Mission to the universe

This paper represents a commentary on the importance of communicating science to the general public, and offers specific suggestions on how best to gain public support for space astronomy. The presentation of space astronomy makes use of the contextual framework called Mission to the Universe, as developed by an international working group of astrophysicists and by the author.Presented at the 2nd UN/ESA Workshop, held in Bogotá, Colombia, 9–13 November, 1992.Humanity has embarked on a great voyage of discovery, with a mission to understand the origin, nature, and fate of our universe. Our ships are an international fleet of space observatories. Our captains are scientists from nearly every country of the world. All of us can be the explorers. Come share in our adventure...     

Heat Flux in the Coastal Zone

Various difficulties with application of Monin–Obukhov similarity theory are surveyed including the influence of growing waves, advection and internal boundary-layer development. These complications are normally important with offshore flow. The transfer coefficient for heat is computed from eddy correlation data taken at a mast two kilometres off the Danish coast in RASEX. For these coastal zone data, the thermal roughness length shows no well-defined relation to the momentum roughness length or roughness Reynolds number, in contrast to previous theories. The variation of the momentum roughness length is dominated by wave state. In contrast, the thermal roughness length shows significant dependence on wave state only for small values of wave age where the mixing is apparently enhanced by wave breaking. The development of thin internal boundary layers with offshore flow substantially reduces the heat transfer and thermal roughness length but has no obvious influence on momentum roughness length. A new formulation of the thermal roughness length based on the internal boundary-layer depth is calibrated to the RASEX data. For the very stable case, the turbulence is mainly detached from the surface and existing formulations do not apply.As an alternative to adjusting the thermal roughness length, the transfer coefficient is related directly to the stability and the internal boundary-layer depth. This avoids specification of roughness lengths resulting from the usual integration of the non-dimensional temperature function. The resulting stability function is simpler than previous ones and satisfies free convection similarity theory without introduction of the gustiness factor. The internal boundary layer also influences the moisture transfer coefficient.     

Impacts of Land Degradation on Historical Temperature Records from the Sonoran Desert

Previous research revealed that severe overgrazing and resultant land degradation in the semiarid areas of northern Mexico created significantly higher temperatures in the border area. In this investigation, the temperature and precipitation records from ten homogeneous stations are identified in the arid and hyperarid areas of northwest Sonora and are compared with the records from ten stations in southwestern Arizona. Our data show that the Mexican stations are again consistently warmer than the Arizona stations when statistical controls are applied to correct for the linear or non-linear effects of latitude and/or elevation. The stations in Sonora warm at a statistically significantly faster pace than the stations in Arizona during the study period. Furthermore, and consistent with other dryland areas undergoing land degradation, the stations in Sonora reveal a significant increase in the diurnal temperature range during the summer season. Local precipitation reduces the temperature differential between nations on the time scale of days, but enhances the differential on the time scale of months and seasons. Among other findings, the results show how land degradation in dryland areas appears to influence local historical temperature records.     

Evidence for a Panafrican volcanic arc and wrench fault tectonics in the Jbel Saghro,Anti-Atlas,Morocco

The Saghro hills constitute the northern branch of the Panafrican mobile belt in the eastern part of the Moroccan Anti-Atlas. The Precambrian terranes are predominantly composed of volcaniclastic and volcanic series witnessing a mainly explosive volcanism, intruded by diorites and granites. Their age attribution is problematic, and has been reconsidered in the present study based on structural evidence and Rb/Sr data of quartzdiorites: penetratively deformed volcano-sedimentaries intruded by these plutons aged between 754 and 722 Ma are now considered as Lower Precambrian II. The Upper PII series have been reattributed, and only formations overlying a basal conglomerate and angular disconformity are considered PIII.Main schistosities are predominantly NE-SW, cut by conjugate sets of strike-slip shear zones. In the Saghro area NW-SE compression can explain the observed structures during this main Panafrican deformation phase, while fault kinematics and dike emplacement related to late deformation events indicate rather a NE-SW compression.The explosive volcanism of the Saghro area can be related to a volcanic arc, active during the subduction- and collision-related Panafrican deformations. This arc would be located on the upper plate in respect to the northward dipping subduction zone evidenced in Bou Azzer — El Graara inlier (Saquaque et al., 1989a).

