Daniel Veres

Rapid ecosystem response to abrupt climate changes during the last glacial period in western Europe, 40-16 ka

We present a high-resolution and independently dated multiproxy lake sediment record from the paleolake at Les Echets in southeastern France that displays synchronous changes in independent limnic and terrestrial ecosystem proxies, in concert with millennial-scale climate oscillations during the last glacial period. Distinct lake-level fluctuations, low lake organic productivity, and open, treeless vegetation indicate cold and dry conditions in response to Heinrich events. Alternating phases of higher and low lake organic productivity, stratified surface waters and long-lasting lake ice cover, decreased or increased catchment erosion, and tree-dominated or herb-dominated vegetation resemble Dansgaard-Oeschger interstadialstadial variability. Transitions between different ecological states occurred in as little as 40–230 yr and seem to have been controlled by the position of the Polar Front. Ecosystem response after 30 ka suggests that local climate conditions became more important. Our results demonstrate that all parts of the terrestrial system responded to the abrupt and dramatic climatic changes associated with Dansgaard-Oeschger and Heinrich events, and that regional factors modulated ecosystem response.

The Campanian Ignimbrite eruption: new data on volcanic ash dispersal and its potential impact on human evolution.

The Campanian Ignimbrite (CI) volcanic eruption was the most explosive in Europe in the last 200,000 years. The event coincided with the onset of an extremely cold climatic phase known as Heinrich Event 4 (HE4) approximately 40,000 years ago. Their combined effect may have exacerbated the severity of the climate through positive feedbacks across Europe and possibly globally. The CI event is of particular interest not only to investigate the role of volcanism on climate forcing and palaeoenvironments, but also because its timing coincides with the arrival into Europe of anatomically modern humans, the demise of Neanderthals, and an associated major shift in lithic technology. At this stage, however, the degree of interaction between these factors is poorly known, based on fragmentary and widely dispersed data points. In this study we provide important new data from Eastern Europe which indicate that the magnitude of the CI eruption and impact of associated distal ash (tephra) deposits may have been substantially greater than existing models suggest. The scale of the eruption is modelled by tephra distribution and thickness, supported by local data points. CI ashfall extends as far as the Russian Plain, Eastern Mediterranean and northern Africa. However, modelling input is limited by very few data points in Eastern Europe. Here we investigate an unexpectedly thick CI tephra deposit in the southeast Romanian loess steppe, positively identified using geochemical and geochronological analyses. We establish the tephra as a widespread primary deposit, which blanketed the topography both thickly and rapidly, with potentially catastrophic impacts on local ecosystems. Our discovery not only highlights the need to reassess models for the magnitude of the eruption and its role in climatic transition, but also suggests that it may have substantially influenced hominin population and subsistence dynamics in a region strategic for human migration into Europe.

Tracing the influence of Mediterranean climate on Southeastern Europe during the past 350,000 years

Loess-palaeosol sequences are valuable archives of past environmental changes. Although regional palaeoclimatic trends and conditions in Southeastern Europe have been inferred from loess sequences, large scale forcing mechanisms responsible for their formation have yet to be determined. Southeastern Europe is a climatically sensitive region, existing under the strong influence of both Mediterranean and continental climates. Establishment of the spatial and temporal evolution and interaction of these climatic areas is essential to understand the mechanisms of loess formation. Here we present high-resolution grain-size, environmental magnetic, spectrophotometric and geochemical data from the Stalać section in the Central Balkans (Serbia) for the past ~350,000 years. The goal of this study is to determine the influence of the Mediterranean climate during this period. Data show that the Central Balkans were under different atmospheric circulation regimes, especially during Marine Isotope Stages 9 and 7, while continental climate prevailed further north. We observe a general weakening of the Mediterranean climate influence with time. Our data suggest that Marine Isotope Stage 5 was the first interglacial in the Central Balkans that had continental climate characteristics. This prominent shift in climatic conditions resulted in unexpectedly warm and humid conditions during the last glacial.

