The phylogenetic diversity of two continental shelf picoplankton communities was examined by analyzing SSU (16S) ribosomal RNA (rRNA) genes amplified from environmental DNA with bacterial-specific primers and the polymerase chain reaction (PCR). Picoplankton populations collected from the pycnocline (10 m) over the eastern continental shelf of the United States near Cape Hatteras, North Carolina, and surface seawater (10 m) from the western continental shelf of the United States 8 km west of Yaquina Head, Oregon, served as sources of bulk nucleic acids used in this study. A total of 285 SSU rRNA gene clones were analyzed in the two libraries, more than doubling the number previously available from seawater samples. In contrast to previous studies of bacterioplankton diversity from the open-ocean, a large proportion of the rDNA clones recovered in this study (38%) were related to plastid SSU rRNA genes, including plastids from bacillariophyte, prymnesiophyte, cryptophyte, chrysophyte, and prasinophyte algae, as well as a number of unique plastid rRNA gene clones for which no close phylogenetic relatives were discovered. A majority of the bacterial gene clones recovered (72% of bacterial clones) were closely related to rRNA gene lineages discovered previously in clone libraries from open-ocean marine habitats, including the SAR86 cluster (�� Proteobacteria), SAR83, SAR11, and SAR116 clusters (all �� Proteobacteria), the marine Gram-positive cluster (Actinomycetes), the marine group A/SAR406 cluster, and a cluster of environmental clones within the flexibacter-cytophaga-bacteroides phylum. A majority of the remaining bacterial clones were phylogenetically related to the �� and �� subclasses of the Proteobacteria, including an rDNA lineage within the Type I methylotroph Glade of the �� subclass. The abundance of plastid rDNAs and the lack of cyanobacterial-related clones, as well as the presence of �� Proteobacteria, are features of these coastal picoplankton gene clone libraries which distinguish them from similar studies of oligotrophic open-ocean sites. Overall, however, these data indicate that a limited number of as yet uncultured bacterioplankton lineages, related to those previously observed in the open-ocean, can account for the majority of cells in these coastal marine bacterioplankton assemblages. / Graduation date: 1998

No description available.

Thesis (Ph.D.)--Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Ocean Engineering; and the Woods Hole Oceanographic Institution), 1999. / Includes bibliographical references (p. 180-184). / During July and August of 1996, a large acoustics/physical oceanography experiment was fielded in the Mid-Atlantic Bight, south of Nantucket Island, MA. Known as the Shelfbreak Front PRIMER Experiment, the study combined acoustic data from a moored array of sources and receivers with very high resolution physical oceanographic measurements. This thesis addresses two of the primary goals of the experiment, explaining the properties of acoustic propagation in the region, and tomographic inversion of the acoustic data. In addition, this thesis develops a new method for predicting acoustic coherence in such regions. Receptions from two 400 Hz tomography sources, transmitting from the continental slope onto the shelf, are analyzed. This data, along with forward propagation modeling utilizing SeaSoar thermohaline measurements, reveal that both the shelfbreak front and tidally-generated soliton packets produce stronger coupling between the acoustic waveguide modes than expected. Arrival time wander and signal spread show variability attributable to the presence of a shelf water meander, changes in frontal configuration, and variability in the soliton field. The highly-coupled nature of the acoustic mode propagation prevents detailed tomographic inversion. Instead, methods based on only the wander of the mode arrivals are used to estimate path-averaged temperatures and internal tide "strength". The modal phase structure function is introduced as a useful proxy for acoustic coherence, and is related via an integral transform to the environmental sound speed correlation function. Advantages of the method are its flexibility and division of the problem into independent contributions, such as from the water column and seabed. / by Brian J. Sperry. / Ph.D.

Atlantic Scotland provides plentiful and often dramatic evidence for settlement during the Iron Age but, like much of Europe, very little is known of the funerary traditions of communities in this region. Formal burial appears to have been rare, and evidence for alternative mortuary treatments is dispersed, varied and, to date, poorly understood. This study sets out to examine for the first time all human remains dating to the Iron Age in Atlantic Scotland, found in a variety of contexts ranging from formal cemeteries to occupied domestic sites. This data-set, despite its limitations, forms the basis for a new understanding of funerary treatment and daily life in later prehistoric Atlantic Scotland, signifying the development of an extraordinary range of different methods of dealing with, and harnessing the power of, the dead during this period. This information in turn can contribute to wider issues surrounding attitudes to the dead, religious belief, domestic life and the nature of society in Iron Age Europe.

