11 million years of Oligocene geomagnetic field behaviour

An 11 million year long record of the Oligocene geomagnetic field has been obtained from pelagic sediments of DSDP Hole 522 An average sample spacing of 4 cm yielded approximately one specimen per 4 to 8 kyr. The rock magnetics are remarkabh consistent across the entire interval. Previous work demonstrated a magnetic mineralogy dominated by magnetically stable magnetite. The natural remanent magnetism (NRM) carries an Oligocene polarity timescale that is in excellent agreement with the Oligocene reversal record as determined from marine magnetic anomalies (MMAs), including many of the so-called 'crypto-chrons'. Normalized NRM intensities from the undisturbed portions of the record yield a time series of variations with features consistent with a number of other palaeointensity time series derived from both sedimentary and lava sequences. These features include consistent, major decreases in palaeointensity (DIPs) at reversal boundaries, and occasional DIPs between reversal boundaries that could correspond to lineated 'tiny wiggles' in the MMA records. The data set suggests that the overall field strength was 40 per cent higher in the first half of the Oligocene when the average reversal frequency was 1.6 Myr^-1 than in the second half when the reversal frequency was 4 Myr^-1. There is also a weak dependence of average field strength on length of polarity interval. Finally, in the three cores suited to spectral analysis (of coherent polarity and relative intensity independent of lithological contamination), there is a persistent ca. 30–50ka periodicity in the variations of the relative intensity, suggesting that the geomagnetic field 'pulses' at about this frequency, not only during the Brunhes (as demonstrated by Tauxe & Shackleton 1994), but in the Oligocene as well.     

Hepatic biomarkers of sediment-associated pollution in juvenile turbot, Scophthalmus maximus L

Hatchery-reared turbot (Scophthalmus maximus L.) were exposed for 3 weeks, under laboratory conditions, to sediment collected from polluted sites in Cork Harbour and a reference site at Ballymacoda, Co. Cork, Ireland. The potential of surficial sediment for inducing hepatic biomarkers was assessed at two levels of biological organisation: expression of cytochrome P450 [Western blotting analysis and 7-ethoxy-resorufin O-dealkylase (EROD), 7-benzoxy resorufin O-dealkylase (BROD), 7-methoxy resorufin O-dealkylase (MROD), 7-pentoxy-resorufin O-dealkylase (PROD) activities] and DNA integrity (Comet assay). Positive controls were generated, either by exposing turbot to cadmium chloride-spiked seawater (Comet assay) or to beta-naphthaflavone by intraperitoneal injection (cytochrome P450 induction). The induction of cytochrome P450 activity (EROD, MROD and PROD) in animals following a 7-day exposure to contaminated sediments was significantly higher than those exposed to reference site sediment and remained elevated thereafter; BROD was not induced. DNA single-strand breaks were also significantly higher following exposure to contaminated sediments throughout the experiment. Although no direct correlation between induction of alkoxyresorufin O-dealkylase activities and a particular chemical class was established, the induction of MROD and PROD activities in fish exposed to sediments containing complex contaminant mixtures, appeared to be more sensitive than conventional EROD activity assays. We conclude from the present laboratory study that S. maximus is a suitable sentinel species for the assessment of moderately contaminated sediments and therefore allows for the further development of this model for future, ecologically relevant, field studies.     

Thermal expansion and decomposition of jarosite: a high-temperature neutron diffraction study

The structure of deuterated jarosite, KFe₃(SO₄)₂(OD)₆, was investigated using time-of-flight neutron diffraction up to its dehydroxylation temperature. Rietveld analysis reveals that with increasing temperature, its c dimension expands at a rate ~10 times greater than that for a. This anisotropy of thermal expansion is due to rapid increase in the thickness of the (001) sheet of [Fe(O,OH)₆] octahedra and [SO₄] tetrahedra with increasing temperature. Fitting of the measured cell volumes yields a coefficient of thermal expansion, α = α₀ + α₁ T, where α₀ = 1.01 × 10⁻⁴ K⁻¹ and α₁ = −1.15 × 10⁻⁷ K⁻². On heating, the hydrogen bonds, O1···D–O3, through which the (001) octahedral–tetrahedral sheets are held together, become weakened, as reflected by an increase in the D···O1 distance and a concomitant decrease in the O3–D distance with increasing temperature. On further heating to 575 K, jarosite starts to decompose into nanocrystalline yavapaiite and hematite (as well as water vapor), a direct result of the breaking of the hydrogen bonds that hold the jarosite structure together.     

