High-Latitude Solar Rotation Traced by Magnetic Elements

Sequential observations at Huairou Solar Observation Station, China, and Kitt Peak, U.S.A., show that polar magnetic elements can live from several to more than 58 hours. This enables measurement of the solar rotation rate near the polar region by tracing magnetic element motions. With observations carried out on 8–15 July 1997, we identify and trace more than 1300 elements at north heliographic latitudes between 55°–85° using two methods, and fit the mean sidereal rotation rate as =14.0±0.54–(2.24±1.22)sin²–(1.78±0.79)sin⁴ deg per day.     

Ecophysiological aspects of the coastal-estuarine distribution of acrochordid snakes

The Acrochordidae consists of three congeneric species of aquatic snakes distributed among fresh water and coastal marine environments in tropical southern Asia. The smallest species,Acrochordus granulatus, is euryhaline and the only acrochordid that permanently inhabits coastal seas and estuaries. The diving and metabolic physiology of this species is highly specialized and reflects the demands of estuarine environments. A capability for prolonged aerobic diving is attributable to low rates of oxygen consumption, high capacity for oxygen storage, nearly complete utilization of the oxygen stores, and cutaneous gas exchange. Recent studies indicate thatA. granulatus is primarily ammonotelic and requires a source of fresh water for elimination of nitrogenous wastes. The requirement for fresh water potentially limits seaward migration of populations due to the dependence of snakes on rivers or coastal rainfall. Adaptations for shallow-water diving conceivably further limit seaward migration, with the result that they have evolved as estuarine specialists that are restricted from deeper waters and the open ocean.     

Sediment dispersal from Vogelsberg Basalt,Hessen, West Germany

Volcanic detritus in sand size stream sediment spreading outward from Vogelsberg extrusive and hypabyssal rocks decreases in abundance from percentages exceeding 90 % to less than 5 % within 20 km of the source area. The rapid decrease results largely from dilution of the stream sediment resulting from disintegration of friable Bunter Sandstone on the plains surrounding the crystalline rocks. The effect is more pronounced in the fine sand fraction of the stream sediment because the Bunter sand is fine grained.If a geologist of the post-Holocene were to sample this stream sand in outcrop, he would have to be located within about 10 km of the present Vogelsberg mass to infer its existence.

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Zusammenfassung Vulkano-klastische Flußsedimente im Korngrößenbereich von Sanden, die sich aus den Ergußgesteinen und hypabyssischen Gesteinen des Vogelsbergs herleiten, nehmen die Häufigkeit von mehr als 90 % bis auf weniger als 5 % innerhalb von 20 km vom Ursprungsgebiet ab.Die starke Abnahme ist als Folge einer Verdünnung der Flußsedimente entstanden. Die Verdünnung ist durch die Zersetzung des leicht verwitterbaren Buntsandsteins auf den Ebenen, die diese vulkanischen Gesteinen geben, verursacht.Da der Buntsandstein von feinkörniger Natur ist, wird der Verdünnungseffekt in der Feinsandfraktion der Flußsedimente besonders deutlich beobachtet.Würde ein Geologe einst Gesteinsproben entnehmen, die aus diesen Sedimenten entstanden sind, so müßte er sich in einem Umkreis von 10 km des heutigen Vogelsberggebietes befinden, um dessen Existenz nachweisen zu können.

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Résumé Les débris volcaniques dans les sédiments fluviaux de granularité sableuse provenant des roches extrusives et hypabyssales du Vogelsberg voient leur proportion décroÎtre de 90 % à moins de 5 % sur une distance de 20 km. à partir de leur origine. Cette décroissance rapide provient principalement de la dilution du sédiment fluvial par suite de la désintégration des grès bigarrés sur les plaines avoisinant les roches cristallines. L'effet est encore plus prononcé dans la fraction fine du sédiment fluvial à cause de la finesse du sable bigarré.Un géologue des temps futurs qui aurait à échantillonner ce sable fluvial dans ses affleurements devrait rester dans les 10 km. de l'actuel Vogelsberg pour en présumer l'existence.

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Reduction of field populations of fiddler crabs by uptake of chlorinated hydrocarbons

Fiddler crabs are particularly sensitive to chlorinated hydrocarbons. Crabs that have been feeding on contaminated material show an impairment of their escape reaction. High concentrations of Aldrin and Dieldrin in plots of marsh experimentally treated with contaminated sewage sludge indicate that these insecticides are responsible for a drastic reduction in fiddler crab populations.     

