Judy R. M. Allen

Rapid environmental changes in southern Europe during the last glacial period

Oxygen-isotope records from Greenland ice cores, indicate numerous rapid climate fluctuations during the last glacial period. North Atlantic marine sediment cores show comparable variability in sea surface temperature and the deposition of ice-rafted debris. In contrast, very few continental records of this time period provide the temporal resolution and environmental sensitivity necessary to reveal the extent and effects of these environmental fluctuations on the continents. Here we present high-resolution geochemical, physical and pollen data from lake sediments in Italy and from a Mediterranean sediment core, linked by a common tephrochronology. Our lacustrine sequence extends to the past 102,000 years. Many of its features correlate well with the Greenland ice-core records, demonstrating that the closely coupled ocean–atmosphere system of the Northern Hemisphere during the last glacial extended its influence at least as far as the central Mediterranean region. Numerous vegetation changes were rapid, frequently occurring in less than 200 years, showing that the terrestrial biosphere participated fully in last-glacial climate variability. Earlier than 65,000 years ago, our record shows more climate fluctuations than are apparent in the Greenland ice cores. Together, the multi-proxy data from the continental and marine records reveal differences in the seasonal character of climate during successive interstadials, and provide a step towards determining the underlying mechanisms of the centennial–millennial-scale variability.

Vegetation history and palaeoclimate of the last glacial period at Lago Grande di Monticchio, Southern Italy

A high-resolution palynological study of a 51 m core from Lago Grande di Monticchio, southern Italy, has provided a palaeonvironmental record for the last glacill. A annual lamination based chronology, supported by radiometric and tephrochronological dates, provides an absolute timescale for this record that spans 76,300 years. Correlations are established between the pollen stratigraphy, the GRIP ice core δ18O record and foraminiferal assemblages from Atlantic core V23-81. Both Dansgaard-Oeschger and Heinrich events are reflected by changes in the pollen stratigraphy. Revised dates are estimated for Heinrich events H1–H6. A quantitative palaeoclimate reconstruction based upon the pollen data provides evidence of the climate changes in southern Italy associated with these and other fluctuations during the last glacial.

Weichselian palynostratigraphy, palaeovegetation and palaeoenvironment; the record from Lago Grande di Monticchio, southern Italy

Abstract The palynostratigraphic record from Lago Grande di Monticchio (S. Italy) is presented. An independent sedimentation-rate-based chronology provides an age of 101,530 calendar years BP for the lowermost sediments sampled. This chronology enables assessment of the rapidity of vegetation changes during the last glacial; contrary to widely held views the vegetation showed numerous large magnitude changes in periods of

Evidence for last interglacial chronology and environmental change from Southern Europe

Establishing phase relationships between earth-system components during periods of rapid global change is vital to understanding the underlying processes. It requires records of each component with independent and accurate chronologies. Until now, no continental record extending from the present to the penultimate glacial had such a chronology to our knowledge. Here, we present such a record from the annually laminated sediments of Lago Grande di Monticchio, southern Italy. Using this record we determine the duration (17.70 ± 0.20 ka) and age of onset (127.20 ± 1.60 ka B.P.) of the last interglacial, as reflected by terrestrial ecosystems. This record also reveals that the transitions at the beginning and end of the interglacial spanned only ≈100 and 150 years, respectively. Comparison with records of other earth-system components reveals complex leads and lags. During the penultimate deglaciation phase relationships are similar to those during the most recent deglaciation, peaks in Antarctic warming and atmospheric methane both leading Northern Hemisphere terrestrial warming. It is notable, however, that there is no evidence at Monticchio of a Younger Dryas-like oscillation during the penultimate deglaciation. Warming into the first major interstadial event after the last interglacial is characterized by markedly different phase relationships to those of the deglaciations, warming at Monticchio coinciding with Antarctic warming and leading the atmospheric methane increase. Diachroneity is seen at the end of the interglacial; several global proxies indicate progressive cooling after ≈115 ka B.P., whereas the main terrestrial response in the Mediterranean region is abrupt and occurs at 109.50 ± 1.40 ka B.P.

