Pollen‐based biome reconstructions for Colombia at 3000, 6000, 9000, 12 000, 15 000 and 18 000 14C yr ago: Late Quaternary tropical vegetation dynamics

Colombian biomes are reconstructed at 45 sites from the modern period extending to the Last Glacial Maximum (LGM). The basis for our reconstruction is pollen data assigned to plant functional types and biomes at six 3000‐yr intervals. A reconstruction of modern biomes is used to check the treatment of the modern pollen data set against a map of potential vegetation. This allows the biomes reconstructed at past periods to be assessed relative to the modern situation. This process also provides a check on the a priori assignment of pollen taxa to plant functional types and biomes. For the majority of the sites, the pollen data accurately reflect the potential vegetation, even though much of the original vegetation has been transformed by agricultural practices. At 18 000 ¹⁴C yr BP, a generally cool and dry environment is reflected in biome, assignments of cold mixed forests, cool evergreen forests and cool grassland–shrub; the latter extending to lower altitudes than presently recorded. This signal is strongly recorded at 15 000 and 12 000 ¹⁴C yr BP, the vegetation at these times also reflecting a relatively cool and dry environment. At 9000 ¹⁴C yr BP there is a shift to biomes thought to result from slightly cooler environmental conditions. This trend is reversed by 6000 ¹⁴C yr BP; most sites, within a range of different environmental settings, recording a shift to more xeric biome types. There is an expansion of steppe and cool mixed‐forest biomes, replacing tropical dry forest and cool grassland–shrub biomes, respectively. These changes in biome assignments from the modern situation can be interpreted as a biotic response to mid‐Holocene climatic aridity. At 3000 ¹⁴C yr BP the shift is mainly to biomes characteristic of slightly more mesic environmental conditions. There are a number of sites that do not change biome assignment relative to the modern reconstruction, although the affinities that these sites have to a specific biome do change. These ‘anomalies’ are interpreted on a site‐by‐site basis. Spatially constant, but differential response of the vegetation to climatic shifts are related to changes in moisture sources and the importance of edaphic controls on the vegetation. The Late Quaternary reconstruction of large‐scale vegetation dynamics in Colombia allows an understanding of the environmental controls on these to be developed. In particular, shifts in the character of the main climatic systems that influence Colombian vegetation are described. Copyright © 2002 John Wiley & Sons, Ltd.     

A Collimated Stellar Wind Emanating from a Massive Protostar

We report multi-wavelength observations towards IRAS 16547–4247, a luminous infrared source with a bolometric luminosity of 6.2 × 10⁴ L _⊙. Dust continuum observations at 1.2-mm indicate that this object is associated with a dust cloud with a size of about 0.4 pc in diameter and a mass of about 1.3 × 10³ M _⊙. Radio continuum observations show the presence of a triple radio source consisting of a compact central object and two outer lobes, separated by about 0.3 pc, symmetrically located from the central source. Molecular hydrogen line observations show a chain of knots that trace a collimated flow extending over 1.5 pc. We suggest that IRAS 16547–4247 corresponds to a dense massive core which hosts near its central region a high-mass star in an early stage of evolution. This massive YSO is undergoing the ejection of a collimated stellar wind which drives the H₂ flow. The radio emission from the lobes arises in shocks resulting from the interaction of the collimated wind with the surrounding medium. We conclude that the thermal jets found in the formation of low-mass stars are also produced in high-mass stars.     

Parameter estimation in semi‐distributed hydrological catchment modelling using a multi‐criteria objective function

