Wagner, Bernd

Accurately reconstructing the scale and timing of dynamic processes, such as Middle-Late Pleistocene explosive volcanism and rapid climatic changes, requires rigorous and independent chronological constraints. In this framework, the study of distal volcanic ash layers, or tephra, transported and deposited over wide regions during explosive volcanic eruptions, is increasingly being recognised as a fundamental chronostratigraphic tool for addressing these challenging issues. Here we present a high-resolution distal tephra record preserved in the lacustrine sedimentary succession of the Fucino Basin, central Italy. The investigated record spans the 430-365 ka time interval, covering the entirety of Marine Isotope Stage 11 (MIS 11), and provides important insights into peri-Tyrrhenian potassic explosive volcanism from sources located in central Italy against a backdrop of Mediterranean palaeooclimate records. The succession of ash fall events of this time interval is reconstructed through a detailed lithostratigraphic, geochemical and 40Ar/39Ar geochronological characterization of the deposits preserved as discrete layers in the Fucino F4-F5 sediment core. This work is complemented by similarly detailed characterization of selected proximal pyroclastic units from the peri-Tyrrhenian potassic volcanoes. Geochemical fingerprinting of the tephra deposits by means of their major, minor and trace elements and Sr isotope composition indicates that all the thirty-two investigated ash layers derived from the peri-Tyrrhenian potassic volcanoes. The stratigraphically continuous succession of the Fucino tephra layers allowed the development of a fully independent, 40Ar/39Ar age-constrained, Bayesian age-depth model for the investigated time interval. The age-model allows us to establish modelled ages for the tephra layers within the succession that are not directly dated. The resulting dated tephra record clearly reveals a highly time resolved and previously unparalelled chronicle of explosive activity from the Vulsini, Vico, Sabatini, Colli Albani and Roccamonfina volcanic complexes. Our study provides a benchmark and valuable geochemical and geochronological dataset to be used as a reference for any future development and application of the tephrostratigraphic methods across the central Mediterranean area both during the investigated 430-365 ka time interval, and deeper in time. This contribution underlines the importance of integrating proximal and distal sedimentary records to more accurately establish long-term and comprehensive volcanic eruption records.

State‐of‐the‐art paleoclimate research strongly depends on the availability of time‐equivalent markers as chronological control to disentangle interrelationships in the climate system from regional to global scale. Geomagnetic reversals are regarded as excellent age constraints because they are global events and independent from climatic conditions. However, spatial variations of timing and internal dynamics of reversals may limit their precision. Our 1.2 Ma high‐resolution (~25 cm/kyr) sediment record from Lake Ohrid is promising to precisely depict the Matuyama‐Brunhes (MB) reversal and the Jaramillo subchron. Two generations of diagenetic ferrimagnetic minerals are present in glacial intervals of the Lake Ohrid record. Early diagenetic greigite acquired a quasi synsedimentary chemical magnetization, while a late diagenetic greigite formation, triggered by the upward diffusion of H2S‐rich waters, obscures the polarity record at the top of the Jaramillo. Interglacial intervals are unaffected by greigite formation, likely due to low iron concentrations. Based on an orbitally tuned age model with tephrostratigraphic markers, the base of Jaramillo can be precisely dated to 1072.4 ka, and the MB reversal to 778.5 ka. Both polarity reversals occurred very rapidly in our record, lasting 2.3 and 1 kyr, respectively. Our results reveal that the dipole component of the Earth's magnetic field fell below the nondipole components only for a short duration in the Mediterranean region. The comparison of the timing of the MB boundary across different archives implies that the onset of the reversal provides a more synchronous age marker compared to often used midpoint ages.

