Displays

Quaternary records provide an opportunity to examine how regional climates and vegetation reflect global climate changes comparable in magnitude and velocity to those expected during the 21st century.  The Dansgaard-Oeschger (D-O) cycles of the last glacial period provide the best documented examples of such rapid climate warmings (Greenland interstadials, GIs). However, the age models of pollen records that document regional responses to D-O events are, in general, poorly constrained beyond the radiocarbon timescale. Here we use a pattern-recognition approach, based on matching oscillations in palaeoclimate records to a template of D-O events seen in the Greenland record, to provide better constrained age models. We create a series of templates of Greenland Interstadials (GIs) and compare these to a normalised and detrended time series from a target record using a sliding window and measuring goodness-of-fit using Euclidian distance. We show that this approach can identify D-O events in well-dated records, including reproducing the Greenland record itself. We then apply this approach to the less well-constrained pollen records from the last glacial period from southern Europe. The re-aligned age models permit a more robust comparison of the reconstructed vegetation and climate changes through time and across sites, allowing for regional differences in the response to individual GIs to be identified.

How to cite: Turner, M. and Harrison, S.: Improving age models for abrupt climate changes during the last glacial by pattern recognition, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2691, https://doi.org/10.5194/egusphere-egu2020-2691, 2020.

Understanding the mechanisms that formed past climatic and environmental changes is essential in order to produce models of future climatic trends. Climatically highly sensitive areas like the Eastern Mediterranean are characterized as key sites for those studies and can imprint regional and large-scale atmospheric patterns as well as the impact of those changes into early human societies. Still, the distinction between regional and global climatic signals is challenging, due to variations between chronological control and environmental factors occurring in each study site. Annually laminated sediments assist to that problem since they can provide information on temperature fluctuations, precipitation, volcanism, solar activity etc, up to seasonal scale through coherent varve chronology. In this study, we present a multi-proxy climate reconstruction of eastern Mediterranean over the last 12000 years, based on a non-continuous varved sediment core from Vouliagmeni lake, located in the eastern part of Gulf of Corinth, Greece. The compiled dataset consists of: (a) grain size analysis and magnetic susceptibility measurements, (b) high-resolution X-ray fluorescence data, (c) mineralogical analysis, (d) Computed Tomography (CT) and μCT analysis (e) AMS radiocarbon dating correlated with varve counting, (f) isotopic composition (δ¹⁸O, δ¹³C) on selected samples and (g) diatom analysis. For the determination of lamination boundaries and thickness, standard Computed Tomography was conducted with the highest possible resolution (0.3 mm) and combined with μCT results from selected sections from the core. Sedimentological changes were also documented through the 2D Haunsfield model that was constructed for the core and further correlated with the other studied proxies. The chronological framework of the core was established at 12,500 cal BP through a combination of Bayesian age-depth modelling and varve counting. Accumulation rates change drastically at around 3000 cal BP at the approximate time of extensive urban growth in the study area, as indicated from historical reports. Different precipitation/temperature and runoff patterns for the catchment area were recognized, through the different proxies examined, providing signals of long scale and regional climatic anomalies. The covariation of δ¹³C_carb and δ¹⁸O characterizes the lake system as evaporatively dominant, whereas elemental ratios and isotopic data determine wet (1200-1800 cal BP, 2200-300 cal BP, 4500-4800 cal BP, 5800-6600 cal BP, 9500-10500 cal BP) and arid phases (3000-3200 cal BP, 3800 cal BP, 7100 cal BP) that correspond also to changes in water level, stratification and the formation of laminations. Addressing the fact that laminated sediments in Eastern Mediterranean that extend in 12 ka years are scarce, Vouliagmeni lake seems to present a very promising geoarchive.

How to cite: Emmanouilidis, A., Unkel, I., Seguin, J., and Avramidis, P.: Eastern Mediterranean climate reconstruction over the last 12,000 yrs based on a non-continuous varve sediment record from Vouliagmeni lake, Gulf of Corinth (Greece), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7718, https://doi.org/10.5194/egusphere-egu2020-7718, 2020.

Radiocarbon dating of terrestrial plant-remains is a traditional method for precise age estimations of lake sediments. The absence of sufficient large plant macrofossils required for AMS dating in continental records, especially large lakes, demands for a satisfactory alternative, such as carbon-containing microfossils. Due to their ubiquitous presence in sedimentary archives pollen grains may be considered for dating. Nevertheless, the isolation and enrichment of pollen without a significant carbon contamination is still challenging. Even though commonly applied separation techniques can be used to remove the predominant portions of foreign particles, the undesirable transfer of these particles into the pollen concentrate cannot be excluded, yet. However, flow cytometry, as a highly promising alternative, offers the possibility to sort huge quantities of particles in a short period of time and to generate pure pollen concentrates from heterogeneous samples suitable for AMS radiocarbon dating.

In this study we present the approach to sort limnic sediment samples using flow cytometry. We are able to unequivocally identify pollen populations in the heterogeneous composition of the sediments and isolate them. The sediments analyzed were taken from the continental record of Lake Van (Eastern Anatolia). Annually laminated layers from the Holocene section of the sediment cores allow a precise temporal classification and validation of generated radiocarbon ages derived from fossil pollen. Although it is now possible to produce pollen concentrates without the contamination of foreign particles, the isolation of a sufficient quantity of pollen grains to generate reliable radiocarbon ages is still difficult. An increase pollen yield is required. Due to the limitation of the initial material, it is therefore especially necessary to improve the efficiency during the cytometric analysis.

