A performance comparison for two lagrangian drifter designs

Abstract

We compare the water‐parcel‐following and position‐reporting performance of two recent drifter designs. One (Tristar‐II ) uses the ARGOS satellite navigation system, has a very large drogue: float frontal area ratio and a small velocity error resulting from wind drag and surface wave forces. The second design uses an internal Loran receiver and transmits its position every half hour by radio. Its drogue: float frontal area ratio is much smaller than the TRISTAR's; we wished to know if this difference caused a significant change in drifter trajectory. Over a 78‐h joint deployment, the two designs had nearly identical trajectories. Measured drift speeds ranged from 10 to 30 cms^?1. Wind speeds (an important potential biasing factor) ranged up to 15 ms^?l. Net velocity difference over the full deployment was only 0.1 cms^?1. Frontal trapping of both drifters during the latter part of the comparison period may have helped to minimize this difference. But we also observed little or no downwind slippage (the net velocity difference was less than 2 cm s^?1 and was nearly normal to the wind and wave directions) during the first third of the deployment, when winds were strongest and the constancy of the water properties measured at drogue depth indicated no frontal trapping. Because the trajectories of the drifters were so similar, the most important differences in their performance were due to their position‐reporting and deployment characteristics. Initial deployment of the tristar was easier, and its positioning method and lower power requirement allow much longer untended deployments. The Loran design gave more frequent and precise positioning information and, therefore, better resolution of short‐time‐scale velocity fluctuations. It was also easier to find at sea, and to recover and redeploy.     

Surface currents in British Columbia coastal waters: Comparison of observations and model predictions

Abstract

Observations of the motion of ocean surface drifters are used to evaluate numerical simulations of surface currents in the region of Queen Charlotte Sound on the West Coast of Canada. More than 30 surface Argos drifters were deployed in the spring and summer of 1995, revealing daily average currents of 10 to 40 cm s^–1 near the coast of Vancouver Island in summer, and less than 10 cm s^–1 in mid‐sound. Wind observations in this region are provided by a network of weather buoys. Comparison of daily average drifter velocities and winds shows that the drifters moved at 2 to 3% of the wind speed, and at about 30 degrees to the right of the wind.

A complex transfer function is computed between daily wind and drifter vectors using least squares techniques. The ratio of variance in the least squares residual currents to the variance of observed drifter currents is denoted γ². A percent goodness‐of‐fit is defined as g(γ²) = 100(1 – γ²), and is 42% for the case of daily winds and drifter currents. Drifter‐measured currents are compared with two numerical simulations of surface currents: Fundy5, a steadystate baroclinic model based on historical water property measurements in summer, and the Princeton Ocean Model (POM), a prognostic, baroclinic model forced by the measured winds. Fundy5 by itself provides a goodness‐of‐fit of only 3%, whereas POM has g(γ²) = 42%. The combination of Fundy5 plus daily wind gives g(γ²) = 43%. Although the prognostic model performs only as well as the winds by themselves, it simulates the near shore currents more accurately and reproduces the speeds and veering in the surface Ekman layer on average without bias. Residual currents unexplained by POM are likely due to advection of water masses into this region and horizontal inhomogeneities in the density field that are not input to the model, as well as to Stokes drift of wind waves and to net Lagrangian tidal motion not represented by the model.     

The igneous geochemistry and tectonic setting of metabasites from the emo metamorphics,Papua New Guinea; A record of the evolution and destruction of a backarc basin

Summary Metabasites from the Emo Metamorphics, occurring as thrust sheets beneath the Papuan ophiolite of Papua New Guinea, fall into four petrographic groups; Group 1 (garnetiferous blueschists), Group 2 (amphibolites), Group 3 (lawsonite blueschists) and Group 4 (greenschists). Most specimens shows a polymetamorphic history with textures grading from crudely foliated to mylonitic. Many contain primary igneous clinopyroxene, suggesting that metamorphism occurred under relatively low . This may explain the coherent magmatic geochemical signatures shown by many major elements normally mobilised during metamorphism. Geochemically the rocks are all tholeiitic in character and fall into three suites; Suite 1 are LREE depleted, resembling N-MORB with Zr/Nb values of > 40, Suite 2 are LREE enriched resembling E-MORB and having significantly lower Zr/Nb values of 8-16. Suite 3 includes ferrobasalts possibly comagmatic with Suite 2 but arbitrarily separated byP₂O₅ contents of > 0.5 and Zr contents of > 250 ppm. The three suites show significantly lower FeO* and higher AI₂O₃ than a Galapagos MORB comparative suite; these, and other trace element characteristics are normally associated with back-arc basin basalts. Two new³⁹Ar-⁴⁰Ar dates are presented, and a tectonic model developed integrating the geochemical and geochronological data with current models of the evolution of the New Guinea Orogen.

