CL1.6

The generally cold climate of the last glacial period was interrupted by numerous abrupt shifts to warmer interstadial conditions in the North Atlantic. The effects of this Dansgaard–Oeschger (D–O) type climatic variability have been found in a number of European and Asian terrestrial paleoclimate archives, including speleothems, lakes and loess deposits. However, only very few of the already sparse precisely dated records provide quantitative information on stadial-interstadial temperature variations over this time period. This is a major impediment to resolving the cause and geographical propagation of D-O events, as well as to understanding the impact they have on continental climates and environments.

Here we present carbonate clumped isotope (Δ₄₇)-based active season paleotemperature (AST) estimates from land snails recovered from Greenland Stadial/Interstadial (GS/GI) 5 and 3 age loess at the Dunaszekcső loess site (Hungary), based on a uniquely detailed AMS ¹⁴C age dataset, alongside a new flowstone (PK-6, Bükkösd, Hungary) stable isotope-based temperature change record ²³⁰Th-dated to 30-26 ka. Stadial ASTs of the investigated periods were found to be in the range of 7–13 °C, corresponding to T_annual of 0–6 °C and T_July of 11–17 °C, agreeing well with the range of model simulation results for the region. Interstadial AST values reconstructed for GI-5.1 and 3 (16–18 °C) indicate warm summers (T_July: 20–22 °C) and relatively high annual mean temperatures (T_annual: 9–11 °C), matching present-day values. The PK-6 flowstone δ¹⁸O_calcite-based temperature change estimates (~0.2 ‰ °C^–1 δ¹⁸O/T gradient) reveal a 7–10 °C T_annual rise for the warmest phases of GI-3 and 4 compared to stadial temperatures, in very good agreement with the land snail TΔ₄₇ values.

Our results show that stadial-interstadial climate variability in East Central Europe was of comparable magnitude to that in Greenland. We propose that large scale ocean-atmospheric variability (NAO-AMO) imparts a major control on transmitting abrupt North Atlantic climate event signals into continental Europe during the last glacial.

This study was funded by the Hungarian National Research, Development and Innovation Office to GÚ (OTKA PD-108639) and SK (OTKA KH-125584). TS is grateful for the support of the Swedish Research Council (2017-03888).

How to cite: Ujvari, G., Bernasconi, S. M., Stevens, T., Kele, S., Pall-Gergely, B., Suranyi, G., and Demeny, A.: Dual archive paleotemperature records over two pre-LGM stadial/interstadials in East Central Europe, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-557, https://doi.org/10.5194/egusphere-egu21-557, 2021.

Extratropical volcanic eruptions are commonly thought to be less effective at driving large-scale surface cooling than tropical eruptions, and only the latter are commonly thought to be able to distribute sulfate globally. Here, we test both of these assumptions using a network of ice cores from the polar regions of Antarctica and Greenland covering the past 15’000 years and climate-aerosol modeling. We employ state-of-the-art analyses of trace elements, cryptoptephra and sulphur isotopes (Burke et al., 2019) to gain new insights into the timing of past eruptions, their stratospheric sulphur mass injections and subsequent sulphate aerosol lifecycle. We use this information to estimate the climate impact potential due to negative radiative forcing caused by Earth’s largest volcanic eruptions since the last Glacial. Our analysis encompasses over 1’000 eruptions and include the caldera-forming eruptions of Okmok II (Alaska, 43 BCE, VEI=6, 53°N; McConnell et al., 2020), Aniakchak II (Alaska, 1600s BCE, VEI=6, 57°N), Crater Lake (Mazama, Oregon, 5600s BCE, VEI=7, 43°N) and Laacher See (Germany, c. 13 ka BP, VEI=6, 50°N).

We use our reconstructed radiative forcing and the coupled earth system models MPI-ESM1.2 and CESM (version 1.2.2) to analyze the climatic impact caused by these eruptions and compare the simulated temperature response with temperature reconstructions based on ultra-long tree-ring chronologies. Finally, based on these comparisons, we propose a number of stratigraphic age tie-points to anchor ice-core chronologies from Greenland (GICC05) and Antarctica (WD2014) to the absolute dated tree-ring chronology. We thereby aim to improve proxy synchronization throughout the Holocene -- a prerequisite for detection and attribution studies -- and invite the paleo-climate community to update climate proxy records based on ice cores to the latest chronologies.    