Our results show the importance to steadily optimize the processing steps during chemical pretreatment, cytometric analysis as well as the radiocarbon dating itself. This facilitates the handling of the ultra-small samples and ensures precise age estimations of the pollen concentrates. Furthermore improving the laboratory routine for the enrichment of pollen will allow the analysis of vast amounts of samples in a short period of time. In consequence, dating pollen concentrates generated by flow cytometry can be used as a robust contribution and independent time control for existing chronologies in continental climate records.

How to cite: Steinhoff, C., Pickarski, N., and Litt, T.: Refining chronologies by dating pollen concentrates – new approach of separating pollen using flow cytometry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10019, https://doi.org/10.5194/egusphere-egu2020-10019, 2020.

The Kerguelen archipelago (around 49°S 69°E) is the emerged part of the Kerguelen Plateau, a large igneous province in the southwestern Indian Ocean. Information on past climatic and environmental conditions in the region is vital for understanding the past behaviour of the southern westerly winds. The cross-disciplinary project SOUTHSPERE seeks to investigate past variations in this weather system through reconstruction of temporal and spatial glacier variability from lake records and glacial landforms N and NE of the Cook Ice Cap. Reliable and accurate chronological control is crucial in this context.

Surface exposure dating of glacial geomorphological features S and SE of the Cook Ice Cap has previously been done using in situcosmogenic Cl-36 [1, 2]. Solifluction and gelifraction processes appear very active in our field area, as do aeolian erosion. Also, highly variable geochemical composition of the basalts and associated intrusions, as well as the degree and type of metamorphosis, lead to strong lithology-dependant weathering and erosion rates, as evident from differential weathering reliefs on cm and m scales. The very active surface environment constitutes a challenge for obtaining accurate surface exposure ages.

In the NW part of the archipelago, basaltic lava units altered by meteoric-hydrothermal fluids contain a wide variety of secondary silicate and carbonate minerals [3]. In settings where quartz-filled geodes and fractures in the basalt are located in favourable positions on bedrock and boulder surfaces, analysis of Be-10 in euhedral and microcrystalline quartz offers a means of validating in situ Cl-36 surface exposure ages. Moreover, multi-nuclide analysis would open up for a wide range of process and landscape development studies on this young archipelago. Percolation of hydrothermal fluids in fractures and geodes is probably related to the intrusion of younger (15-5 Ma) subvolcanic rocks [see 3 and references therein]. A meteoric source of the fluids would imply that the secondary silicates contain meteoric Be-10. As meteoric production is greater than in situ production, this may represent a problem for utilising in situ Be-10 for surface exposure dating. If secondary silicate formation occurred early, rather than late in the intrusive phase, complete radioactive decay of the meteoric Be-10 component is expected prior to surface exposure.

110 rock samples were collected for surface exposure dating with in situ cosmogenic nuclides during a field campaign in November and December 2019. Here we present the first Be-10 data from rock surfaces of glacially transported boulders and exposed bedrock.

[1] Jomelli et al. 2017. Quaternary Science Reviews 162, 128-144.

[2] Jomelli et al. 2018. Quaternary Science Reviews 183, 110-123.

[3] Renac et al. 2010. European Journal of Mineralogy 22, 215-234.

How to cite: Linge, H., Bakke, J., Tuestad, T., Deline, P., Ravanel, L., and Olsen, J.: Cosmogenic Be-10 surface exposure data from the Sub-Antarctic Kerguelen Archipelago, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10917, https://doi.org/10.5194/egusphere-egu2020-10917, 2020.

Yosemite Valley is renowned for its striking topography, with many sheer granite cliffs carved during past glaciations. At the base of these cliffs many large rock avalanche deposits can be found that were deposited since ice retreated from Yosemite Valley. Cosmogenic ¹⁰Be measurements indicate that there are at least 10 different rock avalanche deposits that range in age from 13 to ~1 ka.

In this study, we estimate the time-averaged temperatures experienced by rocks from five of these rock avalanche deposits using cosmogenic noble gas and luminescence paleothermometers. These two systems yield independent estimates of valley floor temperatures during the Holocene, information that is useful for reconstructing the local environmental conditions since deglaciation.

Cosmogenic noble gas paleothermometry utilizes the fact that cosmogenic noble gases like ³He experience thermally-activated diffusive loss at Earth surface temperatures in minerals like quartz. The concentration of cosmogenic ³He in quartz relative to a cosmogenic nuclide that does not experience diffusive loss should therefore be a function of a rock’s thermal history over the duration of its exposure to cosmic ray particles. Apparent ³He boulder exposure ages from these five rock avalanche deposits are 58 to > 98% younger than the corresponding ¹⁰Be exposure ages. Preliminary models that combine these ³He observations and sample-specific diffusion parameters indicate that effective diffusion temperatures (EDTs) recorded by ³He in quartz are similar to or higher than the modern EDT from the instrumental record.

Like with the cosmogenic ³He system, thermoluminescence (TL) paleothermometry of K-feldspars also relies upon the balance between steady signal build-up and thermally-activated loss. The difference is that TL derives from trapped electronic charge at defect sites within the feldspar crystal lattice that accumulates in response to natural background radiation. K-feldspar TL signals comprise a range of stabilities. The least stable sites will experience diffusive loss even at temperatures below 0 °C and the most stable sites will accumulate at upper crustal temperatures. By monitoring which sites are occupied and how long those sites have been accumulating charge, we estimate both the ambient temperature and the time spent at that temperature.

We compare and discuss the history of rock temperatures estimated from these two systems with implications for the post-glacial climate of Yosemite Valley.

How to cite: Brown, N., Tremblay, M., Uebner, M., Stock, G., Balco, G., and Shuster, D.: Constraining post-glacial temperatures of rock avalanche deposits in the Yosemite Valley with cosmogenic noble gas and luminescence paleothermometry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11817, https://doi.org/10.5194/egusphere-egu2020-11817, 2020.

