Displays

Calibration is a key element of the radiocarbon dating methodology and the underlying Bayesian statistical approach taken, and algorithms used, are well established and used in calibration software and associated analysis packages.  These calibration methods are based on a calibration curve which provides a mean estimate for the radiocarbon isotope ratio (fractionation corrected) expected in samples, and the associated standard uncertainty, both as a function of time (or calendar age).  The measured samples also have their radiocarbon isotope ratio reported in the same form and so the calibration process involves comparison of the sample radiocarbon measurements with the calibration curve at different points on the calendar age scale.  This then yields a probability distribution function, with associated highest probability density ranges, for the sample calendar age.  We discuss here how improvements in the construction of the IntCal20 curve offer new opportunities, enabling users to obtain more from the calibration curve than previously possible and address some of the limitations of previous calibration approaches.

Previous approaches to calibration assumed that the values of the calibration curves at any time were normally distributed around their estimated mean. However, there are time periods where the distribution of these curves are not well represented by such a normal distribution. This is potentially significant even for calibrations of single samples. The new IntCal20 curve generates multiple possible calibration curves, providing us with the opportunity to identify and adapt to such non-normality.  A second limitation of previous approaches to calibration arises when multiple determinations are used within a broader chronological model. In such cases the usual assumption is that the calibrated uncertainties are independent.  This is certainly not the case if all the samples are the same age (which is currently addressed by combination before calibration) but also is potentially wrong if the samples are close enough in age for there to be correlated uncertainty in the calibration curve.  Again, using the collection of possible curves provided in the construction of IntCal20, rather than just the summary curve, we look at possible solutions to this challenge.  The implications for high-precision chronologies are also discussed.

How to cite: Bronk Ramsey, C., Heaton, T., Blaauw, M., Blackwell, P., Reimer, P., and Scott, M.: New approaches to radiocarbon calibration arising from statistical developments in IntCal20, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9422, https://doi.org/10.5194/egusphere-egu2020-9422, 2020

With the recent demonstration that millennial timescale Dansgaard-Oeschger oscillations of MIS 3 are predictable in a modern coupled climate model following a Heinrich event-like reduction of AMOC strength (eg. Peltier and Vettoretti, 2014), the stage was set for a renewed attack upon the physics of H-events themselves (see Velay-Vitow et al, 2019, JGR-Oceans). This predicts that the freshwater forcing of the AMOC by individual H-events will be on the order of 0.1 Sv and to be maintained for a period between 500 years and 1500 years in accord with data-based inferences (Hemming, 2004). Whereas in the original analysis of H-event induced D-O oscillations the D-O initiating H-event appeared simply as a sharp reduction in AMOC strength in the spin-up of the coupled model, in the work to be reported we transform the pseudo H-event into one that involves explicit freshwater forcing applied at a strength and over a range of times in accord with observational constraints. This has enabled a detailed analysis of the global climate impacts of these events as represented in the coupled climate model that we continue to employ. A critical focus of this analysis is upon the phase relationship between events recorded in the oxygen isotopic records from Greenland and Antarctic ice cores, analyses which demonstrate that this phase relationship is set by the D-O initiating Heinrich event. We also address the expected global climate impacts of stadial-interstadial transitions and provide an initial discussion of these impacts with those recorded in speliothems and other archives.

How to cite: Peltier, R., velay-Vitow, J., and Chandan, D.: Heinrich Stadials: Globa Climate Impacts and the "Bipolar Seesaw" Phase Relationsip, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1955, https://doi.org/10.5194/egusphere-egu2020-1955, 2020

Using high precision and centennial resolution ice core information on atmospheric nitrous oxide concentrations and its stable nitrogen and oxygen isotopic composition enables us to quantitatively reconstruct changes in the terrestrial and marine N₂O emissions over the last 21,000 years as well as over Heinrich Stadial (HS) 4.

We show that over the deglaciation N₂O emissions from land and ocean increased in parallel by 1.8 ± 0.3 TgN yr^-1 and 0.7 ± 0.3 TgN yr^-1, respectively. However, close to 50% of the terrestrial increase is accomplished within less than 200 years at the end of HS1 starting essentially in parallel with the co-occurring CH₄ increase. A similarly rapid but smaller increase is observed at the end of HS0 and suggested at the end of HS4, showing that terrestrial N₂O emissions respond strongly and rapidly to the northward shift in the Intertropical Convergence Zone connected to the resumption of the Atlantic Meridional Overturning Circulation (AMOC). However, little change in terrestrial N₂O emissions is observed during the onsets of Heinrich Stadials. Assuming that N₂O loss from terrestrial ecosystems is directly connected to nitrogen turnover in soils, the fast increase at the end of Heinrich Stadials suggests that terrestrial ecosystems did not become nitrogen-limited on this relatively short time scales, as also supported by model runs in our LPX-Bern dynamic vegetation/biogeochemical model. However, changes in number of moles of N₂O lost to the atmosphere per mole nitrogen turned over in soils (yield factor) may also contribute to the atmospheric N₂O changes.

Marine N₂O emissions also respond to Heinrich events and AMOC changes, however more gradually and less strongly compared to terrestrial emissions both in our data-based reconstruction and the Bern3D coupled ocean/biogeochemistry model. In fact, reconstructed marine emissions start to slowly increase many centuries before the rapid warmings, connected to a re-equilibration of subsurface oxygen concentrations in response to previous AMOC changes. At the onset of HS1 marine emissions decreased by about 0.5 TgN yr^-1, concomitantly with changes in atmospheric CO₂ and δ¹³C(CO₂), and started to re-increase after about 1500 years, when also rapid CO₂ and CH₄ jumps occurred, pointing to Southern Ocean and low-latitude circulation changes. A similar decrease as at the start of HS1 is found after the onset of HS0, but little N₂O emission change is suggested by N₂O concentrations and their isotopic signature at 39.5 kyr before present when Heinrich Event 4 presumably occurred, as suggested by a co-occurring intermittent CH₄ peak and a sudden increase in CO₂.

How to cite: Fischer, H., Schmitt, J., Bock, M., Seth, B., Joos, F., Spahni, R., Battaglia, G., Stocker, B., Lienert, S., Prentice, C., Otto-Bliesner, B., Liu, Z., Schilt, A., and Brook, E.: N2O changes during Heinrich Stadials - Isotopic source deconvolution over HS0, HS1 and HS4 and its implication for the marine and terrestrial nitrogen cycle, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5638, https://doi.org/10.5194/egusphere-egu2020-5638, 2020

Paleoclimate records from the North Atlantic show some of the most iconic signals of abrupt climate change during the ice ages. Here we use radiocarbon as a tracer of ocean circulation and air-sea gas exchange to investigate potential mechanisms for the abrupt climate changes seen in the North Atlantic over the last deglaciation. We have created a stack of North Atlantic surface radiocarbon reservoir ages over the past 20,000 years, using new synchronized age models from thirteen sediment cores refined with thorium normalization between tie-points. This stack shows consistent and large reservoir age increases of more than 1000 years from the LGM into HS1, dropping abruptly back to approximately modern reservoir ages before the onset of the Bolling-Allerod. We use the intermediate complexity earth system model cGENIE to investigate the potential drivers of these reservoir age changes. We find that sea ice, circulation and CO₂ all play important roles in setting the reservoir age. We use these coherently dated records to revisit the sequence and timing of climatic events during HS1 and the last deglaciation, and show that Laurentide Heinrich Events are a response to stadial conditions, rather than their root cause.

How to cite: Burke, A., Greenop, R., Rae, J., Rees-Owen, R., Reimer, P., and Heaton, T.: Dating rapid climate change in the North Atlantic during Heinrich Stadial 1, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18942, https://doi.org/10.5194/egusphere-egu2020-18942, 2020

During the Last Glacial Maximum, the terrestrially based Connemara ice dome was one of several principal ice accumulation centres in western Ireland, distributing ice radially and terminating along its western margins in the North Atlantic Ocean. Our new beryllium-10 chronology, constrained with surface-exposure ages of erratics on a longitudinal coast-to-interior transect, demonstrates that post-LGM deglaciation of Connemara was rapid and that the ice dome was gone by ~17.5 ka. Coupled with the abundance of landforms in this mountainous region indicative of glacial meltwater production, we interpret the rapid and early deglaciation of Connemara as reflecting pronounced melting during the summer ablation season driven by strong atmospheric warming. While this model contrasts with the traditional view of Heinrich stadials as periods of intense cold in the North Atlantic, we note similarities with glacial records from elsewhere in the Northern Hemisphere and globally, as well as with recent marine-geologic evidence for enhanced melting of European ice sheets during Heinrich stadials.

