Biancamaria Narcisi

One-to-one coupling of glacial climate variability in Greenland and Antarctica.

Precise knowledge of the phase relationship between climate changes in the two hemispheres is a key for understanding the Earth’s climate dynamics. For the last glacial period, ice core studies have revealed strong coupling of the largest millennial-scale warm events in Antarctica with the longest Dansgaard–Oeschger events in Greenland through the Atlantic meridional overturning circulation. It has been unclear, however, whether the shorter Dansgaard–Oeschger events have counterparts in the shorter and less prominent Antarctic temperature variations, and whether these events are linked by the same mechanism. Here we present a glacial climate record derived from an ice core from Dronning Maud Land, Antarctica, which represents South Atlantic climate at a resolution comparable with the Greenland ice core records. After methane synchronization with an ice core from North Greenland, the oxygen isotope record from the Dronning Maud Land ice core shows a one-to-one coupling between all Antarctic warm events and Greenland Dansgaard–Oeschger events by the bipolar seesaw6. The amplitude of the Antarctic warm events is found to be linearly dependent on the duration of the concurrent stadial in the North, suggesting that they all result from a similar reduction in the meridional overturning circulation.

The Postglacial record of environmental history from Lago di Pergusa, Sicily

Lacustrine sedimients from Lago di Pergusa in central Sicily provide a Postglacial record of environmental change in the Mediterranean. Magnetic susceptibility measurements, lithofacies characterization and pollen analysis were carried out anid integrated to obtain a better reconstruction of the past 11000 years. The chronoogy is provided by AMS radiocarbon dates on macrofossils or bulk sediment, and by a tephra correlative with a late-Holocene explosion from the Etna volcano. The transition period related to the present interglacial reafforestation, characterized by increasing humidity, started about 10700 years BP. The onset of the wettest conditions of the Postglacial occurred at about 9000 years BP and lasted until about 7200 years BP. Then a trend towards aridification began. leading to very dry conditions at about 3000 years BP. An unquestionable human impact on vegetation is found from 2800 years BP, although earlier land use cannot be excluded. As the climate had already induced change in the vegetation, the well-known human occupancy during the last three millennia did not produce strong effects on the environment.

Quaternary stratigraphy of distal tephra layers in the Mediterranean—an overview

This paper reviews the results of fifty years of tephra studies in the Mediterranean basin. The tephrostratigraphy of the Eastern Mediterranean is defined well and has been developed in conjunction with detailed biostratigraphy. Currently about thirty marker tephra have been identified and characterised, some being widespread over large sectors of the basin. Sedimentation in both Tyrrhenian and Aegean Seas is influenced by the proximity of the source volcanoes and hence primary tephras frequently exhibit evidence for reworking and post-depositional phenomena. In contrast to the long marine tephrostratigraphy there are still only a few studies reporting continental tephra deposits; these mainly concern lacustrine sequences and archaeological excavations. Recent investigations have employed electron probe microanalysis of discrete glass shards. These have illustrated the considerable geochemical variability of the principal tephra markers including those related to large-volume explosive events. In some instances this variability can be shown to mirror the heterogeneous composition of related pyroclastic formations in the proximal areas. Integration of a wide range of these findings, has enabled the construction and update of distribution maps for the main markers. This will permit revised estimations of the volume of the erupted material enabling consideration of the ecological and climatic impacts of the related explosive events. However, in spite of the increased chronostratigraphical information available for many of the source areas, some significant tephra layers remain uncorrelated. This uncertainty should stimulate further investigation to enable evaluation of the volcanic hazard in these densely populated regions. q 1999 Elsevier Science B.V. All rights reserved.

Tephrochronology of a late quaternary lacustrine record from the Monticchio maar (Vulture volcano, Southern Italy)

Abstract With the aim of defining the chronological framework of the 51 m deep sedimentary sequence (core D) from Lago Grande di Monticchio (Mt Vulture volcano), macroscopic, microscopic and geochemical investigations have been carried out on the 14 thickest (at least 3 cm) tephra layers recorded in the core. The results indicate that the tephras are related to the main late Quaternary explosive events from Ischia, Vesuvius and the Phlegrean Fields districts of the Campanian area. Following these results, a usable time scale has been obtained, according to which the sequence spans the last 70 ka. Beyond the chronological information, this investigation has made it possible: (a) to identify widespread time-parallel markers for reliable correlations in the Central Mediterranean; (b) to collect useful data about past powerful eruptions, particularly from Vesuvius, for a better assessment of volcanic hazards in Central and Southern Italy.

Late Quaternary tephra-derived paleosols in central Italy's carbonate Apennine Range: Stratigraphical and paleoclimatological implications

Abstract Detailed stratigraphical, pedological, and geochronological (14C dating) research was carried out on numerous sections located in the carbonate Apennine Range of central Italy. Two paleosols, Late Pleistocene (Pedomarker A) and Holocene (Pedomarker B) in age, were recognized as having developed from air-fall pyroclastic material. Given their special properties and widespread distribution, both soils represent valuable markers in the Late Quaternary stratigraphy of central Italy. Information about the climatic conditions that have influenced their pedogenesis through time has been obtained. Pedomarker A formed under temperate-wet conditions related to the last interstadial fluctuations of the Pleniglacial; its development ceased after ca. 30 ka because of the onset of Last Glacial Maximum dry-cold conditions. Pedomarker B formed at the beginning of the Holocene under udic and perudic soil moisture regimes; its development ceased in some localities because of a change towards a drier climate after ca. 4.5 ka. Petrographic and geochemical characteristics of the parent materials are discussed, and correlations with the Campanian Ignimbrite (Pedomarker A) and Neapolitan Yellow Tuff (Pedomarker B), both related to activity in the Phlegrean Fields, are proposed.

