Origin of the Belomorian Chupa Gneiss in the Light of New Lithogeochemical Data

The stratotype Chupa Sequence, which makes up the synonymous tectonic nappe and is a member of oldest (Late Archean) rocks in the Belomorian Mobile Belt, is scrutinized. The nappe is mainly composed of the migmatized, coarse-grained garnet–biotite gneiss with kyanite. Relic formations are represented by lenses of the fine-grained (possibly primary) garnet–biotite gneiss. Fine-grained gneisses generally represent primary sedimentary formations, while metadacites are rare. The kyanite-bearing gneiss is presumably a restitic rock produced by migmatization. Chupa metasediments are represented by immature (low-differentiated) metagraywackes and are akin to metaterrigenous rocks from Late Archean greenstone belts of Karelia (Kostomuksha) and Canada (Quetico). The provenance of metasediments comprises the following three components: tonalite (dacite) 70%, mafic rocks 20%, and ultramafic rocks 10%. The Chupa metagraywacke presumably deposited in a fore-arc basin.     

Linear Time-Invariant Compensation of Cup Anemometer and Vane Inertia

We propose a method to compensate for the phase lag and the amplitudeattenuation in the cup anemometer signal. These two effects, caused by theinstrument's inertia, are the major flaws of the cup anemometer in additionto over-speeding. Since the instrument's response is invariant in wavenumber (not frequency) representation, we transform the signals to becompensated from the time domain to the spatial domain by using Taylor'shypothesis. In the spatial domain we apply a linear time-invariant filterto eliminate the phase lag and the amplitude attenuation. The proposedprocedure improves instrument performance down to spatial scales equal toor smaller than the distance constant of the anemometer. The method for cupanemometer compensation is presented in detail and later adapted for vanes.     

Differences in the Feeding Ecology of Two Seagrass-Associated Snails

Grazing by small epifauna on live seagrass leaves was formerly viewed as unimportant in controlling plant biomass and growth, instead researchers focused on the indirect benefits of small invertebrates that crop algal competitors. Recent evidence shows that the emerald nerite Smaragdia viridis preferentially ingests seagrass leaf tissue. In contrast, the button snail Modulus modulus feeds on epiphytes and periphyton coating the leaves. We conducted laboratory microcosm and field experiments to investigate how the different feeding preferences of these seagrass-associated snails affect turtlegrass Thalassia testudinum primary production. Data revealed that after 24 h S. viridis reduced foliar biomass (25%) and chlorophyll (30%) and injured the equivalent of 50% of daily seagrass growth per shoot. Conversely, M. modulus did not affect these variables. Our results emphasize that in subtropical seagrass communities not all small epifauna browse off leaf surfaces and some can have important direct negative impacts on their seagrass host.     

Long-Term Trends of Nutrients and Phytoplankton in Chesapeake Bay

Climate effects on hydrology impart high variability to water-quality properties, including nutrient loadings, concentrations, and phytoplankton biomass as chlorophyll-a (chl-a), in estuarine and coastal ecosystems. Resolving long-term trends of these properties requires that we distinguish climate effects from secular changes reflecting anthropogenic eutrophication. Here, we test the hypothesis that strong climatic contrasts leading to irregular dry and wet periods contribute significantly to interannual variability of mean annual values of water-quality properties using in situ data for Chesapeake Bay. Climate effects are quantified using annual freshwater discharge from the Susquehanna River together with a synoptic climatology for the Chesapeake Bay region based on predominant sea-level pressure patterns. Time series of water-quality properties are analyzed using historical (1945–1983) and recent (1984–2012) data for the bay adjusted for climate effects on hydrology. Contemporary monitoring by the Chesapeake Bay Program (CBP) provides data for a period since mid-1984 that is significantly impacted by anthropogenic eutrophication, while historical data back to 1945 serve as historical context for a period prior to severe impairments. The generalized additive model (GAM) and the generalized additive mixed model (GAMM) are developed for nutrient loadings and concentrations (total nitrogen—TN, nitrate?+?nitrate—NO₂?+?NO₃) at the Susquehanna River and water-quality properties in the bay proper, including dissolved nutrients (NO₂?+?NO₃, orthophosphate—PO₄), chl-a, diffuse light attenuation coefficient (K _D (PAR)), and chl-a/TN. Each statistical model consists of a sum of nonlinear functions to generate flow-adjusted time series and compute long-term trends accounting for climate effects on hydrology. We present results identifying successive periods of (1) eutrophication ca. 1945–1980 characterized by approximately doubled TN and NO₂?+?NO₃ loadings, leading to increased chl-a and associated ecosystem impairments, and (2) modest decreases of TN and NO₂?+?NO₃ loadings from 1981 to 2012, signaling a partial reversal of nutrient over-enrichment. Comparison of our findings with long-term trends of water-quality properties for a variety of estuarine and coastal ecosystems around the world reveals that trends for Chesapeake Bay are weaker than for other systems subject to strenuous management efforts, suggesting that more aggressive actions than those undertaken to date will be required to counter anthropogenic eutrophication of this valuable resource.     

