Anthropogenic trace metals in sediment and settling particulate matter on a high-energy continental shelf (Sydney,Australia)

The anthropogenic contribution of trace metals to settling particulate matter (SPM) and surficial sediments was determined on the high-energy continental shelf adjacent to Sydney, Australia. Settling particulate matter and surficial sediment was collected in the vicinity of a major sewage outfall and at five control sites on the middle shelf (80-100 m water depth). Sediment traps were deployed on 10 occasions for up to 2 weeks during the summer and winter of 1995 and SPM was analyzed for Ag, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn. Cobalt, Fe, Mn and Ni act conservatively in SPM and in sediments regionally and are used as normalizing elements to determine anthropogenic enrichment. Surficial sediments and SPM are enriched in Ag, Cr, Cu, Pb and Zn near a major ocean outfall and at four of the five control sites, although sewage particles contribute < 5% of trace metals in the total sample. Silver is the most sensitive trace metal tracer for establishing the presence of sewage particulate matter. Sewage particulate matter flux near the outfall was estimated using a two end-member mixing model and is below 0.5 g m(-2) day(-1) during all deployment periods. The mean sewage particulate matter flux at sampling locations 30 km and 60 km north of the outfall are <0.13 g m(-2) day(-1) and <0.01 g m(-2) day(-1), respectively, indicating an efficient dispersal of anthropogenic material on this high energy continental shelf.     

Phototoxicity of pyrene and benzo[a]pyrene to embryo-larval stages of the Pacific oyster Crassostrea gigas

There is a growing body of evidence to suggest that certain polycyclic aromatic hydrocarbons (PAHs) pose a greater hazard to aquatic organisms than previously demonstrated, due to their potential to cause photo-induced toxicity when exposed to ultraviolet (UV) radiation. The consequences of photo-induced toxicity are reported here for embryo-larval stages of the pacific oyster Crassostrea gigas, following exposure to pyrene and benzo[a]pyrene. During laboratory investigations, significant increases in toxicity were observed in the presence of environmentally attainable levels of UV-radiation, compared with embryos exposed to PAH alone, at levels previously deemed to have little acute biological effect. The phototoxicity of pyrene and benzo[a]pyrene completely inhibited the development to the D-shell larval stage when embryos were simultaneously exposed to 5 microg l(-1) PAH and ultraviolet light (UVB = 6.3 +/- 0.1 microW/cm2 and UVA = 456.2 +/- 55 microW/cm2). A linear relationship was also demonstrated for benzo[a]pyrene phototoxicity with decreasing UV light intensity.     

An initial demonstration of underwater acoustic communication using time reversal

In July 1999, an at-sea experiment to measure the focus of a 3.5-kHz centered time-reversal mirror (TRM) was conducted in three different environments: an absorptive bottom, a reflective bottom, and a sloping bottom. The experiment included a preliminary exploration of using a TRM to generate binary-phase shift keying communication sequences in each of these environments. Broadside communication transmissions were also made, and single-source communications were simulated using the measured-channel response. A comparison of the results is made and time reversal is shown to be an effective approach for mitigating inter-symbol interference caused by channel multipath.     

Differential model of the hydrophysical fields' vertical structure in a stratified tidal flow over a shelf

This paper studies the influence of shelf tidal flows on the structure of surface and near-bottom turbulent boundary layers.Translated by Vladimir A. Puchkin.     

Response of the blue mussel Mytilus edulis L. following exposure to PAHs or contaminated sediment

The polycyclic aromatic hydrocarbons fluoranthene and benzo(a)pyrene significantly reduced the feeding rate of mussels. For both compounds the tissue concentration resulting in a 50% reduction of the clearance rate (TEC₅₀) was calculated. At high tissue concentrations both aromatic compounds reduced the tolerance of mussels to aerial exposure, whereas at low tissue concentrations an improved response was noticed. The activities of the antioxidant enzymes Superoxide dismutase (SOD) and catalase were elevated only at low tissue concentrations of fluoranthene and benzo(a)pyrene. At the highest measured tissue concentrations the activity of both enzymes was reduced, possibly due to a narcotic effect. The reproductive success rate of mussels appeared to be affected negatively by the investigated hydrocarbons. The results of a pilot experiment indicate that mussels can be used also for the testing of contaminated sediments.     