Cosmogenic production rates (PRs) are the essential conversion factor between AMS cosmogenic concentrations and absolute exposure ages. The accuracy of cosmogenic glacial chronologies and reliability in their comparison to other plaeoclimate systems  is largely contingent on the precision and accuracy of the adopted production rate. This is particularly critical in determining past glacial geochronologies at the scale of millennial temporal resolution. Most PR calibrations are carried out at deglaciation sites where radiocarbon provides the independent chronometric control usually based on calibrated 14C ages in basal sediments or varves  from lake or bog cores which is assumed to represent the minimum age for glacial retreat. Under these conditions PRs should be considered as maximum-limiting values. Given that today most AMS facilities can deliver 10-Be, 26-Al and 36-Cl data with analytical errors less than 2%, the accuracy of a PR for a given scaling method (ie transfer function of the site-specific production rate to a reference sea-level high latitude (SLHL) PR) remains largely dependent  on the error in the independent chronology and accuracy of AMS standards. The history over the past 20 years of the ever-changing value of  SLHL 10-Be cosmogenic spallation PRs  with a continual decreasing value from initial estimates of about 7 atoms/g/a to the current  ‘accepted ‘ value of ~4 atoms/g/a,   is an interesting story in itself and demonstrates the complexity in such determinations.  

Today there are both global (average) SLHL PRs and also regional-specific PR values (referenced to SLHL). For the British Isles, there are a number of 10-Be ‘British Isles’ choices that, for the Lm scaling scheme, range between 3.92±0.11  atoms/g/a  (Putnam et al., QG, v50, 2019) to 4.41±0.25 atoms/g/a (Small et al., JQS, v30, 2015). This range in 10-Be spallation PRs has recently raised some debate and challenges for the assumed extent and timing of the local-LGM and demise of the British Ice Sheet. This work provides a new  British Isles site specific 10-Be PR from the  Arenig Mountains in North Wales. We have measured 10-Be concentrations in 13 selected moraine boulders that are tentatively mapped as outer and inner Younger Dryas deglacial deposits hugging a cirque lake,  Llyn Arenig Fach,  just below the head wall  at  Arenig Fach.   Radiocarbon dating of basal sediments from a number of intermorainal core bogs has provided independent age control.  We will present our results and compare them to the current collection of other British Isles 10-Be production rates.  

How to cite: Fink, D., Hughes, P., Fulop, R., Wilcken, K., Adams, P., and Ryan, P.: Yet another in-situ cosmogenic 10-Be local production rate for the British Isles : Llyn Arenig Fach, North Wales, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20791, https://doi.org/10.5194/egusphere-egu2020-20791, 2020.

Beach ridges are a promising geoarchive to study lake-level variations as they indicate former lake-level maxima. Detecting paleo-shorelines and knowing their elevation, inner structure and age. This helps to quantify lake-level highstands, the duration of elevated lake levels as well as to reconstruct sedimentation processes as important indicators of either external forcing (e.g., higher precipitation/lower evaporation) or anthropogenic impacts (e.g., mill stowage) in the past. In this study, a quantitative paleohydrological reconstruction of lake Schweriner See, NE-Germany, should be achieved by a combination high-resolution multi-proxy analysis on sediment cores from both distal and littoral but also from onshore parts. This poster focuses on the onshore part of the eastern shoreline where a succession of beach ridges is located within a distance of up to 600 m away from the recent shoreline and up to 1.5 m above today’s lake level. This indicates both a greater extension and a higher water level in the past. Here we examine these beach ridges using high-resolution luminescence profiling (POSL, 5-15 cm intervals) with a SUERC portable OSL unit combined with full OSL dating (coarse grain quartz SAR protocol) and independent radiocarbon dating to obtain ages of lake-level maxima as well as a (relative) age distribution within and between individual beach ridges. We measured the water content, loss-on-ignition and grain size variation to characterize the beach ridges and their depositional processes but also to estimate the influences of these parameters on the luminescence signal.

The sandy beach ridges are deposited on peat, which overlays mainly lacustrine silty and calcareous sediment. The upper 20-40 cm are enriched in humus. This stratigraphy demonstrates a silting-up sequence and development of a wetland, which was affected by a dynamic lake-level development.The dominating grain size within the ridges is coarse grained sand with small gravel and occasionally thin organic layers in between. The initial results of full OSL dating gives a hint that all beach ridges were deposited during the Holocene. The luminescence profiles typically show an increase in photon counts with depth in the upper part, which was influenced by humus enrichment. The luminescence in the otherwise mainly organic and lime free sands below behave differently with depth in each beach ridge. The total photon count either 1) decreases perhaps influenced by a higher groundwater table in the past or reworking of older nearby beach ridges, 2) increases, offering the possibility to extract relative sedimentation rates, but sometimes has leaps to smaller values or 3) fluctuates around a mean value indicating a potential rapid sediment accumulation. Fluctuating values might also occur due to bioturbation.

In this study, high resolution POSL profiling in combination with grain-size analysis proved to be a promising tool to investigate lacustrine beach ridges and their depositional processes. The method turned out to be valuable to not only select the right sample for OSL dating but also to get a better understanding of beach ridge deposition at Schweriner See.

How to cite: Adolph, M.-L., Lampe, R., Lorenz, S., and Haberzettl, T.: Using high-resolution portable OSL (POSL) profiling to characterize Holocene beach ridges at Lake Schweriner See, NE-Germany , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-468, https://doi.org/10.5194/egusphere-egu2020-468, 2020.

