at about 5500 calendar years ago, with clear indications of agriculture only after 3000 calendar years ago. Final cultivation of the peatbog in the beginning of the 20^th century caused the record younger than Medieval times to be destroyed.

How to cite: Hoek, W., Donders, T., Schouten, S., van Doorn, V., van Leeuwen, J., and van Eijk, A.: 14,700 years of climate and environmental change recorded in 17.8 meters of lake and peat deposits in the Nieuwe Veen pingo remnant, NE Netherlands, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12137, https://doi.org/10.5194/egusphere-egu24-12137, 2024.