On the use of horizontal acoustic Doppler profilers for continuous bed shear stress monitoring

Continuous monitoring of bed shear stress in large river systems may serve to better estimate alluvial sediment transport to the coastal ocean.Here we explore the possibility of using a horizontally deployed acoustic Doppler current profiler(ADCP) to monitor bed shear stress,applying a prescribed boundary layer model,previously used for discharge estimation.The model parameters include the local roughness length and a dip correction factor to account for sidewall effects.Both these parameters depend on river stage and on the position in the cross-section, and were estimated from shipborne ADCP data.We applied the calibrated boundary layer model to obtain bed shear stress estimates over the measuring range of the HADCP.To validate the results,co-located coupled ADCPs were used to infer bed shear stress,both from Reynolds stress profiles and from mean velocity profiles. From HADCP data collected over a period of 1.5 years,a time series of width profiles of bed shear stress was obtained for a tidal reach of the Mahakam River,East Kalimantan,Indonesia.A smaller dataset covering 25 hours was used for comparison with results from the coupled ADCPs.The bed shear stress estimates derived from Reynolds stress profiles appeared to be strongly affected by local effects causing upflow and downflow,which are not included in the boundary layer model used to derive bed shear stress with the horizontal ADCP.Bed shear stresses from the coupled ADCP are representative of a much more localized flow,while those derived with the horizontal ADCP resemble the net effect of the flow over larger scales.Bed shear stresses obtained from mean velocity profiles from the coupled ADCPs show a good agreement between the two methods,and highlight the robustness of the method to uncertainty in the estimates of the roughness length.     

华北北部古生代大陆地壳增生过程中的岩浆作用与成矿效应

包括前寒武纪克拉通与显生宙造山带两大构造单元的华北北部,古生代时期板块构造体制下古亚洲洋的裂解-扩展-消亡与汇聚大陆边缘的俯冲-碰撞-伸展循环构成了其大陆地壳增生与再造演化的基本图景,并形成了一系列记录这些因果演变连续过程的岩浆侵入与喷发事件。这些物质记录无疑是研究汇聚大陆边缘壳-幔作用和物质交换、大陆地壳演化与大规模成矿作用耦合关系的绝佳窗口。本文在系统总结最近几年积累的年代学和岩石地球化学资料的基础上,以一些带有特定过程印记的标志性岩浆事件为纲领,表征这些古生代岩浆作用形成过程中的地球动力学演变,揭示其所记录的华北北部大陆地壳的多阶段增生与再造演化机制,并初步探讨了有利地球动力学过程制约下的岩浆行为引起的成矿物质聚集效应。     

内蒙古白云鄂博地区基底岩石锆石年代学及对构造背景的指示

白云鄂博地区的克拉通基底岩石主要由糜棱岩化花岗片麻岩(2588±15Ma),正长岩、花岗闪长岩(2018±15Ma)和黑云母花岗片麻岩、含石榴石蓝晶石花岗片麻岩(～1890Ma)等组成,白云鄂博超大型稀土矿床就位于华北克拉通太古代基底之上。太古代克拉通基底在早元古代中晚期(2.0Ga)又经历了一次强烈的碰撞造山运动,造成了闪长质与花岗质岩浆侵位,以及1.9Ga片麻岩相变质事件。     

Detecting genotoxicity using the Comet assay following chronic exposure of Manila clam Tapes semidecussatus to polluted estuarine sediments

Sediments frequently cause damage to biota due to the accumulation of toxic compounds and the bioavailability of sediment-bound contaminants. Damage can be assessed using biomarkers, such as the degree of genotoxic impact following in vivo exposure to pollutants. Genotoxic damage, expressed as single-strand DNA breaks, was measured in cells isolated from haemolymph, gill and digestive gland from the clam Tapes semidecussatus, using the single cell gel electrophoresis (Comet assay). Clams were exposed for three weeks to sediment samples collected from a polluted site and a ‘clean’ reference site.