The high-resolution Monticchio (MON) sediment record has been demonstrated to be a key archive for reconstructing climate and environmental changes in the central Mediterranean for the last glacial-interglacial cycle. New sediment cores have been retrieved in April 2016 to investigate particularly the transition from the Last Glacial Maximum into the Holocene with a new high-resolution methodological approach. A floating varve chronology spanning ca. 8,000 years has been established by varve counting on thin sections using a petrographic microscope and layer thickness based sedimentation rate estimates for non- or poorly varved intervals. Varve counting is based on detailed seasonal deposition models of five different varve types. The resulting floating chronology consist of 66.6% individually counted varves and 33.4% interpolated years. The uncertainty estimate of the floating chronology has been determined by double counting and amounts to ±5.8%.

The floating chronology is anchored to an absolute chronology using the Agnano Pomici Principali tephra, dated at 11,999±52 cal yrs BP from paleosols overlying proximal tephra (Bronk Ramsey et al. 2015), is a suitable anchoring point to cross correlation. The resulting varve-based chronology has been compared with several other marker tephras dated elsewhere including the Soccavo 4 tephra (11,700±150 cal yrs BP), the Neapolitan Yellow Tuff (NYT; 14,194±172 cal yrs BP) and the Greenish tephra (19226±104 cal yrs BP). Further comparison with published (Hajdas et al. 1997) and new radiocarbon dates from different terrestrial macro remains are discussed in this paper. This study presents an independent chronology for the last glacial/interglacial transition for a comparison of MON data with high-resolution lake records western and central Europe.

References

Bronk Ramsey, C., P. G. Albert, S. P. E. Blockley, M. Hardiman, R. A. Housley, C. S. Lane, S. Lee, I. P. Matthews, V. C. Smith & J. J. Lowe (2015) Improved age estimates for key Late Quaternary European tephra horizons in the RESET lattice. Quaternary Science Reviews, 118, 18-32.

Hajdas, I., G. Bonani, B. Zolitschka, A. Brauer & J. Negendank (1997) 14C Ages of Terrestrial Macrofossils from Lago Grande Di Monticchio (Italy). Radiocarbon, 40, 803-807.

How to cite: Zhao, X., Wulf, S., Schwab, M. J., Tjallingii, R., and Brauer, A.: Tephra anchored floating varve chronology covering ca. 19.0-11.0 ka BP in new core from Lake Lago Grande di Monticchio: preliminary results, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-715, https://doi.org/10.5194/egusphere-egu2020-715, 2020.

In addition to ¹⁴C-data, sedimentary excesses in ²³⁰Th  (²³⁰Th_xs) in central Arctic Ocean cored sequences yielded critical time constrains and sedimentation rates estimates, at least, at sites characterized by very low sedimentation rates (<< 1cm/ka). Closer to the Russian margin, where higher accumulation rates are recorded based on ¹⁴C-ages, the setting of a reliable stratigraphy based on ²³⁰Th_xs reveals more challenging, as illustrated here, based on the analysis of  a gravity core raised from the southern Mendeleev Ridge (core ARC7-E25; -179.4°E, 79.0°N; 1200 m water depth; 320 cm long). Subsamples were collected at a 4 to 8 cm interval. Measurements included: AMS ¹⁴C in foraminifera, grain size, bulk Xray mineralogy, clay mineralogy, geochemistry (C_org, C_inorg,¹³C_org, ²³⁸U, ²³⁴U, ²³⁰Th, ²²⁶Ra, ²¹⁰Pb). Data indicate that some sediment were lost at core top. Nevertheless, ¹⁴C and ²³⁰Th_xs  data allow estimating a mean sedimentation rate of about 6 to 7 mm/ka during the last two climatic cycles. A comparison of the ²³⁰Th_xs inventory and distribution pattern with those from other cores allows identifying important parameters involved in the cycling of the water column-produced ²³⁰Th in this basin and its sporadic sedimentary accumulation, in particular linkages with sea-ice production over shelves, thus sea-levels, sea-ice rafting routes, grain-size and mineralogy, potential winnowing of fine fractions, role of brines and relative duration of intervals with reduced or nil sedimentation preceding ²³⁰Th_xs-accumulation intervals.

How to cite: Song, T., Hillaire-Marcel, C., and Liu, Y.: 230Th-excess inventory and distribution in a southern Mendeleev Ridge core (Arctic Ocean): linkage with late Quaternary sedimentological and paleogeographical changes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-824, https://doi.org/10.5194/egusphere-egu2020-824, 2020.

Excursions in the radiocarbon (¹⁴C) record, which are rapid changes on a scale of a few years are presumed to be caused by an increase of incoming cosmic rays. The excursions at AD 774-775AD and 993-994AD have generated widespread interest and have been reproduced in many different tree-ring records (Miyake et al. 2012, 2013, 2017; Büntgen et al. 2018).  Similar structures have also been detailed, such as at 660BC (Park et al. 2017; O’Hare et al. 2019). Other types of change in ¹⁴C production may be due to a mix of SPE and different phenomena, such as around 5480BC (Miyake et al. 2017) and 815BC (Jull et al. 2018). We note that a proposed SPE event about 3371BC (Wang et al. 2018) is currently unconfirmed and this emphasizes the need for an anchored dendro-record to determine possible events. Timing of these events is important to understand the underlying recurrence intervals. A considerable number of processes can affect the cosmic-ray flux, including solar events, gamma-ray bursts, geomagnetic shifts and relatively close supernovae. Such studies are providing a wealth of new information through which to characterize new ‘events’ in ¹⁴C structure and to begin to understand the processes behind them. These effects also have introduced more complexity to the international radiocarbon calibration curve.

This research was supported in part by the European Union and the State of Hungary, co-financed by the European Regional Development Fund in the project of GINOP-2.3.2-15-2016-00009 ‘ICER’.