Lithostratigraphy of the 250,000 year record of lacustrine sediments from the Valle di Castiglione crater, Roma

Abstract Sediments drilled by an 88 m borehole through the middle of the drained lake bed (1 km diameter) were studied by macroscopic, grain size, mineralogical and geochemical analyses. The catchment area (60 km 2 ) is composed of leucitic undersaturated volcanic rocks, mainly of the pyroclastic type. The lithostratigraphic sequence can be summarized as consisting of two alternating lithotypes, which allows different palaeoclimatic influences to be drawn: the first consists mainly of tuffaceous silts, generally enriched with organic matter and aeolian quartz, and contains heavy and weathered minerals. It is interpreted as a sediment deposited with a predominantly terrigenous supply by the abundant surface waters flowing into the lake during wet climatic phases. The second lithotype consists of silts with a predominantly carbonate component, rich in mollusc shells but with low contents of organic matter, aeolian quartz, heavy and weathering minerals. It is interpreted as a sediment deposited during relatively dry climatic phases with an abundant calcium bicarbonate supply, which is relatively higher than the terrigenous one. Most of the sequence can be correlated with the palaeoclimatic variations inferred from oxygen isotopic stratigraphy. Dry intervals seem to be related to the winter solstice in the northern hemisphere when the earth is at perihelion.

Ice record of a 13th century explosive volcanic eruption in northern Victoria Land, East Antarctica

A volcanic event, represented by both coarse ash and a prominent sulphate peak, has been detected at a depth of 85.82 m in a 90 m ice core drilled at Talos Dome, northern Victoria Land. Accurate dating of the core, based on counting annual sulphate and nitrate fluctuations and on comparison with records of major known volcanic eruptions, indicates that the event occurred in 1254 ± 2 AD. The source volcano is most likely to be located within the Ross Sea region. In particular, the glass shards have a trachytic composition similar to rocks from The Pleiades and Mount Rittmann (Melbourne volcanic province), about 200 km from Talos Dome. Sulphate concentration is comparable with that of violent extra-Antarctic explosive events recorded in the same core, but atmospheric perturbation was short-lived and localized, suggesting a negligible impact on regional climate. It is suggested that this eruption may represent the most important volcanic explosion in the Melbourne province during the last eight centuries; thus this event may also represent a valuable chrono-stratigraphical marker on the East Antarctic plateau and in adjoining areas.

First discovery of meteoritic events in deep Antarctic (EPICA‐Dome C) ice cores

Two distinct dust layers in the EPICA-Dome C ice core (75°06′S, 123°21′E, East Antarctic Plateau) have been shown to relate to individual meteoritic events. Particles forming these layers, investigated by electron microprobe, show peculiar textural, mineralogical and geochemical features and closely resemble extraterrestrial debris in deep-sea sediments and polar caps. Preliminary estimates of cosmic debris input at the studied layers, obtained from Coulter Counter measurements, are 4–5 orders of magnitude greater than the yearly micrometeorite flux in East Antarctic snow and ice. The cosmic events are accurately dated through glaciological models at 434 ± 6 and 481 ± 6 ka, respectively and are located in the core climatic stratigraphy near the “Mid-Brunhes Event”. This is the first report of well-dated cosmic horizons in deep Antarctic ice cores. It significantly improves the extraterrestrial record of Antarctica and opens new correlation perspectives between long climatic records of the South polar region.

Caratteristiche e possibile provenienza di due livelli piroclastici nei sedimenti del Pleistocene superiore della Piana del Fucino (Italia centrale)

The results of sedimentological, mineralogical and geochemical investigations carried out on two tephra layers in Upper Pleistocene lacustrine sediment cores from the central sector of the Fucino Plain (Abruzzo) are reported and discussed. The grain size data, in agreement with the macroscopic characteristics, indicate that both layers are of airfall origin. Both the mineralogical association and the chemical composition of the glassy fraction suggest relating the two layers to the volcanic activity of the Alban Hills district of the Roman Perpotassic province (80 km away from Fucino). Actually, a correlation with the products of the final Alban Hills hydromagmatic phase dated 40-50,000 years B.P. is proposed.RiassuntoUna indagine sedimentologica, mineralogica e geochimica è stata condotta su due livelli piroclastici contenuti nei sedimenti lacustri del Pleistocene superiore dell’area centrale della Piana del Fucino (Abruzzo). Le analisi granulometriche, in accordo con le caratteristiche macroscopiche, indicano che i livelli si sono deposti per caduta a seguito di eruzioni fortemente esplosive. Sia l’associazione mineralogica, sia la composizione chimica della frazione vetrosa suggeriscono una attribuzione dei livelli piroclastici all’attività del distretto dei Colli Albani (80 km circa dal Fucino). In particolare, risulta altamente probabile una correlazione con i prodotti della fase finale a carattere idromagmatico del vulcanismo albano, verificatasi 40-50.000 anni fa.