The Venus ionosphere at grazing incidence of solar radiation: Transport of plasma to the night ionosphere

Using a quasi-two-dimensional model of the Venus ionosphere, we calculated the ion number densities and horizontal ion bulk velocities expected for a range of solar zenith angles near the terminator (80 to 100°), and compared them with data obtained from the Pioneer Venus Orbiter retarding potential analyzer. The calculated ion bulk velocity arises entirely from the solar EUV-induced plasma pressure gradient and has a magnitude consistent with observations; ionization by suprathermal electrons is neglected in those computations. We find that while photoionization is the dominant source of ionospheric plasma for solar zenith angles less than 92°, plasma transport from the dayside is the dominant plasma source for solar zenith angles greater than 95°. We also show that the main nightside plasma peak at approximately 140 km altitude is of the F₂ type (i.e., is diffusion controlled). Its altitude and shape are thus quite insensitive to the altitude of the ion source.     

Estimating the underwater light field from remote sensing of ocean color

We present a new approach that incorporates two models to estimate the underwater light field from remote sensing of ocean color. The first employs a series of analytical, semi-analytical, and empirical algorithms to retrieve the spectrum of inherent optical properties (IOPs), including the absorption and the backscatter coefficients, from the spectrum of remote sensing reflectance. The second model computes the profile of photosynthetically available radiation E _0,PAR (z) for a vertically homogeneous water column using the information of the retrieved IOPs and the ambient optical environment. This computation is based on an improved look-up table technology that possesses high accuracy, comparable with the full solution of the radiative transfer equation, and meets the computational requirement of remote sensing application. This new approach was validated by in situ measurements and an extensive model-to-model comparison with a wide range of IOPs. We successfully mapped the compensation depth by applying this new approach to process the SeaWiFS imagery. This research suggests that E _0,PAR (z) can be obtained routinely from ocean-color data and may have significant implications for the estimation of global heat and carbon budget.     

Tropical Deforestation and Climate Change: What Does the Record Reveal?

Tropical deforestation is widely believed to directly influence the climate at a number of scales. Yet while much has been written about the tropical forest-climate relationship, there is little empirical evidence showing if and how local and regional climates are modified by deforestation. This study presents the results of an analysis of deforestation and climate change in a rain forest in southern Mexico. Records from 18 climate stations in the Selva Lacandona of Chiapas, Mexico were examined and related to an analysis of deforestation based on Landsat images. The area surrounding some stations has been deforested since the stations were established, while the area surroundings others has remained forested. Strong climatic trends were generally evident at the deforested stations, including decreases in the average daily maximum temperature and temperature range. No precipitation changes were observed. A comparison of the results with microclimatic experiments and modeling studies suggests that the climatic impacts of deforestation are overgeneralized at the local scale. Landscape heterogeneity appears to influence the biophysical mechanisms linking tropical forests and climate, and should be explicitly represented in modeling studies.     

Teaching GIS in Geography*

Although numerous courses in geographic information systems (GIS) have been introduced into the geography curriculum over the past few years, there has been remarkably little debate over the issues involved. This paper first discusses the arguments for geography as an appropriate disciplinary setting for GIS teaching at the undergraduate level. This is followed by a discussion of the nature of GIS courses and their appropriate place in the undergraduate geography curriculum. The final section of the paper describes the NCGIA Core Curriculum project and examines its significance in this broader context.     

Paleolimnological significance of spinose and non-spinose morphs of Pyrgophorus hibbardi (Leonard and Franzen, 1944)

The basal portion of the Ogallala Formation (=Laverne Formation) (Lower Pliocene) Beaver County, Oklahoma, contains an interesting assemblage of non-marine fossil molluscs that include both spinose and non-spinose forms of the aquatic gastropod species Pyrgophorus hibbardi. The origin and paleolimnological significance of the spinose morph has been a source of much conjecture that has influenced environmental reconstructions of this assemblage. In one hypothesis the spinose forms of P. hibbardi are assumed to be associated with brackish water conditions by analogy with some populations of a related hydrobiid Potamopyrgus jenkinsi. To test the hypothesis that the spinose forms lived under different water conditions than the non-spinose morphs, we analyzed 10 specimens each of the two varieties for stable oxygen and carbon isotope ratios in the shell aragonite.The mean isotope ratios for the smooth and spinose morphs show no significant difference (oxygen: t = 0.28, df = 18, P (T t) 0.78 n.s.; carbon: t = 0.96, df = 18, P (T t) 0.35 n.s). We conclude that the lack of a statistically significant difference between the means of the oxygen and carbon isotope values for the smooth and spinose morphs suggests that the two forms lived in waters having similar isotope signatures. The considerable range in oxygen isotope values recorded by both morphs of P. hibbardi, including values as high as 5–6, suggest that both morphs were associated with waters which were periodically evaporatively enriched in ¹⁸O.