References: Büntgen et al. 2018. Nature Communications 9: 3605; A. J. T. Jull et al. 2014. Geophysics Research Letters 41: 3004-3010; F. Miyake et al. 2012. Nature 486: 282-284; F. Miyake et al. 2013. Nature Communications 4: 1748; F. Miyake et al. 2017. PNAS 114: 881-884; P. O’Hare et al. 2019. PNAS 116: 5961-5966; J. Park et al. 2017. Radiocarbon 59: 1147-1156; F. Y. Wang et al. Nature Communications 18: 1487.

How to cite: Jull, A., Panyushkina, I., Miyake, F., Salzer, M., Baisan, C., Molnar, M., Varga, T., Wacker, L., Brehm, N., and Tegel, W.: Evidence for solar-flare and other cosmic-ray events in the 14C record in tree rings: New information and a cautionary tale., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5377, https://doi.org/10.5194/egusphere-egu2020-5377, 2020.

The hypersaline Dead Sea is a key palaeoclimate archive in the south-eastern Mediterranean region, situated at a critical position between more humid Mediterranean climate and the hyper-arid Saharo-Arabian desert belt. The ca 450 m long ICDP drill core 5017-1, recovered from the deepest part of the Dead Sea, spans the last ~220,000 years as constrained by radiocarbon, U-Th dating and floating δ¹⁸O stratigraphy methods. Nevertheless, an independent dating method is much needed because (i) radiocarbon dating is limited to the last ~40,000 years; (ii) U-Th dating of authigenic carbonates requires a complex correction procedure leading to large age uncertainties; and (iii) wiggle matching of oxygen isotope data is not independent and, hence, does not allow the identification of lead- and lag-phase relationships of changing hydroclimate in comparison to other palaeoclimate records.

Tephrochronology has been demonstrated a powerful tool for dating and synchronisation of palaeoclimate records for regional and global comparison. Due to a lack of visible tephra layers in the Dead Sea sediment record, direct links with the eastern Mediterranean tephrostratigraphical lattice are still absent. Recently, the first cryptotephra ever identified in Dead Sea sediments has been associated with the early Holocene S1-tephra from central Anatolia. This discovery encouraged a systematic search for tephra time-markers in the ICDP deep-basin core 5017-1, with the aim of improving the chronology of the deep record significantly and providing a tool for precise regional synchronisation of proxy records.

In the first phase of the TEPH-ME project focusing on the early last glacial (ca 100-110 ka) and lateglacial (ca 11-15 ka) time intervals in the ICDP core, we have identified more cryptotephra layers than expected. First glass geochemical data suggest that the majority of volcanic ash in the Dead Sea sediments originates from Anatolian volcanic provinces. Even though proximal Anatolian tephra data for comparison are still limited, the identification of cryptotephra in the long Dead Sea record provides novel opportunities to advance the tephrostratigraphical framework in this region, e.g. through synchronising the Dead Sea and Lake Van (eastern Anatolia) sediment records, but also with archaeological and palaeoenvironmental sites that are currently investigated in the Levant and in Arabia.

How to cite: Neugebauer, I., Schwab, M. J., Blockley, S., Lane, C. S., Plessen, B., Tjallingii, R., Wulf, S., and Brauer, A.: CryptoTEPHras in the ICDP Dead Sea deep core to synchronise past eastern MEditerranean hydroclimate (TEPH-ME), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8894, https://doi.org/10.5194/egusphere-egu2020-8894, 2020.

The construction of the new IntCal20 calibration curve was undertaken using a number of new statistical approaches (Heaton et al. 2020), when compared to previous versions.  This was partly due to the nature of some of the new datasets; partly to improve the robustness of the curve; and partly to address particular aspects of radiocarbon within the Earth System such as reservoir effects, incorporation of geological carbon in speleothems, and the uncertainties associated with different timescales.  Here the main approaches taken are summarised with a perspective on their strengths and potential weaknesses.

In particular, the high-resolution extensions to the Hulu speleothem radiocarbon record (Cheng et al. 2018) allow it to be used to anchor the chronology for other key records (Suigetsu, Cariaco, and the Pakistan and Iberian Margins), providing a coherence in the timescale not possible before.  Further, for the first time, we incorporate time varying marine reservoir ages, constrained by the Hamburg Large Scale Geostrophic Ocean General Circulation Model (LSG OGCM)(Butzin et al. 2020).  In addition, work on the relationship to the Greenland ice core timescales (Adolphi et al. 2018) enables us to make direct comparison between radiocarbon dated records and the ice core timescale and here we report on tools to assist with this.

Along with the update to the calibration curve itself, the associated tools for calibration, age-depth modelling and Bayesian modelling have also been updated to make best use of the new resolution and characteristics of the curve.  Here we summarise updates to Bacon, Calib and OxCal.

Heaton, TJ. et al (2020) The IntCal20 approach to radiocarbon calibration curve construction: A new methodology using Bayesian splines and errors-in-variables Radiocarbon: in review.

Cheng, H. et al. (2018) Atmospheric 14C/12C changes during the last glacial period from Hulu Cave. Science, 362(6420), pp.1293-1297. doi:10.1126/science.aau0747

Adolphi, F. et al. (2018) Connecting the Greenland ice-core and U/Th timescales via cosmogenic radionuclides: Testing the synchronicity of Dansgaard-Oeschger events. Climate of the Past, 14, pp.1755-1781. doi:10.5194/cp-2018-85

Butzin, M. et al. (2020) A short note on marine reservoir age simulations used in IntCal20. Radiocarbon: in press.

How to cite: Bronk Ramsey, C., Heaton, T., Blaauw, M., Blackwell, P., Reimer, P., Reimer, R., and Scott, M.: Statistical approaches and tools for IntCal20, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9336, https://doi.org/10.5194/egusphere-egu2020-9336, 2020.

