The sediments of Lake Fimon, N-Italy, contain the first continuous archive of the Late Pleistocene environmental and climate history of the southern Alpine foreland. We present here the detailed ...palynological record of the interval between Termination II and the Last Glacial Maximum. The age–depth model is obtained by radiocarbon dating in the uppermost part of the record. Downward, we correlated major forest expansion and contraction events to isotopic events in the Greenland Ice core records, via a stepping-stone approach involving intermediate correlation to isotopic events dated by TIMS U/Th in Alpine and Apennine stalagmites, and to pollen records from marine cores of the Iberian margin. Modelled ages obtained by Bayesian analysis of deposition are thoroughly consistent with actual ages, with maximum offset of ±1700 years. Sharp expansion of broad-leaved temperate forest and of sudden water table rise mark the onset of the Last Interglacial after a treeless steppe phase at the end of penultimate glaciation. This event is actually a two-step process which matches the two-step rise observed in the isotopic record of the nearby Antro del Corchia stalagmite, respectively dated to 132.5
±
2.5 and 129
±
1.5
ka. At the interglacial decline mixed oak forests were replaced by oceanic mixed forests, the latter persisting further for 7
ka till the end of the Eemian succession. Warm-temperate woody species are still abundant at the Eemian end, corroborating a steep gradient between central Europe and the Alpine divide at the inception of the last glacial. After a stadial phase marked by moderate forest decline, a new expansion of warm broad-leaved forests, interrupted by minor events and followed by mixed oceanic forests, can be identified with the north-alpine Saint Germain I. The spread of beech during the oceanic phase is a valuable circumalpine marker. The subsequent stadial–interstadial succession, lacking the telocratic oceanic phase, is also consistent with the evidence at the north-alpine foreland. The Middle Würmian (full glacial) is marked by persistence of mixed forests dominated by conifers but with significant lime and other broad-leaved species. A major Arboreal Pollen decrease is observed at modelled age of 38.7
±
0.5
ka (larch expansion and last occurrence of lime), which has been related to Heinrich Event 4. The evidence of afforestation persisting south of the Alps throughout most of MIS 3 contrasts with a boreal and continental landscape known for the northern alpine foreland, pointing to a sharp rainfall boundary at the Alpine divide and to southern air circulation. This is in agreement with the Alpine paleoglaciological record and is supported by the pressure and rainfall patterns designed by mesoscale paleoclimate simulations. Strenghtening the continental high pressure during the full glacial triggered cyclogenesis in the middle latitude eastern Europe and orographic rainfall in the eastern Alps and the Balkanic mountains, thus allowing forests development at current sea-level altitudes.
The pollen record of the long succession of marine and continental deposits filling the subsident north-Adriatic foredeep basin (NE Italy) documents the history of vegetation, the landscape evolution ...and the climate forcing during the last 215
ka at the south-eastern Alpine foreland. The chronology relies on several
14C determinations as well as on estimated ages of pollen-stratigraphical and sea-level event tie-points derived from comparison with high-resolution marine records, speleothemes and ice cores.
Mixed temperate rainforests persisted throughout MIS 7a–7c, being replaced by conifer forests after the local glacioeustatic regression during early MIS 6. The Alpine piedmont facing the Adriatic foredeeep was glaciated at the culmination of the penultimate glaciation, as directly testified by in situ fluvioglacial aggradation related to the building of a large morainic amphitheatre. The pollen record allows correlation with other European records and with the IRD from N-Atlantic and off Iberia, thus the duration of the penultimate glacial culmination at the southalpine fringe is estimated less than 13
ka between 148
±
1 and >135
ka. The site was not reached by the Last Interglacial maximum sea transgression and enregistered a typical, though incomplete, Eemian forest record, lacking Mediterranean evergreen trees. A complex sequence of stadial–interstadial episodes is reconstructed during the Early and Middle Würm: major xerophyte peaks match IRD maxima occurred during Heinrich events in deep-sea cores offshore Iberia and in the N-Atlantic and allows to frame lumps of interstadial phases, marked by
Picea peaks, each one including several DO warm events. Broad-leaved thermophilous forests disappeared from the north-eastern plain of Italy at the end of the Early Würm, whereas reduced populations of
Abies and
Fagus probably sheltered even during the Last Glacial Maximum. A renewed fluvioglacial in situ deposition between 30.4
±
0.4 and 21.6
±
0.5
ka
cal
BP sets the time and duration of the last glacial culmination in the pedemontane morainic amphitheatre. Palynomorphs from Plio-Pleistocene marine successions were reworked by glacier erosion and deposited in the lowland during both the penultimate and the last deglaciation phases. This explains a bias affecting previous pollen records from the region.