Here we present the first tephrostratigraphic, palaeomagnetic, and multiproxy data from a new ~98 m deep sediment core retrieved from the Fucino Basin, central Italy, spanning the last ~430 kyr. Palaeoenvironmental proxy data (Ca-XRF, gamma ray and magnetic susceptibility) show a cyclical variability related to interglacial-glacial cycles since the Marine Isotope Stage (MIS) 12-MIS 11 transition. More than 130 tephra layers are visible to the naked eye, 11 of which were analysed (glass-WDS) and successfully correlated to known eruptions and/or other equivalent tephra. In addition to tephra already recognised in the previously investigated cores spanning the last 190 kyr, we identified for the first time tephra from the eruptions of: Tufo Giallo di Sacrofano, Sabatini (288.0 ± 2.0 ka); Villa Senni, Colli Albani (367.5 ± 1.6 ka); Pozzolane Nere and its precursor, Colli Albani (405.0 ± 2.0 ka, and 407.1 ± 4.2 ka, respectively) and Castel Broco, Vulsini (419e490 ka). The latter occurs at the bottom of the core and has been 40Ar/39Ar dated at 424.3 ± 3.2 ka, thus providing a robust chronological constrain for both the eruption itself and the base of the investigated succession. Direct 40Ar/39Ar dating and tephra geochemical fingerprinting provide a preliminary radioisotopic-based chronological framework for the MIS 11-MIS 7 interval, which represent a foundation for the forthcoming multiproxy studies and for investigating the remaining ~110 tephra layers that are recorded within this interval. Such future developments will contribute towards an improved MIS 11-MIS 7 Mediterranean tephrostratigraphy, which is still poorly explored and exploited.

Mediterranean climates are characterized by strong seasonal contrasts between dry summers and wet winters. Changes in winter rainfall are critical for regional socioeconomic development, but are difficult to simulate accurately1 and reconstruct on Quaternary timescales. This is partly because regional hydroclimate records that cover multiple glacial-interglacial cycles2,3 with different orbital geometries, global ice volume and atmospheric greenhouse gas concentrations are scarce. Moreover, the underlying mechanisms of change and their persistence remain unexplored. Here we show that, over the past 1.36 million years, wet winters in the northcentral Mediterranean tend to occur with high contrasts in local, seasonal insolation and a vigorous African summer monsoon. Our proxy time series from Lake Ohrid on the Balkan Peninsula, together with a 784,000-year transient climate model hindcast, suggest that increased sea surface temperatures amplify local cyclone development and refuel North Atlantic low-pressure systems that enter the Mediterranean during phases of low continental ice volume and high concentrations of atmospheric greenhouse gases. A comparison with modern reanalysis data shows that current drivers of the amount of rainfall in the Mediterranean share some similarities to those that drive the reconstructed increases in precipitation. Our data cover multiple insolation maxima and are therefore an important benchmark for testing climate model performance.

We provide a geomorphological analysis of a glacial valley on Mount Pelister, in Macedonia. Three boulders from a frontal moraine were dated with the cosmogenic nuclide isotope 10Be. The results demonstrate that the boulders have been exposed since 15.24 ± 0.85 ka. This age constrains the formation of the frontal moraine to the Oldest Dryas cold event. This age fits with that of other glacier deposits dated to the Older Dryas in the Alps, Balkans, Carpathians and Turkish mountains. The Pelister palaeoglacier has been reconstructed and its equilibrium line altitude extracted, returning a value of 2250 ma.s.l. This is in good agreement with the equilibrium line altitudes of most other reconstructed glaciers of the same age in the circum- Mediterranean mountains, demonstrating a comparable response to the Oldest Dryas event. Other palaeoenvironmental records near the Pelister mountain indicate that the Older Dryas was here characterized by a cold and remarkably dry event. The temporal relationship between Older Dryas glacier advances in the Balkan region and recorded changes in the Atlantic thermohaline circulation during the Laurentide Ice Sheet massive ice discharge (H1 event) confirms the strong climatic link between the pan-Mediterranean regions and the North Atlantic Ocean.

The period corresponding to Marine Isotope Stages 9 (MIS 9) offers the opportunity to study orbital and sub-orbital scale climate variability under boundary conditions different from those of better studied intervals such as the Holocene and the Last Interglacial. Yet, it is poorly represented in independently-dated continental archives around the Mediterranean Region. Here, we present a speleothem stable isotope record (δ18O and δ13C) from the Former Yugoslavian Republic of Macedonia (F.Y.R.O.M., southern Balkans), which consists of two periods of growth broadly covering the ca. 332 to 292 ka and the ca. 264 to 248 ka intervals (MIS 9e-b and late MIS 8). We interpret the speleothem δ18O as mostly related to regional hydrology, with variations that can be interpreted as due to changes in rainfall amount, with higher/lower values associated to drier/wetter condition. This interpretation is corroborated by a change in mineralogical composition between aragonite and calcite at ca. 328 ka, which marks increasing precipitation at the onset of MIS 9 and occurs within a trend of decreasing δ18O values. Also the comparison with the multiproxy climate record available from the nearby Lake Ohrid seems to support the proposed interpretation. The MIS 9e interglacial appears to be characterized by wettest conditions between ca. 326 and 321 ka, i.e. lasting ca. 5 kyr. Decreasing precipitation and enhanced millennial scale variability matches the glacial inception (MIS9 d to b), with drier events at ca. 319 ka (ca. 2 kyr long) and 310 ka (ca. 1 kyr long), and a major rainfall reduction between 306 and 298 ka. The latter is followed by a prominent wetter period between 298 and 295 ka, for which carbon data values suggest high infiltration rate. Rainfall decreases again after 295 ka, and remain low until the growth interruption at ca. 292 ka. Resumption of the growth and progressive soil development, expressed by the carbon isotope record, occurred during the late part of MIS 8. Despite the rather high temporal uncertainty (average 6 ka), the speleothem hydrological record complements the environmental information provided by the Lake Ohrid record and also fits well to the framework of regional and extra-regional variability, showing similarities with pollen records from southern and western Europe, both at orbital and at sub-orbital time