One of the most commonly used methods for dating carbonate deposits, such as speleothems or calcareous sinter deposits, is the ²³⁰Th/U-disequilibrium method. With this approach, ages up to 500 ka can be obtained. However, especially for late Holocene samples, substantial detrital contamination may represent a major problem for radiometric dating. The high ²³²Th content, which is an indicator for the amount of detrital contamination, leads to elevated U/Th-ages and generally larger uncertainties, which limit the potential of the corresponding samples for paleoclimate reconstructions. Ingrowth ²²⁶Ra shows the potential to be used as an alternative dating method. In combination with Ba, U and Th, it is possible to date samples with ages up to 8 ka.

In general, there are three sources of ²²⁶Ra in carbonate samples. (i) excess ²²⁶Ra incorporated during deposition of the material, (ii) detrital material present in the carbonate, and (iii) ingrowth ²²⁶Ra produced by the radioactive decay of its parent ²³⁰Th. Due to the geochemically similar behavior of Ra and Ba, it is possible to correct for the amount of excess ²²⁶Ra. As for the ²³⁰Th/U-disequilibrium method, ²³²Th can be used to correct for detrital contamination.

To test our new method, we applied it to several calcareous sinter samples from different Roman aqueducts, which supplied drinking water to ancient cities such as Jerash or Cordoba . The separation of Ra, Ba, U and Th from the matrix of the samples is performed using a single aliquot of material and different ion exchange resins. Prior to the separation process, a calibrated mixed Ra-Ba-Th-U spike solution was added and equilibrated with the sample solution. The results are not only compared to model simulations for the new system, but also to ages obtained with the conventional ²³⁰Th/U-method.

How to cite: Froeschmann, M.-L., Scholz, D., Vonhof, H., Jochum, K. P., Passchier, C. W., and Sürmelihindi, G.: The potential of ingrowth 226-Ra as a new dating tool for late Holocene carbonate deposits, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13827, https://doi.org/10.5194/egusphere-egu2020-13827, 2020.

Determining the geographic footprint of past climate events is a fundamental step in identifying the mechanisms that drive and propagate these changes around the globe. Glacial deposits are a particularly robust source of such data; glaciers are sensitive indicators of climate that leave records of their past fluctuations on the landscape. Given precise chronologic control, glacial deposits can be used to reconstruct past climate variability. Recent advances in cosmogenic nuclide surface-exposure dating have established past glacial fluctuations as a key climate proxy. However, uncertainties in the application of cosmogenic nuclide production-rate-scaling frameworks hinder efforts to compare past glacial fluctuations with other records of past climate conditions. Production-rate scaling is particularly uncertain in the tropics, where the theorized impacts of changing magnetic field strength on the incoming cosmic ray flux are greatest. Here we present results in-progress from the CoNTESTA [Cosmogenic Nuclide Temporal and Elevation Scaling: Testing and Application] Project, which seeks to establish multiple nuclide production-rate calibration sites of varying age from the low latitudes in order to assess directly the impacts of changing magnetic field strength on nuclide production over time. We also report new data that address empirically the impacts of elevation on nuclide production. The results of this project will strengthen our understanding of cosmogenic nuclide production globally and will improve surface-exposure age calculations from all regions. This in turn will enable more robust assessment of the global phasing of glacial fluctuations and will forward our understanding of landscape dynamics and Earth surface history. 

How to cite: Jackson, M., Bromley, G., Blard, P.-H., and Hemming, S.: The CoNTESTA Project: Impacts of geomagnetic field changes on cosmogenic nuclide production-rate variability and implications for surface-exposure dating, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13991, https://doi.org/10.5194/egusphere-egu2020-13991, 2020.

The quality of uranium-series ages depends on the accuracy and precision at which the decay constants of 234U, 230Th and 238U are determined. Here, we present intermediate results for a revision of the decay constants of 234U and 230Th. Therefore, we examined a selection of different materials in secular equilibrium using isotope dilution multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). New approaches of our study in particular concern the characterization of routines for measuring all isotopes on Faraday cups, i. e. low abundance isotopes on cups with 10^13 Ohm amplifiers, and a different selection of materials in comparison to previous studies.  λ_234 could be determined so far at a precision of 24 ε and agrees with the latest literature value of Cheng et al. (2013) within its error margins.

How to cite: Kerber, I. K., Warken, S., Gerdes, A., and Frank, N.: Towards a revision of 234U and 230Th decay constants, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16588, https://doi.org/10.5194/egusphere-egu2020-16588, 2020.

Reconstruction of a floodplain area over the last 40.000 years (Tisza, Hungary)

              – comparative case study of ¹⁴C and OSL methods

Titanilla Gréta Kertész ^{1 *} , Buró Botond ¹ , Hubay Katalin ¹ , Sipos György ² , Molnár Mihály ¹

¹Isotope Climatology and Environmental Research Centre, Institute for Nuclear Research   

  H-4026, Bem tér 18/c, Debrecen, Hungary

²Szegedi University, Department of Physical Geography and Geoinformatics

   H-6722, Egyetem str. 2-6, Szeged, Hungary

*Correspondence to: Titanilla Gréta Kertész; e-mail: kertesz.titanilla@atomki.mta.hu

  Keywords: Tisza, Jászság-basin, radiocarbon AMS dating, OSL  

Abstract

¹⁴C and OSL results of the 5 parallel, neighbouring cores (avg. depth 19 to 20 meters) were compared for a flood basin area (Jászság-basin). Four major sedimentary horizons were identified: meadow soil on the top; silty clay as the second horizon; a clay-silt section; and fine sand. ¹⁴C and OSL data were integrated into a consolidated age model by BACON software package. Formation of the recent top meadow soil (the upper 1-1.5m) falls in the Holocene. The mean conventional apparent radiocarbon age (940 ± 420 years) was used for correction of the radiocarbon reservoir effect of soil bulk ages. The SubAtlantic + SubBoreal section show increasing apparent deposition rates (~11 cm / ka). The silty-clay strata represents the whole Würm (Weichselian) Last Glacial to Upper Pleniglacial period (aDR ~6.3 cm/ka). The Ságvár-Lascaux interstadial climate period section was apparently much slower (aDR decreases from ~4.2 to ~1.6 cm / ka). About 10 to 60 cms of sediment must be missing from this section. The next part of the section is a very long period (~10 kyrs) with a stable, much greater aDR than even at the end of the Holocene (~20-25 cm/ky). The clayey silt layers fall into the Late Pleistocene / Middle Pleniglacial period, a period of nearly 7.000 years of sedimentation resulting in deposits with a thickness of ~9 m, shown a very high apparent deposition rate (aDR) about ~0.12 m/ka.