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Zusammenfassung Der Saghro repräsentiert den nördlichen Zweig der panafrikanischen Kette im östlichen Teil des marokkanischen Anti-Atlas. Die präkambrischen Serien bestehen weitgehend aus vulkanischem und vulkano-detritischem Material, die Zeugnis einer vorwiegend explosiven Vulkantätigkeit sind. Diese Serien sind intrudiert von Dioriten und Graniten. Die Altersbestimmung dieser Serien ist problematisch, und ihre Einstufung ist in vorliegender Arbeit revidiert auf Grund struktureller Beobachtungen und Rb-Sr Alter der intrusiven Quarzdiorite von 754 bis 722 Ma. Damit gehören die penetrativ deformierten Serien dem unteren PII an und dem oberen PII werden die etwas deformierten Teile des ehemaligen unteren PIII zugeordnet. Nur diejenigen Formationen, die ein charkteristisches Basiskonglomerat oder eine Winkeldiskordanz überlagern, werden als PIII eingestuft.Die Hauptschieferung streicht NE-SW, und wird von einem System konjugierter Scherzonen durchschnitten. Im Saghro können alle Strukturen dieser panafrikanischen Hauptphase durch eine NW-SE gerichtete Einengung erklärt werden. Die Injektion von Gängen und die Kinematik entlang Störungen im späteren Stadium der panafrikanischen Deformation dagegen deutet auf eine NE-SW-Einengung.Der explosive Vulkanismus und die kalk-alkalinen Plutone des Saghro können durch einen Inselbogenmagmatismus im Zusammenhang mit der nordvergenten Subduktion entlang des »accident majeur« von Bou Azzer – El Graara erklärt werden (Saquaque et al., 1989). Seine Aktivität war gleichzeitig mit den die Subduktion und die Kollision begleitenden Deformationen.

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Résumé Les boutonnières du Saghro constituent la branche nord de la zone panafricaine mobile dans la partie est de l'Anti-Atlas marocain. Les terrains précambriens sont essentiellement composés de séries volcano-clastiques et volcaniques témoignant d'un volcanisme à prédominance explosive, qui sont intrudées par des diorites et des granites. Leur attribution stratigraphique est problématique et fut reconsidérée comme PrécambrienII inférieur sur la base des données structurales et des datations Rb/Sr des diorites qaurtziques intrusives entre 754 et 722 Ma. En conséquence la série PII supérieur a été redéfinie, et uniquement des formations surmontant un conglomérat basai caractéristique ou une discordance angulaire sont considérés du PIII.La schistosité principale est NE-SW, recoupé par des systèmes de zones de cisaillement décrochantes conjuguées. Dans la région du Saghro, une compression NW-SE peut expliquer ces structures associées à la phase de déformation pan-africaine majeure, tandis que la cinématique des failles et l'emplacement de dykes liés aux déformations panafricaines tardives indiquent une compression NE-SW.Le volcanisme explosif du Saghro peut être lié à un arc, qui a été actif pendant les événements tectoniques liés à la subduction et la collision panafricaines. Cet arc sera localisé sur la plaque supérieure par rapport à une zone de subduction vers le nord retracée le long de l'accident majeur dans la boutonnière de Bou Azzer — El Graara (Saquaque et al., 1989).

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Paleoecological investigation of recent lake acidification in the Adirondack Mountains,N.Y.

Paleoecological analysis of the sediment record of 12 Adirondack lakes reveals that the 8 clearwater lakes with current pH < 5.5 and alkalinity < 10 eq l^-1 have acidified recently. The onset of this acidification occurred between 1920 and 1970. Loss of alkalinity, based on quanitative analysis of diatom assemblages, ranged from 2 to 35 eq l^-1. The acidification trends are substantiated by several lines of evidence including stratigraphies of diatom, chrysophyte, chironomid, and cladoceran remains, Ca:Ti and Mn:Ti ratios, sequentially extracted forms of Al, and historical fish data. Acidification trends appear to be continuing in some lakes, despite reductions in atmospheric sulfur loading that began in the early 1970s. The primary cause of the acidification trend is clearly increased atmospheric deposition of strong acids derived from the combustion of fossil fuels. Natural processes and watershed disturbances cannot account for the changes in water chemistry that have occurred, but they may play a role. Sediment core profiles of Pb, Cu, V, Zn, S, polycyclic aromatic hydrocarbons, magnetic particles, and coal and oil soot provide a clear record of increased atmospheric input of materials associated with the combustion of fossil fuels beginning in the late 1800s and early 1900s. The primary evidence for acidification occurs after that period, and the pattern of water chemistry response to increased acid inputs is consistent with current understanding of lake-watershed acidification processes.This is the second of a series of papers to be published by this journal which is a contribution of the Paleoecological Investigation of Recent Lake Acidification (PIRLA) project. Drs. D.F. Charles and D.R. Whitehead are guest editors for this series.     

The vertical structure and thickness of Saturn's rings

We have considered the steady state vertical structure of Saturn's rings with regard to whether collapse to a monolayer due to collisions between particles, the end state predicted by Jeffreys (1947a), may be prevented by any of a variety of mechanisms. Given a broad distribution of particle sizes such as a typical power law n(R) = n₀R^?3, it is found that gravitational scattering of small particles by large particles maintains a true ring thickness of several times the radius of the largest particles, or many times the radius of the smallest particles. Thus the “many-particle-thick” condition which best satisfies optical observations, such as the opposition effect, may be reconciled with ongoing particle collisions. If we consider the obvious sources of energy available for such a process, we find that a ring thickness of only tens of meters may be sustained over the lifetime of the solar system. This implies a maximum particle size on the order of a few meters.     