In the DEEP core from the Lake Ohrid ICDP drilling project, the carbon isotope composition of bulk organic matter (δ13CTOC) over the last 516 ka shows a negative correlation with total organic carbon (TOC) and total inorganic carbon (TIC). This relationship is marked by periods of lower δ13CTOC values corresponding to higher TIC and TOC. Along with TOC/TN, the correlation between δ13CTOC and δ13CTIC suggests that most of the organic matter in the core is from aquatic primary production within the lake. The combination of TOC, TIC, and δ13CTOC is able to disentangle long-term glacial/interglacial cycles and, to a lesser extent, millennial scale climate variability. Over the longer term, δ13CTOC shows modest variability, indicating that the δ13C of the dissolved inorganic carbon (DIC) pool is stabilised by the supply of karst spring water characterised by δ13CDIC influenced by the bedrock δ13C value, and the long residence time of the lake water and well mixed upper water column promoting equilibration with atmospheric CO2. However, comparison between arboreal pollen (AP%), TIC and TOC data indicates that the δ13CTOC signal is modulated by the leaching of soil CO2 through runoff and spring discharge, changes in primary productivity, and recycling of organic matter within the lake, all affecting δ13CDIC. Exceptionally low δ13CTOC during some interglacial periods (e.g. MIS7 and MIS9) possibly indicate rapid intensification of organic matter recycling and/or increasing stratification and enhanced methanogenesis, even if the latter process is not supported by the sedimentological data.

This study presents the first cosmogenic 36Cl surface exposure data from a moraine in the Former Yugoslav Republic of Macedonia (FYROM). Five limestone boulders from an end moraine in the Galicica Mountains (40.94°N, 20.83°E, 2050 m a.s.l.) were used for cosmogenic 36Cl surface exposure dating. The 36Cl concentrations from the five boulders are identical within their measurement uncertainties ruling out major effects of inheritance, erosion, or snow cover. The calculated ages are very consistent ranging from 11.3 ± 1.3 to 12.8 ± 1.4 ka (mean 12 ± 0.6 ka) after applying a Ca-spallation production rate of 56 at g−1 a−1 (LSD scaling) and correction for 5 mm ka−1 carbonate weathering and 2% snow shielding. The applied corrections for weathering and snow shielding cause a shift to older ages in the order of magnitude of ca. 5% on average, making the production rate the main impact on exposure ages. The ages point to a moraine formation during the Younger Dryas period, consistent with the timing of the last deglaciation in the Galicica Mountains derived from previous geomorphological studies in the area. The formation of a glacier was likely favoured by several topoclimatic factors, accounting for additional snow input. This interpretation is in line with regional studies on glaciation chronologies from Šara Range (FYROM/Republic of Kosovo), Retezat Mountains (Romania), Mt. Chelmos (Greece), Mount Orjen (Montenegro) and Durmitor (Montenegro). Lake sediment analyses of Prespa (Republic of Albania/FYROM/Greece), Maliq (Republic of Albania) and Dojran lakes (FYROM/Greece) indicate that cold conditions promoted the formation of a local cirque glacier. However, studies of sediment records of the adjacent lakes Ohrid (Republic of Albania/FYROM) and Prespa do not indicate the presence of a proximal glaciation. An explanation might be a combination of the small size of the cirque glacier, generating only small amounts of debris, and the karstic bedrock, which hampers fluvial transport and acts by its aquifer system as a natural sediment trap, as the fluvial transport of the sediments to the lakes is absorbed by the karst system.

