C01_01

Prospects and limitations of marine radiocarbon simulations in (paleo) climate studies

Butzin M¹, Köhler P², Lohmann G^1,2

¹MARUM-Center for Marine Environmental Sciences, University of Bremen, Bremen, Germany, ²Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research , Bremerhaven, Germany

On the timescale of hundreds to thousands of years, the oceans play a key role in the climate system by exchanging momentum, energy, freshwater, and carbon dioxide with the atmosphere. The oceans are also the biggest sink of radiocarbon. Observations of recently dissolved marine radiocarbon have provided, and still are, a benchmark for assessing ocean circulation models, which are an essential ingredient of climate models nowadays. Marine radiocarbon records from older times have been used not only as a dating tool, but also to infer past states of ocean overturning and ocean ventilation. However, these records are sparse, scattered and discontinuous, and their interpretation in terms of past climate change is not straightforward. Numerical simulations could help, but radiocarbon-equipped models often use simplified approaches or setups to keep the computational costs low. In our presentation, we will revisit some of these potential issues and discuss recent developments in ocean-climate-radiocarbon modeling.

C01_02

A dual chronological approach for more robust paleoclimate reconstructions in semi-arid regions – a case study from Mongolian lake sediments

Bliedtner M¹, Strobel P¹, Struck J¹, Salazar G², Szidat S², Nowaczyk N³, Bazarradnaa E⁴, Lloren R^5,6, Dubois N^5,6, Haberzettl T⁷, Zech R¹

¹Institute of Geography, Friedrich Schiller University Jena, Jena, Germany, ²Department of Chemistry, Biochemistry and Pharmaceutical Sciences and Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland, ³Section Climate Dynamics and Landscape Evolution, GFZ German Research Centre for Geosciences, Potsdam, Germany, ⁴Institute of Plant and Agricultural Sciences, Mongolian University of Life Sciences, Darkhan, Mongolia, ⁵Department of Surface Waters Research and Management, Eawag, Dübendorf, Switzerland, ⁶Department of Earth Sciences, ETH Zürich, Zürich, Switzerland, ⁷Physical Geography, Institute for Geography and Geology, University of Greifswald, Greifswald, Germany

Semi-arid Mongolia is a highly sensitive region to paleoclimate changes, but the region’s paleoclimatic evolution and its underlying forcing mechanisms have been controversially discussed. In this context, chronological control of the region’s existing paleoenvironmental reconstructions are often imprecise because chronologies are mostly derived from few ¹⁴C-dates on bulk organic material. Bulk organic carbon has often been used in semi-arid regions due to the absence of terrestrial macrofossils. Compared to terrestrial macrofossils, which are assumed to be rapidly deposited in lakes, bulk organic carbon can be “pre-aged” because organic material accumulates in the catchment over hundreds to thousands of years and possibly overestimates the “true” deposition age when ending up in the lake.

Here we present the chronology of a 7.4 ka sediment record for paleoclimate reconstructions from the high-altitude Shireet Naiman Nuur (Nuur = lake)  in the central Mongolian Khangai Mountains. We extensively ¹⁴C-dated bulk organic carbon and terrestrial macrofossils from the lake sediments and provide a robust and precise chronology for the past 7.4 ± 0.3 cal. ka BP, with mostly all ¹⁴C-ages in stratigraphic order. The ¹⁴C-based chronology is confirmed by paleomagnetic secular variations, which resemble the predictions of spherical harmonic geomagnetic field models. The very good chronological control makes paleomagnetic secular variation stratigraphy a powerful tool for evaluating and refining regional ¹⁴C chronologies when compared to our newly obtained record. Based on our good chronological control, we finally reconstructed variations in paleotemperature and paleohydrology based on established sedimentological proxies and innovative compound-specific δ²H analyzes of specific biomarkers.

C01_03

Combining radiocarbon and stable C isotopes of stalagmites to gain novel insights into geochemical processes at Spannagel Cave

Welte C¹, Fohlmeister J³, Wertnik M², Spötl C⁴

¹LIP, ETH Zurich, Zurich, Switzerland, ²Geological Institute, ETH Zurich, Zurich, Switzerland, ³Federal Office for Radiation Protection, Berlin, Germany, ⁴University of Innsbruck, Innsbruck, Austria

Stable carbon (C) isotope records from stalagmites are readily available as they are often measured alongside stable oxygen isotopes (δ¹⁸O). Their interpretation, however, remains challenging due to myriad processes contributing to changes in the C-isotope ratio. Spatially resolved radiocarbon (¹⁴C) data can help to interpret ¹³C signatures[1],  but are rarely available due to expensive and time-consuming analysis. Rapid and continuous analysis of ¹⁴C concentration in carbonate samples at spatial resolution down to 100 μm is now possible using LA-AMS (laser ablation accelerator mass spectrometry).