How to cite: Foreman, A., Hall, B., and Bromley, G.: Glacial deposits in Connemara, dated with cosmogenic 10Be, document melting of terrestrial ice in Western Ireland during Heinrich Stadial 1, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-889, https://doi.org/10.5194/egusphere-egu2020-889, 2019

The last deglaciation in the northern hemisphere was interrupted by several short cold setbacks of which the Younger Dryas (YD) was the last and most pronounced. This abrupt and extreme cold period provides valuable insights into regional climate and environmental responses. To decipher the rate of such rapid changes continuous climate archives of annually laminated (varved) sediments are crucial.

Lake Gościąż (central Poland) exhibits an iconic varved lake sediment record that is one of the few European lake records preserving varves throughout the complete YD. To re-investigate this archive, 10 new sediment cores have been obtained along a N-S transect through the deepest part of the lake basin. We used a combination of continuous microfacies analyses, XRF element core scanning, µ-XRF mapping, and high-resolution chironomid-inferred mean July air temperature as well as analyses of stable oxygen and carbon isotopes.

Lacustrine sedimentation begins in the late Allerød, is briefly interrupted by a slump during the early YD and proceeds continuously afterwards. Here, we present a first continuous microfacies investigation of the complete YD in Lake Gościąż. Varve composition during the YD is the most complex and variable one, featuring primarily diatom frustules, calcite, re-worked and re-suspended material. Contrastingly, the simpler structured varves during the early Preboreal and late Allerød are characterized predominantly by calcite, rhodochrosite and dissolved organic matter. The change in microfacies at both YD transitions occurs not simultaneously with the other proxy responses.

Causes of and differences in proxy responses in regard to the dynamics of environmental change during a major change in climate are discussed. Further, we conduct a proxy comparison at both YD transitions and provide a detailed documentation of the transitions through µ-XRF mapping.

This study is a contribution to the Virtual Institute of Integrated Climate and Landscape Evolution Analysis (ICLEA) of the Helmholtz Association (grant number VH-VI-415). It is further a contribution to a scientific project financed by the National Science Centre, Poland – No. UMO-2015/19/B/ST10/03039.

How to cite: Müller, D., Tjallingii, R., Plessen, B., Płóciennik, M., Ramisch, A., Neugebauer, I., Schwab, M. J., Słowiński, M., Błaszkiewicz, M., and Brauer, A.: Dynamic environmental response to the Younger Dryas cooling in the sediment record of Lake Gościąż, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-742, https://doi.org/10.5194/egusphere-egu2020-742, 2019

In light of the current rate of anthropogenic climate change, it is becoming increasingly critical to enhance knowledge of past abrupt climate events and subsequent responses of the Earth system. One period that can provide such insight is the last ~28 kyr, with several abrupt changes occurring over the course of the deglaciation. The Portuguese Margin has been an ideal location to study the impacts of these abrupt climate events on marine and terrestrial environments.  The combined effect of the narrow continental shelf and close proximity to the Tagus and Sado rivers, lead to the rapid delivery of a high quantity of sediment, including our pollen and biomarker proxies, to the Tagus Abyssal Plain. Joint terrestrial and palaeoceanographic analyses from the same sediment samples enable an in situ assessment of the relative timing of changes in palaeoceanographic and terrestrial proxies.

Here we document the response of western Iberian vegetation to millennial and centennial-scale changes, particularly changes in moisture availability, over the deglaciation and Holocene, by combining (for the first time at a Portuguese Margin site) pollen and leaf-wax isotopic biomarker records (δ¹³C and δD) from core SHAK06-5K. A high-resolution pollen record (every 2cm) and lower-resolution n-alkane δ¹³C and δD records spanning 28kya are compared with high-resolution XRF sediment and planktonic foraminiferal d¹⁸O analyses from the same core.  The sequence is supported by high-resolution age control, based on 40 Accelerator mass spectrometry (AMS) ¹⁴C dates from monospecific samples of the planktonic foraminifera, Globigerina bulloides.

Our pollen record indicates the rapid response of regional vegetation to centennial changes and millennial-scale climate events, with forest expansion during the warm interglacial/ interstadial Bølling-Allerød and Holocene, and forest contraction and steppe expansion during cold glacial/ stadial conditions of the Last Glacial Maximum and Younger Dryas. Comparing our pollen and n-alkane biomarker data with the XRF Zr:Sr ratio and planktonic foraminiferal δ¹⁸O records, a clear synchroneity can be seen in the timing of millennial-scale changes in all records.  The millennial-scale changes in our leaf wax n-alkane δD and δ¹³C records can be explained by both vegetation composition and growing season water availability. 

How to cite: Cutmore, A., Ausin, B., Eglinton, T., Maslin, M., and Tzedakis, C.: Reconstructing abrupt climate changes of the last deglaciation & Holocene: Pollen & biomarker analyses from the Portuguese Margin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21845, https://doi.org/10.5194/egusphere-egu2020-21845, 2020

The INTIMATE group has, for a number of years, outlined the most robust approaches for comparing high resolution palaeoclimate archives in order to understand the regional pattern of response to climate change, and hence test models of climate forcing. These have tended to focus on the Last glacial and Early Holocene, until recently. However, in the later Holocene there are similar climatic oscillations with a variety of proposed mechanisms and regional responses. One such climatic oscillation, the 2.8 ka BP event, is a cold spell thought to be driven by a grand solar minimum with potential impacts on atmospheric dynamics and hydrology across parts of Western Europe¹. At present there are only a small number of independently-dated, high-resolution records for this event, limiting the extent to which a regional expression of this event can be understood. This is a problem, as there is significant interest in understanding the impact of solar minima on recent and future climates².

High resolution, multiproxy records of this event are limited in the UK, however, annually laminated sediments from Diss Mere, Norfolk, UK, provide an excellent opportunity to improve our understanding of the environmental impacts of this climatic oscillation on ecosystems of the region. Here we consider multiple proxies including diatoms, chironomids, pollen, ẟ¹⁸O and ẟ¹³C isotopes, integrated through a highly constrained age model based on varve counts, radiocarbon dating, tephrochronology and Bayesian modelling³. Our analyses highlight distinct responses linked to the associated cooling of the 2.8 ka BP oscillation. These include an opening of the landscape around the lake, documented in our pollen record, accompanied by diatom community changes, linked to alterations in temperature, nutrients, turbidity and water clarity. These are potentially a result of increased landscape instability changing the nutrients entering the lake water and its clarity, while increased wind shear due to a more open environment, is linked to the changes in turbulence. Chironomid inferred temperatures also indicate cooling during this period. We compare the Diss palaeorecord with another annually-resolved lake record for this event, Meerfelder Maar, Germany, and with peat bog sites in Ireland, where the event is also associated with tephra layers, to outline the similarities and differences in the regional response to this solar induced event. These results are particularly significant for studies of environmental/ecological impact¹ of grand solar minima on future climates in a warming world, through the potential for palaeodata climate model comparisons².

References:

1.      Martin-Puertas, C. et al. (2012). Nat. Geo. 5, 397-401.

2.      Ineson, E. et al. (2015) Nat. Commun. 6, 7535.

3.      Martin-Puertas, C. et al. (2020) European Geosciences Union.

How to cite: Harding, P., Langdon, C., Walsh, A., Biddulph, G. E., Blockley, S. P. E., Milner, A. M., Langdon, P., and Martin-Puertas, C.: The 2.8 BP Event: a high-resolution multiproxy perspective from Diss Mere, Norfolk, UK., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11311, https://doi.org/10.5194/egusphere-egu2020-11311, 2020

The paleoclimatic changes that occurred in the Southern and Northern hemispheres during the last deglaciation are thought to have affected the continental tropical regions. However, the respective impact of North and Southern climatic changes in the tropics are still poorly understood. In the High Tropical Andes, the Antarctic Cold Reversal (ACR, 14.3-12.9 ka BP) was reported to be more represented than the Younger Dryas (12.9-11.7 ka BP) among morainic records. However, in the Altiplano basin (Bolivia), two cold periods of the North Hemisphere (Heinrich Stadial 1a (16.5-14.5 ka) and Younger Dryas) are synchronous with (i) major advances or stillstands of paleo-glaciers and with (ii) the highstands of the giant palaeo-lakes Tauca and Coipasa. Therefore, additional results are needed to disentangle between potential North and South Hemisphere climatic influence on the glacial dynamics in the region.

We present new Cosmic Ray Exposure (CRE) ages from glacial landforms of the Bolivian Andes that extend pre-existing datasets for four different sites spreading from 16 to 21°S. We reconstruct the Equilibrium Line Altitudes (ELA) associated with each moraine with the AAR method and use them in an inverse algorithm that combines both the palaeo-glaciers and palaeo-lake budgets to derive temperature and precipitation reconstructions. Our temperature reconstruction (ΔT vs. Present) shows a consistent trend through the four glacial sites with a progressive warming from ΔT= -5°C (17 ka BP) to –2.5°C (15-14.5 ka BP, at the end of the Tauca highstand). This is followed by a return to colder conditions, around -4°C, during the ACR (15.5-12.9 ka BP). The Coipasa highstand is coeval with another warming trend followed by ΔT stabilization at the onset of the Holocene (circa 10 ka BP), around -3°C. Precipitation is mainly characterized by increases during the lake highstands, modulated by the distance from the glacial sites to the center of the paleolakes that are moisture sources (recycling processes).

