GPR Reflection Profiles of Clark and Commonwealth Glaciers, Dry Valleys, Antarctica

Englacial horizons deeper than 100 m are absent within 100 MHz ground-penetrating radar (GPR) surface profiles we recorded on Clark and Commonwealth Glaciers in the Antarctic Dry Valleys region. Both glaciers show continuous bottom horizons to 280 m, with bottom signal-to-noise ratios near 30 dB. Density horizons should fade below 50 m depth because impermeable ice occurred by 36 m. Folding within Commonwealth Glacier could preclude radar strata beneath about 80 m depth, but there is no significant folding within Clark Glacier. Strong sulfate concentrations and contrasts exist in our shallow ice core. However, it appears that high background concentration levels, and possible decreased concentration contrasts with depth placed their corresponding reflection coefficients at the limit of, or below, our system sensitivity by about 77 m depth. Further verification of this conclusion awaits processing of our deep-core chemistry profiles.

Sticking to Syntax: The Reflection of Story Grammar in Children's and Adult's Recall of Radio and Television Shows

Two studies were conducted to determine how well story grammar predicted recall of televised stories. In Experiment 1, preschoolers viewed a non-narrated televised story from "Sesame Street." In Experiment 2, preschoolers and adults were administered a narrative via television or radio. In both studies, subjects' retention reflected recall of nodal information, regardless of medium of input.

The Underwater Photic Environment of Cape Maclear, Lake Malawi: Comparison Between Rock- and Sand-Bottom Habitats and Implications for Cichlid Fish Vision

Lake Malawi boasts the highest diversity of freshwater fishes in the world. Nearshore sites are categorized according to their bottom substrate, rock or sand, and these habitats host divergent assemblages of cichlid fishes. Sexual selection driven by mate choice in cichlids led to spectacular diversification in male nuptial coloration. This suggests that the spectral radiance contrast of fish, the main determinant of visibility under water, plays a crucial role in cichlid visual communication. This study provides the first detailed description of underwater irradiance, radiance and beam attenuation at selected sites representing two major habitats in Lake Malawi. These quantities are essential for estimating radiance contrast and, thus, the constraints imposed on fish body coloration. Irradiance spectra in the sand habitat were shifted to longer wavelengths compared with those in the rock habitat. Beam attenuation in the sand habitat was higher than in the rock habitat. The effects of water depth, bottom depth and proximity to the lake bottom on radiometric quantities are discussed. The radiance contrast of targets exhibiting diffused and spectrally uniform reflectance depended on habitat type in deep water but not in shallow water. In deep water, radiance contrast of such targets was maximal at long wavelengths in the sand habitat and at short wavelengths in the rock habitat. Thus, to achieve conspicuousness, color patterns of rock-and sand-dwelling cichlids would be restricted to short and long wavelengths, respectively. This study provides a useful platform for the examination of cichlid visual communication.

Observations of the Sensitivity of Beam Attenuation to Particle Size in a Coastal Bottom Boundary Layer

The goal of this study was to test the hypothesis that the aggregated state of natural marine particles constrains the sensitivity of optical beam attenuation to particle size. An instrumented bottom tripod was deployed at the 12-m node of the Martha's Vineyard Coastal Observatory to monitor particle size distributions, particle size-versus-settling-velocity relationships, and the beam attenuation coefficient (c(p)) in the bottom boundary layer in September 2007. An automated in situ filtration system on the tripod collected 24 direct estimates of suspended particulate mass (SPM) during each of five deployments. On a sampling interval of 5 min, data from a Sequoia Scientific LISST 100x Type B were merged with data from a digital floc camera to generate suspended particle volume size distributions spanning diameters from approximately 2 mu m to 4 cm. Diameter-dependent densities were calculated from size-versus-settling-velocity data, allowing conversion of the volume size distributions to mass distributions, which were used to estimate SPM every 5 min. Estimated SPM and measured c(p) from the LISST 100x were linearly correlated throughout the experiment, despite wide variations in particle size. The slope of the line, which is the ratio of c(p) to SPM, was 0.22 g m(-2). Individual estimates of c(p):SPM were between 0.2 and 0.4 g m(-2) for volumetric median particle diameters ranging from 10 to 150 mu m. The wide range of values in c(p):SPM in the literature likely results from three factors capable of producing factor-of-two variability in the ratio: particle size, particle composition, and the finite acceptance angle of commercial beam-transmissometers.