MELTWATER FLUXES AT AN ARCTIC FOREST-TUNDRA SITE

Models of surface energy balance and snow metamorphism are utilized to predict the energy and meltwater fluxes at an Arctic site in the forest–tundra transition zone of north-western Canada. The surface energy balance during the melt period is modelled using an hourly bulk aerodynamic approach. Once a snowcover becomes patchy, advection from the bare patches to the snow-covered areas results in a large spatial variation in basin snowmelt. In order to illustrate the importance of small-scale, horizontal advection, a simple parameterization scheme using sensible heat fluxes from snow free areas was tested. This scheme estimates the maximum horizontal advection of sensible heat from the bare patches to the snow-covered areas. Calculated melt was routed through the measured snowcover in each landscape type using a variable flow path, meltwater percolation model. This allowed the determination of the spatial variability in the timing and magnitude of meltwater release for runoff. Model results indicate that the initial release of meltwater first occurred on the shallow upland tundra sites, but meltwater release did not occur until nearly two weeks later on the deep drift snowcovers. During these early periods of melt, not all meltwater is available for runoff. Instead, there is a period when some snowpacks are only partially contributing to runoff, and the spatial variation of runoff contribution corresponds to landscape type. Comparisons of melt with and without advection suggests that advection is an important process controlling the timing of basin snowmelt.     

Sources of dissolved REE in mountainous streams draining granitic rocks, Sierras Pampeanas (Córdoba, Argentina)

Stream waters draining granitic terrains from the highest part (850 to 2200 m a.s.l.) of Sierras Pampeanas (Córdoba, Argentina, ∼32°S, ∼65°W) were sampled in order to define sources and distribution of dissolved rare earth elements (REE), and to describe the geochemical processes that govern their mobility. The contribution of the regional granite to the dissolved REE pool in stream water is limited due to the physical conditions predominating in the area (i.e., steep slopes and semiarid climate). Therefore, precipitation is considered a seasonally significant source controlling REE concentration in stream water. Dissolved REE concentrations are inversely correlated with monthly precipitation and rainfall frequency. During the rainy season (i.e., the austral summer) REE concentrations in stream water are lower than during the dry season (i.e., austral winter). Such low concentrations reflect the balance between the REE input from precipitation and their removal by adsorption. In contrast, during the dry season, the longer residence time of water within fractures and colluvium determines an increased REE concentration in the base flow. Lower pH values also contribute to raise REE concentration through desorption from mineral surfaces.     

On the Occurrence of Zellia from the Maping Limestone of Chengkung, Central Yunnan

INTRODUCTIONThe specimens described in the present paper were collected in 1939 by the late Mr. T. Y. Hsu and Mr. C. S. Pien from the Maping limestone exposed E of Tuikoshan, Chengkung district, Central Yunnan. All specimens belong to Zellia, a subgenus of Pseudoschwagerina; three forms may be referred to known subspecies while two are new.     

Observational study of the seasonality of the submonthly and intraseasonal signal over the tropics

Summary Atmospheric variability in outgoing long-wave radiation (OLR) and tropospheric relative vorticity (VOR) over the South American region was studied from 1979 to 1996 using the complex Morlet wavelet function. The analyses focus on spatial variation in intraseasonal and submonthly scales. Scalograms were used to measure submonthly intraseasonal oscillations in convection, which were found to be predominant in the tropical regions. However, 7-day and 15-day oscillations were observed at tropical and extratropical latitudes in spring and winter, indicating that transient disturbances play a more prominent role. Regarding VOR, tropical energy intensities were highest in the spring and summer, whereas subtropical and extratropical energy intensities were highest in the autumn and winter. The dynamics of the 25-day and 45-day VOR oscillations indicates a possible correlation with Rossby waves over the eastern tropical Pacific Ocean, mainly during the summer. During winter, the 7-day and 15-day VOR oscillations are more frequent at higher latitudes and are enhanced along storm tracks. It was also observed that convection amplitudes in the regions of maximum intensity change appreciably from year to year and from season to season, showing that the behavior of the submonthly and intraseasonal oscillations is nonperiodic and correlates strongly with El Ni?o/Southern Oscillation years. These results confirm the efficiency of wavelet analysis for time-scale studies of atmospheric variability.     

Sedimentological analysis of two drill cores through the crater moat‐filling breccia,Flynn Creek impact structure,Tennessee

Sedimentological (line‐logging) analysis of two drill cores, FC77‐3 and FC67‐3, situated, respectively, in the northwestern and southeastern quadrants of the Flynn Creek impact structure's crater‐moat area reveals that the ~27 m thick crater moat‐filling breccia consists of three subequal parts. These parts, which were deposited during early modification stage of this marine‐target impact structure, are distinguished on the basis of vertical trends in sorting, grain size, and counts of clasts per meter in comparison with other well‐known marine‐target impact structures, namely Lockne, Tvären, and Chesapeake Bay. The lower part is interpreted to represent mainly slump deposits, and the middle part is interpreted to represent a stage intermediate between slump and marine resurge, that is, a traction flow driven by overriding suspension flow. The upper part (size graded, and relatively well sorted and fine grained) is interpreted to represent marine resurge flow only. The upper part is capped by a relatively thin and relatively fine‐grained calcarenite to calcisiltite deposit.     

Oxygen and hydrogen isotope fractionation in serpentine-water and talc-water systems from 250 to 450 °C, 50 MPa

Oxygen and hydrogen isotope fractionation factors in the talc-water and serpentine-water systems have been determined by laboratory experiment from 250 to 450 °C at 50 MPa using the partial exchange technique. Talc was synthesized from brucite + quartz, resulting in nearly 100% exchange during reaction at 350 and 450 °C. For serpentine, D-H exchange was much more rapid than ¹⁸O-¹⁶O exchange when natural chrysotile fibers were employed in the initial charge. In experiments with lizardite as the starting charge, recrystallization to chrysotile enhanced the rate of ¹⁸O-¹⁶O exchange with the coexisting aqueous phase. Oxygen isotope fractionation factors in both the talc-water and serpentine-water systems decrease with increasing temperature and can be described from 250 to 450 °C by the relationships: 1000 ln  = 11.70 × 10⁶/T² − 25.49 × 10³/T + 12.48 and 1000 ln  = 3.49 × 10⁶/T² − 9.48 where T is temperature in Kelvin. Over the same temperature interval at 50 MPa, talc-water D-H fractionation is only weakly dependent on temperature, similar to brucite and chlorite, and can be described by the equation: 1000 ln = 10.88 × 10⁶/T² − 41.52 × 10³/T + 5.61 where T is temperature in Kelvin. Our D-H serpentine-water fractionation factors calibrated by experiment decrease with temperature and form a consistent trend with fractionation factors derived from lower temperature field calibrations. By regression of these data, we have refined and extended the D-H fractionation curve from 25 to 450 °C, 50 MPa as follows: 1000 ln  = 3.436 × 10⁶/T² − 34.736 × 10³/T + 21.67 where T is temperature in Kelvin. These new data should improve the application of D-H and ¹⁸O-¹⁶O isotopes to constrain the temperature and origin of hydrothermal fluids responsible for serpentine formation in a variety of geologic settings.