On the magnitude of upwelling fluxes in shelf-break canyons

A hydrodynamic model is employed to derive the magnitude of on-shelf fluxes through a shelf-break canyon for a wide range of canyon sizes and ambient oceanic conditions. Predicted canyon-upwelling fluxes are of the order of 0.05–0.1 Sv (1 Sv=1 million m³/s), being several orders of magnitude greater than upslope fluxes in the bottom Ekman layer on the ambient continental slope. On the basis of ∼150 simulations conducted, a bulk formula of upwelling flux in a submarine canyon is derived. For typical conditions, the upwelling flux varies quadratically with forcing strength (speed of incident flow), linearly with canyon depth, and is inversely proportional to the buoyancy frequency of the density stratification inside the canyon. Other parameters such as density stratification above shelf-break depth and bottom friction are found to have minor influences on the resultant canyon-upwelling flux.     

Polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans in sediments from Hong Kong

Concentrations of 2,3,7,8-substituted polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) were determined in 14 sediment samples collected from four sites in the Mai Po Marshes Nature Reserve (within a RAMSAR Site) and from another six sites in Victoria Harbour and along the Hong Kong coastline. Elevated levels of PCDDs, and particularly OCDD, were detectable in all samples collected from the Mai Po Marshes and five of the six sites. In contrast to PCDDs, PCDFs were mainly found in sediment samples collected from industrial areas (Kwun Tong and To Kwa Wan) in Victoria Harbour. PCDD/F levels and congener profiles in the samples from the Mai Po Marshes Nature Reserve in particular show strong similarities to those reported in studies which have attributed similar elevated PCDD concentrations to nonanthropogenic PCDD sources.     

Late Quaternary growth and decay of the Svalbard/Barents Sea ice sheet and paleoceanographic evolution in the adjacent Arctic Ocean

The paleoceanography in the Nordic seas was characterized by apparently repeated switching on and off of Atlantic water advection. In contrast, a continous influx of Atlantic waters probably occurred along the northern Barents Sea margin during the last 150?ka. Temporary ice-free conditions enhanced by subsurface Atlantic water advection and coastal polynyas accelerated the final ice sheet build-up during glacial times. The virtually complete dissolution of biogenic calcite during interglacial intervals was controlled mainly by CO2-rich bottom waters and oxidation of higher levels of marine organic carbon and indicates intensive Atlantic water inflow and a stable ice margin.     

The Plio-Pleistocene glaciation of the Barents Sea–Svalbard region: a new model based on revised chronostratigraphy

Based on a revised chronostratigraphy, and compilation of borehole data from the Barents Sea continental margin, a coherent glaciation model is proposed for the Barents Sea ice sheet over the past 3.5 million years (Ma). Three phases of ice growth are suggested: (1) The initial build-up phase, covering mountainous regions and reaching the coastline/shelf edge in the northern Barents Sea during short-term glacial intensification, is concomitant with the onset of the Northern Hemisphere Glaciation (3.6–2.4 Ma). (2) A transitional growth phase (2.4–1.0 Ma), during which the ice sheet expanded towards the southern Barents Sea and reached the northwestern Kara Sea. This is inferred from step-wise decrease of Siberian river-supplied smectite-rich sediments, likely caused by ice sheet blockade and possibly reduced sea ice formation in the Kara Sea as well as glacigenic wedge growth along the northwestern Barents Sea margin hampering entrainment and transport of sea ice sediments to the Arctic–Atlantic gateway. (3) Finally, large-scale glaciation in the Barents Sea occurred after 1 Ma with repeated advances to the shelf edge. The timing is inferred from ice grounding on the Yermak Plateau at about 0.95 Ma, and higher frequencies of gravity-driven mass movements along the western Barents Sea margin associated with expansive glacial growth.     

A temperature-induced reversible transformation between paratacamite and herbertsmithite

The crystal chemistry of paratacamite has been re-evaluated by studying a crystal from the holotype specimen BM86958 of composition Cu_3.71Zn_0.29(OH)₆Cl₂ using single-crystal X-ray diffraction at 100, 200, 300, 353, 393 and 423 K. At 300 K paratacamite has space group $R\bar{3}$ with unit-cell parameters a 13.644 and c 14.035 Å and exhibits a pronounced subcell, a′ = ½a and c′ = c, analogous to that of the closely related mineral herbertsmithite, Cu₃Zn(OH)₆Cl₂. Between 353 and 393 K, paratacamite undergoes a reversible phase transformation to the herbertsmithite-like substructure, space group $R\bar{3}m$ , unit-cell parameters a 6.839 and c 14.072 Å (393 K). The transformation is characterised by a gradual reduction in intensity of superlattice reflections, which are absent at 393 and 443 K. On cooling from 443 to 300 K at ~10 K min^?1, the superlattice reflections reappear and the refined structures ( $R\bar{3}$ ) of the initial and recovered 300 K states are almost identical. The complete reversibility of the transformation establishes that paratacamite of composition Cu_3.71Zn_0.29(OH)₆Cl₂ is thermodynamically stable at ambient temperatures. The nature of the rhombic distortion of the M(2)O₆ octahedron is discussed by considering two possibilities that are dependent upon the nature of cation substitution in the interlayer sites.     

The Millennium Galaxy Catalogue: bulge–disc decomposition of 10 095 nearby galaxies

We present near-infrared (NIR) adaptive optics-assisted spectroscopic observations of the  CO (Δμ= 2)  absorption bands towards the centre of the giant elliptical galaxy NGC 1399. The observations were made with NAOS-CONICA (on the European Southern Observatory's Very Large Telescope) and have a full width at half-maximum resolution of 0.15 arcsec (14 pc). Kinematic analysis of the observations reveals a decoupled core and strongly non-Gaussian line-of-sight velocity profiles in the central 0.2 arcsec (19 pc). NIR imaging also indicates an asymmetric elongation of the central isophotes in the same region.
We use spherical orbit-superposition models to interpret the kinematics, using a set of orthogonal 'eigen-velocity profiles' that allow us to fit models directly to spectra. The models require a central black hole of mass  1.2^+0.5_−0.6× 10⁹ M_⊙  , with a strongly tangentially biased orbit distribution in the inner 40 pc.