These new results highlight the decorrelation of the glacier dynamics to the temperature signal in regions that are characterized by high precipitation variability. They also provide a theoretical frame to explain how both regional and global forcings can imprint the paleo-glacial records. Our results strongly suggest that during the last deglaciation (20 – 10 ka BP), in the Tropical Andes, atmospheric temperatures follow the Antarctic variability, while precipitation is driven by the changes occurring in the Northern Hemisphere.

How to cite: Martin, L., Blard, P.-H., Lavé, J., Lupcker, M., Charreau, J., Jomelli, V., and Bourles, D.: Antarctic-like temperature variations in the Tropical Andes recorded by glaciers during the last deglaciation (20 – 10 ka BP), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9550, https://doi.org/10.5194/egusphere-egu2020-9550, 2020

The high sensitivity of climate variability to the mean position of the intertropical convergence zone at different time scales is well known. However, due to a lack of absolutely dated high-resolution proxy records, the long-term changes in the tropical Atlantic oceanic and atmospheric circulation system prior to the late Holocene are still not well constrained. Paleo climate reconstructions and model studies suggest a very complex response of the northern hemispheric tropical rain belts in the western tropical Atlantic depending on the nature of the forcing, surface type and surrounding continent-ocean configuration.

Here we present a high resolution multi-proxy speleothem record from Cueva Larga (Puerto Rico) covering the last Glacial between 46 and 15 ka BP. Precise ²³⁰Th/U-dating reveals growth rates between 50 up to more than 1000 µm/year which allow for the investigation of multi-decadal to millennial scale variability in the stable isotope (δ¹⁸O and δ¹³C) and elemental records.

The analysed proxies document a pronounced response of regional precipitation to abrupt centennial to millennial scale climatic excursions across the last Glacial, such as Heinrich Stadials and Dansgaard/Oeschger oscillations. Here, we observe a strong agreement between our paleo-precipitation reconstruction and climate proxy records which are indicative of the strength of the Atlantic meridional overturning circulation and northern hemispheric temperature changes. The coherence of speleothem δ¹⁸O values with sedimentary ²³¹Pa/²³⁰Th also on sub-millennial timescales supports a persistent link of regional precipitation variability to ocean circulation variability. Spectral analysis further suggests that multi-decadal to centennial variability persisted in the western tropical Atlantic hydro-climate not only during stadial and interstadial conditions, but also during the last Glacial maximum, supporting the hypothesis that the Atlantic low-latitude regions respond to internal modes of climate variability on these time scales regardless of the global climate state.

The compilation of our dataset from Puerto Rico with other paleo-precipitation records allows for the reconstruction of past changes in position, strength and extent of the intertropical convergence zone in the western tropical Atlantic and reveal the existence of spatio-temporal gradients in response to millennial to orbital climate change.

How to cite: Warken, S., Vieten, R., Winter, A., Spötl, C., Miller, T., Frank, N., Jochum, K. P., Mielke, A., Schandl, J., Schröder-Ritzrau, A., Mangini, A., and Scholz, D.: Last Glacial multi-decadal to millennial-scale precipitation variability inferred from Puerto Rican speleothems, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19591, https://doi.org/10.5194/egusphere-egu2020-19591, 2020

High-latitude climate variations during Greenland Interstadials (GI) are expected to transfer globally in a complex way through interactions of fast atmospheric as well as slower cryospheric and oceanic processes. Prerequisite for an investigation of the evolution of GI is a climate independent synchronization of the considered paleoenvironmental archives. Measuring and aligning globally common production rate variations of the cosmogenic radionuclide ¹⁰Be in different archives provides a tool for such synchronizations and the investigation of environmental gradients in space and time, with minimized uncertainties in the relative timing.

A ¹⁰Be time-series at < 40-year resolution was measured along with new proxy records down to sub-mm step size from Black Sea sediment core M72/5-22-GC8 around GI-10 (~41 ka BP). We synchronized our ¹⁰Be time-series to that from Central Greenland ice cores based on the globally common production rate variations using the globally optimal fit.

Comparing the synchronized environmental proxy records points to a bipartite response of the Black Sea sediment record at the onset of GI-10. First, synchronous with the abrupt temperature increase in Greenland, costal sea ice decreases on the Black Sea, reflected by reduced sedimentary ice rafted debris contents. Second and with a lag of ~190 years, abrupt increases in the K/Ti proxy point to enhanced regional precipitation causing higher riverine sediment supply into the basin.

This bipartite structure might be connected to both differential thresholds of proxy responses in Black Sea sediments to locally abrupt environmental forcing and/or a bipartite climate transition in the region in response to GI-10. The latter could possibly be explained by an initial fast atmospheric-transmitted warming in the Black Sea region synchronous to the onset of GI-10, followed by a shift from predominantly continental to Mediterranean weather systems ~190 years later, after regional oceanic adjustments. However, further investigations during more GIs are necessary to test the robustness of these results.

How to cite: Czymzik, M., Nowaczyk, N., Dellwig, O., Wegwerth, A., Muscheler, R., Christl, M., and Arz, H.: Bipartite response in the Black Sea sediment record to Greenland-Interstadial 10, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8561, https://doi.org/10.5194/egusphere-egu2020-8561, 2020

The effects of extreme climatic changes on Alpine ecosystems during the last glacial are poorly understood. The recently discovered Nesseltalgraben site in the northern Alps provides a high-resolution sediment sequence covering the Marine Isotope Stage (MIS) 3 (59-28 ka BP), a period characterized by climatic extremes known as Dansgaard-Oeschger cycles or Greenland interstadials/stadials. The radiocarbon-dated composite profile of 21 m stratigraphic height provided a continuous pollen profile, bryophyte macrofossils, and wood remains. Additional to palaeobotanic studies, stable isotope analyses (δ²H, δ¹³C, δ¹⁸O) of bulk sedimentary cellulose and plant macrofossils (wood, monocots, and bryophytes) complemented the palaeoenvironmental and palaeoclimatic studies. Among the terrestrial pollen, Poaceae and arboreal pollen showed an antithetic behaviour and high variability reflecting interstadial-stadial climatic switches. Arboreal pollen are dominated by Pinus sylvestris-type, with admixtures of Picea, Betula, Alnus, and Salix. The arboreal pollen record exhibits several maxima indicating milder climatic conditions, tentatively attributed to Greenland interstadials 5.1, 6, 8, 11/12 and 14-17. During Heinrich events 4 and 5, arboreal pollen show distinct minima underlining a severe impact of these events on regional climate and vegetation. Bryophyte assemblages show dominant wetland conditions at the site during the entire MIS 3. The sudden occurrence of Drepanocladus turgescens after 31.6 ka cal BP indicates a change from a fen to a frequently drying wetland habitat linked to enhanced glacifluvial action caused by glaciers approaching towards the site. Stable isotope analyses of extracted bulk sedimentary cellulose revealed strongly fluctuating values best interpreted by variable mixtures between a terrestrial end member (lignified plants, monocots) with high δ²H, δ¹³C, and δ¹⁸O values on the one hand, and wetland (bryophyte) cellulose sources with low isotope values on the other. Strong negative isotope excursions in the sedimentary and bryophyte cellulose records between 37.3 and 34.8 ka cal BP are best explained by a change to more humid conditions, possibly related to enhanced permafrost, and are contemporaneous with massive increases of Cyperaceae pollen. We conclude that the vegetation at Nesseltalgraben responded to several Greenland stadials/interstadials and Heinrich events. A straightforward correlation between vegetation oscillations and Greenland ice core records, as has been found in Alpine speleothem isotope records, is, however, not always obvious which could be the result of multiple additional abiotic and biotic factors influencing tree dissemination and growth.

How to cite: Mayr, C., Stojakowits, P., Lücke, A., Wissel, H., Hedenäs, L., Lempe, B., Friedmann, A., and Diersche, V.: Impacts of climatic extremes during MIS 3 on Alpine vegetation: evidence from Nesseltalgraben (SE Germany), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5500, https://doi.org/10.5194/egusphere-egu2020-5500, 2020

To better understand the response of Central European vegetation to rapid climate change during the late Quaternary, we have revisited the Füramoos peat bog in southwestern Germany. Located between two moraine ridges of Rissian age and comprising a near-complete sedimentary sequence from late Marine Isotope Stage (MIS) 6 to 1, this peat bog represents the longest continuous pollen record from the last glacial-interglacial cycle north of the Alps. The Füramoos site has been in the focus of several palynological studies in the past, showing that it presents an excellent archive to study the impact of Dansgaard-Oeschger (D-O) events on the Central European ecosystems (e.g., Müller et al., 2003). However, these previous studies were only of limited temporal resolution, which has yet precluded detailed insight into the ecosystem response to short-term climate change. We present a new, highly resolved pollen record (temporal resolution: 80–200 yrs) and XRF core scanning data from Füramoos spanning the past ~130 ka based on two new drill cores that consist of peat and lake sediments (Kern et al., 2019).