The level of DNA damage was assessed using an image analysis package and expressed as Tail Moment. Throughout the study, significant differences in DNA damage were recorded for each tissue type between clams exposed to the two sediment samples. We conclude that the Comet assay is a useful tool for the detection of DNA damage in clams chronically exposed to polluted sediments.     

An assessment of the pollutant status of surficial sediment in Cork Harbour in the South East of Ireland with particular reference to polycyclic aromatic hydrocarbons

Surface sediment from three polluted sites within Cork Harbour, Ireland, and from a relatively clean reference site were collected and analysed for polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), brominated flame retardants (BFRs), organotins (OTs), and heavy metals. PAHs were determined to be the most abundant class of contaminant. Concentrations of the sum (Sigma) of the 21 PAHs measured from the Harbour sites (2877.70 ng g(-1), 1000.7 ng g(-1) and 924.40 ng g(-1) dry weight respectively) were significantly higher than that of the sediment from the reference site (528.30 ng g(-1) dry weight). An inner harbour site, Douglas being the more contaminated of the three harbour sites. A similar pattern was observed with the other contaminants however, these compounds, with the exception of the heavy metals, all tended to be detected at concentrations on or below detection limits.     

Implications of seasonal priming and reproductive activity on the interpretation of Comet assay data derived from the clam, Tapes semidecussatus Reeves 1864, exposed to contaminated sediments

We explore the use of the clam Tapes semidecussatus Reeves 1864 as an indicator for the presence of potentially genotoxic substances in estuarine sediments. The limitations associated with the interpretation of Comet assay data (expressed as % DNA in tail) in terms of clam reproductive state, size (age) and thermal exposure history following laboratory acclimation are discussed. Hatchery-reared clams, subjected to ambient temperature fluctuations during growth, were exposed in vivo under laboratory conditions for three weeks to sediment samples collected from a polluted site and a "clean" reference site. The DNA damage observed in haemocytes, gill and digestive gland cells was significantly higher in animals exposed to contaminated sediment compared to those exposed to sediment from the reference site. The extent of DNA damage recorded was not correlated with size (age). Spawning was not observed during the experiment. Nevertheless, clams with well-developed gonads showed a statistically higher degree of DNA damage in gill and digestive gland cells- but not haemocytes, demonstrating an increased sensitivity to potential genotoxic compounds, possibly caused by impaired DNA repair capacity due to reproductive activity. Furthermore, the degree of DNA damage in clams exposed to contaminated sediments was higher in autumn and winter compared to spring and summer, suggesting an effect of seasonal priming.     

Influence of chronic exposure to silver and mercury in the field on the bioaccumulation potential of the bivalve Macoma balthica

In order to assess the adaptation to metals previously observed in the bioindicator organism, Macoma balthica, subjected to chronic contamination by silver and mercury in the French Loire estuary, the bioaccumulation potential of individual organisms originating from the contaminated Loire estuary and a relatively uncontaminated control estuary (Somme) was evaluated using both radiotracers and stable isotopes of Ag (80 μg Ag litre⁻¹) and Hg (100 μg Hg litre⁻¹). Clams from the contaminated estuary were more sensitive to Ag (LT₅₀ = 9d) than those originating from the Somme estuary (LT₅₀ > 15d), even though the former bioaccumulated Ag to a significantly lower degree. This is attributed to a consequence of the chronic stress induced by Ag while clams were living in their natural environment. Therefore, past history of trace metal contamination should be considered when evaluating the susceptibility of M. balthica to heavy metal exposure. Lower uptake rates obtained for Hg (during the initial uptake phase only) and for Ag in clams from the polluted estuary suggest the presence of an adaptive trait for survival in contaminated areas. However, the lower degree of bioconcentration observed for Ag was not sufficiently low to reduce the sensitivity of the organisms to Ag and allow them to resist the toxic stress. Clams that survived Ag or Hg exposure at LT₅₀ did not protect themselves against metal toxicity by accumulating a significantly lesser amount of these metals than clams which did not survive metal stress. The results suggest that the bioaccumulation potential of each individual was not a factor which can explain the survival ability of M. balthica exposed to chronic Ag and Hg contamination in estuaries. In this case, cellular, biochemical and genetic levels of adaptation are presumed to be of greater importance.