Holocene environmental and climatic changes at Gorgo Basso,a coastal lake in southern Sicily,Italy

We used a new sedimentary record to reconstruct the Holocene vegetation and fire history of Gorgo Basso, a coastal lake in south-western Sicily (Italy). Pollen and charcoal data suggest a fire-prone open grassland near the site until ca 10,000 cal yr BP (8050 cal BC), when Pistacia shrubland expanded and fire activity declined, probably in response to increased moisture availability. Evergreen Olea europaea woods expanded ca 8400 to decline abruptly at 8200 cal yr BP, when climatic conditions became drier at other sites in the Mediterranean region. Around 7000 cal yr BP evergreen broadleaved forests (Quercus ilex, Quercus suber and O. europaea) expanded at the cost of open communities. The expansion of evergreen broadleaved forests was associated with a decline of fire and of local Neolithic (Ficus carica–Cerealia based) agriculture that had initiated ca 500 years earlier. Vegetational, fire and land-use changes ca 7000 cal yr BP were probably caused by increased precipitation that resulted from (insolation-forced) weakening of the monsoon and Hadley circulation ca 8000–6000 cal yr BP. Low fire activity and dense coastal evergreen forests persisted until renewed human activity (probably Greek, respectively Roman colonists) disrupted the forest ca 2700 cal yr BP (750 BC) and 2100 cal yr BP (150 BC) to gain open land for agriculture. The intense use of fire for this purpose induced the expansion of open maquis, garrigue, and grassland-prairie environments (with an increasing abundance of the native palm Chamaerops humilis). Prehistoric land-use phases after the Bronze Age seem synchronous with those at other sites in southern and central Europe, possibly as a result of climatic forcing. Considering the response of vegetation to Holocene climatic variability as well as human impact we conclude that under (semi-)natural conditions evergreen broadleaved Q. ilex–O. europaea (s.l.) forests would still dominate near Gorgo Basso. However, forecasted climate change and aridification may lead to a situation similar to that before 7000 cal yr BP and thus trigger a rapid collapse of the few relict evergreen broadleaved woodlands in coastal Sicily and elsewhere in the southern Mediterranean region.     

Absolute measurements and computed values for Martian irradiance between 10.5 and 12.5 μm

The combination of seasonal and orbital changes in Martian insolation result in complex latitude dependent surface temperature variations that effect the total radiance of the planet as seen from the earth. These surface temperature variations have been calculated, based upon a computer simulation of the thermal environment of the planet. The temperature variations are then integrated to yield the total radiance of the planet as seen from the earth as a function of time. The absolute radiance of Mars was measured on April 4, 1971, with a balloon-borne radiometer system operating in the wavelength range between 10.5 and 12.5 μm. The average brightness temperature of the Mars disk determined from these measurements was 254°K with a 1 σ error of 4°K.     

The Ricker Hills Tillite provides evidence of Oligocene warm-based glaciation in Victoria Land, Antarctica

The relationship between the Ricker Hills Tillite (RHT), which represents the northernmost outcrop of lithified continental glacial deposits in Victoria Land, is discussed with respect to the glacial landscape assemblage of the Ricker Hills, a nunatak at the internal border of the Transantarctic Mountains. A warm-based ice sheet deposited the tillite and induced syn- to post-depositional glacial deformation under wet conditions both of the tillite and of the bedrock. The thickness of the ice sheet on the nunatak is estimated to have been 600 m, at most. The area had been deeply eroded before deposition of the RHT as documented by the low elevation of tillite outcrops located in overdeepened depressions of the nunatak. Micropaleontological analysis evidences only the presence of Permian to Jurassic palynomorphs. X-ray diffraction and SEM–EDS analyses of clay minerals in the RHT indicate continental chemical weathering under wet conditions after the RHT deposition. As documented by clay mineral assemblage variation in CRP drillholes, the progressive cooling of the Antarctic continent allowed chemical weathering in “warm” conditions until the Late Oligocene period in southern Victoria Land, leading to a chronological constrain for RHT deposition. Conservatively estimating the sea level to have been between the tillite outcrops and the erosional trimline limiting horns in the Ricker Hills, at the time of RHT deposition, we suggest that the maximum uplift of the area would not have exceeded 900–1500 m since at least Late Oligocene.     