Our results show that closed temperate forests thrived at Füramoos during full interglacials characterized by Alnus, Corylus, Quercus, and Ulmus. The major difference between the past two interglacials is that Fagus dominates during MIS 1 whereas it is mostly absent during MIS 5e. During MIS 5, the vegetation evolved from closed temperate (MIS 5e) to boreal forests (dominated by Betula, Picea, and Pinus; MIS 5d–5a). The youngest part of the last interglacial (MIS 5d–5a) is marked by six distinct forests contractions (decreases in arboreal pollen by ~30–50%) before the establishment of a steppe vegetation that prevailed throughout the Last Glacial (MIS 2–4). In addition, seven transient increases in tree-pollen percentages document the expansion of boreal forests during MIS 2–4; they are associated with synchronous increases of Si, Ti, K and Fe contents as evidenced in XRF data.

We attribute the forest contractions during MIS 5d–5a to the cooling events C19–C24 known from marine records in the North Atlantic and terrestrial records from southern Europe. Moreover, the forest expansions during MIS 2–4 are associated with warm and moist conditions occurring during D-O events 7–12, and 14. In contrast, D-O events 13 and 15–19 don’t leave an imprint on the vegetation although their presence is clearly documented in the XRF data. Our findings emphasize that the sediments from Füramoos are exceptionally well suited to reconstruct ecosystem dynamics in Central Europe yielding unprecedented insight into the vegetation response to short-term climatic forcing north of the Alps during the past 130 kyrs.

Müller, U.C., Pross, J., Bibus, E., 2003. Vegetation response to rapid climate change in Central Europe during the past 140,000 yr based on evidence from the Füramoos pollen record. Quaternary Research 59, 235–245.

Kern, O.A., Koutsodendris, A., Mächtle, B., et al., 2019. X-ray fluorescence core scanning yields reliable semiquantitative data on the elemental composition of peat and organic-rich lake sediments. Science of the Total Environment 697, 134110.

How to cite: Kern, O., Allstädt, F., Koutsodendris, A., Mächtle, B., Schukraft, G., Heiri, O., and Pross, J.: Central European vegetation and climate dynamics during the past 130 ka at Füramoos, SW Germany, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19955, https://doi.org/10.5194/egusphere-egu2020-19955, 2020

Chronologies for marine sediments are usually constructed by tuning marine proxies for global ice volume (δ18O) to the well understood variations in the Earth's orbit, by the identification of event horizons (e.g. tephra or biostratigraphic markers) and/or by radiocarbon dating. However, these techniques are not universally applicable. Optically stimulated luminescence dating (OSL) is potentially widely applicable to marine cores and may offer significant advantages over more conventional chronometric techniques. However, methodological considerations regarding the application of OSL techniques have yet to be systematically explored. Using material from Ocean Drilling Program (ODP) cores 658B and 659A, we assess the applicability of OSL dating to deep ocean sediments. For these cores, severe uranium-series disequilibrium is found, but the cause and character of this disequilibrium is spatially and temporally variable. Uranium-series disequilibrium causes the environmental dose rate to vary over time, and an iterative dose rate calculation is required to generate accurate ages. For the last glacial-interglacial cycle, these calculations yield OSL ages which are in good agreement with independent age estimates, suggesting that the application of luminescence dating techniques to deep-sea sediments merits further investigation.

How to cite: Armitage, S., Sahy, D., Tindall, J., and Pinder, R.: Direct dating of marine sediments using optically stimulated luminescence techniques: Insights from ODP cores 658B and 659A., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7620, https://doi.org/10.5194/egusphere-egu2020-7620, 2020

The sedimentation rate in the northeastern South China Sea (SCS) is high and it therefore offers an opportunity for a high-resolution paleoceanographic study. This study is based on high-resolution AMS ¹⁴C dating on forams and oxygen isotope data of two planktonic foraminifera species (Globigerinoides ruber and Neogloboquadrina dutertrei) from the sediment core, MD18-3568, collected from the northeastern SCS, to reconstruct upper-ocean stratification since 35 ka.

The marine sediment core MD18-3568 is located on the accretionary wedge off SW Taiwan at a water depth of 1,315 m, the whole core is dominated by hemipelagic sediments and is of 20.7 m in length. Samples for AMS ¹⁴C dating were selected at roughly 2 ka interval with a total of 16 samples. The ages show a continuously younging-upward trend with bottom of this core around 35,000 years BP. Samples for high-resolution oxygen isotope measurements were selected at a nominal 500-year age interval. The difference in δ¹⁸O between G. ruber (mixed layer dwelling species) and N. dutertrei (thermocline dwelling species) is used to reconstruct the upper ocean stratification with large difference indicating significant ocean stratification and vice versa. The results show moderate upper ocean stratification during 35-24 ka, and it became less stratified during the Last Glacial Maximum (LGM, 23-19 ka). During the deglacial stage, the stratification gradually became stronger until the early Holocene (12-9 ka), and it has kept strong upper-ocean stratification since 9 ka. Literature has documented less rainfall intensity during the LGM and heavy rainfall during the Holocene in southern Taiwan. We interpret the upper-ocean stratification in the NE South China Sea near Taiwan is linked to the amount of freshwater inputs from Taiwan. Less Taiwan freshwater input during the LGM led to a weak stratified upper ocean and a large amount of freshwater input from Taiwan led to a strong upper-ocean stratification during the Holocene.

How to cite: Wang, T.-C., Lin, A. T.-S., Mii, H.-S., Horng, C.-S., and Colin, C.: Upper-ocean stratification of the NE South China Sea during the last 35 ka: Implications from oxygen isotope records from planktonic foraminifera, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3222, https://doi.org/10.5194/egusphere-egu2020-3222, 2020

Late Quaternary Antarctic ice-sheet instability is recorded by ice-rafted debris (IRD) in mid- to high-latitude marine sediment, especially during marine isotope stages (MIS) 2-3, but drivers of this instability remain enigmatic (Labeyrie et al., 1986). A key step in resolving this puzzle is to determine the location of iceberg calving sites, thus highlighting ice sheet sectors exhibiting repeated instability. Single-grain U-Pb provenance analysis applied to clastic IRD provides a suitable high-resolution tool for this task, and also permits discrimination of continental IRD from volcanic material. The application of multiple proxies (apatite, rutile, and zircon) is critical in order to reduce source area fertility biases: for example, the near exclusive occurrence of zircon in felsic-intermediate igneous rocks (e.g., Hietpas et al., 2010).

Here, we present detrital apatite, zircon, and rutile U-Pb data from samples taken from a gravity core from the Odyssea contourite drift system, located on the margin of the Ross Sea (Rebesco et al., 2018) and deposited during MIS2-3. Contourites are marine clastic sediment deposits forming by along-slope, bottom currents reworking of fine-grained (clay-silt) sediments delivered by down-slope sedimentary processes (e.g. meltwaters, turbidity currents, debris flows). Crucially, contourite targetting eliminates the challenge of distinguishing IRD from coarse (sand-gravel) turbidite material in basin deposits, as ice-sheet instability is also associated with turbidite production at glaciated shelf margins (e.g., Bart et al., 1999).

We couple our analysis with the multi-proxy sediment analyses previously performed by Lucchi et al. (2019). We consider the implications of our data for the advance and retreat of the Antarctic Ice Sheet during MIS 2-3, and discuss the further applicability of our multi-proxy approach around Antarctica.

Bart, P.J, et al., 1999, Journal of Sedimentary Research, v. 69, p. 1276–1289, doi:10.2110/jsr.69.1276.

Hietpas, J, et al., 2010, Geology, v. 38, p. 167–170, doi:10.1130/G30265.1.

Lucchi, R.G, et al., 2019. EGU General Assembly 2019, Vienna April 7^th–12^th, Geophysical Research Abstracts Vol. 21, EGU2019-10409-1

Rebesco, M, et al., 2018, preliminary results, in POLAR 2018 SCAR/IASC Open Science Conference, v. GG2 Arctic, p. 14133.

Labeyrie, L, et al., 1986, Nature, v. 322, p. 701–706.

