Spectroscopic evidence for two achondrite parent bodies: asteroids 349 Dembowska and 4 Vesta

A Fourier spectrometer was used to obtain IR spectra of asteroids 349 Dembowska and 4 Vesta (0.8–2.5μm; 25cm ^?1 resolution). The spectrum of Dembowska shows olivine and pyroxene (Fs_{24 ± 8}) with an olivine/pyroxene abundance ratio greater than 2, and possibly as high as 10. This is probably an unsampled achondritic composition, similar to the unique achondrite ALHA 77005. Similar olivine-rich compositions have also been proposed for the mantles of basaltic achondrite parent bodies. Dembowska's mineralogy therefore appears related in some way to the achondrites. but a direct link cannot as yet be made. Our IR observations of Vesta have more complete spectral coverage than those first obtained by Larson and Fink (1975b). Pyroxene (Fs_{50 ± 5}) and plagioclase feldspar are both seen, with a pyroxene/feldspar abundance ratio between 1.5 and 2.0. Vesta's mineralogy is consistent with a mixture of eucrites and howardites on its surface. Time-resolved observations over one-half of the rotation period show no spectral variations at the 2% level, indicating compositional homogeneity. Both 349 Dembowska and 4 Vesta can be considered as candidates for the parent bodies of igneous meteorites.     

Report of the working group on water color

This report on water color is divided into two parts: a summary of the formal and informal presentations made at the meeting, and a summary of the conclusions and recommendations reached during the working group meetings. The group's discussions were divided into four categories: inwater studies and algorithms, atmospheric effects and correction algorithms, design of the next generation of spacecraft sensors, and future projects. Naturally, most of the discussion concerned the Coastal Zone Color Scanner on Nimbus-G but discussion was not restricted to this sensor. There were few members of the working group specializing in sediment studies; this is reflected in the fact that the major portion of the report deals with the remote determination of phytoplankton pigments.On leave from Department of Physics, University of Miami, Coral Gables, Florida.     

Upscaling Permeability Measurements Within Complex Heterolithic Tidal Sandstones

We investigate numerically the effect of sample volume on the effective single-phase permeability of heterolithic tidal sandstones, using three-dimensional models reconstructed directly from large rock specimens measuring 45 × 30 × 15 cm. We find that both individual and averaged effective permeability values vary as a function of sample volume, which indicates that permeability data obtained from core-plugs will not be representative at the scale of a reservoir model grid-block regardless of the number of measurements taken. However, the error introduced by averaged data may be minimized using the appropriate averaging scheme for a given facies type and flow direction.     

Variations in eelgrass (<Emphasis Type="Italic">Zostera marina</Emphasis> L.) morphology and internal nutrient composition as influenced by increased temperature and water column nitrate

In an experimental mesocosm system, we evaluated changes in morphology and tissue nutrient content (carbon [C], nitrogen [N], phosphorus [P]) of eelgrass (Zostera marina L.) as influenced by increased temperature and nitrate. During the late summer-fall growing season (14 weeks, August through mid-November), control plants were compared to plants grown at elevated temperatures (3°C to 4°C above ambient, based on 20-yr weekly means) and elevated water column nitrate enrichment (8 μM NO₃ ⁻, pulsed daily). Both increased temperature and increased nitrate led to declines in shoot density (by 40% and 48% for nitrate and temperature treatments, respectively), as well as decreased leaf and root production. High temperature promoted increased total C content of leaf tissues, whereas high nitrate increased the percentage of N in belowground tissues and depressed the C∶N ratio in aboveground tissues. The data indicated that increases in nitrate or temperature can significantly reduce the size ofZ. marine shoots and can also alter the internal C and N content. This reduction was not associated with significant increases in light-attenuating algae as we controlled epiphytic growth, so we suggest that a direct physiological mechanism or other mechanism was involved.     

MODFLOW 2000 head uncertainty,a first-order second moment method

A computationally efficient method to estimate the variance and covariance in piezometric head results computed through MODFLOW 2000 using a first-order second moment (FOSM) approach is presented. This methodology employs a first-order Taylor series expansion to combine model sensitivity with uncertainty in geologic data. MODFLOW 2000 is used to calculate both the ground water head and the sensitivity of head to changes in input data. From a limited number of samples, geologic data are extrapolated and their associated uncertainties are computed through a conditional probability calculation. Combining the spatially related sensitivity and input uncertainty produces the variance-covariance matrix, the diagonal of which is used to yield the standard deviation in MODFLOW 2000 head. The variance in piezometric head can be used for calibrating the model, estimating confidence intervals, directing exploration, and evaluating the reliability of a design. A case study illustrates the approach, where aquifer transmissivity is the spatially related uncertain geologic input data. The FOSM methodology is shown to be applicable for calculating output uncertainty for (1) spatially related input and output data, and (2) multiple input parameters (transmissivity and recharge).