Distribution of PACs in surficial sediments and bioavailability to mussels, Mytilus edulis of Halifax Harbour

Surficial sediments and blue mussels were collected around the perimeter of Halifax Harbour. Samples were analysed for the levels and fingerprint of polycyclic aromatic compounds (PACs). The objective was to explore the relationship between contaminant profiles in sediments and in mussels and to explore the possibility of deducing their sources, pattern of deposition and circulation in the harbour. Combustion derived compounds predominated in both sets of samples, with more variability observed in the level of petroleum derived hydrocarbons in mussel samples. Biota-sediment accumulation factors (BSAF, dry/dry wt.) varied throughout the harbour, ranging from means of 0.006 to 1.26, where generally fluoranthene displayed the highest BSAF. Sediments and mussels give complementary views of the geographical distribution of contaminants, they reflect the state of benthic and pelagic habitats. Results observed for Halifax Harbour are discussed from the perspective of published data.     

Identification of fresh submarine groundwater off the coast of San Diego,USA, using electromagnetic methods

Hydrogeology Journal - Climate change has a pronounced effect on water resources in many semiarid climates, causing populated areas such as San Diego County (USA), to become more vulnerable to...     

Resolution of bridging oxygen signals from O 1s spectra of silicate glasses using XPS: Implications for O and Si speciation

We used an advanced charge compensation system on an X-ray Photoelectron Spectrometer to yield linewidths from O 1s, Si 2p and Pb 4f spectra of 1.22, 1.35, and 1.10 eV, respectively. These linewidths (eV) are the narrowest obtained for silicate glasses, on any X-ray Photoelectron Spectrometer, to date. The exceptional resolution reveals two O 1s peaks in the PbO-SiO₂ glasses studied. One clearly resolved, high binding energy O 1s peak represents the bridging oxygen signal and the second, lower energy peak represents both non-bridging oxygen and metal-bridging oxygen contributions. These data allow quantification of bridging oxygen contents without detailed deconvolution because both the peak width and intensity are determined solely by the spectral data. The intensity of the bridging oxygen signal decreases systematically with decreased SiO₂ content; however, the measured bridging oxygen abundance is greater than predicted if all Pb atoms in the glass are assumed to be associated with two non-bridging oxygen atoms (i.e., O-Pb-O units). There remains, for example, a significant quantity of bridging oxygen in the glass at the orthosilicate composition (Mol. frac.: 0.67 PbO, 0.33 SiO₂). We demonstrate that bridging oxygen, non-bridging oxygen and metal-bridging oxygen exist at this composition and at all glass compositions studied, including the 0.50 PbO, 0.50 SiO₂ glass. Equilibrium thermodynamic (speciation) calculations indicate that at least three silicate species dominate the glass: a network species (SiO₂), a () monomeric species and a trimeric ring-like species (). With these species, the bridging oxygen contents are accurately modeled in PbO-SiO₂ glasses over the compositional range 0.3 PbO, 0.70 SiO₂ to 0.67 PbO, 0.33 SiO₂, and there is a remarkable agreement between the modeled bridging oxygen and the measured bridging oxygen contents with this study and previous studies. However, we do not intend to imply that the SiO₂, () and () are the only species present in the glass structure. In addition, this study shows that the Si 2p spectrum consists of one peak, fitted with one doublet, which shifts systematically to higher binding energy with increased SiO₂ content. We propose that this shift results from a more intense signal from the networked (more siliceous) species that are located at higher binding energy.     

Continuous streamline trajectories on complex grids

Computational Geosciences - Streamlines have been used for reservoir modeling and flow visualization in the petroleum industry and in computational fluid dynamics. When applied to the calculation...     