Combined δ¹³C and ¹⁴C profiles (expressed as dead carbon fraction, dcf) allowed to hypothesize on the interplay of regional climate and contribution of an old organic C reservoir to stalagmite growth at Spannagel Cave, Austria, in a previous study[2]. Here, we present LA-AMS results from a second Holocene stalagmite from Spannagel Cave (SPA 128). Both stalagmites show large and fast variations in the dcf and δ¹³C. SPA 128 has a generally higher dcf (~50%) and a more negative δ¹³C signal that point towards continuous contribution of an old organic C reservoir to the stalagmite C. Even though, the observed signals cannot be explained conclusively so far, it can be stated that the stable oxygen isotopes agree well in both stalagmites. This is an encouraging finding for future studies making use of δ¹⁸O as climate proxy.

[1]D. Rudzka et al., (2011) GCA 75, 4321-4339.

[2] C. Welte et al., (2021). Clim. Past 17, 2165–2177.

C01_04

Toward Reconciling Radiocarbon Production Rates With

Carbon Cycle Changes of the Last 55,000 Years

Köhler P¹, Adolphi F¹, Butzin M¹, Muscheler R²

¹Alfred Wegener Institute Helmholtz Centre For Polar And Marine Research, Bremerhaven, Germany, ²Department of Geology, Lund University, Lund, Sweden

Since it is currently not understood how changes in ¹⁴C production rate (Q), and in the carbon cycle, can be combined to explain the reconstructed atmospheric Δ¹⁴C record, we discuss possible reasons for this knowledge gap. When combining Q with carbon cycle changes, one needs to understand the changes in the atmospheric ¹⁴C inventory, which are partially counterintuitive. For example, during the Last Glacial Maximum, Δ¹⁴C was ∼400‰ higher compared with preindustrial times, but the ¹⁴C inventory was 10% smaller. Some pronounced changes in atmospheric Δ¹⁴C do not correspond to any significant changes

in the atmospheric ¹⁴C inventory, since CO₂ was changing simultaneously. Using two conceptually different models (BICYCLE-SE and LSG-OGCM), we derive hypothetical Qs by forcing the models with identical atmospheric CO₂ and Δ¹⁴C data. Results are compared with the most recent data-based estimates of Q derived from cosmogenic isotopes. Millennial-scale climate change connected to the bipolar seesaw is missing in the applied models, which might explain some, but probably not all, of the apparent model-data disagreement in Q. Furthermore, Q based on either data from marine sediments or ice cores contains offsets, suggesting an interpretation deficit in the current data-based approaches.

C01_06

Ultra-small AMS ¹⁴C sample analysis to reconstruct changes in the water availability of the Atacama Desert

Gwozdz M¹, Heinze S¹, Hackenberg G¹, Herb S¹, Stolz A¹, Dewald A¹, Jaeschke A², Rethemeyer J², Schiffer M¹

¹Institute for Nuclear Physics, University of Cologne, Cologne, Germany, ²Institute for Geology and Mineralog, University of Cologne, Cologne, Germany

Traces of plant and microbial life preserved in the hyper-arid soils of the Atacama Desert show a strong dependency on water availability, which is the main controlling factor determining the presence of life. The ultra-small soil samples with 1-20 µg carbon content will be used to reconstruct changes in the water availability. Ultra-small AMS ¹⁴C sample analysis will be applied for determining ages of organic compounds isolated from the desert soils.

The coupling of an isotope ratio mass spectrometer (irMS) to the AMS system will allow online-analysis of ¹⁴C, δ¹³C, and δ¹⁵N of ultra-small samples. δ¹³C values will be used for correction of fractionation in the AMS system, to increase the measurement accuracy and finally, to solve dating problems in different archives of the desert, e.g. sediments from clay pans, phytoliths and lipid bio markers like plant wax lipids.