A new late glacial to early Holocene palaeobotanical and archaeological record in the Eastern Pre‐Alps: the Palughetto basin (Cansiglio Plateau,Italy)

A late glacial to early Holocene lacustrine and peat succession, rich in conifer remains and including some palaeolithic flint artefacts, has been investigated in the Palughetto intermorainic basin (Venetian Pre‐Alps). The geomorphological and stratigraphical relationships, ¹⁴C dates and pollen analyses allow a reconstruction of the environmental history of the basin and provide significant insights into the reforestation and peopling of the Pre‐Alps. The onset of peat accumulation is dated to 14.4–14.1 kyr cal. BP, coinciding with reforestation at middle altitudes that immediately post‐dates the immigration of Larix decidua and Picea abies subsp. europaea. Plant macrofossils point to the expansion of spruce about 14.3 kyr cal. BP, so far one of the earliest directly dated in the late glacial period of southern Europe. The previous hypothesis of an early Holocene spruce immigration in the Southern Alps from Slovenia needs reconsideration. Organic sedimentation stopped at the end of the Younger Dryas and was followed by the evolution of hydromorphic soils containing lithic artefacts, anthropic structures and wood charcoal. The typological features of the flint implements refer human occupation of the site to the end of the recent Epigravettian. Charcoals yielded dates either consistent with, or younger than, the archaeological chronology, in the early and middle Holocene. Copyright © 2000 John Wiley & Sons, Ltd.     

Decoupled kinematics of two neighbouring permafrost creeping landforms in the Eastern Italian Alps

An overall acceleration of rock glacier displacement rates in the Alps has been observed in recent decades, with several cases of destabilization leading to potential geomorphological hazards. This behaviour has been attributed to the rising permafrost temperature, induced by atmospheric warming and regulated by thermo-hydrological processes. Landforms derived from the interaction of glacier remnants and permafrost are widespread in mountain areas, but are less studied and monitored than talus rock glaciers. This work presents a comparative study of a talus rock glacier and a glacial-permafrost composite landform (GPCL) in the Eastern Italian Alps. The two landforms are only 10 km apart, but have rather different elevation ranges and main slope aspects. The kinematics and ground thermal conditions were monitored from 2001 to 2015 along with geomorphological surveys, analyses of historical maps and remote sensing data. The dynamic behaviour of the rock glacier was similar to the majority of monitored rock glaciers in the Alps, with an acceleration after 2008 and a velocity peak in 2015. In contrast, the GPCL had a nearly unchanged displacement rate during the observation period. Statistical analyses of kinematic vs. nivo-meteorological variables revealed a dynamic decoupling of the two landforms after 2008 that corresponds with increased winter snow accumulation. Although the kinematics of both landforms respond to ground surface temperature variations, the collected evidence suggests a different reaction of ground surface temperature to variations in the precipitation regime. This different reaction is likely due to local topo-climatic conditions that affect snow redistribution by wind. The different reactions of the two systems to the same climatic forcing is likely a legacy of their different origins. GPCL dynamics result from interaction of permafrost and residual glacial dynamics that are associated with possible peculiarities in the internal/basal meltwater circulation, whose future response is uncertain and requires improved understanding. © 2019 John Wiley & Sons, Ltd. © 2019 John Wiley & Sons, Ltd.     

Multiple cosmogenic nuclides document complex Pleistocene exposure history of glacial drifts in Terra Nova Bay (northern Victoria Land, Antarctica)

Geomorphological and glacial geological surveys and multiple cosmogenic nuclide analyses (¹⁰Be, ²⁶Al, and ²¹Ne) allowed us to reconstruct the chronology of variations prior to the last glacial maximum of the East Antarctic Ice Sheet (EAIS) and valley glaciers in the Terra Nova Bay region. Glacially scoured coastal piedmonts with round-topped mountains occur below the highest local erosional trimline. They represent relict landscape features eroded by extensive ice overriding the whole coastal area before at least 6 Ma (pre-dating the build-up of the Mt. Melbourne volcanic field). Since then, summit surfaces were continuously exposed and well preserved under polar condition with negligible erosion rates on the order of 17 cm/Ma. Complex older drifts rest on deglaciated areas above the younger late-Pleistocene glacial drift and below the previously overridden summits. The combination of stable and radionuclide isotopes documents complex exposure histories with substantial periods of burial combined with minimal erosion. The areas below rounded summits were repeatedly exposed and buried by ice from local and outlet glaciers. The exposure ages of the older drift(s) indicate multiple Pleistocene glacial cycles, which did not significantly modify the pre-existing landscape.     

Stress–strain history from the geological evolution of the Orvieto and Radicofani cliff slopes (Italy)

The study proposes geological evolution models for the cliff slopes of the two Italian towns of Orvieto (Umbria) and Radicofani (Tuscany). The models were validated by the use of a stress–strain numerical modelling, implemented by the finite-difference code FLAC 5.0. The numerical modelling was approached in a sequential way, by assuming specific stiffness values related to the evolutionary stages. For this purpose, unconventional laboratory tests were performed aiming at reproducing the stress path related to the geological evolution model, using standard equipment for CID triaxial testing. The geological evolution models infer that deformation in both cases is driven by stress reduction. At the Orvieto plateau, stress reduction is induced by stress relief involving a tuff plate; in the case of Radicofani, stress reduction is due to stress release in consequence of lateral erosion of clay. Numerical simulations refine the lithotechnical zoning of the two investigated slopes, introducing a stress–strain criterion in addition to the conventional geological and geomechanical ones.