The research was supported by the European Union and the State of Hungary, co-financed by the European Regional Development Fund in the project of GINOP-2.3.2-15-2016-00009 ‘ICER’.

How to cite: Kertész, T. G., Buró, B., Hubay, K., Sipos, G., and Molnár, M.: Reconstruction of a floodplain area over the last 40.000 years (Tisza river, Hungary) – comparative case study of 14C and OSL methods , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18900, https://doi.org/10.5194/egusphere-egu2020-18900, 2020.

Pyrogenic carbon constitutes a significant portion of organic carbon in soils of the planet, and in some soils its share raises to 30%. The charcoal-rich archives of forest paleofires are often localized in the geomorphological traps that reveal numerous profiles of pyrogenic soils buried due to the repeated post-fire episodes of erosion and accumulation. The paleokarst and active karst landscapes provide a unique matrix that records pyrogenic and depositional events of the past at the local scale. Polypyrocyclical Podzols of the karst landscapes at the north of the Arkhangelsk region (Russia) are the objects of this study. The fields of closed karst funnels (n x 10 m in diameter, 1–5 m elevation difference) demonstrate accumulative and denudation models of soil formation that are realized at the close distance with the pyrogenic soil archives of the bottoms, slopes and high flat sides of the funnels complementary to each other. This regular grid of archives contains information on pyrogenic events and stages of soil formation throughout the Holocene. We report and discuss here 42 radiocarbon dates (AMS) obtained both for the charcoal material and the total organic carbon (TOC) of the soil organic matter. The 14C age (conventional) of charcoal from the lowest horizons was as old as 9115±30 BP - 8770±30 BP, and the charcoal material of the top pyrogenic horizons was as young as 325±20 BP - 45±20 BP. The 14C age of the soil TOC was in general younger than the age of charcoal enclosed in this soil material. We combine the study of soil horizons morphology and stratigraphy with the set of 14C data to experiment with the several age-depth models explaining post-pyrogenic sedimentation rates on various geomorphological elements of the karst landscape. This study is supported by the Russian Foundation for Basic Research, Project No. 19-29-05238.

How to cite: Zazovskaya, E., Petrov, D., Dolgikh, A., and Mergelov, N.: Radiocarbon dating of various pyrogenic carbon pools in series of buried Podzols (case study from the north of European Russia) , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19650, https://doi.org/10.5194/egusphere-egu2020-19650, 2020.

Uranium series dating is a valuable and well-established tool for age determination of carbonates in paleoclimatology. However, detrital contamination can alter results. A correctional term is commonly used to account for additional Th introduced into the sample material as detritus. This correction requires to make assumptions about the initial ²³⁰Th/²³²Th ratio of the detrital material, since it is not possible to extract it from an individual measurement. Laser ablation multi collector ICPMS equipped with multiple ion counting detectors offers the possibility to use an isochrone technique to extract the initial ²³⁰Th/²³²Th value from heterogeneous samples with a high detrital content. This decreases systematic errors and uncertainties introduced by the detrital correction term and therefore improves the possibility of dating impure carbonates.

How to cite: Förstel, J., Warken, S., Schröder-Ritzrau, A., and Frank, N.: Dating of impure carbonates – Utilizing laser ablation MC-ICPMS to reconstruct initial 230Th/232Th ratios, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21298, https://doi.org/10.5194/egusphere-egu2020-21298, 2020.

Mass movements in the mountains can result in some unexpected discoveries. On September 10, 2017, strikingly white components were found in the western slope of the Val Chavagl, Swiss national Parc. The first inspection identified this as residual material of a lime kiln. Strikingly, the remains of the lime kiln were stuck in the slope, i.e., they were part of the material that built up the scarp and were not merely attached or transported from above. The rest of an old, former lime kiln is part of the terrace. Vast amounts of sediment covered this lime kiln following a storm around the Munt Chavagl - Munt la Schera.

Of interest to the studies of past and most recent mass movements and catastrophic flooding is the timing of the operation and destruction. The age of the lime kiln can be estimated based on historical documents and inventory of lime kilns in the region, where the oldest known so far dates to 1560 CE (Parolini 2012). No charcoal was found in the remains of the newly discovered lime kiln; therefore, another approach was proposed i.e., dating organic remains embedded in deposits of catastrophic flooding. Larch trees, which were discovered at 1840 -1860 m asl, allowed for dendrochronology and radiocarbon analysis. The results obtained indicate that the trees died in the mid 17th century, at the latest. Moreover, our chronology sets Terminus ante quem TAQ for the construction and operation of the lime kiln. Our results are relevant for understanding natural hazards as well as reconstruction and protection of cultural heritage in the region of the Swiss National Parc.

Parolini, J.D., 2012. Vom Kahlschlag zum Naturreservat: Geschichte der Waldnutzung im Gebiet des Schweizerischen Nationalparks. Haupt.