Vegetation history and climate of the last 15,000 years at Laghi di Monticchio, southern Italy

Abstract In southern Italy, vegetation contemporary with the end of the last glacial maximum, from 15,000 to 12,000 years ago, is shown by pollen-analysis to have been treeless and steppe-like in character. At 12,500 BP (years before present), Betula (birch) expanded into the steppe, quickly followed by Quercus (oak), Fagus (beech), Tilia (lime) and other tree genera of mesic forest. High percentages of Tilia point to a rich mesic forest that was contemporary with the ‘Allerod’ interstadial of northern Europe. A major decline in mesic trees with an accompanying return of Betula and steppe genera dated to 10,500 years ago identifies a ‘Younger Dryas ’ climatic reversal. Betula and steppe genera were replaced by forest of Quercus and other mesic trees, notably Ulmus (elm), as the Holocene began. In the later Holocene, ca. 4000 years ago, Abies (fir), Carpinus betulus (hornbeam) and Taxus (yew) appeared. Abies and Taxus became extinct locally about 2500 years ago, either because of climatic change, or perhaps because of the effects of early agriculture. The Full-glacial climate is thought to have been cold and summer-dry with mainly winter precipitation. The Lateglacial ‘Bolling-Allerod’ Interstadial was summer-wet and warm. The response-surface based climate reconstruction indicates an early Holocene climate with markedly colder winter conditions than today, about −5°C compared with 3.9°C today as a mean temperature for the coldest month. The annual temperature sum is reconstructed as somewhat higher than today, 3500 degree days as compared with a calculated value of 2900 for today. The later Holocene had a climate like todays. Rainfall, and variation in its seasonal distribution, has been a critical determinant of the vegetation cover. The fossil pollen record at Laghi Di Monticchio has been complemented by diatom and plant macrofossil studies which provide evidence of former lake environments as well as data on the upland forest. Lake levels remained high during the Full- and Lateglacial with encroachment of shore vegetation during the Holocene. The sediments also have an exceptionally rich record of tephra falls which are of importance in dating and core correlation. Twenty-one macroscopically visible tephras occur in sediments of the last 15,000 years.

Holocene environmental variability—the record from Lago Grande di Monticchio, Italy

Abstract The Holocene pollen record from Lago Grande di Monticchio reveals environmental changes throughout the Holocene. Comparison of this record with other records of Holocene environmental variability indicates that there is a temporal correlation between these changes and north Atlantic events. However, the nature of this relationship and the underlying mechanism(s) is yet to be determined. It is evidently complex with the apparent coincidence of sea-surface temperature cooling events with both species expansions and disappearances. The picture is further complicated by the interaction between human activity and natural environmental changes.

European vegetation during Marine Oxygen Isotope Stage-3

European vegetation during representative “warm” and “cold” intervals of stage-3 was inferred from pollen analytical data. The inferred vegetation differs in character and spatial pattern from that of both fully glacial and fully interglacial conditions and exhibits contrasts between warm and cold intervals, consistent with other evidence for stage-3 palaeoenvironmental fluctuations. European vegetation thus appears to have been an integral component of millennial environmental fluctuations during stage-3; vegetation responded to this scale of environmental change and through feedback mechanisms may have had effects upon the environment. The pollen-inferred vegetation was compared with vegetation simulated using the BIOME 3.5 vegetation model for climatic conditions simulated using a regional climate model (RegCM2) nested within a coupled global climate and vegetation model (GENESIS-BIOME). Despite some discrepancies in detail, both approaches capture the principal features of the present vegetation of Europe. The simulated vegetation for stage-3 differs markedly from that inferred from pollen analytical data, implying substantial discrepancy between the simulated climate and that actually prevailing. Sensitivity analyses indicate that the simulated climate is too warm and probably has too short a winter season. These discrepancies may reflect incorrect specification of sea surface temperature or sea-ice conditions and may be exacerbated by vegetation–climate feedback in the coupled global model.