For the analysis of ultra-small soil samples from the Atacama desert, gas ion source AMS ¹⁴C analysis is applied, due to the achieved reliable results for samples with 2.5-50 µg carbon content and ages higher than 25,000 yr BP. The CO₂ from the sample combustion in an elemental analyzer (EA), which oxidizes solid samples under a constant Helium flow, is split and a small quota is directed towards the irMS, whereas the rest is directed to the AMS ion source by the gas injection system (GIS). While δ¹³C, and δ¹⁵N can be measured with the irMS, the ¹⁴C content is simultaneously measured with the AMS system.

C01_P01

U/Th dating and radiocarbon measurement potentials using marine mollusks around Japanese archipelago

Hirabayashi S¹, Aze T¹, Miyairi Y¹, Kan H², Yokoyama Y¹

¹Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Japan, ²Research Center for Coastal Seafloor, Kyushu University, Nishi-ku, Japan

Radiocarbon dating of mollusks are widely used in paleoclimatology and archeology, while Uranium-thorium (U/Th) dating is generally difficult to provide reliable age using mollusks. However, several recent studies suggested that the U/Th dating potential using marine bivalves in Mediterranean Sea, Caspian Seaand Korea. These studies have investigated using limited mollusks species and regions.

In this study, we investigated the distribution of radiocarbon and uranium in mollusks, including the calcified opercula of Turbo sazae Fukuda, Turbo marmoratus and Tridacnina sp. collected from Ryukyu region and Chiba, Japan, to evaluate the possibility of U/Th dating potentials using marine mollusks around Japanese archipelago. We measured high-resolution radiocarbon and uranium concentration using single stage AMS (Yokoyama et al., 2019) and laser-ablation ICP-MS in Atmosphere and Ocean Research Institute, The University of Tokyo, respectively. Our results showed that uranium in opercula of modern Turbo sazae Fukuda and Tridacnina sp. were unevenly distributed and those concentration were 1000 times-less than that in coral skeletons, while radiocarbon in the shell samples were reflected the radiocarbon values in the ambient seawater as well as corals. The uranium in the calcified opercula of Holocene Turbo marmoratus was also unevenly distributed but concentrated area in the opercula was different from that of the modern samples, which suggested exchange uranium after they were deposited. Our results suggested that the uptake processes of radiocarbon and uranium isotopes into mollusks shell were different, and it is important to understand the criteria of choosing the mollusks species for U/Th dating around Japan.

C01_P02

Climatic signal in tree ring δ¹³C and its temporal stability - case study for Suwałaki region

Pawełczyk S¹, Benisiewicz B²

¹Silesian University Of Technology, Gliwice, Poland, ²Silesian University Of Technology, Gliwice, Poland

Isotopic measurements in tree rings can be very useful in reconstructing past climate. However, such reconstructions may encounter some problems. One of these, especially at the present time, is an environmental change caused by anthropopression, which also affects the stable isotope ratios.

Investigations of stable carbon isotope composition in α-cellulose extracted from tree rings of pines (Pinus sylvestris L.) growing in the ecologically clean Suwałki region, North Eastern part of Poland, are undertaken. Carbon isotopic composition of α-cellulose samples was determined using a mass spectrometer coupled to the elemental analyzer. Analyzed isotope record cover the period from 1932 to 2003. Values of δ¹³C measured in the α-cellulose of tree rings were compared to meteorological data. Values of δ¹³C in cellulose strongly respond to temperature, insolation, relative humidity, and precipitation of the current year. The relative August humidity values yield the best correlation between climate and carbon isotope data (r=-0.65). Relations between isotopic and meteorological data demonstrate that precipitation influences the stable carbon isotopic ratios to a lower extend than the humidity. Using a moving interval technique, the temporal stability of correlation between isotope chronology and climate was investigated. These studies showed no climate signal stability for the years of the maximum industrial human activities.

This work is a part of EU ISONET project No. EVK2-CT-2002-0014 (400 years of Annual Reconstructions of European Climate Variability using a High Resolution Isotopic Network).