Output generated by hydrologic simulation models is traditionally calibrated and validated using split‐samples of observed time series of total water flow, measured at the drainage outlet of the river basin. Although this approach might yield an optimal set of model parameters, capable of reproducing the total flow, it has been observed that the flow components making up the total flow are often poorly reproduced. Previous research suggests that notwithstanding the underlying physical processes are often poorly mimicked through calibration of a set of parameters hydrologic models most of the time acceptably estimates the total flow. The objective of this study was to calibrate and validate a computer‐based hydrologic model with respect to the total and slow flow. The quick flow component used in this study was taken as the difference between the total and slow flow. Model calibrations were pursued on the basis of comparing the simulated output with the observed total and slow flow using qualitative (graphical) assessments and quantitative (statistical) indicators. The study was conducted using the Soil and Water Assessment Tool (SWAT) model and a 10‐year historical record (1986–1995) of the daily flow components of the Grote Nete River basin (Belgium). The data of the period 1986–1989 were used for model calibration and data of the period 1990–1995 for model validation. The predicted daily average total flow matched the observed values with a Nash–Sutcliff coefficient of 0·67 during calibration and 0·66 during validation. The Nash–Sutcliff coefficient for slow flow was 0·72 during calibration and 0·61 during validation. Analysis of high and low flows indicated that the model is unbiased. A sensitivity analysis revealed that for the modelling of the daily total flow, accurate estimation of all 10 calibration parameters in the SWAT model is justified, while for the slow flow processes only 4 out of the set of 10 parameters were identified as most sensitive. Copyright © 2007 John Wiley & Sons, Ltd.     

Relationships between deformation and mixing processes in lava flows: a case study from Salina (Aeolian Islands,Tyrrhenian Sea)

 The massive unit of a lava flow from Porri volcano (Salina, Aeolian Islands) displays many unusual structures related to the physical interaction between two different magmas. The magma A represents approximately 80% of the exposed lava surface; it has a crystal content of 51 vol.% and a dacitic glass composition (SiO₂=63–64 wt.%). The magma B has a basaltic-andesite glass composition (SiO₂=54–55 wt.%) and a crystal content of approximately 18 vol.%. It occurs as pillow-like enclaves, banding, boudin-like and rolling structures which are hosted in magma A. Structural analysis suggests that banding and boudin-like structures are the result of the deformation of enclaves at different shear strain. The linear correlation between strain and stratigraphic height of the measured elements indicates a single mode of deformation. We deduce that the component B deformed according to a simple shear model. Glass analyses of the A–B boundary indicate that A and B liquids mix together at high shear strain, whereas only mingling occurs at low shear strain. This suggests that the amount of deformation (i.e. forced convection) plays an important role in the formation of hybrid magmas. High shear strain may induce stretching, shearing and rolling of fluids which promote both forced convection and dynamical diffusion processes. These processes allow mixing of magmas with large differences in their physical properties. Received: 15 July 1995 / Accepted: 30 May 1996     

Mars mesospheric zonal wind around northern spring equinox from infrared heterodyne observations of CO2

We present direct observations of Mars zonal wind velocities around northern spring equinox (L_S = 336°, L_S = 355°, L_S = 42°) during martian year 27 and 29. Data was acquired by means of infrared heterodyne spectroscopy of CO₂ features at 959.3917 cm^?1 (10.4232 μm) and 957.8005 cm^?1 (10.4405 μm) using the Cologne Tuneable Heterodyne Infrared Spectrometer (THIS) at the McMath–Pierce telescope of the National Solar Observatory on Kitt Peak in Arizona and the NASA Infrared Telescope Facility on Mauna Kea, Hawaii between 2005 and 2008. Winds were measured on the dayside of Mars with an unprecedented spatial resolution allowing sampling of up to nine independent latitudes over the martian disk. Retrieved wind velocities depend strongly on latitude and season with values ranging from 180 m/s prograde to ?94 m/s retrograde. A comparison of the observational results to predicted values from the Mars Climate Database yield a reasonable agreement between modeling and observation.     

Comparison of HIPWAC and Mars Express SPICAM observations of ozone on Mars 2006-2008 and variation from 1993 IRHS observations

Ozone is a tracer of photochemistry in the atmosphere of Mars and an observable used to test predictions of photochemical models. We present a comparison of retrieved ozone abundances on Mars using ground-based infrared heterodyne measurements by NASA Goddard Space Flight Center’s Heterodyne Instrument for Planetary Wind And Composition (HIPWAC) and space-based Mars Express Spectroscopy for the Investigation of the Characteristics of the Atmosphere of Mars (SPICAM) ultraviolet measurements. Ozone retrievals from simultaneous measurements in February 2008 were very consistent (0.8 μm-atm), as were measurements made close in time (ranging from <1 to >8 μm-atm) during this period and during opportunities in October 2006 and February 2007. The consistency of retrievals from the two different observational techniques supports combining the measurements for testing photochemistry-coupled general circulation models and for investigating variability over the long-term between spacecraft missions. Quantitative comparison with ground-based measurements by NASA/GSFC’s Infrared Heterodyne Spectrometer (IRHS) in 1993 reveals 2-4 times more ozone at low latitudes than in 2008 at the same season, and such variability was not evident over the shorter period of the Mars Express mission. This variability may be due to cloud activity.     

