Giovanni Zanchetta

Late Holocene drought responsible for the collapse of Old World civilizations is recorded in an Italian cave flowstone

A severe drought in parts of low-latitude northeastern Africa and southwestern Asia ∼4200 yr ago caused major disruption to ancient civilizations. Stable isotope, trace element, and organic fluorescence data from a calcite flowstone collected from the well-watered Alpi Apuane karst of central-western Italy indicate that the climatic event responsible for this drought was also recorded in mid-latitude Europe. Although the timing of this event coincides with an episode of increased ice-rafted debris to the subpolar North Atlantic, the regional ocean-atmosphere response seems atypical of similar Holocene ice-rafting events. Furthermore, comparison of the flowstone data with other regional proxies suggests that the most extreme part of the dry spell occurred toward the end of a longer-term climate anomaly.

Evidence for Obliquity Forcing of Glacial Termination II

Oblique Reasoning In Milankovich theory, the canonical theory of glaciation and deglaciation, ice sheets wax and wane in response to the amount of summer insolation at a latitude of 65°N, which is consistent with the observed timing of the last deglaciation. The penultimate glaciation behaved quite differently, however. Now, Drysdale et al. (p. 1527, published online 13 August) offer firmer constraints on the timing of the penultimate deglaciation, by correlating a difficult-to-date marine record of ocean volume to a precisely datable nearby speleothem (terrestrial stalagmite). Ocean volume began to increase about 141,000 years ago, thousands of years before the rise in 65°N summer insolation. Thus, instead of the forcing mechanism proposed by Milankovich, variations in Earths obliquity may be mostly responsible for the disappearance of ice sheets. Marine records suggest that the early onset of the penultimate deglaciation was due to changes in Earth’s obliquity. Variations in the intensity of high-latitude Northern Hemisphere summer insolation, driven largely by precession of the equinoxes, are widely thought to control the timing of Late Pleistocene glacial terminations. However, recently it has been suggested that changes in Earth’s obliquity may be a more important mechanism. We present a new speleothem-based North Atlantic marine chronology that shows that the penultimate glacial termination (Termination II) commenced 141,000 ± 2500 years before the present, too early to be explained by Northern Hemisphere summer insolation but consistent with changes in Earth’s obliquity. Our record reveals that Terminations I and II are separated by three obliquity cycles and that they started at near-identical obliquity phases.

Tephrostratigraphy, chronology and climatic events of the Mediterranean basin during the Holocene: An overview:

The identification and characterisation of high-frequency climatic changes during the Holocene requires natural archives with precise and accurate chronological control, which is usually difficult to achieve using only 14C chronologies. The presence of time-spaced tephra beds in Quaternary Mediterranean successions represents an additional, independent tool for dating and correlating different sedimentary archives. These tephra layers are potentially useful for resolving long-standing issues in paleoclimatology and can help towards correlating terrestrial and marine paleoclimate archives. Known major tephras of regional extent derive from central and southern Italy, the Hellenic Arc, and from Anatolia. A striking feature of major Holocene tephra deposition events in the Mediterranean is that they are clustered rather than randomly distributed in time. Several tephra layers occurred at the time of the S1 sapropel formation between c. 8.4 and 9.0 ka BP (Mercato, Gabellotto-Fiumebianco/E1, Cappadocia) and other important tephra layers (Avellino, Agnano Monte Spina, ‘Khabur’ and Santorini/Thera) occurred during the second and third millennia BC, marking an important and complex phase of environmental changes during the mid- to late-Holocene climatic transition. There is great potential in using cryptotephra to overlap geographically Italian volcanic ashes with those originating from the Aegean and Anatolia, in order to connect regional tephrochronologies between the central and eastern Mediterranean.