---

Die magmatische Geochemie und die tektonische Position von Metabasiten in den EmoMetamorphiten, Papua-Neuguinea; die Entwicklung und Zerstörung eines Backarc Beckens

Zusammenfassung Metabasite aus den Emo-Metamorphiten, die als Crustsheets unter dem Papua-Ophiolit von Papua-Neuguinea vorkommen, lassen sich auf petrographischer Basis in vier Gruppen unterteilen: Gruppe 1 (granatführende Blauschiefer) Gruppe 2 (Amphibolite), Gruppe 3 (Lawsonite-führende Blauschiefer) und Gruppe 4 (Grünschiefer). Die meisten Proben lassen eine polymetamorphe Entwicklung erkennen, mit Texturen, die vom grob gefältelten zum mylonitischen reichen. Viele enthalten primären magmatischen Klinopyroxen, was darauf hinweist, daß die Metamorphose bei relativniedrigen stattgefunden hat. Das dürfte auch die eindeutig magmatischen geochemischen Signaturen erklären, die viele Hauptelemente, die sonst während der Metamorphose mobilisiert werden erkennen lassen. Geochemisch sind alle Gesteine als tholeütisch zu bezeichnen und lassen sich in drei Suiten unterteilen: Suite I sind LREE verarmt, und ähneln E-MORB mit signifikant niedrigen Zr-Nb Werten von 8-16. Suite 111 umfaßt Ferrobasalte, die möglicherweise mit Suite 11 komagmatisch sind aber durch P₂O₅ Gehalte von > 0.5 und Zr-Gehalte von > 250 ppm sich von den ersteren unterscheidet. Die drei Suiten zeigen signifikant niedrigere FeO und höhere Al₂O₃ als eine MORB vergleichbare Suite von Galapagos. Diese und andere Spurenelement-Verteilungsmuster sind üblicherweise mit Backarc-Becken Basalten assoziiert. Zwei neue³⁹Ar/⁴⁰Ar Altersbestimmungen werden vorgelegt und ein tektonisches Modell wird entwickelt, das die geochemischen und die geochronologischen Daten mit gängigen Modellen zur Entwicklung des Orogens von Neuguinea integriert.

---

---

With 7 Figures     

Sr,Nd and Pb isotopic compositions of calc-alkaline and peralkaline silicic volcanics from the D'Entrecasteaux Islands,Papua New Guinea,and their tectonic significance

Summary Sr, Nd and Pb isotope data are presented for a transitional basalt-peralkaline rhyolite suite, and spatially associated calc-alkaline rhyolites from the D'Entrecasteaux Islands, eastern Papua New Guinea. Both suites have a typical convergent margin geochemical signature (i.e. high Zr/Nb, La/Nb, and low Ta/Yb compared with OIB). The transitional basalt-peralkaline rhyolite suite and calc-alkaline rhyolites have a restricted range of²⁰⁶Pb/²⁰⁴Pb (18.522–18.661),²⁰⁷Pb/²⁰⁴Pb (15.543–15.631), and²⁰⁸Pb/²⁰⁴Pb (38.31–38.63) values which overlap the fields of volcanics from Tonga, Fiji, and Pacific MORB and sediments. The transitional basalt-peralkaline rhyolite suite also displays a restricted range of¹⁴³Nd/¹⁴⁴Nd values (0.513053–0.512984), but a much broader range of⁸⁷Sr/⁸⁶Sr (0.703989–0.70585) values. The latter reflects uncertainties in the ages of samples with very high⁸⁷Rb/⁸⁶Sr values and the effects of Sr exchange with seawater. The calc-alkaline rhyolites have consistently lower¹⁴³Nd/¹⁴⁴Nd values (0.512923—0.512867), and a more restricted range of⁸⁷Sr/⁸⁶Sr values (0.703864–0.704028) compared with the transitional basalt-peralkaline rhyolite suite.The isotopic and trace element data are consistent with the interpretation that the calc-alkaline rhyolites were produced by partial melting of a young arc protocrust, whereas associated calc-alkaline basic and intermediate magmas were derived from a depleted mantle source which previously had been modified by subduction along the Trobriand Trough. The transitional basalt-peralkaline rhyolite suite was produced by extensive magmatic differentiation of a parental transitional basalt magma in a relatively shallow magma chamber. The parent magma was produced by partial melting of either a depleted MORB-source mantle or a less-depleted OIB-type source which previously had been modified by subduction processes. The hy- and ol-normative transitional basalt magmas were probably generated in response to lithospheric thinning at somewhat higher pressures than qz-normative calc-alkaline magmas.The close spatial and temporal relationship between the transitional basalt-peralkaline rhyolite suite and the tale-alkaline volcanics reflects the complex and dynamic tectonic setting of eastern Papua and the D'Entrecasteaux Islands. In particular, the change from calc-alkaline to alkaline magmatism appears to have occurred following a change from compressional to extensional tectonics resulting from the westward propogation of the Woodlark spreading ridge into eastern Papua.