Phragmites australis is a perennial grass presently invading many intertidal and freshwater wetlands throughout much of the Atlantic Coast of North America. The spread of Phragmites into coastal wetlands is in part determined by available freshwater and nutrients, especially nitrogen, within the watershed where Phragmites populations occur. The Eastern Shore of Virginia is an intensive agricultural area, and watershed landcover may play a major role in Phragmites invasion. Forty-five Phragmites patches were sampled in eight VA Eastern Shore mainland watersheds and on a barrier island. Regardless of watershed landcover characteristics, there was little variation in Phragmites australis patch characteristics along the oceanside of the entire Eastern Shore of Virginia. Phragmites is a generalist with broad environmental tolerances. Thus, successful management and eradication plans may have broad scale application for this invasive grass.

O gênero Doris está representado no Brasil por quatro espécies: Doris verrucosa, Doris bovena, Doris ilo e Doris kyolis, a maioria delas com um histórico taxonômico confuso. Através da revisão taxonômica do gênero Doris, do estudo da anatomia comparada entre as espécies e com dados da literatura foi possível separar D. verrucosa em duas espécies, mantendo D. verrucosa como a espécie com distribuição para a Europa e Mar Mediterrâneo e Doris januarii, um sinônimo revalidado, com distribuição para a costa Atlântica brasileira. Também foi possível confirmar e completar as informações sobre a anatomia de D. bovena, D. ilo e D. kyolis. As principais características anatômicas que corroboram a distinção entre as espécies estudadas foram encontradas no odontóforo, rádula, sistema reprodutor e sistema nervoso / The genus Doris in Brazilian shelf is represented by four species: Doris verrucosa, Doris bovena, Doris ilo e Doris kyolis. This species have a misunderstood taxonomy. In this study was carried out a taxonomy revision, utilizing comparative anatomy and previous literature data. As a result, was possible to separate D. verrucosa in two species, maintaining D. verrucosa with distribution to Europe and Mediterranean Sea, whereas Doris januarii, a revalidated synonym, is restricted in Brazilian Atlantic coast. In addition, anatomical data complementary validates the species status of D. bovena, D. ilo e D. kyolis. The distinctive anatomical characteristics that justify the separation among these species are found in the following structures: odontophore, radula, reproductive system and nervous system.

The overall objective of this study is to address questions concerning the long-term mechanical strength of the lithosphere across the equatorial margin of Brazil. The approach used in this study consists of calculating the frequency response function estimates, also called admittance, using gravity and bathymetry data. These experimental estimates are then compared to theoretical admittance curves for Airy and thin elastic plate models for which estimates on the flexural rigidity or, equivalently, effective elastic thickness may be made. Twelve profiles, each 256 km long, were extracted from gridded gravity and bathymetry data (data sources: project EQUANT, Defense Mapping Agency, National Geophysical Data Center files and GEOS 3/SEASAT altimeter data). Three profiles were specifically used for testing truncation errors introduced by four different data treatment procedures (before Fourier transforming the data) : detrending, applying 10% cosine tapering, mirror imaging and the use of the first derivatives. The method I adopted is similar to the one used by McNutt (1983) and consists of testing how reliably a given admittance estimate can be recovered as a function of the data treatment procedure. A "predicted" gravity anomaly was obtained by convolving each bathymetric profile with a theoretical admittance filter. The edges of this anomaly are then submitted to the same treatment as the corresponding bathymetric profile before Fourier transforming both profiles and calculating admittance. The stability of the long-wavelength admittance estimates, in the presence of noise, was also investigated by introducing Gaussian noise, in the range of -50 to +50 mGals, in the "predicted" gravity signal. The results indicate that relatively unbiased long-wavelength admittance estimates can be obtained by using the first derivative of the data sets. In addition, it is shown that the mirroring technique, used in previous admittance studies across Atlantic-type margins, leads to overestimated admittance values and, therefore, overestimated flexural rigidities. Neither the theoretical curves for the Airy model nor the plate flexure model can explain the experimental admittance estimates. Not only are the experimental admittance estimates higher than the predicted values but they also have a narrower peak than the theoretical curves. This raises the question of the applicability of highly simplified isostatic models for tectonic provinces such as Atlantic-type continental margins. The following reasons may explain the discrepancies between the experimental and theoretical admittance estimates: (1) The abrupt nature of the transition between oceanic and continental crust controlled by the Romanche Fracture Zone - Unlike the eastern North American continental margin which was formed as a result of extensive rifling and pulling apart, the obliquely-rifled equatorial margin of Brazil has undergone a complex tectonic evolutionary process, where additional components such as shear and right-lateral wrenching were present. Therefore, representing the margin as a thin homogeneous elastic plate might be reasonable when the transition is gradual (for which the uniform flexural rigidity assumption seems reasonable) but is probably not a good approximation when it is as abrupt as the equatorial margin of Brazil (2) Presence of subsurface loads - Previous studies have shown that estimates of the average flexural rigidity of continental lithosphere using the admittance approach are biased when subsurface loads are present. In principle, the proximity of the Romanche Fracture Zone and associated volcanism suggest that shallow buried loads, caused by intrusive bodies, might be present in the area. This could partially account for the mismatch between theoretical curves and experimental admittance estimates. (3) "Masked" estimates - The admittance estimates presented here are likely to reflect the combination of two different signals: one related to the compensation of the Barreirinhas/Piaui-Camocim sub-basin which has no topographic/bathymetric expression and the other one related to the topography/bathymetry and its compensation which is of interest in the admittance studies. Since the wavelengths of these signals do not differ by much (around 80-100 km for the basin) it is possible that in the averaging process some overlapping occurs. The combination of these signals could yield anomalous results masking the admittance estimates in the diagnostic waveband. In addition, I present a two-dimensional cross section obtained by forward modelling the gravity anomaly along a profile using the line integral method. The uniform sedimentary infill of the Barreirinhas/Piaui-Camocim basin is enough to account for the gravity low over the inner shelf and no Moho topography is required. A plausible explanation for this "rootless" basin structure is that the lithosphere is capable of supporting the sediment infill load, and thus, has finite flexural rigidity (basin is locally uncompensated). / Graduation date: 1990