The Holocene climatic evolution of Mediterranean Italy: A review of the continental geological data:

We present a synthesis of geological, stratigraphic, geomorphological and stable isotope data collected from continental archives to highlight the environmental and climatic differences between the first and second half of the Holocene of central and southern Italy. The beginning of the Holocene is marked by rapid environmental change. In Mediterranean Italy, between c. 9500 cal. BP and c. 6000—5500 cal. BP, average temperatures were probably higher and environmental conditions were generally stable; between c. 9000 and 7000 cal. BP, meteoric precipitation was at its highest. The end of the wetter period seems to occur later, at c. 6000—5000 cal. BP. Since c. 6000—5000 cal. BP, rapid climatic excursions are apparent in different palaeoclimate proxies, with both variability in meteoric precipitation and temperature evident. Of particular relevance is the event occurring at c. 4200 cal. BP. This event heralds a period of significant environmental change in the Apennines and, more generally, in central Italy. Following this event, environmental variability appears most pronounced and frequent. Some environmental changes during the early Holocene and after 4200 cal. BP seem to be in phase with IRD events in the North Atlantic, which suggest: (1) teleconnections between North Atlantic and Mediterranean areas; and (2) a possible influence of North Atlantic meridional overturning circulation in controlling the advection of moisture over the central Mediterranean basin via westerly air masses. The archives used in this review allow us to consider climate evolution as a driver of most of the observed environmental changes.

Characteristics of May 5–6, 1998 volcaniclastic debris flows in the Sarno area (Campania, southern Italy): relationships to structural damage and hazard zonation

The destructive power of debris flows on alluvial fan surfaces was investigated by studying the event of May 5–6, 1998 in the Sarno area (Campania, southern Italy). We assessed some physical and dynamic properties of debris flows, such as volumes, peak discharge and mobility, in order to obtain velocity profiles along alluvial fan surfaces. Reconstructed peak velocities vary from 20 m s−1 to 14 m s−1, while the runouts from the alluvial fan apexes range between ∼900 m and ∼2000 m. Debris flow velocities exponentially decrease from the alluvial fan apex to the distal depositional zone but abruptly drop to zero after entering the densely inhabited areas. Based on velocity data and estimates of flow density, the values of impact pressure on rigid structures (i.e. buildings) were assessed through the calculation of hydrostatic pressure and dynamic overpressure. The data from the study area show that at flow velocities >4–5 m s−1 the dynamic overpressure accounts for most of the observed damage, whereas at lower velocities the contributions of the hydrostatic and dynamic pressures become similar. The comparisons between the calculated impact pressures and the damage on structures show that for loading >35 kPa (velocity >3 m s−1) most of buildings were destroyed or severely damaged. For values <35 kPa only minor damage occurred to the structures. Finally, an empirical law for the assessment of impact pressure on spreading areas was presented, useful for hazard zonation in similar geomorphologic settings.

Stalagmite evidence for the precise timing of North Atlantic cold events during the early last glacial

Evidence of millennial-scale cold events following the last interglacial are well preserved in North Atlantic marine cores, Greenland ice, and pollen records from Europe. However, their timing was previously undetermined by radiometric dating. We report the first precise radiometric ages for two such events, C23 (105.1 ± 0.9 ka to 102.6 ± 0.8 ka) and C24 (112.0 ± 0.8 ka and 108.8 ± 1.0 ka), based on stable carbon and oxygen isotope measurements on a stalagmite from Italy (CC28). In addition to providing new information on the duration of these events in southern Europe, the age data provide invaluable tuning points for the Melisey I (C24) and Montaigu (C23) pollen zones identified in western Europe. The former event is of particular significance because it represents the end of the Eemian interglacial forest phase in western Europe. The new age data will also allow fine tuning of the timing and duration of Greenland stadial 24 (equivalent to C23) in the North Greenland Ice Core Project ice core and, via a common gasage chronology, tuning of the Vostok and EPICA (European Project for Ice Coring in Antarctica) ice cores.

May 5, 1998, debris flows in circum-Vesuvian areas (southern Italy): Insights for hazard assessment

On May 5, 1998, after 30 h of continuous rainfall (100–180 mm), large areas of the tephra-rich colluvial cover 12–18 km east of Vesuvius volcano (Italy) failed, generating a series of debris flows that killed more than 150 people in the Sarno area. Some 37 basins were affected almost simultaneously by this phenomenon. The Sarno disaster shows that air-fall deposits can create debris-flow hazards that may extend for several decades or even centuries after eruptions. In the Sarno area, the affected basins have the following features: (1) a funnel shape, debouching at the base of the hillslope; (2) an integrated drainage network with a central subrectilinear channel; (3) slopes exceeding 25° on average; and (4) a thin (∼0.5–2.0 m) volcanic-rich colluvial cover related to the past ash fallout of Vesuvius. The stratigraphy of downstream alluvial-fan deposits records the repeated occurrence of large debris flows. On the basis of the 1998 case history, we propose an approach to evaluate hazard potential related to similar debris flows for the neighboring Clanio Valley. This approach is mainly based on morphometric data derived from a digital elevation model and is of potential worldwide application.

