A pollen-based record of late glacial–Holocene climatic variability in the southern lake district, Chile

A pollen record from Puyehue area (40°S; 72°W) in the southern Lake District, Chile, indicates that prior to 13,410 ¹⁴C yr BP (ca. 16,500–15,200 cal yr BP), cold resistant and hygrophilous vegetation, particularly Nothofagus forest and myricaceous vegetation, covered the area. From ca. 15,000 cal yr BP onward, the forest became increasingly dense. Between 10,010 and 7450 ¹⁴C yr BP (ca. 11,000–8000 cal yr BP), the expansion of Nothofagus obliqua and the spread of grasses suggests the climate became warmer and semi-arid. Lowland deciduous forest (Nothofagus obliqua, Aextoxicon punctatum, Laurelia sempervirens) and Valdivian rainforest (Nothofagus dombeyi, Eucryphia cordifolia, Caldcluvia paniculata, Aextoxicon punctatum, Laureliopsis philippiana) were abundant. During the next two thousand years, stable warm climatic conditions prevailed, and the diversity of the vegetation increased. From 5760 to 1040 ¹⁴C yr BP (ca. 6500–900 cal yr BP), the North Patagonian rainforest expanded. The presence of Pilgerodendron/Fitzroya, together with Nothofagus forest, suggests that humid conditions prevailed. During the last millennium, human impact intensified and regional vegetation was disturbed, particularly the lowland deciduous forest and Valdivian rainforest. North-Patagonian and subantartic taxa, such as Podocarpus nubigena, Pilgerodendron/Fitzroya, Nothofagus dombeyi type, Austrocedrus chilensis and Drimys winteri, occupied the low and high-altitude parts of the Cordillera. Five hundred years ago, shrub and grasses expanded in the Nothofagus forest, suggesting that forest became more open under cool–cold, and humid climatic conditions. These conditions prevail to the present day. This is the fourth in a series of eight papers published in this special issue dedicated to the 17,900 year multi-proxy lacustrine record of Lago Puyehue, Chilean Lake District. The papers in this special issue were collected by M. De Batist, N. Fagel, M.-F. Loutre and E. Chapron.     

Landscape evolution and origin of Lake Fúquene (Colombia): Tectonics, erosion and sedimentation processes during the Pleistocene

The Basin of Ubaté–Chichinquirá (5°28′N, 73°45′ W, c. 2580 m altitude) includes the Fúquene Valley and is located in the central part of the Eastern Cordillera of Colombia. Rocks and sediments were folded and faulted during the Miocene, uplifted during the (late) Pliocene, and affected by glaciers during the Pleistocene. Successive glacial and interglacial periods left significant marks in the landscape which were used to reconstruct six stages in the development of the landscape along a relative chronology. During early Pleistocene episode 1 glaciers formed U-shape valleys. Evidence of the impact of ice sheets has been found as far downslope as ca. 2900 m elevation. During episode 2 moraines developed which were cut by the present San José River. During episode 3 abundant sediment was produced by glacial erosion. It accentuated the sculpturing of hard rock and deepening of the drainage basin. The ancestral Ubaté–Suarez River constituted a dynamic erosive system that gave rise to deep V-shaped valleys and progressively formed a set of intricate valleys with a high sediment production. Finally, intense glacial and fluvio-glacial erosion led to a geomorphological system with high energy levels and intensive sediment transport leading to wide valleys. During episode 4 the Ubaté–Suarez River eroded and deepened its valley until it captured the old El Hato–San José Valley. It caused intense erosion of the moraine and the fluvio-glacial gravels. Deep V-shaped valleys stabilized in the high areas of the main drainage system and these valleys form the present-day fluvial sub-basins. During episode 5 the deep valley in the northern part of the Basin of Ubaté–Chichinquirá developed. During middle Pleistocene episode 6 colluvial sediments formed the Saboya dam and a lake was formed in the river valley of which the present Lake Fúquene is only a small remnant. Lithological changes indicate fluctuating water levels and Lake Fúquene must have expanded periodically up to an area 5 to 10 times the present-day surface.     