Afro-descendant communities in Central America have recently made important legal strides by enshrining their right to equal treatment under the law and in some cases their ability to claim a distinct group status in national constitutions. The United Nations recently issued a draft resolution declaring that access to water and sanitation is a universal right, furthering the tools available to marginalized afro-descendant peoples in their battles against poverty and underdevelopment. Unfortunately, implementation of these measures has been slow in some areas and non-existent in others. Though there have been some advances, the situation for Afro-descendant communities remains largely unchanged and the availability of the basic requirements of life for Afro-descendant populations remains among the lowest in the region. Increased attention to the political, social, and especially the material situation of Afro-descendant communities is needed in political circles, as well as in the academic community. There is a lack of scholarly work on the material well-being of Afro-descendent populations in Central America. An important initial contribution in this area would be the compilation, and accumulation of statistical information as a primary step in developing the literature. The focus of this study then is on the Atlantic Coast Afro-descendant populations in Nicaragua. This document will outline the current material circumstances of Nicaraguan Afro-descendant communities using data gathered from a variety of sources, identify the causes of inadequate access to water and sanitation, and suggest strategies to improve the situation of these communities. It is my sincere hope that, at the very least, increased attention will be brought to the situation. / text

A quantitative forward model has been developed to investigate the controls on the deposition, erosion, and preservation of passive rift margin stratigraphy. The model includes thermal subsidence, variable absolute sealevel, flexural isostasy, subaerial and submarine deposition on fluvial and marine equilibrium profiles, and the facility to vary sediment supply through time. Results from the quantitative model can be used to reproduce elements of the sequence stratigraphic depositional model. Conducting sensitivity tests demonstrates that variables such as sediment supply and fluvial profile behaviour are likely to be of equal importance to thermal subsidence and eustasy in passive margin stratigraphy. Sensitivity tests with the quantitative model also demonstrate the problems associated with attempting to use a discretised stratigraphic model to investigate unforced cyclicty resulting from complex interactions in stratigraphic systems. Although the model appears capable of producing such unforced cyclical behaviour, this cyclicity is shown to be due to a numerical instability within the model which occurs with certain initial conditions and assumptions. The applicability of the model to observed stratigraphy is tested by comparing specific model output to patterns of stratigraphy from the North American Atlantic margin. The results from this test demonstrate that although the model is in many respects simplistic when compared to the complexities of natural systems, it is nevertheless capable of reproducing some of the basic elements of the observed stratigraphic patterns.

Graduation date: 1980