Large aperture seismic imaging at a convergent margin: Techniques and results from the Costa Rica seismogenic zone

In March and April 1995 a cooperative German, Costa Rican, and United States research team recorded onshore-offshore seismic data sets along the Pacific margin of Costa Rica using the R/V Ewing. Off the Nicoya Peninsula we used a linear array of ocean bottom seismometers and hydrophones (OBS/H) with onshore seismometers extending across much of the isthmus. In the central area we deployed an OBS/H areal array consisting of 30 instruments over a 9 km by 35-km area and had land stations on the Nicoya Peninsula adjacent to this marine array and also extending northeast on the main Costa Rican landmass. Our goal in these experiments was to determine the crustal velocity structure along different portions of this convergent margin and to use the dense instrument deployments to create migrated reflection images of the plate boundary zone and the subducting Cocos Plate. Our specific goal in the central area was to determine whether a subducted seamount is present at the location of the 1990, M 7 earthquake off the Nicoya Peninsula and can thus be linked to its nucleation. Subsequently we have processed the data to improve reflection signals, used the data to calculate crustal velocity models, and developed several wide-aperture migration techniques, based on a Kirchhoff algorithm, to produce reflection images. Along the northern transect we used the ocean bottom data to construct a detailed crustal velocity model, but reflections from the plate boundary and top and bottom of the subducting Cocos plate are difficult to identify and have so far produced poor images. In contrast, the land stations along this same transect recorded clear reflections from the top of the subducting plate or plate boundary, within the seismogenic zone, and we have constructed a clear image from this reflector beneath the Nicoya shelf. Data from the 3-D seismic experiment suffer from high-amplitude, coherent noise (arrivals other than reflections), and we have tried many techniques to enhance the signal to noise ratio of reflected arrivals. Due to the noise, an apparent lack of strong reflections from the plate boundary zone, and probable structural complexity, the resulting 3-D images only poorly resolve the top of the subducting Cocos Plate. The images are not able to provide compelling evidence of whether there is a subducting seamount at the 1990 earthquake hypocenter. Our results do show that OBS surveys are capable of creating images of the plate boundary zone and the subducting plate well into the seismogenic zone if coherent reflections are recorded at 1.8 km instrument spacing (2-D) and 5 km inline by 1 km crossline spacing for 3-D acquisition. However, due to typical high amplitude coherent noise, imaging results may be poorer than expected, especially in unfavorable geologic settings such as our 3-D survey area. More effective noise reduction in acquisition, possibly with the use of vertical hydrophone arrays, and in processing, with advanced multiple removal and possibly depth filtering, is required to achieve the desired detailed images of the seismogenic plate boundary zone.     

Lead and Aroclor 1254 disrupt reproductive neuroendocrine function in Atlantic croaker

We have previously shown that lead (lead chloride) and a polychlorinated biphenyl (PCB) mixture (Aroclor 1254) can alter hypothalamic serotonin (5-hydroxytryptamine, 5-HT) content, and pituitary gonadotropin II (GTH II) release in vitro, in the Atlantic croaker (Micropogonias undulatus). In the present study we investigated whether impairment of the hypothalamic 5-HT pathway involves alterations in tryptophan hydroxylase (TPH), the rate-limiting enzyme in 5-HT biosynthesis, or monoamine oxidase (MAO), the catabolic enzyme. Aroclor 1254 (1 mg/kg body wt. for 30 days) significantly inhibited hypothalamic TPH activity without altering MAO activity, and caused a significant decline in 5-HT content. On the other hand, lead exposure (15 mg/kg body wt. for 30 days) only induced a slight decrease in hypothalamic 5-HT content and TPH activity, and a minor increase in MAO activity. However, both Aroclor 1254 and lead significantly inhibited the GTH II response to stimulation by a luteinizing hormone-releasing hormone analog (LHRHa) in vivo and caused reduced gonadal growth. These results demonstrate that impairment of hypothalamic serotonin metabolism by Aroclor 1254 involves inhibition of 5-HT synthesis, whereas lead does not exert a profound influence on 5-HT metabolism. The decline in 5-HT availability due to reduced 5-HT synthesis in the PCB-exposed fish may result in disruption of the stimulatory 5-HT-GnRH pathway controlling GTH II secretion leading to impairment of gonadal growth.     