Shift of large-scale atmospheric systems over Europe during late MIS 3 and implications for Modern Human dispersal

Understanding the past dynamics of large-scale atmospheric systems is crucial for our knowledge of the palaeoclimate conditions in Europe. Southeastern Europe currently lies at the border between Atlantic, Mediterranean, and continental climate zones. Past changes in the relative influence of associated atmospheric systems must have been recorded in the region’s palaeoarchives. By comparing high-resolution grain-size, environmental magnetic and geochemical data from two loess-palaeosol sequences in the Lower Danube Basin with other Eurasian palaeorecords, we reconstructed past climatic patterns over Southeastern Europe and the related interaction of the prevailing large-scale circulation modes over Europe, especially during late Marine Isotope Stage 3 (40,000–27,000 years ago). We demonstrate that during this time interval, the intensification of the Siberian High had a crucial influence on European climate causing the more continental conditions over major parts of Europe, and a southwards shift of the Westerlies. Such a climatic and environmental change, combined with the Campanian Ignimbrite/Y-5 volcanic eruption, may have driven the Anatomically Modern Human dispersal towards Central and Western Europe, pointing to a corridor over the Eastern European Plain as an important pathway in their dispersal.

Multi-method luminescence investigations on quartz grains of different sizes extracted from a loess section in Southeast Romania interbedding the Campanian Ignimbrite ash layer

In this study we present luminescence investigations of four samples of loess bracketing the Campanian Ignimbrite/Y5 tephra at the Rasova-Valea cu Pietre site, on the eastern bank of the Danube River, southeastern Romania. Investigations involved SAR-OSL dating on aliquots of fine (4–11 μm) and medium-grained (63–90 μm) quartz, as well as single grain analyses on 125–180 μm quartz. Luminescence dating results coupled with glass-shard chemical fingerprinting assign the depositional age and origin of the ash layer to that of the Campanian Ignimbrite/Y5 tephra, dated elsewhere using 40Ar/39Ar to 39.28 ± 0.11 ka. Fine-grained (4–11 μm) quartz SAR-OSL analyses yielded ages of 44.4 ± 4.5 ka below the ash, and 41.4 ± 4.2 ka above the ash layer. Single grain analysis on coarse-grained quartz, however, demonstrates that coarse material from these samples exhibits low sensitivity and responds poorly to internal checks of the SAR protocol in comparison with the finer sediment. This observation highlights the need for more extensive investigations into the luminescence properties of quartz as well as into the origin of quartz contributions from different primary sources in the Lower Danube loess steppe.

Mineralogy of the Dehner and Jungferweiher maar tephras (Eifel, Germany).

This study reports on the mineral assemblages of two long cores from the Eifel volcanic field covering the Upper Pleistocene and the Holocene. Pyroxene is the most abundant mineral followed by olivine, but amphibole, leucite and sphene as well as other minerals are also randomly present in different amounts. The mineral assemblage titanoaugite (mg# about 90) ± olivine is typical of the foidite and olivine-nephelinite and basanite suite while the assemblage titanaugite (mg# lower than 90) ± olivine ± amphibole ± leucite ± sphene could be representative of the less common tephrite and phonolites suites. The presence of aegirine-augitic and enstatitic pyroxene in two samples suggests the presence of tephras with further different signature. These observations might be very important in better correlating and chronologically define the Eifel volcanic episodes which occurred during the Late Quaternary. Moreover, it seems possible to correlate the JW30 layer at about 90ka to the Rocourt Tephra.

The lithostratigraphy of the Les Echets basin, France: tentative correlation between cores

Two new long sediment cores (EC1 and EC3), recovered from different locations within the infilled basin at Les Echets, France, provide a new high-resolution record of terrestrial and lacustrine responses to climatic changes during Marine Isotope Stages (MIS) 3 and 2. The lithologies of the cores are described in detail and correlated with each other by stratigraphic marker horizons, fluctuations in organic matter and AMS radiocarbon ages. The tentative correlation of the new cores to those described and analysed by de Beaulieu et al. (1980) and de Beaulieu & Reille (1984a) provides a preliminary chronostratigraphic framework. Sedimentation during MIS3 started with accumulation of sands and silts and was followed by alternating gyttja and clayey gyttja silts. Exceptionally high sedimentation rates during MIS2 led to the infilling of the basin. Alternating organic-rich and minerogenicrich sediments appear to coincide with changes in pollen assemblages (de Beaulieu & Reille 1984a) and suggest that millennial-scale climatic changes controlled lake productivity and catchment stability during most of MIS3.