The European Research Council Grant 820047 under the European Union’s Horizon 2020 research and innovation program funded the research project THERA - Timing of Holocene Volcanic eruptions and their radiative aerosol forcing. 

References:

Burke, A., Moore, K. A., Sigl, M., Nita, D. C., McConnell, J. R., and Adkins, J. F.: Stratospheric eruptions from tropical and extra-tropical volcanoes constrained using high-resolution sulfur isotopes in ice cores, Earth Planet Sc Lett, 521, 113-119, 2019.

McConnell, J. R., Sigl, M., Plunkett, G., Burke, A., Kim, W., Raible, C. C., Wilson, A. I., Manning, J. G., Ludlow, F. M., Chellman, N. J., Innes, H. M., Yang, Z., Larsen, J. F., Schaefer, J. R., Kipfstuhl, S., Mojtabavi, S., Wilhelms, F., Opel, T., Meyer, H., and Steffensen, J. P.: Extreme climate after massive eruption of Alaska’s Okmok volcano in 43 BCE and effects on the late Roman Republic and Ptolemaic Kingdom, Proceedings of the National Academy of Sciences, 117, 15443-15449, 2020.

How to cite: Sigl, M., Adolphi, F., Burke, A., Cole-Dai, J., Fischer, H., Kim, W. M., Krüger, K., Lorenz, S., McConnell, J., Nicolussi, K., Niemeier, U., Pearson, C., Reinig, F., Salzer, M., Severi, M., Timmreck, C., and Toohey, M.: Insights on the timing, global sulfate lifecycle and climate impact of Earth’s largest (pre-) historic volcanic eruptions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-946, https://doi.org/10.5194/egusphere-egu21-946, 2021.

Seasonal floods are life-supporting events in the Nile Valley and have been crucial to the development of complex societies. Present populations depend on their occurrence but the alteration of fluvial dynamics under climate change remains elusive. In order to better understand how fluvial dynamics respond to climatic changes, we explore past flood dynamics of the Nile River using a unique finely laminated sequence from the Nile deep-sea fan.

Today, floods occur during the summer, when monsoonal rainfall hits the Ethiopian highlands and feeds the Blue Nile. Core P362/2-33 covers the past 9.5 ka BP and is ideally located to record changes in fluvial dynamics during periods of stronger monsoon activity such as the Saharan Humid Periods. The absence of oxygen in the Mediterranean bottom waters during the last Saharan Humid Period (during sapropel S1 deposition) allowed to preserve the laminated structure between 9.5 and 7.5 ka BP.

We focus here on examining the nature of the laminations in order to 1) understand the deposition mechanism and 2) obtain a reconstruction of past fluvial dynamics at seasonal resolution.

Microfacies analysis and elemental micro-XRF scanning indicate that couplets of alternating dark- and light-coloured layers represent seasonal deposits of Nile discharge and marine hemipelagic sedimentation, respectively. Preliminary lamination counts suggest that couplets were deposited at an annual rate for most of the record. Increases in layer thickness is observed around 9.5 and 9.1 ka BP, followed by a gradual decrease until 8 ka. Careful examination of lamination structure and time-series analysis of layer counts will permit to further explore sub-annual changes in flood dynamics during the Saharan Humid Period. Finally, due to its high temporal resolution, our record has the potential to link reconstructions of Nile discharge to other regional archives of hydrological changes (e.g., speleothems, lakes) and thereby identify overarching forcing mechanisms.

How to cite: Blanchet, C., Ramisch, A., Tjallingii, R., and Brauer, A.: Nile floods during the last African Humid Period: a seasonal record from the deep-sea fan, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3391, https://doi.org/10.5194/egusphere-egu21-3391, 2021.