This study reviews and synthesises existing information generated within the SCOPSCO (Scientific Collaboration on Past Speciation Conditions in Lake Ohrid) deep drilling project. The four main aims of the project are to infer (i) the age and origin of Lake Ohrid (Former Yugoslav Republic of Macedonia/Republic of Albania), (ii) its regional seismotectonic history, (iii) volcanic activity and climate change in the central northern Mediterranean region, and (iv) the influence of major geological events on the evolution of its endemic species. The Ohrid basin formed by transtension during the Miocene, opened during the Pliocene and Pleistocene, and the lake established de novo in the still relatively narrow valley between 1.9 and 1.3 Ma. The lake history is recorded in a 584m long sediment sequence, which was recovered within the framework of the International Continental Scientific Drilling Program (ICDP) from the central part (DEEP site) of the lake in spring 2013. To date, 54 tephra and cryptotephra horizons have been found in the upper 460m of this sequence. Tephrochronology and tuning biogeochemical proxy data to orbital parameters revealed that the upper 247.8m represent the last 637 kyr. The multi-proxy data set covering these 637 kyr indicates longterm variability. Some proxies show a change from generally cooler and wetter to drier and warmer glacial and interglacial periods around 300 ka. Short-term environmental change caused, for example, by tephra deposition or the climatic impact of millennial-scale Dansgaard–Oeschger and Heinrich events are superimposed on the long-term trends. Evolutionary studies on the extant fauna indicate that Lake Ohrid was not a refugial area for regional freshwater animals. This differs from the surrounding catchment, where the mountainous setting with relatively high water availability provided a refuge for temperate and montane trees during the relatively cold and dry glacial periods. Although Lake Ohrid experienced significant environmental change over the last 637 kyr, preliminary molecular data from extant microgastropod species do not indicate significant changes in diversification rate during this period. The reasons for this constant rate remain largely unknown, but a possible lack of environmentally induced extinction events in Lake Ohrid and/or the high resilience of the ecosystems may have played a role.

We present the first integrated tephrochronological study (major and trace elemental glass composition, Sr and Nd isotope analyses, and 40Ar/39Ar dating) for the last one tenth (∼82 m) of the ∼900 m-thick Quaternary lacustrine succession of the Fucino Basin, the largest and probably only Central Apennine intermountain tectonic depression that hosts a continuous lacustrine succession documenting the Plio-Quaternary sedimentary history up to historical times. Major element glass compositions, determined using a wavelength-dispersive electron microprobe (WDS-EMPA), yielded the geochemical fingerprinting needed for a reliable identification of most of the 23 stratigraphically ordered tephra layers under investigation. These include tephra from Italian volcanoes such as Campi Flegrei, Etna, Colli Albani, Ischia, Vico, Sabatini, and undefined volcanic sources in the Neapolitan area and Latium region. The recognition of key Mediterranean marker tephra layers (e.g. X-5 and X-6) is supported by trace element data acquired by Laser Ablation Inductively Couple Plasma Mass Spectrometry (LA-ICP-MS). The Sr and Nd isotope compositions of selected layers where also determined for circumscribing the volcanic source of distal tephra and for supporting correlations with individual eruptive units. We also propose a new, more expeditious covariation diagram (CaO/FeOtot vs Cl) for identifying the volcanic source of trachytic to phonolitic and tephrytic to phonolitic tephra, that are the most common compositions of pyroclastic rocks from volcanoes of Campania and Latium regions. Finally, we present five new 40Ar/39Ar age determinations, including a new, analytically well-supported, and more precise 40Ar/39Ar age for the widespread Y-7 tephra, and the first 40Ar/39Ar age determinations for one tephra from the Sabatini volcanic district (∼126 ka) and one tephra from Neapolitan volcanic area (Campi Flegrei?; ∼159 ka). These newly dated tephra are widely dispersed (e.g. Monticchio, southern Italy, Adriatic Sea and Lake Ohrid, Macedonia-Abania) and have thus the potential to become important Mediterranean MIS 5 and MIS 6 tephrochronological markers. Altogether the new geochemical data and 40Ar/39Ar ages precisely constrain the chronology of the investigated Fucino succession spanning the last ∼190 ka. In light of these results and by considering that this sedimentary succession possibly extends back to ∼2 Ma, Fucino is likely to provide a very long, continuous tephrostratigraphic record for the Mediterranean area and become a key node in the dense network of tephra correlations of this region.