C01_P03

Evidence of Holocene Hydroclimate Variability in Northern India and Links to the Indus Civilization

Cherkinsky A¹, Niederman E², Porinchu D¹, Kotlia B³

¹University Of Georgia, Athens, United States, ²Stetson University, Deland, United States, ³Kumaun University, Nainital, India

Multi-proxy analysis of a lake sediment core from Uttarakhand, India was undertaken to: characterize regional hydroclimate variability during the middle to late Holocene; and determine if evidence of Indus civilization characterized by well developed agriculture between 4200-3900 cal yr is present at the site. Deoria Tal is a small (2.7 ha), moderately deep (16.0 m), tectonically formed lake situated in a high-grade metamorphic terrain above the Main Central Thrust zone in the Garhwal Himalaya. Chronological control is based on ten AMS ¹⁴C dates obtained on Trapa seed cases. The age-depth model, developed using BACON, indicates that the core spans ~ 5300 years and that a notable increase in the sedimentation rate occurs at 2100 cal yr BP. The results of non-destructive, radiological analyses (XRF, CT scans) suggest that elevated detrital input, greater sediment density, decreased lake ventilation, and lower autochthonous productivity, reflecting a deepening of the lake, occurred between 4350 and 4200 cal yr BP.  An abrupt shift in elemental concentrations and sediment density indicated the onset of lake drawdown at 4200 cal yr BP and a negative hydroclimate anomaly between 4200 and 4050 cal yr BP. At present, we cannot distinguish if the hydroclimate anomalies identified at Deoria Tal are due to variations in summer and/or winter precipitation; however, it is notable that the positive hydroclimate anomalies at Deoria Tal are associated with intervals of strengthened mid-latitude Westerlies.

C01_P04

Holocene fire recorded in dune footslope deposits at the Cooloola Sand Mass, Australia

Patton N^1,2, Shulmeister J^1,2, Hua Q³, Almond P⁴, Rittenour T⁵, Hanson J^1,2, Grealy A², Gilroy J², Ellerton D^2,6

¹School of Earth and Environment, University of Canterbury, Christchurch, New Zealand, ²School of Earth and Environmental Sciences, The University of Queensland, Brisbane, Australia, ³Australian Nuclear Science And Technology Organisation, Lucas Heights, Australia, ⁴Department of Soil and Physical Sciences, Lincoln University, Christchurch, New Zealand, ⁵Department of Geology, Utah State Luminescence Laboratory, Utah State University, Logan, USA, ⁶Department of Geological Sciences, Stockholm University, Stockholm, Sweden

Fire is one of the most dominant landscape disturbances on Earth. There are large and growing paleo-fire datasets, but they are strongly biased towards wetland areas (e.g., peat bogs, swamps and lakes). In this study, we investigate whether terrestrial depositions within the Cooloola Sand Mass coastal dune field, Australia, contain a reliable record of fire history. We excavated four profiles at the base of dune slipfaces (foot-slopes) and calculated charcoal concentrations for three size classes (180-250μm, 250-355μm and 355μm-2mm) at predetermined depth intervals. Bayesian age-depth models were constructed for these profiles using radiocarbon measurements on charcoal (n = 46) and basal OSL dates (n = 4). All records appeared intact with little evidence of post depositional mixing as demonstrated by minimal age-reversals and consistent trends in charcoal concentration and accumulation rates amongst size classes. Aggregating all four records, we generated a terrestrial fire history for the past ca. 7 ka that depicts five distinct peaks representing periods of increased local fire activity: ca. present-0.25, 0.4-1.2, 1.8-2.2, 2.6-3.6 and 5.2-6.7 ka. In general, the charcoal peaks increase in frequency after ca. 4 ka, possibly related to the onset of ENSO. Our findings parallel those recorded outside the dune field and highlight their utility as an ecological and geomorphological record that is abundant across the landscape. As dune fields are much more common than wetlands and lakes in semi-arid and arid areas, these deposits have the potential to increase the spatial resolution of fire records globally.

C01_P05

Sedimentary environment and depositional process of reworked materials in the subaqueous Yangtze Delta during the middle and late Holocene

Wang K^1,2, Saito K², Tada R^2,3, Irino T¹, Zheng H⁴, Sugisaki S⁵, Uchida M⁶

¹Hokkaido University, Sapporo, Japan, ²University of Tokyo, Hongo, Japan, ³Chiba Institute of Technology, Tsudanuma, Japan, ⁴Yunnan University, Kunming, China, ⁵National Institute of Advanced Science and Technology (AIST), Tsukuba, Japan, ⁶National Institute for Environmental Studies (NIES), Tsukuba, Japan