How to cite: Neofitu, R., Mark, C., Rebesco, M., Lucchi, R. G., Douss, N., Morigi, C., Kelley, S., and Daly, J. S.: Tracking Late Quaternary ice sheet dynamics by multi-proxy detrital mineral U-Pb analysis: A case study from the Odyssea contourite, Ross Sea, Antarctica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5011, https://doi.org/10.5194/egusphere-egu2020-5011, 2020

The Eastern Mediterranean is an important region for understanding the late Quaternary, as there is evidence for a complex pattern of climatic and environmental change, influenced by orbital forcing and complex feedback mechanisms (Rohling et al., 2013). It is also a key region for examining the dispersal of humans out of Africa. Consequently, it is important to develop robust chronologies for palaeoclimatic, environmental and archaeological records in the region, to allow synchronisation, comparison and hypothesis testing. Tephrochronology is a vital tool for correlating such records, but the fine detail of the Eastern Mediterranean tephra depositional history is not yet well defined. Part of the problem relates to a lack of cryptotephra (non-visible ash) studies on long stratigraphic records. It is well known from the Atlantic and Central Mediterranean that cryptotephra studies can significantly improve tephra inventories, and constrain the relationship between key tephra markers and important environmental transitions. Another key problem for the region is that for distal tephra there is a relatively limited geochemical database from different volcanic centres, especially in terms of trace element compositions. One important method for addressing this problem is to develop detailed tephrostratigraphic records and tephra geochemical inventories from long sediment sequences (e.g. Bourne et al., 2010; Satow et al., 2015).

Here we present the first marine crypto-tephrostratigraphy from the Levantine Sea, covering approximately the last ~200,000 years, from a long marine core (MD81-LC31). The new data for the core include tephra shard concentrations, major and trace element geochemistry, correlations to the eruptive record of the Aegean and Anatolian volcanic centres, and new radiometric age information. Our new data is compared to existing chronological information from LC-31, including sedimentological, geochemical, paleomagnetic and radiocarbon evidence. Our data helps to refine the chronology for this important record and will underpin ongoing studies into the detail of palaeoceanographic and environmental change in the region.

Bourne, A.J., Lowe, J.J., Trincardi, F. et al. 2010. Distal tephra record for the last ca 105,000 years from core PRAD 1-2 in the central Adriatic Sea: implications for marine tephrostratigraphy. Quaternary Science Reviews, 29(23-24), 3079-3094.

Rohling, E.J., Grant, K.M., Roberts, A.P. et al. 2013. Paleoclimate variability in the Mediterranean and Red Sea regions during the last 500,000 years: implications for hominin migrations. Current Anthropology, 54(S8), S183-S201.

Satow, C., Tomlinson, E.L., Grant, K.M. et al. 2015. A new contribution to the Late Quaternary tephrostratigraphy of the Mediterranean: Aegean Sea core LC21. Quaternary Science Reviews, 117, 96-112.

How to cite: Zhang, S., Manning, C., Satow, C., Armitage, S. J., and Blockley, S.: Developing a multi-methods dating framework for the Eastern Mediterranean region over the Late Quaternary, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5925, https://doi.org/10.5194/egusphere-egu2020-5925, 2020

Geochemically distinct volcanic ash (tephra) deposits have the potential to act as a key geochronological tool to independently synchronize independent paleoclimate archives. Recent advances in the detection of invisible (crypto) tephra have led to the ongoing development of regional tephra frameworks. These frameworks provide an overview of the spatial coverage of existing geochemically distinct tephra horizons attributed to dated eruptions. Hence, these developing frameworks produce an essential tool for precise correlation of different and/or disparate climate archives within a certain region. Here, using cryptotephra analysis, we investigate the potential occurrence of two well-known tephra horizons from the Last Glacial Period (i.e. FMAZ II-1 (26.7 ka b2k) and NAAZ II (II-RHY-1) (55.3 ka b2k)), in five different marine sediment cores from the Denmark Strait, as well as the Nordic, Irminger and Labrador Seas. We have successfully identified FMAZ II-1 in both the Nordic and Irminger Seas. Even more so, this study presents the first identification of an isochronous FMAZ II-1 horizon detected in the Irminger Sea. This clearly demonstrates an increased potential for tephrochronology within this region. In addition, NAAZ II (II-RHY-1) was also recorded in the Denmark Strait, the Irminger Sea and the Labrador Sea. Using those identified tephra time-markers allows us to discuss the synchronization of paleoclimate records retrieved from the in this study and previously investigated marine sediment cores. We focus on both time periods when the tephra time-markers were deposited (i.e. Greenland Stadial-3 (FMAZ II-1) and Greenland Interstadial-15 (NAAZ II (II-RHY-1)) with the aim to provide synchronized records of ocean temperature and salinity changes. Therefore, we use Mg/Ca ratios of benthic foraminifera and stable isotopes (d¹⁸O & d¹³C) of benthic and planktonic foraminifera. By coupling the paleoclimatic information with the identified tephra time-markers, we provide a robust overview of the climatic conditions in the North Atlantic Ocean during these two time periods.

How to cite: Rutledal, S., Berben, S. M. P., Dokken, T. M., Tisserand, A. A., and Jansen, E.: Tephra-based time-markers from the Last Glacial Period recorded in the North Atlantic: an emerging tool for an east-west synchronization of paleoclimate records, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6707, https://doi.org/10.5194/egusphere-egu2020-6707, 2020

It has been shown that during Heinrich stadials northern deep water production ceased leading to an enhanced inflow of southern sourced water. Although Heinrich events are not considered to represent the primary trigger of Heinrich stadials the reorganisation of Atlantic ocean dynamics during their occurrences is an active field of research. In particular, Heinrich stadial 2 (HS2) is of high interest, based on the observation that the interplay with the climate system was very different during HS2 compared to HS1, although the magnitude of iceberg and freshwater discharge was similar (Hemming, 2004). During HS2 sea-level was still decreasing while the atmospheric CO­₂ content was relatively stable unlike the climatic evolution during Heinrich HS1.

The notion of a reduced Atlantic Meridional Overturning Circulation (AMOC) during Heinrich Stadials is mainly strengthened by the ²³¹Pa/²³⁰Th records from the Bermuda Rise. However, other influencing factors, capable of increasing the sedimentary ²³¹Pa/²³⁰Th without according decreases in AMOC strength, need to be considered as well. Besides biogenic opal, high dust fluxes may also result in enhanced scavenging rate of both radionuclides and consequently higher sedimentary ²³¹Pa/²³⁰Th signals, since another distinct feature that accompanies Heinrich Stadials is the high atmospheric concentration of dust in the northern hemisphere. Furthermore, high dust concentrations might be an indicator of a vigorous wind system and therefore strong ocean mixing, which can lead to the enhanced formation of nepheloid layers These layers are suspected to cause strong bottom scavenging and consequently high sedimentary ²³¹Pa/²³⁰Th. Very high dust fluxes were observed e.g. during HS2 and MIS4. Here, we compare ²³¹Pa/²³⁰Th with dust records in order to disentangle the effects of scavenging and circulation on the recorded sedimentary ²³¹Pa/²³⁰Th from the northwestern Atlantic.

How to cite: Lippold, J., Süfke, F., Grützner, J., and Pöppelmeier, F.: Disentangling the effects of particles and circulation on 231Pa/230Th during Heinrich Stadials, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8106, https://doi.org/10.5194/egusphere-egu2020-8106, 2020

The nature and expression of climate change in the Eastern Mediterranean, the Levant and further into Arabia is of considerable interest across a range of communities. This is in part due to the need to understand the potential for future climate forcing on environments given the complex range of climatic forcing factors that play out in the region. These include the role of prevailing winds across the Mediterranean, Northerly winds pushing down into the region during cold glacial conditions, and the influence of the Afro-Arabian Monsoon. The last glacial to interglacial period is a critical window to examine such processes, as a range of climatic signals are recorded, many of which have been proposed as correlatives of events seen in the North Atlantic. Dating issues are as ever an issue when trying to precisely compare different climate archives. To address such, the INTIMATE event stratigraphy has been developed for the North Atlantic region, with recent extensions into parts of the Mediterranean. This couples the stratigraphic framework of the Greenland Ice core records as a regional stratotype, with  a number of tephra horizons in the North Atlantic and Europe, aiding the process of correlation. The last INTIMATE event stratigraphy coupled the extended GICC05 timescale for Greenland back to 128 b2k (Blockley et al., 2014). This paper reports on attempts to test the potential for tephrochronology to be extended into the Levant and potentially Arabia, through the identification of tephra layers in sediment focussing archives, such as archaeological cave sequences. We have examined tephra presence in archaeological sites, principally in Israel, that record sediment deposition from ~30ka BP through to >100ka BP. Analyses of these records show that tephra is present in almost all of the studied sites (e.g., Kebara, Tabun, Amud, Shovakh). Moreover, tephra in these sequences can be chemically correlated to known volcanic systems, demonstrating the potential going forward to analyse long lake and marine records around the region for cryptotephra. At the same time clear challenges are emerging. Firstly, there is a range of chemistry in many of the layers and careful analyses is needed to pick apart the geochemical signal and to identify reworking, as opposed to chemically heterogeneous ash layers from a single volcano. This process is complicated by the relatively limited range of published geochemical data from some volcanic centres. This presentation will outline the current state of knowledge of key volcanic centres, particularly in the Aegean and Turkey, alongside the new Levantine data, to consider the steps needed to establish a secure extension of the INTIMATE approach into this region.