We present a paleoenvironmental reconstruction for the mountain fringe between the South-Eastern Alps and the Northern Dinarides (NE-Italy/W-Slovenia) during the Last Glacial Maximum. We focused on a ...new sedimentary and paleoecological archive spanning the LGM acme, located in an aggrading, permanently flooded and ponded plain, dammed by an active fluvioglacial megafan. The ecosystem reconstruction, based on two high resolution pollen records, is supported by a rich plant macrofossil flora and constrained by a robust radiocarbon chronology between 26 and 22calka BP. We show evidence for persistence of boreal trees and of different open boreal forest types throughout the LGM at the south-eastern mountain fringe of the Alps and the Northern Dinarides. Fire frequency is responsible for high, oscillating forest openness. The paleobotanical record is discussed in the light of the ecogeographic diversity of the region. A belt formed by Swiss stone pine, larch and dwarf mountain pine on limestone bedrock, and accompanied by Spruce in the floodplain, extended uphill, while proximal outwash plain supported Scots pine and dwarf mountain pine. These differences arise from groundwater regimes rather than from local climate variability. A steep moisture gradient from the semiarid pedoclimatic regime prevailing in the Adriatic alluvial plain to the forested mountain fringe is related to the orographic rainout triggered by southern air circulation. Mesophytic broad-leaved forest trees did not withstand the LGM temperature extremes in zonal ecosystems at the Alpine–Dinaric fringe; however, the fossil evidence suggests a number of microrefugia in karstic and thermal spring habitats of the northern Adriatic.
•Paleoenvironmental reconstruction at Alps–Dinarides fringe during the Last Glacial Maximum•Relationships between regional geological frame, sedimentary environments, and forest history•Persistence of trees and of different types of open boreal forest throughout the LGM
In this paper, the ensembles of repeat multiple- accumulate codes (RAm), which are obtained by interconnecting a repeater with a cascade of m accumulate codes through uniform random interleavers, are ...analyzed. It is proved that the average spectral shapes of these code ensembles are equal to 0 below a threshold distance epsiv m and, moreover, they form a nonincreasing sequence in m converging uniformly to the maximum between the average spectral shape of the linear random ensemble and 0. Consequently the sequence epsiv m converges to the Gilbert-Varshamov (GV) distance. A further analysis allows to conclude that if m ges 2 the RA m are asymptotically good and that epsiv m is the typical normalized minimum distance when the interleaver length goes to infinity. Combining the two results it is possible to conclude that the typical distance of the ensembles RA m converges to the Gilbert-Varshamov bound.
Iterative shrinkage-thresholding algorithms provide simple methods to recover sparse signals from compressed measurements. In this paper, we propose a new class of iterative shrinkage-thresholding ...algorithms which preserve the computational simplicity and improve iterative estimation by incorporating a soft support detection. Indeed, at each iteration, by learning the components that are likely to be nonzero from the current signal estimation using Bayesian techniques, the shrinkage-thresholding step is adaptively tuned and optimized. Unlike other adaptive methods, we are able to prove, under suitable conditions, the convergence of the proposed methods. Moreover, we show through numerical experiments that the proposed methods outperform classical shrinkage-thresholding in terms of rate of convergence and of sparsity-undersampling tradeoff.
In this paper, we analyze a new class of iterative re-weighted least squares (IRLS) algorithms and their effectiveness in signal recovery from incomplete and inaccurate linear measurements. These ...methods can be interpreted as the constrained maximum likelihood estimation under a two-state Gaussian scale mixture assumption on the signal. We show that this class of algorithms, which performs exact recovery in noiseless scenarios under suitable assumptions, is robust even in presence of noise. Moreover these methods outperform classical IRLS for ℓ τ -minimization with τ ∈ (0; 1 in terms of accuracy and rate of convergence.
