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.

Funding: This work was funded by the Max Planck Society through the project “Lower Danube Survey for Palaeolithic Sites”. D. Veres acknowledges the support of CNCS-UEFISCDI through grant PN-II-RU-TE-2011-3-0062, contract no. 73/05.10.2011. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Introduction

The Phlegrean Fields super-eruption and caldera collapse that produced the Campanian Ignimbrite (CI)/Y-5 tephra, which took place 39.28±0.11 ka [1], was one of the most explosive eruptions affecting Europe in the late Pleistocene [2], in terms of both eruption magnitude and volume of volcanic ejecta. The distal ashfall of CI tephra was widely distributed from its source vent near Naples in southern Italy [3], [4], eastward over the Balkans [5] and Black Sea [6] to the Russian plain more than 2200 km distant [7]–[9], and over 1000 km southward to the north African coast [10]–[12]. The CI tephra thereby provides a powerful chronostratigraphic marker horizon for palaeoclimatic and archaeological records during Marine Isotope Stage (MIS) 3. Moreover, the timing of this eruption coincides with the onset of the cold, dry climatic phase Heinrich Event 4 (HE4) [13], [14]. It has been proposed that the conjunction of these two events may have triggered a positive feedback cycle affecting global, and particularly European, climates for hundreds or even thousands of years [11], [15]. Significantly, the timing of the eruption, and of the extreme environmental conditions during HE4, also coincides with significant changes in the archaeological record in Europe; specifically, the arrival of anatomically modern humans (AMHs) [16]–[18], a substantial shift in hominin lithic technology [18]–[20], and the disappearance of Neanderthals from the continent [21], [22]. However, the role of the CI super-eruption in the interaction between sudden climatic change, the demise of the Neanderthals, and their replacement by AMHs, remains a matter of hypothesis [10], [15], [23].

The CI super-eruption took place in the Phlegrean fields of southern Italy [2], and has been dated based on a composite 40Ar/39Ar age of 39.28±0.11 ka obtained from proximal ignimbritic deposits [1]. The volcanic cataclysm involved a two-step eruption, consisting of an initial phase with a volcanic column at least 40 km high, followed by collapse and creation of the caldera, a rejuvenated volcanic column, and widespread ignimbritic deposition extending at least 1500 km2 from the eruption point [9], [24] with sufficient force to ascend the surrounding topography to over 1000 m altitude [25]. A peak in sulphate concentration within the GISP2 Greenland ice core, only slightly lower than the Icelandic Z2 ash or Toba eruptions, was correlated with the CI eruption [26]. However, subsequent investigations failed to identify tephra shards at the same depth within the core or a comparable peak within other Greenland ice core records, urging caution when such correlations are proposed based on only geochemical proxies [27], [28].

Interaction of the volcanic column with high altitude wind currents transported finer-grained volcanic particles (<250 µm) northeastward and southward, as far as the Russian Plain, eastern Mediterranean, Black Sea and north Africa (Figure 1a) [3], [6], [12]. Recent modeling of tephra transport [12], based on measured tephra thickness from several sites in the Balkans, Russian Plain and from eastern Mediterranean sea cores, suggested that the magnitude of the eruption was more than twice that of previous estimates. The modeling study also predicted the thickness of ash cover for regions beneath the ash plume for which data previously did not exist. Depending on the model parameters, the thickness of tephra deposited across the Balkans proximal to the Adriatic Sea should average 5–10 cm, decreasing to 2–5 cm in eastern Europe (Romania, Moldova, southern Ukraine), with the plume tapering northeastwards over the Russian Plain (Figure 1a) [12]. However, the model output, while providing a useful estimate of the magnitude of the eruption, contains no data points spanning the 1500 km between the Balkan sites and the Don River on the Russian Plain (Figure 1b).

Significant thick deposits corresponding to the CI tephra have recently been identified in southern Romania [5], [29]–[31], and could provide important information for better constraining the magnitude of the eruption and its likely environmental impact. Moreover, elucidating the nature and spatial extent of the tephra fallout, as well as its likely forcing on regional climates, is also important for assessing the regional impact on hominin populations and their resilience during this critical period of time. In this paper we provide significant new data from the loess steppe environments of Dobrogea in southeastern Romania, a narrow land corridor between the Danube River and Black Sea. Our data not only expand on the critical mass of new data points from a region previously unaccounted for in the models of tephra dispersal, but also indicates an average tephra thickness substantially greater than the models predict (Figure 1b). These observations could present major implications for the magnitude of the eruption and its role within climate and environmental feedbacks.