Blockley, S., et al., 2014. Quaternary Science Reviews. 106, 88-100. doi:10.1016/j.quascirev.2014.11.002.

How to cite: Blockley, S., White, D., Timms, R., Lincoln, P., Armitage, S., and Stringer, C.: Challenges and opportunities extending the INTIMATE tephra event stratigraphy into the Levant and Arabia., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9051, https://doi.org/10.5194/egusphere-egu2020-9051, 2020

The last glacial was an interval characterized by a sequence of abrupt millennial-scale events well documented mainly from the Greenland and Antarctica ice-cores. Although the triggers are not fully understood, most of the works agree that they occurred in consonance with oscillations in the strength of the Atlantic Meridional Overturning Circulation (AMOC). Paleoceanographic reconstructions have shown that cold millennial-scale stadials were accompanied by high temperatures in the subsurface to intermediate waters of the Atlantic Ocean that may have acted in both the basal melting of ice-sheets and in the rapid atmospheric warming during the onset of warm interstadials. Assuming that recent transient models indicated an accentuated response of the subsurface western South Atlantic to the millennial-scale disturbances, here we present a paleoceanographic reconstruction in this area based on the deep-dwelling planktic foraminifer Globorotalia inflata. Our high-resolution oxygen isotope (d¹⁸O) presents a sequence of millennial-scale variability that strongly resembles the structure of the Greenland Dansgaard-Oeschger cycles, mainly during Marine Isotope Stage (MIS) 5. On the other hand, during MIS 3, this millennial-scale feature is absent or weakly represented. Cross-spectral analyzes indicate a meaningful north-to-south forcing over the western South Atlantic subsurface during early-glacial. Mg/Ca-derived temperature and ice-volume free seawater d¹⁸O (d¹⁸O_IVF-SW) executed for the MIS 5 interval demonstrated that the subsurface western South Atlantic was warmer and saltier (colder and fresher) during early glacial stadial (interstadials). We hypothesized that a wide reorganization of the northward heat transport throughout the last glacial occurred, in which regions so far south as 24 ºS worked as prominent heat reservoirs in periods of weakened AMOC during MIS 5 but not necessarily during MIS 3. Our data suggest that future impacts over the AMOC along the Brazilian margin will likely be recognized in the subsurface layers of the western South Atlantic.

How to cite: Santos, T., Ballalai, J., Franco, D., Oliveira, R., Lessa, D., Venancio, I., Chiessi, C., Kuhnert, H., Johnstone, H., and Albuquerque, A. L.: Modes of response of the subsurface western South Atlantic to the last glacial Dansgaard-Oeschger cycles , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10124, https://doi.org/10.5194/egusphere-egu2020-10124, 2020

Pollen analysis is one of the methods that allow revealing ecological and climatic changes in the
past based on vegetation reconstruction. Spitsbergen (Svalbard) archipelago, as well as other
regions of the Arctic, is difficult for creation of regional models of vegetation and climate
development during the Holocene. This is primarily due to the limited distribution, low thickness
and relative young ages (usually this is the late Holocene) of organogenic deposits, which are
most suitable for palynological studies.
Nordenskiöld Land is located in the central part of the West Spitsbergen Island and different the
most favorable climatic conditions. The largest number of sites suitable for paleobotanical
researches is located here. The Coles valley has length about 12 km, well-developed profile and
situated on the north shore of Nordenskiöld Land. The field campaign with studying of
floodplain peat sediments from Coles River valley was carried out in August 2018. Two sites
(K18-15, K18-16) were studied on the remains of first terrace. Excavated deposits are
represented by leafy peat of varying degrees of decomposition with silt lenses. The laboratory
studies of sediments included radiocarbon dating, pollen and non-pollen palynomorph analyses.
They were carried out in Laboratory of St-Petersburg State University and Russian chemical-
analytical Lab on the Spitsbergen archipelago.
The pollen analysis of two sections from Coles River valley allowed us to reconstruct
paleovegetation changes. Samples from K18-15 site contain more mineral components and more
pollen and spores than samples from K18-16 site. This is probably due to the inflow of pollen
with water. The main components of spore-pollen spectra are Poaceae, Cyperaceae, Salix and
Betula sect. Nanae. The relationship between these taxa shows a different degree of moisture of
the study area under the dominance of the grass - sedge tundra. Thus, a significant influence on
the formation of spores and pollen spectra in the studied deposits is played by the dynamics of
the sedimentation.
Results of radiocarbon dating showed that studied deposits formed during mid and late
Holocene.
A generalization of all available palynological data on the Nordenskjöld land made it possible to
construct a scheme of dwarf birch (Betula sect. Nanae) distribution during the Middle and Late
Holocene. A comparison of received data with our previous data and published data from
Nordenskiöld Land shows the asynchronous of appear and distribution of shrubs on these area
from ~5000 to ~2500 yrs ago.

How to cite: Soloveva, D., Savelieva, L., and Verkulich, S.: Holocene vegetation and climate changes inferred from pollen record of Nordenskiöld Land (West Spitsbergen Island), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11910, https://doi.org/10.5194/egusphere-egu2020-11910, 2020

Geological archives record multiple reversals of Earth’s magnetic poles, yet the potential impacts of these events remain unknown. The lack of any obvious association between the last major inversion, the Laschamps Excursion ~41 thousand years ago (ka), and polar ice paleoclimate records has underpinned the view that geomagnetic reversals do not have major environmental consequences. We find this is not the case. Importantly, the weakened geomagnetic field causes rapid production of atmospheric radiocarbon, and the lack of accurate calibration records has complicated dating of environmental and archaeological events in other parts of the world. Here we exploit the first detailed record of radiocarbon levels across the Laschamps Excursion using New Zealand swamp kauri (Agathis australis) trees to precisely align Pacific Basin environmental changes with polar paleoclimate records (via ¹⁰Be). Comprehensive radiocarbon-dated and glacial sequences are consistent with global chemistry climate modelling, and show synchronous climate changes across the mid to low latitudes that are concentrated during the geomagnetic field minima (42.2-41.5 ka) in the transitional phase that precedes the Laschamps Excursion. Critically, the revised timing reveals associations with a wide range of extinction events and major changes in the global archaeological record, which we hereby term the Adams Event. The climatic, environmental, and evolutionary impacts of past magnetic reversals now form a critical issue for future investigation.

How to cite: Cooper, A. and Turney, C. and the Adams Event Team: The Adams Event, a geomagnetic-driven environmental crisis 42,000 years ago, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12314, https://doi.org/10.5194/egusphere-egu2020-12314, 2020

During the last glacial period, abrupt climate events known as Dansgaard-Oeschger (DO) and Heinrich events have been observed in various types of Northern Hemispheric (NH) paleoclimate archives. It has been speculated that volcanism may play a role in the abrupt climate variability of the last glacial period, for example as a trigger of abrupt changes. The investigation of a possible link between abrupt climate events and volcanic eruptions has been hampered by the lack of a global volcanic eruption record from the last glacial period. A recent identification of 80 major bipolar volcanic eruptions in Greenland and Antarctic ice core records within the interval 12-60 ka BP now enables us to investigate this link.

Using high-resolution ice-core records of climate (δ¹⁸O), atmospheric circulation changes (calcium) and volcanic eruptions (sulfate and other volcanic proxies) we investigate the timing of abrupt climate events and large volcanic eruptions at decadal resolution. We consider possible links between major volcanic eruptions and DO onsets (NH warming), DO terminations (NH cooling), and Heinrich stadials (strong NH cooling). Heinrich stadials are cold Greenland stadial periods during which Heinrich events occurred; large Hudson Strait iceberg discharge events that are characterized by deposition of significant amounts of ice rafted debris in North Atlantic marine sediments.

Significant links of volcanic and climatic events are tested in a statistical framework under the null hypothesis of random and memoryless volcanic activity. Our analysis shows that while certainly not all abrupt climate change of the last glacial period is associated with volcanism, we find that volcanism may have induced some abrupt Greenland warming events and perhaps several of the extreme North Atlantic cold Heinrich stadials; no significant link is found between volcanism and DO terminations. We speculate that volcanic cooling can drive such transitions when the coupled system of Atlantic Ocean circulation and North Atlantic sea ice is close to a tipping point.