The Bartonian unit stratotype (S. England): Assessment of its correlation problems and potential

The problems of correlation of strata belonging to the unit Bartonian Stage in its type area of the Hampshire Basin, UK, are reviewed. These problems involve not only correlation outside the Hampshire Basin, through biostratigraphy and magnetostratigraphy, but also within the basin in terms of understanding patterns of facies distributions and reliability of local biostratigraphy. On the basis of a combination of calcareous nannoplankton, dinoflagellate cyst and magnetostratigraphic evidence, the base of the type unit Bartonian lies within Chron C18r. However, no reliable biostratigraphic indicators have yet been found to allow a more precise correlation of the base. It is suggested that more detailed microfossil and palaeomagnetic sampling at key sites could resolve these problems in order to help further the quest for an appropriate Global Stratotype Section and Point (GSSP) for the Bartonian Stage.     

Improved Constraints on Models of Glacial Isostatic Adjustment: A Review of the Contribution of Ground-Based Geodetic Observations

The provision of accurate models of Glacial Isostatic Adjustment (GIA) is presently a priority need in climate studies, largely due to the potential of the Gravity Recovery and Climate Experiment (GRACE) data to be used to determine accurate and continent-wide assessments of ice mass change and hydrology. However, modelled GIA is uncertain due to insufficient constraints on our knowledge of past glacial changes and to large simplifications in the underlying Earth models. Consequently, we show differences between models that exceed several mm/year in terms of surface displacement for the two major ice sheets: Greenland and Antarctica. Geodetic measurements of surface displacement offer the potential for new constraints to be made on GIA models, especially when they are used to improve structural features of the Earth’s interior as to allow for a more realistic reconstruction of the glaciation history. We present the distribution of presently available campaign and continuous geodetic measurements in Greenland and Antarctica and summarise surface velocities published to date, showing substantial disagreement between techniques and GIA models alike. We review the current state-of-the-art in ground-based geodesy (GPS, VLBI, DORIS, SLR) in determining accurate and precise surface velocities. In particular, we focus on known areas of need in GPS observation level models and the terrestrial reference frame in order to advance geodetic observation precision/accuracy toward 0.1 mm/year and therefore further constrain models of GIA and subsequent present-day ice mass change estimates.     

Records of large earthquakes in lake sediments along the North Anatolian Fault,Turkey

In 1999, the large surface-rupturing earthquakes of Izmit and Duzce completed a 60-year cycle that included a westward migration of nine consecutive large earthquake failures (>50 km surface rupture), which started with the 1939 Erzincan earthquake in eastern Turkey. In this study, we focused on seismic cycles and seismic risk predictability along the North Anatolian Fault (NAF). Toward the west end of the NAF (26°E–32°E, i.e. Bolu), large earthquake frequency is measured from either historic earthquake catalogs, or geologic records from isolated outcrops and marine sediment cores from the Marmara Sea. In comparison, the eastern part of the NAF zone (32°E–42°E) is less well documented by palaeo-seismologic archives. Thus, the sediment records of lake basins located on the eastern NAF zone constitute a unique opportunity for testing a new palaeo-seismologic approach. To this end, we used a diverse array of complementary methods involving: (1) a 600-km transect of fault-related lakes, (2) sedimentologic observations on cores from six lakes, and (3) a comparison between records of catastrophic sediment transfers in lakes (i.e. radionuclide chronomarkers and erosion tracers) and historic earthquake reports. Our study indicates that lakes along the NAF are sensitive geologic recorders of large surface-rupturing earthquakes (surface-wave magnitude (M _s) ≥ 6.9); smaller intensities are not recorded. The most responsive lake systems exhibit increases in sediment accumulation by a factor of >40 for a >3-m strike-slip displacement (M _s ≥ 7). However, based on results from the 1939 Erzincan earthquake (M _s = 7.8) chronostratigraphic marker, large surface-rupturing earthquakes are detected only by certain lake records and not by others. Matching multiple lake records along the NAF provides information both on the location of a surface rupture of a paleo-earthquake as well as its magnitude. Finally, the shallow lake basins along the NAF could potentially document cycles of large seismic events for at least the late Holocene.