The timing of the CI super-eruption coincided with the onset of Heinrich Event 4 (HE4) [32], [33], a short-lived stadial (Greenland Stadial 9, GS9) associated with enhanced ice-rafting in the North Atlantic Ocean and cold, dry conditions over Europe [34], [35]. This was followed by a series of centennial- to millennial-scale warm interstadials (separated by stadials), of which Greenland Interstadial 8 (GIS8) [14] was the longest and most pronounced event, occurring at the transition from Middle to Upper Pleniglacial [36]. Climatic conditions across the northern hemisphere during HE4 were generally cool and dry [35] due to a southward shift of the polar front driven by the collapse of the thermohaline circulation in the northern oceans. Palynological records from the Lago Grande di Monticchio in southern Italy, not far from the Phlegrean Fields, suggest abrupt cooling and more arid conditions during HE4 immediately following CI tephra deposition [32], [37], [38]. Indications of cooler climates during HE4 within existing eastern European records are not as clearly defined as in the Italian and other Mediterranean palaeoclimate archives [39]–[41]. In this respect, the sedimentary deposits of the temperate eastern European loess steppe are particularly poorly understood [41], [42]. Aside from the limitations of existing records to preserve evidence of HE4 intensity and its connection to the CI-super-eruption, the potential feedback link is difficult to establish beyond mere hypothesis given existing datasets, often of low analytical and consequently low temporal resolution [11]. However, comparable attempts to identify a causal link between volcanic winters and climatic change in the case of the earlier Toba super-eruption in Sumatra have so far proven similarly inconclusive [43]–[46], although recent chronological constraints have linked the Toba eruption with a substantial cooling event [46]. A better understanding both of the nature and intensity of climate change during HE4 across Europe, the temporal connection with the CI, and potential for establishment of positive climate feedbacks, is clearly necessary to establish the significance of the CI super-eruption within the global climate system.

The timing and impact of the CI super-eruption is of particular interest and relevance to human evolution in Europe, since it coincides with a substantial shift in the archaeological record, associated with the arrival of AMHs to the continent [16]–[18], and the demise of the Neanderthals [21], [22]. Archaeological records within the CI ashfall zone presently provide an inconsistent picture of the eruption’s influence on hominin occupation [10], [47], [48]. In southern Italy, the region closest to the volcanic cataclysm, both open air and rock shelter sites preserve a significant hiatus in occupation during the period immediately following the CI eruption [3], [49], [50]. This indicates widespread abandonment of habitation sites in the region for some hundreds, if not thousands, of years following the eruption [11], [48]. The archaeological record from further afield is contradictory. Several rock shelters in the Balkans and northern Africa preserve CI tephra shards within their stratigraphy, yet interpretations of archaeological records within these sites postulate no significant disruption of the archaeological record and conclude that the CI super-eruption did not affect hominin populations there [10]. Conversely, the open air site of Kostenki 14 on the Russian Plain preserves an archaeological assemblage suggesting sudden catastrophic destruction of a human settlement [51], despite the fact that the tephra layers in that sequence appear to be redeposited [52]. Moreover, thick deposits of tephra within the Montenegran cave site of Crvena Stijena clearly divide the Middle and Upper Palaeolithic [53].

The localised impacts of large volcanic eruptions are not exclusively climatic. Chemical reactions between acidic volatile volcanic gases, and atmospheric and soil moisture, produce acid rain and soil acidification in ashfall zones, contamination of freshwater systems, and fluorosis of herbivores ingesting contaminated vegetation, with associated effects on humans dependent on affected ecosystems [54], [55]. Therefore, in considering the impact of the CI super-eruption on human evolution within an ashfall zone, more than just the influence of climate comes into play. In this sense, accurate data on tephra distribution and thickness within the ashfall region becomes critically important.

The lower Danube River valley and its major tributaries in eastern Europe has long been proposed to represent one of the major migration routes for AMHs into Europe [17], [56]. Yet this is precisely the region most likely to have been affected by the ecological impacts of the CI ashfall and related impacts on the regional ecosystem. Consequently, at this stage not only is it unclear what impact the CI eruption might have had on hominin occupation; the conjunction between hypothesized migration routes into Europe, potential interaction between hominin species, and tephra deposition may well have intensified this impact.

In this paper we present new data from a tephra deposit in the CI distal ashfall region of the lower Danube basin in southeast Romania, consolidated with recently published data confirming widespread CI tephra from other sites nearby [5]. Based on the characteristics of the deposit, we show that the CI tephra was deposited not only rapidly but also more thickly than predicted, 1200 km east of the eruption. We hereby propose that models of the magnitude of the eruption be reassessed using the new data points from this distal region for which data previously did not exist. Although we do not remodel the volcanic event within this paper, we do hypothesise that the eruption was substantially more explosive than previously estimated. We speculate on the potential impact of such rapid, thick deposition of ash on hominin populations in this region, and for the spatial variability of this impact, both climatically and directly on the ecosystem. Our hypotheses not only hold significant implications for human evolution within Europe in general, but also highlight the complexity and potential vulnerability of hominin dispersals and occupations at varying scales across the continent at a critical time in human evolution.