Biochemical and histochemical responses to environmental contaminants in clam, Tapes philippinarum, transplanted to different polluted areas of Venice Lagoon, Italy.

In this study the clam, Tapes philippinarum, a filter-feeding bivalve living in soft bottoms, was used to investigate the water/sediment pollution in Venice Lagoon (Venice, Italy), a heavily urbanised and industrialised area. To this end, clams collected from indigenous populations in a clean farming area (Val Dogà) were transplanted into a relatively low contaminated site (Palude della Rosa) and in a heavily polluted area (Porto Marghera), for 5 weeks. A range of possible induced stress indices were measured, on the basis of potential toxicity mechanisms, including specific enzymatic activities [Bap hydroxylase and NADPH cytochrome c reductase, superoxide dismutase, catalase, glutathione peroxidase and propionaldehyde dehydrogenase (PDH)] and general cellular responses (lysosomal latency). Moreover, chemical analyses (polychlorinated biphenyls, polycyclic aromatic hydrocarbon, DDTs) were carried out on sediments and animal tissues at the beginning and end of the transplantation experiments. The chemical results show an active bio-accumulation activity from sediment in clams translocated to the most polluted area. Correspondingly, biological data indicate marked effects on PDH activity and latency in T. philippinarum from the same site. In contrast, no similar pattern has been observed in the other considered indices, possibly due to antagonistic effects of the complex contaminant mixture present in the environment.     

The requirements for stable metallothionein clusters examined using synthetic lobster domains.

Metallothioneins (MTs) are small, cysteine-rich proteins which detoxify xenobiotic metals such as cadmium (Cd) and mercury (Hg). In crustaceans and mammals they consist of two independent domains which are folded around metal-thiolate clusters. MT clusters of different origins, exhibiting distinct, highly conserved cysteine positions on their sequences, show differences in metal-cysteine coordination and reactivity. Lobster-MT, containing two Cd3 beta domains, is an important model for structure-function relationships among the clusters. The influence of (1) the position of the cysteine residues and (2) steric and electrostatic effects of neighboring amino acids on the folding and stability of MT cluster were investigated. Thus, the native lobster beta C and beta N domains (each having nine cysteines and binding three M2+ ions) and a modified domain Cd3 beta C-->N, in which the cysteines of the C-terminal domain were relocated to match the positions of those in the N-terminal domain, were chemically prepared and characterized. The synthetic native domains (Cd3 beta C and Cd3 beta N) were found to exhibit spectroscopic properties, metal-binding affinities and kinetic reactivity similar to the holo-protein. However, the modified Cd3 beta C-->N domain was unusually reactive and in the presence of Chelex, metal chelation resin, aggregated to a Cd5(beta C-->N)2 dimer, which exhibited unusual structure as observed by its 113Cd-nuclear magnetic resonance. These differences in structure and reactivity demonstrated that the requirements for formation of a stable Cd3S9 beta-cluster are more stringent than simply the sequential positions of the cysteines along the peptide chain and must include interactions involving neighboring, noncysteine amino acids.     

Distribution of the CO2 partial pressure along an Atlantic meridional transect

Atmospheric and oceanic pCO₂ were measured continuously along an Atlantic Meridional transect (50°N–50°S) in September–October 1995 and 1996 (U.K. to the Falklands Islands) and in April–May 1996 (Falklands Islands to the UK). The Atlantic ocean was a net sink for atmospheric CO₂ for all 3 transects. The largest sinks were located at high latitudes, in regions of high wind speed, where strong CO₂ undersaturations, associated with high biological activity, were observed. In these regions the partial pressure difference between the ocean and the atmosphere reached −110 μatm. A CO₂ source occurred in the equatorial region between 0° and 10°S, where ΔpCO₂ of up to 40 μatm was found. Another source was in the northern subtropical gyre where its extension varied according to the season. Along the whole transect the October cruises exhibited similar pCO₂ distributions suggesting a dominance of the seasonal variability and small year to year changes.