Trends of seasonal maximum and minimum temperatures and precipitation in Southern Brazil for the 1913–2006 period

Long-term variations of monthly average maximum and minimum temperature (TMAX and TMIN) and precipitation records in southern Brazil are investigated for the 1913–2006 period. These variations are carefully analyzed for seasonal and annual indices, taken as regional averages. For this purpose, the serial correlation and trend of the indices are investigated using the run and Mann–Kendall tests. The significant trends are obtained from linear least-square fits. The annual and seasonal TMIN indices show significant warming trends with magnitudes (1.7°C per 100 years for annual index) comparable to those reported by the Intergovernmental Panel on Climate Change, but lower than those found for the southern Brazil in another previous work. Regarding the two other variables, the indices show significant trends only for summer, being a cooling trend of 0.6°C per 100 years for the TMAX and an increasing trend of 93 mm per 100 years over an average summer precipitation of 367 mm. Concerning the decadal analysis, the 1920s present the lowest annual, autumn, and spring TMIN and the 1990s, the highest ones. The 1970s is the decade with the lowest summer TMAX, and the 1940s the decade with the highest one. The driest decade is the 1940s and the wettest, the 1980s.     

Anthropogenic "Litter" and macrophyte detritus in the deep Northern Gulf of Mexico

A deep-sea trawl survey of the Northern Gulf of Mexico has documented the abundance and diversity of human-generated litter and natural detrital plant material, from the outer margin of the continental shelf out to the Sigsbee abyssal plain. Plastics were the most frequently encountered type of material. Litter and debris were encountered more frequently in the eastern than in the western GoM. Land-derived plant material was located primarily within the head of the Mississippi Canyon, whereas ocean-derived plant material was spread evenly throughout the NE GoM. Human discards were principally from ships offshore. Some of the material was contained in metal cans that sank to the sea floor, probably in order to conform to international agreements that prohibit disposal of toxic material and plastics. The Mississippi Canyon was a focal point for litter, perhaps due to topography, currents or proximity to shipping lanes.     

Changes in atmospheric circulation and the Arctic Oscillation preserved within a millennial length reconstruction of summer cloud cover from northern Fennoscandia

Cloud cover currently represents the single greatest source of uncertainty in General Circulation Models. Stable carbon isotope ratios (δ¹³C) from tree-rings, in areas of low moisture stress, are likely to be primarily controlled by photosynthetically active radiation (PAR), and therefore should provide a proxy record for cloud cover or sunshine; indeed this association has previously been demonstrated experimentally for Scots pine in Fennoscandia, with sunlight explaining ca 90% of the variance in photosynthesis and temperature only ca 4%. We present a statistically verifiable 1011-year reconstruction of cloud cover from a well replicated, annually-resolved δ¹³C record from Forfjord in coastal northwestern Norway. This reconstruction exhibits considerable variability in cloud cover over the past millennium, including extended sunny periods during the cool seventeenth and eighteenth centuries and warm cloudy periods during the eleventh, early fifteenth and twentieth centuries. We find that while a generally positive relationship persists between sunshine and temperature at high-frequency, at lower (multi-decadal) frequencies the relationship is more often a negative one, with cool periods being sunny (most notably the Little Ice Age period from 1600 to 1750 CE) and warm periods more cloudy (e.g. the mediaeval and the twentieth century). We conclude that these long-term changes may be caused by changes in the dominant circulation mode, likely to be associated with the Arctic Oscillation. There is also strong circumstantial evidence that prolonged periods of high summer cloud cover, with low PAR and probably high precipitation, may be in part responsible for major European famines caused by crop failures.     

Paleoindian bison procurement and paleoenvironments in Middle Park of Colorado

The Upper Twin Mountain Site, located within a geologic slump scar at 2548 m altitude, provides significant information on Paleoindian bison procurement. As the highest known Paleoindian bison bone bed, the site contained the partial skeletal remains of at least 15 adult Late Pleistocene bison (B. antiquus), Goshen projectile points, and debitage. Radiocarbon dates of 10,240±70 and 10,470±50 yr B.P. place Upper Twin Mountain midway between the northern Plains Goshen and southern Plains Plainview sites. With a late fall or early winter mortality of the bison and the presence of only local stone, year round occupation of Middle Park is indicated. Analysis of the geology, soil, and pollen, from the archaeological and nonarchaeological deposits at the Upper Twin Mountain and elsewhere in the region are used to describe the paleoenvironmental conditions in Middle Park. © 1999 John Wiley & Sons, Inc.     

A priori error estimates for the numerical solution of a coupled geomechanics and reservoir flow model with stress-dependent permeability

In this paper we consider the numerical solution of a coupled geomechanics and a stress-sensitive porous media reservoir flow model. We combine mixed finite elements for Darcy flow and Galerkin finite elements for elasticity. This work focuses on deriving convergence results for the numerical solution of this nonlinear partial differential system. We establish convergence with respect to the L ²-norm for the pressure and for the average fluid velocity and with respect to the H ¹-norm for the deformation. Estimates with respect to the L ²-norm for mean stress, which is of special importance since it is used in the computation of permeability for poro-elasticity, can be derived using the estimates in the H ¹-norm for the deformation. We start by deriving error estimates in a continuous-in-time setting. A cut-off operator is introduced in the numerical scheme in order to derive convergence. The spatial grids for the discrete approximations of the pressure and deformation do not need be the same. Theoretical convergence error estimates in a discrete-in-time setting are also derived in the scope of this investigation. A numerical example supports the convergence results.     

Shaking table tests to investigate the influence of various factors on the liquefaction resistance of sands

This paper presents the shaking table studies to investigate the factors that influence the liquefaction resistance of sand. A uniaxial shaking table with a perspex model container was used for the model tests, and saturated sand beds were prepared using wet pluviation method. The models were subjected to horizontal base shaking, and the variation of pore water pressure was measured. Three series of tests varying the acceleration and frequency of base shaking and density of the soil were carried out on sand beds simulating free field condition. Liquefaction was visualized in some model tests, which was also established through pore water pressure ratios. Effective stress was calculated at the point of pore water pressure measurement, and the number of cycles required to liquefy the sand bed were estimated and matched with visual observations. It was observed that there was a gradual variation in pore water pressure with change in base acceleration at a given frequency of shaking. The variation in pore water pressure is not significant for the range of frequency used in the tests. The frequency of base shaking at which the sand starts to liquefy when the sand bed is subjected to any specific base acceleration depends on the density of sand, and it was observed that the sand does not liquefy at any other frequency less than this. A substantial improvement in liquefaction resistance of the sand was observed with the increase in soil density, inferring that soil densification is a simple technique that can be applied to increase the liquefaction resistance.     

Correlations between microbial indicators, pathogens, and environmental factors in a subtropical Estuary

The objective of this study was to evaluate whether indicator microbes and physical–chemical parameters were correlated with pathogens within a tidally influenced Estuary. Measurements included the analysis of physical–chemical parameters (pH, salinity, temperature, and turbidity), measurements of bacterial indicators (enterococci, fecal coliform, Escherichia coli, and total coliform), viral indicators (somatic and MS2 coliphage), viral pathogens (enterovirus by culture), and protozoan pathogens (Cryptosporidium and Giardia). All pathogen results were negative with the exception of one sample which tested positive for culturable reovirus (8.5 MPN/100 L). Notable physical–chemical parameters for this sample included low salinity (<1 ppt) and high water temperature (31 °C). Indicator bacteria and indicator virus levels for this sample were within average values typically measured within the study site and were low in comparison with levels observed in other freshwater environments. Overall results suggest that high levels of bacterial and viral indicators were associated with low salinity sites.