Origin and formation mechanism of the subaqueous Yangtze Delta is of primary importance owing to massive inputs of terrestrial materials from the Yangtze River. It is necessary to examine the transportation mechanism of Yangtze-derived sediment including sediment reworking / re-deposition by coastal current, tide and local input, the migration of shoreline and estuary of the Yangtze River, as well as changes of depocenter in the Yangtze Delta associated with the postglacial sea-level rise in order to interpret and further understand paleoclimatic information record in the Yangtze Delta. YD13 core recovered from the subaqueous Yangtze Delta at 37-m water depth was used to examine the depositional process through time. The age model of YD13 core was established on the basis of the AMS¹⁴C dates of shell fossil, which revealed that the top 10 m of YD13 core corresponds to the last 5.1 ka. The top 10 m of YD13 core sediments are mainly composed of gray silt with intercalations of many thin coarse silt to sand layers. Comparison among ages of shell fossil, benthic foraminifera, particulate organic carbon (POC) and optically stimulated luminescence (OSL) dating, we assumed that YD13 core sediments deposited during 5.1 to 2.3 ka were significantly affected by the reworked materials, which were originally deposited during the transgression in the early to middle Holocene in addition to the riverine sediments discharged directly from the Yangtze estuary.

C01_P06

Updated radiocarbon age-depth model from Lake Baikal sediment: Implication for past hydrological changes for last glacial to the Holocene

Nara F^1,2,3, Watanabe T⁴, Lougheed B⁵, Obrochta S⁶

¹Nagoya University, Nagoya, Japan, ²Kanazawa University, Kanazawa, Japan, ³Chukyo University, Nagoya, Japan, ⁴Japan Atomic Energy Agency, Gifu, Japan, ⁵Uppsala University, Uppsala, Sweden, ⁶Akita University, Akita, Japan

We present an updated ¹⁴C age model using IntCal20 to calibrated new AMS data applied to a Lake Baikal sediment core (VER99G12) in south Siberia. ¹⁴C measurements showed that the core extends to 32 ka BP. To take into account uncertainties in ¹⁴C age and sedimentation depth in the core, a new age-depth modeling routine, undatable, was used in this study. Undatable revealed that the significant changes in the sedimentation rate correspond to global climate events, either warm or cold, which are the Meltwater pulses (MWP) at 19 and 14 ka BP and the Last glacial maximum (LGM) at 21 - 20 ka BP. Since the Selenga River accounts for 50 % of the total river inflow to Lake Baikal, we interpret that these changes in sedimentation rate could be signals of significant increase in Selenga River discharge to the lake, which is expected to be affected by global climate change. Total organic carbon content and mean grain size increase concurrent with sedimentation rate, suggesting river inflow increased available nutrients for biological activity. Our results indicate that hydrological changes corresponding to MWP events can be observed in continental area of the Northern hemisphere.

C01_P07

Paleoclimate study in the Indonesian throughflow region using carbon and beryllium isotopes

Nemoto K¹, Yokoyama Y¹, Horiike S¹, Obrochta S², Miyairi Y¹, Aze T¹

¹The University Of Tokyo, Kashiwa, Japan, ²Akita University, Akita, Japan

The Indonesian throughflow (ITF), the only pathway between the Pacific and Indian Oceans, transports relatively cool, less saline water from the Pacific to the Indian Ocean. Air-sea interactions change dynamically in correspondence with ITF variability, which in turn affects climate (Song & Gordon, 2004). It is also known that the strength of the ITF fluctuates with glacial cycles (Hendrizan et al., 2017; Fan et al., 2018) Thus, reconstruction of past changes in ITF strength is important to better understand global climate. Even though several previous studies address the reconstruction of past ITF variability, more spatially high-resolution data are needed considering the complex pathway of the ITF.

In this study, two cosmogenic isotopes are measured to reconstruct past climate change around the Timor Sea, which is one of the ITF pathways. Radiocarbon dating was performed on planktonic foraminifera and total organic carbon. The offset between each age and carbon nitrogen ratio provides information on past changes in terrigenous material movement. In addition, beryllium 10, another cosmogenic nuclide, and its stable isotope beryllium 9, sourced from weathering, are measured. The effect of environmental components such as grain size can be removed by measuring these two isotopes (Simon et al., 2016). This is the first study to apply multiple cosmogenic nuclides (carbon 14 and beryllium 10) to reconstruct the paleoclimate of the ITF region.