How to cite: Hajdas, I., Schlüchter, C., Haller, R., and Nicolussi, K.: Old lime kilns buried in Val Chavagl (Swiss National Parc), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22193, https://doi.org/10.5194/egusphere-egu2020-22193, 2020.

The Arabian Gulf is a small shallow marginal sea of the Indian Ocean. Its Pleistocene-Holocene sea-level history is of great interest for reconstructing human migration routes into Mesopotamia as well as for better understanding the recent convergence rate between the Arabian and Eurasian plates. For establishing the sea-level history, the ages of past shoreline deposits must be known.

Here we present the optical dating procedure of intertidal carbonate deposits sampled in the coastal area south of Abu Dhabi city (United Arab Emirates). We focus on the challenge of determining a reliable dose rate of samples that are in secular disequilibrium and compare our results with age data obtained from AMS ¹⁴C dating.

For optical dating quartz grains of 90-150 mm were extracted and the equivalent dose was determined from 1 mm aliquots using a standard single-aliquot regenerative dose protocol. Data analysis employed statistical analysis to approximate the palaeodose assuming that all grains measured were sufficiently bleached at time of deposition. For determining the dose rate the radionuclide activities were first quantified by simulating the radiation field of the chemically and physically described samples using gamma spectrometry. These modern activities were then taken to back calculate the activities using well-described double differential equations for open systems. This approach leads to multiple solutions.

We show details of the approach and discuss on the basis of the solutions reasonable open-system assumptions for various sedimentary environments.

How to cite: Lang, A., Alsuwaidi, M., and Mauz, B.: Optical dating of arid coastline deposits – the challenge of dating evaporitic sediments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22250, https://doi.org/10.5194/egusphere-egu2020-22250, 2020.

We present the first floating varve chronology in arid Central Asia of a finely laminated lake sediment record from the high-mountain Lake Chatyr Kol (Kyrgyz Republic). The record was retrieved from the deepest part (~20m) of the lake basin and comprises seasonal laminations (varves) from 11,619 ± 603 years BP to 360 ± 40 BP years. The identification of varves is based on seasonal deposition models established from continuous thin section analyses of the entire sediment profile. The varves comprise a complex pattern of six different micro-facies types throughout the Holocene. All varve types include a pronounced clastic-detrital sublayer, but the composition of their summer sublayers varies between organic, diatom, calcite, and aragonite sublayers. Based on replicate varve counts on overlapping petrographic thin sections an uncertainty of ± 5 % has been calculated for the varve chronology. The chronology is floating because in the uppermost part of the sediment profile varves have been only occasionally formed or preserved which prevented from continuous varve counting in this interval. Instead, the non-varved interval has been dated with ²¹⁰Pb and ¹³⁷Cs γ-spectrometry providing an age for anchoring the floating chronology to the absolute time scale. The resulting chronology is supported by two ¹⁴C ages obtained from terrestrial plant macrofossils. In contrast, radiocarbon dating of aquatic materials showed significantly older ages and prove reservoir effects. Through comparison with the varve chronology changes in reservoir effects throughout the Holocene have been determined. We find a stepwise decline of reservoir ages from up to ~6150 years in the early Holocene to lowest reservoir ages of less than 1000 years in the late Holocene. In addition to their value as chronological tool, changes in varve thickness and seasonal sublayer composition are used as proxies for hydro-climatological reconstruction of Holocene climate evolution.

This is a contribution to the CAHOL project, part of the BMBF-funded and integrated project CAME II.

How to cite: Kalanke, J., Mingram, J., Lauterbach, S., Usubaliev, R., and Brauer, A.: First Holocene floating varve chronology in Central Asia from the Lake Chatyr Kol sediment record (Kyrgyz Republic), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22554, https://doi.org/10.5194/egusphere-egu2020-22554, 2020.

The Ardèche river canyon (Ardèche, France), is famous for its deep ingrown meanders and represent one of the most touristic assets of the region. It is also a central place of Upper Paleolithic human occupancy with numerous caves containing some of the most ancient and impressive rock art ever discovered like in the Chauvet cave, located at the canyon entrance, which artwork was dated at more than 36000 years cal BP (Quilès et al., 2016). The highly elaborated artwork of the cave, dated at more than 36000 years cal BP (Quilès et al., 2016), was kept in an exceptional state because of successive rock collapses of the cliff overhanging the cave that led to the complete closing of the entrance about 21,000 years ago (Sadier et al., 2012). 

However, the late Quaternary river evolution remains poorly constrained as no absolute dating was conducted on the alluvial deposits, nor in other rivers of the Central Massif mountain eastern margin.

We present here the results of two independent dating campaigns based on the karst / river base level relationship and geomorphological observations conducted in both environments. We conducted topographical and geophysical surveys in the Ardèche river meanders and floodplains in order to map the different alluvial banks generations. Geomorphological observations were also conducted inside the canyon cavities and were compared to external observations on an altitudinal grids ranging from the current river thalweg to the + 45 m alluvial deposits.

We exploited U/Th dating method on some cave speleothems located along the river and sampled corresponding alluvial sediments for ESR dating, at the same altitudes. Results were thus compared to a relative chronological model in order to deliver a bayesian statistical model for the Upper Pleistocene deposits of the Ardèche river.

Chronological modelling can thus be compared to long term Pleistocene climatic evolution and show correlations with glacial/interglacial Upper Pleistocene cycles, and landscape modifications like meander shortcuts.

How to cite: Genuite, K., Delannoy, J.-J., Bahain, J.-J., Gresse, M., Jaillet, S., Pons-Branchu, E., Voinchet, P., and Revil, A.: New chronology for the Ardèche river Upper Pleistocene evolution: relationships to glacial/interglacial cycles, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21250, https://doi.org/10.5194/egusphere-egu2020-21250, 2020.