黄河口及渤海中南部沉积物工程特性及其机理

采用Ｋａｓｔｅｎ取样器从黄河口及渤海湾中南部海底沉积物中取样，对样品通过土工性质、微结构研究以及粘土矿物分析，阐明本研究区三维空间展布的海底沉积物形成机理及其工程地质规律，论证水动力作用和斜坡不稳定性对工程特性和微结构的重要影响．     

A shipborne magnetic survey in Hudson Bay

A marine magnetic total-field survey of Hudson Bay was conducted from 1975 to 1978. Approximately 62 000 line-km of data, or 35 000 five-minute averages, were acquired. The data were corrected for secular variation by means of a polynomial in latitude, longitude, and time, first fitted to annual mean differences from nine observatories and then integrated over time. The data were corrected for diurnal and transient variations by means of a linear interpolation, over geomagnetic latitude, of running hourly mean values from two neighbouring magnetic stations (numbering seven in all). Crossover differences are analysed in terms of a mixture of normal distributions resulting from the intermittent transient variations, and indicate the effectiveness of the corrections. The variance of the data is reduced, as a result of the corrections, by 87% during quiet periods and by 53% during disturbed periods, the weighted variance being reduced by 66%. Navigational accuracy is estimated, from a novel method utilizing crossover differences and field gradients, to be approximately 300 m. Anomalies are presented in profile form, and discussed briefly.Contribution from the Earth Physics Branch No. 973.     

Trace metals in the Western Pacific: temporal and spatial variability in the concentrations of Cd, Cu, Mn and Ni

Profiles of total dissolvable Cd, Cu, Mn and Ni are reported for samples collected from the southwest Pacific in 1989, from the western equatorial Pacific along 155°E at 5°S, 0° and 5°N in 1990 and 1993, and along the equator from 143°E to 152°E and in the Bismarck Sea in 1997 and 2000. Profiles of Cd along 155°E in 1990 and along the equator were essentially the same but, in 1993, Cd values at 5°N were higher by a factor of about 1.5–2 than at 5°S over the depth range 500–1500 m. Similar, but less pronounced, differences were observed for PO₄ and Ni. Cd and Ni were both strongly correlated with PO₄, and an even stronger correlation was found between Ni and Cd. The concentration of Ni did not fall below ≈2 nmolkg⁻¹, even in the nitrate-depleted waters of the western equatorial Pacific, where primary production is strongly dependent on recycled nitrogen (mainly ammonia and urea). It is proposed that this residual Ni is not bioavailable and that Ni could be biolimiting, since the metabolism of urea requires the nickel-containing enzyme urease. The impact of the Sepik River on Cd, Cu and Ni concentrations was small but elevated concentrations of Mn were observed near the Sepik River and close to the coast suggesting that the rivers and sediments on the north coast of New Guinea are a significant local source of Mn to the Bismarck Sea. Simple mass balance calculations show that the elevated levels of Mn observed in the Equatorial Undercurrent cannot be due to input from the rivers of New Guinea and they were attributed to the trapping of particulate matter due to strong current shear. A strong hydrothermal source of Mn was observed in the central Bismarck Sea.     

Oxidative stress in ecotoxicology: from the analysis of individual antioxidants to a more integrated approach

An integrate approach will be discussed for investigations on oxidative stress in xenobiotic toxicity. While the analysis of individual antioxidants is useful for their sensitivity and to understand the mode of action of a stressor, the integration with the analysis of the total antioxidant capacity provides a more holistic assessment of the overall biological significance of such variations. TOSC has a greater predictive value on the health condition of the organisms and allows to discriminate the different role of specific ROS in oxidative stress syndrome.     