---

Sr, Nd und Pb Isotopenzusammensetzung saurer kalkalkalischer und peralkalischer Vulkanite der D' Entrecasteaux Inseln, Papua Neuguinea, und ihre tektonische Bedeutung

Zusammenfassung In dieser Arbeit werden Sr, Nd und Pb Isotopendaten transitionaler Basalt-peralkalischer Rhyolithabfolgen und räumlich mit diesen assoziierter kalkalkalischer Rhyolithe der D' Entrecasteaux Inseln im östlichen Papua Neuguinea vorgestellt. Beide Abfolgen zeigen für konvergiernde Plattenränder typische geochemische Signaturen (z.B. hohe Zr/Nb, La/Nb und niedrige Ta/Yb Verhältnisse im Vergleich mit OIB). Die transitionale Basalt-peralkalische Rhyolithabfolge und die kalkalkalischen Rhyolithe zeigen eine geringe Variation in ihren²⁰⁶Pb/²⁰⁴Pb (18.522–18.661),²⁰⁷/²⁰⁴Pb (15.543–15.631) und²⁰⁸Pb/²⁰⁴Pb (38.31–38.63) Verhältnissen, die mit denen von Vulkaniten aus Tonga, Fiji und den pazifischen MOR-Basalten und Sedimenten übereinstimmen. Die transitionale Basalt-peralkalische Rhyolithabfolge zeigt weiters eine geringe Variationsbreite der¹⁴³Nd/¹⁴⁴Nd Verhältnisse (0.513053–0.512984), aber eine größere Streuung der⁸⁷Sr/⁸⁶Sr Verhältnisse (0.703989–0.70585). Letztere reflektiern die Unsicherheiten der Alterseinstufung der Proben mit sehr hohen⁸⁷Rb/⁸⁶Sr Verhältnissen und die Effekte des Sr-Austausches mit Meerwasser. Die⁸⁷Sr/⁸⁶Sr Verhältnisse kalkalkalischer Rhyolithe variieren im Vergleich dazu gerigfügiger (0.703864–0.704028).Isotopen und Spurenelementdaten sind mit der Interpretation, daß die kalkalkalischen Rhyolithe durch partielle Anatexis junger Inselbogen-Protkruste entstanden sind, kompatibel. Die mit ihnen vergesellschafteten basischen bis intermediären klakalkalischen Magmen entstammen einer abgereicherten Mantelquelle, die zuvor durch Subduktionsprozesse entlang des Trobriandgrabens modifiziert wurde. Die transitionale Basalt-peralkalische Rhyolithabfolge entstand durch extensive magmatische Differentiation eines transitionalen basaltischen Stammagmas in einer relativ seicht liegenden Magmenkammer. Das Stammagma wurde durch partielle Aufschmelzung entweder eines abgereicherten MORB-Mantels oder einer weniger stark abgereicherten OIBQuelle, die zuvor durch Subduktionsprozesse modifiziert wurde, gebildet. Die Hyund O1-normativen transitionalen Basaltmagmen wurden wahrscheinlich im Zuge der Ausdünnung von Lithosphäre unter etwas höheren Drucken gebildet als die Quarznormativen kalkalkaischen Magmen.Die enge räumliche und zeitliche Beziehung der transitionalen Basalt-peralkalischen Rhyolithabfolge mit kalkalkalischen Vulkaniten spiegelt die komplexen und dynamischen geotektonischen Vorgänge im östlichen Papua Neuguinea wieder. Der Wechsel von kalkalkalischem zu alkalischem Magmatismus könnte durch die Umstellung von Kompressions- auf Extensionstektonik, die mit der Verlagerung des westlich gelegenen Woodlark Spreadingzenrums in das östliche Papua Neugiunea in Beziehung gebracht wird, erklärt werden.