C01_P08

A 900-Year Isotopic Proxy Rainfall Record from central Botswana

Patrut R¹, Woodborne S², Patrut A^1,3, Hall G⁴, Robertson I⁵, Winterbach C⁶, Rakosy L⁷

¹Babes-Bolyai University, , Faculty of Chemistry and Chemical Engineering, Cluj-Napoca, Romania, ²iThemba LABS, Johannesburg, South Africa, ³Babes-Bolyai University, Raluca Ripan Institute for Research in Chemistry, Cluj-Napoca, Romania, ⁴Mammal Research Institute, University of Pretoria, Pretoria,  South Africa, ⁵Swansea University, Department of Geography, Swansea, UK, ⁶Tau Consultants (Pty) Ltd, Maun, Botswana, ⁷Babes-Bolyai University, Faculty of Biology and Geology, , Cluj-Napoca, Romani

High resolution climate archives for southern Africa are essential for designing and validating climate projections. For southern Africa and Botswana in particular, the interannual rainfall variability is associated with sea surface temperatures in the Agulhas Current Core region, which determine the east-west displacement of tropical temperate troughs (TTTs). Stable carbon isotope analysis and radiocarbon dating of the African baobab (Adansonia digitata L.) can provide reliable reconstructions of rainfall variability in its distribution area. We obtained a proxy rainfall record for central Botswana based on the historic Chapman baobab, which collapsed in 2016 during an intense El Niño event. The two investigated samples of the oldest stems of the baobab, which exhibited an open ring-shaped structure composed of 6 stems, provide insight into the precipitation regime over the last millennium, showing centennial and decadal scale variability. The results indicate that the lowest rainfall occurred during the Little Ice Age (1300-1350), while the Warm Medieval Period was marked by relatively stable precipitation. Previous studies suggested positive sea surface temperature (SST) anomalies in the Mozambique Channel led to an eastward movement of the TTTs but our proxy record shows a westward displacement in the past, causing drought in north-eastern South Africa and wetter conditions in the central part of southern Africa. The positive rainfall correlation with SST anomalies and ENSO reversed after 1900, causing a gradual decrease in precipitation and confirming the current aridity trend for Botswana.

The research was funded by the Romanian Ministry of Research CNCS-UEFISCDI under grant PN-III-P4-ID-PCE-201620-2567, No. 145/2021.

C01_P09

Improving radiocarbon based chronologies in semi-arid regions using paleomagnetic secular variations – a case study from Mongolian high-altitude lakes

Strobel P¹, Haberzettl T², Struck J¹, Salazar G³, Szidat S³, Nowaczyk N⁴, Bazarradnaa E⁵,  Zech R¹, Bliedtner M¹

¹Institute of Geography, Friedrich Schiller University Jena, Jena, Germany, ²Physical Geography, Institute for Geography and Geology, University of Greifswald, Greifswald, Germany, ³Department of Chemistry, Biochemistry and Pharmaceutical Sciences and Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland, ⁴Section Climate Dynamics and Landscape Evolution, GFZ German Research Centre for Geosciences, Potsdam, Germany, ⁵Institute of Plant and Agricultural Sciences, Mongolian University of Life Sciences, Darkhan, Mongolia

The paleoenvironmental evolution of semi-arid Mongolia is not well understood so far. To some degree, this is because chronologies in the region are often imprecise limiting the reliability of paleoenvironmental reconstructions. Most chronologies rely on a limited number of ¹⁴C-dates on bulk organic material, which comprises aquatic and terrestrial organic material potentially effected by “hard water” and “pre-ageing” effects. However, it is often impossible to disentangle both effects and resulting age-offsets lead to an overestimation of the true sedimentation age. To overcome these issues, paleomagnetic secular variations (PSV) can be a valuable independent chronological control tool to evaluate and refine ¹⁴C-based chronologies in semi-arid regions.

Here we present a chronological approach including ¹⁴C dating of different sediment compounds and PSV from Lake Khar Nuur, which is located in the Mongolian Altai Mountains. While ¹⁴C-ages of aquatic macrofossils are stratigraphically consistent, ¹⁴C-ages of bulk organic material show partly age-offsets due to pre-aging and sediment relocation. However, we cannot exclude that both compounds are additionally affected by a hard water effect resulting in a general overestimation of the true depositional age. Therefore, analyses of PSV are currently in progress and will be compared to the recently established PSV record from the high-altitude Lake Shireet Naiman Nuur (Bliedtner et al., 2022), which is located in the Mongolian Khangai Mountains and has a very precise chronological control. Comparison of the two ¹⁴C independent PSV records will allow to evaluate and potentially refine our ¹⁴C-based chronology at Lake Khar Nuur.