Diel fluctuations in dissolved free amino acids and monosaccharides in Chesapeake Bay dinoflagellate blooms

The accumulation of phytoplankton biomass in recurring summer dinoflagellate blooms of Chesapeake Bay is accompanied by large pools of dissolved organic matter (DOM). Two fractions of the DOM, free amino acids (DFAA) and monosaccharides (MONO), were measured at 3 h intervals in mixed species dinoflagellate blooms (Katodinium rotundatum, Gymnodinium spp.) and related to productivity, biomass and photoperiod. Peak chlorophyll levels for the three blooms were 28, 65 and 938 μg1⁻¹. In general, DFAA and MONO concentrations increased with increasing biomass of bloom-forming species, reaching 203 and 844 μg1⁻¹. MONO appeared to accumulate during the day while there was no consistent pattern for DFAA. The accumulations of DFAA and MONO in blooms indicate that bloom production might stimulate microheterotrophy, thereby enhancing carbon and nutrient cycling in bloom-impacted regions.     

Magnetic studies over the northern extension of the Prathap Ridge complex,eastern Arabian Sea

The northern parts of the Prathap and Laccadive Ridge system, eastern Arabian Sea, consist of three parallel basement ridge peaks at varied depths. The topographic highs are associated with either well-developed or subdued magnetic signatures. Model studies, constrained by seismic results, determine the varied nature and depth to the top of the causative basement bodies. Similarities of the geophysical signatures of the ridges and their structural resemblance perhaps point to their common origin. Hence we propose that the Prathap Ridge complex may be a part of the Chagos-Laccadive Ridge system and formed because of the Reunion hotspot activity.     

Short period internal waves over the Huanghe (Yellow River) delta front

Internal waves with periods of about 5 minutes and trough to crest heights of up to 6.2 m were observed acoustically over the actively accreting delta front of the Huanghe (Yellow River) in the western portion of the Gulf of Bohai, Peoples Republic of China. The radian frequency of the internal waves was close to the locally-observed Brunt-Vaisala frequency. Through the relatively short (one hour) duration of an internal wave train, the amplitude was observed to decrease progressively with time. These internal waves may cause resuspension of delta-front sediments.     

Precise positioning for near-bottom equipment using a relay transponder

The Marine Physical Laboratory of the Scripps Institution of Oceanography has developed an acoustic relay transponder for precise relative positioning of near-bottom instruments and geologic sampling devices. Although specifically designed to position equipment lowered on standard wire ropes without a need to maintain direct electrical contact with the surface ship, the relay transponder may be used to track free vehicles, such as deep submersibles, from the surface. The relay transponder is positioned relative to an array of bottom-anchored acoustic transponders. It is interrogated acoustically from the surface ship; it then sequentially interrogates the bottom transponders which, in turn, reply to the ship. From the measurement of the total travel time (ship to relay transponder to bottom transponder to ship) and assuming, or knowing, the sound velocity of the water, we obtain a relayed range measurement. These relayed ranges, used in conjunction with ship to bottom-transponder ranges, allow us to calculate the position of the relay transponder. A recent application of this technique is described in which several gravity core samples from the crest of the Horizon Guyot were positioned with respect to the detailed bathymetry and the geology within the area. The estimated error in positioning the samples is less than 20 m inside a navigational net extending over 100 km².Contribution of the Scripps Institution of Oceanography, new series.     

Voltammetric estimation of iron(III) thermodynamic stability constants for catecholate siderophores isolated from marine bacteria and cyanobacteria

Thermodynamic stability constants have been estimated for the complexation of iron(III) with catecholate-type siderophores isolated from the marine bacterium Alteromonas luteoviolacea and from the marine cyanobacterium Synechococcus sp. PCC 7002. Stability constants were determined utilizing the “chelate scale” of Taylor et al. (1994). The scale is based upon a linear relationship between the reduction potentials and the pH-independent thermodynamic stability constants for known iron(III) complexes. Log K values for the alterobactin B ferric iron complex are 43.6 ± 1.5 at pH 8.2 and 37.6 ± 1.2 at pH 6, consistent with a shift from bis-catecholate to monosalicylate/monocatecholate iron coordination with decreasing pH. Synechococcus isolates PCC 7002 Nos. 1 and 3 formed iron(III) complexes with stability constants of approximately 38.1 ± 1.2 and 42.3 ± 1.5, respectively. The binding strengths of the iron(III) complexes examined in this study are quite high, suggesting that catecholate siderophores may play a role in the solubilization and biological uptake of iron in the marine environment.