---

---

With 13 Figures     

Hydrogeologic investigations of contaminant movement in karst aquifers in the vicinity of a train derailment near Lewisburg,Tennessee

A train derailment near Lewisburg, Tennessee, in October 1990 prompted two series of groundwater investigations. The first was to determine the subsurface flow route of chloroform and styrene that sank into the underlying karst aquifer. The second was to determine the source of contamination for two nearby residential wells which were found to be contaminated with trichloroethylene (TCE). Water-sample analysis and a dye trace performed at the time of the train derailment indicated groundwater flow to Wilson Spring. A dam was constructed to contain the entire discharge from the spring so that it could be treated before being discharged into Big Rock Creek. Three springs and three water wells were contaminated with chloroform and styrene. Dye traces were performed to determine groundwater flow directions in the vicinities of the TCE-contaminated wells and in the vicinities of potential sources. At the train derailment, the chloroform and styrene sank into the Upper Ridley Karst Aquifer and pooled on top of the Lower Ridley Confining Layer. An exploratory well revealed a layer of chloroform (a Dense Non-Aqueous Phase Liquid DNAPL) on the bottom, a layer of groundwater in the middle, and a layer of styrene (a Light Non-Aqueous Phase Liquid LNAPL) on top. Groundwater with relatively low levels of chloroform and styrene in solution was carried by a small cave stream southeast along the strike to Wilson Spring. Chloroform product moved by gravity southwest down-dip along weathered bedding planes. Treatment of contaminated groundwater from Wilson Spring and recovery wells at the spill site has occurred continuously since October, 1990.     

The petrology and geochemistry of Miller Range 05035: A new lunar gabbroic meteorite

Miller Range (MIL) 05035 is a lunar gabbroic meteorite. The mineralogy, Fe/Mn ratios in olivine and pyroxene, bulk-rock chemical composition and the bulk oxygen isotope values (δ¹⁷O = 2.86-2.97‰ and δ¹⁸O = 5.47-5.71‰) are similar to those of other mare basalts, and are taken as supporting evidence for a lunar origin for this meteorite. The sample is dominated by pyroxene grains (54-61% by area mode of thin section) along with large plagioclase feldspar (25-36% by mode) and accessory quartz, ilmenite, spinel, apatite and troilite. The bulk-rock major element composition of MIL 05035 indicates that the sample has a very low-Ti (VLT) to low-Ti lunar heritage (we measure bulk TiO₂ to be 0.9 Wt.%) and has low bulk incompatible trace element (ITE) concentrations, akin to samples from the VLT mare basalt suite. To account for these geochemical characteristics we hypothesize that MIL 05035’s parental melt was derived from a mantle region dominated by early cumulates of the magma ocean (comprised principally of olivine and orthopyroxene). MIL 05035 is likely launch paired with the Asuka-881757 and Yamato-793169 basaltic lunar meteorites and the basaltic regolith breccia MET 01210. This group of meteorites (Y/A/M/M) therefore may be a part of a stratigraphic column consisting of an upper regolith environment underlain by a coarsening downwards basalt lava flow.     

On the origin and excitation of the extended nebula surrounding NGC 1275

We use line-of-sight velocity information on the filamentary emission-line nebula of NGC 1275 to infer a dynamical model of the nebula's flow through the surrounding intracluster gas. We detect outflowing gas and flow patterns that match simulations of buoyantly rising bubbles from which we deduce that some of the nebula filaments have been drawn out of NGC 1275. We find a radial gradient of the ratio [N  ii ]λ6584/Hα which may be due to a variation in metallicity, interactions with the surrounding intracluster medium or a hardening of the excitation mechanism. We find no preferred spatial correlation of stellar clusters within the filaments and there is a notable lack of [O  iii ]λ5007 emission, therefore it is unlikely that the filaments are ionized by stellar ultraviolet.