Declining Temporal Effectiveness of Carbon Sequestration: Implications for Compliance with the United National Framework Convention on Climate Change

Carbon sequestration is increasingly being promoted as a potential response to the risks of unrestrained emissions of CO₂, either in place of or as a complement to reductions in the use of fossil fuels. However, the potential role of carbon sequestration as an (at-least partial) substitute for reductions in fossil fuel use can be properly evaluated only in the context of a long-term acceptable limit (or range of limits) to the increase in atmospheric CO₂ concentration, taking into account the response of the entire carbon cycle to artificial sequestration. Under highly stringent emission-reduction scenarios for non-CO₂ greenhouse gases, 450 ppmv CO₂ is the equivalent, in terms of radiative forcing of climate,to a doubling of the pre-industrial concentration of CO₂. It is argued in this paper that compliance with the United Nations Framework Convention on Climate Change (henceforth, the UNFCCC) implies that atmospheric CO₂ concentration should be limited, or quickly returned to, a concentration somewhere below 450 ppmv. A quasi-one-dimensional coupled climate-carbon cycle model is used to assess the response of the carbon cycle to idealized carbon sequestration scenarios. The impact on atmospheric CO₂ concentration of sequestering a given amount of CO₂ that would otherwise be emitted to the atmosphere, either in deep geological formations or in the deep ocean, rapidly decreases over time. This occurs as a result of a reduction in the rate of absorption of atmospheric CO₂ by the natural carbon sinks (the terrestrial biosphere and oceans) in response to the slower buildup of atmospheric CO₂ resulting from carbon sequestration. For 100 years of continuous carbon sequestration, the sequestration fraction (defined as the reduction in atmospheric CO₂ divided by the cumulative sequestration) decreases to 14% 1000 years after the beginning of sequestration in geological formations with no leakage, and to 6% 1000 years after the beginning of sequestration in the deep oceans. The difference (8% of cumulative sequestration) is due to an eflux from the ocean to the atmosphere of some of the carbon injected into the deep ocean.The coupled climate-carbon cycle model is also used to assess the amount of sequestration needed to limit or return the atmospheric CO₂ concentration to 350–400 ppmv after phasing out all use of fossil fuels by no later than 2100. Under such circumstances, sequestration of 1–2 Gt C/yr by the latter part of this century could limit the peak CO₂ concentration to 420–460 ppmv, depending on how rapidly use of fossilfuels is terminated and the strength of positive climate-carbon cycle feedbacks. To draw down the atmospheric CO₂ concentration requires creating negative emissions through sequestration of CO₂ released as a byproduct of the production of gaseous fuels from biomass primary energy. Even if fossil fuel emissions fall to zero by 2100, it will be difficult to create a large enough negative emission using biomass energy to return atmospheric CO₂ to 350 ppmv within 100 years of its peak. However, building up soil carbon could help in returning CO₂ to 350 ppmv within 100 years of its peak. In any case, a 100-year period of climate corresponding to the equivalent of a doubled-CO₂ concentration would occur before temperatures decreased. Nevertheless, returning the atmospheric CO₂concentration to 350 ppmv would reduce longterm sea level rise due to thermal expansion and might be sufficient to prevent the irreversible total melting of the Greenland ice sheet, collapse of the West Antarctic ice sheet, and abrupt changes in ocean circulation that might otherwise occur given a prolonged doubled-CO₂ climate. Recovery of coral reef ecosystems, if not already driven to extinction, could begin.     

Measurements of Reynolds stress in a wind-driven lagoonal estuary

Acoustic Doppler current profilers (ADCPs) have been used to measure Reynolds stresses in tidally dominated environments where wave action was minimal. In this paper, we examine observations from a microtidal estuary where the effects of wind stress and surface waves dominate the velocity variance. Reynolds stress measurements in this setting require a technique for addressing surface gravity wave contamination. We present here a method of reducing the effect of wave motion on Reynolds stresses by subtracting coincident observations along the axis of the ADCP beam. Linear wave theory is used to account for the attenuation of wave orbital velocities with depth. Using this method, Reynolds stress values are brought in line with those predicted by drag laws at the surface and bottom. The apparent Reynolds stress that is removed by the along-axis subtraction is shown to be largely due to the interaction of a slight tilt (1°) in the ADCP and the wave orbital velocity. During periods of stronger wind and waves, there is evidence of enhanced near-surface turbulence and momentum flux, presumably due to breaking waves. During these events, our calculated Reynolds stress magnitudes still appear reasonable, although the directions are suspect. We develop a diagnostic technique that clearly demarcates this region when it occurs. Coincident density profile measurements are used with the ADCP data to compute gradient Richardson numbers throughout the water column. Enhanced Reynolds stresses appear to correspond to Richardson numbers less than one. Responsible editor: Alejandro Souza     

Magnetic Field Properties of Solar X-Ray Jets

From a list of X-ray jets made by Shimojo et al. (1996), we selected events for which there were magnetic field data from NSO/Kitt Peak. Using co-aligned SXT and magnetograms, we examined the magnetic field properties of X-ray jets. We found that 8% of the jets studied occurred at a single pole (SP), 12% at a bipole (BP), 24% in a mixed polarity (MP) and 48% in a satellite polarity (ST). If the satellite polarity region is the same as the mixed polarity region, 72% of the jets occurred at the (general) mixed polarity region.We also investigated the magnetic evolution of jet-producing areas in active regions NOAA 7067, NOAA 7270, and NOAA 7858. It is found that X-ray jets favored regions of evolving magnetic flux (increasing or decreasing).