C01_P10

Optically stimulated luminescence dating of marine sediments from the Bering Sea

Sugisaki S¹, Buylaert J, Murray A³, Uchida M⁴, Stephan R⁴, Mantoku K⁴, Sakai S⁵, Harada N⁶, Tada R⁷

¹Geological Survey of Japan, AIST, Tsukuba, Japan, ²Department of Physics, Technical University of Denmark, Roskilde, Denmark, ³Nordic Laboratory for Luminescence Dating, Department of Earth Sciences, Aarhus University, Roskilde, Denmark, ⁴Earth System Division, National Institute for Environmental Studies, Tsukuba, Japan, ⁵Biogeochemistry Research Center, Japan Agency for Marine-Earth Science and Technology, Yokosuka, Japan, ⁶Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Japan, ⁷Institute for Geo-Cosmology, Chiba Institute of Technology, Narashino, Japan

Marine sediments contain important archives of past ocean and climate changes, but at high latitudes, such as the polar regions, the absence of carbonate has prevented the construction of accurate chronological models. To establish an age model, a method which does not rely on carbonate is needed. Optically stimulated luminescence (OSL) dating makes use of the omnipresent quartz and feldspar grains in the sediment so there is no limitation in the presence of the dosimeter.

In this study, we have investigated the potential of fine-grained (4-11 µm) quartz OSL dating to establish a chronology for deep sea sediment core (MR0604 PC23A, 60˚09.52’N, 179˚27.82’W, water depth of 1,002m) from the Bering Sea. In addition, we check the accuracy of OSL ages by comparison with AMS ¹⁴C dating on planktonic foraminifera and with marine oxygen isotope stratigraphy where possible.

The obtained OSL ages are in good agreement with AMS ¹⁴C ages during Younger Dryas (YD) and Heinrich Event H0, however, there is an offset between the OSL and AMS ¹⁴C ages during MIS 3. Our study confirms that OSL dating using fine-grained quartz that is distributed all over the ocean has great potential in the establishment of an absolute chronology for deep sea sediments.

C01_P11

Mid- to Late- Holocene sea level changes recorded in corals from Philippines

Yokoyama Y¹, Maeda Y², Siringan F³, Miyairi Y¹, Aze T¹, Sawada C¹

¹The University Of Tokyo, Kashiwa, Japan, ²University of Hyogo, Kobe, Japan, ³University of Philippines, Quezon City, Philippines

Sea level observations in the fields (relative sea level: RSL) can provide information on both climate and solid earth properties. Sites located far-away from former ice sheets (ie. far-fields) are useful to reconstruct polar ice sheets melting histories because they are relatively less sensitive to solid Earth properties (Yokoyama & Purcell, 2021). Since Antarctic ice sheets deglacial pathways are still not well understood, mid- to late- Holocene far-filed sea levels can constraint the ice sheets behavior in the past with respect to global climate changes (eg., Yokoyama et al., 2019). The Philippines is in a far-filed site, and coral reefs, which is a reliable RSL indicator (Yokoyama & Esat, 2015), can be found in widespread areas of the country’s coastline. We retrieved fossil micro atoll corals in different part of the Philippines and have conducted series of radiocarbon dating. In this presentation, we will discuss melting histories of Holocene Antarctic ice sheets and vertical tectonic movements of the Philippines coastline obtained from fossil coral data.

References:

Yokoyama, Y. and Purcell, A. (2021) On the geophysical processes impacting palaeo-sea-level observations. Geoscience Letters 8:13.

Yokoyama, Y., et al. (2019) Holocene Indian Ocean sea level, Antarctic melting history and past tsunami deposits inferred using sea level reconstructions from the Sri Lankan, Southeastern Indian and Maldivian coasts. Quaternary Science Reviews 206:150–161

Yokoyama, Y., Esat, T.M. (2015) Coral Reefs. In: Long A, Horton B, Shennan I (eds) Handbook of sea-level research. Wiley, Chichester, pp 104–124