Continental climate in the East Siberian Arctic during the last interglacial: Implications from palaeobotanical records

To evaluate the consequences of possible future climate changes and to identify the main climate drivers in high latitudes, the vegetation and climate in the East Siberian Arctic during the last interglacial are reconstructed and compared with Holocene conditions. Plant macrofossils from permafrost deposits on Bol'shoy Lyakhovsky Island, New Siberian Archipelago, in the Russian Arctic revealed the existence of a shrubland dominated by Duschekia fruticosa, Betula nana and Ledum palustre and interspersed with lakes and grasslands during the last interglacial. The reconstructed vegetation differs fundamentally from the high arctic tundra that exists in this region today, but resembles an open variant of subarctic shrub tundra as occurring near the tree line about 350 km southwest of the study site. Such difference in the plant cover implies that, during the last interglacial, the mean summer temperature was considerably higher, the growing season was longer, and soils outside the range of thermokarst depressions were drier than today. Our pollen-based climatic reconstruction suggests a mean temperature of the warmest month (MTWA) range of 9–14.5 °C during the warmest interval of the last interglacial. The reconstruction from plant macrofossils, representing more local environments, reached MTWA values above 12.5 °C in contrast to today's 2.8 °C. We explain this contrast in summer temperature and soil moisture with a combination of summer insolation higher than present and climatic continentality in arctic Yakutia stronger than present as result of a considerably less inundated Laptev Shelf during the last interglacial.     

Uncertainty quantification in the calibration of a dynamic viscoplastic model of slow slope movements

Most landslides occurring in Italy consist of shallow-translational movements, which involve fine, essentially clayey material. They are usually characterized by low velocities, typically of few centimeters per year. The main triggering factor is hydrologic, since movements are usually strictly connected to groundwater level fluctuations. This slow and periodical trend can be interpreted by a viscous soil response, and in order to catch the actual kinematics of the soil mass behavior, a dynamic analysis should be adopted. This paper discusses the case of the Alverà mudslide, located in the Northern Alps (Italy), for which a very detailed and almost 9-year-long monitoring database, including displacements and groundwater levels records, is available. A well-defined dynamic viscoplastic model, capable of returning a displacement prediction and a mobilized shear strength angle estimate from a groundwater level input, was considered. A first deterministic calibration proved the ability of the model to reproduce the mudslide overall displacements trend if a suitable reduction of the mobilized angle _0\varphi ^{\prime }_{0} is allowed. Then, an uncertainty quantification analysis was performed by measuring the model parameters variability, and all parameters could be represented using a probability density function and a correlation structure. As a consequence, it was possible to define a degree of uncertainty for model predictions, so that an assessment of the model reliability was obtained. The final outcome is believed to represent an important advancement in relation to hazard assessment and for future landslide risk management.     

Seasonal temperatures over Italy and their relationship with low-frequency atmospheric circulation patterns

An analysis of Italian seasonal temperatures from 1961 to 2006 was carried out, using homogenized data from 49 synoptic stations well distributed throughout Italy. The results show remarkable differences among seasons. Stationarity characterizes winter series, except for Northern Italy (where a warming trend from 1961 is identified); a positive trend over the entire period is recognized for spring series. Summer series are marked by a negative trend until 1981 and by a positive trend afterwards; finally, autumn series show a warming starting from 1970. The relationship between seasonal temperatures and four teleconnection patterns (North Atlantic Oscillation, East Atlantic Pattern, Scandinavian Pattern and Arctic Oscillation) influencing European climate was investigated through Spearman rank correlation and composites. Among the results, the strong linear correlation with the East Atlantic Pattern in all seasons but autumn is remarkable; moreover, the explained variance varies between 31.9% and 50.4% (leaving out autumn). Besides these four atmospheric patterns the role of other factors (e.g. soil moisture) is not dealt with, but their importance and the need for more investigation is pointed out.