How to cite: Svensson, A., Lohmann, J., Rasmussen, S. O., and Buizert, C.: The role of volcanism for abrupt climate change during the last glacial period, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12846, https://doi.org/10.5194/egusphere-egu2020-12846, 2020

Deep marine sediments may provide insights of past climate and oceanographic events. Knowledge of the past events can aid in scenario setting of future climate and their oceanographic consequences. A deep sea sediment core from the western side of Bohol Sea, a marginal sea located south of the Philippines, was used to reconstruct precipitation and identify the impacts of sea level rise on the circulation of Bohol Sea.  Five radiocarbon dates from bulk organic matter provide age control spanning back to the Last Glacial Maximum. Sedimentological (lithics and carbonate fractions; bulk density; sedimentation rate and mass accumulation rate) and geochemical (Ti, Al, Zr, Ti/Al and Y/Ni) data were used to reconstruct the sediment input for the area. Sediment input was decreasing from 20-15ka, followed by a relatively stable trend until ~9ka. After ~9ka sediment input increased up until the most recent years. Sedimentation trend follows the average winter (DJF) insolation curve at 10^oN. This signifies that the sediment input reflects the general changes in precipitation in the area. Lithics and carbonate contents reflect a shift in sediment source that could be attributed to the change in circulation in the basin as the sea level rose to overtop the Surigao Strait located at the northeastern side of the basin. Greater westward transport of suspended material from large rivers to the east would contribute to the sedimentation in the western part of Bohol Sea.

How to cite: Buen, S., Siringan, F., and Lloren, R.: Sediment record of precipitation and changes in circulation in Bohol Sea area since the Last Glacial Maximum, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13383, https://doi.org/10.5194/egusphere-egu2020-13383, 2020

The impact of global temperature changes on hydroclimate, especially on regional spatial scales, is difficult to predict with global climate models. These models are generally too coarse in resolution and do not fully constrain complex atmospheric processes. We can study past climatic changes to understand the evolution of hydroclimate and identify its mechanisms on regional scales. The Younger Dryas (YD) cold period ca. 12.000 years ago was the last major abrupt climate change in Earth history and as such provides us with a natural laboratory to better understand impacts of such change on both global and regional scales. Increasingly, high resolution datasets from terrestrial archives throughout Europe are being developed which suggest atmospheric controls on abrupt changes in local ecosystems, such as the southward movement of the jet stream during the YD period. Therefore, regions located at the boundary between major moisture sources are particularly interesting, such as NW Iberia, which is situated between Atlantic and Mediterranean moisture sources and their effects. Here we present terrestrial lipid biomarker (n-alkane) stable hydrogen (δ²H_wax) and carbon (δ¹³C_wax) isotope records from lake Laguna de la Roya (LR) (NW Iberia), covering the YD. In combination with pollen and chironomid reconstructed temperature data, we aim to identify the evolution of atmospheric conditions during the YD in NW Iberia. Since LR is located close to the Atlantic Ocean and the reconstructed maximum YD sea-ice extent, we are specifically interested in amplitude and variability of local hydroclimatic changes compared to more continental sites during the YD-Holocene transition. During the YD, La Roya δ²H_wax values were characterized by ~6‰ more negative values compared to the preceding Allerød, indicative of colder and drier conditions, which is supported by local temperature reconstruction and pollen analysis. More continental records from western Europe such as Lake Meerfelder Maar (MFM) showed ~12‰ more negative values during YD. This doubling in depletion of MFM samples compared to LR could be, in part, attributed to the stronger temperature drop in continental Europe of about 4-6°C. For the same time at LR, the chironomid data show a drop of only 2.5°C. In general, δ²H_wax from LR were more positive, on average, compared to MFM, by ~27‰ in the Allerød and ~33‰ during the YD. However, in the Holocene both records converge to an average difference of 15‰, which is close to the modern measured 10‰ difference in δ²H_precipition (source water for δ²H_wax) and consistent with a shared Atlantic moisture origin and subsequent Rayleigh rainout towards the East. Considering possible temperature related depletions in the LR δ²H_wax record during YD, the 27‰ difference in the Allerød implies additional influences on the recorded signal. A different moisture source area (Mediterranean) for LR during Allerød/YD period, and/or increased air mass transport distances from LR to MFM compared to Holocene conditions can explain the δ²H_wax differences. These findings suggest significant changes in the atmospheric circulation at the YD-Holocene transition when the jet stream shifted northward due to lower seasonal sea-ice expansions and intensification of the Atlantic Meridional Overturning Circulation.

How to cite: Rach, O., Heiri, O., Muñoz Sobrino, C., Vieth-Hillebrand, A., and Sachse, D.: Reconstruction of regional humidity variations during the Younger Dryas - Holocene transition in NW Iberia using lipid biomarker stable isotope ratios, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13928, https://doi.org/10.5194/egusphere-egu2020-13928, 2020

During the last deglaciation, the North Atlantic was punctuated by evident millennial-scale climate variability – surface cooling during Heinrich Event 1 (H1), followed by abrupt warming during the Bølling-Allerød (BA). Given its abundance of available proxy records, the last deglaciation is thus a perfect testbed for us to assess the triggering dynamics of these abrupt events. Here, a water-isotope enabled, coupled atmosphere-ocean general circulation model COSMOS-wiso (Werner et al., 2016) is applied to test different mechanisms potentially responsible for a BA abrupt warming. First, two sets of experiments are conducted to test the sensitivity to background boundary conditions: one is based on the Last Glacial Maximum (LGM), and the other was 16ka BP background climate. We also consider the spatial distribution of freshwater flux (FWF) forcing. We find that during the LGM a weak freshwater forcing cannot trigger an Atlantic Meridional Overturning Circulation (AMOC) mode transition. However, the same freshwater forcing can rapidly weaken the AMOC at 16ka BP, including an abrupt AMOC resumption in the subsequent one thousand years. Our experiments support the idea that ice volume plays a dominant role in the stability of AMOC during the termination. Furthermore, we explore the impact of different initial fields on the timing of AMOC recovery. Based on the above 16ka hosing experiment mimicking H1, several phases before the AMOC recovery are selected as initial fields, also with different FWF forcing. Our experiments indicate that the larger the FWF forcing, the longer it would take for the AMOC to recover. In all simulations, we detect an overshoot behavior typically for the BA transition. Finally, we implement a transient experiment from H1 to BA with changing GHGs and orbital forcing to explore the mechanisms of the sequence of rapid climate changes during the last termination.

Werner, M., Haese, B., Xu, X., Zhang, X., Butzin, M., and Lohmann, G.: Glacial–interglacial changes in H218O, HDO and deuterium excess – results from the fully coupled ECHAM5/MPI-OM Earth system model, Geosci. Model Dev., 9, 647-670, doi:10.5194/gmd-9-647-2016, 2016.

How to cite: Sun, Y., Zhang, X., Werner, M., Knorr, G., and Lohmann, G.: Sequence of Heinrich Event 1 to the Bølling-Allerød in transient climate model simulations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13933, https://doi.org/10.5194/egusphere-egu2020-13933, 2020

Rapid climatic reorganizations during the last Termination (i.e. Heinrich Stadials 0-1) had major impacts on the Atlantic Meridional Overturning Circulation (AMOC) strength and on global atmospheric circulation patterns. However, if and how this high-latitude forcing affected low-latitude climate variability is still poorly constrained. Here we present a high-resolution multi-proxy record from marine sediment core M125-3-35 recovered in the western tropical South Atlantic combining foraminiferal Mg/Ca, Ba/Ca ratios, stable oxygen isotope measurements and organic biomarker-based sea surface temperature (SST) proxies (TEX86 and UK’37). The near-shore core position of M125-3-35 off the Paraíba do Sul river mouth in southeastern Brazil and the means of foraminiferal Ba/Ca ratios, which depends on the quantity of continental freshwater input, enables us to investigate direct coupling of continental hydroclimate and oceanographic changes.

The data show a complex interplay of oceanic and atmospheric forcing dominating the tropical South American climate, which is mainly controlled by the strength and position of the Intertropical Convergence Zone (ITCZ) and South Atlantic Convergence Zone (SACZ). During times of weakest AMOC in Heinrich Stadial 1 (HS1) , a distinct SST peak in the tropical South Atlantic points to an enhanced Brazil Current and strong recirculation of heat within the southern hemisphere. Further, wet conditions prevailed during this time in tropical South America caused by a maximum southward shift of the ITCZ. This happened in coincidence with a temperature drop and weakening of the North Brazil Current (NBC) in the tropical North Atlantic (Bahr et al., 2018) as result of maximum AMOC slowdown. Therefore, for the first time, we reveal a clear seesaw-like pattern of the NBC and BC during times of abrupt AMOC variability.

While HS1 is generally characterized by a warm and wet anomaly in our record, Ba/Ca ratios and SST show a distinct centennial-scale alternation between warmer (colder) and wetter (drier) phases indicating a distinct climate instability during this climatic phase. A distinct offset exists between SST reconstructed using Mg/Ca, TEX86, and UK’37 which points to strong seasonal differences in the oceanographic settings and/or changes in the terrestrial input from the south American continent. These findings illustrate the strong sensitivity of hydroclimate variability in tropical South America to oceanic forcing as expected also during future climate change, in line with recent studies that showed a severe impact on modern South American climate by changes in (tropical) South Atlantic SSTs (Rodrigues et al., 2019, Utida et al., 2018).