Stable isotope analyses on the last 30 ka molluscan fauna from Pampa grassland, Bonaerense region, Argentina

Abstract Fossil and living shells of terrestrial and freshwater molluscs collected from various sites in the Bonaerense and Patagonia regions of Argentina were analysed for their stable isotope content as a possible tool for palaeoclimatic and palaeoenvironmental reconstruction. The oxygen isotope composition of calcareous shell from freshwater samples was interpreted in terms of a change in moisture condition and the related evaporative effect on surficial bodies of water, linked to a climatic shift. The carbon isotope composition mainly records changes in biological productivity. Interpretation of the isotopic composition of the land snail carbonate is more complex and worldwide data from living shells have been used to decipher to some extent the palaeoenvironmental record contained in their isotopic composition. Overall, the interpretations deduced from isotopic data of land snails as well as from nearby freshwater molluscs are quite comparable. The isotopic data suggest that arid conditions occurred between 35 and 15 ka B.P. and warmer conditions around 35–25 ka B.P. A shift toward a new phase comparable with the present meteorological and climatic situation probably began around 9 ka B.P. and it was linked to some short but severe climatic fluctuations, thus suggesting that high climatic stress characterised this period. Moreover, a trend toward slightly arid conditions is suggested by isotopic data, possibly sometimes after 5 ka. The differences arising from the geographical location and the short duration of each single series studied still hamper an extensive interpretation of the isotopic data.

Volcaniclastic debris flows in the Clanio Valley (Campania, Italy): insights for the assessment of hazard potential

Abstract The rugged and steep slopes of the Clanio Valley (Campania, Southern Italy), mantled by volcaniclastic deposits from explosive eruptions of Somma-Vesuvius and Phlegraean Fields volcanoes, have a great potential for generating volcaniclastic debris flows. During the well-known meteorological event of May 5–6, 1998, which triggered tens of debris flows causing enormous damage and casualties in the area of Sarno–Quindici–Siano–Bracigliano (SQSB), the Clanio Valley was also affected by these hazardous phenomena. Debris flows were triggered by the failure of the volcaniclastic cover of the carbonate relief in the form of soil slips, mainly on the sides of steep valleys (slope between 26° and 45°). A map of the hazard potential was created on the basis of both field and computer-assisted morphometric data. Three classes, characterised by a high, medium and low hazard potential, were distinguished. Within the higher class, a better and more detailed zonation was obtained by studying the shape of the disrupted and undisrupted basins during the May 5–6, 1998 event in the nearby Sarno–Quindici–Siano–Bracigliano area. This type of morphometric analysis can be applied rapidly by using a digital elevation model (DEM), which allows a rapid investigation of large-scale areas. Such an approach can be useful in areas characterised by similar geological and geomorphological settings.

Duration and dynamics of the best orbital analogue to the present interglacial

Past orbital analogues to the current interglacial, such as Marine Isotope Stage 19c (MIS 19c, ca. 800 ka), can provide reliable reference intervals for evaluating the timing and the duration of the Holocene and factors inherent in its climatic progression. Here we present the first high-resolution paleoclimatic record for MIS 19 anchored to a high-precision 40Ar/39Ar chronology, thus fully independent of any a priori assumptions on the orbital mechanisms underlying the climatic changes. It is based on the oxygen isotope compositions of Italian lake sediments showing orbital- to millennial-scale hydrological variability over the Mediterranean between 810 and 750 ka. Our record indicates that the MIS 19c interglacial lasted 10.8 ± 3.7 k.y., comparable to the time elapsed since the onset of the Holocene, and that the orbital configuration at the time of the following glacial inception was very similar to the present one. By analogy, the current interglacial should be close to its end. However, greenhouse gas concentrations at the time of the MIS 19 glacial inception were significantly lower than those of the late Holocene, suggesting that the current interglacial could have already been prolonged by the progressive increase of the greenhouse gases since 8–6 ka, possibly due to early anthropogenic disturbance of vegetation.