The High Atlas mountains of Morocco represent a climatological frontier between the Atlantic and Saharan realms as well as a site of major Pleistocene glacier expansion. However, Late-glacial and Holocene environmental change is weakly constrained, leaving open questions about the influence of high- and low-latitude climate forcing and the expression of North Atlantic rapid climate changes. High elevation lakes on the sandstone plateaux of the High Atlas have been recognised as archives of Late Quaternary environmental change but remain little explored. Here, we present findings from new sedimentological, palaeoecological and geochronological investigation of a lake marginal sediment core recovered in June 2019 from the Ifard Lake located on the Yagour Plateau. The plateau is a distinctive sandstone upland located to the southeast of Marrakech in the High Atlas (31.31°N, 7.60°W, 2460 m.a.s.l.). The lake is located within a small, perched catchment area, offering an opportunity to isolate catchment effects and investigate atmospheric deposition of organic and inorganic tracers of past environmental change. The core stratigraphy reveals shifts between inorganic sands and lake muds with fluctuations in grain sizes and sediment reddening. The differences in these stratigraphic layers are most likely linked to hydrological changes associated with changing snowpack conditions and local catchment erosion dynamics. The core chronology is well-constrained by AMS radiocarbon dating of pollen concentrates, with the core sequence spanning the last ca. 14,000 years. The driving agents of environmental change on the plateau are inferred using a multiproxy approach, combining sedimentological analyses (particle-size by laser granulometry, elemental analysis by core-scanning XRF, C/H/N/S analysis), palynology (pollen, spores, non-pollen palynomorphs) and contiguous macrocharcoal analysis. High-resolution, well-constrained proxies therefore permit novel regional insights into past environmental and climatic changes at centennial timescales. A prime working hypothesis is that the imprint of wider palaeoclimatic changes of both the North Atlantic region and Saharan realm (African Humid Period, AHP) is detected at this site. Key climatic periods such as the Younger Dryas and multi-centennial cooling episodes around 8000 and 4200 years ago are distinctly characterised in the record by finer grain sizes and the accumulation of pollen-rich material and charcoal. These responses are thought to be governed by regional climate forcing and local snowmelt moisture supply to the Yagour Plateau. An increase in fine sediment supply, magnetic susceptibility and Fe content in the upper part of the core may be related to enhanced atmospheric dust deposition following the end of the AHP. Whilst taking anthropological influences on the local environment into account, this study will contribute to the detection of long-term and rapid climate changes in a sensitive mountain region at the rim of the Atlantic and Saharan climate systems.

How to cite: Cornelissen, H., Fletcher, W., Hughes, P., Bell, B., Rhoujjati, A., Ewague, A., and Fink, D.: Rapid environmental changes of the Late-glacial and Holocene in a sediment record from the Yagour Plateau, High Atlas, Morocco, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13021, https://doi.org/10.5194/egusphere-egu21-13021, 2021.

Late Pleistocene stadials were global events, associated with weakened Asian monsoons and Atlantic Meridional Overturning Circulation (AMOC), shifts in atmospheric boundaries and precipitation belts, and warming of the Southern Hemisphere and tropics. In the Northern Hemisphere, stadials are traditionally viewed as dramatic cooling events centred on the North Atlantic, with their abrupt onset attributed to meltwater-induced suppression of the AMOC due to melting of large Northern Hemisphere ice sheets. As warmer temperatures are required for sustained meltwater input, however, there is an apparent inconsistency with this model of Northern Hemisphere stadial cooling. To investigate this inconsistency, we reconstructed the timing and nature of glacial fluctuations in Connemara, western Ireland, located within the in the North Atlantic basin, during Heinrich Stadial 1 (HS1). Fifteen internally consistent cosmogenic beryllium-10 ages of erratic boulders indicate rapid and widespread deglaciation of the former Connemara ice centre at ~17.5 ka. The apparent abruptness of ice retreat, coupled with stratigraphic correlation with geomorphic features indicative of meltwater, suggest that HS1 deglaciation was driven by enhanced melting during the summer ablation season. This interpretation supports evidence for enhanced meltwater discharge and summertime warming elsewhere in Europe during HS1 but may conflict with the traditional view of stadials as severe cooling events.

How to cite: Foreman, A., Bromley, G., Hall, B., and Jackson, M.: A 10Be-dated record of glacial retreat in Connemara, Ireland, after the Last Glacial Maximum and implications for North Atlantic climate, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13747, https://doi.org/10.5194/egusphere-egu21-13747, 2021.