Bahr, A., Hoffmann, J., Schönfeld, J., Schmidt, M. W., Nürnberg, D., Batenburg, S. J., & Voigt, S. (2018). Low-latitude expressions of high-latitude forcing during Heinrich Stadial 1 and the Younger Dryas in northern South America. Global and Planetary Change, 160, 1-9.

Rodrigues, R. R., Taschetto, A. S., Gupta, A. S., & Foltz, G. R. (2019). Common cause for severe droughts in South America and marine heatwaves in the South Atlantic. Nature Geoscience, 12(8), 620-626.

UTIDA, Giselle, et al. Tropical South Atlantic influence on Northeastern Brazil precipitation and ITCZ displacement during the past 2300 years. Scientific reports, 2019, 9. Jg., Nr. 1, S. 1698.

How to cite: Meier, K. J. F., Jaeschke, A., Hoffmann, J., Hennrich, B., Friedrich, O., Chiessi, C. M., Albuquerque, A. L. S., Rethemeyer, J., Nürnberg, D., and Bahr, A.: South American climatic response to changes in the tropical South Atlantic Ocean hydrography during Termination 1, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16361, https://doi.org/10.5194/egusphere-egu2020-16361, 2020

The lacustrine record of Lake Diss Mere, Norfolk (UK) is 15 m long, and shows 4.2 m of finely-laminated sediments, which are present between 9 and 13 m of core depth. The microfacies analysis identified three major seasonal patterns of deposition (microfacies 1 – 3), which corroborate the annual nature of sedimentation throughout the whole interval. The sediments are diatomaceous organic and carbonate varves with an average thickness of 0.45 mm. Microfacies 1 consists of a pale layer made of authigenic calcite crystals and diatom frustules, and a dark layer composed of a planktonic diatoms and filaments of organic matter. Microfacies 2 is similar to microfacies 1 but includes a mono-specific diatom bloom layer preceding the calcite layer. Microfacies 3 are varves with an occasional very thin calcite layer and mono-specific diatom blooms in spring and autumn.

A total of 8252 varves were counted with an error of up to  27 varves. To tie the resulting floating varve chronology to the IntCal 2013 radiocarbon timescale, we used a Bayesian Deposition model (P_Sequence with outlier detection) on all available chronological data. The data included seven radiocarbon dates, six tephra layers with known radiocarbon ages, and the relative varve counts between dated points. The resulting age uncertainties are decadal in scale (95% confidence) and allow detailed comparisons to other high-resolution Holocene varved lake and ice-core records on absolute timescales. The potential for this record as a palaeoclimate archive for the British Isles is enhanced by the Glen Garry¹(2172 ± 107 cal a BP) and OMH-185²(2667 ± 38 cal a BP) volcanic eruptions which lie amongst 3 further late-Holocene cryptotephra layers at ca 2400 cal a BP, 2540 cal a BP, and 3870 cal a BP, and a mid-Holocene cryptotephra layers at ca 6420 cal a BP. Initial investigations and geochemical characterisation suggest Icelandic eruption centres for these cryptotephra layers which are known to be present in sites in the British Isles and elsewhere in Europe.

¹ Barber, K., Langdon, P., Blundell, A. Dating the Glen Garry tephra: a widespread late-Holocene marker horizon in the peatlands of northern Britain. The Holocene, 18: 31-43. 2008.

² Plunkett, G.M., Pilcher, J.R., McCormac, F.G., Hall, V.A. New dates for first millennium BC tephra isochrones in Ireland. The Holocene, 14: 780-786. 2004

How to cite: Martin-Puertas, C., Walsh, A., Blockley, S. P. E., Biddulph, G. E., Palmer, A., Ramisch, A., and Brauer, A.: Holocene chronology and tephrostratigraphy for the varved record of Lake Diss Mere (UK), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18522, https://doi.org/10.5194/egusphere-egu2020-18522, 2020

Oxygen-isotope ratios can be measured on a range of materials (e.g. ostracods, bulk carbonates, diatom silica) and this, alongside their sensitivity to changes in temperature and precipitation has resulted in oxygen-isotope analyses becoming a well-established tool for investigating palaeoclimatic change. We use δ¹⁸O of calcite from ostracod shells to reconstruct palaeotemperature and palaeo-precipitation variability during an early Holocene abrupt climatic event in Crudale Meadow, SW Orkney Mainland, Scotland, UK. The research ultimately aims to further our understanding of the driving mechanisms of palaeoclimatic change during the early Holocene by producing a high-resolution palaeoclimate record from Crudale Meadow and comparing this to the existing data of NW Europe. 

Crudale Meadow is an ideal study site for this research. Spatially, it completes a transect of published early Holocene δ¹⁸O records that span Western Ireland¹, NW England² and into Scandinavia³. It has a ~3m thick early Holocene carbonate sequence which offers a multi-decadal or multi-centennial scale study resolution and its proximity to the N. Atlantic makes it highly likely to have been influenced by any climatic changes in the region. A previous study⁴ presented a bulk carbonate δ¹⁸O record for Crudale Meadow but the skeletal chronology limits its usefulness for comparing with regional trends. Here, we present an improved chronology using  tephra and pollen stratigraphy, in addition to the ostracod-derived δ¹⁸O record. The studied sequence is anchored by the previously identified Saksunarvatn visible tephra layer dated to 10,210 ± 70 cal. years BP⁵.

Ostracods are micro-crustaceans with low-Mg calcite shells which take on the isotopic signal of the water body they are in, at the time of shell calcification. In this study, we use winter calcifying Candona spp. for isotopic analysis. These were abundant and well preserved throughout the sequence. Members of this genus have a well-characterised vital offset⁶ so the δ¹⁸O curve can be reliably corrected for vital effects. Moreover, the species analysed are probable winter calcifers, thus reducing the impact of isotopic enrichment through lake water evaporation during summer months. The high-resolution study allows us to identify structure within the identified isotopic excursion and suggest palaeotemperature estimates from the ostracod- and chironomid-inferred temperatures.

The new data presents a clear climatic event with internal structure, which with the current chronology, we hypothesise to be the 9.3ka event. The 9.3ka event has fewer detailed records in comparison to other early Holocene abrupt climatic events (e.g. 8.2ka). Consequently, to identify a structured isotopic signal of the 9.3ka event in NW Europe is an important contribution to our early Holocene records. It emphasises the need for high-resolution δ¹⁸O studies during the early Holocene across NW Europe in order to be able to fully identify subtle abrupt climatic events. 

References: ¹Holmes, J.H. et al. (2016) QSR, p.341-349; ²Marshall, J.D. et al. (2007) Geology, 35, p.639–642; ³Hammarlund, D. et al. (2002) The Holocene, 12, p.339–351; ⁴Whittington, G. et al. (2015) QSR, 122, p.112–130; ⁵Timms, R.G.O. et al. (2018) Quat. Geochron. 46, p.28–44; ⁶Holmes, J.H & Chivas, A. (2002) AGU Geophysical Monograph, p.118-204.

How to cite: Tindall, J., Holmes, J., Candy, I., Leng, M., Timms, R., Francis, C., Petts, D., Blockley, S., Matthews, I., and Palmer, A.: A high-resolution ostracod-derived δ18O record of early Holocene abrupt climatic change from N. Scotland., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18990, https://doi.org/10.5194/egusphere-egu2020-18990, 2020

Despite a substantial body of evidence on millennial-scale climate variability during Marine Isotope Stage 3, uncertainty remains over the precise sequence of changes in different parts of the climate system, and ultimately their causes.  Here, we present results of joint marine and terrestrial proxy analyses from the Portuguese Margin, showing the typical succession of cold stadials and warm interstadials over the interval 35-57 ka, with most extreme changes occurring during Heinrich Stadials (HS).  The planktonic and benthic foraminiferal isotope records map onto Greenland and Antarctic temperature variations, respectively, while the pollen record bears a close similarity to changes in the Asian summer monsoon, atmospheric methane and dust concentrations, indicating coupled changes in hydroclimate in middle-to-low latitudes.  Closer inspection of HS4 and HS5 reveals considerable structure, with a relatively fast transition to maximum cooling and aridity associated with a peak in ice-rafted detritus, containing detrital carbonate grains originating from the Hudson Strait.  This was followed by an interval of slowly increasing sea-surface temperatures (SST) and moisture availability, in line with evidence indicating a gradual evolution in low-latitude hydroclimate.  A climate model experiment closely reproduces the gradual increase in SST and precipitation in W. Iberia during the final part of HS4 as a result of the recovery of the Atlantic overturning circulation, but does not capturethe abrupt warming in Greenland.  What emerges is a diversity of response timescales, from centuries in low-to-mid latitude SST and precipitation to decades in Greenland temperatures.

How to cite: Tzedakis, C., Margari, V., Skinner, L., Menviel, L., Capron, E., Rhodes, R., Vautravers, M., Ezat, M., Martrat, B., Grimalt, J., and Hodell, D.: Fast and slow components of millennial-scale climate changes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20608, https://doi.org/10.5194/egusphere-egu2020-20608, 2020