A backbarrier overwash record of intense storms from Brigantine, New Jersey

Analysis of aerial photographs and historic charts indicates that the barrier beach at Brigantine, NJ has migrated landward 300 to 400 m since 1869, primarily as a result of overwash during hurricanes and winter storms. A series of vibracores from the backbarrier salt marsh reveals a millennial-scale stratigraphic record of overwash deposition. Carbon-14 (C-14) and Cesium-137 (Cs-137) radioisotopic methods were used to date overwash deposits (washovers). The ages of recent washovers are consistent with deposition during intense storms in 1938, 1944, 1950, and 1962. An additional overwash deposit recovered in five of the sediment cores was likely deposited by an intense hurricane strike in 1821 or possibly in 1788. Two prehistoric overwash fans were likely deposited by intense storms striking the New Jersey Coast in the 7th to 14th centuries and 6th to 7th centuries A.D. The landward barrier migration indicates that the older overwash sediments were likely transported a considerably greater distance than the more recent overwash fans. The greater distance of transport may indicate that the prehistoric storms that deposited overwash fans across the study site were more intense than the most intense storm to strike this coast in the historic period, the hurricane of 1821. The spatially variable occurrence of overwash deposition at this site points to a need for multisite stratigraphic surveys of extensive stretches of the coast in order to develop reliable records of past intense storm frequency from backbarrier environments.     

Continental margin off Sergipe and Alagoas, northeastern Brazil: A reconnaissance geophysical study of morphology and structure

The stable continental margin of northeastern Brazil is unusually narrow, probably because of the small size and tropical character of the drainage basins of the hinterland, and correspondingly low rates of land erosion and marine sedimentation. The continental shelf, which is mainly a marine erosion surface, is also remarkably shallow, either because of upwarping or, more probably, because of the ineffectiveness of Pleistocene marine erosional processes on steeply sloping continental margins. Sediment accumulation is confined to the Sāo Francisco delta, seaward of which are fossil (?) lagoonal deposits, and to a poorly developed nearshore sand prism.The margin formed by seaward progradation of sediment on a subsiding basement, but the present morphology of the continental slope reflects chiefly Pleistocene canyon cutting and mass gravitational movements of sediment, which have exposed older strata in the upper slope. Beneath the continental slope is a magnetic anomaly (like the slope anomaly off the eastern U.S.A.), probably caused by a deeply buried dike of oceanic basalt, and apparently associated with a buried ridge which may have formed the seaward margin of the Sergipe—Alagoas Basin during the early history of the South Atlantic. Similar structures may be typical of the narrow easternmost part of the Brazilian margin.     

A laser-based fluorometry system for investigations of seawater and porewater fluorescence

A highly sensitive laser-induced fluorescence (LIF) system has been developed to study the fluorescence of dissolved organic carbon (DOC) in the marine environment. The LIF detector has a detection limit of 10 attomoles (10 × 10⁻¹⁸ moles) of pterin and eliminates internal quenching in highly fluorescent samples such as anoxic porewaters encountered when using conventional fluorometry. LIF analysis is rapid, reproducible, and uses only 100 μl of a sample. This small size requirement permits fluorescence analyses of samples often available only in limited amounts, such as porewaters, hydrothermal vent waters, and rainwaters. In addition, the LIF detection system may greatly simplify extraction and separation procedures required to characterize the fluorescent components of DOC.     

Geologic setting of the Snake Pit hydrothermal site: An active vent field on the Mid-Atlantic Ridge

TheSnake Pit Hydrothermal Site lies on the axis of the Mid-Atlantic Ridge at 23°22′ N latitude, about 30 km south of the Kane Transform Intersection. Active ‘black smoker’ vents and a surrounding field of hydrothermal sediment occur at the crest of a laterally extensive neovolcanic ridge. It is one of the first active hydrothermal vent fields to be found on a slow-spreading ridge axis and despite significant differences in its geologic setting from those of the East Pacific Rise, has many similarities to its fast-spreading counterparts. Although preliminary reports have documented many interesting aspects of these vents and their surroundings, new data collected from the manned submersible ALVIN and the deep-towed ANGUS camera system define the regional tectonic setting as well as the local geologic environment of this fascinating area. The Snake Pit vents are located on a local peak of a volcanic constructional ridge at a depth of 3450 m, 700–800 m deeper than vents known from the East Pacific Rise, Galapagos, or Juan de Fuca spreading centers. The vent field is at least 600 m long and up to 200 m wide and is covered by a thick blanket of greenish to yellow-orange hydrothermal sediment. Both active and extinct vents are perched along the crests of steep-sided sulfide mounds that reach heights of over 40 m. High-temperature (350° C) fluids are vented from black smoker chimneys and low-temperature (226° C) fluids seep from sulphide domes and subordinate anhydrite constructions. Water temperatures, flow rates, fluid chemistries, and mineralization are strikingly similar to vents of faster spreading ridge crests; however, a somewhat distinct fauna inhabit the area.