Late Glacial and Early Holocene summer temperatures were reconstructed based on fossil chironomid assemblages at Lake Latorica (Lacul Iezerul Latoritei; Pareng Mountains, 1530 m a.s.l.) with a joint Norwegian – Swiss transfer function, providing an important addition to the late glacial quantitative climate reconstructions from eastern-central Europe. The reconstructed pattern of the Late Glacial faunal and chironomid-inferred temperature changes in Lake Latorica shows some differences from the NGRIP δ¹⁸O record and other European chironomid-based reconstructions; however, it is consistent with the chironomid results of Lake Brazi from the neighbouring Retyezat Mountains (1740 m a.s.l.). Our reconstruction shows that the summer air temperature at Lake Latorica increased by ~ 3°C at the Oldest Dryas/Bølling transition (GS-2/GI-1) and reached 8.1-10.8°C during the Late Glacial interstadial. The Younger Dryas (GS-1) climate reversal in the chironomid-based temperature reconstruction is shown by only a weak decrease (~1°C), while slow temperature increase (9.7–11°C) is observed in the second half of the period. At the Holocene transition temperature increase of nearly 2°C was observed in the reconstruction. Before the Preboreal Oscillation (PO) the mean summer air temperature in the Early Holocene was 12.5°C. During PO the temperature reconstruction shows a decrease of 1.8°C. This cold event coincides with cooling in the Greenland ice core records and other European temperature reconstructions. After the Preboral oscillation the summer air temperatures increase to ~12.8°C in the Early Holocene.

How to cite: Szabó, Z., Heiri, O., Darabos, G., Pálfi, I., Molnár, M., Korponai, J. L., and Magyari, E. K.: A chironomid-based reconstruction of late glacial summer temperatures in the Pareng Mountains (Romania), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15568, https://doi.org/10.5194/egusphere-egu21-15568, 2021.

Over the last 10 years several alpine lakes were studied from the Southern Carpathian Mountains (SCM) using paleoecological, geochemical and stable isotope techniques. The aim of these studies were to obtain quantitative climate reconstructions for the alpine region for the Late Glacial (LG) and Holocene, reconstruct tree and timberline changes and examine how rapid climate change events manifested in this region, what are the regions characteristics. Absolute chronologies were also supported here for the first time with tephra chronology in the Early Holocene. In addition, environmental DNA studies were used to explore what molecular techniques can add to a more exact and often species level reconstruction of past floristic compositions. This talk will summarize these researches and use multivariate statistics to examine leads and lags in ecosystem response at multiple sites (Retezat, Pareng, Fogaras, Ciomadul Mts). These analyses first of all demonstrate that the amplitude of warming was attenuated in the SCM at the GS-2/GI-1 transition relative to NW Europe (~2,8-3 ^oC), summer temperatures increased abruptly already at 16.2 ka cal BP in direct response to the weakening polar circulation and the tripartite GS-1 had weak summer temperature decrease (<1 ^oC), but winter cooling was strong. Regarding the order of ecosystem changes, lead and lag analysis revealed <50 yr lag in vegetation response, 0-100 lag in aquatic floristic response and ~100-150 yr lag in aquatic faunal response to external forcing. Environmental DNA studies showed that despite the method is capable to better capture grass (Poaceae) floristic diversity and replicates woody specie composition obtained by plant macrofossil data, it fails to provide higher resolution for the herbaceous flora around the studied lakes that feature was explained partly by the incompleteness of reference DNA sequences for the trnL region and the DNA preservation characteristics of alpine lakes. Using these pioneer studies, several promising research directions were identified for this region: modelling of projected tree and timberline changes in combination with reconstructed data, using eDNA techniques to decipher alpine farming histories in the mountains and its impact on late Holocene tree and timberline change, reconstruction the accelerating speed of ecosystem change over the last 100 yr. in alpine lakes and calling attention for the irreversibility of these changes, demonstrating tipping points. These will be discussed in the presentation.

How to cite: Magyari, E., Korponai, J., Tóth, M., Braun, M., Hubay, K., Szabó, Z., Darabos, G., Pálfi, I., Bálint, M., Pató, Z., Veres, D., and Buczkó, K.: Late Glacial and Holocene multi-proxy paleoecology in the Southern Carpathian Mountains: quantitative reconstructions and promising new molecular research directions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16242, https://doi.org/10.5194/egusphere-egu21-16242, 2021.