In this paper, we propose a method for estimating the sparsity of a signal from its noisy linear projections without recovering it. The method exploits the property that linear projections acquired ...using a sparse sensing matrix are distributed according to a mixture distribution whose parameters depend on the signal sparsity. Due to the complexity of the exact mixture model, we introduce an approximate two-component Gaussian mixture model whose parameters can be estimated via expectation-maximization techniques. We demonstrate that the above model is accurate in the large system limit for a proper choice of the sensing matrix sparsifying parameter. Moreover, experimental results demonstrate that the method is robust under different signal-to-noise ratios and outperforms existing sparsity estimation techniques.
The late Quaternary history of fossil spruces in southern Europe (
Picea abies (L.) Karsten and
Picea omorika (Pancic) Purkyne) is based on 163 selected pollen, charcoal and macrofossil records. The ...timing of immigration of
P. abies is estimated from data where the
Picea curve passed the threshold value of 4%.
P. abies occupied the southern European mountain ranges – excluding the Pyrenees – during the middle part of the last interglacial. Spruce reached its late Quaternary maximum expansion during the early Weichselian, after which it retired from central Europe and expanded in southern Europe during the middle Weichselian interstadials. A general decline in geographical distribution occurred during the last glacial maximum, and populations were most restricted during the Alpine deglaciation. The concept of ‘glacial refugia’ does not apply to residual populations because current climatic reconstructions relate periods of maximum spruce decline to maximum continental dryness during the growth season, rather than to full glacial conditions. Spruce took part in late glacial and early Holocene tree expansions in the eastern Alps and Carpathian, but failed to spread from residual populations in the Apennines and the Pirin–Rila–Rhodopes Mountains. These differences are explained by the influence of oceanic air masses on upper forest belts with relation to geographic location and maximum elevation of mountain ranges. Late glacial spruce expansion in the Alps coincides with the abrupt warming at 14 700–14 500 yr cal BP. High migration rates were reached in the upper forest belts (e.g. 1500–2300 masl) during the early Holocene, and decreased since about 6 kyr cal BP, as a result of climatic cooling during the Neoglaciation (treeline depression), ecological competition with other tree species (
Abies alba), climatic and physical setting of the highest ranges in western Alps, and human impact. The long late Quaternary fossil history of presently isolated spruce stands from the Apennines accounts for their state of genetic differentiation, which could not be fully understood from the shorter time interval of postglacial events.
A previously unrecognised complex of deep-seated gravitational slope deformations (DSGSD) extends 20 km along upper Venosta Valley in the eastern Alps, Italy. Mt. Watles exhibits spectacular features ...indicative of DSGSDs including double ridges, trenches, and counterscarps. The slope deformation occurs along a nappe boundary now corresponding to the Schlinig normal fault, is also conditioned by recent faults marked by shallow earthquakes, and shows glacial/paraglacial controls on slope evolution.
The Mt. Watles DSGSD is a complex, deep-seated, compound slide along a basal shear zone, involving the Schlinig fault. Gravitational reactivation of NE-trending fractures formed gravitational scarps, counterscarps, and half-grabens in the upper slope, whereas the lower part of the slope partially collapsed. Although our work indicates the importance of the Schlinig fault and recent fracturing on slope failure, the trigger seems to be postglacial debuttressing of the valley walls. Radiocarbon dating of peat deposits within one of the major counterscarps indicates that slope deformation started during the Lateglacial period and continued during the Holocene in several slope sectors.
The $ell _{0}/ell _{1}$ -regularized least-squares approach is used to deal with linear inverse problems under sparsity constraints, which arise in mathematical and engineering fields. In particular, ...multiagent models have recently emerged in this context to describe diverse kinds of networked systems, ranging from medical databases to wireless sensor networks. In this paper, we study methods for solving $ell _{0}/ell _{1}$ -regularized least-squares problems in such multiagent systems. We propose a novel class of distributed protocols based on iterative thresholding and input driven consensus techniques, which are well-suited to work in-network when the communication to a central processing unit is not allowed. Estimation is performed by the agents themselves, which typically consist of devices with limited computational capabilities. This motivates us to develop low-complexity and low-memory algorithms that are feasible in real applications. Our main result is a rigorous proof of the convergence of these methods in regular networks. We introduce a suitable distributed, regularized, least-squares functional, and we prove that our algorithms reach their minima using results from dynamical systems theory. Furthermore, we propose numerical comparisons with the alternating direction method of multipliers and the distributed subgradient methods, in terms of performance, complexity, and memory usage. We conclude that our techniques are preferable for their good memory-accuracy tradeoff.
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