Variability of Freezing Levels, Melting Season Indicators, and Snow Cover for Selected High-Elevation and Continental Regions in the Last 50 Years

We have used NCEP/NCAR Reanalysis data and a Northern Hemisphere snow cover data set to analyze changes in freezing level heights and snow cover for the past three to five decades. All the major continental mountain chains exhibit upward shifts in the height of the freezing level surface. The pattern of these changes is generally consistent with changes in snow cover, both over the course of the year and spatially. We examined different free-air temperature parameters (dry bulb temperature, virtual temperature, and 700–500 hPa thickness) using the Reanalysis grid point valueslocated over the different mountain areas as defined in this study. The different trend values were in reasonably good agreement with each other, particularly over the second half of the record.Freezing level changes in the American Cordillera are strongly modulated by the El Niño/Southern Oscillation (ENSO) phenomenon and the freezing level heights (FLH) respond to both interannual and decadal-scale change in tropical Pacific sea surface temperature (SST). The 0.5 °C increase in SST recorded in the tropical Pacific since the 1950s accounts for approximately half of the increase in FLH in tropical and subtropical latitudes of the Cordilleran region during that same time.     

Plio-Quaternary megasequence geometry and its tectonic controls within the Maghrebian thrust belt of south-central Sicily

Sequence stratigraphy in marine foredeep and thrust-top basins is controlled by the conventional variations in eustatic sea-level and sedimentation rate together with tectonics. Vertical motions reflect combinations of subsidence due to regional flexure and uplift on local thrust anticlines which act to modify the volume and shape of accommodation space together with syn-depositional slopes. Plio-Pleistocene successions on Sicily were deposited in thrust-top and foredeep basins, above and ahead of evolving structures of the Maghrebian fold and thrust belt. Collectively the sediments represent a single megasequence defined at its base by a maximum flooding surface of earliest Pliocene age following reconnection with global sea-level at the end of the Messinian. The internal stratigraphy of this megasequence consists of Trubi chalks, blue marls and a coastal calcarenite package with subordinate silciclastic sand. Plankton biostratigraphy allows these facies to be placed in a chronostratigraphic framework. Regionally the upper assemblage progrades away from the orogenic hinterland, recording a tectonically forced regression in response to regional uplift from late Pliocene times. This uplift may be associated with isostatic unloading in the orogenic hinterland due to tectonic collapse of the more internal thrust sheets. Prior to this, flexure from orogenic loading is inferred to have been sufficient for regional subsidence locally to outstrip uplift associated with the growth of some thrust structures. For shallow-water facies the competition between thrust-related uplift and flexural subsidence can be investigated from the stacking patterns of parasequence sets. For structures developed at greater palaeobathymetries receiving fine-grained pelagic sediment, active tectonics may be recognized from depositional hiatuses.     

Transport parameters identification: application of the Sentinel method

In this paper, the Sentinel method is applied to groundwater pollution parameter identification. First, the inverse problem is solved in the linear case to estimate pollutant mass flow rates. Then, the non-linear case, which is the determination of the pollutant source coordinates, is developed. Finally, numerical tests, conducted on the Rhenan aquifer, south of Strasbourg, are presented. This revised version was published online in July 2006 with corrections to the Cover Date.     

Search for Transits of a Short-Period, Sub-Saturn Extrasolar Planet Orbiting HD 46375

Precise brightness measurements of HD 46375 have been acquired with an automatic telescope to search for transits of its short-period, sub-Saturn extrasolar planet. Transits of the companion do not occur, indicating that the inclination of the orbit i is less than 83 degrees and sini is less than 0.992. This upper limit on sini still preserves the possibility that the mass of the planet is less than Saturn's. Analysis of the photometry for HD 46375 reveals no photometric variability larger than 0.0001+/-0.0002 mag at the orbital period of the planet. This effectively eliminates starspots and stellar pulsations as the cause of the radial velocity variations used to infer the planet's existence.