An ocean bottom,microprocessor based seismometer

We describe the design and construction of an ocean bottom seismometer configured as a computer, based on an Intersil IM6100 microprocessor plus appropriate peripheral devices. The sensors consist of triaxial 1 Hz seismometers and a hydrophone, each sensor channel being filtered prior to digitizing so that typical noise spectra are whitened. Digital data are recorded serially on magnetic tape. The instrument is placed on the ocean bottom by allowing it to fall freely from just below the surface. An acoustic system allows precise determination of instrument position, acoustic recall, and transmission of operational information to the surface. Release from an expendable anchor is accomplished by redundant pyrotechnic bolts which can be fired by acoustic command or by precision timers.The operational flexibility provided by the micro-computer, which executes the DEC PDP8/E instruction set, enables optimum use of the 6-hr recording capacity (at 128 samples/second/channel) in the context of the particular experiment being performed.

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Species, tissue and gender-related organochlorine bioaccumulation in white-sided dolphins, pilot whales and their common prey in the northwest Atlantic

Organochlorine concentrations were measured in white-sided dolphins, pilot whales, and their prey from the Gulf of Maine and used to identify species, tissue, and gender differences, and trophic transfer trends, in bioaccumulation. Polychlorinated biphenyl concentrations ([PCB]) in dolphin blubber (13 +/- 7.1 micrograms/g fresh wt.) were twice those in pilot whales, but pesticide concentrations (20 +/- 13 micrograms/g fresh) were similar between species. 4,4'-DDE, trans-non-achlor, Cl6(153) and Cl6(138) concentrations were highest. Skin tissues had more recalcitrant organochlorines than the internal organs. Male dolphins bioaccumulated higher concentrations of nonmetabolizable PCBs and hexachlorocyclohexane (HCH) isomers, whereas pilot whales had no gender-related differences in bioaccumulation. Pilot whales, mackerel, and herring had proportionately higher concentrations of DDTs, whereas [PCB] were higher in dolphins and squid. Although these odontocetes feed at the same trophic level and store a similar suite of contaminants, dolphins bioaccumulated higher and potentially hazardous 4,4'-DDE and PCB concentrations from food in their more geographically restricted range.     

Methods of fitting the Fisher-Tippett type 1 extreme value distribution

Methods are described for estimating the parameters of the Fisher-Tippet Type 1 extreme value distribution and associated return values from measured extremes, such as maximum wave height. A comparison of these methods, with simulated data, shows that those using Gumbel's plotting position are least satifactory. Maximum likelihood methods give the smallest mean square errors, but the very much simpler method of moments is nearly as good.     

Acoustic reflectors in the surface layers of deep sea sediments

Using ultrasonic scanning it is possible to display the position of an acoustic discontinuity within a sediment core and the amplitude of the reflected signal which results from it. From these results it has been possible to examine the effect of variations in the geotechnical properties on the reflection of compressional waves at normal incidence within the core at a frequency of 100 kHz. The occurrence of acoustic reflectors in the surface layers of North Atlantic sediments has also been examined.Two ultrasonic scanning systems for the non-destructive testing of marine sediment cores have been developed. The performance of the two systems has been evaluated using the results from measurements made on a suite of marine sediment cores from the North Atlantic in conjunction with X-ray scanning and geological analysis of the same cores.     

Trace metals and hydrocarbons in sediments from the Southampton water region,with particular reference to the influence of oil refinery effluent

The concentrations of a number of trace metals (Co, Ni, Cu, Zn, Ag, Cd and Hg) have been determined in sediments from cores collected in the Southampton Water region. Measurements of total hydrocarbons were also made on several of the cores. Markedly elevated concentrations of copper, up to 362 μg/g dry wt, were found in sediments which were collected close to the discharge points of oil refinery outfalls and which also showed concentrations of total hydrocarbons considerably greater than the background levels for the estuary. The results of selective chemical extractions showed that much of the copper was present in the non-lattice fraction of the sediment. Although the concentrations of Co, Ni, Zn and Cd were significantly correlated with those of copper in the core showing the highest concentrations of this element, these metals were not enhanced in comparison with the levels found in several other parts of the estuary. Variations in concentrations of metals in sediments throughout the estuary were not correlated with differences in organic carbon content.