The past ecology of Abies alba provides new perspectives on future responses of silver fir forests to global warming

Paleoecology can provide valuable insights into the ecology of species that complement observation and experiment-based assessments of climate impact dynamics. New paleoecological records (e.g., pollen, macrofossils) from the Italian Peninsula suggest a much wider climatic niche of the important European tree species Abies alba (silver fir) than observed in its present spatial range. To explore this discrepancy between current and past distribution of the species, we analyzed climatic data (temperature, precipitation, frost, humidity, sunshine) and vegetation-independent paleoclimatic reconstructions (e.g., lake levels, chironomids) and use global coupled carbon-cycle climate (NCAR CSM1.4) and dynamic vegetation (LandClim) modeling. The combined evidence suggests that during the mid-Holocene (;6000 years ago), prior to humanization of vegetation, A. alba formed forests under conditions that exceeded the modern (1961–1990) upper temperature limit of the species by ;5–78C (July means). Annual precipitation during this natural period was comparable to today (.700–800 mm), with drier summers and wetter winters. In the meso-Mediterranean to sub-Mediterranean forests A. alba co-occurred with thermophilous taxa such as Quercus ilex, Q. pubescens, Olea europaea, Phillyrea, Arbutus, Cistus, Tilia, Ulmus, Acer, Hedera helix, Ilex aquifolium, Taxus, and Vitis. Results from the last interglacial (ca. 130 000–115 000 BP), when human impact was negligible, corroborate the Holocene evidence. Thermophilous Mediterranean A. alba stands became extinct during the last 5000 years when land-use pressure and specifically excessive anthropogenic fire and browsing disturbance increased. Our results imply that the ecology of this key European tree species is not yet well understood. On the basis of the reconstructed realized climatic niche of the species, we anticipate that the future geographic range of A. alba may not contract regardless of migration success, even if climate should become significantly warmer than today with summer temperatures increasing by up to 5–78C, as long as precipitation does not fall below 700–800 mm/yr, and anthropogenic disturbance (e.g., fire, browsing) does not become excessive. Our finding contradicts recent studies that projected range contractions under global-warming scenarios, but did not factor how millennia of human impacts reduced the realized climatic niche of A. alba.

Weichselian palynological records from southern Europe: correlation and chronology

Abstract The high resolution, independently dated palynostratigraphic record from Lago Grande di Monticchio spanning the last 101,530 calendar years provides a basis for re-evaluating the correlations between palaeoenvironmental events in Europe during the last glacial as well as a means to determine their chronology. The interstadial events recorded from various localities throughout Europe are combined into a single scheme of correlations and a chronological framework is suggested. This provides a basis for assessing the evolution of the vegetation and environmental patterns across Europe during the last glacial, revealing a general tendency for the latitudinal climatic gradient to have been steeper than it has been during the Holocene. The vegetation has also generally been subject to greater moisture deficiency, either because of prevailing climatic conditions or as a reflection of the lower atmospheric concentration of CO 2 . The scheme of correlations is shown to be capable of being extended beyond Europe, not only to marine and ice-core records from the North Atlantic region, but also to a palynological record from north-west North America.

Palaeoclimate, chronology and vegetation history of the Weichselian Lateglacial: comparative analysis of data from three cores at Lago Grande di Monticchio, southern Italy

Abstract Palynological and chronological data are presented for the Lateglacial from three cores taken at different locations in the basin of Lago Grande di Monticchio. Plant macrofossil data from one core provide complementary evidence of the palaeovegetation. Quantitative palaeoclimate reconstructions are made from the pollen data using pollen-climate response surfaces. The chronological framework for Late-glacial events as well as the palaeoclimate are compared with other sources of evidence of Lateglacial palaeoenvironments. Surface conditions in the North Atlantic appear to be more directly linked to climatic conditions in Italy than is the temperature in Greenland. Nonetheless, the palynological record exhibits high-frequency variability that reflects high-frequency climatic changes paralleling those seen in the ice core records from Greenland.