Atmospheric flux, transport and mass balance of 210Pb and 137Cs radiotracers in different regions of Romania

This study focuses on the determination of (210)Pb and (137)Cs fluxes from different areas in Transylvania, Romania and on the determination of transport and mass balance within the lacustrine system of Red Lake. In order to achieve this, samples were taken from six different locations (Bihor County area, Ighiel area, Red Lake area, Mluha Peatbog, Mohos Peatbog and Zanoaga Rosie Peat bog in the Semenic Mountains) throughout Romania, these being compared to the values of the Danube Delta area. The activity concentrations of the soil samples were measured by gamma spectrometry (HPGe detector) for both (210)Pbtotal, (210)Pbsup ((226)Ra) and (137)Cs, while peat samples were measured by both alpha ((210)Po) spectrometry (PIPS detectors) as well. The mean value for the (210)Pb flux was measured in the Danube Delta region (42±8Bqm(-2) yr(-1)), while the highest was measured in the Semenic Peatbog (227±54Bqm(-2) yr(-1)); the average being 132±8Bqm(-2) yr(-1). In case of (137)Cs the mean was 298±3Bqm(-2) yr(-1), maximum being 1683±15Bqm(-2) yr(-1) in case of Ighiel area and minimum being 32±1Bqm(-2) yr(-1) in the Danube Delta region. In case of the Red Lake, from the total inventory of 410±23Bqm(-2) yr(-1) in the sediments, the loss by outflows is 100±12Bqm(-2) yr(-1), the catchment to lake transfer factor being 0.84%.

Persani Mountains: Karst of Vârghis Gorge

Vârghiș karst, with its limited spatial development but well-preserved features, is a peculiarity in the karst inventory of Romania. It shows several well-marked karstification levels, and a relatively high number of caves, the majority harboring thick clastic deposits. However, its most important asset is that it hosts numerous traces of past human occupation. For example, recent investigations of rock shelter Abri 122 produced one of the most significant Middle Paleolithic lithic assemblages for Romania, covering the time interval from Marine Isotope Stage (MIS) 5/7 to MIS 3. The occurrence of a volcanic ash layer within Bear’s (Ursului) Cave originating from the Ciomadul volcanic complex (East Carpathians) and dated to ~43/50 ka highlights the potential of Vârghiș karst in preserving such isochronous marker horizons, calling for further research.

Quantitative assessment of Pb sources in isotopic mixtures using a Bayesian mixing model

Lead (Pb) isotopes provide valuable insights into the origin of Pb within a sample, typically allowing for reliable fingerprinting of their source. This is useful for a variety of applications, from tracing sources of pollution-related Pb, to the origins of Pb in archaeological artefacts. However, current approaches investigate source proportions via graphical means, or simple mixing models. As such, an approach, which quantitatively assesses source proportions and fingerprints the signature of analysed Pb, especially for larger numbers of sources, would be valuable. Here we use an advanced Bayesian isotope mixing model for three such applications: tracing dust sources in pre-anthropogenic environmental samples, tracking changing ore exploitation during the Roman period, and identifying the source of Pb in a Roman-age mining artefact. These examples indicate this approach can understand changing Pb sources deposited during both pre-anthropogenic times, when natural cycling of Pb dominated, and the Roman period, one marked by significant anthropogenic pollution. Our archaeometric investigation indicates clear input of Pb from Romanian ores previously speculated, but not proven, to have been the Pb source. Our approach can be applied to a range of disciplines, providing a new method for robustly tracing sources of Pb observed within a variety of environments.